U.S. patent application number 11/790981 was filed with the patent office on 2007-12-13 for machine for intraoperative radiation therapy.
This patent application is currently assigned to GIO' - MARCO S.P.A.. Invention is credited to Mario Fantini, Aquilino Gava, Vincenzo Iacoboni.
Application Number | 20070287878 11/790981 |
Document ID | / |
Family ID | 11456334 |
Filed Date | 2007-12-13 |
United States Patent
Application |
20070287878 |
Kind Code |
A1 |
Fantini; Mario ; et
al. |
December 13, 2007 |
Machine for intraoperative radiation therapy
Abstract
A machine for intraoperative radiation therapy or IORT (Intra
Operative Radio Therapy), includes a mobile body, having at least
two driving wheels and at least an idle wheel, each driving wheel
being operated by a corresponding moving engine, the machine
including a radiating head connected to the body, for emitting an
electron beam, handling elements which are integral with the
radiating head, engine unit for moving the radiating head, for
impressing to the radiating head at least a vertical translation
motion. The handling elements include at least three bidirectional
sensors, for measuring both a traction stress and a compression
stress, each of which sends to a control processor an electric
signal proportional to a measured stress which is orthogonal to the
sensor. The control processor operates the moving engines of each
driving wheel and the engine unit proportionally to the stresses
measured by the at least three bidirectional sensors.
Inventors: |
Fantini; Mario; (Rome,
IT) ; Iacoboni; Vincenzo; (Rome, IT) ; Gava;
Aquilino; (S. Vendemiano (TV), IT) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET
2ND FLOOR
ARLINGTON
VA
22202
US
|
Assignee: |
GIO' - MARCO S.P.A.
TESSERA (VE)
IT
|
Family ID: |
11456334 |
Appl. No.: |
11/790981 |
Filed: |
April 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10515991 |
Jul 20, 2005 |
|
|
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PCT/IT03/00336 |
May 29, 2003 |
|
|
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11790981 |
Apr 30, 2007 |
|
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Current U.S.
Class: |
600/1 |
Current CPC
Class: |
A61N 5/10 20130101; A61N
2005/1089 20130101; A61N 2005/1094 20130101; A61N 5/1048
20130101 |
Class at
Publication: |
600/001 |
International
Class: |
A61N 5/00 20060101
A61N005/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2002 |
IT |
RM2002A000301 |
Claims
1. Machine for intraoperative radiation therapy or IORT (Intra
Operative Radio Therapy), comprising a mobile body, provided with
at least two driving wheels (21, 22) and at least an idle wheel
(24, 25), each driving wheel (21, 22) being operated by a
corresponding moving engine, the machine comprising a radiating
head (23) connected to the body, apt to emit an electron beam, the
machine being characterised in that it further comprise handling
means (19) which are integral with the radiating head (23), engine
means for moving the radiating head (23), apt to impress to the
radiating head (23) at least a vertical translation motion, said
handling means (19) comprising at least three bidirectional sensors
(20), apt to measure both a traction stress and a compression
stress, each one of which sends to a control processor an electric
signal which is proportional to a measured stress which is
orthogonal to the sensor, said control processor operating the
moving engines of each of said at least two driving wheels (21, 22)
and the engine means for moving the radiating head (23)
proportionally to the stresses which are measured by said at least
three bidirectional sensors (20).
2. Machine according to claim 1, characterised in that said engine
means for moving the radiating head (23) is apt to impress to the
radiating head (23) a rotational motion on at least a plane, in
that said handling means (19) comprises at least four bidirectional
sensors (20), and in that said control processor operates the
moving engines of each of said at least two driving wheels (21, 22)
and the engine means for moving the radiating head (23) on the
basis of an orientation of said handling means (19).
3. Machine according to claim 2, characterised in that said engine
means for moving the radiating head (23) is apt to impress to the
radiating head (23) a pitch rotational motion and a roll rotational
motion, and in that said handling means (19) comprises at least
five bidirectional sensors (20).
4. Machine according to claim 3, characterised in that said control
processor performs the following operations: determining an
orientation of the handling means (19) with respect to a first
Cartesian triad which is integral with the body of the machine,
composing the stresses which are measured by the bidirectional
sensors (20), obtaining a resulting vector and a resulting torque
with respect to a second Cartesian triad which is integral with
said handling means (19), calculating the projections of the
resulting vector and of the resulting torque onto the first fixed
Cartesian triad, obtaining a vector of translation of the body, a
torque of rotation of the body, a vector of vertical translation of
the radiating head (23), a torque of roll rotation of the radiating
head (23), and a torque of pitch rotation of the radiating head
(23); and operating the moving engines of each of said at least two
driving wheels (21, 22), so as to linearly move the body
proportionally to said vector of translation of the body and to
rotate the body proportionally to said torque of rotation of the
body, and operating the engines for moving the radiating head (23),
so as to vertically translate the radiating head (23)
proportionally to said vector of vertical translation of the
radiating head (23), to impress a roll rotation to the radiating
head (23) proportionally to said torque of roll rotation of the
radiating head (23), and to impress a pitch rotation proportionally
to said torque of pitch rotation of the radiating head (23).
5. Machine according to claim 1, characterised in that each one of
said at least three bidirectional sensors is formed by a pair of
opposed sensors (20), each of which is apt to measure a compression
stress which is orthogonal to it.
6. Machine according to claim 5, characterised in that each one of
said compression stress sensors (20) is inserted in a mechanical
housing (26), provided with elastic means (27), mobile between a
first not stressed limit position and a second limit position of
maximum stress onto the sensor (20), wherein the maximum stress
onto the sensor (20) is not larger than the full scale of this.
7. Machine according to claim 1, characterised in that each one of
said at least two driving wheels (21, 22) is provided with a clutch
which is apt to uncouple the wheel from the respective engine
making it idle.
8. Machine according to claim 1, characterised in that it comprises
housing compartments which are sealed against external
humidity.
9. Machine according to claim 1, characterised in that it has a
weight lower than 400 Kg.
10. Machine according to claim 1, characterised in that it has a
width not larger than 100 cm, preferably not larger than 80 cm, and
a length not longer than 2.5 metres, preferably not longer than 2
metres.
11. Machine according to claim 1, characterised in that it is
provided with a system for diffusing the electron beam, leaving an
accelerating structure (4), which comprises a divergent magnetic
lens (28), apt to make the trajectories of the electrons crossing
it diverge.
12. Machine according to claim 1, characterised in that it is
provided with timer means apt to operate an acoustic device for a
duration T before the start of the electron beam emission.
13. Machine according to claim 12, characterised in that the
duration T is adjustable.
14. Machine according to claim 1, characterised in that it is
provided with a system for measuring the total dose of the electron
beam, emitted during a IORT treatment for a period of duration R,
comprising an amperometric transformer, apt to measure the
instantaneous current I.sub.beam of the emitted electron beam, the
instantaneous dose D being calculated as a function of said
instantaneous current I.sub.beam, the total dose being calculated
through a time integration of the instantaneous dose for the
treatment period.
15. Machine according to claim 14, characterised in that said
instantaneous dose D is calculated on the basis of a quadratic
dependency from said instantaneous current I.sub.beam:
D=K*I.sub.beam.sup.2.
16. Machine according to claim 14, characterised in that said
instantaneous dose D is calculated on the basis of a linear
dependency from said instantaneous current I.sub.beam,
D=D.sub.0+A*.DELTA.I.sub.beam where
.DELTA.I.sub.beam=I.sub.beam-I.sub.beam.sub.--.sub.Ref wherein
I.sub.beam.sub.--.sub.Ref is a reference value of the instantaneous
current of the emitted electron beam, and the coefficients Do and A
are experimentally determined in a phase of clinical dosimetry of
the machine.
17. Machine according to claim 1, characterised in that the
electron beam comes out from an accelerating structure (4)
comprising tuning means (18, 47), placed in corresponding slots of
the accelerating structure, said tuning means (18, 47) being
directly and locally welded to the accelerating structure onto each
of said slots through an electrical arc welding in controlled
atmosphere.
18. Machine according to claim 17, characterised in that the
accelerating structure presents, in correspondence of each slot, a
profile apt to dissipating heat.
19. Machine according to claim 17, characterised in that said
tuning means (18, 47) comprises a tuning screw (18) covered by a
cap (45).
20. Process for moving a machine for intraoperative radiation
therapy or IORT (Intra Operative Radio Therapy), comprising a
mobile body, provided with at least two driving wheels (21, 22) and
at least an idle wheel (24, 25), each driving wheel (21, 22) being
operated by a corresponding moving engine, the machine comprising a
radiating head (23) connected to the body, apt to emit an electron
beam, the machine further comprising handling means (19) which is
integral with the radiating head (23), engine means for moving the
radiating head (23) and which is apt to impress to the radiating
head (23) a vertical translation motion, a pitch rotational motion
and a roll rotational motion, said handling means (19) comprising
at least five bidirectional sensors (20), the process being
characterised in that it comprises the following step: determining
an orientation of the handling means (19) with respect to a first
Cartesian triad which is integral with the body of the machine,
composing the stresses which are measured by the bidirectional
sensors (20), obtaining a resulting vector and a resulting torque
with respect to a second Cartesian triad which is integral with
said handling means (19), calculating the projections of the
resulting vector and of the resulting torque onto the first fixed
Cartesian triad, obtaining a vector of translation of the body, a
torque of rotation of the body, a vector of vertical translation of
the radiating head (23), a torque of roll rotation of the radiating
head (23), and a torque of pitch rotation of the radiating head
(23); and operating the moving engines of each of said at least two
driving wheels (21, 22), so as to linearly move the body
proportionally to said vector of translation of the body and to
rotate the body proportionally to said torque of rotation of the
body, and operating the engines for moving the radiating head (23),
so as to vertically translate the radiating head (23)
proportionally to said vector of vertical translation of the
radiating head (23), to impress a roll rotation to the radiating
head (23) proportionally to said torque of roll rotation of the
radiating head (23), and to impress a pitch rotation proportionally
to said torque of pitch rotation of the radiating head (23).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of copending U.S. application
Ser. No. 10/515,991, which is the national stage of international
application PCT/IT/03/00336 filed on May 29, 2003, which claims
foreign priority to Italian application No. RM 2002 A000301 filed
May 31, 2002. The entire contents of each of these applications is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention concerns a machine for intraoperative
radiation therapy or IORT (Intra Operative Radio Therapy) which is
easily movable, having reduced weight and size, and which makes
possible, in a reliable, simple and efficient way, to radiate an
electron beam drastically reducing the diffusion of X rays,
accurately controlling environmental radiation, and very precisely
measuring the radiation dose.
BACKGROUND OF THE INVENTION
[0003] It is known that Intraoperative Radiotherapy consists in
treating the patient with ionising radiations in the course of the
surgical operation. IORT, initially developed by some, mainly
Japanese and US, research institutes, since sixties to eighties,
began to ripen in the following decade, with the creation of a
specific international society, the ISIORT, and increasingly
participated biennial meetings methodically following one
another.
[0004] However, in mid-nineties the conviction spread among the
experts that IORT would have remained prerogative of large
university centres which could face the big logistical costs that
IORT involved. In fact, out of the institutions dedicated to
research, it could not be proposed to invest considerable amounts
of money for a therapy that, due to limited Figures, could not
produce statistically reliable data. Hence, IORT remained a branch
of excellence performed by researchers who tried to find a
standardisation in order to have data which were comparable and
therefore apt to be added among different centres. The main reason
for constituting the ISIORT intraoperative radiotherapy
international society was in fact creating a common and commonly
accepted reference point issuing protocols and procedures
eliminating the local particular differences which inevitably set
up.
[0005] For radiating a particular organ which is exposed due to the
surgical opening, it is not convenient to use X rays which are
commonly used for conventional radiotherapy; in fact these are
highly penetrative and once aimed at the area to be treated they
involve everything being along their aiming direction, distributing
undesired radiation doses also to other organs which are thereby
damaged.
[0006] Instead, IORT uses a beam of electrons, which are the
primary particles being accelerated in order to obtain, after a
conversion, the X rays. In fact, the electrons are slightly
penetrative ionising radiations and their penetration is precisely
controlled through the kinetic energy that they are given by the
accelerator. A cursory empirical rule establishes that the
electrons penetrate in a biological tissue for a number of
centimetres equal to their kinetic energy, expressed in MeV,
divided in half; hence, a 6 MeV beam shall be completely absorbed
within the first 3 centimetres of tissue.
[0007] Hence, the use of electrons takes away from the danger of
damaging organs beneath the bottom of the tumour bed which is
exposed by the surgeon. Moreover, the electron beams, thanks to the
reduced penetration, are easily shaped and transversely limited,
being thereby possible to treat only parts to be radiated, reducing
the morbidity induced by applications of considerable doses such as
the ones used in IORT.
[0008] The doses normally used in conventional radiotherapy range
from 25 to 75 Gray, where 1 Gy=1 Joule/1 Kg. These doses are
delivered to the patient by means of a series of usually biweekly
applications, of 1-2 Gy per application. In IORT typical doses
range from 10 to 25 Gy, applied only once. It is evident that an
error in dosimetry in IORT may be much more dangerous than in
classical radiotherapy. Therefore, apparatus dedicated to IORT has
to very precisely detect the dose of electron radiancy.
[0009] The shape of beams is obtained by making the electron beam
pass within an applicator made by a tube in plastic material having
a wall thickness of the order of 5-8 millimetres. This thickness is
generally sufficient to prevent accelerated particles from
spreading outside the beam. Beam shape is generally circular, and
rarely polygonal.
[0010] When it was initially developed, IORT was performed by
moving the anesthetized patient from surgical room to radiotherapy
bunker where there was the accelerator that was prearranged to emit
electrons (the accelerator is usually an X ray source); the
electron beam was applied through applicators in light material
capable to shape and limit the beam itself. In order to eliminate
or at least minimise patient movement, some institutes have built
surgical rooms next to or within the radiotherapy bunker; in any
case these were extremely expensive solution which have in fact
limited the diffusion of IORT.
[0011] Hence, a procedure IORT comprises the following steps:
[0012] conventional surgical operation; [0013] preparing the
patient for transport; [0014] transporting the patient; [0015]
preparing the patient for radiation; [0016] treatment with
electrons; and [0017] ending of the surgical operation.
[0018] From an electromagnetic point of view, a machine for
radiotherapy is very similar to a radar transmitter, since it is
substantially a very short pulse transmitter, pulses having a
duration of 1/5 .mu.sec, and very powerful, having a power of the
order of 2/5 MW, operating in the microwave range, with frequency
of the order of 3 Ghz corresponding to a wavelength .lamda.=10 cm.
This microwave pulse enters an accelerator comprising a series of
cascrewses, which may be resonant or aperiodic, where it generates
extremely strong instantaneous electric fields which cause a beam
of charged particles, i.e electrons, to be accelerated due to
electrostatic attraction.
[0019] With reference to FIG. 1, a high voltage power supply 1
transforms the line voltage into a continuous voltage, having a
value ranging from 9 to 18 kV, which charges a system of capacitors
wherein the energy needed to generate a single pulse is stored.
Through a suitable switch called thyratron, a pulse generator 2
transforms the previously stored energy into a pulse having a short
duration, equal to about 1/5 .mu.sec, and a voltage of the order of
50 kV.
[0020] This pulse is applied to a microwave generating thermionic
tube 3, said magnetron, that transforms it into a train of
electromagnetic oscillations which are inputted into an
accelerating structure 4 for carrying out the accelarating process
of an electron beam.
[0021] For a proper operation, all the mentioned devices need
auxiliary circuits and apparatus which provide for proper operation
or for stabilizing the whole system depending on the
circumstances.
[0022] In particular, a synchronizer 5 comprises a set of circuits
producing the pulses that make all the pulse devices of the
impulsivi del pulse generator 2 coordinatedly work, providing for
their proper operation sequence. A tuning control circuit 6
provides for keeping resonance frequency of magnetron 3 in step
with the frequency needed for a proper operation of the
accelerator. A vacuum pump 7 maintains a ultra high vacuum level,
of the order of 10.sup.8 hPa (hectoPascal), within the accelerating
structure 4, which is essential in order that the accelaration
process occurs without impediments due to an excessive impact of
particles with gas molecules within the accelerating structure 4. A
system 8 for measuring the energy quantity conveyed by the beam and
that is incident on the tissues of the patient allows the emitting
process to be stopped when the radiated energy quantity reaches a
value which is sufficient for the desired therapeutic purposes.
Finally, a processing computer 9 controls the operations of the
machine.
[0023] The conventional machines for radiotherapy present some
drawbacks.
[0024] First of all, as it has been already observed, they do not
satisfy the requirement for mobility, also because the apparatus is
heavy and bulky.
[0025] In fact, in case of immobile machine for radiotherapy, even
if it is placed within a surgical room, yet the patient must be
moved in order to be positioned under it. This implies a complex
and difficult logistic organisation, since the above is a procedure
which is extraneous to the normal conduct of a surgical operation,
and a time extension of the anesthesia, further causing a physical
stress for the patient.
[0026] Moreover, an immobile machine placed in a surgical room may
treat patients at a frequency equal to the one of the surgical
operation, that is, typically, one patient per day for abdominal
applications and up to three per day in case of mammary tumours.
However, the time of real use is greatly shorter, since the
radiation lasts about one minute and the whole operation of
positioning and subsequent removal of the patient does not
generally reach 15 minutes. Hence, this results in keeping mostly
unused a machine potentially capable of treating an high number of
patients.
[0027] Although some mobile machines for radiotherapy have been
developed, these have drawbacks due to weight and size and to the
need of calibration after movements.
[0028] Moreover, a machine, either immobile or mobile, is driven
onto the patient to be radiated by a radiotherapy technician
skilled in driving, who is, however, not sterile, since he has to
handle objects, such as the remote control, which cannot be
sterilised. The machine is considered sterile only for the
applicator portion fixed thereto. The positioning of the machine
consists in joining the two portions of the applicator (one of
which is positioned in contact with the surgical opening of the
patient, and the other one is connected to the machine). The
technician controlling this action cannot get close to the patient,
since he is not sterile, and he is therefore led through vocal
instructions by the (sterile) radiotherapist who is close to the
patient. This procedure is quite dangerous, because the one driving
the machine has a very limited sight of the operating zone and
there is the risk of hitting or compressing internal organs of the
patient which are quite fragile.
[0029] Further drawbacks of the known machines for radiotherapy are
due to the system for diffusing the electron beam.
[0030] In fact, the accelerated electron beam leaves the vacuum
environment of the accelerating structure emerging through a
titanium thin foil, which is interposed in order to keep the vacuum
level within the structure sealed. The transverse size, that is the
diamater, of the beam at the moment of leaving are of the order of
millimetre. Thanks to the electrostatic repulsion among the
electrons and to the diffusion with the crossed air, the beam opens
with an angle depending on the beam power that, at 10 MeV, is of
the order of .+-.10.degree. around the geometric axis.
[0031] As shown in FIG. 2a, when the energy conveyed by the beam is
analysed according to relative units by sectioning it with a plane
containing the axis, a Gaussian type distribution is obtained. In
order to be usable onto the patient, the beam has instead to have a
constant value in the whole range of application, as shown in FIG.
2b. For obtaining such a transformation, as shown in FIG. 2c, the
beam is diffused by making it cross a metallic plate 10 having
variable thickness and sectioning it with a light material tube 11,
capable to absorb the undesired side portion of the beam.
[0032] However, such beam flattening solution is inadequate for
machines for Intraoperative Radiotherapy, since the diffusing plate
10 produces a significant quantity of braking X rays which permeate
the surgical room environment and are difficult to be shielded.
This imposes a noticeable shielding which causes high values of the
machine weight, making the use of special floors be necessary.
[0033] In this regard, the problem of environmental radiation in
surgical room is particularly important.
[0034] Besides the already mentioned X radiations due to the
diffusing filters crossing, the environmental radiations which are
present during operation of an electron accelerator for IORT in
surgical room comprise electron radiations due to electrons leaving
the collimator, also known as secondary electrons, and X radiations
generated by the patient, i.e. the electron beam braking radiations
due to the fact that the patient brakes the electron beam absorbing
almost its whole energy.
[0035] The secondary electron radiations, even being of noticeable
number, have a very low energy, estimated in few keV, and generally
remained confined within the surgical room. It is therefore
sufficient to leave the room during radiation.
[0036] However, the warning and control procedures are not
completely accurate.
[0037] The braking X radiations are the most harmful and
inevitable. The percentage of beam energy which is converted into X
rays amounts to 0.3% of the incident energy, the generated X
radiations having energy ranging from 0 to the energy of the most
energetic electron. As shown in FIG. 3, from a geometric point of
view the radiation is extremely anisotropic, having a lobe 12 along
the running direction of the original electron beam. The aperture
of the lobe 12 is very restricted and at a angle of few degrees
deviating from the axis its intensity is halved, while at
90.degree. its intensity is reduced to one hundredth of the value
on the axis. This remarkable anistotropy makes possible an
effective beam, interposing an absorbing mass 13 along the beam
axis prolongation so as to prevent the radiation from propagating
outside the surgical room. The absorbing mass 13 is made of lead
slabs. Considering that the decivalency thickness (that is the
thickness of material reducing to one tenth the intensity of the
incident beam) at the energies normally used in IORT is equal to 4
cm, in order to attenuate the incident radiation by a factor
ranging from 50 to 1000 the thickness of the absorbing mass 13
normally ranges from 6 and 12 centimetres.
[0038] However, while in the case of immobile machines for
radiotherapy the absorbing mass 13 is oriented in fixed position
with respect to the accelerator axis, in the case of mobile
machines for radiotherapy the correct positioning of the absorbing
mass 13 is not simple, taking also into account the accuracy
imposed by the law for the safety of the operators.
[0039] A further drawback present in known machines for
radiotherapy is due to the system for measuring the beam, needed in
all the accelerators for radiotherapy in order to determine that
the prescribed dose quantity has been really delivered by the
machine and to stop delivering.
[0040] In fact, transmission ionization chambers are commonly used,
which are crossed by the radiation beam. The chamber is made of two
foils of conductor which is very thin (so as to not attenuate the
beam) and spaced 1-2 millimetres and between which a potential
difference of some hundreds of volts is maintained. The particles,
either electrons or photons, crossing the space between the foils
ionize an amount of air molecules proportionally to their own
kinetic energy and to their number. The ionized molecules are hence
attracted by the negative electrode while the electrons which are
stripped from the external orbitals migrate to the positive
electrode; this current which is generated by the passage of the
beam is collected by a capacitor and is transformed in a charge
amount which is measured by a suitable circuit. Considering that
the dose flow is equal to the ratio of pulse dose to pulse
duration, the ionization chambers remain linear with dose flows of
the maximum order of about 100 Gy/sec, beyond which the flow
generates a number of electrons and ionized molecules so high that
these recombine before reaching the ionization chamber electrodes,
therefore subtracting a charge amount from the measure.
Microscopically this effect is translated into a progressive
desensitization of the chambers up to being no more usable.
[0041] In case of mobile machines for Intraoperative Radiotherapy,
in order to maintain environmental radiation quantity minimum, the
electron beam is not diffused and must be measured, for reasons of
efficient machine architecture, directly at the accelerator output,
where it still has transverse size of the order of few millimetres.
Since the typical flow of a mobile machine for Intraoperative
Radiotherapy is of the order of 20,000 Gy/sec, the ionization
chambers operate in a very low sensitivity region that does not
allow them to appreciate variations lower than some point percent.
Considering that the precision limit of clinical dosimetry is of
the order of 2%, it is evident that the transmission ionization
chambers are unusable.
[0042] The solution which is used in some mobile machines is to
employ a scattering filter so as to lower the electron current by a
factor ranging from 10 to 40 and prevent the transmission chambers
from being affected by noticeable recombination phenomena. However,
such a solution implies a very high environmental radiation
quantity which imposes the use of a circular attenuator (a sort of
collimator for the diffusion) in heavy material (depleted uranium).
The use of such a shielding causes the radiating head to be heavy
and, due to balancing reasons, this propagates in cascade on the
weights of the whole machine.
[0043] A further drawback of the known machines for radiotherapy is
due to the accelerating structure.
[0044] With reference to FIG. 4, the accelerating structure is
composed by a series of resonant cascrewses 14 coupled among them,
which are equivalent to a series of elementary oscillating pure
resonant circuits, comprising an inductor L and a capacitor C,
coupled between them. In this circuit, the resonance frequencies of
the elementary cells are adjusted so as to have a 90.degree. phase
displacement between the voltages at the capacitors of two
contiguous cells.
[0045] With reference to FIG. 5, it may be observed that the
accelerating structure cascrewses are of two types which
alternately follow: accelarating cascrewses 15 and coupling
cascrewses 16. In particular, the accelerating cascrewses 15 have a
large indictance and a small capacitance; their configuration
comprises central protrusions 17 which are the capacitive
component, around which it is formed the electric field that is
used to do the acceleration work. Vice versa, the coupling
cascrewses 16 have a large capacitance and a small inductance;
their function is to transfer the radiofrequency (RF) energy by
displacing its phase of 90.degree., without participating in the
accelerating process. In order to accurately adjust the resonance
frequencies, the accelerating structure comprises tuning micrometer
screws 18 which vary the volume of variano il volume accelerating
and coupling cascrewses 15 and 16.
[0046] However, the presence of tuning screws 18 creates a
significant technological difficulty as far as the vacuum level is
concerned.
[0047] In fact, within the accelerating structure, the ultrahigh
vaccum level, of the order of 10-8 hPa, has to be maintained and in
order to obtain it it is necessary a pump continuously operating
for the whole operative life of the accelerator. Hence, each tuning
screw 18 has to be accurately sealed by means of a suitable vacuum
brazing. This involves the necessity to heat the whole structure up
to temperatures of the order of 500-600.degree. C. These thermal
cycles, besides being expensive, since they conspicuously extend
the production time of the accelerator, also tend to make the
building material get relaxed and, hence, to vary its physical size
impairing the precision of tuning.
SUMMARY OF THE INVENTION
[0048] It is therefore an object of the present invention to
provide a machine for IORT which is easily movable and to be
positioned.
[0049] It is still an object of the present invention to provide
such a machine which makes possible, in a reliable, simple and
efficient way, to radiate an electron beam drastically reducing the
diffusion of X rays, accurately controlling and shielding
environmental radiation.
[0050] It is a further object of the present invention to provide
such a machine which makes possible to very precisely measure the
radiation dose.
[0051] It is another object of the present invention to provide
such a machine which is technologically simple to be realised.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] The present invention will be now described, by way of
illustration and not by way of limitation, according to its
preferred embodiments, by particularly referring to the Figures of
the enclosed drawings, in which:
[0053] FIG. 1 shows an electromagnetic block diagram of a machine
for IORT;
[0054] FIG. 2a shows the profile of the energy conveyed by the
electron beam at the output of an accelerating structure;
[0055] FIG. 2b shows the profile of the energy conveyed by the
electron beam which is necessary for a IORT treatment;
[0056] FIG. 2c shows an electron beam diffusion system used in the
machines of the prior art;
[0057] FIG. 3 shows a geometrical section draft of radiations
generated during a IORT treatment;
[0058] FIG. 4 shows a circuit which is equivalent to an
accelerating structure;
[0059] FIG. 5 shows a particular of an accelerating structure of
the prior art;
[0060] FIG. 6 shows a schematic perspective view of the handling
means of a preferred embodiment of the machine according to the
invention;
[0061] FIG. 7 shows a bottom plan view of a preferred embodiment of
the machine according to the invention;
[0062] FIG. 8 shows a schematic side view of the handling means of
FIG. 6 in a first stressing condition;
[0063] FIG. 9 shows a schematic side view of the handling means of
FIG. 6 in a second stressing condition;
[0064] FIG. 10 shows a schematic side view of the handling means of
FIG. 6 in a third stressing condition;
[0065] FIG. 11 shows a schematic side view of the handling means of
FIG. 6 in a fourth stressing condition;
[0066] FIG. 12 shows a schematic side view of the handling means of
FIG. 6 in a fifth stressing condition;
[0067] FIG. 13 shows a schematic side view of the handling means of
FIG. 6 in a sixth stressing condition;
[0068] FIG. 14 shows a schematic side view of the handling means of
FIG. 6 in a seventh stressing condition;
[0069] FIG. 15 shows a schematic side view of the handling means of
FIG. 6 in an eighth stressing condition;
[0070] FIG. 16a shows a sectional view of a sensor of the handling
means of FIG. 6 in a first configuration;
[0071] FIG. 16b shows a sectional view of a sensor of the handling
means of FIG. 6 in a second configuration;
[0072] FIG. 17 shows an electron beam diffusion system of the
machine of FIG. 7;
[0073] FIG. 18 shows a first particular of the X ray shield of the
machine of FIG. 7;
[0074] FIG. 19 shows a second particular of the X ray shield of the
machine of FIG. 7;
[0075] FIG. 20 shows a luminous signalling device of the machine of
FIG. 7;
[0076] FIG. 21 shows a particular of the electron beam total dose
measuring system of the machine of FIG. 7;
[0077] FIG. 22 shows a block diagram of the electron beam total
dose measuring system of the machine of FIG. 7; and
[0078] FIG. 23 shows a particular of the accelerating structure of
the machine of FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0079] In the following of the description same references will be
used to indicate alike elements in the Figures.
[0080] The machine for IORT according to the invention has a
considerable mobility. In particular, the preferred embodiment has
a weight lower than 400 Kg, eliminating any problem in floor
statics and, most of all, in capacity of elevators and vehicles;
moreover, it has reduced sizes, having a width of 80 cm, in order
to make possible the movement through the elevator doors, and a
length not larger than 2 metres; still, the turning radius is such
to allow the machine to rotate around a vertical axis placed within
the same machine; finally, the preferred embodiment of the machine
is provided with autonomy of movement so that it can move without
necessity to be supplied during transfer.
[0081] The machine for IORT according to the invention allows a
sterile person, for example the radiotherapist, to directly control
movement. This mobility can be obtained with a "sterile handle",
whose mechanical stresses caused by the operator's hand are
translated into electrical signals controlling the movements of the
machine so as to favour the same stresses.
[0082] With reference to FIG. 6, from a mechanical point of view,
the handle of the preferred embodiment of the machine is like a
prism 19 suspended from ten stress sensors 20, which translate the
stress caused by the operator's hand into electrical signals which,
after being interpreted by a control processor, not shown, generate
mechanical movements apt to nullify the same stress. In particular,
with reference to FIG. 7 the processor operates two, respectively
right and left, moving engines of the machine which act on the two
front wheels, respectively right 21 and left 22, of the machine,
and engines for moving the radiating head 23 of the machine, from
which the electron beam comes out. The sterile handle is placed in
correspondence with the radiating head 23. The machine still
comprises two rear wheels, respectively right 24 and left 25, which
are idle and pivoting. Preferably, the two driving wheels 21 and 22
are provided with a clutch, that may be operated through a suitable
tool, which uncouples them from the respective engine and makes
them idle; this makes possible a rapid push motion in case of
shutdown or failure. Moreover, the machine is provided with engine
supplying batteries which make it autonomous during transfers.
[0083] Thanks also to the independence of the two driving wheels 21
and 22, the servomechanism formed by the ten sensors 20, the
processor, the two moving engines of the machine and the engines
for moving the radiating head 23 of the machine allows the machine
to have five degrees of freedom: [0084] rectilinear motion of the
whole machine onto a plane, [0085] rotational motion of the whole
machine onto a plane, [0086] vertical translation motion of the
radiating head 23, [0087] roll motion of the radiating head 23, and
[0088] pitch motion of the radiating head 23.
[0089] The ten sensors 20 form the five bidirectional sensors
needed for the listed five degrees of freedom, apt to measure both
the traction stress and the compression stress. For reasons of
simplicity and reliability, the preferred embodiment of the machine
according to the invention comprises, instead of five bidirectional
sensors, ten sensors 20 apt to react only to compression stresses,
being much more sturdy and precise than bidirectional sensors.
[0090] The user takes the prism 19 in correspondence of its centre
and may impress a force in any direction. With reference to FIG. 8,
assuming that the user impress a forward uniform stress, as
indicated by the arrow in FIG. 8, the two front sensors,
respectively top 20uF and bottom 20lF, are stressed, detecting a
compression, and give two equal signals; in particular, in FIG. 8
the stressed sensors are shown in grey. The control processor of
the servomechanism analyses the signals coming from all the ten
sensors 20 and operates the two moving engines at identical speed
so as to impress to the machine a forward movement. Similarly, with
reference to FIG. 9, if the user impress a rearward uniform stress,
as indicated by the arrow in FIG. 9, the two rear sensors,
respectively top 20uB and bottom 20lB, shown in grey, are stressed
and give two equal signals that the control processor interprets
for operating the two moving engines at identical speed so as to
impress to the machine a left sideways movement. In particular, in
the following of the present description a stress involving only
two sensors 20 placed on the same side is indicated as an equally
directed stress.
[0091] Still with reference to FIG. 6, it is evident that if the
equally directed stress is impressed to two side sensors,
alternatively to the right sensors 20uR and 20lR or the two left
sensors 20uL and 20lL, the control processor generates an inverted
rotation of the two moving engines (the right engine rotates
clockwise and the left one rotates anticlockwise or vice versa)
which is proportional to the stress, that causes a rotation around
a vertical axis which is central with respect to the segment
joining the axis of the two driving wheels.
[0092] These movements may be combined in an infinite series of
elementary translations and rotations, since the control processor
continuously analyses the stresses which are impressed to the prism
19 and consequently modifies the commands sent to the moving
engines.
[0093] Differently, differential stresses onto the sensors 20
produce corresponding signals that the control processor analyses
so as to operate the engines for moving the radiating head 23 of
the machine which generate rotations of the radiating head 23, and
precisely, depending on which pair of sensors 20 is stressed, roll
or pitch rotations. In particular: in the case when the front top
sensor 20uF and the rear bottom sensor 20lB are stressed, a pitch
rotation is generated as shown by the arrow of FIG. 10; in the case
when the front bottom sensor 20lF and the rear top sensor 20uB are
stressed, a pitch rotation is generated which is the opposite of
the previous one, as shown by the arrow of FIG. 11; in the case
when the right top sensor 20uR and the left bottom sensor 20lL are
stressed, a clockwise roll rotation is generated; finally, in the
case when the right bottom sensor 20lR and the left top sensor 20uL
are stressed, an anticlockwise roll rotation is generated.
[0094] Also in this case it is possible to have movements which are
a combination of pitch rotations and roll rotations, that may be
furthermore combined with the previously illustrated movements.
[0095] Finally, a stress onto the 20T placed at the top of the
prism 19 generates a lifting of the radiating head 23, as shown in
FIG. 12, while a stress onto the sensor 20D placed at the base of
the prism 19 generates a lowering of the radiating head 23, as
shown in FIG. 13.
[0096] The movements of the servomechanism, above illustrated with
reference to FIGS. 8-13, are related to a configuration of the
radiating head 23, to which the handle 19 is integral, placed in
vertical position, that is in transport position. The control
processor allows the machine to be correctly moved even when the
radiating head 23, and consequently the axis of the prism 19, has a
different orientation and, hence, the directions toward which the
operatore impress in order to obtain a certain movement involve
other sensors.
[0097] Purely by way of illustration and not by way of limitation,
it is assumed that the radiating head is rotated of 45.degree.
forward, as shown in FIG. 14. In order to lift it, the operator
upward pushes the whole prism 19 which transmits the stress,
besides the top sensor 20T, also to the two front sensors 20uF and
20lF, all pointed out in grey in FIG. 14. Similarly, in the limit
case (usually not possible) of the radiating head 23 and the prism
19 rotated of 90.degree., in order to lift the head only the front
sensors 20uF and 20lF are stressed, as shown in FIG. 15.
[0098] In order to correctly operate the engines for moving the
radiating head 23 or the whole machine, the control processor
performs the following operations:
[0099] determining the orientation of the prism 19 with respect to
a first Cartesian triad which is integral with the machine;
[0100] composing, according to the determined orientation of the
prism 19, the stresses which are measured by the sensors 20 (each
one of which detects only the stresses which are orthogonal to it),
until a resulting vector and a resulting torque are obtained with
respect to a second Cartesian triad which is integral with the
prism 19;
[0101] calculating the projections of the resulting vector and of
the resulting torque onto the first fixed Cartesian triad of the
machine, obtaining the vector of translation of the whole machine,
the torque of rotation of the whole machine, the vector of vertical
translation of the radiating head 23, the torque of roll rotation
of the radiating head 23, and the torque of pitch rotation of the
radiating head 23; and
[0102] operating the two engines for moving the whole machine and
the engines for moving the radiating head 23 proportionally to the
obtained vectors and torques.
[0103] The stress sensors 20, also known as load cells, suffer for
possible, even modest, overloads, because they break at a stress
equal to 1.5 times their full-scale maximum charge. With reference
to FIGS. 16a and 16b, in order to detect stresses which are
proportional to the ones impressed by the operator, the preferred
embodiment of the machine according to the invention has a
protection of the sensors 20. In particular, each sensor 20 is
inserted into a mechanical housing 26 that, by means of a
deformable elastic element 27, such as a spring, limits the
accidental maximum stress that can be applied to the sensor 20. In
particular, FIG. 16a shows the housing 26 in its not stressed limit
position, while FIG. 16b shows the housing 26 in its limit position
of maximum stress onto the sensor 20. As shown in FIG. 16b, the
elastic element 27 deforms up to the housing 26 reaches a
mechanical stop, such as a beat with the handle structure, the
maximum stress exerted onto the sensor 20 in this case being non
larger than the full-scale of the same sensor.
[0104] Moreover, all the electronic, electromagnetic, and
mechanical components of the machine, which are sensitive to
humidity, are enclosed in sealed compartment, so as to make
sterilization of the whole machine in autoclave possible.
[0105] In order to make flatt, instead of Gaussian, the energetic
profile of the diffused electron beam and eliminating the problem
of the generation of braking X rays due to a diffusing plate, the
machine for IORT according to the invention provides that the beam
diffusion system comprises, as shown in FIG. 17, a divergent
magnetic lens 28 for diffusing the beam. The lens 28 does not
produce any radiation and is limited to make the electron
trajectories diverge; in particular, a tube 11 in light material
selects the diffused beam, absorbing the undesired side portion of
it, obtaining the needed uniformity over the range of application,
according to the profile shown in FIG. 2b.
[0106] Advantageously, the machine has luminous devices for
signalling the condition of machine on and of beam emission.
Moreover, the machine may further be provided with a timer of
duration T, preferably equal to 30 seconds, still more preferably
adjustable, during which an acoustic device is operated to indicate
the requirement of leaving the forbidden areas before the start of
the beam emission. Such signalling devices facilitate the
delimitation of suitable guard areas which have to be left only for
the short radiating period, usually of lasting 30 to 60 seconds,
avoiding the use of uncomfortable and bulky mobile shields which
uneasily are maintained sterile.
[0107] As mentioned with reference to FIG. 3, in order to shield
the braking X radiations generated by the patient, it is necessary
to position an absorbing mass 13, comprising one or more lead,
along the the beam axis prolongation.
[0108] With reference to FIGS. 18 and 19, the preferred embodiment
of the machine according to the invention comprises a shield
including a mobile steel stand 29, preferably provided with
lockable wheels 30, to which an absorbing mass 13 is coupled which
is mobile with respect to the stand 29 by means of a sliding
mechanism 31.
[0109] An anchorage dome 32 of a detecting device 33 is integrally
coupled to the centre of the absorbing mass 13, the detecting
device 33 being integrally coupled to the machine 34, substantially
at the same height of the duomo 32. In particular, the detecting
device 33 measures through two potenziometers 35, the azimuth angle
and the distance from the centre of the absorbing mass 13 with
respect to the machine 34. These data, together with the elevation,
the roll angle and the pitch angle of the radiating head, are
processed by a processor, preferably the same control processor of
the servomechanism of the machine, for univocally determining the
position of the beam axis on the surface of the absorbing mass
13.
[0110] With reference to FIG. 20, the processor also drives a
luminous signalling device 36 that gives indications to the
operator for signalling the possible needed movements for correctly
positioning the shield or the reached attainment of the correct
position.
[0111] The preferred embodiment of the machine according to the
invention further comprises a radiated beam measuring system that,
instead of a transmission ionization chamber, which cannot be used
for the high dose flows used for IORT, includes an amperometric
transformer that measures the electron beam current at the output
of the titanium window of the accelerating structure.
[0112] The electron beam energy fluency, which may be measured in
terms of dose only after being absorbed by a material, is given by
the product V.sub.accelerating.times.I.sub.beam, where
V.sub.accelerating is the accelerating voltage and I.sub.beam is
the electron beam current. In the machine according to the
invention, which comprises a stationary wave accelerator, the
current production is related to the resonance of the cascrewses,
like also the creation of the accelerating electric fields and,
consequently, the voltage V.sub.accelerating. Hence, assuming the
electron injection constant, an equal variation of kinetic energy
corresponds to a small variation .DELTA.I.sub.beam of the current
I.sub.beam. Therefore, instead of using a system for measuring the
accelerating voltage V.sub.accelerating, the measure of the dose is
based on the measure of the beam current I.sub.beam, the
instantaneous dose having a dependency of quadratic type from this
D=K*I.sub.beam.sup.2 which results linearizeable for small
variations .DELTA.I.sub.beam that usually are observed during the
operation around the reference value
I.sub.beam.sub..ltoreq..sub.Ref, wherein .DELTA.I.sub.beam<0.1
I.sub.beam.sub.--.sub.Ref, usually plus
.DELTA.I.sub.beam.ltoreq.0.03 I.sub.beam.sub.--.sub.Ref. Therefore,
the instantaneous dose D is obtained through the following linear
relation from the measure of the beam current I.sub.beam, i.e. from
the variation .DELTA.I.sub.beam of this
(.DELTA.I.sub.beam=I.sub.beam-I.sub.beam.sub.--.sub.Ref):
D=D.sub.0+A*.DELTA.I.sub.beam where D.sub.0 and A are
experimentally determined in the phase of clinical dosimetry of the
machine, phase which employs dosimetries certified indipendent from
the energy and from the dose portion, preferably according to Frike
dosimetry.
[0113] The main advantage is the absolute linearity of the
measuring device and the great stability and independence of the
amperometric transformers from environmental factors, such as
pressure, humidity and temperature. Moreover, with respect to the
conventional use of transmission ionization chambers, the use of an
amperometric transformer also eliminates the need for long and
complex calibration measures after the movement of the machine,
since an amperometric transformer is insensitive to vibrations and
to acceleration due to transport.
[0114] As shown in FIG. 21, from a constructive point of view the
measuring system comprises a toroidal transformer would on a
ferrite toroidal core 37 of suitable rating: the primary of such
transformer is the electron beam that, passing through the hole 38
of the torus 37 magnetically links with the wounded secondary 39.
The short circuit current in the secondary has a value equal to 1/n
of the electron beam current I.sub.beam, where n is the number of
turns of the secondary 39 which are wounded on the core 37.
[0115] With reference to FIG. 22, the current generated on the
secondary of the toroidal transformer 40, which is proportional to
the current I.sub.beam of the beam to be measured, is inserted in a
current buffer circuit 41, which is arranged to increase the
impedance of the circuit downstream the transformer 40. The output
of the buffer 41 supply an integrator circuit 42 which adds the
several current contributions due to the electron beam pulses,
giving at the output a voltage which is proportional to the total
energy flow of the emitted electron beam. Such voltage is
digitalised by an analog/digital converter or ADC 43, whose output
is sent to the logical circuits which carry out the comparison of
the digitalised voltage with the pre-set dose value, in order to
determine the moment when the irradiation process has to be
stopped.
[0116] Finally, the preferred embodiment of the machine according
to the invention uses, instead of the vacuum brazing, a new seal of
the tuning screw of the accelerating structure which avoid the
heating of the whole structure. In particular, with reference to
FIG. 23, each tuning screw 18, once inserted into the accelerating
structure 44 in the adjustment final position, is covered by a cap
45, preferably in copper, which is directly and locally welded to
the accelerating structure 44 on each screw 18 through an arc
welding in controlled atmosphere. In order to prevent the heat from
propagating, particular profiles of the structure 44 have been
studied which avoid this phenomenon. In particular, the structure
44 presents, in correspondence of each slot for the screws 18, a
lip 46 that is welded to the cap 45 favouring heat dissipation;
also the cap 45 has a protruding frame 47 dissipating heat.
[0117] The direct and local electrical arc welding on each screw 18
in controlled atmosphere shortens of about one third the
accelerator manufacturing time and presents the great advantage of
allowing, in case of loss of seal of a tuning screw 18, the defect
to be corrected through passing again the electrical arc only onto
the defective part, without putting at risk the seal of the other
screws 18 as, instead, in the case when these are brazed with
eutectic alloy.
[0118] It is evident that the machine according to the invention
offers the advantage of a high mobility, being much lighter and
having a reduced bulkiness with respect to the conventional
machines. In particular, the machine according to the invention may
be easily moved with common elevators, may autonomously cover paths
even of some hundreds of metres inside and outside an hospital, and
may be transported with a suitably equipped vehicle from a clinic
to another with no need of recalibration.
[0119] The present invention has been described, by way of
illustration and not by way of limitation, according to its
preferred embodiments, but it should expressly be understood that
those skilled in the art can make other variations and/or changes,
without so departing from the related scope of protection, as
defined by the following claims.
* * * * *