WO2014195986A1

WO2014195986A1 - Radiotherapy treatment device for cancer patients

Info

Publication number: WO2014195986A1
Application number: PCT/IT2014/000157
Authority: WO
Inventors: Giuseppe FELICI
Original assignee: S.I.T. - Sordina Iort Technologies S.P.A.
Priority date: 2013-06-07
Filing date: 2014-06-06
Publication date: 2014-12-11
Also published as: ITVI20130149A1

Abstract

A radiotherapy treatment device for cancer patients, comprising a medical accelerator of charged particles, which includes a RF accelerant guide from which a particle beam irradiating organs affected by a disease exits, and a tubular element (11), which is configured to shape said beam in order to obtain a suitable irradiation of said organs, wherein a measuring block (19) is inserted between an end portion (10) of said charged particle accelerator and said tubular element (11), said measuring block (19) being formed by at least two RF resonant cavities (25, 26) which are mechanically coupled together and being connected, on one side, to an outlet opening of said medical accelerator and, on the other side, to at least one support flange (14, 15) of the tubular element (11). Each of said resonant cavities (25, 26) is placed so as to have its internal surface perpendicular to the lines of the magnetic field generated by the current flow of the particle beam and is tuned to the resonance frequency of the working mode of the accelerant guide.

Description

RADIOTHERAPY TREATMENT DEVICE FOR CANCER PATIENTS

The present invention relates to a radiotherapy treatment device for cancer patients.

More particularly, the invention relates to a device which performs an instantaneous measurement of the dose which is emitted for each pulse during a radiotherapy treatment performed with charged particles (electrons, protons, carbon-ions) and radiated on organs and tissues downstream the device; the invention also relates to a machine for intraoperative radiation therapy (IORT) provided with said device.

The measurement is achieved through a system of integrated passive resonant cavities which perform an instantaneous measurement (a real-time measurement) of the electron beam exiting from an accelerator of charged particles for radiotherapy.

It is well known that intraoperative radiotherapy (IORT) is an innovative technique that is gradually spreading worldwide in the treatment of various forms of cancer also thanks to the development of mobile machines; in particular, the intraoperative radiotherapy consists of an irradiation performed during the surgical removal of the tumor mass, which is generally done using, as ionizing particles, a widespread and uniform beam of electrons with a kinetic energy varying from 4 to 12 MeV.

In particular, IORT is a radiation treatment which consists in sending a high dose (about 1/3 of a traditional RT) of electron radiation to the surgically exposed tumor mass, through a collimated beam of electrons .

Among the most feared diseases of our times is no doubt that the tumor is believed to be relevant because of the mortality's rate of some types of tumor and taking into account the difficulty of care.

The tumor, or, less commonly, neoplasia or cancer, if malignant, is a class of diseases characterized by an uncontrolled reproduction of some cells, which cease to fulfill the physiological mechanisms of cellular control as a result of damage to their genetic heritage .

A tumoral cell is a crazy cell, that is to say there is an error in the system that controls reproduction of said cell.

All pre-cancerous and cancerous cells have in fact very extensive alterations of their set of chromosomes; in particular, the number of chromosomes of their nucleus is altered and the chromosomes themselves are damaged, multiple or missing.

The chromosome damage of cancer cells is so severe and extended to provide evidence that in all cases of cancer all cancer cells result from a single parent changed cell.

This random genetic disorder explains the extreme variability in appearance, effects, symptoms and prognosis of known many forms of cancer.

Therefore, tumors, despite the general mechanism of the origin, may have a very broad range of changes and symptoms .

However, a constant increase in the number of cancerous cells, due to the greater speed of cell reproduction, is performed and therefore a greater number of tumor cells multiply and fewer of them die, while the cells which survive go on to multiply.

Usually the growth of a tumor follows a geometric law: it is very slow in the beginning, but it accelerates with increasing the tumor's mass.

The critical size of a tumor is about one cubic centimeter; when said size is reached, the tumor begins to grow very quickly and gives rise to early symptoms and becomes detectable with medical examinations and analysis; however, the initial symptoms are often ignored or underestimated.

The great speed of reproduction of the cancer cells is the basis of the need and urgency to cure it as soon as possible and the more drastically, i.e. making sure to remove with the highest degree of certainty all cells which are "infected", as, as mentioned above, the tumor may evolve, and then revive, even by a single mutated cell.

The best-known treatment of tumors is surgery.

Using surgery it is possible to remove what is defined as the tumor mass, i.e. the set of mutated cells and their surroundings.

This method of treatment is not always usable or, when used, is not always sufficient to ensure the desired result .

In fact, it is not possible to know whether the cancer has also affected the surrounding or adjacent cells that seem healthy; furthermore, it is possible that the surgical operation leads to a dissemination of the tumor cells.

For these reasons, in combination with or as an alternative to surgery, chemotherapy and radiotherapy are also used.

Radiotherapy or radiation therapy is an irradiance, by ionizing radiation, of tumor tissues and/or tissues adjacent to the tumor. Chemotherapy is based on the specific sensitivity of each tumor to certain substances and a specific blend of multiple drugs is studied for each patient; almost always, the mixture also includes one or more inhibitors of mitosis so as to prevent the cell proliferation.

Said inhibitors are however cause some serious and unwanted side effects, such as hair loss, which affect patients undergoing chemotherapy.

Radiotherapy involves side effects too.

In fact, radiotherapy, as chemotherapy, significantly weakens the body and submit to its direct effects, even if only partially, even the healthy organs of the patient .

In both cases, therefore, it is important to minimize the application so as not to become too significant side effects for the patient.

The technological development of recent years has led, through the development of different technologies and "imaging" techniques, to optimize the dose of ionizing radiation on the target, thus ensuring protection of healthy tissues of the organs.

According to the above reasons, a common element to each particle accelerator for radiotherapy is the need to include a system for a real-time measurement of the output ionizing radiation and the dose of ionizing radiation to be sent on the target for each emitted radiation pulse.

The main object of the present invention is therefore to provide a radiotherapy treatment device for cancer patients, which allows to measure in real time the output radiation of a medical accelerator of charged particles . Another object of the present invention is to provide a radiotherapy treatment device for cancer patients, whose features are liable to comply with the technical standard EN 60601-2-1, ed. III.

A further object of the invention is to provide a radiotherapy treatment device for cancer patients, which uses a measuring system composed of two independent subsystems, one of said subsystems having constituted by a crossing system, according to the requests of the technical standard EN 60601-2-1.

These and other objects are achieved by a radiotherapy treatment device for cancer patients according to the attached claim 1; other technical characteristics are included in the subsequent claims .

An object of the present invention is also a machine for performing a treatment of intraoperative radiation therapy (IORT) having the above mentioned radiotherapy treatment device, according to claim 10.

The treatment device which is the object of the present invention is advantageous with respect to the known devices, which are based on ionisation chambers and whose problems have long been known and well reported in the literature, especially for IORT accelerators, since it is not possible to use scattering filters which are able to obtain a nearly uniform fluence on the surface of the chamber.

In fact, it is well known that the ionization chambers must operate in conditions of "good geometry" so that they can be described according to the theory of Bragg- Gray that allows the dose calculation on the basis of the charge collection; only in these conditions the charge collected between the electrodes of the ionization chamber is proportional to the dose which is deposited by the electron beam.

Therefore, the electron beam exiting from the accelerator guide has to interact with a massive filter in order to cause a scattering effect for increasing the cross section, so that the ionization chamber is invested by a flow which is substantially spatially homogeneous .

Said interaction inherently produces a large amount of X-rays and, because the low scattered radiation is one of the design specifications that an IORT accelerator has to meet, a massive scattering filter is strongly discouraged in a IORT machine.

On the other hand, the device according to the invention is based on the use of a system of integrated resonant cavities and, therefore, since the resonant cavity works on a completely different physical principle, as it measures the current passing through it, it works perfectly with a beam of particles having a small cross section and does not require any scattering filter.

Thus, the measurement of the beam current is inherently proportional to the absorbed dose; in fact, from the definition of dose,

dE_

D pulse

dm

and for one single pulse

where Vbeam is the average kinetic energy of the pulse, Ibeam is the current, m(E)* is the mass where the electrons entirely put the carried energy and Tpulse is the period of the pulse.

As the IORT treatment is carried out with fixed energy, the previous equation says that the measurement of the beam current allows to immediately assess the dose to be deposited on the target.

Therefore, the device of the present invention is completely different, both in the physical operating principle and in the implementations, with respect to the known ionization chambers, which currently represent the standard means that are used in all medical accelerators and such a device can advantageously replace the measurement system based on said known ionization chambers for all accelerators employing charged particles (electrons, protons, ions, etc. ) .

Finally, the device of the invention, as will be shown below, allows a direct measurement of a physical quantity (the current) which is immediately related to the dose deposition on the target and is finally inherently linear and not subject to saturation phenomena, as can happen for known devices (such as the monitor chambers) .

The present invention will be now described according to a preferred embodiment and with particular reference to the attached figures, in which:

- figure 1 is a partial and partially sectioned view of the radiotherapy treatment device for cancer patients, according to the present invention;

- figure 2 is a perspective partial and partially sectioned view of the treatment device, according to the present invention;

- figures 3 and 4 show block diagrams relating to the operating electronic system of the device of figures 1 and 2, according to the present invention;

- figure 5 is an exploded perspective view of one of the components belonging to the treatment device for cancer patients, according to the present invention; - figure 6 is a perspective view of the component of figure 5, according to the invention;

- figure 7 is a perspective and sectioned view of the component of figure 5, according to the present invention.

With reference to the above mentioned figures, 10 indicates a terminal portion of a medical accelerator of charged particles, from where a particle beam, which is configured to irradiate the organs affected by the disease, exits, while 11 indicates an applicator, which allows to obtain a suitable shaping of the beam exiting from the accelerator before the application of said beam on the organ to be treated; the applicator 11 consists of a tube-holder 12 with a shaped upper 13 and support elements 14, 15, respectively made in PTFE and aluminum, and a terminal pipe 16, connected to the tube-holder 12 by means of a lower flange 17 and a terminal flange 18.

According to the present invention, a measuring block 19 is inserted between the end portion 10 of the accelerator of charged particles and the applicator 11; the measuring block 19 is formed by two passive RF resonant cavity 25, 26, which are integrated with each other, and is coupled, on one side, to the exiting opening of the particle beam accelerator and, on the other side, to the support flanges 14, 15 of the applicator 11, as shown in the enclosed fig. 1 and 2. In particular, each of said RF resonant cavities 25, 26 is tuned to the same resonant frequency of the main mode of the accelerating guide which is inserted in the terminal portion 10 (outgoing radiation) of the particle accelerator and said two resonant cavities are mechanically coupled, so that they can be simultaneously thermostated.

In particular, as shown in the enclosed fig. 5, 6 and 7, the measurement block 19 is formed by a shaped body 20 having a dual cavity, with a top and bottom shell 21 fixed to the body 20, from which the particle beam passes, lateral channels 22 for temperature control and tuning screws 23.

The signal of the beam current is drawn by the capacitive pick-up 24 (a loop pick-up) , which are placed nearby the internal diameter of the cavities 25, 26 of the body 20; furthermore, the internal cavities 25, 26 are oriented so as to have the surfaces perpendicular to the lines of the magnetic field generated by the passage of the beam current, taking into account that the charged particle beam exiting the accelerator enters the passive cavity 25 (input beam 27 in the enclosed fig. 3) and exits the passive cavity 26 (output beam 28 in the enclosed fig. 3) .

The signals which are picked up by the loop pick-up 24 are sent to respective electronic circuits 29 for counting the dose and from here, via the serial ports 31, to a control unit 30 of the electromagnetic radiation (with analog buffer 32 and interlock buffer 33), and to a general control unit 34, which is connected to a display 35.

Moreover, each electronic circuit 29 is composed of a detector 36 of the radio frequency signal, an analog amplifier 37 and a feedback circuit consisting of a signal conditioning block 38, connected to an A/D converter 39 and to a microprocessor 40 with memory 41. The measurement block 19 may obviously be implemented to any RF accelerating structure, irrespective of the working frequency (L-band, S, C or X) and, in particular, the block 19 provides a direct measure of the dose of electromagnetic radiation for all medical accelerators that use charged particles, such as electrons, protons and/or ions.

The radiotherapy treatment device for cancer patients, according to the present invention, is able to work as follows .

The current accelerated by the electrons accelerator (for example, a LINAC) , which is powered from a RF source (klystron, magnetron) and which emits the electron beam 27 sent to the organs to be treated, can always be represented as a Fourier series, with the main frequency equal to the resonance frequency ωθ of the working mode of the accelerant guide, so that:

oo

/( =∑/„ sininay)

The magnetic field generated by the electron beam at each capacitive pick-up 24 is:

while the magnetic field that is actually detected, due to the filtering of the measurement block 19 having a double resonant cavity, is

In which d is the distance between the electron beam passing through the body 20 of the measurement block 19 and the center of the loop of each pick-up 24, μθ is the vacuum magnetic permeability and II is the first harmonic .

The passive resonant cavities 25, 26 are tuned so as to have its own resonance frequency equal to ωθ to the desired operating temperature and the voltage measured across the loop of each capacitive pick-up 24 is thus given by:

V(t) = - cos(e¾

in which A is the area of the loop.

The signal, which is integrated over time using the electronic circuit 29, provides a measure which is inherently proportional to the charge carried by the electron beam passing through the measurement block 19 and, therefore, proportional to the dose of charged particles which are deposited on the organ to be treated.

The metallic material of each resonant cavity 25, 26 is chosen so as to comply with the need to ensure an efficient temperature control of the double resonant cavity and the use of two integrated resonant cavities 25, 26 allows to perform the measurement of the beam current exiting from the accelerator.

The response of the measurement block 19 is independent of the environmental conditions (temperature, pressure and humidity) and, further, the main advantage of the device according to the invention is the response's linearity with respect to the current, at a given predetermined energy; as already said, the above feature is the reason why the device according to the present invention is preferable with respect to the use of known ionization chambers.

The two resonant cavities 25, 26 are designed so as to measure one independently of each other, according to the technical requirements of the standard EN 60601-2- 1, thus ensuring the electromagnetic isolation between the two cavities, with a scattering parameter S12 measured between the two cavities 25, 26 which is less than -30dB.

The above features ensure that the maximum possible variation of the electrical signal measured at the output (i.e. at the connector of the loop of the pickup 24 onto which the transmission line that carries the signal to the data acquisition electronic device 29 is inserted) of one of the two cavities, which is caused by the other cavity, is less than 0,1%.

The device according to the invention achieves the above results in at least three different ways.

According to a first embodiment, it is possible to use a channel 42 for travelling the electron beam, said channel connecting the two resonant cavities 25, 26. Said transport channel 42 has a length and a diameter suitable for having electromagnetic insulation and for obtaining that the transverse section of the charged particles beam along the path taken within the measurement block 19 is less than the section of said transport channel 42; alternatively, the transport channel 42 has a geometry such that the electromagnetic field is damped at the resonant frequency of each single resonant cavity 25, 26.

According to another embodiment, it is possible to use, in place of the channel 42, a third resonant cavity, placed between the two cavities 25, 26 and tuned to a frequency which is significantly different from the tuning frequency of the cavities 25, 26.

Moreover, the sizing of each loop of the pick-up 24 is performed so as to ensure a suitable signal/noise ratio and the electromagnetic isolation between the two cavities, while the implementation of the device according to the invention varies depending on the working frequency of the accelerant guide; said working frequency substantially defines the size of each resonant cavity 25, 26, based on the atmosphere inside the system (air, specific mixture of gas or vacuum) , as well as on the type of charged particles which have to be accelerated.

For example, according to a preferred embodiment of the invention, in correspondence of the terminal portion 10 of the particle accelerator, an electrons accelerant guide is used, which operates at 2998 MHz, with a measurement block 19 comprising two air-integrated resonant cavities 25, 26.

The cavities 25, 26 are realized in the S-band and are resonant at 2998 MHz; moreover, the cavities are decoupled from each other, separately tunable and globally thermostated and each of them is equipped with a magnetic pick-up 24.

Each cavity 25, 26 has a circular cross section and a transport channel 42 with cylindrical geometry; in particular, the transport channel 42 which passes through the two cavities 25, 26 consists of a cylinder of internal diameter equal to 20 mm and height 24 mm and the loops have a rectangular section with a first side of 3 mm and a second side of between 2 and 4 mm. From the foregoing description, the characteristics of the radiotherapy treatment device for cancer patients, which is the object of the present invention, are clear as well as the related advantages are also clear.

Finally, it is clear that many other variations may be made to the device of the invention, without departing from the principles of novelty inherent in the inventive idea and in the scope of protection as claimed in the appended claims.

Claims

1. Radiotherapy treatment device for cancer patients, comprising a medical accelerator of charged particles, which includes a RF accelerant guide from which a particle beam irradiating organs affected by a disease exits, and a tubular element (11) , which is configured to shape said beam in order to obtain a suitable irradiation of said organs, characterized in that a measuring block (19) is inserted between an end portion (10) of said charged particle accelerator and said tubular element (11) , said measuring block (19) being formed by at least two RF resonant cavities (25, 26) which are mechanically coupled together and being connected, on one side, to an outlet opening of said medical accelerator and, on the other side, to at least one support flange (14, 15) of said tubular element (11), each of said resonant cavities (25, 26) being positioned so as to have its internal surface perpendicular to the lines of the magnetic field generated by the current flow of said particle beam and being tuned to the resonance frequency of the working mode of said accelerant guide.

2. Device according to claim 1, characterized in that said measuring block (19) is formed by a shaped body (20) within which said resonant cavities (25, 26) are made and which has a shell (21) , side channels (22) for a temperature control and tuning screws (23) .

3. Device according to at least one of the preceding claims, characterized in that at least one pick-up intake (24) is coupled with said measuring block (19) and comprises at least one loop that extends within said resonant cavities (25, 26) , so that at said pickup intake (24) a current signal of said particle beam is picked up starting from a measurement of the magnetic field generated by said particles beam, said current signal being sent to electronic control circuits (29) electronic control units (30, 34) , in order to provide a direct measure of the radiation dose exiting from said medical accelerator, which is proportional to said current signal of the charged particles beam.

4. Device according to at least one of the preceding claims, characterized in that said measuring block (19) includes two integrated resonant cavities (25, 26) , which are provided for carrying out a measure one independently from the other and for ensuring the electromagnetic isolation.

5. Device as claimed in at least one of the preceding claims, characterized in that said resonant cavities (25, 26) are connected by means a transport channel (42) having a length and a diameter so as to ensure the electromagnetic isolation and so that the cross section of said charged particles beam along the path taken within said measuring block (19) is smaller than the cross section of said transport channel (42) .

6. Device according to claim 5, characterized in that said transport channel (42) has a geometry such that within said channel (42) the electromagnetic field is damped at said resonance frequency of each resonant cavity (25, 26) .

7. Device as claimed in at least one of claims 1 to 3, characterized in that a third resonant cavity is provided between said two resonant cavities (25, 26), said third resonant cavity being tuned to a frequency which is substantially different with respect to the tuning frequency of said two cavities (25, 26) .

8. Device as claimed in at least one of the preceding claims, characterized in that said medical accelerator has an electrons accelerant guide operating at 2998 MHz and said resonant cavities (25, 26) are realized in the S-band, are resonant at 2998 MHz, said cavities (25, 26) also being decoupled between them and separately tunable and thermostated.

9. Device as claimed in at least one of the preceding claims, characterized in that each cavity (25, 26) has a circular cross section, while said transport channel (42) has a cylindrical shape.

10. Machine for intraoperative radiation therapy (IORT) , comprising a radiotherapy treatment device according to at least one of claims 1-9.