Abstract— The construction of a new radiological centre, based on INR proton linac in Troitsk near Moscow, is now in progress. Its 1-st stage with one horizontal-beam treatment room and one conventional-therapy treatment room will be completed and put in action during one year. The proton linac energy variation (70 - 250 MeV) and the patient chair design will allow to treat any tumors from eye tumors up to 10 cm wide deep-sited tumors. The boost method, combining conventional radiotherapy and proton therapy, will increase the effectiveness of linac work. Very thin multichannel ion chambers, the patient chair, a new individual beam formation system, a digital x-ray position control system and others original systems were developed in INR for the purposes of the centre. On the first stage, the dose will be delivered by the passive scattering method. However, the linac beam parameters are suitable for the beam scanning as well. The next stage of the centre may include a non-horizontal beam treatment room (gantry or vertical beam) and the beam scanning. The proton accelerator and the beam channel were designed for the simultaneous acceleration and delivering of several beams. This allows to combine the patient treatment with the isotope production and scientific work, for example, on neutron sources. One of possible applications of the parallel beams is the neutron capture radiotherapy with the help of gadolinium or other targeting materials since the neutron flux may be sufficiently high. Taking into account that several radioisotopes, including short living ones, may be produced and applied in the same place, the INR centre may become a really universal radiological centre for the practical radiotherapy and researches in this field.

Keywords— proton therapy, linear accelerators, radiology

 I. INTRODUCTION

It is known that about 20% of all oncological patients die because of their primary tumors without metastases. In many of these cases, the loco-regional treatment with the help of surgery and conventional radiotherapy is complicated by difficult localizations of tumors when neighbor critical organs prevent the application of conventional methods.

The hadrontherapy alone or in combination with conventional methods may allow us to significantly reduce the above number. The principal advantages of radiotherapy with proton beams, as a particular case of hadrontherapy, are due to physical properties of proton beams in matter: 1) protons, as all ions, have a unique inverse dose profile (the Bragg peak) and loose a large fraction of their initial kinetic energy in a narrow region near the end of their path in matter, 2) protons do not produce any irradiation behind the Bragg peak, which has an energy-dependent position, 3) protons have a relatively small range and lateral scattering, 4) protons, as all charged particles, can be steered by magnetic fields allowing precise shaping of the treatment volume by means of dynamic scanning of the beam. Although these advantages of proton beams are known since 1946, technical difficulties prevent a wide application of hadrontherapy. By now about 30000 patients have been treated using this method in the world and about 4000 - in Russia. Each year, only about 1% of patients with prescriptions for proton therapy will have a chance to get this kind of treatment. Since proton and heavier ion accelerators (as well as beam delivery, monitoring and control systems) are quite complicated facilities, most of working hadrontherapy centres, except LCUMC are still based on physical research institutes. For example, in Germany, the Pilot project for proton therapy was realized in GSI on a basis of research synchrotron prior to construct the Heidelberg ion beam medical centre. The proton therapy medical centre with a GANTRY and beam scanning techniques is successfully working at PSI. The second stage of this centre is now under construction in the same building. In Russia, three proton therapy centres are now in action in nuclear research institutes (see Table 1) and the fourth is now under construction in INR.

Table 1: Accelerators for proton therapy

Fig.1 INR proton linac

In order to irradiate targets at different depths, the beam energy must be variable in the range 70 – 250 Mev. From the other side, for the purposes of beam monitoring and scanning, the pulse duration and the pulse frequency (the duty cycle) must be as large as possible. From the Table 1 it follows that among operating accelerators in Russia only the accelerator in Troitsk fits all basic requirements of proton therapy for beam parameters (the energy range, duration and frequency of pulses).

The uniqueness of the INR accelerator (Fig.1) is that it can provide not only the proton therapy of all kind of tumors, but also other basic methods of beam therapy and diagnostics: brachytherapy, diagnostics and therapy with radiopharmaceuticals, and also the neutron - capture therapy (NCT). This is due to an opportunity to vary not only the energy, but also the intensity of beams in a wide range. Though the linac was designed for higher beam intensities with average currents in the range of several mA, the necessary therapeutic currents of about 1 nA are simply obtained with the help of collimators in the initial part of accelerator. Moreover, the additional injector for H^- -ions, which is now under construction, will allow to simultaneously produce two different beams: one low-intensity beam for therapy and another high-intensity beam for other applications. 

II. Present status of the Centre

The first stage of the Centre, which will completed next year, includes one treatment room for proton therapy with horizontal fixed beam and one treatment room for photon therapy with 6 MeV medical electron accelerator SL-75-5-MT. The patient positioning system in the proton treatment room, as well as control systems, are designed in a way to allow the irradiation of any targets from small eye tumors up to large deep-sited tumors of the body. This means that a patient may be fixed in a sitting and lying positions. The original passive dose formation system gives an upper limit for the target size of the order of 10 cm. The universal and very precise treatment chair for the fixation of patient in any position is also the original product of INR (Fig.2).

The photon therapy treatment room (see Fig.2) is completed and will acquire first patients by the end of this year.

Fig.2 Proton therapy treatment room (under construction) and photon therapy treatment room

For many reasons, the proton beam time is quite expensive, in particular for research accelerators. The special control system for beam distribution among the physical and medical installations of the experimental hall of INR is being designed [1]. The control system will provide the simultaneous operation of different installations and will increase the effectiveness of proton beams.

The fact that for larger tumors the number of irradiation fractions may exceed 20 will reduce the number of treated patients . However, the boost-method of tumor irradiation, when more than half of the dose is delivered using conventional radiotherapy and only the remaining part of the dose will be delivered by a more precise but expensive proton beam, makes the perspectives of the Centre quite promising. In average, the boost-method reduces the number of proton irradiation fraction by more than 50% with almost the same results of the treatment.

For the needs of the Centre, the ambulatory with a modern engineering equipment was constructed in the main experimental building of the Institute (see Fig.3). This ambulatory will allow to treat more than 50 patients per day. The radiological department of the Troitsk hospital, which will provide the clinical support of patients, is now being organized.

Fig.3 Ambulatories

Some unique devices and systems for radiotherapy were designed and created in INR:

-       Unique for their transparency and sensitivity narrow-gap (~2mm) air ionization chambers, allowing to carry out measurements of a doze and a structure of a beam during an irradiation of patients,

-       Universal and very precise computer-driven treatment chair for the fixation of patient in any position,

-       The digital X-ray patient centration system .

Unique narrow-gap (~2mm) air ionization chambers are developed on a basis of polyimide films, allowing to carry out measurements of a doze and a doze distribution during the radio-therapy irradiation with protons and light ions [2] (see Fig.4). The original technology of extremely thin polyimide film (1.5 and 3 μm) manufacturing is patented in INR RAS.

Fig.4 Narrow-gap air ionization chamber

Radial-oriented films of polyimide have high elastic modulus, high thermo stability and stability to radiation. A tensile strength of the synthesized thin film is ten times higher than that of a standard kapton film and therefore is much more preventing microphone effect. Nano-layers of metal serve as electrodes. It was no observed microphone or ageing effects during three years of exploitation.

On the basis of INR high current proton linac, the production of radioisotopes for generators Sr 82-Rb, needed for  PETs, is organized. Full-cycle production of isotopes for radiology will be carried out in few years.

III. PERSPECTIVES OF THE CENTRE

As it was already mentioned, the parameters of the accelerator allow us to further develop the irradiation techniques. The INR main experimental hall, where both present treatment rooms are located, allows us to install without huge investments some additional systems. Projected 2-nd stage of the Radiological center will have an additional treatment room with vertical and horizontal beams of protons, laboratory for diagnostics and therapy with radionuclides. Existing and projected treatment rooms are shown on Fig.5.

Fig.5 Treatment rooms of INR radiological Centre.

On the Fig.5: 1 is the existing proton treatment room with horizontal beam, 2 is the existing photon treatment room with SL-75-5-MT electron accelerator, 3 is the projected second proton treatment room with horizontal and vertical beams. The lower picture shows the design of  the next proton therapy treatment room.

Another perspective of the Centre is connected to isotope production at the INR linac. At present, several isotopes for medical application are produced or can be produced at INR. Among them are Pd-103, Sr-82, Cu-67, Sn-117 and other isotopes. In the domain of isotope production, INR is one of the leading institutions in the world. The new laboratory for isotope extraction from irradiated samples, whose project is now approved, will allow to complete the technology of medical isotope production. In this case, the INR Radiological centre may become a universal radiological centre, where most modern methods of radiology may be developed and applied.

IV. CONCLUSIONS

The radiological centre of Institute for nuclear researches of the RAS in Troitsk, the Moscow region, is intended for combined radiotherapy of malignant tumor using proton, photon and X-ray beams. It is created on the basis of the INR proton linac and experimental complex. Using the advantages of proton beams, it will be possible to cure oncological patients with any type and location of tumors.

Among operating proton accelerators in Russia, only the accelerator in Troitsk fits all basic requirements of proton therapy for beam parameters (the energy range, duration and frequency of pulses). The linac properties provide not only the proton therapy, but also other main methods of radiology: brachytherapy, diagnostics and therapy with radiopharmaceuticals and the neutron - capture therapy. That is due to the possibility to vary not only the energy, but also the intensity of beams in a wide range.

Projected 2-nd stage of the Radiological centre will have additional treatment room with vertical and horizontal beams of protons, laboratory for diagnostics and therapy with radionuclides. The preparation of a full-cycle production of radioisotopes for medical purpose and the developing and of a neutron - capture therapy technology is in progress. Concluding, the INR Radiological centre may become an universal radiological centre, where most modern methods of radiology will be developed and applied.

REFERENCES

1.       Novikov-Borodin A., Akulinichev S., et al (2006) Control System Design for Multipurpose Beam Delivery System at MMF of INR. WC-2006.

2.       Potashev S., Akulinichev S. et al (2004) A thin-wall air-ionization chamber for proton therapy. Nuclear Instruments and Methods in Physics Research A vol. 535, pages 115-120.