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by Leonid SHIRSHOV, Senior Researcher, State Research Center "Institute of High-Energy Physics"
In December of last year the town of Protvino near Moscow was the venue of an all-Russia Conference "Fundamental Research and Scientific and Technological Progress". It completed a series of meeting of our leading scientists who discussed the progress and results of studies conducted in the leading "science towns" of the Moscow Region. The program of the forum included, among other subjects, the medical uses of accelerators and charged particles detectors.
Radiotherapy came into being on the verge of 19th-20th centuries and marked a new approach to the treatment of what were regarded as incurable ailments. The first such attempt was made in 1886 when an Austrian cancer patient was bombarded with rays discovered by the German physicist Konrad Roentgen less than a year before. The new therapy was a success which was confirmed by a clinical examination of the patient carried out 70 years later. But, as shown by medical experience, the use of X-rays for the treatment of malignant tumors has serious limitations. The thing is that in this kind of therapy the "main blow" falls on the surrounding body tissues, with the dose maximum being focused on the skin, while the tumor is usually located much deeper.
A way out of this seeming impasse was indicated in 1946 by the American scientist R. Wilson who suggested using against tumors not X-rays but beams of accelerated protons. In 1954 this idea was put into practice at Berkeley (USA) where it was an immediate success which paved the way for rapid progress. Today there are 16 such centers in the world, including three in Russia - at the Moscow Institute of Theoretical and Experimental Physics, the Yefremov Scientific Research Institute of Electro-physical Apparatuses in St. Petersburg and the Joint Institute for Nuclear Research (Dubna).
The participants in the aforesaid Protvino conference discussed the present state of affairs at the juncture of physics and medicine and some of the promising projects in that field. A representative of the RAS Institute of Nuclear Research (Troitsk), Gennady Vyalov, Cand. Sc. (Phys. & Math.) reported on the construction of what they call a proton therapy complex on the basis of a linear accelerator of the Moscow Meson Factory*. It will be used for the treatment of malignant tumors not only with proton beams,
* See: V. Matveyev, V. Laptev, "From Cloth Mill to Basic Research", Science in Russia, No. 6, 1999. - Ed.
but also beams of electrons and X-rays which can be used either in combination or separately. There will also be conducted the diagnostic inspections of patients and research into new methods of therapy.
All in all, it is planned to launch three proton units: one for eye therapy (of 70 MeV), one for the treatment of tumors of the brain and lungs (150 MeV) and an absolutely unique device, called gantry (of 250 MeV) which turns, or rotates, the beam of accelerated particles around the patient. Provisions are also made for using therapeutic electron accelerators (SL-75-5 and SL-20) and X-ray and positron-electron tomography. Work on this project has already started and equipment is being developed for measurements of intensity, energy, beam profile and the parameters of spatial distribution of radiation doses absorbed by the environment.
A report on a Center which is using for cancer therapy hadrons (bartons, mesons, etc.) was presented by Dr. Yevgeny Cherevatenko from Dubna. He pointed out that in the Moscow Region alone there are more than 2 thousand registered patients which have to undergo a year-long course of radiation therapy. This problem is being tackled by scientists of the Joint Institute for Nuclear Research who now have at their disposal a phasotron - a charged particles accelerator of 600 MeV It can produce the whole spectrum of the known radiations and can be used for medical applications since it can impact tumors with broad and narrow horizontal beams of protons from 70 to 660 MeV, negative -mesons* at the level of 30-80 MeV and neutrons (with mean energy of 350 MeV) and either independently from one another or in any combinations. And the Center has yet one more potential: the beams thus obtained can be channeled into 7 treatment rooms at one and the same time, making it possible to attend to more patients.
To provide for more accurate planning and the follow-up verification of the irradiation results, local specialists have developed some original methods of what they call reconstructive X-ray, proton and positron emission tomog-
* -mesons-a group of 3 non- stable hadrons with zero spin and mass of about 270 electron masses (the smallest for hadrons); consists of two charged ( and ) and one neutral one ( ). - Ed .
raphy. Experts have designed, and are testing now, medico- technical equipment which makes it possible to use new methods of irradiation, including rotation-scanning of deeply located tumors and simultaneous scanning irradiation of bigger targets by 14 narrow proton beams, etc.
Special software has been developed for working out new strategies of radiation therapy. Calculations of the space distribution of a proton flux doses are facilitated by the use of X-ray tomograms which examine patient tissues layer by layer with the help of a horizontal computer tomograph attached to the therapeutic chair. All of these innovations provide for greater accuracy of radiotherapy.
Innovations in Dubna include the opening of the first stage of a specialized oncologo-radiological clinic for 30 patients whose annual capacity is expected to be up to 150 patients.
The work of the High-Energy Lab of the Joint Institute for Nuclear Research was described in a report by Ser-gei Stetsenko, Cand. Sc. (Phys. & Math.). He said its staff are investigating new anti- cancer therapies but with a somewhat different approach. They suggest new radiotherapy using not protons, but carbon ions. And the way scientists put it, if the impact of the former can be compared to dumdum bullets, the latter act more like grenades.
Putting this idea into practice is facilitated by using the lab's cryogenic synchrotron which accerates the nuclei of heavy ions in a vacuum chamber measuring 4х10 cm 2 . This unit generates up to 10 8 ions of carbon per second, launching a massive "attack" on a tumor.
An integral part of this unit is a device rotating the beam of accelerated particles around the patient-the already mentioned gantry In its traditional version the unit is too large in size and weighs nearly 160 tons. This being so, specialists of the lab have developed special equipment for what they call the autonomous cooling of the windings of the magnets of the nuclotron- cryocoolers. These make it possible to cut down appreciably its operational costs, reducing the mass of the magnets' system by 5 to 10 times, making the whole unit more convenient for the user.
One more report on the use of carbon ions for the treatment of oncological cases was presented by another re-
searcher from our Institute, Yuri Antipov, Cand. Sc. (Phys. & Math.). He said Protvino experts, working in conjunction with Russian Center of Medical Studies (Obninsk) and the Scientific- Research Institute of Electrophysical Equipment (named after D. Yefremov), are engaged on a project of a new Center of Proton- Ionic Radiation Therapy. It will be based on two linear accelerators (URAL-30 and ISTO) and two annular units-a booster and the "main ring" U-70*.
Work has already begun on the development of a laser source of carbon ions which will provide for the "removal" of electrons from its atoms and the generation of ions + 5C or + 6 and up to 10 9 in the pulse. The next stage of construction includes the building of a channel for the beam injection into the booster.
As has been said before, the currently available equipment for cancer treatment is very bulky and expensive and cannot be "moved up" to the patient. This being so, time must have come for the development of more compact medical equipment of this kind. Plans to that effect were discussed in a report by the Director of the Protvino branch of the Institute of Nuclear Physics named after G. Budker of the RAS Siberian Branch, RAS Corresponding Member V. Balakin. The technical "base" of the new therapeutic complex is a small-size proton synchrotron. At the energy of the accelerated protons of up to 230 MeV, the unit will consume only 50 kW of electricity, and the dimensions of the ring with an external diameter of 5 m will make it possible for the unit to be installed in a treatment room of not more than 63 m2 . The new unit will be far superior to all of its analogs in the world by its technical parameters and cost. At the end of 2002 the first such unit will be installed at the Proton Therapy Center in Protvino and a second one should be launched in 2003 at the Medical Radiological Center of the Russian Medical Academy (in Obninsk).
Before one starts to cure a medical disorder, it is necessary to conduct the right diagnosis. And it is no simple matter detecting a cancer case at its early stages. This being so, emphasis is being laid at the present time on what are called systems of digital diagnostics.
* See: L. Shirshov, "High Energy of Protvino", Science in Russia, No. 5, 2000 -Ed.
This problem was discussed in a report by one of our research scientist Alexei Vorobyev, Cand. Sc. (Phys. & Math.). He said progress in this field depends to a large extent on the development of solid-state coordinates detector-instruments which can register X-rays and gamma-quanta from radioactive isotopes. Attempts to use for these purposes germanium or silicon failed due to some of their specific properties. The same happened with gallium arsenide (GaAs). Finally, researchers of the Institute of High-Energy Physics (Protvino), the Siberian Physical-Technical Institute of the Tomsk State University and the Scientific Research Institute of Semiconductor Instruments (Tomsk) found the required material on the basis of a unique technique of alloying GaAs with chromium atoms. The detector structures found upon it have a sensor area of 600-700 mc in thickness which is just right for medical diagnostics and paves the way for the development of the necessary devices. Putting these plans into reality will make it possible to broaden the range of measurements, improve the contrast range and substantially reduce the radiation doses received by patients.
Another interesting subject - the production of radionuclides for medical applications - was discussed by Boris Zhuykov, Cand. Sc. (Phys. & Math.) of the RAS Institute of Nuclear Research. He said that using a "branch" of a proton beam of 160 MeV from a powerful linear accelerator functioning in the town of Troitsk near Moscow and bombarding a target of metal rubidium, it has been possible to obtain strontium-82. This isotope can be successfully used in positron-emission tomography. Another nuclide- palladium 103 - is very promising for prostate therapy, although its production is yet to be launched on a required scale.
Different methods for the isolation of radionuclides from irradiated targets which are being developed at the RAS Institute for Nuclear Research make it possible to obtain cadmium-109, sodium-22, selenium-72, tin-117, etc.
The speaker also pointed out that these experiments are being conducted in cooperation with the Los-Alamos and Brookheaven labs (USA) and the TRIUMF National Center (Canada).
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