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Electron and X-ray Therapy

#0510


Development of Apparatus and Methods for Radiotherapy by Super-Short Electron and x-ray Beams.

Tech Area / Field

  • MED-RAD/Radiomedicine/Medicine

Status
8 Project completed

Registration date
06.12.1995

Completion date
16.06.2000

Senior Project Manager
Lapidus O V

Leading Institute
NIIIT (Pulse Techniques), Russia, Moscow

Supporting institutes

  • VNIIEF, Russia, N. Novgorod reg., Sarov\nAssociation of Medical Physicists of Russia (AMFR), Russia, Moscow

Collaborators

  • Forschungszentrum Karlsruhe Technik und Umwelt / Institut für Neutronenphysik und Reaktortechnik, Germany, Karlsruhe\nCEA / DTA / DAMRI/CEN Saclay, France, Saclay\nKrolinska Institute / Department of Medical Radiation Physics, Sweden, Stockholm

Project summary

Scientific investigations on ultrashort pulse therapy by means of electron and X-ray both with apparatus design for tests are the project tasks.

Radiotherapy is one of the most effective methods of malignant neoplasm treatment and is applied in medical treatment of 40% patients as an independent method. Its efficiency depends, on the type of radiation that effects the tumour and the possibility to minimize ray loading to normal tissue. Nowadays linear accelerators and installations with radioactive sources such as Co60 are applied in this field. In such situation the solution of irradiation planning problem that consists of providing the required therapeutic dose for tumor and ray load to healthy tissue minimization conflicts with the outer location of radiation source. Moreover, such devices are rather expensive.

The idea of the electromagnetic pulse or the electron beam transport into the region of tumor location is at the basis of the method being developed. The transport tract consists of the flexible tube of small section with the window for electron beam outlet or element that converse either electron beam into X-ray radiation or electromagnetic pulse into electron or X-ray pulse with specified dose field distribution. Dose control sensors are located at the same place. Intracavitary location of the radiation source that allows to limit the zone under effect and to sharpen the treatment efficiency while minimizing radiation attack to other organs is the advantage of the method. There is not analogy in the medical radiology to the radiotherapy methods being proposed, and there is the reason to suppose that these methods will take the perceptible place among other ways that are used in medicine. Ultrashort pulse length that is comparable with relaxation time of some chemical compounds has the special scientific and practical interest. There is the reason to expect the specific biological effect of ultrashort pulses to the biological tissue that may touch the new fundamental radiobiology aspects and open the ways of increasing the efficiency of using the radiotherapy methods.

The goal of the project is the enlargement of the possibility to increase the efficiency of intracavitary and surface tumors ray treatment. This goal in work to first is achieved by development of small size (in comparison with linear accelerator) picosecond electron accelerator of direct action that have no analog in medicine radiology. Such accelerator guarantees the required value of therapeutically dose per pulse and allows to introduce the source of radiation directly to tumor location inside the body by means of flexible line. The prototype for accelerator being proposed is accelerator being designed in Russia. Ultrashort pulse duration has the special practical and scientific interest.

That is why the radiation generation at the tumour surface location is technically possible. On the other hand, when pulse duration is comparable with relaxation time of ions and some of the other chemical composites, the specific radiobiological effect may be expected. Specific technical problems include the development of pulse high-voltage power source, high-voltage block of accelerator, flexible line of high-voltage pulse transmission, tubes with electron characteristic X-ray radiation outlets. Technical characteristic of every items being enumerated must guarantee the improvement of output parameters for accelerator as a whole in comparison with the nearest analogous in radiation energy, pulse duration and dose power to the factor of 1.5-2. The problems to be solved are as follows: to develop the system of on-line pulse radiation dose control, to determine the position of accelerator in radiotherapy, to develop radiotherapy methodology and to correlate physical and technical problems with medical requirements.

The other method of electron beam transfer to organ under irradiation that is declared in the paper as a goal to second direction is the use of flexible hollow drift tubes with length up to 1 m and diameter of about 1 cm. At the end of the tube as foil for electron output as converter of electron energy into bremshtrahlung or characteristic radiation may be placed. The small tube diameter and it's flexibility guarantee the access to any zone of the body and also the possibility of intracavitary irradiation.

Physical mechanism of beam transfer along the tube is based on two phenomena that arise in its space charge compensation by excess ions injection into neutral gas or rare plasma. The own magnetic field of the beam firstly performs of its self-focusing regime and secondly returns it on drift tube axes when shifts take place. The latter effect follows from beam ability to reflect from metal surfaces in interaction with currents produced in metal wall. To render the plastic tube walls conductivity the walls must be covered with metal layer of about skin thickness. It's size for times under consideration and copper conductivity is about 20 mkm that doesn't prevent from tube flexibility.

Described principle of beam transport was confirmed by experiments of Russia and USA laboratories.

Technically the problem of transport through flexible drift tube reduces to solving of some electrophysical and technological problems. The first of it is the formation of focused beam with required parameters in the accelerator diode for injection into drift tube.

The second, the most important problem is neutralization of space charge in the drift tube. It may be achieved by choice of initial neutral gas pressure -1 Torr. In this case erosion of beam front during ionization time will take place and electron losses on the tube walls will arise. Bremsstrahlung in electron interaction with the wall will be reduced significantly because of the low effective atomic number of wall material. Erosion losses may be significantly reduced by using gas preionization in the tube by means of auxiliary sources that works without X-ray radiation.

Beam formation at the end of the tube for dose field optimization at the organ under irradiation will be required just as for the first direction. The treatment of this problem will require the development of beam defocusing methods, converters and output units for radiation and, if would be required, for electron removal. Technological task of drift tube design, that is joined with accelerator output and output face design will require the long term study and optimization during experiment.

Thorough justification of method of local including intracavitary radiotherapy, it's practical adoption in proper medical institutions and development of new fundamental direction in radiobiology must be the result of the work.

The second serious result will be the development of new class of electron accelerators with remote emitter of X-ray and electron beams. There is no doubt in wide using of these devises in modern technique and technology.


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