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Proton Beam Scanner for Medicine

#0800


Multichannel Computerized System for the Measurements of 3D Medical Proton Beam Dose Distributions

Tech Area / Field

  • MED-RAD/Radiomedicine/Medicine
  • MED-DID/Diagnostics & Devices/Medicine

Status
3 Approved without Funding

Registration date
11.11.1996

Leading Institute
ITEF (ITEP), Russia, Moscow

Supporting institutes

  • ITEF (ITEP) / AO Medical Physics, Russia, Moscow\nNIIIT (Pulse Techniques), Russia, Moscow\nAssociation of Medical Physicists of Russia (AMFR), Russia, Moscow

Collaborators

  • Lawrence Berkeley National Laboratory, USA, CA, Berkeley\nNational Institute of Radiological Science / Division of Accelerator Physics and Engineering, Japan, Chiba\nPaul Scherer Institute, Switzerland, Villigen

Project summary

Radiation Therapy (RT) is a most widespread treatment modality of oncological and other severe diseases. RT is prescribed to 40-70 % of all oncological patients both independently and in combination with other treatments.

Currently RT uses various sources of ionizing radiation, such as roentgen, gamma- and neutron sources, electron and bremsstrahlung beams, and finally, the beams of accelerated protons and heavy ions.

Correlation between irradiated volume and target volume is the key point to achieve higher effectiveness and better clinical results of RT. The advances in techniques and methods of required dose distribution forming and physical properties of the radiation interaction with human tissues both govern the extent of such correlation (conformity). From this point of view, Proton Radiation Therapy (PRT) is a most promising modality of radiation treatment.

The beams of accelerated protons can generate dose distributions that are unique clinically. The maximum of their energy deposition is concentrated in the end of the beam range (Bragg Peak) which (depending on the initial beam energy) can easily overlap the target, while the radiation load on patient surface and transient tissues is minimized. The radiation load on the tissues behind the target is totally eliminated. Protons undergo little scattering in tissues, which results in minimizing radiation load on healthy tissues surrounding the target.

It must be emphasized that practical realization of aforementioned principal advantages of proton irradiation is possible only in case if specialized high-precision equipment for on-line 3D dose distributions forming and measurements is available.

Current radiobiological data and clinical experience show that the accuracy of clinical dose distributions required both to achieve prescribed clinical effect and for clear classification of the clinical results obtained should be within 2-3 %. Since it is still impossible to measure 3D dose distributions during the irradiation session, a technique of simulation of a process of irradiation interaction with human tissues and subsequent energy deposition (dose) calculations is currently accepted in RT in general and in PRT in particular. The aforementioned accuracy of such a simulation can be achieved provided experimental data taking into account dosimetric features of interaction of a given radiation with the object to be irradiated and specific properties of the irradiation source (the type of a source, its spatial and energy spectrum, phase space, the influence of dose delivery system, etc.) are included.

Owing to this, all modern radiation sources used in RT (both experimental and commercial ones) are usually supplied with a set of dosimetric equipment and a phantom both for fast 3D dose distribution measurements in tissue-equivalent media and for routine calibration of the radiation source. This Project proposes a development of a similar kit of dosimetric equipment, comprising an ionization chamber, semiconductor detectors and a phantom with drives for 3D detectors scanning. The kit, originally designed for use in PRT facilities and centers would have the following distinguishing features:


- capability to measure the dose of protons with the accuracy no worse than ±3 % over the wide range of dose and dose rate,
- capability to measure the dose of proton beams having various spatial characteristics and time structure,
- improved (to 0.1 mm) accuracy of detector positioning and its reproducibility,
- availability of multichannel measurement mode,
- capability of film information processing (two-dimensional dose distributions obtained by film exposing in radiation fields),
- capability to measure the influence of inhomogeneous anatomical structures of various shapes and densities on dose distributions,
- relatively low cost (3 to 5 times lower than that of foreign analogs). The development of the system would make it possible:
- fast forming of various dose distributions used for proton irradiation of oncological and other severe patients. Taking into account potentially high variability and flexibility of proton dose distributions this feature (the high speed of measurements) is of special importance for inpidual dose distribution optimization (for each particular clinical case),
- to measure aforementioned dose distributions with the accuracy no worse than ±3 % and with spatial resolution constituting fractions of a mm. which is required for PRT and matches or exceeds the modern standards for dosimetry equipment used in RT,
- to measure with the required accuracy proton radiation dosimetric parameters, which are used in 3D medical dose distribution calculation and optimization software,
- to study the influence of inhomogeneities on dose distributions,
- to carry out absolute dose calibrations on proton beams.

The development of this system would also represent a certain commercial interest, since there are currently about 20 PRT centers in the world, which are the potential users of such equipment. Moreover, this system can be subsequently customized to the particular customer requirements specific for conventional radiation sources (roentgen, gamma and electron radiation) making a market of dozen thousands units worldwide. Such distinguishing features of the system, as its low cost (3 to 5 times lower than that of the foreign analogs), a capability to measure the dose over a wide dose and dose rate ranges, as well as improved accuracy of dose measurements and detector positioning would make this system competitive on the world market.


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