An evaluation of very high energy electron beams (up to 250 MeV) in radiation therapy

Colleen M DesRosiers, Purdue University

Abstract

The purpose of this study was to evaluate very high energy electron beams in radiation therapy. Radiation therapy for cancer treatment has evolved towards increased radiation dose conformality on a targeted volume. Although heavy charged particles potentially provide the most conformal therapy, photon beams are more common due to cost. A recent innovation in photon beam treatment is the use of dynamic multileaf collimation to produce small beams which are effectively scanned within a treatment field. This technique is cumbersome relying upon moving mechanical parts rendering the procedure time consuming, compared with beams which may be electromagnetically scanned. Electrons may be electromagnetically scanned. Clinically available electron energies, less than 50 MeV, have limitations with regard to penetration depth, penumbra and large angle scattering. Monte Carlo simulations with the PENELOPE code were performed to evaluate very high energy electrons, up to 250 MeV and it was found that the limitations of clinically available electron energies were overcome. Very high energy electrons were found to be adequately penetrating to treat deep seated targets, with penumbra comparable to photons. Large angle scattering which occur as the electron approaches the end of its range is irrelevant clinically with very high energy electrons as the range of these beams extends beyond the patient volume. Additionally, it was found that very high energy electrons do not exhibit loss of electronic equilibrium in low density media as do conventional photons equating to improved dose distributions predicted for site specific targets. The applicability of normal tissue complication probability and tumor control probability were evaluated for both very high energy electrons and photons. Treatment unit design was evaluated based on electron accelerator designs. The scanning magnet strength required for the proposed accelerator was calculated to be approximately 1.0 Tesla. Secondary radiation production from neutrons produced in tissue and induced radioactivity thereof was estimated to increase dose by less than three percent. Based on these investigations, very high energy electrons have potential application in radiation therapy as they can provide very fine intensity modulated treatment with promising advantages for targets in low density regions, such as the lung.

Degree

Ph.D.

Advisors

Papiez, Purdue University.

Subject Area

Oncology|Radiology|Biomedical research|Biophysics

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