SU‐E‐T‐346: Evaluation of Inverse‐Compton Scattering Gamma‐Ray Sources for Clinical Use in Radiotherapy

• Published in: Medical Physics 2011-06, Vol.38 (6), p.3567-3567
• Main Author: Tonner, B. P.
• Format: Article
• Language: English
• Subjects: Backscattering; Brightness; Electron scattering; Emission spectra; Inverse scattering; Medical treatment planning; Radiation therapy; Radiosurgery; Radiotherapy sources; Relativistic electron beams
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3612300

Purpose: To evaluate the potential clinical uses of gamma‐ray beams generated by the process of laser‐Compton backscattering from relativistic electron beams. Methods: Inverse‐Compton backscattering has been demonstrated to produce short pulse‐length, high brightness, gamma‐ray beams with energy in the neighborhood of 1 MV (F. Albert et al., Phys. Rev. ST 13, 070704 (2010)). The reported experimental parameters for inverse‐ Compton beams in the high orthovoltage energy range are used to estimate potential future performance of >1 MV sources, with realistically achievable parameters for spectral bandwidth and beam emittance. A model source based on these parameters is implemented in a commercial treatment planning system (Pinnacle 8.0) and used to deliver small‐field treatments to phantoms, and to compare to retrospective stereotactic radiosurgery plans. Results: The emittance of current and future laser‐gamma sources are compared to the requirements of SRS and SBRT. These features have a measurable effect on the beam penumbra that can be beneficially exploited in radiotherapy. Not unexpectedly, the principle limitation of such sources would appear to be the peak flux that can be obtained, since these sources are high brightness, but not necessarily high flux producers, leading to long treatment times that would not be clinically useful. Relaxation of some beam parameters, such as larger source size, would not significantly affect the use of such a source in SRS. Conclusions: The generation of highly collimated gamma‐rays of energy 1 MV and above is possible using the Thompson‐Compton scattering of laser photons from linac accelerated electron beams. The flux produced by these beams has been increasing steadily with each new construction project, and theoretical estimates of the achievable flux indicate that they may reach clinically relevant levels of output in the future. Certain characteristics of these beams, specifically the angular divergence and small source size, can be beneficially employed in radiotherapy.