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Commissioning and Potential Clinical Implementation and Advantages of a 2.5 MV Photon Beam for Selected Radiotherapy Cases

H Chen

H Chen, F Guo , D Carlson , J Deng , R Nath , Z Chen*, Department of Therapeutic Radiology, Yale Univ. School of Medicine, New Haven, CT


WE-RAM1-GePD-T-3 (Wednesday, August 2, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge

Purpose: The purpose of this study was to investigate the feasibility of clinical implementation and potential therapeutic advantages of a 2.5 megavoltage (MV) photon beam recently introduced to the Varian TrueBeam Linac.

Methods: The 2.5MV photon beam was for imaging applications. In this study, beam data for 2.5MV photons including PDDs, profiles, and output factors using a scanning water phantom. The 2.5MV beam was then modeled in the Eclipse treatment planning system (TPS) using a pencil beam algorithm. Beam output was calibrated per TG-51 protocol. Point dose measurements in a solid water phantom were compared with dose calculations for various square fields. Virtual cuboid water phantoms with separations of 4, 8, 12, and 16 cm were designed to investigate dose distributions generated by 2.5MV AP and PA beams. Furthermore, 20 previously treated cases were recalculated with 2.5MV beams, and compared with the original plans in terms of dose distributions and DVHs.

Results: The 2.5MV beam has a lower effective energy compared to the 6MV beam, resulting in less penetration and more dose build-up on the surface. A dmax of 0.48 cm was observed for the 2.5MV beam. The virtual cuboid phantom study indicated that AP-PA 2.5MV beams can provide sufficient surface coverage without compromising penetration power up to 12cm of separation. Analysis of DVHs and dose distributions in 4 clinical cases (pediatric/right humerus, pediatric/hemangioma, right skull, and left calf) showed that 2.5MV photon beam improved target coverage (V95) by 3~4% as compared to 6MV.

Conclusion: A novel 2.5MV photon beam has been successfully commissioned in the Eclipse TPS. Dosimetric patient studies indicated potential clinical benefits of 2.5MV beam for selected pediatric and extremity cases. The 2.5MV photon beam can be incorporated into treatment planning optimization as an alternative energy or as one of multiple energies for energy-modulated photon radiotherapy.

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