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Is There a Dosimetric Advantage of Using 2.5 MV Over 6 MV Photons for Stereotactic Radiosurgery?

G Ding*, G Luo, M Price, Vanderbilt University, Nashville, TN

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Stereotactic radiosurgery relies on very small field sizes on the order of a few millimeters to ablate lesions and spare normal structures. Although a 6 MV photon beam is most often utilized, there is an interest in lower photon energy beams for stereotactic radiosurgery due to their sharper dose fall off. This study provides a dosimetric comparison to determine if there is advantage of using 2.5 MV over 6 MV photons for stereotactic radiosurgery.

Methods:
The Monte Carlo simulation codes BEAM/dosexyz were used to simulate 2.5 MV form a Varian TrueBeam and 6 MV beams from a Varian TX accelerator. The details of the incident beams including cone accessory were simulated, with calculated doses benchmarked against measurements. The dose calculations were based on a realistic treatment plan for thalamotomy treatment delivering over 145 Gy at isocenter using a 6 MV (4 mm cone) beam with 21 arcs. The calculations were repeated with a 2.5 MV beam with the same cone and delivery arcs.

Results:
For a realistic patient treatment plan using 21 arcs with 4 mm cone beams delivered 15000 cGy, a significant dose reductions of 37% to brainstem and 50% to chiasm were obtained for 2.5 MV beams comparing to 6 MV beams. From the DVH analysis, the maximum doses to brainstem and Chiasm were 880.5 cGy (552.3 cGy) and 272.2 cGy (134.3 cGy) for 6 MV (2.5 MV) beams respectively.

Conclusion:
A significant reduced dose to organ-at-risks can be achieved by a 2.5 MV beam while providing same target dose. There is a clear dosimetric advantage of using 2.5 MV over 6 MV photons for stereotactic radiosurgery. The current 2.5 MV beam is for imaging and observed significant dosimetric benefit should encourage manufactures to develop lower energy photons for therapy treatment using LINAC-based radiosurgery system.

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