Treatment planning with a 2.5MV photon beam for radiation therapy.

Abstract

The shallow depth of maximum dose and higher dose fall-off gradient of a 2.5MV beam along the central axis that is available for imaging on linear accelerators is investigated for treatment of shallow tumors and sparing the organs at risk (OARs) beyond it. In addition, the 2.5MV beam has an energy bridging the gap between kilo-voltage (kV) and mega-voltage (MV) beams for applications of dose enhancement with high atomic number (Z) nanoparticles. We have commissioned and utilized a MATLAB-based, open-source treatment planning software (TPS), matRad, for intensity-modulated radiation therapy (IMRT) dose calculations. Treatment plans for prostate, liver, and head and neck (H&N), nasal cavity, two orbit cases, and glioblastoma multiforme (GBM) were performed and compared to a conventional 6MV beam. Additional Monte Carlo calculations were also used for benchmarking the central axis dose. Both beams had similar planning target volume (PTV) dose coverage for all cases. However, the 2.5MV beam deposited 6%-19% less integral doses to the nasal cavity, orbit, and GBM cases than 6MV photons. The mean dose to the heart in the liver plan was 10.5% lower for 2.5MV beam. The difference between the doses to OARs of H&N for two beams was under 3%. Brain mean dose, brainstem, and optic chiasm max doses were, respectively, 7.5%-14.9%, 2.2%-8.1%, and 2.5%-19.0% lower for the 2.5MV beam in the nasal cavity, orbit, and GBM plans. This study demonstrates that the 2.5MV beam can produce clinically relevant treatment plans, motivating future efforts for design of single-energy LINACs. Such a machine will be capable of producing beams at this energy beneficial for low- and middle-income countries, and investigations on dose enhancement from high-Z nanoparticles.