Room: Exhibit Hall | Forum 5
Purpose: To use a commercial TPS (Eclipse) to calculate and compare patient dose from 2.5 MV and 6 MV portal images on a TrueBeam. To the best of our knowledge, previous studies only used non-clinical Monte Carlo packages.
Methods: The accuracy of the AcurosXB calculation algorithm for the 2.5 MV beam was verified using MPPG 5.a guidelines. A pair of orthogonal portal images was simulated with a field size of 20x20 cm^2 centered at the treatment isocenter for numerous treatment sites, including thorax, abdomen, male pelvis, and female pelvis. The monitor units per image for the 2.5 MV (un-flattened) and 6 MV (flattened) beams were set to TrueBeam default settings.
Results: For the 2.5 MV and 6 MV images, the average patient doses at isocenter were 1.14 cGy and 2.28 cGy, respectively, and the doses to the hottest 0.5 cc of the body were 2.05 cGy and 3.66 cGy, respectively. The dose at the overlap of orthogonal beams is notably higher for 6 MV than 2.5 MV images since the flattened 6 MV spectrum is softer off-axis. Organ dose was higher with a 6 MV beam for all imaging sites. The number of imaging pairs to reach 5 % of the therapeutic dose â€“ the threshold above which imaging dose is recommended to be accounted for in treatment planning â€“ for the 2.5 MV and 6 MV images are approximately 100 and 60, respectively.
Conclusion: This work shows that a commercial TPS can be used to calculate patient dose from the 2.5 MV imaging beam. We confirmed that the organ dose reduction by using a 2.5 MV beam instead of a 6 MV beam is about 50%.