Room: Exhibit Hall
Purpose: The Imaging and Radiation Oncology Core (IROC) anthropomorphic moving proton lung phantom has shown a discrepancy between planning systemsâ€™ analytic dose calculations and measurements in the target and distal region of the treatment fields. This study investigates the accuracy of five proton therapy dose calculation algorithms (2 pencil beam and 3 Monte Carlo) using a static geometrical lung phantom.
Methods: A geometrical lung phantom was designed to create a simple configuration to mimic a diseased human lung, decoupling the motion uncertainties and bone heterogeneities introduced in the typical proton lung phantom. Solid water and balsa wood, with tissue-equivalent CT and stopping power values, were used to mimic human tissue and lung, respectively. Radiochromic film was inserted into the center of the phantom at a 5Â° angle with respect to both the left and the anterior wall, in order to try to minimize film quenching and streaming effects. CT simulations were used to create proton pencil beam scanning treatment plans (6 Gy(RBE) prescription) at three different institutions with an anterior and a left lateral field. The measured film dose distributions were compared to each institutionâ€™s clinical TPS pencil beam (PB) and Monte Carlo (MC) algorithm dose calculations
Results: Left-right and anterior-posterior profiles in the center of the target were analyzed. For two institutions (A and B) (using Eclipse PB and in-house MC), the film showed slight under-dosing in the shoulder regions when compared to TPS and MC, which agreed well with each other. Nevertheless, Institution C (using RayStation PB and MC) presented great agreement between measurement and MC, both showing an underdosing of the shoulder compared to TPS.
Conclusion: In our static lung phantom, in-house MC agreed better with Eclipse TPS, while RayStation Commercial MC agreed better with measurement; especially in the underdosed distal shoulder.
Funding Support, Disclosures, and Conflict of Interest: IROC Houston grant #CA180803.