Room: Exhibit Hall
Purpose: Monte Carlo (MC) simulation, as the most accurate dose calculation algorithm, is available for MultiPlan system of Cyberknife. The main purpose of this work was to perform experiments to thoroughly investigate the accuracy of the Monte Carlo (MC) dose calculation algorithm.
Methods: Besides the basic MC beam commissioning, two test scenarios were designed. First, single beam tests were performed with a solid water phantom to verify the MC source model in simple geometry. Then, a lung treatment plan based on a CIRS thorax phantom was created to mimic the clinical patient treatment. The plan was optimized and calculated using ray tracing (RT) algorithm and then recalculated using MC algorithm. Measurements were performed in both a homogeneous phantom and the heterogeneous CIRS phantom. Ion-chamber and radiochromic film were used to obtain absolute point dose and dose distributions.
Results: Ion-chamber results showed that the differences between the measured and MC calculated dose were within 3% for all tests. For the film measurements, MC calculation results showed good agreements with the measured dose for all single beam tests. As for the lung case, the gamma passing rate between the measured and MC calculated dose was 98.31% and 97.28% for homogeneous and heterogeneous situation respectively, using a 3%/2mm criteria. However, RT algorithm failed with the passing rate of 79.25% (3%/2mm) for heterogeneous situation.
Conclusion: The results demonstrated that MC dose calculation algorithm in the Multiplan system is accurate enough for patient dose calculation, especially having distinct advantages in heterogeneous media.
Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China (Grant number 81071237,81372420).
Commissioning, Radiochromic Film, Dose
TH- External beam- photons: Small/nonstandard field Monte Carlo dosimetry