Informatics in Medicine Unlocked (Jan 2022)
Performance evaluation of a Monte Carlo-based treatment planning system in out-of-field dose estimation during dynamic IMRT with different dose rates
Abstract
Aim: The present study aimed to investigate the effect of dose rate variations in the out-of-field regions on the dose calculation accuracy of an algorithm based on the Monte Carlo (MC) method implemented in Monaco (V.5.11.03) Treatment Planning System (TPS). Materials and methods: Nine fields of the IMRT plan for the CShape structure were created in the CIRS IMRT Thorax phantom, and the related doses were calculated using the MC-based algorithm of the Monaco TPS. Afterward, the CIRS IMRT Thorax phantom was irradiated by an Elekta Synergy linear accelerator and the 160-leaf MLC Agility 6 MV photon beams using the Dynamic Intensity Modulated Radiation Therapy (D-IMRT) technique. To this end, 3 ion chambers were inserted in 3 cavities, which were equivalent to water, bone, and lung, and were located in the out-of-field regions within the phantom. Finally, the dose measurements were performed, and the values were compared with the doses calculated by the Monaco TPS. Results: Findings revealed that the Monaco TPS underestimated the dose by an average of 40% for most of the out-of-field measurement distances. Moreover, at distant positions of the out-of-field edge, out-of-field doses were significantly underestimated for all media and dose rates. Finally, the percentage of the TPS error and out-of-field dose values were different for each dose rate. Conclusions: Results in the present research showed remarkable differences between the measured and calculated doses. Thus, it was concluded that the dose calculation accuracy of the Monaco TPS was not reliable for out-of-field regions at different dose rates, and the application of the current commercial treatment planning systems in these regions could lead to underestimating the risk of secondary cancer development.
