Clinical implementation of a Monte Carlo based independent TPS dose checking system

The increase in complexity of treatment plans over time through modalities such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) has often not been met with an increase in capability of the secondary dose calculation checking systems typically used to verify the treatment planning system. Monte Carlo (MC) codes such as EGSnrc have become easily available and are capable of performing calculations of highly complex radiotherapy treatments. This educational note demonstrates a method for implementing and using a fully automated system for performing and analysing full MC calculations of conformal, IMRT and VMAT radiotherapy plans. Example calculations were based on BEAMnrc/DOSXYZnrc and are performed automatically after either uploading exported plan DICOM data through a Python-based web interface, or exporting DICOM data to a monitored network location. This note demonstrates how completed MC calculations can then be analysed using an automatically generated dose point comparison report, or easily re-imported back into the treatment planning system. Agreement between the TPS and MC calculation was an improvement on agreement between RadCalc and the TPS, with differences ranging from 1.2 to 5.5% between RadCalc and the treatment planning system (TPS), and 0.1–1.7% between MC and TPS. Comparison of the dose-volume histogram (DVH) parameters $$\text {D}_\text {mean}$$ , $$\text {D}_{98\%}$$ , $$\text {D}_{2\%}$$ , and $$\text {D}_\text {max}$$ for the example VMAT plans showed agreement for the mean planning target volume dose within $$0.25\%$$ , $$\text {D}_{98\%}$$ and $$\text {D}_{2\%}$$ generally within $$1\%$$ with the exception of a brain case, and $$\text {D}_\text {max}$$ within $$1\%$$ . Overall, this note provides a demonstration of a system that has been integrated well into existing clinical workflow, and has been shown to be a valuable additional tool in the secondary checking of treatment plan calculations.