Monte Carlo simulation for verification of lung stereotactic treatment plans delivered with an Elekta beam modulator collimator systems

This paper makes use of Monte Carlo (MC) simulation to verify the dosimetric accuracy lung SBRT treatment plans delivered with an Elekta beam modulator multileaf collimator (MLC) system.

Treatment plans of twenty early stage non-small cell lung carcinoma (NSCLC) patients were retrospectively re-calculated using the collapsed cone convolution (CCC) algorithm of the Pinnacle treatment planning system (TPS). Dose distributions were also calculated using the BEAMnrc and DOSXYZnrc MC user codes. A comparative analysis of target volume and organ at risk (OAR) dosimetry was performed between the TPS and MC dose calculation. A statistical analysis of the two dose distributions and parameters generated by the TPS and MC was performed to examine the significance of any differences.

The results showed that the TPS matched within 6% of the MC calculations for the planning treatment volume (PTV) coverage, mean and maximum PTV doses, and conformity index. The differences over all plans for the PTV were not statistically significant. For the organ at risk, the TPS overestimated the mean dose parameters over all patients but was only statistically significant for some organ at risks including the mean lung dose (MLD), V20Gy to the lung and V30Gy to the chest wall.

The TPS dose calculation of lung SBRT using CCC Pinnacle3 algorithms is relatively closer to the MC calculation, however there may be inaccuracies in the TPS dose calculation for some patients, manifesting in some of the key dosimetric parameters that are used as correlates for irradiation related complications.