Dosimetric comparison of RapidPlan and manually optimised volumetric modulated arc therapy plans in prostate cancer

Purpose: The aim of this study was to evaluate whether RapidPlan (RP) could generate clinically acceptable prostate volumetric modulated arc therapy (VMAT) plans. Methods: The in-house RP model was used to generate VMAT plans for 50 previously treated prostate cancer patients, with no additional optimisation being performed. The VMAT plans that were generated using the RP model were compared with the patients' previous, manually optimised clinical plans (MP), none of which had been used for the development of the in-house RP prostate model. Differences between RP and MP in planning target volume (PTV) doses, organs at risk (OAR) sparing, monitor units (MU) and planning time required to produce treatment plans were analysed. Assessment of PTV doses was based on the conformation number (CN), homogeneity index (HI), D-2%, D-99% and the mean dose of the PTV. The OAR doses evaluated were the rectal V-50 Gy, V-65 Gy, V-70 Gy and the mean dose, the bladder V-65 Gy, V-70 Gy and the mean dose, and the mean dose to both femurs. Results: D-99% and mean dose of the PTV were lower for RP than for MP (p = 0.006 and p = 0.040, respectively).V-50 Gy, V-65 Gy and the mean dose to rectum were lower in RP than in MP (p < 0.001). V-65 Gy, V-70 Gy and the mean dose to bladder were lower in RP than in MP (p < 0.001). RP had enhanced the sparing of both femurs (p < 0.001) and significantly reduced the planning time to less than 5% of the time taken with MP. MU in RP was significantly higher than MP by an average of 52.5 MU (p < 0.001) and 46 out of the 50 RP plans were approved by the radiation oncologist. Conclusion: This study has demonstrated that VMAT plans generated using an in-house RP prostate model in a single optimisation for prostate patients were clinically acceptable with comparable or better plan quality compared to MP. RP can add value and improve treatment planning efficiency in a high-throughput radiotherapy department through reduced plan optimisation time while maintaining consistency in the plan quality.