Purpose: Imaging solutions such as MIM Software are commonly utilized to perform dose accumulation for previous treatment. The purpose of this study was to evaluate the dosimetry of dose accumulation performed using algorithms in MIM and Pinnacle treatment planning system (TPS).
Methods: Six SBRT NSCLC patients with a previous SBRT lung treatment were retrospectively analyzed in this study. The new treatment planning CT was used as the primary dataset. Rigid image registration was performed in Pinnacle TPS. In the first technique, a Pinnacle host script was used to transfer and recompute the previous treatment beams to the new CT; and then summed with the dose from the current treatment beams. The image registration, original RT dose files, original CT datasets, and the new RT structures were exported to MIM software. In the second technique, MIM utilized the imported image registration from Pinnacle to transfer the original old dose from the old CT to the new CT followed by a second dose accumulation generated in MIM. To remove sampling grid bias, both MIM and Pinnacle generated dose accumulations were evaluated in MIM. Dosimetric analysis was performed based on clinical OAR dose limitations.
Results: The OAR doses in the composite plans were similar between the two software. For the Dmax(0.1cc) constraints for spinal cord, heart, esophagus, etc, the mean and standard deviation of the absolute difference between the two methods were 0.24 ± 0.28Gy (range: 0 to 1.31Gy). A significant statistical difference was not observed (p>0.5). The difference between the two methods for the volumetric dose constraints were within 0.36%. Neither was statistically significant.
Conclusion: Minimal dose differences were observed between the dose accumulation generated from Pinnacle recalculation method and MIM direct summation. These differences are not clinically nor statistically significant. Either methods of dose accumulation can be clinically implemented.