Poster - Thurs Eve-39: Full 3D dose calculation for total body irradiation: A comparison study between treatment planning systems in homogeneous and heterogeneous conditions.

Purpose: To perform full 3D heterogeneous dose calculations for total body irradiation (TBI) cases and compare different treatment planning softwares (TPS).
Method: A retrospective study was performed on 7 patients. Dose distributions obtained with Pinnacle ³ v.7.9u (Philips Medical Systems) were compared with the ones calculated using our actual TBI planning system Theraplan Plus (TPP) by MDS Nordion/Nucletron. Two different Pinnacle ³ models were studied: standard beam commissioning (std_Pinnacle ³ ) and TBI commissioning (TBI_Pinnacle ³ ). For the later case, commissioning was adapted for the special TBI conditions (extended SSD of 190cm, large field, acrylic beam spoiler, and out of field dose (OFD)).
Results: Significant differences are found between the TPP, std_Pinnacle ³ and TBI_Pinnacle ³ dose distributions. For the relative mid-line doses, differences up to 12% were observed. Systematic overestimations of 5% were found in patients extremities between TPP and TBI_Pinnacle ³ . Average dose underestimation of 3% was observed between std_Pinnacle ³ and TBI_Pinnacle ³ . Differences in patient extremities are attributed to the OFD contribution which is not correctly computed in TPP and std_Pinnacle ³ . Dose comparison outside the patient's mid-line showed greater differences (up to 20%) between models. Accurate 3D heterogeneous dose calculations with TBI_Pinnacle ³ model show major differences (homogeneous versus heterogeneous) in high and low density regions. Dose overestimation of 5% was observed in bony regions and dose underestimation of 5% to 10% was observed in lung regions.
Conclusion: Those results are of major interest since they show a strong dependence of the dose calculation outcome on both TPS and commissioning used, potentially leading to significant dose misevaluation.
(© 2008 American Association of Physicists in Medicine.)