Original Article
Evaluation of dose calculation accuracy of treatment planning systems in the presence of tissue heterogeneities
Abstract
Background: Accuracy of five dose calculation algorithms within three treatment planning systems (TPS): BrainLAB iPlan 4.2 (BL: pencil beam and Monte Carlo), Philips Pinnacle (PL: Collapsed Cone Calculation, CCC), and Varian Eclipse (VR: AAA and Acuros XB) is investigated in this multi-institutional study.
Methods: A Monte-Carlo based TPS (BL) was first validated against benchmark measurements in heterogeneous-slab phantoms consisting of tissue-equivalent plastic, lung-equivalent cork, and bone density materials. Ion chamber/EDR film measurements of depth-dose and dose-profiles for 6MV enface photons in a range of field-sizes (12 mm × 12 mm – 60 mm × 60 mm) were performed. A common CT dataset for each phantom was sent to four participating institutions. Measured versus calculated dose differences for all dose algorithms considered in this study were quantified using two dose-profile indices: Ddiff within the central 80% of photon field, and Dspill for dose outside the field-edge (50–10% dose).
Results: BrainLAB TPS BL: MC and measured doses agreed well (Ddiff <3%) for all field-sizes and phantom depths investigated. The agreement improved with increasing field size (2.6% for 12 mm × 12 mm vs. 1.1% for 60 mm × 60 mm at 60 mm depth in lung phantom). In contrast, for lung phantom, pencil beam (PB) calculations significantly over-predicted the measured dose (34% and 6.7% respectively). In general, PB vs. measured dose differences increased with decreasing field-size, decreasing phantom density and increasing depth within heterogeneity. Pinnacle TPS PL: pinnacle showed the best agreement with measured data in the presence of tissue heterogeneities and modeled dose changes at the tissue-lung interface better than AAA and PB. Varian TPS VR: AAA over-predicted measured results and was unable to replicate dose variation near heterogeneities. In contrast, Acuros XB showed good agreement with measurements for heterogeneous media as well as superior agreement in the interface region.
Conclusions: Based on the results of this multi-institutional study, appropriate corrections may be applied to lung stereotactic body radiotherapy (SBRT) plans for patients enrolled in RTOG protocols.
Methods: A Monte-Carlo based TPS (BL) was first validated against benchmark measurements in heterogeneous-slab phantoms consisting of tissue-equivalent plastic, lung-equivalent cork, and bone density materials. Ion chamber/EDR film measurements of depth-dose and dose-profiles for 6MV enface photons in a range of field-sizes (12 mm × 12 mm – 60 mm × 60 mm) were performed. A common CT dataset for each phantom was sent to four participating institutions. Measured versus calculated dose differences for all dose algorithms considered in this study were quantified using two dose-profile indices: Ddiff within the central 80% of photon field, and Dspill for dose outside the field-edge (50–10% dose).
Results: BrainLAB TPS BL: MC and measured doses agreed well (Ddiff <3%) for all field-sizes and phantom depths investigated. The agreement improved with increasing field size (2.6% for 12 mm × 12 mm vs. 1.1% for 60 mm × 60 mm at 60 mm depth in lung phantom). In contrast, for lung phantom, pencil beam (PB) calculations significantly over-predicted the measured dose (34% and 6.7% respectively). In general, PB vs. measured dose differences increased with decreasing field-size, decreasing phantom density and increasing depth within heterogeneity. Pinnacle TPS PL: pinnacle showed the best agreement with measured data in the presence of tissue heterogeneities and modeled dose changes at the tissue-lung interface better than AAA and PB. Varian TPS VR: AAA over-predicted measured results and was unable to replicate dose variation near heterogeneities. In contrast, Acuros XB showed good agreement with measurements for heterogeneous media as well as superior agreement in the interface region.
Conclusions: Based on the results of this multi-institutional study, appropriate corrections may be applied to lung stereotactic body radiotherapy (SBRT) plans for patients enrolled in RTOG protocols.
