TU‐C‐AUD B‐03: A Comparison of Heterogeneity Correction Algorithms

Abstract

Purpose: To compare the measured dose distribution to the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center has constructed an anthropomorphic thorax phantom that includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was irradiated by 33 institutions with results that meet criteria established for the RTOG 0236 protocol. TLDs and radiochromic films were used as dosimeters within the target region. Institutions were asked to design plans using 3D‐CRT and IMRT techniques. The TLD dose was compared to the dose calculated by the TPS at the center of the target. Film response was normalized to TLD doses and a 2D‐gamma analysis comparison to the planned distribution was performed. Institutions whose irradiation of the phantom did not meet the RTOG 0236 criteria were not included. Results: A 2D‐Gamma analysis was done in the axial, sagittal and coronal planes through the PTV. 5% / 5mm criteria were applied. Due to limitations of the analysis software only the comparison over the axial plane is reported. 21 of the cases were planned with a superposition/convolution or AAA algorithm. For these cases, 92% ± 12% of the pixels in the analyzed region met the criteria. 12 of the cases were planned with a pencil beam or Clarkson algorithm. 74% ± 25% of the pixels meet the criteria for these cases. Conclusion: The superposition convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms.Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.