Fifty-seventh annual meeting of the American association of physicists in medicine
TH-AB-BRA-02: Generation of 3D Dosimetric Reference Datasets for Commissioning and Validation of 192Ir Brachytherapy Model-Based Dose Calculation Software
Previously, generic HDR 192Ir source and shielded applicator were designed by WG- MBDCA, the AAPM-ESTRO-ABG Working Group on model-based dose calculation algorithms. TPS vendors have incorporated both into their TPS. A charge of WG-MBDCA is to develop a limited number of well-defined test cases and perform MBDCA dose calculations and comparisons. Here, we describe the test cases proposed, the 3D dosimetric data generation process and the 3D gamma analysis performed.
A voxelized phantom of 512×512×512 voxels (HU=-1024,Air), with each voxel being 1×1×1 mm3, containing a concentric cubic contour structure (HU=0,Water) of dimension 201×201×201 voxels, was created in the DICOM- RT format. Three configurations were tested: i) source located at the center with surrounding structure assigned to water to mimic TG-43 conditions, ii) source displaced +7 cm along the × axis, iii) source located at the center with the shielded applicator in place. Advanced Collapsed-cone Engine (ACE, Elekta) and AcurosBV (Varian) were benchmarked. Reference datasets were independently produced by different groups using BrachyDose (1010 photons), GEANT4(4×1010), Penelope (2×1010), MCNP5(2 x1010), MCNP6(1011), and ALGEBRA(4×1010) Monte Carlo (MC) dose calculation platforms.
For the three configurations, MC agreed within 1% for the volume bounded by the 1% isodose surface; MCNP6 data sets were designated as reference (statistical error < 0.2% across the phantom). A 2%/1mm 3D γ- index criteria was used, within the volume bounded by 5% isodose surface, to account for both dose difference and source placement errors in TPS. Voxel pass rates were 95.2%, 99.5% and 90% for ACE and 98%, 98.4% and 95.9% for AcurosBV, respectively.
The evaluated test cases are suitable for MBDCA QA. DICOM-RT files are being integrated into the joint AAPM/IROC Houston registry to support end-user TPS software commissioning.