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MO‐D‐BRB‐01: Non‐Voxel‐Based‐Broad‐Beam (NVBB) Framework for IMRT Treatment Planning— II . Ultra‐Fast Intermediate Dose Calculation
Author(s) -
Lu W,
Chen M,
Chen Q,
Olivera G
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3469053
Subject(s) - imaging phantom , algorithm , convolution (computer science) , tomotherapy , kernel (algebra) , radiosurgery , radiation treatment planning , dosimetry , mathematics , beam (structure) , nuclear medicine , computer science , physics , optics , radiation therapy , artificial intelligence , medicine , combinatorics , artificial neural network
Purpose : IMRT treatment plan optimization requires a fast yet accurate algorithm to calculate intermediate dose in each iteration. Conventional finite size pencil beam (FSPB) approaches have limitations such as: limited resolution, significant pre‐calculation time, huge memory demand, and limited accuracy in the presence of heterogeneity. In this work, we present a fast dose calculation algorithm that overcomes the limitations of FSPB approaches. Material and Methods : By decomposing the infinitesimal beam dose kernel into the central axis (CAX) and lateral (LSF) components and taking the beam eye view (BEV), we established a Fluence‐map‐Convolution‐Broad‐Beam (FCBB) dose calculation formula. The Collapsed‐cone convolution/superposition (CCCS) doses on water phantom with standard setups and various field sizes are used to derive LSF and CAX, the commissioning data for FCBB. The proposed dose calculation involves a 2D fluence map convolution with LSF followed by table‐lookup with inverse square correction of CAX based on radiological distance calculated via ray‐tracing the density volume. The complexity of FCBB is O(N 3 ) both spatially and temporally, which is orders of magnitude smaller than FSPB in spatial complexity and orders of magnitude faster than CCCS. We implemented FCBB algorithm in C++ language and compared it with CCCS using both simulated and clinical cases. The clinical cases include prostate, H&N and lung patients that were optimized with TomoTherapy TPS. Results : For all tested cases, simulated or clinical, the dose calculation time for CCCS varied from hundreds to thousands of seconds when run on a single PC. It was reduced to sub‐seconds to seconds for FCBB on the same PC. As for the dose differences between FCBB and CCCS, about 90–95% of voxels have Gamma indexes less than 1 for the 3mm/3% criteria. Conclusions : The FCBB algorithm has low memory demand, is ultra‐fast and accurate enough for intermediate dose calculation during IMRT optimization.