On Voxel Based Iso‐Tumor‐Control Probability and Iso‐Complication Maps for Selective Boosting and Selective Avoidance Intensity‐Modulated Radiotherapy

Summary Voxel‐based iso‐tumor‐control probability (TCP) maps and iso‐Complication maps are proposed as a plan‐review tool especially for functional image‐guided intensity‐modulated radiotherapy (IMRT) strategies such as selective boosting (dose painting) and conformal avoidance IMRT. The maps employ voxel‐based phenomenological biological dose–response models for target volumes and normal organs. Two IMRT strategies for prostate cancer, namely conventional uniform IMRT delivering an equivalent uniform dose (EUD) = 84 Gy to the entire planning target volume (PTV) and selective boosting delivering an EUD = 82 Gy to the entire PTV, are investigated, to illustrate the advantages of this approach over iso‐dose maps. Conventional uniform IMRT did yield a more uniform isodose map to the entire PTV while selective boosting did result in a non‐uniform isodose map. However, when employing voxel‐based iso‐TCP maps selective boosting exhibited a more uniform TCP map compared to what could be achieved using conventional uniform IMRT, which showed TCP cold spots in high‐risk tumor subvolumes despite delivering a higher EUD to the entire PTV. Voxel‐based iso‐Complication maps are presented for rectum and bladder, and their utilization for selective avoidance IMRT strategies are discussed. We believe as the need for functional image‐guided treatment planning grows, voxel‐based iso‐TCP and iso‐Complication maps will become an important tool to assess the integrity of such treatment plans.