Does one size fit all? Adaptive radiotherapy for bladder cancer: A feasibility study

Introduction: Adaptive techniques to deliver radiotherapy to the bladder may ensure treatment accuracy whilst sparing organs at risk. This study assesses the frequency of when an alternative plan to the current standard may be beneficial and establish the treatment resource implications of adaptive techniques. Assess the variation in accuracy of skeletal surrogate compared to the target. Additionally describes a training package for therapeutic radiographers evaluating CBCT datasets for adaptive techniques. Methods: A library of three plans was created for each patient, small, standard and large. Weekly CBCT and planar imaging data were acquired from 10 bladder cancer patients receiving radical radiotherapy. Bladder volumes from weekly CBCT were compared to the planning scan. Image registration was performed using bone and soft tissue structures on the CBCT images. A database of images was created to develop competency assessment and a training package. Results: Matching to a skeletal surrogate may under estimate movement of the target. Bladder volume can vary significantly during the course of treatment, even in the presence of bladder preparation protocols. The additional time required to implement this technique is 4 min per fraction compared to standard treatment with planar imaging. Conclusions: This feasibility study is a useful process to facilitate the implementation of adaptive techniques. However a limitation of this study is the low number of CBCT datasets evaluated. The advent of IGRT and adaptive techniques gives increased confidence to reduce margins, consequently facilitating hypo-fractionation, and may provide a gain in linear accelerator efficiency and reduce the number of hospital visits for the patient. CBCT paired with a development programme for therapeutic radiographers is an effective and efficient means of implementing adaptive radiotherapy.