Adaptive Radiotherapy for Bladder Cancer – A Review

Radiotherapy plays an important role in organ preservation for bladder cancer. Delivering radiation accurately can be challenging, in part because the bladder and surrounding organs may change position, volume, and shape between and during the fractions of a treatment course. This variability has been accounted for by increasing the margins around the treatment targets, which can expose more normal tissue to radiation, and increase the likelihood of normal tissue complications. An alternative strategy is to alter, or adapt, the radiotherapy treatment plan to account for such inter-fraction changes, a strategy termed ‘adaptive radiotherapy’ (ART). ART allows smaller target volumes to be treated, and may reduce complications. Approaches to ART include offline adaptation strategies and online strategies, which includes choosing a plan of the day (PoD) based on pre-treatment imaging and magnetic resonance (MR), or with cone-beam CT (CBCT)-guided daily plan re-optimisation. Here, the authors review these ART strategies and trials exploring the dosimetric and clinical benefits of ART relative to non-ART bladder radiotherapy.