A review of adaptive radiotherapy for bladder cancer

Radiation therapy (RT) for muscle invasive bladder cancer (MIBC) is challenging, with observed variations in bladder shape and size resulting in inappropriate coverage of the target volumes (CTV). Large margins were historically applied around the CTV, increasing the dose delivered to organs at risk (OAR). With repositioning imaging and visualization of soft tissues during image guided RT, an opportunity to consider these movements and deformations appeared possible with an adaptive RT approach (ART). A bibliographic search on the PubMed database has been done in January 2019. Studies focusing on patients with MIBC, treating on ART, with the objectives of feasibility, clinical and/or dosimetric evaluation and comparison with a standard irradiation technique were eligible. The purpose of this review was to define the different ART techniques used in clinical practice, to discuss their advantages compared to conventional RT in terms of target volume's coverage and OAR dose and to describe their feasibility in clinical practice. A total of 30 studies were selected. The strategies known as "composite offline", "plan of the day" not individualized or individualized, and "re-optimization" have been identified. All the studies have shown a significant benefit of ART in target coverage and dose of OAR, especially the rectum and small bowel. All ART plans produced are not used during RT sessions. Inter-observer variability for the selection of these plans can be observed. The practical implementation within a department required staff education and training, and increases the duration of treatment preparation. The "A-POLO" approach seems to be the most suitable for practice. ART is the technique of choice for bladder cancer RT. The "plan of the day" approach, individualized according to the A-POLO methodology, seems to be the most effective. The emergence of daily re-optimization, especially using MRI-Linac, is promising. The correlation between dosimetric benefits and clinical efficacy and safety results should be demonstrated into future trials.