Evaluating the need for adaptive therapy when delivering conformal bladder radiotherapy

Background and Purpose: To audit positioning errors during bladder Image Guided Radiotherapy (IGRT) and quantify survival outcomes. Materials and Methods: Retrospective review of 141 patients treated between March 2007 and July 2010 with 3D conformal radiotherapy (CRT). An offline imaging protocol using kV cone beam CT (CBCT) was used. Positioning errors, clinical interventions and re-planning rates were quantified. Cancer outcomes and survival were collected by review of patient notes and a registry search. Results: 43% of patients required no intervention. Isocentre corrections were used for systematic bony set-up error (SUE) in 13% and to improve bladder coverage in 28%. Clinical interventions to improve bladder coverage were required in 16% and repeat CT planning in a further 16%. Overall, 44% of patients demonstrated some form of organ deformation that would have resulted in inadequate dose to the bladder or significant overdose to an organ at risk if not corrected for. Post treatment check cystoscopy was undertaken in 107 patients (76%) with 72 noted to have a complete response. Overall survival was 47.8% at 3 years. Conclusions: Organ deformation during radiotherapy for bladder cancer is a significant problem for over 40% of patients. Strategies to compensate are essential to ensure optimal plan delivery.