A contribution to improved radiotherapy for muscle-invading urinary bladder cancer

Abstract

Due to the possible side-effects of radical cystectomy for muscle-invading urinary bladder cancer (UBC), radiotherapy remains an attractive organ-sparing treatment option, either alone or combined with increasingly effective chemotherapy. Radiation dose escalation may further improve the results obtained with radiotherapy. This Ph.D. program aimed at developing improved conformal radiotherapy techniques required for dose escalation in bladder irradiation. Initially, computer-controlled movement of the collimators during beam delivery was applied to shape partially wedged beams (PWBs), designed to conform the dose distribution to bladder targets. The dosimetric verification and treatment planning implementation of PWBs were addressed. Particular attention was given to dynamic beam isodose verification with the BMS-96 diode array. The theoretical clinical impact of PWBs in bladder irradiation was evaluated in a planning study. Using PWBs the dose homogeneity inside bladder targets improved and normal tissue (small intestine and rectum) doses were reduced. Judged from normal tissue complication probability (NTCP) modeling, PWBs would allow radiation dose escalation with 2–6 Gy in up to 60% of the patients without increasing the estimated combined NTCP relative to the standard setup. This work also demonstrated the uncertainty in intestine and rectum tolerance data and the differences between the various NTCP models. Finally, the internal bladder motion and patient setup variation were quantified from weekly repeat CT scans and electronic portal images, and new bladder treatment margins were derived. Currently, a bladder dose escalation trial using the PWB principle is performed, testing if the whole bladder target dose can be increased from 64 to 68 Gy while maintaining a low level of treatment-induced complications. © 2003, American Association of Physicists in Medicine. All rights reserved.