Partially wedged beams improve radiotherapy treatment of urinary bladder cancer

Background and purpose: Partially wedged beams (PWBs) having wedge in one p arr of the field only, can be shaped using dynamic jaw intensity modulation . The possible clinical benefit of PWBs was tested in treatment plans for m uscle-infiltrating bladder cancer. Material and methods: Three-dimensional treatment plans for 25 bladder canc er patients were analyzed. The originally prescribed standard conformal fou r-field box technique, which includes the use of lateral ordinary wedge bea ms, was compared to a modified conformal treatment using customized lateral PWBs. In these modified treatment plans, only the anterior parts of the tw o lateral beams had a wedge. To analyze the potential clinical benefit of t reatment with PWBs, treatment plans were scored and compared using both phy sical parameters and biological dose response models. One tumour control pr obability model and two normal tissue complication probability (NTCP) model s were applied. Different parameters for nor mal tissue radiation tolerance presented in the literature were used. Results: By PWBs the dose homogeneity throughout the target volume was impr oved for all patients, reducing the average relative standard deviation of the target dose distribution from 2.3 to 1.8%. A consistent reduction in th e maximum doses to surrounding normal tissue volumes was also round. The mo st notable improvement was demonstrated in the rectum where the volume rece iving more than the prescribed tumour dose was halved. Treatment with PWBs would permit a target dose escalation of 2-6 Gy in several of the patients analyzed, without increasing the overall risk for complications. The number of patients suitable For dose escalation ranged from 3 to 15, depending on whether support from all or only one of the five applied NTCP model/parame ter combinations were required in each case to recommend dose escalation. Conclusion: PWBs represent a simple dose conformation tool that may allow r adiation dose escalation in the treatment of muscle-infiltrating urinary bl adder tumours. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.