Urinary obstruction in prostate cancer patients from the dutch trial (68 Gy vs. 78 Gy): Relationships with local dose, acute effects, and baseline characteristics

Purpose: To investigate the relationship between late urinary obstruction and the details of the dose distribution of irradiated prostate cancer patients, taking into account their baseline symptoms and acute complaints. Patients and Methods: We selected patients from the Dutch multicenter trial randomized between 68 Gy and 78 Gy, for whom toxicity data and dose data were available (n = 557). The absolute dose surface parameters of the delineated bladder were calculated. Next, we constructed three-dimensional dose maps of the area around the prostate, providing an approximate identification of the corresponding anatomic locations. The dose difference maps were constructed by subtracting the mean dose maps of the patients with and without late urinary obstruction. Selected local dose points were analyzed using Cox regression analysis. Results: Urinary obstruction was scored for 40 patients, including 19 of 296 patients who received 68-72 Gy and 21 of 261 patients who received 76-78 Gy. A total of 19 events occurred within 2 years after irradiation and 21 events after 2 years. The bladder surface receiving ≥80 Gy predicted (p <.01) the occurrence of obstruction within 2 years. The dose difference map indicated highly significant differences in the bladder neck situated in the trigonal region (p < .001) that were especially predictive of obstruction after 2 years and of the diagnosis of bladder neck obstruction. Baseline complaints and transurethral resection of the prostate and acute complaints were mainly predictive for obstruction within 2 years. Conclusion: Relatively early events of urinary obstruction were associated with urinary problems existing before RT, acute toxicity, previous transurethral resection of the prostate, and hotspots in the bladder. Events after 2 years were associated with the local dose in the trigonal area.

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