Learning curve in the application of a hydrogel spacer to protect the rectal wall during radiotherapy of localized prostate cancer.

To evaluate the effect of increasing experience on hydrogel dimensions, rectal dose, and acute toxicity, and to discuss important technical issues gained from this experience. Sixty-four consecutive patients with prostate cancer were included in this analysis (G1/G2 corresponding to first/second 32 patients) after injection of 10 mL spacer gel. All patients were treated with a 5-field intensity-modulated radiotherapy technique to 76-78 Gy. Treatment toxicity was evaluated with a validated quality of life questionnaire (expanded prostate cancer index composite) before and after radiotherapy. Rectum volume could be entirely excluded from the planning target volume in 31% in G1 vs 56% in G2 (P = .04). Increasing symmetry was detected comparing the first 15 patients to the subsequent rest, with mean differences between right and left of 0.6 cm vs 0.3 cm at the midgland (P = .03). Mean distance between prostate and anterior rectal wall increased from 0.8 cm/1.1 cm/0.8 cm (G1) at the base/middle/apex to 1.3 cm/1.5 cm/1.2 cm (G2), respectively, so that the dose to the rectum decreased significantly (6% vs 2% of the volume inside the 70 Gy isodose; P <.01). Bowel function and bother score changes were smaller comparing baseline with last day of radiotherapy levels (mean 16/18 in G1 vs 9/12 in G2). A learning curve could be demonstrated in our patient population, respecting improved and more symmetrical spacer placement, improved treatment planning, and less treatment-related acute toxicity. Several important technical aspects need to be considered.