[Use of hydrogel as spacer in Denovier's space: optimization of IMRT radiotherapy of localized prostate cancer].

Background: Radiotherapy is an appropriate primary therapy for localized prostate cancer in accordance with urological guidelines. Especially in tumors of higher grade malignancy, dose escalation up to 80,0 Gy seems to be an advantage; however rectum toxicity can be a problem. By injecting a synthetic hydrogel (SpaceOAR®) as a spacer between the prostate and rectum, rectal toxicity can be reduced. We report on our experiences with 47 patients and an average follow-up of 241 days.

Methods: From February 2012 to November 2012, 47 patients were included in the study series. Before external radiotherapy the hydrogel was injected between prostate and rectum in the so-called Denovier space. This interdisciplinary procedure was carried out with the patient under general anesthesia using transrectal ultrasound guidance and video documentation. The patients were hospitalized for 1 day. The exact position of the gel was assessed by means of magnetic resonance imaging (MRI). Radiotherapy was initiated 7-14 days after gel application in a dose escalation manner by means of intensity modulated radiation therapy (IMRT) up to a dose of 80,0 Gy. Average follow-up was 241 (100-386, SD 91) days.

Results: No early side effects specific for the application were observed. The achieved distance between rectum and the mid-plane of the prostate gland was on average 13.8 (6-24, SD=3.8) mm. Calculated V70 (rectal volume irradiated with 70.0 Gy or more) could be reduced to an average of 1.5 (0-8, SD=1.7) %. One patient showed an asymptomatic lesion of the rectal mucosa after irradiation with 38,0 Gy. This lesion was closely controlled and gel penetration was found. As a result radiotherapy was discontinued. Without further treatment the necrosis had completely healed 3 months later.

Conclusions: Hydrogel application between prostate and rectum allows dose escalation up to 80,0 Gy and seems to reduce morbidity in patients with localized prostate cancer receiving radiotherapy. However, before final judgement of the new technique further studies must follow.