Absorbable hydrogel spacer use in men undergoing prostate cancer radiotherapy: 12 month toxicity and proctoscopy results of a prospective multicenter phase II trial

Abstract

Background: Radiation therapy is one of the recommended treatment options for localized prostate cancer. In randomized trials, dose escalation was correlated with better biochemical control but also with higher rectal toxicity. A prospective multicenter phase II study was carried out to evaluate the safety, clinical and dosimetric effects of the hydrogel prostate-rectum spacer. Here we present the 12 months toxicity results of this trial.

Methods: Fifty two patients with localized prostate cancer received a transperineal PEG hydrogel injection between the prostate and rectum, and then received IMRT to a dose of 78 Gy. Gastrointestinal and genitourinary toxicity were recorded during treatment and at 3, 6 and 12 months following irradiation by using the RTOG/EORTC criteria. Additionally, proctoscopy was performed 12 months after treatment and the results were scored using the Vienna Rectoscopy Scale (VRS).

Results: Of the patients treated 39.6% and 12.5% experienced acute Grade 1 and Grade 2 GI toxicity, respectively. There was no Grade 3 or Grade 4 acute GI toxicity experienced in the study. Only 4.3% showed late Grade 1 GI toxicity, and there was no late Grade 2 or greater GI toxicity experienced in the study. A total of 41.7%, 35.4% and 2.1% of the men experienced acute Grade 1, Grade 2 and Grade 3 GU toxicity, respectively. There was no Grade 4 acute GU toxicity experienced in the study. Late Grade 1 and Grade 2 GU toxicity was experienced in 17.0% and 2.1% of the patients, respectively. There was no late Grade 3 or greater GU toxicity experienced in the study. Seventy one percent of the patients had a VRS score of 0, and one patient (2%) had Grade 3 teleangiectasia. There was no evidence of ulceration, stricture or necrosis at 12 months.

Conclusion: The use of PEG spacer gel is a safe and effective method to spare the rectum from higher dose and toxicity.

Figure 1

Dose distribution a) pre- and b) post injection of spacer gel.

Figure 2

Comparison of gastrointestinal toxicity ≥ Grade 2 with other trials. Lips et al. [18]: PTV = Prostate + seminal vesicles + 8 mm margin, 76 Gy mean dose, not more than 5% of rectum received ≥ 72 Gy. Vora et al. [19]: PTV = Prostate + seminal vesicles + 6-10 mm margin, 50.4 Gy + Boost (median 75.6 Gy), not more than 40%/30%/10% of Rectum received ≥ 65 Gy/70 Gy/75 Gy, not more than 1.8 cm² of rectum received 81 Gy. Zietman et al. [8]: PTV = Prostate + seminal vesicles + 10 mm margin for Photontherapy (50.4 Gy) and 5mm margin for proton Boost (28.8 GyE).

Figure 3

Comparison of Vienna rectoscopy scores at 12 months for men treated with SpaceOAR vs. the literature [[21]].