Thus far, the literature has suggested that space created by absorbable biomaterials between the prostate and rectum can potentially lead to a reduction
in acute toxicity. In 2007, Prada et al. (26) reported on 27 patients in whom a hyaluronic acid injection created a median of 2 cm of space between the prostate and rectum without causing acute side effects and led to a 28% reduction in the maximum rectal dose during an HDR brachytherapy boost. The same group performed a clinical trial of 69 patients receiving LDR monotherapy in which the 36 patients who received the GSI-IX clinical trial spacer had a significantly lower risk of rectal mucosal damage at the planned proctoscopic examinations (5% vs. 36%, p < 0.002) (27). The group from Cancer Centers of Irvine has reported on 10 patients who had a median of 1.3 cm of space from a cross-linked hyaluronan gel selleck chemical spacer before HDR brachytherapy (2200 cGy) with supplemental intensity-modulated radiation therapy (IMRT) (5040 cGy) and found no Grade 1, 2, or 3 acute diarrhea, compared with 29.7% among historical controls (p = 0.04) (28). The same group also reported on 30 patients who received the same gel spacing and found that those patients reported an improved Expanded Prostate Cancer Index Composite Bowel Bother scores (p = 0.03) compared with controls who did not receive the spacer (29). A recently published study by Noyes et al. (30) reported on the investigational use of human collagen to increase the distance between the prostate and the anterior rectal wall. Before the start of a course of 75.6 Gy IMRT for prostate cancer, 11 patients were injected through a transperineal approach with 20 mL of human collagen into the perirectal space, resulting in
mean separation between the prostate and anterior rectum of 12.7 mm with a mean reduction in dose to the anterior rectal wall of 50%. All patients denied any rectal symptoms during the study. More recently PEG has been used to increase distance between the Isoconazole rectum and the prostate. Noyes et al. (30) have suggested that PEG or hydrogel products may have advantages over hyaluronic acid for this application because hyaluronic acid appears to be more viscous and may not distribute as evenly and may be susceptible to radiation degradation (31). Tokita et al. (32) from the Cancer Center of Irvine reported on the use of a PEG spacer as a viable means to enhance rectal dose sparing. Twenty-four combined HDR brachytherapy and IMRT patients were administered the spacing material in the prostate rectal interspace transperineally at the time of catheter implantation. Results showed an increase in the mean prostate rectal spacing of 0.8–0.9 cm and an average decrease in rectal V70 from 41.4% to 33.6% with a maximum rectal dose decrease of 36.6%.