Assessment of Polyethylene Glycol Hydrogel Spacer and Its Effect on Rectal Radiation Dose in Prostate Cancer Patients Receiving Proton Beam Radiation Therapy

Abstract

Purpose: To assess the efficacy of placing a polyethylene glycol (PEG) spacing hydrogel in patients undergoing proton beam radiation therapy for prostate cancer. This study also aims to assess the effect on rectal radiation dose of prostateerectum separation in various anatomic planes.Methods and Materials: Seventy-two consecutive prostate cancer patients undergoing conventionally fractionated pencil beam scanning proton radiation therapy with and without hydrogel placement were compared. Magnetic resonance images taken after hydrogel placement measured prostateerectum separation and were correlated to rectal dosing and rectal toxicity. Univariate analysis of clinical variables and radiation dosing was conducted using nonparametric Wilcoxon rank-sum test with continuity correction between groups (hydrogel spacer vs controls). Spearman's rank correlation coefficient assessed relationships between the various anatomic dimensions of perirectal space and rectal radiation dosing.Results: Fifty-one patients had hydrogel placement before therapy and 21 did not. There was a 42.2% reduction in rectal dosing (mL 3 rectum) in hydrogel patients (P < .001). Increasing midline sagittal lift resulted in a greater mitigation of total rectal dose (P Z .031). The degree of prostate surface area coverage on coronal plane did not correlate with further reductions in rectal radiation dose (P Z .673). Patients who had PEG hydrogels placed reported more rectal side effects during treatment compared with those patients who did not (35.3% vs 9.5%, P Z .061). At median 9.5-month follow-up, there was no difference in reporting of grade 2 rectal toxicity between the 2 groups (7.7% vs 7.1%, P Z .145).Conclusions: Polyethylene glycol hydrogel placement before pencil proton beam radiation therapy for prostate cancer reduced rectal radiation dose. The most important factor reducing total rectal dose was the degree of sagittal midline separation created by the PEG hydrogel. This is the largest study with the longest follow-up to investigate hydrogel placement in the proton beam radiation setting.

Dosimetric and clinical outcomes of SpaceOAR in men undergoing external beam radiation therapy for localized prostate cancer: A systematic review

“…Furthermore, three other studies 24,25,27 also reported significant reductions in rectal dose volumes when comparing between the SpaceOAR and control groups; relative reductions were 37.5% in V70 (P < 0.01) for one study, 24 71.6% in V75 (P < 0.0001) for another study, 25 and 41.8% in V75 (P < 0.001) for the third study. 27 Three studies 16,18,22,24 showed SpaceOAR to not increase the radiation dose volume in neighbouring organs, particularly the bladder and penile bulb. The RCT 16 and a study by Whalley et al 22 reported no significant differences in dosimetry values (V40, V50, V70) for the bladder when comparing pre-SpaceOAR to post-SpaceOAR treatment plans.…”

“…1). Of the 13 articles, five were of the same RCT, [16][17][18][19][20] two were prospective studies, 21,22 five were retrospective studies [23][24][25][26][27] in which two were of the same study, 25,26 and one was a pooled analysis 28 of the RCT 18 and a retrospective study. 24 Characteristics of the included articles are outlined in Table 2.…”

“…Three studies, published in five articles, 16,17,20,22,27 reported SpaceOAR insertion to create a mean prostaterectum separation ranging from 10.5 mm to 11.0 mm. The RCT reported that MRI imaging showed the hydrogel to still be present at 3-month but completely absorbed into the body at 12-month.…”

“…The RCT reported that MRI imaging showed the hydrogel to still be present at 3-month but completely absorbed into the body at 12-month. 16,17,20 The impact of SpaceOAR on radiation dosimetry was reported in six studies, published in eight articles [16][17][18]21,22,24,25,27 and is presented in Table 3. V(x) was defined as the per cent volume of tissue receiving more than x Gy of radiation.…”

“…Four studies published in six articles 16,17,20,21,22,27 reported the safety of SpaceOAR insertion. The RCT 16,17,20 reported that 15 patients (10.0%) experienced grade 1 (6.7%) or grade 2 (3.3%) procedure-related complications such as anorectal pressure, perianal pain, discomfort while sitting, hematospermia and hematuria.…”