Objective: To evaluate the efficacy of the balloon spacer when used to reduce the radiation dose delivered to the rectum in prostate cancer patients undergoing external beam radiotherapy. Method: A single center retrospective analysis including 75 PC patients with localized T1-T3a disease who received balloon spacer followed by EBRT. Pre- and post-implantation computed tomography (CT) scans were utilized for treatment planning for standard EBRT (78-81 Gy in 1.8-2 Gy fractions). Rectal dosimetry was assessed using DVHs, and toxicities were graded with CTCAE v.4. Results: A median (IQR) prostate-rectum separation resulted in 1.6 cm (1.4-2.0) post balloon spacer implantation. Overall, 90.6 % (68/75) of patients had a clinically significant 25 % relative reduction in the rectal with a median relative reduction of 91.8 % (71.2-98.6 %) at rV70. Three (4.0 %) patients reported mild procedural adverse events, anal discomfort and dysuria. Within 90 days post-implantation, five patients (6.67 %) and 1 patient (1.33 %) reported grade 1 and grade 2 rectal toxicities (anal pain, constipation, diarrhea and hemorrhoids). Genitourinary (GU) grade 1 toxicity was reported in 37 patients (49.33 %), with only one patient (1.33 %) experiencing grade 2 GU toxicity. No grade >= 3 toxicity was reported. Conclusion: Balloon spacer implantation effectively increased prostate-rectum separation and associated with dosimetric gains EBRT for PC stage T1-T3a. Further controlled studies are required to ascertain whether this spacer allows for radiotherapy dose escalation and minimizes gastrointestinal (GI) toxicity.

PURPOSE/OBJECTIVES:Rectal spacers have been shown to reduce rectal side effects in patients receiving prostate radiation. However, concerns remain regarding precise and reproducible gel injection. We evaluated efficacy and safety of a novel rectoprostatic spacer balloon that allows potential for controlled, adaptable deployment. This study tested co-primary hypotheses: (1) balloon spacer would result in ≥25% reduction of rectal V70 in >75% of subjects and (2) implantation procedure-related and rectal ≥grade 1 adverse events within 6 months (duration ≥2 days, Common Terminology Criteria for Adverse Events 4.0) would be noninferior in balloon versus control subjects. METHODS AND MATERIALS:A total of 222 subjects were enrolled at 16 centers. All patients had T1-T3 prostate cancer without magnetic resonance imaging evidence of posterior extraprostatic invasion. Randomization was 2:1 (balloon: control) and subject-blinded. Patients underwent transperineal transrectal ultrasound axial and sagittal-guided fiducial placement ± balloon, followed by Intensity-Modulated Radiation Therapy (81 Gy in 1.8 Gy fractions or biologically equivalent hypofractionated dose). For efficacy comparisons, plans were generated by a central core lab on pre- and postimplant computed tomography scans. RESULTS:The primary efficacy endpoint was met, with 97.9% of balloon subjects (139/142) having rectal V70 reduction >25% (P < .001). Mean V70 was 7.0 % pre- versus 1.1% postimplant. The primary safety endpoint was met with balloon subjects experiencing fewer ≥grade 1 events, 18% versus 23% (P < .001 for noninferiority). On predefined secondary endpoint of ≥grade 2 events, rates trended lower in balloon subjects (4.3% vs 6.5%, P = .527). Mean perirectal spacing was 19 ± 3.7 mm and maintained through radiation treatment (18 ± 3.9 mm). Balloon resorption was observed on 6-month computed tomography in 98.5% (133/135) of subjects. The Expanded Prostate Cancer Index quality of life instrument was collected throughout study, and did not differ statistically between the study arms. CONCLUSIONS:Biodegradable rectal spacer balloon was effective in significantly reducing dose to rectum, and associated with decreased cumulative rectal plus implantation-related adverse events. Balloon resorption was consistently observed by 6 months.

You have accessJournal of UrologyCME1 Apr 2023PD15-11 EFFICACY AND SAFETY OF BIODEGRADABLE RECTAL SPACER BALLOON IN PATIENTS RECEIVING PROSTATE IMRT: AN INTERNATIONAL PHASE 3 RANDOMIZED TRIAL Daniel Song, Mateusz Dabkowski, Warsaw Poland, Paulo Costa, Rizwan Nurani, Michael Kos, Ben Vanneste, David Margel, Eli Sapir, Shawn Zimberg, Oleksandr Boychak, Edward Soffen, Abdulla Alhasso, Kenneth Tokita, Dian Wang, Zvi Symon, and Richard Hudes Daniel SongDaniel Song More articles by this author , Mateusz DabkowskiMateusz Dabkowski More articles by this author , Warsaw PolandWarsaw Poland More articles by this author , Paulo CostaPaulo Costa More articles by this author , Rizwan NuraniRizwan Nurani More articles by this author , Michael KosMichael Kos More articles by this author , Ben VannesteBen Vanneste More articles by this author , David MargelDavid Margel More articles by this author , Eli SapirEli Sapir More articles by this author , Shawn ZimbergShawn Zimberg More articles by this author , Oleksandr BoychakOleksandr Boychak More articles by this author , Edward SoffenEdward Soffen More articles by this author , Abdulla AlhassoAbdulla Alhasso More articles by this author , Kenneth TokitaKenneth Tokita More articles by this author , Dian WangDian Wang More articles by this author , Zvi SymonZvi Symon More articles by this author , and Richard HudesRichard Hudes More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003262.11AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Rectal gel spacers have been shown to reduce rectal side effects in patients receiving prostate radiation. However, concerns remain regarding precise and reproducible gel injection. We report on a novel rectoprostatic spacer balloon which allows potential for controlled, adaptable deployment without time constraints associated with hydrogel injection. To determine efficacy and safety, the study had co-primary hypotheses: 1) Balloon spacer would result in ≥25% reduction of rectal V70 in >75% of subjects, and 2) Implantation procedure-related and rectal ≥ Grade 1 adverse events would be non-inferior in balloon vs control subjects (events with duration ≥2 days within 6 months, CTCAE 4.0). METHODS: 222 subjects were enrolled at 16 centers. All patients had biopsy-proven T1-T3 prostate cancer without MRI evidence of posterior extraprostatic invasion. Patients receiving brachytherapy or whole pelvic RT were excluded. Randomization was 2:1 (balloon:control) and subject-blinded. All patients underwent transperineal TRUS-guided fiducial marker placement±biodegradable balloon, followed by IMRT. For efficacy endpoint comparisons, plans were generated by central core lab on pre- and post-implant CT scans (81 Gy in 1.8 Gy fractions). Adverse events were reviewed by blinded, independent Clinical Events Committee. RESULTS: The primary efficacy endpoint was met, with 97.9% of balloon subjects (139/142) having rectal V70 reduction of >25% (pre- vs post-implant; p<0.001, 95% CI (94.0, 99.6%). Mean V70 was 7.0 % pre- vs 1.1% post-implant. Similar decreases were observed in rectal V40–V80. Mean prostate-rectal spacing achieved (19+3.7mm) was maintained through radiation treatment (18+3.9mm). Balloon placement was successful in 99% of subjects. The primary safety endpoint was met with balloon subjects experiencing fewer ≥ Grade 1 events, 18% vs 23% (p<0.001, 95% CI -15.7%, 5.5%). Event rate was higher in balloon subjects in early post-implant period, but control arm surpassed balloon group at/beyond day 44 post-implant. On pre-defined secondary endpoint of ≥Grade 2 events, rates were lower in balloon subjects (4.3% vs 6.5%). Complete balloon resorption was observed on 6-month CT in 98.5% (133/135) of subjects. CONCLUSIONS: Biodegradable rectal spacer balloon was effective in significantly reducing dose to rectum, and associated with decreased cumulative rectal plus implantation-related adverse events. Balloon resorption was consistently observed by 6 months. Source of Funding: BioProtect, Ltd © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e423 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Daniel Song More articles by this author Mateusz Dabkowski More articles by this author Warsaw Poland More articles by this author Paulo Costa More articles by this author Rizwan Nurani More articles by this author Michael Kos More articles by this author Ben Vanneste More articles by this author David Margel More articles by this author Eli Sapir More articles by this author Shawn Zimberg More articles by this author Oleksandr Boychak More articles by this author Edward Soffen More articles by this author Abdulla Alhasso More articles by this author Kenneth Tokita More articles by this author Dian Wang More articles by this author Zvi Symon More articles by this author Richard Hudes More articles by this author Expand All Advertisement PDF downloadLoading ...

AbstractPurposeA multicenter, double‐arm, central core lab, retrospective study was performed to compare the rectal dosimetry of patients implanted with two injectable, biodegradable perirectal spacers, in conventional fractionation (CF), as well as ultrahypofractionation (UH) treatment plans.Methods and materialsFifty‐nine patients were enrolled into the study in five centers: two centers in Europe, which implanted a biodegradable balloon spacer in a total of 24 subjects and three centers in the US, which implanted the SpaceOAR in 35 subjects. Anonymized CTs (pre and post‐implantation) were reviewed by the central core lab. For VMAT CF plans rectal V50, V60, V70, and V80 were calculated. For UH plans, a corresponding rectal V22.6, V27.1, V31.37, and V36.25 were established representing 62.5%, 75%, 87.5%, and 100% of the 36.25 Gy prescribed dose.ResultsFor CF VMAT, a comparison between the balloon spacer and the SpaceOAR revealed a significant difference of 33.4% decrease in mean rectal V50 (71.9% vs. 38.5%, p < 0.001), 27.7% in mean rectal V60 (79.6% vs. 51.9%, p < 0.001), 17.1% difference in mean rectal V70 (84.1% vs. 67.0%, p = 0.001), and a significant difference of 3.0% (p = 0.019) in mean rectal V80 (87.2% vs. 84.2%). With UH analysis, the mean rectal dose reduction for the balloon spacer compared to the SpaceOAR was 79.2% and 53.3% for V27.1 (p < 0.001), 84.1% and 68.1% for V31.71 (p = 0.001), and 89.7% and 84.8% for V36.25 (p = 0.012), respectively.ConclusionRectal dosimetry is more favorable for treatment with the balloon spacer compared with SpaceOAR. Further research, particularly in the context of a prospective randomized clinical trial design, is needed to assess the acute and late toxicity experience as well as physician satisfaction with achieving symmetrical implantation, and ease of use in light of increasing clinical use.

PurposePreviously a phase III trial of a hydrogel rectal spacer during prostate radiation therapy found decreased toxicity and a clinically significant improvement in bowel quality of life (QOL) at 3 years by the Expanded Prostate Cancer Index. We performed a secondary analysis to identify men less likely to benefit.Methods and MaterialsClinical and dosimetric data for the 222 patients enrolled on the SpaceOAR phase III trial were analyzed. The volume of rectum treated to 70 Gy (V70) and the quantitative analysis of normal tissue effects in the clinic (QUANTEC) rectal dose goals were used as surrogates for clinical benefit and plan quality. Mean bowel QOL was assessed at 15 and 36 months posttreatment and the likelihood of 1× (5 points) or 2× (10 points) minimally important difference changes were assessed.ResultsRectal V70 was correlated with physician scored toxicity (P = .033) and was used as a surrogate for plan quality. There was no correlation between prostate volume and rectal V70 (r = 0.077). Rectal V70 pre- and post-hydrogel was 13% and 3% for the smallest prostates (<40 mL) and 12% and 2% for the largest (>80 mL). The relative reduction in rectal V70 of 78% did not vary by prespacer V70, but the absolute reduction was greater for a higher V70. All spacer plans met the 5 QUANTEC rectal dose constraints, although 92% of control plans met all constraints. At 3 years, those not meeting all QUANTEC goals had a 15.0-point (standard deviation 15.1) decline, control patients meeting QUANTEC goals had a 4.0-point (9.5) decline, and spacer had >0.5 (7.6; P < .01). Previous surgery was not correlated with QOL (P = .8). Across prognostic groups, including age, body mass index, previous surgery, target volume, or quality of radiation plans, there was no statistically significant heterogeneity in the relative benefit of spacer in decreasing the risk of 1× or 2× the minimally important difference declines.ConclusionsThere was little heterogeneity in the likelihood of spacer reducing the risk of declines in bowel QOL across clinical and dosimetric variables. Even for the >95% of plans meeting QUANTEC rectal criteria, hydrogel spacer provided potentially meaningful benefits.

A phase III rectal spacer (Sp) trial of prostate RT found a clinically significant 5.8 pt difference in bowel quality of life (QOL) by EPIC and a 27% absolute lower rate of minimally important decline (MID). We performed a secondary analysis to identify men less likely to benefit from Sp. The volume of rectum treated to 70 Gy (V70) as well as the QUANTEC rectal dose goals were utilized as surrogates for plan quality and clinical benefit. The likelihood of 1x (5 pt) or 2x (10 pt) MID changes were assessed as a function of clinical variables with odds ratios reported from logistic models. There was no correlation between prostate volume and rectal V70 (R2=0.006) or V70 reduction with Sp placement (p>0.5). Rectal V70 pre and post Sp was 13/3% for the smallest prostates (<40 cc) and 12/2% for the largest (>80 cc). The relative reduction in rectal V70 of 78% did not vary by pre Sp V70, but the absolute reduction was greater for higher V70 (18.3% reduction if rectal V70>20% vs. 3.4% for rectal V70≤5%). All Sp plans met the 5 QUANTEC rectal dose constraints while 92% of Cntrl plans met all 5 constraints. Declines in bowel QOL were directly correlated with rectal dosimetry from V50 through V70 (all p<0.05). Those not meeting all QUANTEC goals had -15.0 pt (stdev 15.1) decline, Cntrl pts meeting QUANTEC goals had -4.0 (9.5) pt decline and Sp had +0.5 (7.6) (p<0.01). Previous abdominal/pelvic surgery did not change baseline QOL (p>0.1) while at 3 mo there was a small and clinically insignificant greater decline in bowel QOL in those with prior surgery (-6.4 pt (no surgery) vs. -8.1 pt (surgery), p>0.1) with this small difference persistent over time. Across prognostic groups including: age, body mass index, previous surgery, target volume, or quality of radiation plans there was no statistically significant heterogeneity in the relative benefit of Sp in decreasing the risk of 1x or 2xMID declines (Table). There was little heterogeneity in the likelihood of Sp reducing the risk of declines in bowel QOL across clinical and dosimetric variables. Even for the >95% of plans meeting QUANTEC rectal criteria Sp provided meaningful benefit. Further analysis into biologic differences that predict changes in bowel QOL after RT are needed.Abstract SU_27_2269; Table 1Impact of Spacer on Likelihood of Bowel MID at 3-yearsVariableNumber1x MID Odds Ratio (95%CI)Ctrl %Sp %2x MID Odds Ratio (95%CI)Ctrl %Sp %Overall1370.23 (0.1-0.5)41140.22 (0.07-0.7)215Age <67680.20 (0.06-0.7)44140.08 (0.01-0.5)334Age >67690.26 (0.08-0.8)39140.57 (0.11-3.1)127BMI <28660.33(0.11-1.01)42190.32 (0.08-1.3)2510BMI >28710.16(0.05-0.6)40100.11 (0.01-1.2)152No Previous Surgery590.13(0.04-0.4)46100.07 (0.01-0.6)232Previous Surgery630.42(0.12-1.3)36200.49 (0.11-2.2)1810Prostate660.30 (0.08-1.2)28100.22 (0.03-1.4)174Prostate + SV710.22 (0.07-0.6)50180.24 (0.05-1.1)237Plan didn't meet all 5 QUANTEC rectal goals5-80--60-Plan met all 5 QUANTEC rectal goals1320.29 (0.12-0.7)36140.31 (0.09-1.1)155 Open table in a new tab

Purpose: SpaceOAR, a Food and Drug Administration approved hydrogel intended to create a rectal prostate space, was evaluated in a single-blind phase III trial of image guided intensity modulated radiation therapy. A total of 222 men were randomized 2:1 to the spacer or control group and received 79.2 Gy in 1.8-Gy fractions to the prostate with or without the seminal vesicles. The present study reports the final results with a median follow-up period of 3 years.Methods and Materials: Cumulative (Common Terminology Criteria for Adverse Events, version 4.0) toxicity was evaluated using the log-rank test. Quality of life (QOL) was examined using the Expanded Prostate Cancer Index Composite (EPIC), and the mean changes from baseline in the EPIC domains were tested using repeated measures models. The proportions of men with minimally important differences (MIDs) in each domain were tested using repeated measures logistic models with pre specified thresholds.Results: The 3-year incidence of grade >= 1 (9.2% vs 2.0%; P=.028) and grade >= 2 (5.7% vs 0%; P=.012) rectal toxicity favored the spacer arm. Grade >= 1 urinary incontinence was also lower in the spacer arm (15% vs 4%; P=.046), with no difference in grade >= 2 urinary toxicity (7% vs 7%; P=0.7). From 6 months onward, bowel QOL consistently favored the spacer group (P=.002), with the difference at 3 years (5.8 points; P<.05) meeting the threshold for a MID. The control group had a 3.9-point greater decline in urinary QOL compared with the spacer group at 3 years (P<.05), but the difference did not meet the MID threshold. At 3 years, more men in the control group than in the spacer group had experienced a MID decline in bowel QOL (41% vs 14%; P=.002) and urinary QOL (30% vs 17%; P=.04). Furthermore, the control group were also more likely to have experienced large declines (twice the MID) in bowel QOL (21% vs 5%; P=.02) and urinary QOL (23% vs 8%; P=.02).Conclusions: The benefit of a hydrogel spacer in reducing the rectal dose, toxicity, and QOL declines after image guided intensity modulated radiation therapy for prostate cancer was maintained or increased with a longer follow-up period, providing stronger evidence for the benefit of hydrogel spacer use in prostate radiation therapy. (C) 2017 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenseqby-ne-nd/4.0/).

BACKGROUND:We previously reported the results of a phase 3 trial evaluating a prostate/rectal hydrogel spacer during prostate intensity modulated radiation therapy, which resulted in decreased rectal dose and toxicity and less decline in bowel quality of life (QOL). A secondary analysis was performed to correlate penile bulb dose and sexual QOL. METHODS AND MATERIALS:Sexual QOL was measured with the Expanded Prostate Cancer Index Composite (EPIC) by mean scores, the proportion of patients with a minimal clinically important difference (MID), and analyses of the different items composing the sexual domain. RESULTS:A total of 222 men enrolled with median follow-up of 37 months. Hydrogel reduced penile bulb mean dose, maximum dose, and percentage of penile bulb receiving 10 to 30 Gy (all P < .05) with mean dose indirectly correlated with erections sufficient for intercourse at 15 months (P = .03). Baseline EPIC was low (53 [standard deviation ± 24]) with no difference between arms (P > .1). A total of 41% (88/222) of men had adequate baseline sexual QOL (EPIC >60 (mean, 77 [± 8.3]). This subgroup at 3 years had better sexual function (P = .03) with a spacer with a smaller difference in sexual bother (P = .1), which resulted in a higher EPIC summary on the spacer arm (58 [±24.1] vs control 45 [± 24.4]) meeting threshold for MID without statistical significance (P = .07). There were statistically nonsignificant differences favoring spacer for the proportion of men with MID and 2× MID declines in sexual QOL with 53% vs 75% having an 11-point decline (P = .064) and 41% vs 60% with a 22-point decline (P = .11). At 3 years, more men potent at baseline and treated with spacer had "erections sufficient for intercourse" (control 37.5% vs spacer 66.7%, P = .046) as well as statistically higher scores on 7 of 13 items in the sexual domain (all P < .05). CONCLUSIONS:The use of a hydrogel spacer decreased dose to the penile bulb, which was associated with improved erectile function compared with the control group based on patient-reported sexual QOL.

Purpose: Perirectal spacing, whereby biomaterials are placed between the prostate and rectum, shows promise in reducing rectal dose during prostate cancer radiation therapy. A prospective multicenter randomized controlled pivotal trial was performed to assess outcomes following absorbable spacer (SpaceOAR system) implantation.Methods and Materials: Overall, 222 patients with clinical stage T1 or T2 prostate cancer underwent computed tomography (CT) and magnetic resonance imaging (MRI) scans for treatment planning, followed with fiducial marker placement, and were randomized to receive spacer injection or no injection (control). Patients received postprocedure CT and MRI planning scans and underwent image guided intensity modulated radiation therapy (79.2 Gy in 1.8-Gy fractions). Spacer safety and impact on rectal irradiation, toxicity, and quality of life were assessed throughout 15 months.Results: Spacer application was rated as "easy" or "very easy" 98.7% of the time, with a 99% hydrogel placement success rate. Perirectal spaces were 12.6 +/- 3.9 mm and 1.6 +/- 2.0 mm in the spacer and control groups, respectively. There were no device-related adverse events, rectal perforations, serious bleeding, or infections within either group. Pre-to postspacer plans had a significant reduction in mean rectal V70 (12.4% to 3.3%, P<.0001). Overall acute rectal adverse event rates were similar between groups, with fewer spacer patients experiencing rectal pain (P=.02). A significant reduction in late (3-15 months) rectal toxicity severity in the spacer group was observed (P=.04), with a 2.0% and 7.0% late rectal toxicity incidence in the spacer and control groups, respectively. There was no late rectal toxicity greater than grade 1 in the spacer group. At 15 months 11.6% and 21.4% of spacer and control patients, respectively, experienced 10-point declines in bowel quality of life. MRI scans at 12 months verified spacer absorption.Conclusions: Spacer application was well tolerated. Increased perirectal space reduced rectal irradiation, reduced rectal toxicity severity, and decreased rates of patients experiencing declines in bowel quality of life. The spacer appears to be an effective tool, potentially enabling advanced prostate RT protocols. (C) 2015 The Authors. Published by Elsevier Inc.

Purpose/Objective(s)Perirectal spacers are hypothesized to reduce rectal dose and toxicity in men undergoing prostate radiation therapy (RT). A multicenter trial was designed, and approved by an institutional review board, to evaluate rectal dose and toxicity in men with and without spacers, with an endpoint of >25% rectal V70 reduction in at least 70% of spacer patients.Materials/MethodsMen with T1 or T2 stage PCa, Gleason <7, prostate-specific antigen (PSA) <20, prostate <80 mL, <50% positive cores, and signed informed consent underwent 1) CT/MR dose planning, 2) fiducial marker placement and 2:1 randomization to transperineal spacer placement or control (no spacer), 3) CT/MR dose planning, and 4) 79.2 Gy at 1.8 Gy per fraction image guided intensity modulated RT (IG-IMRT). All adverse events (AEs) through RT and at 3, 6, 12, and 15 mos were adjudicated by a blinded independent Clinical Events Committee, scoring rectal toxicity with Common Terminology Criteria for Adverse Events version 4. Spacer measurements and dosimetric analysis was performed by an independent Core Lab.ResultsPoster Viewing Abstracts 2488; Table 1Rectal V70 Absolute Volume (mL)Rectal V70 (%)SpacerControlp-value *SpacerControlP value *Pre7.2 + 3.17.3 + 3.30.86812.4 + 5.412.4 + 6.2.948Post1.9 + 2.07.8 + 4.0<0.00013.3 + 3.211.7 + 4.7<.0001% reduction73.6%-6.9%<0.000173.5%5.7%<.0001Aside from a significant reduction in acute rectal pain in the spacer group (P=.022), there was no significant difference in acute rectal or urinary toxicity. Late rectal toxicity of 2.0% and 7.0% was noted in the spacer (max Grade 1) and control (max Grade 3) groups, respectively, with a significant reduction in the spacer late rectal toxicity severity (P=.044). There was no significant difference in late urinary toxicity between the groups. Open table in a new tab ConclusionSpacer application was well tolerated, resulting in consistent perirectal space creation and significant reductions in rectal dose. Relative to control, the spacer group had less acute rectal pain, with less severe late rectal toxicity, with a 71% reduction in incidence. The V70 of 3.3% and 11.7% with spacer versus control compared favorably to RTOG 0126. The reduced absolute volume for rectal V70 of 73.6% with spacer has promise for limiting maximal dose in the anterior rectal wall for SBRT or brachytherapy as well as IMRT. Study limitations include the 15 month toxicity assessment. Purpose/Objective(s)Perirectal spacers are hypothesized to reduce rectal dose and toxicity in men undergoing prostate radiation therapy (RT). A multicenter trial was designed, and approved by an institutional review board, to evaluate rectal dose and toxicity in men with and without spacers, with an endpoint of >25% rectal V70 reduction in at least 70% of spacer patients. Perirectal spacers are hypothesized to reduce rectal dose and toxicity in men undergoing prostate radiation therapy (RT). A multicenter trial was designed, and approved by an institutional review board, to evaluate rectal dose and toxicity in men with and without spacers, with an endpoint of >25% rectal V70 reduction in at least 70% of spacer patients. Materials/MethodsMen with T1 or T2 stage PCa, Gleason <7, prostate-specific antigen (PSA) <20, prostate <80 mL, <50% positive cores, and signed informed consent underwent 1) CT/MR dose planning, 2) fiducial marker placement and 2:1 randomization to transperineal spacer placement or control (no spacer), 3) CT/MR dose planning, and 4) 79.2 Gy at 1.8 Gy per fraction image guided intensity modulated RT (IG-IMRT). All adverse events (AEs) through RT and at 3, 6, 12, and 15 mos were adjudicated by a blinded independent Clinical Events Committee, scoring rectal toxicity with Common Terminology Criteria for Adverse Events version 4. Spacer measurements and dosimetric analysis was performed by an independent Core Lab. Men with T1 or T2 stage PCa, Gleason <7, prostate-specific antigen (PSA) <20, prostate <80 mL, <50% positive cores, and signed informed consent underwent 1) CT/MR dose planning, 2) fiducial marker placement and 2:1 randomization to transperineal spacer placement or control (no spacer), 3) CT/MR dose planning, and 4) 79.2 Gy at 1.8 Gy per fraction image guided intensity modulated RT (IG-IMRT). All adverse events (AEs) through RT and at 3, 6, 12, and 15 mos were adjudicated by a blinded independent Clinical Events Committee, scoring rectal toxicity with Common Terminology Criteria for Adverse Events version 4. Spacer measurements and dosimetric analysis was performed by an independent Core Lab. ResultsPoster Viewing Abstracts 2488; Table 1Rectal V70 Absolute Volume (mL)Rectal V70 (%)SpacerControlp-value *SpacerControlP value *Pre7.2 + 3.17.3 + 3.30.86812.4 + 5.412.4 + 6.2.948Post1.9 + 2.07.8 + 4.0<0.00013.3 + 3.211.7 + 4.7<.0001% reduction73.6%-6.9%<0.000173.5%5.7%<.0001Aside from a significant reduction in acute rectal pain in the spacer group (P=.022), there was no significant difference in acute rectal or urinary toxicity. Late rectal toxicity of 2.0% and 7.0% was noted in the spacer (max Grade 1) and control (max Grade 3) groups, respectively, with a significant reduction in the spacer late rectal toxicity severity (P=.044). There was no significant difference in late urinary toxicity between the groups. Open table in a new tab Aside from a significant reduction in acute rectal pain in the spacer group (P=.022), there was no significant difference in acute rectal or urinary toxicity. Late rectal toxicity of 2.0% and 7.0% was noted in the spacer (max Grade 1) and control (max Grade 3) groups, respectively, with a significant reduction in the spacer late rectal toxicity severity (P=.044). There was no significant difference in late urinary toxicity between the groups. ConclusionSpacer application was well tolerated, resulting in consistent perirectal space creation and significant reductions in rectal dose. Relative to control, the spacer group had less acute rectal pain, with less severe late rectal toxicity, with a 71% reduction in incidence. The V70 of 3.3% and 11.7% with spacer versus control compared favorably to RTOG 0126. The reduced absolute volume for rectal V70 of 73.6% with spacer has promise for limiting maximal dose in the anterior rectal wall for SBRT or brachytherapy as well as IMRT. Study limitations include the 15 month toxicity assessment. Spacer application was well tolerated, resulting in consistent perirectal space creation and significant reductions in rectal dose. Relative to control, the spacer group had less acute rectal pain, with less severe late rectal toxicity, with a 71% reduction in incidence. The V70 of 3.3% and 11.7% with spacer versus control compared favorably to RTOG 0126. The reduced absolute volume for rectal V70 of 73.6% with spacer has promise for limiting maximal dose in the anterior rectal wall for SBRT or brachytherapy as well as IMRT. Study limitations include the 15 month toxicity assessment.