Rectal Hydrogel Spacer Research Articles

Validation of a Quality Metric Score to Assess the Placement of Hydrogel Rectal Spacer in Patients Treated With Prostate Stereotactic Radiation Therapy

To evaluate the quality of the interspace between the prostate and rectum and assess the effect on the dose to the rectum by measuring the spacer quality score (SQS) before and after implanting a hydrogel rectal spacer. Thirty patients with prostate cancer were treated with stereotactic ablative body radiation therapy as part of the SPORT clinical trial. Each patient had a 10 mL polyethylene glycol hydrogel spacer inserted transperineally. Computed tomography scans were acquired before and after spacer insertion, 10MV flattening filter free (FFF) stereotactic ablative body radiation therapy (SABR) treatment plans were generated using each image set. To calculate the SQS, the prostate-rectal interspace (PRI) was measured in the anterior-posterior orientation, parallel to the anatomic midline at the prostate base, apex, and midgland on the prespacer and postspacer computed tomography. Measurements were taken in 3 transverse positions between the prostate and the rectum, and PRI scores of 0, 1, and 2 were assigned if the interspace between prostate and rectum was <0.3, 0.3 to 0.9, or ≥1 cm, respectively. The overall SQS was the lowest of the PRI scores. Differences between prespacer and postspacer PRIs and SQS were investigated by performing Fisher's exact test and differences between doses to the rectum were investigated by performing the paired samples Wilcoxon rank-sum test and Student t test. Statistically significant differences between prespacer versus postspacer patients were found when grouping patients according to their overall SQS. The PRI summary score did not reach statistical significance between prespacer and postspacer at the base but was significantly higher for the prostate midline and apex. Statistically significant differences in some rectum dose-volume metrics were found when grouping patients according to their PRIs and SQS. SQS before and after the spacer insertion was evaluated and was found to be correlated with pre- and postspacer rectal dosimetry. Sources of improvement of the SQS scoring metric and limitations are discussed.

CT-based online adaptive radiotherapy improves target coverage and organ at risk (OAR) avoidance in stereotactic body radiation therapy (SBRT) for prostate cancer

IntroductionStereotactic body radiation therapy (SBRT) is an emerging treatment modality for clinically localized prostate cancer (PCa). Online daily adaptive radiotherapy (ART) could potentially improve the therapeutic ratio of prostate SBRT by accounting for inter-fraction variation in target and OAR volumes. To our knowledge, no group has evaluated the clinical utility of a novel AI-augmented CT-based ART system for prostate SBRT. In this study we hypothesized that adaptive prostate SBRT plans would result in improved target coverage and lower dose to OARs in comparison to unadapted treatment plans. MethodsSeven patients with favorable intermediate to oligometastatic PCa treated with 5-fx prostate adaptive SBRT were retrospectively reviewed. Patients were treated with 3625 cGy to the prostate and seminal vesicles. 6 patients additionally received 2500 cGy to the pelvic nodes, 5 patients underwent a boost to 4000 cGy to the prostate. For each fraction, a CBCT was acquired and OARs (rectum, bladder, bowel, sigmoid, femurs) were segmented/deformed using AI. CTVs were rigidly registered. Volumes were adjusted manually and PTV expansions added. Adaptive treatment plans were developed based on the contoured targets and OARs and dose to these volumes for the adapted vs. initial plans were compared for each fraction. V100 and the D0.03 cc between scheduled and adapted treatment plans were compared using a Student’s t-test, with significance threshold of P < 0.05. ResultsSeven patients completed 35 Fx’s of adaptive RT. Daily adaptation resulted in a statistically significant mean improvement in PTV V100 for all targets: [21.4 % ± 4.3 % for PTV 4000 (p < 0.0001); 8.7 % ± 1.1 % for PTV 3625 (p < 0.0001); and 11.5 % ± 3.1 % for PTV 2500 (p = 0.0013)]. Mean rectal D0.03 was significantly reduced by 38.8 cGy ± 5.95 cGy (p < 0.0001) per fraction (194 cGy/5 fractions) compared to the initial plans. There was a modest increase in bladder dose of 10.9 cGy ± 4.93 cGy per fraction (p = 0.0424) for the adaptive plans. The adaptive plans met bladder constraints for every fraction. There were no statistically significant differences between sigmoid or bowel dose for adapted vs. initial plans. No patients experienced acute CTCAE grade ≥ 3 GI/GU adverse events (median F/U 9.5 months). All statistically significant differences were maintained in the presence and absence of rectal hydrogel spacer (p < 0.05). ConclusionsCT-based online adaptive SBRT resulted in statistically significant and clinically meaningful improvements in PTV coverage and D0.03 cc dose to the rectum. A trial evaluating CT adaptive whole-pelvis prostate SBRT is underway.

A pooled long-term follow-up after radiotherapy for prostate cancer with and without a rectal hydrogel spacer: impact of hydrogel on decline in sexual quality of life.

The purpose of this study was to analyze the impact of prostate rectal spacers on sexual quality of life (QOL) following external beam radiation therapy (RT). Patient- reported QOL was evaluated using the Expanded Prostate Cancer Index Composite (EPIC). Patients were pooled from two sources: a randomized controlled trial and a non-randomized cohort of patients from a single institution. Both cohorts used the same spacing product and QOL instrument. Analysis was limited to those with good baseline pre-treatment sexual QOL (EPIC >/= 60). Differences in QOL summary score and individual items were assessed compared with baseline and between treatment arms. A total of 128 men had good baseline sexual function and were evaluated (64% with spacer and 36% without) with QOL data available for median 33 months (range: 2.5-69.4 months). Men without spacer were more likely to have declines in sexual function (p < 0.0001), bother (p = 0.0002), and sexual summary score (p < 0.0001). A minimally important difference of 10 points (1xMID) and 20 point (2xMID) was more likely without rectal spacer [10 points: odds ratio 3.53, (95% confidence interval 1.11-11.2), p = 0.032; 20 points: odds ratio 3.29, (95% confidence interval 1.16-9.33), p = 0.025]. Seven of 13 QOL items were statistically superior with hydrogel (six of nine functional and one of four bother), while no items were statistically superior for control. At baseline, more men treated with hydrogel had erections sufficient for intercourse; however, when analyzed only by the men with best baseline erectile potential and excluding those with worse function, the benefit of rectal spacing was maintained with a higher likelihood of preservation of erections sufficient for intercourse in those treated with hydrogel. In this pooled analysis of QOL after prostate RT, the utilization of a hydrogel spacer was associated with better sexual QOL, less men with measurable declines in sexual QOL, and higher rates of adequate erectile function.

CT vs. MRI: Which is More Accurate in Grading Rectal Wall Infiltration after Hydrogel Spacer Placement for Prostate Cancer Patients?

The purpose of this study was to evaluate the incidence and severity of rectal wall infiltration (RWI) in prostate cancer patients after rectal hydrogel spacer implantation, a commonly used procedure to minimize rectal radiation exposure during prostate radiotherapy. The study aimed to determine correlation of RWI using computed tomography (CT) scans and magnetic resonance imaging (MRI) scans in order to determine the optimal post-placement imaging modality. This retrospective study was conducted on 370 patients diagnosed with localized prostate cancer who underwent rectal hydrogel spacer placement from 2020 to 2022. CT scans were performed on all patients, with a smaller subset also undergoing MRI scans. The images were independently evaluated by three radiation oncologists to grade RWI levels using a standardized scoring system based on CT and MRI images after hydrogel placement. The levels were categorized as 0 (no RWI), 1 (focal RWI), 2 (moderate RWI), and 3 (significant RWI). Any grade of RWI was identified in 79.8% of men with the majority (41%) being RWI grade 1. The median time for CT scans was 9 days after hydrogel spacer placement and 14.5 days for MRI scans. For the subset of patients with both CT and MRI scans after spacer (mostly SpaceOAR Vue), RWI was detected in 58.33% of patients based on CT and 61.11% of patients based on MRI. Table 1 shows the mean percentage of patients with each score of RWI for each imaging modality. MRI was more likely to lead to a designation of RWI of any grade compared to CT and more often led to detection of RWI grades 2-3. Our findings demonstrate that the incidence and severity of RWI may be higher than previously reported in clinical trials and that MRI may be a more sensitive imaging modality. Caution is needed in the utilization of rectal spacer gels given the potential for complications with misplacement prior to radiation therapy. Further study is warranted to determine the potential impact of low-grade RWI on the safety of subsequent treatment.

Does Stereotactic Online Adaptive MRgRT to the Prostate Preclude the Need for Rectal Spacer

Historical prospective trials have shown that hydrogel rectal spacers can be very effective at decreasing rectal wall dose, and in turn rectal toxicity, in patients undergoing curative intent fractionated courses of radiotherapy for prostate cancer. However, in the modern era of stereotactic online adaptive MR guided radiation (MRgRT), it's not yet determined if rectal spacers improve the potential daily need for plan adaptation. A prospective database of MRgRT patients were queried for intact prostate cancer patients who received stereotactic online adaptive MR guided radiation. Patients were reviewed for the presence of a hydrogel rectal spacer present on the planning images. The number of adaptive fractions as well as the organs at risk out of tolerance were noted for each patient. Comparisons between number of fractions adapted as well as the number of fractions adapted for rectal constraints, were noted. For each case within this patient group that required plan adaptation, pre-specified dose constraints were finally met prior to treatment delivery. A total of 27 patients were treated with stereotactic online adaptive MRgRT from 2020 to 2022. 8 patients had a hydrogel rectal spacer placed prior to treatment. Out of the 95 fractions delivered to non-hydrogel patients, 78 were adapted, with 52 for urethra, 31 for bladder, 5 for bladder neck, and 35 for rectum. Of the 40 fractions delivered to patients with a hydrogel spacer, 20 were adapted. The corresponding reasons for adaptation in this group were 14 times for the urethra, 19 times for the bladder, 8 times for the bladder neck, and 8 times for the rectum. It was common for multiple at-risk organs to require adaptation for a single fraction within both cohorts. Although the percentage of patients requiring adaptation for rectal constraints was greater in the non-hydrogel patients (36.8% vs. 20%), this was not found to be statistically significant; p value greater than 0.1. The presence of a rectal spacer did not significantly reduce the need for online plan adaptation of the rectum for stereotactic online adaptive MRgRT. Furthermore, patients with a rectal spacer continued to often require adaptation to meet other prescription constraints. Further work is necessary to better select patients who would benefit from hydrogel spacers in the setting of online adaptive MRgRT. Additionally, longer follow-up of this patient population coupled with a larger patient cohort overall remains needed to increase the power of this analysis and to further explore the clinical outcomes of this patient group.

PO70: Combining External Beam Radiation, Brachytherapy, and Rectal Hydrogel Spacer for Prostate Cancer: A Study of Gastrointestinal Toxicity and Implant Quality

PO70: Combining External Beam Radiation, Brachytherapy, and Rectal Hydrogel Spacer for Prostate Cancer: A Study of Gastrointestinal Toxicity and Implant Quality

Cs-131 prostate brachytherapy boost and effect of hydrogel rectal spacer on long-term patient-reported rectal bleeding and bowel quality of life

This study evaluates long-term patient-reported bowel quality of life (QOL), rectal bleeding, and bleeding bother in patients with prostate cancer treated with external beam radiation therapy (EBRT) and Cesium-131 LDR brachytherapy (LDR-BT) boost with and without hydrogel rectal spacer. This is a retrospective analysis of prostate cancer patients treated between 2007 and 2022 with 45 Gy EBRT followed by 85 Gy Cs-131 LDR-BT boost with or without hydrogel rectal spacer. Expanded Prostate Cancer Index Composite (EPIC) QOL questionnaires pre-treatment and at each follow-up were collected. Patient-reported rectal bleeding occurring more than "rarely" and bother from rectal bleeding occurring more than a "very small problem" were deemed clinically significant. Fisher's exact test was used to test the association of rectal spacer use and the incidence of clinically significant rectal bleeding and bleeding bother. Paired samples t-test was used to analyze mean bowel scores at each time point. Three hundred and forty-one patients were included in the analysis. The rectal spacer was used in 108 patients. Overall median follow-up was 48 months (IQR, 24-72), with a median follow-up of 24 months (IQR, 12-37.5) for the hydrogel group and 60 months (IQR, 36-84) for the non-hydrogel group. EPIC questionnaire response rates at median follow-up were 33% and 37% for the hydrogel and non-hydrogel groups, respectively. A clinically significant decrease in mean bowel domain scores was seen in the bowel bother domain at 6 and 12 months for patients who did not receive a rectal spacer. At the last follow-up of 60 months, the prevalence of clinically significant rectal bleeding and bleeding bother were 2.2% and 2.2%, respectively. The cumulative incidence of clinically significant long-term rectal bleeding was 2.8% and 18.9% in the hydrogel group and non-hydrogel group, respectively (Fisher's exact test, p < 0.0001). The cumulative incidence of clinically significant long-term bowel bother was 4.6% and 19.7% in the hydrogel group and non-hydrogel group, respectively (Fisher's exact test, p < 0.001). Use of hydrogel rectal spacer with EBRT and Cs-131 LDR-BT boost was significantly associated with a lower incidence of patient-reported rectal bleeding and bother from rectal bleeding, and better long-term bowel QOL. Cumulative incidence was 2.8% (hydrogel group) versus 18.9% (non-hydrogel group) and 4.6% (hydrogel group) versus 19.7% (non-hydrogel group) for clinically significant long-term rectal bleeding and long-term bleeding bother, respectively.

Long-Term Outcomes of a Prospective Study on Highly Hypofractionated Intensity Modulated Radiation Therapy for Localized Prostate Cancer for 3 Weeks

Reports of radiation therapy for prostate cancer using dose fractions between moderate hypofractionation and ultrahypofractionation are limited. This pilot study involved the application of highly hypofractionated intensity modulated radiation therapy (IMRT) in 15 fractions for 3 weeks and the number of fractions was intermediate between the 2 previously mentioned dose fractions. The long-term outcomes are reported. From April 2014 to September 2015, patients with low- to intermediate-risk prostate cancer received 54 Gy in 15 fractions (3.6 Gy per fraction) for 3 weeks using IMRT without intraprostatic fiducial markers or a rectal hydrogel spacer. Neoadjuvant hormone therapy (HT) was administered for 4 to 8 months. Adjuvant HT was not administered to any patients. Rates of biochemical relapse-free survival, clinical relapse-free survival, overall survival, and the cumulative incidence of late grade ≥2 toxicities were analyzed. Twenty-five patients were enrolled in this prospective study; 24 of them were treated with highly hypofractionated IMRT (17% had low-risk and 83% had intermediate-risk disease). The median neoadjuvant HT duration was 5.3 months. The median follow-up period was 77 months (range, 57-87 months). Biochemical relapse-free survival, clinical relapse-free survival, and overall survival rates were 91.7%, 95.8%, and 95.8% at 5 years, and 87.5%, 86.3%, and 95.8% at 7 years, respectively. Neither grade ≥2 late gastrointestinal toxicity nor grade ≥3 late genitourinary toxicity was observed. The cumulative incidence rates of grade 2 genitourinary toxicity were 8.5% and 18.3% at 5 and 7 years, respectively. Highly hypofractionated IMRT delivering 54 Gy in 15 fractions for 3 weeks for prostate cancer without intraprostatic fiducial markers facilitated favorable oncological outcomes without severe complications. This treatment approach may be a possible alternative to moderate hypofractionation, but further validation is needed.

A dosimetric analysis of rectal hydrogel spacer use in patients with recurrent prostate cancer undergoing salvage high-dose-rate brachytherapy

We hypothesize rectal hydrogel spacer (RHS) improves rectal dosimetry in patients undergoing salvage high-dose-rate brachytherapy (HDR-BT) for intact, recurrent prostate cancer (PC). A prospectively collected institutional database was queried for recurrent PC patients treated with salvage HDR-BT from September 2015 to November 2021. Patients were offered RHS beginning June 2019. Dosimetric variables were compared between RHS and no-RHS groups for the average of two fractions using Wilcoxon rank-sum tests. Primary outcomes were rectal volume receiving 75% of prescription dose (V75%) and prostate volume receiving 100% of prescription dose (V100%). Generalized estimating equation (GEE) model was used to evaluate the association between other planning variables and rectal V75%. Forty-one PC patients received salvage HDR-BT, of whom 20 had RHS. All patients received 2400cGy in 2 fractions. Median RHS volume was 6.2cm3 (Standard deviation [SD]: ± 3.5cm3). Median follow-up was 4 months and 17 months in the RHS and no-RHS groups, respectively. Median rectal V75% with and without RHS were 0.0cm3 (IQR: 0.0-0.0cm3) and 0.06cm3 (IQR: 0.0-0.14cm3), respectively (p<0.001). Median prostate V100% with and without RHS were 98.55% (IQR: 97.86-99.22%) and 97.78% (IQR: 97.50-98.18%), respectively (p = 0.007). RHS, rectum, and prostate volumes did not significantly affect rectal V75% per GEE modeling. There was 10% G1-2 and 5% G3 rectal toxicity in RHS group. There was 9.5% G1-2 and no G3+ rectal toxicities in the no-RHS group. Absolute improvement in rectal V75% and prostate V100% was significant with RHS in PC patients undergoing salvage HDR-BT, but clinical benefit is marginal.

PD15-12 IMPACT OF MRI DETECTED HYDROGEL SPACER RECTAL WALL INFILTRATION ON RADIATION-RELATED TOXICITY FOLLOWING 5-FRACTION PROSTATE STEREOTACTIC BODY RADIATION THERAPY

You have accessJournal of UrologyCME1 Apr 2023PD15-12 IMPACT OF MRI DETECTED HYDROGEL SPACER RECTAL WALL INFILTRATION ON RADIATION-RELATED TOXICITY FOLLOWING 5-FRACTION PROSTATE STEREOTACTIC BODY RADIATION THERAPY Jonathan W. Lischalk, Jonathan A. Haas, Vianca Santos, Christopher Mendez, Astrid Sanchez, Ankur Doshi, David Sadowsky, Samir S. Taneja, Aaron Katz, and Angela Tong Jonathan W. LischalkJonathan W. Lischalk More articles by this author , Jonathan A. HaasJonathan A. Haas More articles by this author , Vianca SantosVianca Santos More articles by this author , Christopher MendezChristopher Mendez More articles by this author , Astrid SanchezAstrid Sanchez More articles by this author , Ankur DoshiAnkur Doshi More articles by this author , David SadowskyDavid Sadowsky More articles by this author , Samir S. TanejaSamir S. Taneja More articles by this author , Aaron KatzAaron Katz More articles by this author , and Angela TongAngela Tong More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003262.12AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: The use of rectal spacers in the treatment of localized prostate cancer treated with definitive radiotherapy has revolutionized the ability to minimize radiation dose to the rectum. In the present study, we investigate MRI identified rectal wall involvement and the subsequent clinical manifestations following prostate SBRT. METHODS: We identified all patient treated with 5-fraction SBRT for localized prostate cancer from 1/2020 to 9/2021 who underwent pre-treatment hydrogel rectal spacer placement. All MRIs were evaluated for the following spacer parameters: prostate-rectal distance, symmetry, and degree of rectal wall infiltration. Prostate-rectal distance was measured at the level of the prostatic apex, midgland, and base. Symmetry of rectal spacer was measured using right or left lateralization from midgland. Degree of rectal wall invasion was categorized as follows: none, muscularis, submucosal, and intraluminal. Radiation toxicity was assessed using the Common Terminology Criteria for Adverse Events (CTCAE) v5. RESULTS: A total of 336 patients underwent MRI following hydrogel rectal spacer placement from 1/2020 to 9/2021. The mean prostate-rectal distance measured at the apex, midgland, and base was 9 mm, 11 mm, and 14 mm, respectively. Spacer symmetry relative to midgland was within 0-10 mm in the vast majority of cases (n=289, 86%), and less commonly either 10-20 mm (n=42, 13%) or >20 mm (n=5, 1%). There was no MRI evidence of rectal wall invasion in the bulk of cases (n=229, 68%). For those with any invasion, the spacer commonly infiltrated only into the muscularis (n=83, 25%). However, in the remaining patients there was more dramatic evidence of invasion submucosally (n=21, 6%) or through the entire rectum into the luminal space (n=3, 1%). Of the patients who were found to have submucosal or intraluminal invasion, there were no patients who developed grade 2+ GI toxicity with a median follow up of 10.7 months (sans spacer historical rate of <4%). Of note, the only hydrogel placement parameter found to be significantly different in those patients with submucosal invasion or higher was midgland prostate-rectal distance (13 vs. 11 mm, p=0.04). CONCLUSIONS: Evidence of MRI detected hydrogel spacer rectal wall invasion is common and was observed in 32% of our cohort of 336 patient. However, only 7% of patients demonstrated rectal invasion beyond the muscularis, and in these cases we observed no grade 2 or higher CTCAE GI toxicity. Source of Funding: None © 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 Jonathan W. Lischalk More articles by this author Jonathan A. Haas More articles by this author Vianca Santos More articles by this author Christopher Mendez More articles by this author Astrid Sanchez More articles by this author Ankur Doshi More articles by this author David Sadowsky More articles by this author Samir S. Taneja More articles by this author Aaron Katz More articles by this author Angela Tong More articles by this author Expand All Advertisement PDF downloadLoading ...

Geometry of hydrogel rectal spacer placement and risk of MRI-identified rectal wall infiltration.

312 Background: The use of rectal spacers in the management of localized prostate cancer treated with definitive radiotherapy has become ubiquitous in recent years. However, pre-treatment MRIs often identify varying degrees of hydrogel involvement within the rectal wall. In the present study, we evaluate the geometry of spacer placement and its association with radiological rectal wall infiltration. Methods: We identified all patients who underwent hydrogel rectal spacer placement in preparation for 5-fraction prostate SBRT from 1/2020 to 9/2021. Two specialty trained body radiologists evaluated all MRIs independently. Scans were evaluated for the following spacer parameters: spacer thickness, prostate-rectal distance, symmetry, and degree of rectal wall infiltration. Prostate-rectal distance was measured at the level of the prostatic apex, midgland, and base. Symmetry of the rectal spacer was measured using right or left lateralization from midgland. Degree of rectal wall invasion was categorized as follows: none, muscularis, submucosal, and intraluminal. Results: A total of 336 patients underwent MRI following hydrogel rectal spacer placement from 1/2020 to 9/2021. Patients were excluded from MRI if they had AICD/pacemaker, foreign body, or patient refusal. In those patients with any rectal wall invasion, gel thickness as measured at the base (11 vs. 10 mm, p = 0.02), midgland (14 vs. 10 mm, p &lt; 0.001), and apex (12 vs. 8 mm, P &lt; 0.001) was significantly larger than those patients without invasion. This translated into significantly larger distances between the posterior aspect of the prostate and anterior aspect of the rectum at the level of the apex (12 vs. 8 mm, p &lt; 0.001) and midgland (13 vs. 11, p &lt; 0.001), but not at the base (14 vs. 14 mm, p = 0.5). There was no association seen with asymmetrical spacer placement and rectal wall invasion (p = 0.7). Subgroup analysis of patients with more extensive invasion into the muscularis or submucosa confirmed significantly larger gel thickness at all prostate levels, as well as a larger prostate-rectal distance at the level of the apex and midgland. Significant associations remained consistent with both independent radiological evaluations. Conclusions: Hydrogel spacer rectal wall infiltration was associated with increased axial gel thickness, specifically at the level of the prostatic midgland and apex. Rectal wall infiltration was not associated with lateralization of gel. Rectal infiltration may be a result of surplus hydrogel placed particularly in the region where the potential space between the prostate and the rectum is limited.

Quality Metric to Assess Adequacy of Hydrogel Rectal Spacer Placement for Prostate Radiation Therapy and Association of Metric Score With Rectal Toxicity Outcomes

Although hydrogel spacer placement (HSP) minimizes rectal dose during prostate cancer radiation therapy, its potential benefit for modulating rectal toxicity could depend on the achieved prostate-rectal separation. We therefore developed a quality metric associated with rectal dose reduction and late rectal toxicity among patients treated with prostate stereotactic body radiation therapy (SBRT). A quality metric consisting of prostate-rectal interspace measurements from axial T2-weighted magnetic resonance imaging simulation images was applied to 42 men enrolled in a multi-institutional phase 2 study using HSP with prostate SBRT (45 Gy in 5 fractions). A score of 0, 1, or 2 was assigned to a prostate-rectal interspace measurement of <0.3 cm, 0.3 to 0.9 cm, or ≥1 cm, respectively. An overall spacer quality score (SQS) was computed from individual scores at rectal midline and ±1 cm laterally, located at the prostate base, midgland, and apex. Associations of SQS with rectal dosimetry and late toxicity were evaluated. The majority of the analyzed cohort had an SQS of 1 (n=17; 41%) or 2 (n=18; 43%). SQS was associated with maximum rectal point dose (rectal Dmax; P=.002), maximum dose to 1 cc of rectum (D1cc; P=.004), and volume of rectum receiving ≥100% of prescription dose (V45; P=.046) and ≥40 Gy (V40; P=.005). SQS was also associated with a higher incidence of (P=.01) and highest-graded late rectal toxicity (P=.01). Among the 20 men who developed late grade ≥1 rectal toxicity, 57%, 71%, and 22% had an SQS of 0, 1, and 2, respectively. Men with an SQS of 0 or 1 compared with 2 had 4.67-fold (95% CI, 0.72-30.11) or 8.40-fold (95% CI, 1.83-38.57) greater odds, respectively, of developing late rectal toxicity. We developed a reliable and informative metric for assessing HSP, which appears to be associated with rectal dosimetry and late rectal toxicity after prostate SBRT.

Rectal Dosimetry Using Rectal Hydrogel Spacer in Patients with Recurrent Prostate Cancer Undergoing Salvage High-Dose-Rate Brachytherapy

<h3>Purpose/Objective(s)</h3> We hypothesize using rectal hydrogel spacer (RHS) will improve rectal dosimetry in patients undergoing salvage high-dose-rate brachytherapy (HDR-BT) for intact, recurrent prostate cancer (PC) without compromising prostate coverage. <h3>Materials/Methods</h3> A prospective institutional database was queried for recurrent PC patients treated with salvage HDR-BT from 09/2015 to 11/2021. Patients were offered RHS beginning 06/2019. Dosimetric variables were compared between RHS and no-RHS groups for the average of two fractions using Wilcoxon rank-sum tests. Primary outcomes were rectal volume receiving 75% of prescription dose (rV75%) and prostate volume receiving 100% of prescription dose (pV100%). Generalized estimating equation (GEE) model was used to evaluate the association between dosimetric variables and rV75%. Acute toxicity outcomes are descriptively described per Common Terminology Criteria for Adverse Events v5.0. <h3>Results</h3> A total of 41 PC patients received salvage HDR-BT, of whom 20 had RHS. All patients received 2400cGy in 2 fractions for a total of 82 treatments. Median RHS volume was 6.65 cm³ [Interquartile range (IQR): 3.47-8.43 cm³). In the RHS group, median age and follow-up were 73 years (IQR: 67-76 years) and 4 months (IQR: 4-9.5 months), respectively. In the no-RHS group, median age and follow-up were 70 years (IQR: 67-77 years) and 17 months (IQR: 15.3-30.3 months), respectively. Prostate volume and pre-treatment PSA were also similar between the groups. Median rV75% in patients with and without RHS were 0.0 cm³ (IQR: 0.0-0.0 cm³) and 0.06 cm³ (IQR: 0.0-0.14 cm³), respectively (p<0.001). Median pV100% in patients with and without RHS were 98.55% (IQR: 97.86-99.22%) and 97.78% (IQR: 97.50-98.18%), respectively (p=0.007). Additional dosimetric variables are in Table 1. RHS, rectum, and prostate volumes did not significantly affect rV75% per GEE modeling. There were 10% G1-2 and 5% G3 rectal toxicity in RHS group. One patient with G3 toxicity developed an enterovesicular fistula. There was 9.5% G1-2 and no G3+ rectal toxicities in the no-RHS group. <h3>Conclusion</h3> Use of RHS improves rV75% in PC patients undergoing salvage HDR-BT. Prostate coverage with prescription dose is also improved. Toxicity appears to be low in both groups but longer follow up is needed to adequately compare long-term safety.

CT-Based Online Adaptive Prostate SBRT Improves Target Coverage and Reduces Rectal Dose

<h3>Purpose/Objective(s)</h3> Stereotactic body radiation therapy (SBRT) is an emerging treatment modality for clinically localized prostate cancer (PCa). Online daily adaptive radiotherapy (ART) could potentially improve the therapeutic ratio of prostate SBRT by accounting for inter-fraction variation in target and OAR volumes. To-date no group has evaluated the clinical utility of a novel AI-augmented CT-based ART system for prostate SBRT. In this study we hypothesized that adaptive prostate SBRT plans would result in improved target coverage and lower dose to OARs versus the unadapted treatment plan. <h3>Materials/Methods</h3> Eight patients with unfavorable intermediate or high-risk PCa treated with 5-fx whole-pelvis prostate adaptive SBRT were reviewed. Patients were treated to the elective nodes (2500 cGy) with simultaneous boosts to the prostate/seminal vesicles (3625 cGy) and prostate (4000 cGy). 4 of 8 had rectal hydrogel spacer. For each Fx, CBCT was acquired and OARs (rectum, bladder, bowel, sigmoid, femurs) were segmented/deformed using AI. CTVs were rigidly registered. Volumes were adjusted manually and PTV expansions added. Adaptive treatment plans were developed based on the contoured targets and OARs and dose to these volumes for the adapted vs. initial plans were compared. The V100 (% PTV receiving prescription dose) and the D0.03 cc between scheduled and adapted treatment plans were compared using a Student's t-test, with significance threshold of <i>P<0.05</i>. <h3>Results</h3> Eight patients successfully completed 40 Fx's of adaptive RT as scheduled. Daily adaptation resulted in a statistically significant mean improvement in PTV V100 for all targets: [11.9% ± 2.1% for PTV 4000 (p <0.0001); 7.9% ± 1.5% for PTV 3625 (p <0.0001); and 6.1% ± 1.6% for PTV 2500 (p= 0.0007)]. Mean rectal D0.03 was significantly reduced by 45.4 cGy ± 10.8 cGy (p= 0.0002) per fraction (227 cGy/5 fractions) compared to the initial plans. There were no statistically significant differences between scheduled and adapted D0.03 to the bladder, sigmoid, or bowel (Table). No patients experienced acute CTCAE grade ≥3 GI/GU adverse events (median F/U 9.5 months). All statistically significant differences were maintained in the presence and absence of rectal hydrogel spacer. <h3>Conclusion</h3> CT-based online adaptive SBRT resulted in statistically significant and clinically meaningful improvements in PTV coverage and D0.03cc dose to the rectum. A trial evaluating CT adaptive prostate SBRT is underway.

Dosimetric Analysis of Radiation Treatment Plans Based on a Deep Learning Auto Contouring Model for Patients with Localized Prostate Cancer

<h3>Purpose/Objective(s)</h3> To evaluate the feasibility and safety of creating radiation treatment plans based on a convolutional neural network auto-contouring (AC) model for patients receiving radiation for localized prostate cancer with a radio-opaque rectal spacer hydrogel. <h3>Materials/Methods</h3> The deep learning model produces ACs for target volumes (prostate, proximal seminal vesicle), OARs (rectum, bladder, penile bulb, femoral heads), and rectal hydrogel spacers. ACs were compared to manual contours (MC) by MDs for clinical use. Individual volumes and overall performance (composite score) were previously evaluated and reported, qualitatively using a 1 (minor discrepancy), 2 (moderate discrepancy), 3 (significant discrepancy), and 4 (rejected, gross error) scale and quantitatively using Dice Similarity Coefficient (DSC) and mean distance to agreement. VMAT treatment plans were created on unedited AC volumes from five composite 1 (C1) cases and five composite 2 (C2) cases and dose volume metrics were computed for the final MCs. Dosimetry comparison was performed to assess the safety of delivering a treatment plan created from unedited ACs. Cases were planned to 50.4 Gy in 28 fractions to the SVs, with a SIB of 70 Gy the prostate. PTV expansions were CTV+5 mm (CTV+4 mm posteriorly). <h3>Results</h3> Of 62 initial cases evaluated, 11 were scored as a C1, 28 were scored as a C2, and 23 received a C3. 10 cases were randomly selected for treatment planning. For prostate (CTV P) in selected C1 and C2 cases, mean score was 1 and 1.8 and mean DSC was 0.919 and 0.876, respectively. Clinical goals for planning and dosimetric data from treatment plans are shown in Table 1. The mean V70 Gy for prostate CTV/PTV was 99.83%/90.05% for C1 cases and 99.46%/89.15% for C2 cases. All clinical goals for OARs were met in both cohorts. <h3>Conclusion</h3> 63% of all cases evaluated received a C1 or C2 score. Our results indicate the treatment plans generated from unedited ACs on these cases respected all clinical goals for OARs. Although C1 plans produced better PTV coverage than C2, almost all plans had sub-optimal PTV coverage, indicating the need for MDs to edit target volumes before treatment planning.

Systematic study of the iodinated rectal hydrogel spacer material discrepancy on accuracy of proton dosimetry.

PurposeIodination of rectal hydrogel spacer increases the computed tomography (CT) visibility. The effect of iodinated hydrogel spacer material on the accuracy of proton dosimetry has not been fully studied yet. We presented a systematic study to determine the effect of iodination on proton dosimetry accuracy during proton therapy (PT).MethodsPT plans were designed for 20 prostate cancer patients with rectal hydrogel spacer. Three variations of hydrogel density were considered. First, as the ground truth, the true elemental composition of hydrogel true material (TM), verified by our measurement of spacer stopping power ratio, was used for plan optimization and Monte Carlo dose calculation. The dose distribution was recalculated with (1) no material (NM) override based on the CT intensity of the iodinated spacer, and (2) the water material (WM) override, where spacer material was replaced by water. The plans were compared with the ground truth using the metrics of gamma index (GI) and dosimetric indices.ResultsThe iodination of hydrogel spacer affected the proton dose distribution with the NM scenario showing the most deviation from the ground truth. The iodination of spacer resulted in a notable increase in CT intensity and led to the treatment planning systems mistreating the iodinated spacer as a high‐density material. Among the structures adjacent to the target, neurovascular bundles showed the largest dose difference, up to 350 cGy or about 5% of the prescribed dose with NM. Compared to the WM scenario, dose distribution similarity and GI passing ratios were lower in the NM scenario.ConclusionThe inaccurate CT intensity‐based material for iodinated spacer resulted in errors in PT dose calculation. We found that the error was negligible if the iodinated spacer was replaced with water. Water density can be used as a clinically accessible and convenient alternative material override to true spacer material.

Delphi study to identify consensus on patient selection for hydrogel rectal spacer use during radiation therapy for prostate cancer in the UK

ObjectivesTo identify consensus on patient prioritisation for rectal hydrogel spacer use during radiation therapy for the treatment of prostate cancer in the UK.DesignDelphi study consisting of two rounds of online...

Assessment of planning target volume margins in 1.5 T magnetic resonance‐guided stereotactic body radiation therapy for localized prostate cancer

AbstractObjectiveWe aimed to determine the planning target volume margins applicable to magnetic resonance‐guided stereotactic body radiation therapy (MRgSBRT) of localized prostate cancer on a 1.5 T MR‐Linac.MethodsA total of 10 patients with low‐ to intermediate‐risk prostate cancer were retrospectively enrolled. All patients received five‐fraction MRgSBRT treatments, and underwent daily endorectal ballooning and bladder control. Five patients were implanted with the hydrogel rectal spacer. Three MR scans at each fraction were acquired to evaluate the intrafractional prostate motion. The required planning target volume margin was determined using the van Herk margin recipe based on direct MR‐MR prostate registration. The set‐up margin for localization using bony anatomy was also estimated.ResultsThe mean and standard deviation of translational displacement in left‐right (LR), superior‐inferior (SI), and anterior‐posterior (AP) directions were –0.3 ± 0.7, 2.0 ± 1.5, and 1.4 ± 1.1 mm, respectively. Planning target volume margins over the MRgSBRT fraction duration were 2.8 (LR), 5.3 (SI), and 3.9 mm (AP). Set‐up margins were estimated to 2.6 (LR), 3.3 (SI), and 3.3 mm (AP). Prostate motion increased considerably with treatment duration. Adapt‐to‐position had smaller intrafractional motions than adapt‐to‐shape. The rectal spacer insignificantly (p &gt; 0.1) reduced the prostate motion in SI and AP.ConclusionOnline workflow efficiency enhancement and intrafractional motion monitoring are vital for planning target volume margin reduction and precision enhancement in MRgSBRT.

Utilisation of a rectal hydrogel spacer for vaginoplasty in a cadaver model

Background: A major source of complications in vaginoplasty results from injury to the rectum during dissection of the neovaginal cavity. The SpaceOAR™ System is a rectal hydrogel spacer mostly used as a safety technique during prostate cancer treatment. Objective: This was a feasibility study performed in a single cadaveric perineum.Methods: Prior to standard cavity dissection, SpaceOAR was injected transperineally into the Denonvilliers’ fascia under guidance of transrectal ultrasound. Dissection of the neovaginal cavity with spacer gel was qualitatively assessed to be significantly easier, allowing for a blunt and quick approach. Results: A satisfactory vaginal length was achieved rapidly and safely. Conclusions: We show that transgender vaginoplasty using this adaptation of SpaceOAR is technically feasible in the cadaveric model and may reduce the incidence of rectal injury or rectovaginal fistula during neovaginal cavity creation. Future experimental endeavours should focus on the reproducibility of this approach and characterise the degree of rectal protection provided. Level of evidence: Not applicable

Prostate Cancer Treatment with Pencil Beam Proton Therapy Using Rectal Spacers sans Endorectal Balloons.

PurposeProton beam radiotherapy (PBT) has been used for the definitive treatment of localized prostate cancer with low rates of high-grade toxicity and excellent patient-reported quality-of-life metrics. Technological advances such as pencil beam scanning (PBS), Monte Carlo dose calculations, and polyethylene glycol gel rectal spacers have optimized prostate proton therapy. Here, we report the early clinical outcomes of patients treated for localized prostate cancer using modern PBS–PBT with hydrogel rectal spacing and fiducial tracking without the use of endorectal balloons.Materials and MethodsThis is a single institutional review of consecutive patients treated with histologically confirmed localized prostate cancer. Prior to treatment, all patients underwent placement of fiducials into the prostate and insertion of a hydrogel rectal spacer. Patients were typically given a prescription dose of 7920 cGy at 180 cGy per fraction using a Monte Carlo dose calculation algorithm. Acute and late toxicity were evaluated using the Common Terminology Criteria for Adverse Events (CTCAE), version 5. Biochemical failure was defined using the Phoenix definition.ResultsFrom July 2018 to April 2020, 33 patients were treated (median age, 75 years). No severe acute toxicities were observed. The most common acute toxicity was urinary frequency. With a median follow-up of 18 months, there were no high-grade genitourinary late toxicities; however, one grade 3 gastrointestinal toxicity was observed. Late erectile dysfunction was common. One treatment failure was observed at 21 months in a patient treated for high-risk prostate cancer.ConclusionEarly clinical outcomes of patients treated with PBS–PBT using Monte Carlo–based planning, fiducial placement, and rectal spacers sans endorectal balloons demonstrate minimal treatment-related toxicity with good oncologic outcomes. Rectal spacer stabilization without the use of endorectal balloons is feasible for the use of PBS–PBT.