Rectal Spacer Research Articles

Painless Rectal Bleeding in a Patient With Prostate Cancer

Painless Rectal Bleeding in a Patient With Prostate Cancer

Remote surgical education using synthetic models combined with an augmented reality headset

ObjectiveThe objective was to investigate the use of an augmented reality headset to remotely train clinicians on medical devices using anatomic models. DesignDisease-specific phantoms were developed to train physicians in mpMRI-guided fusion prostate biopsy, brachytherapy, and rectal spacer insertion. Training was remotely demonstrated using 1-way virtual video conferencing format. Participants responded to an educational content survey. A heads-up display with software and augmented reality was used for remote 2-way training with the proctor and student using on their own phantoms. SettingThe virtual video meeting took place during a prostate cancer conference in 2020, while the augmented reality training occurred in 2021. The proctor and student wore a heads-up display containing a projector and webcam where the ultrasound image was displayed onto a see-through optic along with the physician's hands. The heads-up display allowed the proctor to teach by line-of-sight while the student watched and repeated the steps. ParticipantsFaculty with expertise with the medical devices used in these procedures provided training to urologists unfamiliar with these techniques. ResultsParticipants responded that the 1-way training on the phantoms was realistic and mimicked human tissue. A total of 70.9% requested more training or training on the phantoms. The remote training platform was successfully beta tested at the 2 locations in transperineal prostate biopsy and rectal spacer insertion. ConclusionRemote training using augmented reality eliminates the need for travel. For training programs and workshops, this technology may mitigate the risk of infectious exposures, reduce training cost, and increase proctor availability, allowing training from their own institution or clinic.This investigation qualifies for the Accreditation Council for Graduate Medical Education competency in medical knowledge.

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 > 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.

PO-1819 partial brachytherapy in prostate cancer phantoms with and without rectum spacer

PO-1819 partial brachytherapy in prostate cancer phantoms with and without rectum spacer

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.

Rationale for Utilization of Hydrogel Rectal Spacers in Dose Escalated SBRT for the Treatment of Unfavorable Risk Prostate Cancer.

In this review we outline the current evidence for the use of hydrogel rectal spacers in the treatment paradigm for prostate cancer with external beam radiation therapy. We review their development, summarize clinical evidence, risk of adverse events, best practices for placement, treatment planning considerations and finally we outline a framework and rationale for the utilization of rectal spacers when treating unfavorable risk prostate cancer with dose escalated Stereotactic Body Radiation Therapy (SBRT).

Simultaneous integrated boost (SIB) to dominant intra-prostatic lesions during extreme hypofractionation for prostate cancer: the impact of rectal spacers

PurposeBoosting dominant intra-prostatic lesions (DILs) has the potential to increase the therapeutic ratio in prostate cancer radiotherapy. In this study, employing 5-fraction stereotactic ablative radiotherapy (SABR) volumetric modulated arc therapy (VMAT) to deliver 40 Gy to the prostate clinical target volume (CTV) while boosting the DIL up to 50 Gy was evaluated for patients before and after rectal spacer insertion.Materials and methods24 Computed Tomography (CT) scans of 12 prostate cancer patients with unfavourable intermediate or high risk prostate cancer were employed in this study. At least two treatment plans were generated for each patient to compare pre- and post-spacer insertion plans. Plans were evaluated for target coverage, organs-at-risk doses, and the achievable boost dose level.ResultsThe CTV coverage was significantly better in plans with a spacer, V40Gy 98.4% versus 97.0% (p = 0.012). Using spacers significantly reduced rectal dose in all 12 patients in this study. It was possible to boost DIL to 50 Gy to without violating dose constraints in 6 of 12 patients and to 47.5 Gy in 3 patients post-spacer insertion. For 3 patients (25%) it was not possible to boost DIL above 45 Gy even with a spacer in situ. Without a spacer, for 6 patient (50%) clinically acceptable plan were only achieved when the DIL dose was lowered to 45 Gy. In five of these 6 patients the dose limiting structure was the urethra (urethra planning risk volume V45Gy [cc] ≤ 0.1 cc constraint).ConclusionsClinically acceptable plans for 5 fraction SABR, 40 Gy to the prostate CTV, with a SIB to DIL (45–50 Gy) were achieved. The boost dose achieved was DIL location dependent and primarily affected by DIL’s proximity to the urethra. Compared to plans before spacer insertion, higher DIL dose were achieved with spacer in situ for 25% of the patients. Moreover, significant reduction in rectal dose and better target coverage were also achieved for all patients with spacers in situ.

Impact of rectal spacer on toxicity reduction in men treated with proton versus photon therapy.

247 Background: Dose escalation in prostate cancer (PCa) radiotherapy (RT) is limited by toxicity to surrounding tissue, including the rectum. Rectal spacers improve bowel toxicity in men treated with photons (i.e. IMRT). However, the relative benefit of rectal spacers in men treated with protons remains unknown. Further, proton therapy may result in high-dose exposure to the anterior rectal wall due to lateral penumbra with conventional opposed lateral beam arrangement. We hypothesize that rectal spacers will confer greater toxicity benefit in the setting of proton therapy compared with photon therapy. Methods: We conducted an IRB approved, single institution, retrospective review of patients receiving definitive conventional or moderate hypofractionated photon IMRT or pencil-beam scanning proton RT for localized PCa from 2018-2021. Four cohorts were compared: Photon with (Ph+RS) or without (Ph-RS) rectal spacer, and proton with (Pr+RS) or without (Pr-RS) rectal spacer. Rates of pelvic nodal treatment were equivalent between protons and photons within the +/- rectal spacer cohorts. Acute (<3 months) and late (≥ 3 month) toxicity was compared amongst the four cohorts. Cumulative incidence of physician-reported grade 1-2 gastrointestinal (GI) toxicity (CTCAE V5.0) was compared using Chi-square or Fisher’s exact test. Patient-reported bowel toxicity was evaluated using International Prostate Expanded Prostate Composite Index- Clinical Practice (EPIC-CP) and compared using linear mixed modeling. Results: 164 patients were eligible for analysis: 38 Ph-RS, 50 Ph+RS, 26 Pr-RS, & 50 Pr+RS. Median follow-up was 17.6 months. In men treated with protons, physician-reported acute G1-2 GI toxicity was significantly lower in men with versus without rectal spacer (6.12 vs 30.77%, Pr+RS vs Pr-RS, respectively; p=0.009) and there was a trend towards lower late G1-2 GI toxicity (8.51 vs 26.09%, Pr+RS vs Pr-RS, respectively; p=0.08). In men treated with photons, there were no significant differences in physician-reported acute or later GI toxicity with versus without rectal spacer. No significant differences in patient-reported outcomes were observed with versus without spacer in the proton or photon cohorts. Conclusions: Rectal spacer use was associated with a lower CTCAE grade 1-2 acute GI toxicity in men treated with protons, and this difference was not observed in men treated with photons. While this study is limited by low sample size, a relatively greater benefit of rectal spacer with proton vs. photon therapy was observed. Further prospective analyses in larger cohorts are ongoing to validate these hypothesis-generating findings.

Magnetic resonance imaging-guided versus computed tomography-guided stereotactic body radiotherapy for prostate cancer (MIRAGE): Interim analysis of a phase III randomized trial.

255 Background: Magnetic resonance imaging (MRI) guidance offers several theoretical advantages over computed tomography (CT) guidance in the context of stereotactic body radiotherapy (SBRT) for intact prostate cancer. Here we report the results of an interim analysis of the phase III MIRAGE trial, which directly compared MRI- and CT-guidance with a pragmatic primary endpoint of acute grade ≥2 genitourinary (GU) toxicity. Methods: MIRAGE is a single center, randomized phase 3 trial. Men undergoing SBRT for localized prostate cancer were randomly assigned to either CT-guidance or MRI-guidance. Planning margins of 4 mm (CT-arm) and 2 mm (MRI-arm) were placed around the prostate and proximal seminal vesicles, and this volume received 40 Gy in five fractions. Elective nodal radiotherapy and rectal spacers were allowed per physician discretion. The primary outcome was the incidence of acute (i.e., within 90 days of SBRT) grade ≥2 GU physician-reported toxicity (by CTCAE version 4.03). Secondary outcomes of interest included the incidence of acute grade ≥2 GU physician-reported toxicity, changes in IPSS scores at 1 and 3 months, and changes in EPIC-26 bowel domain summary scores at 1 and 3 months. A pre-specified efficacy analysis was planned once the 100th patient was eligible for evaluation of the primary endpoint. Results: On 9/1/2021, 100 patients became eligible for evaluation for the interim analysis (51 CT arm, 49 MRI arm). Acute grade ≥2 GU toxicity was significantly reduced in men receiving MRI-guided SBRT (incidence of 24 (47.1%) vs. 11 (22.4%), p = 0.01). Acute grade ≥2 GI toxicity was also significantly reduced in men receiving MRI-guided SBRT (incidence of 7 (13.7%) vs. 0 (0%), p = 0.01.). The increase in IPSS scores from baseline was significantly higher in men receiving CT-guided SBRT at 1 month post-SBRT (median change of 10 vs. 6, p = 0.03), but not at 3 months (median change of 3 vs. 2, p = 0.3). The decrement in EPIC-26 bowel domain scores was significantly greater at 1 month in men receiving CT-guided SBRT (median change of -8.3 vs. 0, p = 0.03), but not at 3 months (median change of -2.3 vs. 0, p = 0.4). Given the large primary endpoint signal seen, our protocol was amended to reduce the projected sample size to 154 while still maintaining 89% power to detect a difference. Conclusions: This interim analysis demonstrates a statistically significant reduction in acute grade ≥2 GU toxicity with MRI-guidance versus CT-guidance in the context of prostate SBRT. Patient-reported urinary and bowel function metrics are also better preserved at the 1 month time point with MRI-guidance, though this difference dissipates (potentially due to side-effect management) at the 3 month time point. Accrual has been completed as of October 2021 and a final analysis for the primary endpoint is anticipated in early 2022. Clinical trial information: NCT04384770.

Rationale for Utilization of Hydrogel Rectal Spacers in Dose Escalated SBRT for the Treatment of Unfavorable Risk Prostate Cancer

Rationale for Utilization of Hydrogel Rectal Spacers in Dose Escalated SBRT for the Treatment of Unfavorable Risk Prostate Cancer

SpaceOAR hydrogel spacer injection prior to stereotactic body radiation therapy for men with localized prostate cancer: A systematic review.

Background:Conventionally fractionated radiotherapy is a common treatment for men with localized prostate cancer. A growing consensus suggests that stereotactic body radiation therapy (SBRT) is similarly effective but less costly and more convenient for patients. The SpaceOAR hydrogel rectal spacer placed between the prostate and rectum reduces radiation-induced rectal injury in patients receiving conventionally fractionated radiotherapy, but spacer efficacy with SBRT is unclear. The purpose of this research was to assess the clinical utility of the hydrogel rectal spacer in men receiving SBRT for prostate cancer.Methods:We performed systematic searches of Medline, Embase, and the Cochrane Central Register of Controlled Trials for studies in men who received the SpaceOAR hydrogel spacer prior to SBRT (≥5.0 Gy fractions) for treatment of localized prostate center. Rectal irradiation results were compared to controls without spacer implant; all other outcomes were reported descriptively owing to lack of comparative data incuding perirectal separation distance, rectal irradiation on a dosimetric curve, gastrointestinal (GI) toxicity, and freedom from biochemical failure. GI toxicity was reported as the risk of a grade 2 or 3+ bowel complication in early (≤3 months) and late (>3 months) follow-up.Results:In 11 studies with 780 patients, SBRT protocols ranged from 7 to 10 Gy per fraction with total dose ranging from 19 to 45 Gy. Perirectal distance achieved with the rectal spacer ranged from 9.6 to 14.5 mm (median 10.8 mm). Compared to controls receiving no spacer, SpaceOAR placement reduced the radiation delivered to the rectum by 29% to 56% across a dosimetric profile curve. In early follow-up, grade 2 GI complications were reported in 7.0% of patients and no early grade 3+ GI complications were reported. In late follow-up, the corresponding rates were 2.3% for grade 2 and 0.3% for grade 3 GI toxicity. Over 16 months median follow-up, freedom from biochemical failure ranged from 96.4% to 100% (pooled mean 97.4%).Conclusions:SpaceOAR hydrogel spacer placed between the prostate and rectum prior to SBRT is a promising preventative strategy that increases the distance between the prostate and rectum, reduces rectal radiation exposure, and may lower the risk of clinically important GI complications.

Impact of Hydrogel and Hyaluronic Acid Rectal Spacer on Rectal Dosimetry and Toxicity in Low-Dose-Rate Prostate Brachytherapy: A Multi-Institutional Analysis of Patient Outcomes

To report on rectal dosimetry and toxicity outcomes in men with prostate cancer (PCa) treated with I125 low-dose rate brachytherapy (LDR-BT) with or without hydrogel (HS) or hyaluronic acid (HA) rectal spacer (RS) insertion. The working hypothesis is the increased retroprostatic distance achieved from RS insertion results in reduced rectal dosimetry and subsequent reduction in rectal toxicity outcomes.Seventy consecutive men treated with LDR-BT between December 2017 and July 2019 were included in this study, twenty-eight (40%) men had RS insertion according to the preference of the referring urologist, compared to a group of forty-two men (60%) without RS. Descriptive statistics were used to compare the RS safety, dosimetric effects on organs at risk (rectum and urethra), as well as gastrointestinal (GI) and genitourinary (GU) toxicities (assessed using the CTCAEv4) between the two groups.The mean prostate-rectal separation with RS at mid prostate was 9.9mm (SD 2.8mm). There were no post-operative complications for RS insertion. There was significantly reduced rectal dosimetry in RS group vs non-RS group, the median RV100 was 0cc (IQR = 0-0.0cc) vs 0.4cc (IQR = 0.1-1.1cc) (P < 0.001) respectively. Mean rectal D1cc and D2cc were 52.4% vs 84.2% (P < 0.001) and 45.7% vs. 70.0% (P < 0.001) for RS and non-RS group respectively. There were no discernible differences in the mean urethral D20, D5, and D1. There were significantly less ≥ grade 1 acute and late GI toxicities in the RS group when compared to the non-RS group (0% vs 24% P = 0.004 for acute GI toxicity: 4% vs 33%, P = 0.003 for late GI toxicity). Strong association remained for RS with late GI toxicity (odds ratios < 0.2) even after accounting for the confounding effects of post-implant RV100, D1cc and D2cc.Insertion of RS in men treated with LDR-BT is safe and results in significantly lower values in rectal dosimetry. The reduction in rectal dosimetry with RS insertion translates into significantly reduced rates of acute and late GI toxicities.

Patient and Dosimetric Predictors of Genitourinary and Gastrointestinal Toxicity After Prostate SBRT: A Secondary Analysis of a Prospective, Multi-Institutional Phase II Trial

Stereotactic body radiation therapy (SBRT) is an emerging treatment option for localized prostate cancer. However, optimal patient selection & normal tissue tolerances for prostate SBRT are not well defined. We therefore analyzed patient factors & dosimetric correlates for genitourinary (GU) and gastrointestinal (GI) toxicity on a multi-institutional prospective trial.Patients (pts) with low- and intermediate-risk prostate cancer were enrolled on a phase II trial from 2011-2020. A dose of 36.25 Gy in 5 fractions to the PTV and 40 Gy to the prostate gland was administered on non-consecutive days. No androgen deprivation therapy or rectal spacer were used. Pts received a CT simulation with Foley catheter for urethral delineation. The clinical target volume was prostate (low-risk) or prostate plus 2cm of proximal seminal vesicles (intermediate-risk). Multiple dosimetric measures for bladder, urethra, & rectum were prospectively recorded. The maximum acute & late GU and GI toxicities using CTCAE v.3.0 were assessed at protocol-specific time points. Linear logistic regression was used to assess factors associated with Grade 1+ GI & GU toxicities. A multivariate (MV) model was constructed using all covariates with P-values < 0.2 on univariate (UV) analysis.A total of 160 evaluable men were enrolled. Median age was 67.9 years (IQR 62.6-73.2), 60 men (37.5%) were low risk, and 100 (62.5%) were intermediate risk. Median follow-up was 2.2 years. No patient factor or dosimetric correlate predicted acute Grade 1+ GU toxicity (all tested covariates P > 0.2). Treatment isodose line (P = 0.065) & age (P = 0.098) reached borderline significance for acute Grade 1+ GI toxicity on UV analysis, though neither were significant on MV analysis (P = 0.057 and P = 0.103, respectively). For late Grade 1+ GU toxicity, prior TURP, bladder V37(cc), bladder D10%, baseline AUA, & treatment isodose line reached borderline significance on UV analysis. On MV analysis, treatment isodose line trended towards significance at P = 0.055. For late Grade 1+ GI toxicity, rectum D20%, rectum D10%, rectum D5%, & history of coronary artery disease reached borderline significance on UV analysis, & a history of coronary artery disease predicted Grade 1+ GI toxicity on MV analysis (odds ratio 4.7, 95% CI 1.37-15.9, P = 0.009).No patient factor or dosimetric correlate predicted acute GI or GU toxicity after prostate SBRT. Late GU toxicity is possibly attributable to dose inhomogeneity. A history of coronary artery disease predicts for late GI toxicity, possibly due to anticoagulation.

Quality Metric to Assess Adequacy of Hydrogel Rectal Spacer Placement for Prostate Radiotherapy and Association of Metric Score With Dosimetric and Gastrointestinal Toxicity Outcomes

<h3>Purpose/Objective(s)</h3> Hydrogel rectal spacer placement (HSP) has been shown to minimize rectal dose during prostate cancer radiotherapy, yet its potential benefit for modulating rectal toxicity could in large part depend upon the quality of prostate-rectal separation achieved from HSP. We therefore developed a practical quality metric to evaluate HSP, validating its association with rectal dose reduction, as well as physician- and patient-reported rectal toxicity using a prospective dataset of men treated with prostate stereotactic body radiotherapy (SBRT). <h3>Materials/Methods</h3> Using the axial T2-weighted MRI images from a small pilot cohort of men with HSP who had been treated at our institution with prostate SBRT, a hydrogel spacer quality metric was devised from prostate-rectal space thickness (PRST) measurements. A score of 0, 1, or 2 was assigned to a PRST of < 0.3 cm, 0.3-0.9 cm, or ≥1 cm, respectively; an overall spacer quality score (SQS) was computed from individual scores (total of 9) at rectal midline and 1 cm to the right and left, located at the level of the prostate base, midgland, and apex. This quality metric was then applied to MRI simulation scans of 43 men with low/intermediate risk prostate cancer who had been enrolled on a multi-institutional phase II study to assess safety and efficacy of HSP during prostate SBRT. Associations between SQS and rectal dosimetry, late gastrointestinal (GI) toxicity, and EPIC bowel quality of life were quantified in these men treated with 45 Gy in 5 fractions. <h3>Results</h3> Among this cohort, the majority had a SQS of 1 (n = 18; 42%) or 2 (n = 18; 42%). SQS was associated with maximum rectal point dose (rectal Dmax; <i>P</i> = 0.001), maximum dose to 1 cc of rectum (D1cc; <i>P</i> = 0.003), and volume of rectum receiving ≥100% of prescription dose (V45; <i>P</i> = 0.03). For those with SQSs of 0, 1 and 2, the median rectal Dmax (cGy) was 4683, 4600, and 3921, respectively. SQS was associated with incidence of late GI toxicity (<i>P</i> = 0.03) and highest late GI toxicity score (<i>P</i> = 0.02). Among the 20 men who developed late GI toxicity, 57%, 67% and 22% with Grade ≥1 had a SQS of 0, 1, and 2, respectively. Men with SQSs of 2 compared to 0-1 had 1.36 times lower odds of an increased rectal Dmax (95% CI: 1.14-1.63); and 1.20 times lower odds of an increased rectal D1cc (95% CI: 1.07-1.34). Men with SQSs of 2 versus 0-1 had 3.30 times lower odds of a higher late GI toxicity score (95% CI: 1.18-9.28). While evidence of a significant difference in baseline EPIC bowel summary score between SQSs was not observed (<i>P</i> = 0.07) as expected, men with SQSs of 2 compared to 0-1 had 3.52 times higher odds (95% CI: 0.91-13.64) of a superior bowel summary score 12 months from prostate SBRT. <h3>Conclusion</h3> We developed a reliable, easy to use, and informative metric for assessing HSP, which appears to be associated with rectal dosimetry and late GI toxicity in men treated with prostate SBRT.

Qualitative and Quantitative Analysis of a Deep Learning Auto Contouring Model for Radiotherapy in Localized Prostate Cancer

Purpose/Objective(s)To evaluate a convolutional neural network auto-contouring (AC) model created for treatment planning in patients receiving radiotherapy for localized prostate cancer after insertion of a radiopaque rectal spacer hydrogel.Materials/MethodsThe deep learning model, trained by 125 patients, auto contours target volumes (prostate and proximal seminal vesicles), OARs (bladder, rectum, femoral heads and penile bulb) and radiopaque rectal spacers. ACs were evaluated against MD manual contours (MCs) submitted for treatment planning. ACs were not available for MD review while creating MCs. Individual volumes as well as composite volumes (overall performance) were qualitatively evaluated by a radiation oncologist using a 1 (minor discrepancy, little to no dose-volume impact), 2 (moderate discrepancy or editable with substantial efficiency gain), 3 (significant discrepancy or editable with meaningful efficiency gain), and 4 (rejected due to gross error or editable without efficiency gain) scoring scale. Quantitative evaluation of geometric differences was performed with mean distance to agreement (MDA) and Dice Similarity Coefficient (DSC) for each volume.ResultsA total of 68 cases were evaluated by quantitative and qualitative metrics (Table 1). MCs were performed by 4 experienced MDs. Average composite score of 2.22 (SD 0.73) indicates substantial to meaningful efficiency gain in contouring process. Composite scores for 100% of cases evaluated indicate a meaningful efficiency gain in the contouring process, with 60% of composite scores indicating only minor to moderate discrepancy between contours. Prostate and SV AC average scores were above 2. Mean prostate MDA and DSC were 1.71 and 0.85, respectively, both within tolerance range recommended by AAPM TG 132.ConclusionThe model can accurately auto contour target volumes, OARs and spacer with meaningful to substantial efficiency gain, with a majority of target volumes qualitatively evaluated by a physician as having only mild to moderate discrepancies. Quantitative analysis shows contours for most OARs have only minor geometric differences unlikely to have significant dose-volume impacts. Further analysis with comparison of treatment plans generated from ACs and MCs is warranted. To evaluate a convolutional neural network auto-contouring (AC) model created for treatment planning in patients receiving radiotherapy for localized prostate cancer after insertion of a radiopaque rectal spacer hydrogel. The deep learning model, trained by 125 patients, auto contours target volumes (prostate and proximal seminal vesicles), OARs (bladder, rectum, femoral heads and penile bulb) and radiopaque rectal spacers. ACs were evaluated against MD manual contours (MCs) submitted for treatment planning. ACs were not available for MD review while creating MCs. Individual volumes as well as composite volumes (overall performance) were qualitatively evaluated by a radiation oncologist using a 1 (minor discrepancy, little to no dose-volume impact), 2 (moderate discrepancy or editable with substantial efficiency gain), 3 (significant discrepancy or editable with meaningful efficiency gain), and 4 (rejected due to gross error or editable without efficiency gain) scoring scale. Quantitative evaluation of geometric differences was performed with mean distance to agreement (MDA) and Dice Similarity Coefficient (DSC) for each volume. A total of 68 cases were evaluated by quantitative and qualitative metrics (Table 1). MCs were performed by 4 experienced MDs. Average composite score of 2.22 (SD 0.73) indicates substantial to meaningful efficiency gain in contouring process. Composite scores for 100% of cases evaluated indicate a meaningful efficiency gain in the contouring process, with 60% of composite scores indicating only minor to moderate discrepancy between contours. Prostate and SV AC average scores were above 2. Mean prostate MDA and DSC were 1.71 and 0.85, respectively, both within tolerance range recommended by AAPM TG 132. The model can accurately auto contour target volumes, OARs and spacer with meaningful to substantial efficiency gain, with a majority of target volumes qualitatively evaluated by a physician as having only mild to moderate discrepancies. Quantitative analysis shows contours for most OARs have only minor geometric differences unlikely to have significant dose-volume impacts. Further analysis with comparison of treatment plans generated from ACs and MCs is warranted.

Effect of Hydrogel Rectal Spacer on Intrafraction Prostate Motion During Radiotherapy of Prostate Cancer Patients

<h3>Purpose/Objective(s)</h3> Insertion of hydrogel rectal spacer may potentially stabilize the prostate by reducing intrafraction prostate motion. The purpose of this study was to investigate the effect of hydrogel rectal spacer on intrafraction prostate motion. <h3>Materials/Methods</h3> A retrospective review was conducted of prostate cancer patients treated from September 2015 to November 2018 who underwent external beam radiation therapy (EBRT) with intrafraction motion management using implanted electromagnetic transponders. There were 87 patients (73%) who received conventional fractionation, 16 (13%) moderate hypofractionation, 10 (8%) stereotactic body radiation therapy (SBRT) and 7 (6%) EBRT plus brachytherapy. The threshold for gating was set at 4 mm for conventional fractionation, 3 mm for moderate hypofractionation, and 2 mm for SBRT. Maximum prostate motion was measured by displacement outside of the gating threshold during treatment per fraction. Independent samples t-test was performed to compare prostate motion with and without hydrogel rectal spacer. <h3>Results</h3> We identified 120 patients with a total of 4447 fractions eligible for analysis. 49 patients (41%) were treated with hydrogel spacer and 71 (59%) without hydrogel rectal spacer. Mean displacement of prostate outside of the gating threshold was 4.9 mm (range, 2.1 – 12.8) and 5.6 mm (4.1 – 14.6) anteriorly, 2.6 mm (1.1 – 7.6) and 19.4 mm (4.0 – 25.8) posteriorly, 4.7 mm (2.2 – 8.3) and 12.5 mm (4.0 – 20.8) superiorly, 3.1 mm (1.1 – 8.2) and 14.2 mm (3.7 – 22.7) inferiorly, 4.3 mm (3.0 -12.4) and 4.5 mm (4.2 -7.6) left and 3.1 mm (3.1 – 4.1) and 4.3 mm (4.1 – 11.6) right for patients treated with and without hydrogel rectal spacer, respectively. There was a significant reduction of mean displacement in the posterior (2.6 mm vs. 19.4 mm, <i>P</i> = 0.04) and inferior direction (3.1 mm vs. 14.2 mm, <i>P</i> = 0.04) in patients with hydrogel rectal spacer compared to those without hydrogel rectal spacer during "beam on time". <h3>Conclusion</h3> The use of hydrogel rectal spacer can mitigate intrafraction prostate motion in posterior and inferior directions, suggesting a potential dosimetric advantage with the use of hydrogel rectal spacer. However, longer follow-up may be needed to confirm whether this translates into significant clinical benefit outweighing potential risk.

Characterization of an Iodinated Rectal Spacer for Prostate Photon and Proton Radiation Therapy

PurposeConventional rectal spacers (nonI-SPs) are low-contrast on computed tomography (CT), often necessitating magnetic resonance imaging for accurate delineation. A new formulation of spacers (I-SPs) incorporates iodine to improve radiopacity and CT visualization. We characterized placement, stability, and plan quality of I-SPs compared to nonI-SPs. Methods and MaterialsPatients with intact prostate cancer (n = 50) treated with I-SPs and photons were compared to randomly selected patients (n = 50) with nonI-SPs (photon or proton therapy). The I-SP was contoured on the planning CT and cone beam CTs at 3 timepoints: first, middle, and final treatment (n = 200 scans). I-SPs Hounsfield units (HU), volume, surface area (SA), centroid position relative to prostate centroid, and distance between prostate/rectum centroids were compared on the planning CTs between each cohort. I-SP changes were evaluated on cone beam CTs over courses of treatment. Dosimetric evaluations of plan quality and robustness were performed. I-SP was tested in a phantom to characterize its relative linear stopping power for protons. ResultsI-SPs yielded a distinct visible contrast on planning CTs compared to nonI-SPs (HU 138 vs 12, P < .001), allowing delineation on CT alone. The delineated volume and SA of I-SPs were smaller than nonI-SPs (volume 8.9 vs 10.6 mL, P < .001; SA 28 vs 35 cm2, P < .001), yet relative spacer position and prostate-rectal separation were similar (P = .79). No significant change in HU, volume, SA, or relative position of the I-SPs hydrogel occurred over courses of treatment (all P > .1). Dosimetric analysis concluded there were no significant changes in plan quality or robustness for I-SPs compared to nonI-SPs. The I-SP relative linear stopping power was 1.018, necessitating HU override for proton planning. ConclusionsI-SPs provide a manifest CT contrast, allowing for delineation on planning CT alone with no magnetic resonance imaging necessary. I-SPs radiopacity, size, and relative position remained stable over courses of treatment from 28 to 44 fractions. No changes in plan quality or robustness were seen comparing I-SPs and nonI-SPs.

Early outcomes of high-dose-rate brachytherapy combined with ultra-hypofractionated radiation in higher-risk prostate cancer

This study evaluated outcomes associated with a high-dose-rate (HDR) brachytherapy boost combined with stereotactic body radiation therapy (SBRT) for patients with higher-risk localized prostate cancer. We identified 101 patients with National Comprehensive Cancer Network high-risk, unfavorable intermediate-risk, or favorable intermediate-risk with probable extra-prostatic extension treated with HDR brachytherapy (15 Gy x 1 fraction) followed by SBRT (5 Gy x 5 daily fractions to the prostate and/or seminal vesicles and/or pelvic lymph nodes).Androgen deprivation therapy was used in 55.4% of all patients (90% of high-risk, 33% of intermediate-risk).Toxicities according to Common Terminology Criteria for Adverse Events (CTCAE) v4.0 and International Prostate Symptom Scores were prospectively documented at each followup visit. Biochemical relapse was defined as PSA nadir +2ng/mL. The median follow-up time after SBRT was 24.1 months. No grade ≥3 toxicities were observed. The incidence of acute and late grade 2 gastrointestinal toxicities was both 0.99%. Acute and late grade 2 genitourinary (GU) toxicities were observed in 5.9% and 9.9%, respectively. Median time to a grade 2 GU toxicity was 6 months with a 14% 2-year actuarial rate of grade 2 GU toxicity. Median International Prostate Symptom Scores at 24 months was not significantly different than baseline (6 vs. 5; p = 0.24). Inclusion of pelvic lymph nodes and absence of a rectal spacer were significantly associated with more frequent grade ≥1 GU toxicity, but not grade ≥2 GU or gastrointestinal toxicity. The 2-year biochemical relapse free survival was 97%. HDR brachytherapy combined with SBRT was associated with a favorable early toxicity profile and encouraging cancer control outcomes.

Bleeding Risk Following Stereotactic Body Radiation Therapy for Localized Prostate Cancer in Men on Baseline Anticoagulant or Antiplatelet Therapy

PurposePatients on anticoagulant/antiplatelet medications are at a high risk of bleeding following external beam radiation therapy for localized prostate cancer. SBRT may reduce the bleeding risk by decreasing the volume of bladder/rectum receiving high doses. This retrospective study sought to evaluate the rates of hematuria and hematochezia following SBRT in these patients.MethodsLocalized prostate cancer patients treated with SBRT from 2007 to 2017 on at least one anticoagulant/antiplatelet at baseline were included. The minimum follow-up was 3 years with a median follow-up of 72 months. Patients who had a rectal spacer placed prior to SBRT were excluded. Radiotherapy was delivered in 5 fractions to a dose of 35 Gy or 36.25 Gy utilizing the CyberKnife system. Hematuria and hematochezia were prospectively assessed before and after treatment using the Expanded Prostate Cancer Index Composite (EPIC-26). Toxicities were scored using the CTCAE v4. Cystoscopy and colonoscopy findings were retrospectively reviewed.ResultsForty-four men with a median age of 72 years with a history of taking at least one anticoagulant and/or antiplatelet medication received SBRT. Warfarin (46%), clopidogrel (34%) and rivaroxaban (9%) were the most common medications. Overall, 18.2% experienced hematuria with a median time of 10.5 months post-SBRT. Altogether, 38.6% experienced hematochezia with a median time of 6 months post-SBRT. ≥ Grade 2 hematuria and hematochezia occurred in 4.6% and 2.5%, respectively. One patient required bladder neck fulguration and one patient underwent rectal cauterization for multiple non-confluent telangiectasia. There were no grade 4 or 5 toxicities. Cystoscopy revealed bladder cancer (40%) and benign prostatic bleeding (40%) as the most common hematuria etiology. Colonoscopy demonstrated hemorrhoids (54.5%) and radiation proctitis (9.1%) as the main causes of hematochezia. There was no significant change from the mean baseline EPIC-26 hematuria and hematochezia scores at any point during follow up.ConclusionIn patients with baseline anticoagulant usage, moderate dose prostate SBRT was well tolerated without rectal spacing. High grade bleeding toxicities were uncommon and resolved with time. Baseline anticoagulation usage should not be considered a contraindication to prostate SBRT.