Absorbable Hydrogel Spacer Use in Prostate Radiotherapy: A Comprehensive Review of Phase 3 Clinical Trial Published Data

Randomized Trial of Concomitant Hypofractionated Intensity Modulated Radiation Therapy Boost Versus Conventionally Fractionated Intensity Modulated Radiation Therapy Boost for Localized High-Risk Prostate Cancer (pHART2-RCT)

PURPOSE

The aim of this work is to report on the results of a phase 2 randomized trial of moderately hypofractionated (MH) versus conventionally fractionated (CF) radiation therapy to the prostate with elective nodal irradiation.

METHODS AND MATERIALS

This was a single-center, prospective, phase 2 randomized study. Patients with high-risk disease (cT3, prostate-specific antigen level >20 ng/mL, or Gleason score 8-10) were eligible. Patients were randomized to either MH using a simultaneous integrated boost (68 Gy in 25 fractions to prostate; 48 Gy to pelvis) or CF (46 Gy in 23 fractions with a sequential boost to the prostate of 32 Gy in 16 fractions), with long-term androgen deprivation therapy. The primary endpoint was grade ≥2 acute gastrointestinal (GI) and genitourinary (GU) toxicity (Common Terminology Criteria for Adverse Events version 3.0). Secondary endpoints included late GI and GU toxicity, quality of life, and oncologic outcomes.

RESULTS

One-hundred eighty patients were enrolled; 90 were randomized to and received MH and 90 to CF. The median follow-up was 67.4 months. Seventy-five patients (41.7%) experienced a grade ≥2 acute GI and/or GU toxicity, including 34 (37.8%) in the MH and 41 (45.6%) in the CF arms, respectively (P = .29). Late grade ≥2 GI (P = .07) and GU (P = .25) toxicity was not significantly different between arms; however, late grade ≥3 GI toxicity was worse in the MH group (P = .01). There were no statistically significant quality-of-life differences between the 2 treatments. There were no statistically significant differences observed in cumulative incidence of biochemical failure (P = .71) or distant metastasis (P = .31) and overall survival (P = .46).

CONCLUSIONS

MH to the prostate and pelvis with androgen deprivation therapy for men with high-risk localized prostate cancer was not significantly different than CF with regard to acute toxicity, quality of life, and oncologic efficacy. However, late grade ≥3 GI toxicity was more common in the MH arm.

Transient, Image-Guided Gel-Dissection for Percutaneous Thermal Ablation

Image-guided tumor ablative therapies are mainstay cancer treatment options but often require intra-procedural protective tissue displacement to reduce the risk of collateral damage to neighboring organs. Standard of care strategies, such as hydrodissection (fluidic injection), are limited by rapid diffusion of fluid and poor retention time, risking injury to adjacent organs, increasing cancer recurrence rates from incomplete tumor ablations, and limiting patient qualification. Herein, a "gel-dissection" technique is developed, leveraging injectable hydrogels for longer-lasting, shapeable, and transient tissue separation to empower clinicans with improved ablation operation windows and greater control. A rheological model is designed to understand and tune gel-dissection parameters. In swine models, gel-dissection achieves 24 times longer-lasting tissue separation dynamics compared to saline, with 40% less injected volume. Gel-dissection achieves anti-dependent dissection between free-floating organs in the peritoneal cavity and clinically significant thermal protection, with the potential to expand minimally invasive therapeutic techniques, especially across locoregional therapies including radiation, cryoablation, endoscopy, and surgery.

SpaceOAR Complication Affecting the Treatment of Prostate Cancer

A 60-year-old male presented with an elevated prostate-specific antigen (PSA) of 10 ng/ml. A transrectal ultrasound-guided prostate biopsy showed prostate adenocarcinoma GS 4+3 (grade 3) with 5 out of 12 cores positive for malignancy. He initially planned to have prostate stereotactic body radiation therapy (SBRT) with SpaceOAR gel insertion in his rectoprostatic space to reduce radiation to the rectum. Magnetic resonance imaging (MRI) two months after SpaceOAR insertion showed evidence of infiltration of the SpaceOAR within the anterior rectal wall. This delayed his treatment and he was started on a short course of androgen deprivation therapy with Leuprolide while waiting for absorption of the gel. After completion of androgen deprivation therapy, the patient was treated with external beam radiation therapy (EBRT) to the prostate, seminal vesicles, and pelvis to a total dose of 6000 centigray (cGy) in 20 fractions at a dose per fraction of 300 cGy. He did well after treatment with minimal side effects.

Increasing rectum-prostate distance using a hydrogel spacer to reduce radiation exposure during proton beam therapy for prostate cancer

SpaceOAR, a polyethylene-glycol hydrogel, reduces rectal radiation exposure during radiation therapy for prostate cancer. Previously, our group reported the modified technique of hydrogel insertion, which achieves greater separated distance at prostate-apex. This study aimed to investigate the impact of separated distance at prostate-apex and our modifier technique, on radiation exposure reduction during proton beam therapy (PBT). We included 330 patients undergoing PBT with the relative biological effectiveness (RBE) of 63 Gray (Gy) for localized prostate cancer, and categorized them into groups 0 (no spacer, n = 141), 1 (separated distance of spacer at the prostate-apex level < 7.5 mm, n = 81), and 2 (distance ≥ 7.5 mm, n = 108). The rectal volumes to receive 30-60 Gy (RBE), was estimated and described as Rectal V30-60 (ml) in 10 Gy increments. The Rectal V30-60 (ml) was significantly lower in group 2 than in group 1, and in group 1 than in group 0. After propensity score matching, the multivariate logistic regression analysis revealed that the most significant factor to reduce radiation exposure was our modified technique of hydrogel insertion. Therefore, using a hydrogel spacer to expand the prostate-rectum distance not only at prostate-mid to prostate-base level but also at the prostate-apex level can reduce the radiation exposure in PBT for prostate cancer.

ESTRO ACROP guideline on prostate bed delineation for postoperative radiotherapy in prostate cancer

Purpose/Objective

Radiotherapy to the prostate bed is a potentially curative salvage option after radical prostatectomy. Although prostate bed contouring guidelines are available in the literature, important variabilities exist. The objective of this work is to provide a contemporary consensus guideline for prostate bed delineation for postoperative radiotherapy.

Methods

An ESTRO-ACROP contouring consensus panel consisting of 11 radiation oncologists and one radiologist, all with known subspecialty expertise in prostate cancer, was established. Participants were asked to delineate the prostate bed clinical target volumes (CTVs) in 3 separate clinically relevant scenarios: adjuvant radiation, salvage radiation with PSA progression, and salvage radiation with persistently elevated PSA. These cases focused on the presence of positive surgical margin, extracapsular extension, and seminal vesicles involvement. None of the cases had radiographic evidence of local recurrence on imaging. A single computed tomography (CT) dataset was shared via FALCON platform and contours were performed using EduCaseTM software. Contours were analyzed qualitatively using heatmaps which provided a visual assessment of controversial regions and quantitatively analyzed using Sorensen-Dice similarity coefficients. Participants also answered case-specific questionnaires addressing detailed recommendations on target delineation. Discussions via electronic mails and videoconferences for final editing and consensus were performed.

Results

The mean CTV for the adjuvant case was 76 cc (SD = 26.6), salvage radiation with PSA progression was 51.80 cc (SD = 22.7), and salvage radiation with persistently elevated PSA 57.63 cc (SD = 25.2). Compared to the median, the mean Sorensen-Dice similarity coefficient for the adjuvant case was 0.60 (SD 0.10), salvage radiation with PSA progression was 0.58 (SD = 0.12), and salvage radiation with persistently elevated PSA 0.60 (SD = 0.11). A heatmap for each clinical scenario was generated. The group agreed to proceed with a uniform recommendation for all cases, independent of the radiotherapy timing. Several controversial areas of the prostate bed CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences where the panel achieved consensus on the prostate bed CTV to be used as a novel guideline for postoperative prostate cancer radiotherapy.

Conclusion

Variability was observed in a group formed by experienced genitourinary radiation oncologists and a radiologist. A single contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in prostate bed delineation, independent of the indication.There is important variability in existing contouring guidelines for postoperative prostate bed (PB) radiotherapy (RT) after radical prostatectomy. This work aimed at providing a contemporary consensus guideline for PB delineation. An ESTRO ACROP consensus panel including radiation oncologists and a radiologist, all with known subspecialty expertise in prostate cancer, delineated the PB CTV in 3 scenarios: adjuvant RT, salvage RT with PSA progression, and salvage RT with persistently elevated PSA. None of the cases had evidence of local recurrence. Contours were analysed qualitatively using heatmaps for visual assessment of controversial regions and quantitatively using Sorensen-Dice coefficient. Case-specific questionnaires were also discussed via e-mails and videoconferences for consensus. Several controversial areas of the PB CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences. Finally, a contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in PB delineation, independent of the indication.

Electropatterning-Contemporary developments for selective particle arrangements employing electrokinetics

The selective positioning and arrangement of distinct types of multiscale particles can be used in numerous applications in microfluidics, including integrated circuits, sensors and biochips. Electrokinetic (EK) techniques offer an extensive range of options for label-free manipulation and patterning of colloidal particles by exploiting the intrinsic electrical properties of the target of interest. EK-based techniques have been widely implemented in many recent studies, and various methodologies and microfluidic device designs have been developed to achieve patterning two- and three-dimensional (3D) patterned structures. This review provides an overview of the progress in electropatterning research during the last 5 years in the microfluidics arena. This article discusses the advances in the electropatterning of colloids, droplets, synthetic particles, cells, and gels. Each subsection analyzes the manipulation of the particles of interest via EK techniques such as electrophoresis and dielectrophoresis. The conclusions summarize recent advances and provide an outlook on the future of electropatterning in various fields of application, especially those with 3D arrangements as their end goal.

The Use of Hydrogel-Based Materials for Radioprotection

Major causes of the radiation-induced disease include nuclear accidents, war-related nuclear explosions, and clinical radiotherapy. While certain radioprotective drug or bioactive compounds have been utilized to protect against radiation-induced damage in preclinical and clinical settings, these strategies are hampered by poor efficacy and limited utilization. Hydrogel-based materials are effective carriers capable of enhancing the bioavailability of compounds loaded therein. As they exhibit tunable performance and excellent biocompatibility, hydrogels represent promising tools for the design of novel radioprotective therapeutic strategies. This review provides an overview of common approaches to radioprotective hydrogel preparation, followed by a discussion of the pathogenesis of radiation-induced disease and the current states of research focused on using hydrogels to protect against these diseases. These findings ultimately provide a foundation for discussions of the challenges and future prospects associated with the use of radioprotective hydrogels.

Proton therapy for high-risk prostate cancer: Results from the Proton Collaborative Group PCG 001-09 prospective registry trial

BACKGROUND

Data for proton therapy in high-risk prostate cancer (HRPC) are limited. Using the Proton Collaborative Group prospective registry, we evaluated outcomes for HRPC patients treated with proton therapy.

METHODS

A totsl of 605 men with localized HRPC treated with proton therapy from 8/2009 to 3/2019 at nine institutions were selected. Outcomes examined included freedom from progression (FFP), metastasis free survival (MFS), overall survival (OS), and toxicity. Multivariable cox/binomial regression models were used to assess predictors of FFP and toxicity.

RESULTS

Median age was 71 years. Gleason grade groups 4 (49.4%) and 5 (31.7%) were most common, as were clinical stage T1c (46.1%) and cT2 (41.3%). The median pretreatment prostate specific antigen (PSA) was 9.18 and median International Prostate Symptom Score (IPSS) was 6. Androgen deprivation therapy was given in 63.6%. Median dose was 79.2 GyE in 44 fractions. Pelvic lymph nodes were treated in 58.2% of cases. Pencil beam scanning was used in 54.5%, uniform scanning in 38.8%, and a rectal spacer in 14.2%. At a median followup of 22 months, the 3- and 5-year FFP were 90.7% and 81.4%, respectively. Five-year MFS and OS were 92.8% and 95.9%, respectively. Independent correlates of FFP included Gleason ≥8, PSA > 10, and cT2 (all p < 0.05). No grade 4 or 5 adverse events were reported. There were 23 (5%) grade 2 and 0 grade 3 gastrointestinal events. Prevalence of late grade 3, late grade 2, acute grade 3, and acute grade 2 genitourinary toxicity was 1.7%, 5.8%, 0%, and 21.8%, respectively. Prevalence of grade 2 and 3 erectile dysfunction at 2 years was 48.4% and 8.4%, respectively.

CONCLUSIONS

In the largest series published to date, our results suggest early outcomes using proton therapy for HRPC are encouraging for both safety and efficacy. Further evaluation is needed to determine if an advantage exists to use protons over other radiation techniques in this population.

Comprehensive review of the use of hydrogel spacers prior to radiation therapy for prostate cancer

OBJECTIVES

To provide a comprehensive narrative review of the published data on the impact of hydrogel spacers on rectal dosimetry and toxicity and to outline the practicalities of inserting hydrogel spacers.

RESULTS

A growing body of evidence suggests that the administration of hydrogel spacers is safe and is associated with limited peri-operative morbidity. The impact on rectal dosimetry has been clearly established and use of hydrogel spacers is associated with reduced rectal morbidity. These results have been corroborated by several Phase II and III clinical trials and subsequent meta-analysis. There are several areas for future research, including the role of hydrogel spacers in prostate stereotactic beam radiotherapy and post-radiotherapy local recurrence.

CONCLUSIONS

Hydrogel spacers provide a low-morbidity method to potential reduce rectal toxicity after radiation therapy in men with prostate cancer. Data outlining sexual function and oncological outcomes are limited to date. Future studies, currently being conducted, may provide further clarification of the role of hydrogel spacers in prostate cancer management.

Silk-elastinlike protein-based hydrogels for drug delivery and embolization

Silk-Elastinlike Protein-Based Polymers (SELPs) can form thermoresponsive hydrogels that allow for the generation of in-situ drug delivery matrices. They are produced by recombinant techniques, enabling exact control of monomer sequence and polymer length. In aqueous solutions SELP strands form physical crosslinks as a function of temperature increase without the addition of crosslinking agents. Gelation kinetics, modulus of elasticity, pore size, drug release, biorecognition, and biodegradation of SELP hydrogels can be controlled by placement of amino acid residues at strategic locations in the polymer backbone. SELP hydrogels have been investigated for delivery of a variety of bioactive agents including small molecular weight drugs and fluorescent probes, oligomers of glycosaminoglycans, polymeric macromolecules, proteins, plasmid DNA, and viral gene delivery systems. In this review we provide a background for use of SELPs in matrix-mediated delivery and summarize recent investigations of SELP hydrogels for controlled delivery of bioactive agents as well as their use as liquid embolics.

Polyethylene glycol-based gels for treatment of prostate cancer: pictorial review of normal placement and complications

Rectal spacers are commonly used in the radiotherapy for prostate cancers, serving as a means to protect the rectum and surrounding structures from radiation toxicity. Polyethylene Glycol-Based Gels (SpaceOAR ™ and Space-OAR Vue™, Boston Scientific) are the most commonly used rectal spacers. Given their increasingly widespread use and the relative paucity of radiology literature on this topic, it is imperative for the radiologist to recognize both the normal and abnormal placement of these polyethylene glycol-based rectal spacers, particularly as the latter may be associated with suboptimal therapy and/or complications.

Impact of intrafraction changes in delivered dose of the day for prostate cancer patients treated with stereotactic body radiotherapy via MR-Linac

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Beam on MR acquisition on the MR-Linac can be used to compute DDOTD.

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Intrafraction motion via volumetric variability of OARs can impact dosimetry.

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Computation of the DDOTD may help inform prospective fractions for SBRT prostate.

Purpose

The purpose of this study is to evaluate the impact of intrafraction pelvic motion by comparing the adapted plan dose (APD) and the computed delivered dose of the day (DDOTD) for patients with prostate cancer (PCa) treated with SBRT on the MR-Linac.

Methods

Twenty patients with PCa treated with MR-guided adaptive SBRT were included. A 9-field IMRT distribution was adapted based on the anatomy of the day to deliver a total prescription dose of 3000 cGy in 5 fractions to the prostate plus a 5 mm isotropic margin. Prostate, bladder, and rectum were re-contoured on the MR-image acquired during treatment delivery (MR_BO). DDOTD was computed by propagating the dose from the daily adapted plan generated during treatment onto the MR_BO.

Results

Target coverage was met for all fractions, however, computed DDOTD was significantly less than the APD (p < 0.05). During an average treatment of 53 min, mean bladder volume increased by 116%, which led to a significant decrease in the DDOTD bladder D40% (p < 0.001). However, DDOTD to bladder 5 cc was significantly higher (p < 0.001) than APD. Rectum intrafraction changes were observed based on a volume change of −20% to 83% and presence of significant dose changes from APD to DDOTD for rectum D20% (p < 0.05) and D1cc (p < 0.0001).

Conclusions

Intrafraction motion observed during prostate SBRT treatment on the MR-Linac have dosimetric impacts on both the target and organs at risk. Post-treatment computation using DDOTD may inform adaptation beyond anatomic changes in subsequent treatment fractions to best capitalize on MR-Linac technology and widen the therapeutic index of SBRT for PCa.

Prevention of radiation enteritis by interposition of an intra-abdominal spacer before irradiation of an appendiceal tumour abscess drainage route

The initial presentation of a mucinous adenocarcinoma of the appendix can be a peri-appendicular abscess. The abdominal wall muscles can be invaded during radiological or surgical drainage. The management of such a tumour is complex. The resection of a drainage route can be uncertain and R1. In this case, further treatment with adjuvant radiotherapy may be necessary. One possible deleterious side effect of radiotherapy on the abdominal wall is radiation injury to the bowel. As a preventive measure, a spacer (here a breast prosthesis) can be interposed.

Prostate MRI in Stereotactic Body Radiation Treatment Planning and Delivery for Localized Prostate Cancer

Prostate MRI is increasingly being used to make diagnoses and guide management for patients receiving definitive radiation treatment for prostate cancer. Radiologists should be familiar with the potential uses of prostate MRI in radiation therapy planning and delivery. Radiation therapy is an established option for the definitive treatment of localized prostate cancer. Stereotactic body radiation therapy (SBRT) is an external-beam radiation therapy method used to deliver a high dose of radiation to an extracranial target in the body, often in five or fewer fractions. SBRT is increasingly being used for prostate cancer treatment and has been recognized by the National Comprehensive Cancer Network as an acceptable definitive treatment regimen for low-, intermediate-, and high-risk prostate cancer. MRI is commonly used to aid in prostate radiation therapy. The authors review the uses of prostate MRI in SBRT treatment planning and delivery. Specific topics discussed include the use of prostate MRI for identification of and dose reduction to the membranous and prostatic urethra, which can decrease the risk of acute and late toxicities. MRI is also useful for identification and appropriate dose coverage of the prostate apex and areas of extraprostatic extension or seminal vesicle invasion. In prospective studies, prostate MRI is being validated for identification of and dose intensification to dominant intraprostatic lesions, which potentially can improve oncologic outcomes. It also can be used to evaluate the placement of fiducial markers and hydrogel spacers for radiation therapy planning and delivery. ^©RSNA, 2022.

Urethra Sparing With Target Motion Mitigation in Dose-Escalated Extreme Hypofractionated Prostate Cancer Radiotherapy: 7-Year Results From a Phase II Study

Purpose

To explore whether the rectal distension-mediated technique, harnessing human physiology to achieve intrafractional prostate motion mitigation, enables urethra sparing by inverse dose painting, thus promoting dose escalation with extreme hypofractionated stereotactic ablative radiotherapy (SABR) in prostate cancer.

Materials and Methods

Between June 2013 and December 2018, 444 patients received 5 × 9 Gy SABR over 5 consecutive days. Rectal distension-mediated SABR was employed via insertion of a 150-cm³ air-inflated endorectal balloon. A Foley catheter loaded with 3 beacon transponders was used for urethra visualization and online tracking. MRI-based planning using Volumetric Modulated Arc Therapy - Image Guided Radiotherapy (VMAT-IGRT) with inverse dose painting was employed in delivering the planning target volume (PTV) dose and in sculpting exposure of organs at risk (OARs). A 2-mm margin was used for PTV expansion, reduced to 0 mm at the interface with critical OARs. All plans fulfilled D_mean ≥45 Gy. Target motion ≥2 mm/5 s motions mandated treatment interruption and target realignment prior to completion of the planned dose delivery.

Results

Patient compliance to the rectal distension-mediated immobilization protocol was excellent, achieving reproducible daily prostate localization at a patient-specific retropubic niche. Online tracking recorded ≤1-mm intrafractional target deviations in 95% of treatment sessions, while target realignment in ≥2-mm deviations enabled treatment completion as scheduled in all cases. The cumulative incidence rates of late grade ≥2 genitourinary (GU) and gastrointestinal (GI) toxicities were 5.3% and 1.1%, respectively. The favorable toxicity profile was corroborated by patient-reported quality of life (QOL) outcomes. Median prostate-specific antigen (PSA) nadir by 5 years was 0.19 ng/ml. The cumulative incidence rate of biochemical failure using the Phoenix definition was 2%, 16.6%, and 27.2% for the combined low/favorable–intermediate, unfavorable intermediate, and high-risk categories, respectively. Patients with a PSA failure underwent a ⁶⁸Ga-labeled prostate-specific membrane antigen (⁶⁸Ga-PSMA) scan showing a 20.2% cumulative incidence of intraprostatic relapses in biopsy International Society of Urological Pathology (ISUP) grade ≥3.

Conclusion

The rectal distension-mediated technique is feasible and well tolerated. Dose escalation to 45 Gy with urethra-sparing results in excellent toxicity profiles and PSA relapse rates similar to those reported by other dose-escalated regimens. The existence of intraprostatic recurrences in patients with high-risk features confirms the notion of a high α/β ratio in these phenotypes resulting in diminished effectiveness with hypofractionated dose escalation.

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

Microwave for focal therapy of prostate cancer: Non-clinical study and exploratory clinical trial

OBJECTIVE

The objective of this non-clinical study and clinical trial (phase II) was to examine the safety and efficacy of microwave tissue coagulation (MTC) for prostate cancer and assess its use in lesion-targeted focal therapy.

METHODS

In the non-clinical study using Microtaze®-AFM-712 (Alfresa-pharma Corporation) with an MTC-needle, MTC was performed by a transperineal approach to canine prostatic-targeted tissue under real-time ultrasound guidance. Using various MTC-output and irradiation-time combinations, the targeted and surrounding tissues (rectum, bladder, and fat) were examined to confirm the extent of coagulative necrosis or potential cell death, and to compare intra-operative ultrasound and pathology findings. The exploratory clinical trial was conducted to examine the safety and efficacy of MTC. Five selected patients underwent transperineal MTC to clinically single magnetic resonance imaging (MRI)-visible lesions with Gleason score 3+4 or 4+4. Prostate-specific antigen (PSA), MRI, and Expanded Prostate Cancer Index Composite questionnaire findings were compared before and 6 months after surgery.

RESULTS

The region of coagulative necrosis was predictable by monitoring of ultrasonically visible vaporization; thus, by placing the MTC-needle at a certain distance, we were able to perform a safe procedure without adverse events affecting the surrounding organs. Based on the non-clinical study, which used various combinations of both output and irradiation time, MTC with 30-W output for 60-sec irradiation was selected for the prostate. Based on the predictable necrosis, the therapeutic plan (where to place the MTC-needle to achieve complete ablation of the target and how many sessions) was strictly determined per patient. There were no serious adverse events in all patients and only temporary urinary symptoms related to MTC-therapy were observed. Furthermore, satisfaction of having undergone treatment was very high. All pre-operative MRI-visible lesions disappeared, and PSA decreased 55% 6 months after surgery.

CONCLUSION

MTC may be an option for lesion-targeted focal therapy for prostate cancer.

Biological effective dose in analysis of rectal dose in prostate cancer patients who underwent a combination therapy of VMAT and LDR with hydrogel spacer insertion

This study aimed to evaluate rectal dose reduction in prostate cancer patients who underwent a combination of volumetric modulated arc therapy (VMAT) and low‐dose‐rate (LDR) brachytherapy with insertion of hydrogel spacer (SpaceOAR). For this study, 35 patients receiving hydrogel spacer and 30 patients receiving no spacer were retrospectively enrolled. Patient was treated to doses of 45 Gy to the primary tumor site and nodal regions over 25 fractions using VMAT and 100 Gy to the prostate using prostate seed implant (PSI). In VMAT plans of patients with no spacer, mean doses of rectal wall were 43.6, 42.4, 40.1, and 28.8 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively. In patients with SpaceOAR, average rectal wall doses decreased to 39.0, 36.9, 33.5, and 23.9 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively (p < 0.01). In PSI plans, rectal wall doses were on average 78.5, 60.9, 41.8, and 14.8 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively, in patients without spacer. In contrast, the doses decreased to 34.5, 28.4, 20.6 (p < 0.01), and 8.5 Gy (p < 0.05) to rectal wall volume of 0.5, 1, 2, and 5 cm³, respectively, in patient with SpaceOAR. To demonstrate rectal sum dose sparing, dose‐biological effective dose (BED) calculation was accomplished in those patients who showed >60% overlap of rectal volumetric doses between VMAT and PSI. In patients with SpaceOAR, average BED_sum was decreased up to 34%, which was 90.1, 78.9, 65.9, and 40.8 Gy to rectal volume of 0.5, 1, 2, and 5 cm³, respectively, in comparison to 137.4, 116.7, 93.0, and 50.2 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively, in those with no spacer. Our result suggested a significant reduction of rectal doses in those patients who underwent a combination of VMAT and LDR with hydrogel spacer placement.

Natural history of lower urinary tract symptoms among men undergoing stereotactic body radiation therapy for prostate cancer with and without a Rectal Hydrogel Spacer

PURPOSE

Stereotactic body radiation therapy (SBRT) is increasingly used for prostate cancer, but has morbidity as both the bladder and rectum are radiated during treatment. Our goal was to document and compare lower urinary tract symptoms (LUTS) among men who underwent SBRT with and without SpaceOAR hydrogel (Augmenix, Inc., Bedford, MA).

METHODS

We performed a retrospective analysis of 87 men (50 SpaceOAR and 37 non-SpaceOAR) who underwent SBRT. Primary outcomes were patient reported symptoms during radiation therapy, pharmacotherapy usage, and urologic and bowel survey scores up to 6-months post-SBRT.

RESULTS

78% of men were on α-inhibitors at the end of SBRT, an increase from 27.6% baseline usage (p < 0.001). Post-SBRT urinary frequency was more common in the non-SpaceOAR group versus the SpaceOAR group (68% versus 38%, p = 0.006), as was nocturia (35% vs. 8%, p = 0.002). Acute gastrointestinal symptoms did not differ. 58.8% of men were on α-inhibitors at 6-months of follow-up post-SBRT, an increase from 27.6% baseline usage (p < 0.001). Importantly, there was a difference of α-inhibitor use between non-SpaceOAR and SpaceOAR groups at the end of SBRT and at 1.5-, 3-, and 6-months follow up (86% vs. 53% [p = 0.002], 83% vs. 53% [p = 0.005], 72% vs. 49% [p = 0.038], respectively).

CONCLUSION

LUTS after SBRT remains a significant problem for men undergoing treatment for prostate cancer. LUTS affects men during and up to 6-months following SBRT. Owing to these increased LUTS, preemptive minimally invasive solutions and their mechanisms of protection, including the SpaceOAR, should be further investigated.

Creation of a protective space between the rectum and prostate prior to prostate radiotherapy using a hydrogel spacer

The placement of a polyethylene glycol (PEG) hydrogel spacer is a recently developed technique employed to reduce the radiation dose administered to the rectum during prostate radiotherapy. This procedure has been adopted by urologists and radiation oncologists involved in transperineal prostate biopsy and brachytherapy, and more recently by radiologists with experience in transperineal prostate procedures. Radiologists should be familiar with the product, which may be encountered on computed tomography (CT) or magnetic resonance imaging (MRI). Radiologists may wish to become involved in the delivery of this increasingly utilised procedure. This review familiarises radiologists with the technique and risks and benefits of the use of transperineal delivery of hydrogel spacers with imaging examples.

Patient Reported Quality of Life Outcomes After Definitive Radiation Therapy With Absorbable Spacer Hydrogel for Prostate Cancer

Purpose

SpaceOAR is a device approved for conventional radiation in prostate cancer. We sought to observe prospectively how SpaceOAR Hydrogel effected quality of life and dosimetry to organs at risk at our institution.

Methods and Materials

We prospectively enrolled patients with low risk or favorable-intermediate risk localized prostate cancer. Baseline Expanded Prostate Cancer Index Composite (EPIC-26) scores along with baseline American Urology Association Symptom Index (AUA-SI) scores were collected. SpaceOAR was placed for all patients who then received stereotactic body radiation therapy, low dose rate brachytherapy, conventionally fractionated radiation therapy, or moderately hypofractionated radiation therapy. We evaluated postimplant dosimetry to critical structures, and prospectively collected follow-up EPIC-26 and AUA-SI scores. We performed a repeated measures analysis of variance to compare patient-specific responses and correlated survey data with dosimetric metrics by generating linear regression models.

Results

We enrolled 59 patients in this study with a median follow-up of 366 days (interquartile range, 507). At final follow-up, the "?>prostate-specific antigen had a significant decline compared with baseline (P < .0001). There were no grade 3 toxicities on treatment. There were no significant changes in the AUA-SI score (P = .69) at final follow-up compared with baseline, nor was there any change in EPIC-26 domain scores (P = .19) during the course of the study period. There were no significant associations between AUA scores and EPIC-26 scores and the dose to the rectum, bladder, or urethra with the exception being dose to the 2 mL rectum correlated with decline in EPIC-26 rectal score (β, −0.002; P = .006). Patient-reported declines in bowel domains were less than previously reported data.

Conclusions

Use of SpaceOAR results in favorable dosimetry to the organs at risk and portends excellent short-term quality of life as measured by the association with the patient reported outcome measures. Longer-term follow-up is ongoing and necessary to assess the long-term effect and association of the hydrogel.

Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers

The aim of the present study was to investigate the effects on the dose distribution and beam delivery time in spot scanning proton beam therapy (PBT) incorporating the spot deletion technique. A spot scanning plan was created for 30 patients with prostate cancer. The plan was then modified via two processes: Spots with lower weighting depositions were deleted (process A) and spots that were distant from the clinical target volume (CTV) were deleted (process B). The dose distribution to the organs at risk (OAR), the expanded CTV (exCTV), which was defined by a uniform expansion of the CTV by a radius of 5 mm, and the beam delivery time were compared among initial and modified plans. The V_{50Gy [relative biological effectiveness (RBE)]} to the rectum and bladder, and V_{60 Gy(RBE)} to the urethral bulb, inhomogeneity index (INH) of the exCTV showed a difference (P=1.1x10^-14, P=6.4x10^-14, P=2.7x10^-7, P=3.2x10^-17), although only changes by process B were significant. Modified plan by process B showed the V_{50 Gy(RBE)} to the rectum and bladder decreased by -2.4±1.6 and -2.3±1.4%, and the V_{60 Gy (RBE)} to the urethral bulb decreased by -15.9±19.4%. The INH of the exCTV increased by 0.05±0.03%. On the other hand, modification of the initial plan by process A did not affect the dose of the OAR, exCTV or beam delivery time. In spot scanning PBT, modification of the initial radiotherapy plan by systemic deletion of spots distant from the CTV could result in a dose reduction to the OAR.

Separation effect and development of implantation technique of hydrogel spacer for prostate cancers

PURPOSE

The purpose was to improve the placement of a hydrogel spacer in prostate cancer patients receiving radiotherapy.

METHODS AND MATERIALS

One hundred and sixty patients with prostate cancer were classified into 3 groups as follows: group 1, no spacer (n = 30); group 2, spacer placed using conventional technique (n = 100); and group 3, spacer placed using new technique (n = 30). When placing the spacer, the tip of the needle was placed at the middle of the prostate gland (group 2) or at a level corresponding to a cranial:caudal ratio of 6:4 and as close to the prostate gland as possible (group 3). The separation effect was then examined and compared among the groups.

RESULTS

The separation in group 2 was larger than that in group 1 from the base to the apex (4 mm) level of the prostate, while the separation in group 3 was larger than that in group 2 from the middle to the apex (4 mm) level of the prostate. The separation values for the middle to the apex, the spacer thickness from the apex (10 mm) level to the apex, the rectal exclusion from the middle to the apex, and the laterality were correlated with the 50 and 60 Gray relative biological effectiveness (Gy(RBE)) rectal dose (p = 4.1 × 10^-9 - 0.046). The separation vales were strongly correlated with the spacer thickness at the apex (10 mm) and apex (4 mm) (p = 1.1 × 10^-18 - 1.8 × 10^-17). The rectal volumes at 10-60 Gy(RBE) differed among the groups (p = 5.1 × 10^-19 - 5.4 × 10^-3). The rectal volumes in group 2 were smaller than those in group 1 at all dose levels, while those in group 3 were smaller than those in group 2 at dose levels of 30-50 Gy(RBE).

CONCLUSIONS

The separation, spacer thickness and rectal exclusion from the middle to the apex of the prostate and the laterality of the hydrogel spacer affected the reduction in the rectal dose. The rectal dose can be further reduced by implanting a spacer on the caudal and the prostate side.

Use of a Biodegradable, Contrast-Filled Rectal Spacer Balloon in Intensity-Modulated Radiotherapy for Intermediate-Risk Prostate Cancer Patients: Dosimetric Gains in the BioPro-RCMI-1505 Study

Background/purpose

Dose-escalated external beam radiotherapy (RT) is effective in the control of prostate cancer but is associated with a greater incidence of rectal adverse events. We assessed the dosimetric gain and safety profile associated with implantation of a new biodegradable rectal spacer balloon.

Materials/methods

Patients scheduled for image-guided, intensity-modulated RT for intermediate-risk prostate cancer were prospectively included in the French multicenter BioPro-RCMI-1505 study (NCT02478112). We evaluated the dosimetric gain, implantation feasibility, adverse events (AEs), and prostate-cancer-specific quality of life associated with use of the balloon spacer.

Results

After a scheduled review of the initial recruitment target of 50 patients by the study's independent data monitoring committee (IDMC), a total of 24 patients (including 22 with dosimetry data) were included by a single center between November 2016 and May 2018. The interventional radiologist who implanted the balloons considered that 86% of the procedures were easy. 20 of the 24 patients (83.3%) received IMRT and 4 (16.7%) received volumetric modulated arc therapy (78-80 Gy delivered in 39 fractions). The dosimetric gains associated with spacer implantation were highly significant (p<0.001) for most variables. For the rectum, the median (range) relative gain ranged from 15.4% (-9.2-47.5) for D20cc to 91.4% (36.8-100.0) for V70 Gy (%). 15 patients (62%) experienced an acute grade 1 AE, 8 (33%) experienced a late grade 1 AE, 1 (4.2%) experienced an acute grade 2 AE, and 3 experienced a late grade 2 AE. No grade 3 AEs were reported. Quality of life was good at baseline (except for sexual activity) and did not markedly worsen during RT and up to 24 months afterwards.

Conclusion

The use of a biodegradable rectal spacer balloon is safe, effective and associated with dosimetric gains in modern RT for intermediate-risk prostate cancer.

Patient-reported outcomes after Low-dose-rate versus High-dose-rate brachytherapy boost in combination with external beam radiation for intermediate and high risk prostate cancer

PURPOSE

Addition of a brachytherapy boost to external beam radiation therapy (EBRT) reduces prostate cancer (PCa) recurrence at the expense of genitourinary (GU) toxicity. Whether brachytherapy boost technique, specifically low-dose-rate (LDR-BT) versus high-dose-rate (HDR-BT), impacts treatment-related toxicity is unclear.

METHODS

Between 2012-2018, 106 men with intermediate/high risk PCa underwent EBRT (37.5-45 Gy in 1.8-2.5 Gy/fraction) plus brachytherapy boost, either with LDR-BT (110 Gy I-125 or 100 Gy Pd-103; n = 51) or HDR-BT (15 Gy x1 Ir-192; n = 55). Patient-reported outcomes (PRO) were assessed by International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index Composite (EPIC-CP) surveys at 3-6-month intervals for up to three years following treatment, with higher scores indicating more severe toxicity. Provider-reported GU and gastrointestinal (GI) toxicity was graded per CTCAE v5.0 at each follow-up. Linear mixed models comparing PROs between LDR-BT versus HDR-BT were fitted. Stepwise multivariable analysis (MVA) was performed to account for age, gland size, androgen deprivation therapy use, and alpha-blocker medication use. Incidence rates of grade 2+ GU/GI toxicity was compared using Fisher's exact test.

RESULTS

Use of LDR-BT was associated with greater change in IPSS (p=0.003) and EPIC-CP urinary irritative score (p = 0.002) compared with HDR-BT, but effect size diminished over time (LDR-BT versus HDR-BT: baseline to 6-/24-month mean IPSS change, +6.4/+1.4 versus +2.7/-3.0, respectively; mean EPIC-CP irritative/obstructive change, +2.5/+0.1 versus +0.9/+0.1, respectively). Results remained significant on MVA. Post-treatment grade 2+ GU toxicity was significantly higher in the LDR-BT group (67.5% versus 42.9% for LDR-BT and HDR-BT, respectively; p <0.001). There were no differences between groups in incontinence, bowel function, and erectile function, or grade 2+ GI toxicity.

CONCLUSION

Compared with LDR-BT, HDR-BT was associated with lower acute patient- and provider-reported GU toxicity.

Cost-effectiveness analysis of hydrogel spacer for rectal toxicity reduction in prostate external beam radiotherapy

INTRODUCTION

Contemporary methods of external beam radiotherapy for prostate cancer have reduced toxicity rates through beam modulation and image guidance, however, rectal injury has not been eliminated completely in this population. For patients at greatest risk of developing rectal toxicities, hydrogel spacers are a viable option for risk reduction. Translation of clinical trial results into routine clinical practice relies on an understanding of the economic implications. This study completed a cost-effectiveness analysis of hydrogel spacers in the Australian healthcare setting.

METHOD

Simulation of possible health states following treatment was performed using a Markov model. Model outcomes included the incremental cost-effectiveness ratio and the net monetary benefit (NMB) at three published willingness-to-pay thresholds derived from literature. Probabilistic sensitivity analyses were provided on these results. A baseline cohort without hydrogel spacer use was compared to treat all and selective use cohorts. Cost variation scenarios were also investigated to assess the impact of hydrogel spacer cost on outcomes.

RESULTS

Using hydrogel spacers in a selective cohort was more likely to be cost-effective than giving to all patients (NMB -$43 versus -$997, respectively); however, the incremental cost-effectiveness ratio was not below the $28 000 willingness-to-pay threshold for a healthcare provider perspective. These outcomes were influenced by large parameter uncertainty. Cost variation strategies are worth investigating further as a method to achieve willingness-to-pay threshold targets.

CONCLUSION

The influence of parameter uncertainty currently limits the cost-effectiveness of this intervention in the Australian public health setting. However, a cost variation solution has been demonstrated to improve cost-effectiveness estimates for selected patients and should be examined further.

Optimization of polyethylene glycol-based hydrogel rectal spacer for focal laser ablation of prostate peripheral zone tumor

PURPOSE

Focal Laser ablation therapy is a technique that exposes the prostate tumor to hyperthermia ablation and eradicates cancerous cells. However, due to the excessive heating generated by laser irradiation, there is a possibility of damage to the adjacent healthy tissues. This paper through in silico study presents a novel approach to reduce collateral effects due to heating by the placement of polyethylene glycol (PEG) spacer between the rectum and tumor during laser irradiation. The PEG spacer thickness is optimized to reduce the undesired damage at common laser power used in the clinical trials. Our study also encompasses novelty by conducting the thermal analysis based on the porous structure of prostate tumor.

METHODS

The thermal parameters and two thermal phase lags between the temperature gradient and the heat flux, are determined by considering the vascular network of prostate tumor. The Nelder-Mead algorithm is applied to find the minimum thickness of the PEG spacer.

RESULTS

In the absence of the spacer, the predicted results for the laser power of 4 W, 8 W, and 12 W show that the temperature of the rectum rises up to 58.6 °C, 80.4 °C, and 101.1 °C, while through the insertion of 2.59 mm, 4 mm, and 4.9 mm of the PEG spacer, it dramatically reduces below 42 °C.

CONCLUSIONS

The results can be used as a guideline to ablate the prostate tumors while avoiding undesired damage to the rectal wall during laser irradiation, especially for the peripheral zone tumors.

Expanding the Utilization of Rectal Spacer Hydrogel for Larger Prostate Glands (>80 cc): Feasibility and Dosimetric Outcomes

Purpose

The Hydrogel Spacer Prospective Randomized Pivotal Trial achieved mean rectoprostatic spacing of 12.6 mm resulting in lowering of rectal V70 from 12.4% (without spacer) to 3.3% (with spacer) in patients with glands up to 80 cm³. The value of this approach in patients with larger glands is inadequately established. This study assesses the feasibility and dosimetric outcomes of perirectal spacing in patients with prostate cancer with larger glands (>80 cm³).

Methods and Materials

Between January 2017 and December 2019, 33 patients with prostate glands >80 cm³ (mean 108.1 cm³; range, 81.1-186.6 cm³) were treated, 15 with glands >80 to 100 cm³ and 18 >100 cm³. Median follow-up was 10 months (range, 3-26). The median international prostate symptom score was 9 (range, 1-18). Hydrogel was placed under local anesthesia in all cases. Treatment modality included intensity modulated radiation therapy in 15 and proton therapy (PT) in 18 patients. Treatment targeted the prostate plus seminal vesicles in 21 patients and 12 also had elective nodal irradiation. Conventional fractionation (CF) to 78 Gy in 39 fractions was used in 16 and moderate hypofractionation (HF) to 70 Gy in 28 fractions in 17 patients.

Results

In the CF group, mean rectum (r) V75, 70, 60, 50 was 0.87%, 2.25%, 5.61%, and 10.5%, respectively. For glands >80 to 100 cm³ and >100 cm³, rV70 was 2.55% and 2%, respectively. In HF patients, mean rV65, 63, 60, and 50 was 1.67%, 2.3%, 3.4%, and 8.6%. For glands >80 to 100 cm³ and >100 cm³, rV63 was 2% and 2.56%, respectively. Overall, the mean midgland rectoprostatic hydrogel separation was 9.3 mm (range, 4.7-19.4 mm). All patients tolerated treatment well; no acute grade 2 or higher adverse gastrointestinal events were observed.

Conclusions

Hydrogel placement is feasible in prostate glands larger than 80 cm³ with favorable dosimetric outcomes.

Salvage re-irradiation using stereotactic body radiation therapy for locally recurrent prostate cancer: the impact of castration sensitivity on treatment outcomes

Background

Advances in imaging, biomaterials and precision radiotherapy provide new opportunities to salvage locally recurrent prostate cancer (PC). This study evaluates the efficacy and safety of re-irradiation using stereotactic body radiation therapy (SBRT). We hypothesized that patients with castrate-resistant PC (CRPC) would benefit less from local salvage.

Methods

A prospective clinical database was reviewed to extract 30 consecutive patients treated with prostate re-irradiation. Gallium prostate specific membrane antigen (PSMA) ligand positron emission tomography was performed following prostate-specific antigen failure in all patients and biopsy was obtained in 18 patients (60%). Re-irradiation was either focal (n = 13) or whole-gland (n = 17). Endo-rectal balloons were used in twenty-two patients and hydrogel spacers in eight patients. The median prescription dose was 5 fractions of 6.5 (range: 6–8) Gray (Gy).

Results

Median follow-up was 28 months. Failure occurred in 10 (out of 11) CRPC patients versus 6 (out of 19) castrate-sensitive patients (91% vs. 32%, p = 0.008) after a median of 13 and 23 months, respectively. Metastases occurred in 64% (n = 7) of CRPC patients versus 16% (n = 3) of castrate-sensitive patients (p = 0.007). Two patients experienced local in-field recurrence, thus local control was 93%. The 2 and 3-year recurrence-free survival were 84% and 79% for castrate-sensitive patients versus 18% and 9% for CRPC patients (p < 0.001), and 3-year metastasis-free survival was 90% versus 27% (p < 0.01) for castrate-sensitive and CRPC patients, respectively. Acute grade II and III genitourinary (GU) toxicity occurred in 27% and 3%, and late GU toxicity in 30% and 3%, respectively. No ≥ grade II acute gastrointestinal (GI) toxicity occurred, and only one patient (3%) developed late grade II toxicity.

Conclusions

Early delivery of salvage SBRT for local recurrence is associated with excellent 3-year disease control and acceptable toxicity in the castrate-sensitive phenotype. PSMA imaging for detection of local recurrence and the use of precision radiotherapy with rectal protective devices should be further investigated as a novel salvage strategy for radio-recurrent PC.

Multi-institutional retrospective analysis of ultrahypofractionated radiotherapy for Japanese prostate cancer patients

To report outcomes and risk factors of ultrahypofractionated (UHF) radiotherapy for Japanese prostate cancer patients. This multi-institutional retrospective analysis comprised 259 patients with localized prostate cancer from 6 hospitals. A total dose of 35–36 Gy in 4–5 fractions was prescribed for sequential or alternate-day administration. Biochemical failure was defined according to the Phoenix ASTRO consensus. Toxicities were assessed using National Cancer Institute Common Toxicity Criteria version 4. Tumor control and toxicity rates were analyzed by competing risk frames. Median follow-up duration was 32 months (range 22–97 months). 2- and 3-year biochemical control rates were 97.7% and 96.4%, respectively. Initial prostate-specific antigen (p < 0.01) and neoadjuvant androgen deprivation therapy (p < 0.05) were identified as risk factors for biochemical recurrence. 2- and 3-year cumulative ≥ Grade 2 late genitourinary (GU) toxicities were 5.8% and 7.4%, respectively. Corresponding rates of gastrointestinal (GI) toxicities were 3.9% and 4.5%, respectively. Grade 3 rates were lower than 1% for both GU and GI toxicities. No grade 4 or higher toxicities were encountered. Biologically effective dose was identified as a risk factor for ≥ Grade 2 late GU and GI toxicities (p < 0.05). UHF radiotherapy offered effective, safe treatment for Japanese prostate cancer with short-term follow-up. Our result suggest higher prescribed doses are related to higher toxicity rates.

Personalized Radiation Attenuating Materials for Gastrointestinal Mucosal Protection

Cancer patients undergoing therapeutic radiation routinely develop injury of the adjacent gastrointestinal (GI) tract mucosa due to treatment. To reduce radiation dose to critical GI structures including the rectum and oral mucosa, 3D-printed GI radioprotective devices composed of high-Z materials are generated from patient CT scans. In a radiation proctitis rat model, a significant reduction in crypt injury is demonstrated with the device compared to without (p < 0.0087). Optimal device placement for radiation attenuation is further confirmed in a swine model. Dosimetric modeling in oral cavity cancer patients demonstrates a 30% radiation dose reduction to the normal buccal mucosa and a 15.2% dose reduction in the rectum for prostate cancer patients with the radioprotectant material in place compared to without. Finally, it is found that the rectal radioprotectant device is more cost-effective compared to a hydrogel rectal spacer. Taken together, these data suggest that personalized radioprotectant devices may be used to reduce GI tissue injury in cancer patients undergoing therapeutic radiation.

Polyethylene glycol-based hydrogel rectal spacers for prostate brachytherapy: a systematic review with a focus on technique

INTRODUCTION

Radiation dose to the rectum in prostate brachytherapy (PBT) can be reduced by the use of polyethylene glycol (PEG) hydrogel spacers. This reduces the rate of rectal toxicity and allows dose escalation to the prostate. Our objectives were to provide an overview of technique for injection of a PEG hydrogel spacer, reduction in rectal dosimetry, gastrointestinal toxicity and potential complications.

METHODS

We systematically reviewed the role of PEG hydrogel spacers in PBT using the Cochrane and PRISMA methodology for all English-language articles from January 2013 to December 2019. Data was extracted for type of radiotherapy, number of patients, type of PEG-hydrogel used, mean prostate-rectum separation, rectal dosimetry, acute and late GI toxicity, procedure-related complications and the technique used for hydrogel insertion.

RESULTS

Nine studies (671 patients and 537 controls) met our inclusion criteria. Of these 4 used DuraSeal® and 5 used SpaceOAR®. The rectal spacing achieved varied between 7.7-16 mm. Failure of hydrogel insertion was seen only in 12 patients, mostly related to failure of hydrodissection in patients undergoing salvage PBT. Where reported, the rectal D2 cc was reduced by between 21.6 and 52.6% and the median rectal V75% cc was reduced by between 91.8-100%. Acute GI complications were mostly limited to grade 1 or 2 toxicity (n = 153, 33.7%) with low levels of grade 3 or 4 toxicity (n = 1, 0.22%). Procedure-related complications were limited to tenesmus (0.14%), rectal discomfort (1.19%), and bacterial prostatitis (0.44%).

CONCLUSIONS

PEG hydrogel spacers are safe to insert. Gel insertion is easy, fast and has a low rate of failure. These studies convincingly demonstrate a significant reduction in rectal dosimetry. Although the results of spacers in reducing rectal toxicity is promising, these need to be confirmed in prospective randomised trial.

Clinical effects of rectal retractor application in prostate cancer radiotherapy

Background: Radiation-induced rectal toxicities remain as a major risk during prostate radiotherapy. One approach to the reduction of rectal radiation dose is to physically increase the distance between the rectal wall and prostate. Therefore, the aim of this study was to evaluate whether the application of the rectal retractor (RR) can reduce rectal dose and toxicity in prostate cancer 3-dimensional conformal radiotherapy (3D-CRT).

Methods: Overall, 36 patients with localized prostate cancer were randomized into the 2 groups, 18 patients with RR in-place and 18 without RR. All patients underwent planning computed tomography (CT). Patients were treated with 70 Gy in 35 fractions of 3D-CRT. In the RR group, RR was used during cone-down 20 treatment fractions. Acute and late gastrointestinal (GI) toxicities were assessed using EORTC/RTOG scoring system weekly during radiotherapy, 3, and 12 months after treatment. Device-related events were recorded according to CTCAE version 4.0. Patient characteristics, cancer differences, and dosimetric data for the RR and non-RR groups were compared using a Man-Whitney U test for continuous variables, and Fisher exact test for categorical data. The EORTC/RTOG scores for the 2 groups were compared using Fisher exact test. A P value <0.05 was considered statistically significant.

Results: A RR significantly reduced mean dose (Dmean) to the rectum as well as rectal volume receiving 50% to 95% (V50-95%) of prescribed dose. The absolute reduction of rectal Dmean was 10.3 Gy. There was no statistically significant difference in acute GI toxicity between groups during treatment or at 3 months. At 12 months, 2 patients in the RR group and 9 in the control group experienced late grade ≥ 1 GI toxicity (p=0.027). No patients in the RR group reported late grade ≥ 2 GI toxicity, whereas 3 patients in the control group experienced late grade 2 GI toxicity. In the RR group, 6 patients reported grade 1 rectal discomfort and pain according to CTCAE version 4.0.

Conclusion: The application of the RR showed a significant rectum sparing effect, resulting in substantially reducing late GI toxicity.

Safety and Efficacy of Virtual Prostatectomy With Single-Dose Radiotherapy in Patients With Intermediate-Risk Prostate Cancer: Results From the PROSINT Phase 2 Randomized Clinical Trial

Importance

Ultra-high single-dose radiotherapy (SDRT) represents a potential alternative to curative extreme hypofractionated stereotactic body radiotherapy (SBRT) in organ-confined prostate cancer.

Objective

To compare toxic effect profiles, prostate-specific antigen (PSA) responses, and quality-of-life end points of SDRT vs extreme hypofractionated SBRT.

Design, Setting, and Participants

The PROSINT single-institution phase 2 randomized clinical trial accrued, between September 2015 and January 2017, 30 participants with intermediate-risk prostate cancer to receive SDRT or extreme hypofractionated SBRT. Androgen deprivation therapy was not permitted. Data were analyzed from March to May 2020.

Interventions

Patients were randomized in a 1:1 ratio to receive 5 × 9 Gy SBRT (control arm) or 24 Gy SDRT (test arm).

Main Outcomes and Measures

The primary end point was toxic effects; the secondary end points were PSA response, PSA relapse-free survival, and patient-reported quality of life measured with the International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index Composite (EPIC)-26 questionnaires.

Results

A total of 30 men were randomized; median (interquartile range) age was 66.3 (61.2-69.9) and 73.6 (64.7-75.9) years for the SBRT and SDRT arms, respectively. Time to appearance and duration of acute and late toxic effects were similar in the 2 trial arms. Cumulative late actuarial urinary toxic effects did not differ for grade 1 (hazard ratio [HR], 0.41; 90% CI, 0.13-1.27) and grade 2 or greater (HR, 1.07; 90% CI, 0.21-5.57). Actuarial grade 1 late gastrointestinal (GI) toxic effects were comparable (HR, 0.37; 90% CI, 0.07-1.94) and there were no grade 2 or greater late GI toxic effects. Declines in PSA level to less than 0.5 ng/mL occurred by 36 months in both study arms. No PSA relapses occurred in favorable intermediate-risk disease, while in the unfavorable category, the actuarial 4-year PSA relapse-free survival values were 75.0% vs 64.0% (HR, 0.76; 90% CI, 0.17-3.31) for SBRT vs SDRT, respectively. The EPIC-26 median summary scores for the genitourinary and GI domains dropped transiently at 1 month and returned to pretreatment scores by 3 months in both arms. The IPSS-derived transient late urinary flare symptoms occurred at 9 to 18 months in 20% (90% CI, 3%-37%) of patients receiving SDRT.

Conclusions and Relevance

In this randomized clinical trial among patients with intermediate-risk prostate cancer, SDRT was safe and associated with low toxicity, and the tumor control and quality-of-life end points closely match the SBRT arm outcomes. Further studies are encouraged to explore indications for SDRT in the cure of prostate cancer.

Trial Registration

ClinicalTrials.gov Identifier: NCT02570919.

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

SpaceOAR, an absorbable polyethylene glycol hydrogel, increases the space between the prostate and rectum to reduce the radiation received by the rectum during prostate cancer radiation therapy. The objective of this systematic review was to evaluate controlled studies on the dosimetric and clinical outcomes of SpaceOAR in men undergoing external beam radiation therapy for localized prostate cancer. Eight studies were included in the review. All of the studies showed SpaceOAR to reduce the radiation dose volume to the rectum over numerous dosimetry levels. Of the four studies that assessed toxicity, one reported SpaceOAR to significantly decrease acute Grade 1 diarrhoea and two reported SpaceOAR to significantly decrease late Grade 1 and Grade ≥2 rectal toxicities. Two studies assessed cumulative incidence of toxicity at 3 years in which one reported SpaceOAR to significantly decrease urinary incontinence and Grade ≥1 and Grade ≥2 rectal toxicities, and the other reported SpaceOAR to significantly decrease Grade 1 diarrhoea and Grade 2 proctitis. Moreover, one study reported that fewer SpaceOAR patients experienced 10-point declines in bowel quality of life at 3 years, but another study reported no significant difference in 10-point declines in bowel quality of life between the SpaceOAR and control groups at 5 years. With the current research available, SpaceOAR may be beneficial to those who did not meet the standard rectal dose-volume criteria, have higher risk factors of developing rectal toxicities post-radiation, or wish to decrease the length and costs of radiotherapy by increasing the dose of radiation per fraction.

Employing hydrogels in tissue engineering approaches to boost conventional cancer-based research and therapies

Cancer is a complicated disease that involves the efforts of researchers to introduce and investigate novel successful treatments. Traditional cancer therapy approaches, especially chemotherapy, are prone to possible systemic side effects, such as the dysfunction of liver or kidney, neurological side effects and a decrease of bone marrow activity. Hydrogels, along with tissue engineering techniques, provide tremendous potential for scientists to overcome these issues through the release of drugs at the site of tumor. Hydrogels demonstrated competency as potent and stimulus-sensitive drug delivery systems for tumor removal, which is attributed to their unique features, including high water content, biocompatibility, and biodegradability. In addition, hydrogels have gained more attention as 3D models for easier and faster screening of cancer and tumors due to their potential in mimicking the extracellular matrix. Hydrogels as a reservoir can be loaded by an effective dosage of chemotherapeutic agents, and then deliver them to targets. In comparison to conventional procedures, hydrogels considerably decreased the total cost, duration of research, and treatment time. This study provides a general look into the potential role of hydrogels as a powerful tool to augment cancer studies for better analysis of cancerous cell functions, cell survival, angiogenesis, metastasis, and drug screening. Moreover, the upstanding application of drug delivery systems related to the hydrogel in order to sustain the release of desired drugs in the tumor cell-site were explored.

Dosimetric feasibility of neurovascular bundle-sparing stereotactic body radiotherapy with periprostatic hydrogel spacer for localized prostate cancer to preserve erectile function

Objective:

We aim to test the hypothesis that neurovascular bundle (NVB) displacement by rectal hydrogel spacer combined with NVB delineation as an organ at risk (OAR) is a feasible method for NVB-sparing stereotactic body radiotherapy.

Methods:

Thirty-five men with low- and intermediate-risk prostate cancer who underwent rectal hydrogel spacer placement and pre-, post-spacer prostate MRI studies were treated with prostate SBRT (36.25 Gy in five fractions). A prostate radiologist contoured the NVB on both the pre- and post-spacer T2W MRI sequences that were then registered to the CT simulation scan for NVB-sparing radiation treatment planning. Three SBRT treatment plans were developed for each patient: (1) no NVB sparing, (2) NVB-sparing using pre-spacer MRI, and (3) NVB-sparing using post-spacer MRI. NVB dose constraints include maximum dose 36.25 Gy (100%), V34.4 Gy (95% of dose) <60%, V32Gy <70%, V28Gy <90%.

Results:

Rectal hydrogel spacer placement shifted NVB contours an average of 3.1 ± 3.4 mm away from the prostate, resulting in a 10% decrease in NVB V34.4 Gy in non-NVB-sparing plans (p < 0.01). NVB-sparing treatment planning reduced the NVB V34.4 by 16% without the spacer (p < 0.01) and 25% with spacer (p < 0.001). NVB-sparing did not compromise PTV coverage and OAR endpoints.

Conclusions:

NVB-sparing SBRT with rectal hydrogel spacer significantly reduces the volume of NVB treated with high-dose radiation. Rectal spacer contributes to this effect through a dosimetrically meaningful displacement of the NVB that may significantly reduce RiED. These results suggest that NVB-sparing SBRT warrants further clinical evaluation.

Advances in knowledge:

This is a feasibility study showing that the periprostatic NVBs can be spared high doses of radiation during prostate SBRT using a hydrogel spacer and nerve-sparing treatment planning.

SpaceOAR Hydrogel Present 32 Weeks After Instillation Prevents Neobladder Creation in Patient Undergoing Robot-Assisted Laparoscopic Radical Cystoprostatectomy

Background: The injection of hydrogel in between the anterior rectal wall and prostate protects the rectum from the radiation field in men undergoing radiotherapy for prostate cancer. Multicenter prospective trials have demonstrated safety of the material, and that liquefication and reabsorption of the material occur roughly 12 weeks after injection. Other studies have noted the presence of the hydrogel up to 24 weeks after injection and documented significant complications with its use. In this study we discuss a patient in whom hydrogel was discovered in the anterior rectal wall who was undergoing radical cystoprostatectomy 32 weeks after injection, and how this precluded creation of a neobladder. Case Presentation: A 64-year-old Caucasian man with a history of diabetes mellitus and hypertension was diagnosed with unfavorable intermediate risk prostate cancer. He underwent injection of hydrogel followed by radiotherapy. He subsequently developed hematuria and carcinoma in situ and high grade T1 nonmuscle invasive bladder cancer were diagnosed. Thirty-two weeks later, he underwent robot-assisted radical cystoprostatectomy. The patient was originally planned for neobladder creation but intraoperative findings of persistent hydrogel in between rectum and prostate precluded this reconstruction and necessitated construction of an ileal conduit. Conclusion: Urologists should be aware of the fact that SpaceOAR hydrogel can persist beyond the expected 12- to 24-week dissolution period. In a patient who requires a radical cystectomy, the persistent presence of that gel may preclude the creation of a neobladder. Preoperative imaging to identify persistence vs dissolution of the gel would facilitate better preoperative patient counseling.

Utilization of Iodinated SpaceOAR Vue™ During Robotic Prostate Stereotactic Body Radiation Therapy (SBRT) to Identify the Rectal-Prostate Interface and Spare the Rectum: A Case Report

We describe the utilization of SpaceOAR Vue™, a new iodinated rectal spacer, during Robotic Stereotactic Body Radiation Therapy (SBRT) for a Prostate Cancer Patient with a contraindication to Magnetic Resonance Imaging. A 69-year-old Caucasian male presented with unfavorable intermediate risk prostate cancer and elected to undergo SBRT. His medical history was significant for atrial fibrillation on Rivaroxaban with a pacemaker. He was felt to be at increased risk of radiation proctitis following SBRT due to the inability to accurately contour the anterior rectal wall at the prostate apex without a treatment planning MRI and an increased risk of late rectal bleeding due to prescribed anticoagulants. In this case report, we discuss the technical aspects of appropriate placement and treatment planning for utilizing SpaceOAR Vue™ with Robotic SBRT.

Rectourethral fistula following SpaceOAR gel placement for prostate cancer radiotherapy: A rare complication

After undergoing a SpaceOAR® gel placement prior to planned radiotherapy for Gleason 4 + 4 prostate cancer, a 70-year-old male experienced severe right buttock pain and urine passing from his rectum. A colonoscopy and follow-up pelvic MRI demonstrated a large rectourethral fistula. The fistula was treated surgically with a robot-assisted radical prostatectomy, primary rectal repair, omental flap and diverting loop ileostomy. Pathology demonstrated extensive treatment effect with no residual prostate cancer. This is the first case study of a rectourethral fistula attributable to SpaceOAR® gel placement.

Smart nanotheranostic hydrogels for on-demand cancer management

Theranostics is a revolution in cancer therapy. Hydrogels have many implications as a drug delivery vehicle and theranostics hydrogels could be a model nanotherapeutic for simultaneous cancer diagnosis and treatment.

Spontaneous remission of rectal ulcer associated with SpaceOAR® hydrogel insertion in radiotherapy for prostate cancer

INTRODUCTION

The SpaceOAR® hydrogel system separates the prostate and rectum to reduce rectal irradiation during prostate radiotherapy. However, it could induce rectal toxicity.

CASE PRESENTATION

A 75-year-old man with localized prostate cancer underwent external beam radiotherapy with the use of SpaceOAR® System. However, postimplant magnetic resonance imaging showed hydrogel infiltration to the rectum. Three months after implantation, he complained of bowel symptoms, including bloody stool. Colonofiberscopy and computed tomography revealed a rectal ulcer associated with SpaceOAR® hydrogel insertion. He was treated with fasting, fluid replacement, and blood transfusion. One year after implantation, complete healing was confirmed during outpatient follow-up.

CONCLUSION

To our knowledge, this is the first report of a rectal ulcer associated with SpaceOAR® hydrogel insertion assessed by magnetic resonance imaging beforehand. Postimplant magnetic resonance imaging evaluation might be a useful follow-up tool in such cases.

Modelling the lifetime cost-effectiveness of radical prostatectomy, radiotherapy and active monitoring for men with clinically localised prostate cancer from median 10-year outcomes in the ProtecT randomised trial

BACKGROUND

Optimal management strategies for clinically localised prostate cancer are debated. Using median 10-year data from the largest randomised controlled trial to date (ProtecT), the lifetime cost-effectiveness of three major treatments (radical radiotherapy, radical prostatectomy and active monitoring) was explored according to age and risk subgroups.

METHODS

A decision-analytic (Markov) model was developed and informed by clinical input. The economic evaluation adopted a UK NHS perspective and the outcome was cost per Quality-Adjusted Life Year (QALY) gained (reported in UK£), estimated using EQ-5D-3L.

RESULTS

Costs and QALYs extrapolated over the lifetime were mostly similar between the three randomised strategies and their subgroups, but with some important differences. Across all analyses, active monitoring was associated with higher costs, probably associated with higher rates of metastatic disease and changes to radical treatments. When comparing the value of the strategies (QALY gains and costs) in monetary terms, for both low-risk prostate cancer subgroups, radiotherapy generated the greatest net monetary benefit (£293,446 [95% CI £282,811 to £299,451] by D'Amico and £292,736 [95% CI £284,074 to £297,719] by Grade group 1). However, the sensitivity analysis highlighted uncertainty in the finding when stratified by Grade group, as radiotherapy had 53% probability of cost-effectiveness and prostatectomy had 43%. In intermediate/high risk groups, using D'Amico and Grade group > = 2, prostatectomy generated the greatest net monetary benefit (£275,977 [95% CI £258,630 to £285,474] by D'Amico and £271,933 [95% CI £237,864 to £287,784] by Grade group). This finding was supported by the sensitivity analysis. Prostatectomy had the greatest net benefit (£290,487 [95% CI £280,781 to £296,281]) for men younger than 65 and radical radiotherapy (£201,311 [95% CI £195,161 to £205,049]) for men older than 65, but sensitivity analysis showed considerable uncertainty in both findings.

CONCLUSION

Over the lifetime, extrapolating from the ProtecT trial, radical radiotherapy and prostatectomy appeared to be cost-effective for low risk prostate cancer, and radical prostatectomy for intermediate/high risk prostate cancer, but there was uncertainty in some estimates. Longer ProtecT trial follow-up is required to reduce uncertainty in the model.

TRIAL REGISTRATION

Current Controlled Trials number, ISRCTN20141297: http://isrctn.org (14/10/2002); ClinicalTrials.gov number, NCT02044172: http://www.clinicaltrials.gov (23/01/2014).

Planning With Patient-Specific Rectal Sub-Region Constraints Decreases Probability of Toxicity in Prostate Cancer Radiotherapy

Background: A rectal sub-region (SRR) has been previously identified by voxel-wise analysis in the inferior-anterior part of the rectum as highly predictive of rectal bleeding (RB) in prostate cancer radiotherapy. Translating the SRR to patient-specific radiotherapy planning is challenging as new constraints have to be defined. A recent geometry-based model proposed to optimize the planning by determining the achievable mean doses (AMDs) to the organs at risk (OARs), taking into account the overlap between the planning target volume (PTV) and OAR. The aim of this study was to quantify the SRR dose sparing by using the AMD model in the planning, while preserving the dose to the prostate.

Material and Methods: Three-dimensional volumetric modulated arc therapy (VMAT) planning dose distributions for 60 patients were computed following four different strategies, delivering 78 Gy to the prostate, while meeting the genitourinary group dose constraints to the OAR: (i) a standard plan corresponding to the standard practice for rectum sparing (STD_pl), (ii) a plan adding constraints to SRR (SRR_pl), (iii) a plan using the AMD model applied to the rectum only (AMD_RECT_pl), and (iv) a final plan using the AMD model applied to both the rectum and the SRR (AMD_RECT_SRR_pl). After PTV dose normalization, plans were compared with regard to dose distributions, quality, and estimated risk of RB using a normal tissue complication probability model.

Results: AMD_RECT_SRR_pl showed the largest SRR dose sparing, with significant mean dose reductions of 7.7, 3, and 2.3 Gy, with respect to the STD_pl, SRR_pl, and AMD_RECT_pl, respectively. AMD_RECT_SRR_pl also decreased the mean rectal dose by 3.6 Gy relative to STD_pl and by 3.3 Gy relative to SRR_pl. The absolute risk of grade ≥1 RB decreased from 22.8% using STD_pl planning to 17.6% using AMD_RECT_SRR_pl considering SRR volume. AMD_RECT_SRR_pl plans, however, showed slightly less dose homogeneity and significant increase of the number of monitor units, compared to the three other strategies.

Conclusion: Compared to a standard prostate planning, applying dose constraints to a patient-specific SRR by using the achievable mean dose model decreased the mean dose by 7.7 Gy to the SRR and may decrease the relative risk of RB by 22%.