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

Complications and Influential Perioperative Factors Associated with SpaceOAR Hydrogel Placement

Objective

To examine one academic institution's experiences with SpaceOAR placement, its associated complications, and periprocedural characteristics that affect outcomes for the purpose of quality improvement.

Materials and Methods

We conducted a retrospective review of 233 patients who received SpaceOAR from four surgeons and one radiation oncologist between 2018 and 2021. Variables such as demographics, oncologic parameters, radiation plan, and radiographic assessment of hydrogel placement were recorded. The Charlson Comorbidity Index (CCI) was used to assess comorbidity risk. Mann-Whitney and Fisher's exact tests were performed to compare patients with and without complications.

Results

Of the 233 patients who received SpaceOAR, 24 (10.3%) experienced toxicity. All complications were Clavien I or II, such as pelvic pain postplacement, pelvic fullness, bleeding, and lower urinary tract symptoms. 16 patients (6.9%) had some portion of the hydrogel injected into the rectal wall, but it was never clinically significant. The average CCI was 3.2 ± 0.95 for patients who experienced complications; the average CCI was 3.6 ± 1.6 (p=0.48) in the group without complications. Of the physicians with higher procedure volumes, Physician #1 had the highest rate of patient-reported complications at 11 out of 68 (16.2%) and Physician #2 had the lowest rate of complications at 4 out of 96 placements (4.2%). Multivariate analysis found that patients who had received hormone therapy previously had less odds of reporting complications after SpaceOAR placement.

Conclusions

The listed attending on the procedure had a significant correlation to complications with SpaceOAR placement on univariate analysis, and hormone therapy had some benefits to the tolerance for the procedure on multivariate analysis. Overall, the hydrogel placement was well tolerated with low incidence of mild and transient procedure-related toxicity.

Impact of Rectal Spacer on Toxicity Reduction in Men Treated With Proton Versus Photon Therapy

Purpose

Rectal toxicity after prostate cancer (PCa) radiation therapy (RT) may be greater with protons compared with photon intensity-modulated RT, perhaps due to lateral penumbra and end-of-range uncertainty. Rectal spacers (RSs) have been shown to mitigate RT-associated acute/late rectal toxicity in men treated with photons. The relative benefit of RS in men treated with protons versus photons is unknown. We hypothesize that RS will confer greater bowel toxicity benefits in PCa treated with protons versus photons.

Materials and Methods

We conducted a single institution, retrospective review of men receiving photon intensity-modulated RT or pencil-beam scanning proton RT for localized PCa. Four cohorts were compared: photon with or without RS, and proton with or without RS. Acute (<3 months), late (≥3 months), and most recent toxicity were compared among the 4 cohorts. The cumulative incidence of physician-reported grade 1 to 2 gastrointestinal (GI) toxicity (common terminology criteria for adverse events V5.0) was compared using χ2 or Fisher exact test. Patient-reported toxicity was evaluated using the International Prostate Expanded Prostate Composite Index-Clinical Practice and compared using linear mixed modeling.

Results

In total, 164 patients were eligible for analysis: 38 photons without RS, 50 photons with RS, 26 protons without RS, and 50 protons with RS. The median follow-up was 17.6 months. In proton patients, acute (6.12% vs 30.77%, P = .009) and most recent (4.26% vs 26.09%, P = .01) G1-2 GI toxicity was lower with versus without RS. In photon patients, there were no significant differences in toxicity with versus without RS. No significant differences in patient-reported outcomes were observed with versus without RS in photon or proton groups.

Conclusion

The rectal spacer was associated with lower G1-2 acute and most recent GI toxicity in men treated with protons; this difference was not observed in men treated with photons. While this study is limited by sample size, a relatively greater benefit of RS with proton versus photon therapy was observed.

An optimal method of hydrogel spacer insertion for stereotactic body radiation therapy of prostate cancer

PURPOSE

This study aimed to explore an ideal method for hydrogel spacer insertion by analyzing the efficacy and safety of our originally developed apex expansion method.

MATERIALS AND METHODS

Overall, 100 patients with low- and intermediate-risk localized prostate cancer treated with stereotactic body radiation therapy were included. A hydrogel spacer was inserted in 64 and 36 patients using the conventional and apex expansion methods, respectively. For dosimetry, we trisected the rectum into the upper rectum, middle rectum, and lower rectum on the sagittal section of magnetic resonance imaging. We compared the dose to each part of the rectum between the two methods using dose-volume histograms. Genitourinary and gastrointestinal toxicity assessments were conducted until 3 months of follow-up.

RESULTS

The whole rectal dose in the apex expansion method group was lower than that in the conventional method group, which was significant in all dose regions (V5-V35). Similarly, in the apex expansion method group, the dose to the middle rectum was lower in the low- to high-dose region (V10-V35), and the dose to the lower rectum was lower in the middle- to high-dose region (V15-35). No Grade ≥ 3 toxicity or procedure-related complications were observed. Additionally, Grade 2 genitourinary and gastrointestinal toxicities during the treatment showed no significant differences between the two methods.

CONCLUSION

The apex expansion method may be safe and effective in achieving a more efficient rectal dose reduction by expanding the anterior perirectal space in the prostatic apex area.

Quality rectal hydrogel placement allows for gel-enabled dose-escalated EBRT (GEDE-EBRT) without rectal interference in prostate cancer

Multiple trials have shown that dose-escalation of radiation for prostate cancer provides a biochemical progression-free survival benefit (bPFS); however, rectal constraints are often limiting. In this dosimetric study, we hypothesized that a well-placed rectal hydrogel (RH) would permit improved dose-escalation and target coverage. We selected patients with good-quality RH and created plans with and without RH, prescribing 70 Gy in 28 fractions to the prostate and proximal seminal vesicles (PSV), and a peripheral zone (PZ) boost to 84 Gy, 98 Gy, or 112 Gy. We then compared plans with and without RH, prescribing a 112 Gy boost to 1 to 2 cm simulated dominant intraprostatic lesions (DIL). In the 18 plans created with a PZ boost, the PTV_boost D95% was higher in RH plans compared to non-RH plans (median 98.5 Gy vs 75.53 Gy, p < 0.01). The PSV planning target volume (PTV_PSV) D95% was also marginally higher with RH (71.87 Gy vs 71.04 Gy, p < 0.01). All rectal metrics were improved with RH. For the 32 plans created for simulated DILs treated to 112 Gy, the PTV_boost coverage (median D95% 112.48 Gy vs 102.63 Gy, p < 0.01) and rectal metrics were improved with RH. Four non-RH plans with at least a 4 mm rectal-PTV_boost gap achieved D95% > 98% of the prescription dose for the PTV_boost. Our study showed that placement of a high-quality RH allowed for GEDE-EBRT up to 112 Gy in 28 fractions (EQD2 160 Gy with α/β = 2.5). This concept should be tested prospectively, particularly to assess for increases in nonrectal toxicities.

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.

Expanding access to rectal spacers in the United Kingdom: an examination of current evidence and an early review of data from a single institution

Background:

Prostate cancer is a common malignancy with rising incidence in Western countries such as the United Kingdom. In localised disease there are a variety of curative treatment modalities. Patients can be referred for surgery, or for a combination of hormonal therapies and radiotherapy (external beam radiotherapy or brachytherapy). Each treatment option comes with side effects and in the case of radiotherapy one potential complication is bowel toxicity from radiation exposure. New technologies are being developed to try and mitigate the side effects and long term morbidity of this treatment, and to expand access to radiotherapy for patients who may previously have been excluded (i.e those with inflammatory bowel disease). Rectal Spacers are absorbable polyethylene glycol hydrogels injected into the perirectal space. These position the anterior rectal wall away from the prostate, subsequently minimising radiation dose to the rectum. Rectal Spacers have been introduced to National Healthcare Service (NHS) practice as part of the Innovation and Technology Payment (ITP) programme, however, their use is now under review.

Methodology and Results:

In this editorial we conduct a narrative review of some of the available evidence for Rectal Spacers, discuss their utilization within the NHS and the barriers to their wider use. We also explore preliminary dosimetry and quality of life data for use of Rectal Spacers in our centre where we have been part of the NHS ITP programme. Dosimetry data and Quality of life questionnaires were gathered from 22 treated patients and 11 matched controls. This indicated lower radiation doses to the prostate in those treated with Rectal Spacers.

Conclusion:

Rectal Spacers are an effective method to reduce radiation dose to the prostate in men treated for localised prostate cancer, however, their use remains under review in the NHS and there are a variety of barriers to upscaling their use.

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

Purpose

Proton 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 Methods

This 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.

Results

From 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.

Conclusion

Early 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.

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.

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.

Exploratory Investigation of Dose-Linear Energy Transfer (LET) Volume Histogram (DLVH) for Adverse Events Study in Intensity Modulated Proton Therapy (IMPT)

PURPOSE

We proposed a novel tool-a dose linear energy transfer (LET)-volume histogram (DLVH)-and performed an exploratory study to investigate rectal bleeding in prostate cancer treated with intensity modulated proton therapy.

METHODS AND MATERIALS

The DLVH was constructed with dose and LET as 2 axes, and the normalized volume of the structure was contoured in the dose-LET plane as isovolume lines. We defined the DLVH index, DLv%(d,l) (ie, v% of the structure) to have a dose of ≥d Gy and an LET of ≥l keV/μm, similar to the dose-volume histogram index Dv%. Nine patients with prostate cancer with rectal bleeding (Common Terminology Criteria for Adverse Events grade ≥2) were included as the adverse event group, and 48 patients with no complications were considered the control group. A P value map was constructed by comparison of the DLVH indices of all patients between the 2 groups using the Mann-Whitney U test. Dose-LET volume constraints (DLVCs) were derived based on the P value map with a manual selection procedure facilitated by Spearman's correlation tests. The obtained DLVCs were further cross-validated using a multivariate support vector machine (SVM)-based normal tissue complication probability (NTCP) model with an independent testing data set composed of 8 adverse event and 13 control patients.

RESULTS

We extracted 2 DLVC constraints. One DLVC was obtained, Vdose/LETboundary:2.5keVμmat 75 Gy to 3.2keVμmat8.65Gy <1.27% (DLVC1), revealing a high LET volume effect. The second DLVC, V(72.2Gy,0keVμm) < 2.23% (DVLC2), revealed a high dose volume effect. The SVM-based NTCP model with 2 DLVCs provided slightly superior performance than using dose only, with an area under the curve of 0.798 versus 0.779 for the testing data set.

CONCLUSIONS

Our results demonstrated the importance of rectal "hot spots" in both high LET (DLVC1) and high dose (DLVC2) in inducing rectal bleeding. The SVM-based NTCP model confirmed the derived DLVCs as good predictors for rectal bleeding when intensity modulated proton therapy is used to treat prostate cancer.

Transrectal Ultrasound Guided Hydrodistension - A New Surgical Way in Transgender Surgery

BACKGROUND

Creating the neovaginal canal in transwomen is one of the most delicate steps of Genital Gender Affirming Surgery (GGAS). Injury to the rectum is a rare but serious complication that can lead to further surgery and even creation of a colostomy.

AIM

Implementation of a novel hydrospacing technique (HST) based on transrectal ultrasound (TRUS)-guided hydrodistension.

METHODS

Between June 2018 and June 2020 54 transwomen received GGAS with HST. Immediately before GGAS transperineal hydrodistension was performed using a TSK-Supra-Needle (20 Gauge, 120 mm length), that was placed under direct TRUS-guided visual control between Denonvilliers' fascia and the anterior rectal wall. 40 - 60 ml normal saline were administered perineally to separate Denonvilliers' fascia from the anterior rectal wall to create a dissection of at least 20 mm. For better intraoperative visualization the hydrodissected space was also dyed using 2ml of methylenblue while retracting the needle. A retrospectively analysed, clinically and demographically comparable series of 84 transwomen who underwent GGAS between June 2016 and June 2018 served as control group. All 138 surgeries were performed by the same experienced surgeon.

OUTCOMES

The effect of the novel hydrospacing technique on neovaginal dimensions and operating time.

RESULTS

Patients in both groups did not differ in baseline patient characteristics such as age and body mass index (HST 35 vs 38 years in control group, P = .44 and body mass index 26 vs 25 kg/m², P = .73). Vaginal depth and width were significantly larger in the HST subgroup as compared to controls (14.4 cm vs 13.5 cm, P = .01 and 4.2 cm vs 3.8 cm, P < .001). No statistically significant difference occurred in intraoperative rectal injury (n = 0 in HST group, n = 2 in control group, P = .26). Median total OR-time was comparable for GGAS including HST before vaginoplasty to standard technique (211 minutes for HST vs 218 minutes; P = 0.19).

CLINICAL IMPLICATIONS

The proposed additional surgical step during GGAS is minimally invasive and safe, simplifies GGAS and potentially helps to avoid complications such as rectal injury.

STRENGTH & LIMITATIONS

Single-surgeon series, limited follow-up time and no prospective randomization.

CONCLUSION

HST is a safe and feasible procedure, which facilitates a safe preparation of the neovaginal canal during male to female GGAS. Panic A, Rahmani N, Kaspar C, et al. Transrectal Ultrasound Guided Hydrodistension - A New Surgical Way in Transgender Surgery. J Sex Med 2021;18:1135-1141.

SpaceOAR Hydrogel Spacer for Reducing Radiation Toxicity During Radiotherapy for Prostate Cancer. A Systematic Review

OBJECTIVE

To evaluate the association between SpaceOAR and radiation dosing, toxicity and quality-of-life vs no spacer across all radiotherapy modalities for prostate cancer.

METHODS

A systematic search of the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase was performed from database inception through May 2020. Two reviewers independently screened titles/abstracts and full papers. Data extraction was performed, and quality assessed by 1 reviewer and checked by a second, using a third reviewer as required. The synthesis was narrative.

RESULTS

19 studies (3,622 patients) were included (only 1 randomized controlled trial, in image-guided intensity-modulated radiotherapy (IG-IMRT), 18 comparatives non-randomized controlled trials in external-beam radiotherapy (EBRT), brachytherapy, and combinations thereof). No hypofractionation studies were found. Regardless of radiotherapy type, SpaceOAR significantly reduced rectal radiation dose (eg, V40 average difference -6.1% in high dose-rate brachytherapy plus IG-IMRT to -9.1% in IG-IMRT) and reduced gastrointestinal and genitourinary toxicities (eg, late gastrointestinal toxicity 1% vs 6% (P = .01), late genitourinary toxicity of 15% vs 32% (P < .001) in stereotactic body radiotherapy). Improvements were observed in most Expanded Prostate Cancer Index Composite quality-of-life domains (eg, bowel function score decrease at 3 and 6 months: Average change of zero vs -6.25 and -3.57 respectively in low dose-rate brachytherapy plus EBRT).

CONCLUSION

The randomized controlled trial in IG-IMRT demonstrated that SpaceOAR reduces rectal radiation dose and late gastrointestinal and genitourinary toxicities, with urinary, bowel, and sexual quality-of-life improvement. These advantages were verified in observational studies in various radiotherapy types. Further research is required in hypofractionation.

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.