LDR Brachytherapy Research Articles

Friday, July 12, 20241:30 PM - 2:45 PM PL01 Presentation Time: 1:30 PM: A Randomized Comparison of LDR or HDR Brachytherapy Boost Combined with Pelvic External Beam Radiation for Unfavorable Intermediate or High-Risk Prostate Cancer. Efficacy Results at Median 6 Years Follow Up

Friday, July 12, 20241:30 PM - 2:45 PM PL01 Presentation Time: 1:30 PM: A Randomized Comparison of LDR or HDR Brachytherapy Boost Combined with Pelvic External Beam Radiation for Unfavorable Intermediate or High-Risk Prostate Cancer. Efficacy Results at Median 6 Years Follow Up

PSOR09 Presentation Time: 12:10 PM: Initial Clinical Outcomes of a Phase II Trial of Focal Salvage LDR Brachytherapy for Local Recurrence of Prostate Cancer after External Beam Radiation Therapy

PSOR09 Presentation Time: 12:10 PM: Initial Clinical Outcomes of a Phase II Trial of Focal Salvage LDR Brachytherapy for Local Recurrence of Prostate Cancer after External Beam Radiation Therapy

PO0429: Initial Experiences from a Newly Established Prostate LDR Brachytherapy Program in a Developing Country

PO0429: Initial Experiences from a Newly Established Prostate LDR Brachytherapy Program in a Developing Country

PO0417: Feasibility of Balloon Rectal Spacer Implementation in HDR and LDR Brachytherapy for Prostate Cancer Treatment

PO0417: Feasibility of Balloon Rectal Spacer Implementation in HDR and LDR Brachytherapy for Prostate Cancer Treatment

69 A Randomized Comparison of LDR or HDR Brachytherapy Boost Combined with Pelvic External Beam Radiation for Unfavourable Intermediate or High-Risk Prostate Cancer: Efficacy Results at Median 6 Years Follow Up

69 A Randomized Comparison of LDR or HDR Brachytherapy Boost Combined with Pelvic External Beam Radiation for Unfavourable Intermediate or High-Risk Prostate Cancer: Efficacy Results at Median 6 Years Follow Up

Optimized needle configuration for operational seed (ONCOSEED) efficiency and deployment for prostate seed implants

Due to anatomical changes between pre-planning and implantation, there exists a need for tools that can streamline the adjustment of needle and seed configurations in low dose rate brachytherapy for prostate cancer. Specifically, upon taking a second ultrasound on the day of treatment, the distribution of seeds and needles will differ drastically from the original plan. Clinics that employ this method must then spend time and resources to generate a workflow to manipulate the original configuration to the new configuration. ONCOSEED extracts data from VariSeed treatment plans, calculating a labor score (LScore) to optimize adjustments to needle configurations. A case study of three simulated VariSeed treatment plans was used to compare the ONCOSEED software to the manual method of generating a workflow. In the same method that was used at the authors’ clinic, several assistants annotated by hand the original plan to convert it to the new plan. The time taken to do so was recorded and compared to the runtime of the software when generating a workflow for the same plan. Results showed that ONCOSEED was on average 28 times faster than generating a workflow by hand. ONCOSEED enhances the efficiency of seed replacement in LDR brachytherapy, promoting the adoption of adaptive brachytherapy practices.

Comparison of perioperative and subacute postoperative complications between LDR and HDR monotherapy brachytherapy for prostate cancer

We aim to investigate perioperative and subacute postoperative complications in patients undergoing LDR or HDR monotherapy for prostate cancer. We hypothesize a low rate of complications, and a favorable toxicity profile in patients treated with HDR compared to LDR. A prospectively collected institutional database was queried for patients treated with HDR or LDR prostate monotherapy between 1998 and 2021. Toxicities were determined per CTCAE. Claims based billing codes were obtained to identify additional events. Events occurring within 4 months of treatment were defined as perioperative or subacute postoperative complications. 759 patients were identified, 446 received LDR with 125I, and 313 received HDR with 192Ir. HDR patients had higher risk features: 75.7% with Gleason score 7+ versus 2.4% of LDR, and 16% with initial PSA 10+ ng/mL versus 2.7% of LDR. Toxicities were mild with the most common being grade 1 GU frequency and nocturia at ∼50%. HDR patients had significantly less grade 2 dysuria (2.6% vs. 9.0%), frequency (4.8% vs. 9.4%), hematuria (1.0% vs. 5.2%), nocturia (3.8% vs. 9.4%), and urinary obstructive symptoms (7.3% vs. 11.2%), all statistically significant. 11 (1.4%) patients had infection requiring antibiotics: 8 (1.8%) from the LDR group and 3 (1%) from the HDR group. Cardiopulmonary events were low at <2% overall, without difference between HDR and LDR. Overall toxicity rates support the safety of prostate brachytherapy. HDR monotherapy is associated with significantly less perioperative and subacute postoperative GU events when compared to LDR monotherapy. Cardiopulmonary events were equally rare in both groups.

2370: Is there a link between the dose to prostate sectors in LDR brachytherapy and biochemical outcomes?

2370: Is there a link between the dose to prostate sectors in LDR brachytherapy and biochemical outcomes?

1123: Early results of LDR brachytherapy 108 Gy and ultrahypofractionated 5*5 Gy SBRT for prostate cancer

1123: Early results of LDR brachytherapy 108 Gy and ultrahypofractionated 5*5 Gy SBRT for prostate cancer

Net survival of men with localized prostate cancer after LDR brachytherapy

OBJECTIVESTo compare survival of patients who received LDR prostate brachytherapy relative to that of peers in the general population of England, UK. PATIENTS AND METHODSNet survival was estimated for 2472 cases treated between 2002 and 2016 using population-based analysis guidelines. Life tables adjusted for social deprivation in England from the Office for National Statistics were used to match patients by affluence based on their postcode. RESULTSThe median (range) age at time of brachytherapy was 66 (55–84) years, 84% resided in Southeast England, 51% under an index of deprivation quintile 5 (most affluent), 55% were clinical stage T1 and the remainder T2. Death from any cause occurred in 270 patients at a median (range) of 7 (1–17) years postimplant.Five and 10-year estimates (95% CI) of overall survival were 96% (95–97) and 90% (89–92), and net survival 103% (102–104) and 109% (107–110) respectively. The net survival remained above 100% in all age-at-treatment and clinical stage groups. CONCLUSIONNet survival above 100% indicates patients survive longer than the matched general population. The study shows for the first time the net survival of patients treated with a radical therapy for localized prostate cancer in England. The impact of treatment choice on the long-term net survival advantage requires further investigation.

Focal brachytherapy as definitive treatment for localized prostate cancer: A systematic review and meta-analysis

PURPOSEIn this systematic review and meta-analysis, we describe the oncologic and toxicity outcomes of definitive focal brachytherapy for prostate cancer. METHODS AND MATERIALSA PROSPERO registered study (CRD42023410170) was conducted following the Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) guidelines. PubMed, Embase, and The Cochrane Library were searched for studies between 2000 and 2022. Two authors independently performed the initial search. Biochemical recurrence-free survival (bRFS) was defined as the primary endpoint for the meta-analysis. Generalized linear mixed-effects models were conducted to calculate effect size and quantify heterogeneity. We also describe the side effects and local recurrence patterns of focal brachytherapy. RESULTSTen studies were identified and included 315 patients treated using focal brachytherapy as a definitive treatment. Mean (SD) age was 67.65 (7.9) years and mean (SD) PSA was 7.15 (2.7) ng/mL. Most patients (n = 236, 75%) underwent LDR Brachytherapy and 25% received HDR brachytherapy. Among the participants, 147 (46.5%) had a Gleason score ≤6, and 169 (53.5%) had a Gleason score ≥7. Only 11 (3.5%) patients received ADT. Overall, bRFS rate at median follow-up 4 years (Range: 1–6.42 years) was 91% (95% confidence interval [CI], 82–95%). Acute Grade ≤ 2 GU and GI toxicities were reported in 22 (7%) and 11 (3.5%) patients, respectively. Late Grade ≤ 2 GU and GI toxicity were reported in 6 (2%) and 14 (4.4%) patients, respectively. One case of prostate hemorrhage due to improper foley removal was noted but otherwise no acute or late Grade 3 or higher GI or GU toxicity related to radiotherapy was reported. CONCLUSIONOverall, definitive focal brachytherapy has a favorable toxicity profile. Oncologic outcomes are yet to mature. The evidence is limited by the small number of studies with low patients’ number, across study heterogeneity, and possibility of publication bias.

Alterations of Sexual and Erectile Functions after Brachytherapy for Prostate Cancer Based on Patient-Reported Questionnaires.

The aim of the study was to compare the side effects of high-dose-rate brachytherapy (HDRBT) and low-dose-rate brachytherapy (LDRBT), with a particular focus on the effects on sexual functions and sexual well-being (PROMOBRA study, NCT02258087). Localized low-risk and low-intermediate-risk prostate cancer patients were treated with mono LDR (N = 123, 145 Gy dose) or mono HDR brachytherapy (N = 117, 19/21 Gy). Prior to the treatment and during follow-up (at 3, 6, 9, 12, 18, and 24 months after treatment, and then annually after two years), patients completed patient-reported outcome measurement (PROM) questionnaires EORTC QLQ-PR-25, International Index of Erectile Function (IIEF), and IIEF-5 (SHIM). We compared the patients in different group breakdowns (HDR vs. LDR, hormone naïve and hormone-receiving HDR vs. LDR, hormone naïve and hormone-receiving patients in general, and 19 Gy HDR vs. 21 Gy HDR). In the hormone-naive LDR group, erectile function, orgasm function, sexual desire, satisfaction with intercourse, and overall satisfaction functions significantly decreased compared to baseline throughout the whole follow-up period. However, there were significant decreases in function at a maximum of three time points after HDR therapy without hormone therapy. In hormone-receiving patients, the orgasm function was significantly better in the HDR group at multiple time points compared to the baseline, and sexual desire improved at four time points. According to our results, both LDRBT and HDRBT can be safely administered to patients with localized prostate cancer. In hormone-naive patients, the HDR group showed only recovering decreases in sexual functions, while the LDR group showed a lasting decline in multiple areas. Thus, HDR appears to be more advantageous to hormone-naive patients.

Optimization and experimental characterization of the innovative thermo-brachytherapy seed for prostate cancer treatment.

Adjuvant administration of hyperthermia (HT) with radiation therapy in the treatment of cancer has been extensively studied in the past five decades. Concurrent use of the two modalities leads to both complementary and synergetic enhancements in tumor management, but presents a practical challenge. Their simultaneous administration using the same implantable thermo-brachytherapy (TB) seed source has been established theoretically through magnetically mediated heat induction with ferromagnetic materials. Careful consideration, however, showed that regular ferromagnetic alloys lack the required conductivity to generate enough power through eddy current to overcome heat dissipation due to blood perfusion at clinically measuredrates. We characterized the TB implant that combines a sealed radioactive source with a ferrimagnetic ceramic (ferrite) core, serving as a self-regulating HT source when placed in an alternating electromagnetic field. To increase the heat production and uniformity of temperature distribution the empty spacers between radioisotope seeds were replaced by hyperthermia-only (HT-only)seeds. The heat generation due to eddy currents circulating in the seed's thin metal shell, surrounding the core, depends drastically on the core permeability. We identified a soft ferrite material ( ) as the best candidate for the core, owing to its high permeability, the HT-range Curie temperature, adjustable through material composition, and a sharp Curie transition, leading to heat self-regulation, with no invasive thermometry required. The core permeability as a function of temperature was calculated based on measured resistor-inductor (RL) circuit parameters and material B-H curves. The thickness of the shell was optimized separately for TB and HT-only seeds, having slightly different dimensions. Heat generation was calculated using the power versus temperature approximation. Finally, the temperature distribution for a realistic prostate LDR brachytherapy plan was modeled with COMSOL Multiphysics for a set of blood perfusion rates found in theliterature. The small size of the investigated ferrite core samples resulted in demagnetization significantly decreasing the relative permeability from its intrinsic value of ∼5000 to about 11 in the range of magnetic field amplitude and frequency values relevant to HT. The power generated by the seed dropped sharply as the shell thickness deviated from the optimal value. The optimized TB and HT-only seeds generated 45 and 267 mW power, respectively, providing a HT source sufficient for >90% volume coverage even for the highest blood perfusion rates. The toxicity of the surrounding normal tissues was minimal due to the rapid temperature fall off within a few millimeters distance from aseed. The investigated TB and HT-only seed prototypes were shown to provide sufficient power for the concurrent administration of radiation and HT. In addition to being used as a source for both radiation and heat at the onset of cancer therapy, these implanted seeds would be available for treatment intensification in the setting of salvage brachytherapy for locally radiorecurrent disease, possibly as a sensitizer to systemic therapies or as a modulator of the immune response, without another invasive procedure. Experimentally determined parameters of the ferrite material cores provided in this study establish a mechanistic foundation for future pre-clinical and clinical validationstudies.

Dose and fractionation regimen for brachytherapy boost in cervical cancer in the US

PurposeCurative-intent radiotherapy for locally advanced and select early stage cervical cancer in the US includes external beam radiotherapy (EBRT) with brachytherapy. Although there are guidelines for brachytherapy dose and fractionation regimens, there are limited data on practice patterns. This study aims to evaluate the contemporary utilization of cervical cancer brachytherapy in the US and its association with patient demographics and facility characteristics. MethodsWe retrospectively analyzed clinical covariates of cervical cancer patients diagnosed and treated in 2018–2020 with curative-intent radiotherapy from the 2020 National Cancer Database. Associations between patient and institutional factors with the number of brachytherapy fractions were identified with logistic regression. Factors with association (p < 0.10) were then included in a multivariable logistic regression model. All tests were two-sided with significance <0.05 unless specified otherwise. ResultsAmong the eligible 2517 patients, 97.3% received HDR or LDR and is further analyzed. More patients received HDR than LDR brachytherapy (98.9% vs 1.1%) and intracavitary than interstitial brachytherapy (86.4% vs 13.6%). The most common number of HDR fractions prescribed were 5 (51.0%), 4 (32.9%), and 3 (8.6%). After adjusting for the other variables in the model, ethnicity, private insurance status, overall insurance status, and facility type were the only factors that were significantly associated with the number of brachytherapy factions (p < 0.0001, p = 0.028, p = 0.001, and p < 0.0001, respectively, n = 2184). ConclusionsIn the US, various HDR brachytherapy regimens are utilized depending on patient and institutional factors. Future research may optimize cervical cancer brachytherapy by correlating specific dose and fractionation regimens with patient outcomes.

P047 - Long-term results of LDR brachytherapy in localized prostate cancer

P047 - Long-term results of LDR brachytherapy in localized prostate cancer

Long Term Results of Prostate Cancer Patients Treated with Cs131 LDR Brachytherapy Compared with Recently Published SBRT Data.

The use of LDR prostate brachytherapy (PB) as monotherapy has been established as a definitive treatment for prostate cancer patients with low and favorable intermediate risk. Patients choose PB in part due to it being minimally invasive with a quick return to full activity. Recently, there has been more interest in using shorter courses of radiotherapy, citing the same rationale. We present patient-reported outcomes from a cohort of patients treated at our institution treated with PB using Cs131to compare our outcomes with the 5-year data from the published RTOG 0938 MATERIALS/METHODS: We analyzed data from patients treated at our institution with Cs131 PB monotherapy who completed the EPIC questionnaire at baseline and at 1, 2, and 5 years after treatment. Urinary and bowel functions were evaluated based on the EPIC questionnaire the same way they were evaluated in the recently published RTOG 0938, assessing the proportion of patients with deterioration from baseline of >5 for urinary function and >2 for bowel function. We also report the 5- and 10-year bDFS calculated using the Kaplan Meier method RESULTS: A total of 138 patients were included in this analysis with a median age of 66 and median follow-up of 121.5 months. Change in urinary score of >2 at 1, 2, and 5 years was 62%, 53%, and 43% respectively (compared with 44.3, 51.7, and 41.3 respectively for RTOG 0938). Change in bowel score of >5 at 1, 2, and 5 years was 27%, 23%, and 25% (compared with 29.3, 28.7, and 30.6 respectively for RTOG 0938). Interestingly, there were a number of patients who reported improvement in their urinary score at 1, 2, and 5 years (26%, 36%, and 46%, respectively), The same held for patients who reported improvement in their bowel score at 1, 2 and 5 years (37%, 38% and 41%, respectively). Hence, the median urinary score was 6.25 lower at year 1, but only 2.08 lower at year 2 with no difference by year 5. The median bowel score showed zero difference at every time point. The 5-year bDFS in our cohort was 97.8% (compared to 91.3% in RTOG 0938). Our 10-year bDFS was 96%. Single modality PB with Cs131 provides excellent long-term bDFS, especially when compared to recently published RTOG 0938 as 47% of our patients had intermediate-risk disease (RTOG 0938 had low-risk disease only and only 5-year data). Our patients had modest changes in urinary and bowel QOL compared to baseline, also comparable to published SBRT data. At 5 years in our cohort, 46% and 41% reported improvement in their urinary and bowel EPIC scores. The reason for this needs to be explored.

MR-Guided HDR Brachytherapy Boost in Localized Prostate Cancer - Results of a Phase II Trial.

Dose escalation in localized prostate cancer using brachytherapy combined with external beam radiation (EBRT) has demonstrated improved biochemical control compared to EBRT alone. However, ultrasound guided LDR brachytherapy might be associated with increased GU toxicity. We report the results of a prospective study of MR-guided HDR brachytherapy (MRgHDR) in combination with EBRT for localized prostate cancer. Intermediate- (IR) and high-risk (HR) prostate cancer patients were eligible. Patients received either 15Gy single fraction or 10Gy x 2 fractions using MRgHDR technique, followed by EBRT (37.5 Gy, [prostate only] -IR or 45-46 Gy - [prostate + pelvic nodes] -HR). Toxicity (CTCAE v4) and HRQoL (EPIC) were recorded at 1, 3 and 6 months, then at 1, 2, 3, and 5 years. Androgen deprivation therapy (ADT) was used according to the appropriate disease risk category. Biochemical failure was defined according to Phoenix definition (nadir+2). From 2010-2018, 120 patients were enrolled, 53 (44%) had IR and 67 (56%) had HR disease. Median age was 69 years (range, 46-78), median PSA was 12.1 ng/ml (3.2-148). ADT was used in 84 (70%) of patients, of whom 51 (60%) patients received <1 year and 33 (40%) received >1 year of ADT. A single fraction of 15Gy was given to 94 patients (78%) and the remaining 26 patients (22%) received 10Gy x 2 fractions. EBRT dose was 37.5Gy in 52 (43%) patients while 67 (56%) received 45-46Gy. One patient received only the first fraction of 10Gy, declined the second fraction and subsequently received 60Gy EBRT to the prostate. The median follow up was 58 months (11-134). Overall, 5-year biochemical control was 90% while it was 95% and 86% for IR and HR, respectively. At 5 years 7% patient had nodal or distant relapse or both. While the 5-yr distant control rates were 95% and 91% in the IR, HR, respectively. Acute grade ≥2 GU and GI toxicity was 6.7% and 5% respectively. Acute toxicity trended back to baseline by 6 months in all patients except one. Late grade ≥ 2 GU and GI worst toxicity was seen in 10% and 4.2%, respectively. As with acute toxicity, late toxicity tended to improve over time. Only one patient experienced severe toxicity (Grade 3 GU - frequency) at 6 months but subsequently this resolved. HRQol will be reported separately. MRgHDR brachytherapy boost in conjunction with EBRT provides comparable biochemical outcomes compared to the literature. Severe toxicity rates were minimal. Further follow-up will determine if these outcomes are sustained.

Initial Clinical Outcomes of a Phase II Trial of Focal Salvage LDR Brachytherapy for Local Recurrence of Prostate Cancer after External Beam Radiation Therapy.

To evaluate the clinical outcomes of focal salvage low dose rate brachytherapy (FSB) for biopsy proven local recurrence of prostate cancer after definitive external beam radiation therapy (EBRT). Patients with a Phoenix definition PSA recurrence (nadir + 2.0ng/dL) after definitive EBRT for localized prostate cancer and a negative metastatic work up were enrolled in a Phase II clinical trial. Patients first underwent MR-guided transperineal mapping biopsy of the prostate using a template grid. Patients with a pathologically confirmed recurrence underwent FSB using iodine-125 seeds to a prescription dose of 145 Gy. The brachytherapy planning target volume (PTV) was defined by the positions of the pathologically negative core biopsies adjacent to the positive core biopsies as recorded on the template grid during the biopsy procedure. An intraoperative treatment plan was then developed to cover the PTV with the 145 Gy isodose line. Follow up included assessment of genitourinary (GU) and gastrointestinal (GI) toxicities using Common Terminology Criteria for Adverse Events version 4.03 (CTCAEv4.03), patient reported outcomes using the International Prostate Symptom Score (IPSS) and Expanded Prostate Cancer Index-26 (EPIC-26) forms, and serial PSA blood draws. Ten patients underwent FSB. The median prior EBRT dose was 7805 cGy (interquartile range IQR 7560-7920) and the median time from completion of EBRT to FSB was 81 months (IQR 68-134). The median PSA prior to FSB was 3.2 ng/dL (IQR 2.3 - 4.5). The median follow up after FSB was 32 months (IQR 18-57). Eight patients were free of Phoenix definition PSA failure at last follow up. Of the two patients who experienced a PSA failure, one developed distant metastases 5 months after FSB and the other a biopsy proven seminal vesicle recurrence 3 years after FSB. The median change in post FSB IPSS score compared to the pre-FSB IPSS score was an increase of 1.5 (IQR -1.5 to 8) at 3 month follow up and an increase of 3.5 (IQR 0.5 to 5.5) at last follow up (≥1 year). The median change in post FSB EPIC-26 urinary domain score compared to the pre-FSB score was -1 (IQR -26 to +14.5) at 3 month follow up and +2 (IQR -12.5 to +14.5) at last follow up (≥1 year). The median change in post FSB EPIC-26 bowel domain score compared to the pre-FSB score was -2 (IQR -9.5 to 0.0) at 3 month follow up and 0 (IQR -6.0 to +3.0) at last follow up (≥1 year). No patients experienced post FSB Grade 3 or higher GU or GI toxicities. High dose FSB for a local recurrence of prostate cancer after EBRT can be delivered with good biochemical control and a favorable toxicity profile. Further clinical trial enrollment and longer follow up will be needed to better assess long term outcomes.

Sexual Function and Dosimetric Relationships to Erectile Structures among Patients Treated Definitively with Pd-103 LDR Prostate Brachytherapy

Sexual potency and erectile function are important quality of life metrics for many men and is a significant consideration when planning and treating prostate cancer. There are limited long-term data correlating post-implant dosimetry with patient-reported sexual toxicity outcomes following LDR prostate brachytherapy using Pd-103, specifically as it pertains to genital substructures. Our aim was to correlate dosimetric patterns with quality-of-life outcomes to determine if dose to the pudendal arteries and neurovascular bundles is a significant consideration when planning prostate LDR brachytherapy. We analyzed a prospectively collected IRB-approved database of men receiving LDR prostate brachytherapy between 11/2014-04/2019 at our institution. Patients received either LDR brachytherapy only, or combined with intensity-modulated radiation therapy (IMRT) to the prostate with or without pelvic lymph node coverage. Patients were given quality of life questionnaires at consultation and at subsequent follow up visits. Outcomes data related to sexual toxicity were evaluated based on the Sexual Health Inventory (SHIM) Questionnaire. The right/left pudendal arteries, and right/left neurovascular bundles (NVB) were contoured retrospectively on CT-MRI fusion sequences. Dosimetric data for each of the erectile substructures was analyzed. Statistical analyses included generalized linear mixed effects models with random intercept for patient to explore the association between dose and SHIM confidence. A total of 50 patients met criteria for inclusion in the analysis. 5 patients received combined IMRT to 45 Gy with Pd-103 (90-100 Gy) and 45 patients received Pd-103 monotherapy (125 Gy). Median follow-up was 18 months for 50 patients; 40 (80%) patients had follow-up greater than 2 years, and 15 (30%) greater than 5 years. There were 344 individual questionnaires completed. 28% of records reported low or very low confidence level (Question #1 of SHIM questionnaire). Likelihood of moderate-very high confidence increased up to 2 years after beginning of treatment (p = 0.052) and then subsequently decreased between 2- and 5 years post treatment (p = 0.042). NVB doses were not associated with SHIM confidence level. D100 greater than 150 cGy to either pudendal artery was associated with worse SHIM confidence score after treatment (p = 0.003). Sexual function is variable in the post treatment setting following definitive prostate radiation with Pd-103 LDR-brachytherapy. Avoiding pudendal artery dose may improve sexual outcomes and should be considered when planning prostate brachytherapy. Further investigation with a larger prospective, cohort may be warranted.

Biological Effective Dose (BED) in Evaluation of Rectal Dose in Prostate Cancer Patients with Hydrogel Spacer Who Underwent an EBRT with Different Fractionation Schemes

To evaluate rectal dose sparing in prostate cancer patients with hydrogel spacer who underwent an external beam radiotherapy (EBRT) with different fractionation schemes. In a previous study, we have reported that rectal sparing was achieved in prostate cancer patients with hydrogel spacer who underwent a combination therapy of EBRT and LDR brachytherapy (Zhang H, et al. J Appl Clin Med Phys, 2022). In this study, we focused on evaluation of spacer-related rectal sparing in patients who underwent an EBRT with conventional fractionation (81 Gy in 45 fractions), hypofractionation (70 Gy in 28 fractions), or stereotactic body radiotherapy (SBRT) for 40 Gy or 42.5 Gy in 5 fractions. In 172 patients, 119 patients were applied with injection of polyethylene-glycol hydrogel and others without the injection as control. In VMAT plans, doses to rectal wall were examined and converted to BED according to AAPM TG-137 (α/β ratio = 4 Gy). On average, an interspace of 1cm between prostate and rectum was achieved by spacer insertion. Rectal wall was defined as 0.4cm thickness inside the outer contour of rectum, and the volume ranged from 4.5 cm3 to 21.3cm3 for patients with spacer and from 8.2cm3 to 35.1cm3 for those with no spacer. In conventional scheme, an average rectal BED was 120.0 Gy, 116.9 Gy, 114.0 Gy, 108.6 Gy, 87.6 Gy and 55.6 Gy to the volume of 0.1, 0.5, 1, 2, 5 and 10cm3, respectively, and BEDmean was 55.3 Gy in patients with no spacer. The BED decreased to 105.1 Gy, 96.3 Gy, 86.1 Gy, 75.4 Gy, 51.7 Gy and 26.9 Gy to the volume of 0.1, 0.5, 1, 2, 5 and 10cm3, respectively (p < 0.01), and BEDmean was 46.0 Gy in patients with spacer. In hypofractionation, rectal BED was in average of 115.8 Gy, 112.3 Gy, 109.8 Gy, 103 Gy, 81.6 and 52.8 Gy to the volume of 0.1, 0.5, 1, 2, 5 and 10cm3, respectively, and BEDmean was 48.6 Gy in patients with no spacer. Patients with spacer had significantly decreases of rectal BED, an average of 103 Gy, 91.7 Gy, 84.1 Gy, 72.8 Gy, 48.8 Gy and 26.0 Gy to the volume of 0.1, 0.5, 1, 2, 5 and 10cm3, respectively (p < 0.01), BEDmean was 42.4 Gy. In SBRT, average rectal BED in patients with spacer decreased to 93.6 Gy, 78.4 Gy, 69 Gy, 57.5 Gy, 38.5 Gy and 21.5 Gy, in comparison of 124.1 Gy, 117,4 Gy, 110.9 Gy, 97.3 Gy, 59.7 Gy and 32.3 Gy to the volume of 0.1, 0.5, 1, 2, 5 and 10cm3 in those without spacer, respectively (p <0.01). BEDmean decreased to 32.0 Gy in patient with spacer, compared with 43.2 Gy in those with no spacer. Insertion of hydrogel spacer significantly improved rectal dose sparing, about 11.1% to 50.8% in conventional scheme, 12.4% to 51.6% in hypofractionation scheme, and 24.6% to 40.9% in SBRT patients. Furthermore, relatively more dose sparing on rectum was seen on the volume from 0.1cm3 to 2cm3 in SBRT patients.