Dose to the bladder neck is the most important predictor for acute and late toxicity after low-dose-rate prostate brachytherapy: implications for establishing new dose constraints for treatment planning

Urinary organs-at-risk for prostate cancer external beam radiotherapy: contouring guidelines on behalf of the Francophone Group of Urological Radiation Therapy (GFRU)

PURPOSE

Occurrence of genitourinary (GU) toxicity is a common adverse event observed after external beam radiotherapy (EBRT) for prostate cancer (PCa). Recent findings suggest that the dose delivered to specific urinary organs-at-risk (OARs) such as ureters, bladder trigone, and urethra is involved in the development of GU toxicity.

METHODS AND MATERIALS

A multidisciplinary task force including three radiation oncologists, a uroradiologist, and a urologist was created in 2022. First, OARs potentially involved in GU toxicity were identified and discussed. A literature review was performed, addressing several questions relative to urinary OARs: anatomical and radiological definition, radiation-induced injury, dose-volume parameters. Secondly, results were presented and discussed with a panel of radiation oncologists, members of the "Francophone Group of Urological Radiation Therapy" (GFRU). Thereafter, GFRU experts were asked to answer a dedicated questionnaire, including 35 questions on the controversial issues related to the delineation of urinary OARs.

RESULTS

The following structures were identified as critical for PCa EBRT: ureters, bladder, bladder neck, bladder trigone, urethra (intraprostatic, membranous, spongious), striated sphincter, and post-enucleation or post-transurethral resection of the prostate (TURP) cavity. A consensus was obtained for 32 out of 35 items.

CONCLUSION

This consensus highlights contemporary urinary structures in both upper and lower urinary tract to be considered for EBRT treatment planning of PCa. The current recommendations also propose a standardized definition of urinary OARs, for both daily practice and future clinical trials.

Impact of Interfractional Bladder and Trigone Displacement and Deformation on Radiation Exposure and Subsequent Acute Genitourinary Toxicity: A Post Hoc Analysis of Patients Treated with Magnetic Resonance Imaging-Guided Prostate Stereotactic Body Radiation Therapy in a Phase 3 Randomized Trial

PURPOSE

Emerging data suggest that trigone dosimetry may be more associated with poststereotactic body radiation therapy (SBRT) urinary toxicity than whole bladder dosimetry. We quantify the dosimetric effect of interfractional displacement and deformation of the whole bladder and trigone during prostate SBRT using on-board, pretreatment 0.35T magnetic resonance images (MRI).

METHODS AND MATERIALS

Seventy-seven patients treated with MRI-guided prostate SBRT (40 Gy/5 fractions) on the MRI arm of a phase 3 single-center randomized trial were included. Bladder and trigone structures were contoured on images obtained from a 0.35T simulation MRI and 5 on-board pretreatment MRIs. Dice similarity coefficient (DSC) scores and changes in volume between simulation and daily treatments were calculated. Dosimetric parameters including Dmax, D0.03 cc, Dmean, V40 Gy, V39 Gy, V38 Gy, and V20 Gy for the bladder and trigone for the simulation and daily treatments were collected. Both physician-scored (Common Terminology Criteria for Adverse Events, version 4.03 scale) as well as patient-reported (International Prostate Symptom Scores and the Expanded Prostate Cancer Index Composite-26 scores) acute genitourinary (GU) toxicity outcomes were collected and analyzed.

RESULTS

The average treatment bladder volume was about 30% smaller than the simulation bladder volume; however, the trigone volume remained fairly consistent despite being positively correlated with total bladder volume. Overall, the trigone accounted for <2% of the bladder volume. Median DSC for the bladder was 0.79, whereas the median DSC of the trigone was only 0.33. No statistically significant associations between our selected bladder and trigonal dosimetric parameters and grade ≥2 GU toxicity were identified, although numerically, patients with GU toxicity (grade ≥2) had higher intermediate doses to the bladder (V20 Gy and Dmean) and larger volumes exposed to higher doses in the trigone (V40 Gy, V39 Gy, and V38 Gy).

CONCLUSIONS

The trigone exhibits little volume change, but considerable interfractional displacement/deformation. As a result, the relative volume of the trigone receiving high doses during prostate SBRT varies substantially between fractions, which could influence GU toxicity and may not be predicted by radiation planning dosimetry.

Stereotactic body radiation therapy for prostate cancer after surgical treatment of prostatic obstruction: Impact on urinary morbidity and mitigation strategies

In the past decade, stereotactic body radiation therapy (SBRT) has emerged as a valid treatment option for patients with localized prostate cancer. Despite the promising results of ultra-hypofractionation in terms of tolerance and disease control, the toxicity profile of SBRT for prostate cancer patients with a history of surgical treatment of benign prostate hyperplasia is still underreported. Here we present an overview of the available data on urinary morbidity for prostate cancer patients treated with SBRT after prior surgical treatments for benign prostate hyperplasia. Technical improvements useful to minimize toxicity and possible treatments for radiation-induced urethritis are discussed.

Redefining bladder neck dose in low-dose-rate prostate brachytherapy-Can we improve urinary toxicity without impacting disease control?

BACKGROUND

We sought to assess the impact of bladder neck dose (BND) on patient reported urinary toxicity, and feasibility of relative urethral sparing technique in prostate brachytherapy (PB).

METHODS AND MATERIALS

We retrospectively identified bladder neck as a point dose on post-implant CT scans in patients treated with 131Cs PB. Urinary symptoms were assessed through EPIC questionnaires. Patient cohorts were identified based on mean BND as a percentage of prescription dose with toxicity assessment at each time point.

RESULTS

In our cohort of 542 patients, BND was associated with clinically significant acute urinary symptoms and chronic symptoms, as patients receiving >70% of the prescription dose had significantly worse overall EPIC scores than patients receiving ≤70% of prescription dose. There was no difference in bDFS between patients receiving BND ≤70% (96% bDFS) and >70% (94% bDFS) at a median follow up of 57 months.

CONCLUSIONS

BND has a significant impact on both acute and chronic urinary symptoms, with reduced symptoms reported with BND <70% of prescription dose. With a median follow up of 4.7 years, excellent bDFS has thus far been achieved with relative urethral and bladder neck sparing. Utilizing this constraint should improve urinary symptoms without impacting disease control.

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.

Feature Importance Analysis of a Deep Learning Model for Predicting Late Bladder Toxicity Occurrence in Uterine Cervical Cancer Patients

(1) In this study, we developed a deep learning (DL) model that can be used to predict late bladder toxicity. (2) We collected data obtained from 281 uterine cervical cancer patients who underwent definitive radiation therapy. The DL model was trained using 16 features, including patient, tumor, treatment, and dose parameters, and its performance was compared with that of a multivariable logistic regression model using the following metrics: accuracy, prediction, recall, F1-score, and area under the receiver operating characteristic curve (AUROC). In addition, permutation feature importance was calculated to interpret the DL model for each feature, and the lightweight DL model was designed to focus on the top five important features. (3) The DL model outperformed the multivariable logistic regression model on our dataset. It achieved an F1-score of 0.76 and an AUROC of 0.81, while the corresponding values for the multivariable logistic regression were 0.14 and 0.43, respectively. The DL model identified the doses for the most exposed 2 cc volume of the bladder (BD_2cc) as the most important feature, followed by BD_5cc and the ICRU bladder point. In the case of the lightweight DL model, the F-score and AUROC were 0.90 and 0.91, respectively. (4) The DL models exhibited superior performance in predicting late bladder toxicity compared with the statistical method. Through the interpretation of the model, it further emphasized its potential for improving patient outcomes and minimizing treatment-related complications with a high level of reliability.

Validation of the bladder neck as an important organ at risk in prostate seed brachytherapy based on D2cc: A single-institution, retrospective review

Purpose

International guidelines recommend urethral dose volume constraints to minimize the risk of urinary toxicity after prostate brachytherapy. An association between dose to the bladder neck (BN) and toxicity has previously been reported, and we sought to evaluate the impact of this organ at risk on urinary toxicity, based on intra-operative contouring.

Material and methods

Rates of acute and late urinary toxicity (AUT and LUT, respectively) were graded according to CTCAE version 5.0 for 209 consecutive patients who underwent low-dose-rate (LDR) brachytherapy monotherapy, with approximately equal numbers treated before and after we began routinely contouring the BN. AUT and LUT were compared in patients treated before and after we began contouring the OAR, and also for those treated after we began contouring who had a D2cc of greater than or less than 50% prescription dose.

Results

AUT and LUT fell after intra-operative BN contouring was instituted. Rates of grade ≥ 2 AUT fell from 15/101 (15%) to 9/104 (8.6%), p = 0.245. Grade ≥ 2 LUT decreased from 32/100 (32%) to 18/100 (18%), p = 0.034. Grade ≥ 2 AUT was observed in 4/63 (6.3%) and 5/34 (15%) of those with a BN D2cc >/≤ 50%, respectively, of prescription dose. Corresponding rates for LUT were 11/62 (18%) and 5/32 (16%).

Conclusions

There were lower urinary toxicity rates for patients treated after we commenced routine intra-operative contouring of the BN. No clear relationship was observed between dosimetry and toxicity in our population.

MRI-defined treatment margins, urinary toxicity, and PSA response in LDR prostate brachytherapy

PURPOSE

Implant quality metrics as measured by D90 and V100 do not address the adequacy of periprostatic margins. Relative margin deficiencies may relate to efficacy and margin excesses to post-implant toxicity. Our purpose is to determine MRI-defined treatment margins on prostate achieved with LDR brachytherapy.

METHODS AND MATERIALS

Post implant CT and MR images from 487 consecutive patients who received LDR brachytherapy from 2010 to 14 were co-registered. Four prostate quadrants were defined; anterior-superior (AS), posterior-superior (PS), anterior-inferior (AI), posterior-inferior (PI). Dosimetric variables were measured for prostate, and for each quadrant with a 0-, 2-, 3-, and 5-mm margin, as well as for the membranous urethra defined on MRI.

RESULTS

Prostate D90 (no margin) was associated with D90 to the volume enclosed by 2 mm, 3 mm and 5 mm margins (R2 = 0.9 - 1.0) with an average 7.1% decrease in dose per mm of margin. Mean D90 for PS, AI and PI quadrants were > 110% of prescription dose for margins of 2-, 3-, and 5-mm. AS quadrant mean D90s were generally lower (83.2% for 2 mm, 76.4% for 3 mm and 62.2% for 5 mm). Urethral strictures (n = 9) were associated with higher doses in the AI quadrant, and higher membranous urethral V125 (51 vs. 32%, p 0.013) and V150 (34.5 vs. 17.6%, p 0.01).

CONCLUSIONS

Using MR-CT post implant dosimetry, margin coverage up to 5 mm was excellent with less margin coverage in the AS quadrant. Late ≥ grade 2 toxicity and urinary strictures are more likely to occur with relative margin excess in the anterior-inferior quadrant and higher doses caudal to the prostate apex. Within this analysis, there was no relationship between treatment margins, and PSA outcome.

Radiation Dose to the Intraprostatic Urethra Correlates Strongly With Urinary Toxicity After Prostate Stereotactic Body Radiation Therapy: A Combined Analysis of 23 Prospective Clinical Trials

PURPOSE

Clinical trials assessing evaluation prostate stereotactic body radiation therapy (SBRT) have used a wide range of allowed doses to the intraprostatic urethra, but the relationship between urethral dose and urinary toxicity has not been thoroughly evaluated. The goal of this study was to characterize urinary toxicity outcomes according to urethral dose administered during prostate SBRT.

METHODS AND MATERIALS

The MEDLINE (PubMed) database was searched for published prospective studies of prostate SBRT through August 2020 that documented a maximum urethral dose metric (MUDM). Reported acute and late urinary toxicity rates were collected. Logistic regression and weighted Pearson correlation models were used to assess associations between urinary toxicity rates and MUDM.

RESULTS

Twenty-three unique studies (n = 2232 patients) met the inclusion criteria and included a wide range of MUDMs (equivalent dose in 2 Gy fractions [EQD₂]: 69-141.75 Gy; α/β = 3 Gy). The median follow-up ranged from 3 to 67 months (median, 32 months). On logistic regression analysis, the MUDM EQD₂ was significantly associated with multiple urinary toxicity endpoints, including acute grade (G) 2+ (odds ratio [OR], 1.02; P < .001), late G2+ (OR, 1.03; P < .0001), and late G3+ (OR, 1.04; P = .003) urinary toxicity. On weighted Pearson correlation analysis, the MUDM was more closely associated with all evaluated urinary toxicity endpoints than prescription dose, including acute G2+ (r = 0.51; P = .02), late G2+ (r = 0.9; P < .0001), and late G3+ toxicity (r = 0.7; P = .003). Multivariate analysis accounting for age, prostate size, bladder dosimetry, and baseline urinary function confirmed associations between urinary outcomes and MUDM. Within the studied dose range, each increase of 1 Gy to the MUDM corresponded to a 0.8% and 1.0% increase in acute G2+ and late G2+ toxicity, respectively.

CONCLUSIONS

Radiation dose to the urethra correlates closely with urinary toxicity in patients with prostate cancer treated with SBRT. Attention should be paid to the urethral dose when delivering prostate SBRT to high doses, and approaches for urethral dose reduction warrant further investigation.

Computer-aided segmentation on MRI for prostate radiotherapy, Part I: Quantifying human interobserver variability of the prostate and organs at risk and its impact on radiation dosimetry

BACKGROUND AND PURPOSE

Quantifying the interobserver variability (IoV) of prostate and periprostatic anatomy delineation on prostate MRI is necessary to inform its use for treatment planning, treatment delivery, and treatment quality assessment.

MATERIALS AND METHODS

Twenty five prostate cancer patients underwent MRI-based low-dose-rate prostate brachytherapy (LDRPBT). The patients were scanned with a 3D T2-weighted sequence for treatment planning and a 3D T2/T1-weighted sequence for quality assessment. Seven observers involved with the LDRPBT workflow delineated the prostate, external urinary sphincter (EUS), seminal vesicles, rectum, and bladder on all 50 MRIs. IoV was assessed by measuring contour similarity metrics, differences in organ volumes, and differences in dosimetry parameters between unique observer pairs. Measurements from a group of 3 radiation oncologists (G1) were compared against those from a group consisting of the other 4 clinical observers (G2).

RESULTS

IoV of the prostate was lower for G1 than G2 (Matthew's correlation coefficient [MCC], G1 vs. G2: planning-0.906 vs. 0.870, p < 0.001; postimplant-0.899 vs. 0.861, p < 0.001). IoV of the EUS was highest of all the organs for both groups, but was lower for G1 (MCC, G1 vs. G2: planning-0.659 vs. 0.402, p < 0.001; postimplant-0.684 vs. 0.398, p < 0.001). Large differences in prostate dosimetry parameters were observed (G1 maximum absolute prostate ΔD90: planning-76.223 Gy, postimplant-36.545 Gy; G1 maximum absolute prostate ΔV100: planning-13.927%, postimplant-8.860%).

CONCLUSIONS

While MRI is optimal in the management of prostate cancer with radiation therapy, significant interobserver variability of the prostate and external urinary sphincter still exist.

Low dose rate brachytherapy for primary treatment of localized prostate cancer: A systemic review and executive summary of an evidence-based consensus statement

PURPOSE

The purpose of this guideline is to present evidence-based consensus recommendations for low dose rate (LDR) permanent seed brachytherapy for the primary treatment of prostate cancer.

METHODS AND MATERIALS

The American Brachytherapy Society convened a task force for addressing key questions concerning ultrasound-based LDR prostate brachytherapy for the primary treatment of prostate cancer. A comprehensive literature search was conducted to identify prospective and multi-institutional retrospective studies involving LDR brachytherapy as monotherapy or boost in combination with external beam radiation therapy with or without adjuvant androgen deprivation therapy. Outcomes included disease control, toxicity, and quality of life.

RESULTS

LDR prostate brachytherapy monotherapy is an appropriate treatment option for low risk and favorable intermediate risk disease. LDR brachytherapy boost in combination with external beam radiation therapy is appropriate for unfavorable intermediate risk and high-risk disease. Androgen deprivation therapy is recommended in unfavorable intermediate risk and high-risk disease. Acceptable radionuclides for LDR brachytherapy include iodine-125, palladium-103, and cesium-131. Although brachytherapy monotherapy is associated with increased urinary obstructive and irritative symptoms that peak within the first 3 months after treatment, the median time toward symptom resolution is approximately 1 year for iodine-125 and 6 months for palladium-103. Such symptoms can be mitigated with short-term use of alpha blockers. Combination therapy is associated with worse urinary, bowel, and sexual symptoms than monotherapy. A prostate specific antigen <= 0.2 ng/mL at 4 years after LDR brachytherapy may be considered a biochemical definition of cure.

CONCLUSIONS

LDR brachytherapy is a convenient, effective, and well-tolerated treatment for prostate cancer.

Patient assessment of lower urinary tract symptoms using the international prostate symptom score following low-dose-rate prostate brachytherapy

PURPOSE

To correlate changes in urinary patient-reported outcomes including the International Prostate Symptom Score (IPSS), acute urinary retention and urethral stricture with urethral dose in those treated with low dose rate (LDR) prostate brachytherapy.

MATERIALS AND METHODS

Patients treated with prostate LDR between 2012 and 2019 (n=117) completed IPSS urinary symptom assessments prior to treatment and at each follow-up. CT simulation was obtained with urinary catheter 1-month post-implant for dosimetric analysis. 113 patients with pre- and ≥1 post-LDR IPSS score available were analyzed. Urethral dosimetric parameters including U75, U100, U125, U150 and U200 were abstracted from post-implant dosimetry and assessed for association with urinary toxicity using bivariate logistic regression and Spearman correlation. Outcomes included clinically significant change (CSC, defined as 4 or more points or 25% rise above baseline) in IPSS score at 6 and 12 months, acute urinary retention (AUR), and urethral stricture (US).

RESULTS

89 (79%) patients were treated with LDR monotherapy (145 Gy) and 24 (21%) with LDR boost (110 Gy) with external beam radiation therapy. Twenty (18%) had baseline IPSS ≥15. Median IPSS scores were: baseline 6 (3-12; n=113), 1-month 17 (10-25; n=110), 6 months 12 (7-18; n=77), 1 year 8 (5-14; n=52). CSC-6 was observed in 59 (77%), CSC-12 in 26 (50%), AUR in 12 (11%), and US in 4 (4%). No association was identified between urethral dose parameters and CSC-6, CSC-12, AUR, or US. No correlation between urethral dose and IPSS at 6- and 12-months was identified. The IPSS ≥15 group exhibited lower rates of CSC-12 (13% v. 57%, p=0.05) but not CSC-6 (55% v. 80%, p=0.12).

CONCLUSIONS

We did not find a relationship between urethral dose and IPSS elevation, AUR or US. We did identify a significantly lower change in IPSS at 12 months for those with baseline IPSS ≥15 compared to those with low baseline scores.

PSA outcomes and late toxicity of single-fraction HDR brachytherapy and LDR brachytherapy as monotherapy in localized prostate cancer: A phase 2 randomized pilot study

PURPOSE

To evaluate the PSA outcomes and the late patient's reported health related quality of life (HRQOL) and toxicity after single-fraction High-Dose-Rate brachytherapy (HDRB) and Low-Dose-Rate brachytherapy (LDRB) for prostate cancer.

METHODS

Men with low and favorable intermediate-risk prostate cancer across 3 centres were randomized between monotherapy brachytherapy with either Iodine-125 LDRB or 19 Gy single-fraction HDRB. Biochemical outcomes were evaluated using the Phoenix definition, PSA nadir and absolute PSA value <0.4 ng/mL. Toxicities and HRQOL were recorded at 24 and 36 months.

RESULTS

A total of 31 patients were randomized, 15 in the LDRB arm and 16 patients in the HDRB arm. After a median follow-up of 45(36-53) months, 3 patients in the HDRB arm experienced biochemical failure (p = 0.092). Nineteen Gy single-fraction HDRB was associated with significantly higher PSA nadir compared to LDRB (1.02 ± 0.66vs 0.25 ± 0.39, p < 0.0001). Moreover, a significantly larger proportion of patients in the LDRB group had a PSA <0.4 ng/mL (13/15 vs 2/16, p < 0.0001). For late Genito-Urinary, Gastro-Intestinal, and sexual toxicities at 24 and 36 months, no significant differences were found between the 2 arms. As for HRQOL, the IPSS and EPIC-26 urinary irritative score were significantly better for patients treated with HDRB over the first 36 months post-treatment (p = 0.001 and p = 0.01, respectively), reflecting superior HRQOL.

CONCLUSION

HDRB resulted in superior HRQOL in the irritative urinary domain compared to LDRB. PSA nadir was significantly lower in the LDRB group and a higher proportion of patients in the LDRB group reached PSA <0.4 ng/mL.

Tensor Regression-based Model to Investigate Heterogeneous Spatial Radiosensitivity After I-125 Seed Implantation for Prostate Cancer

BACKGROUND/AIM

We established a data-driven method for extracting spatial patterns of dose distribution associated with radiation injuries, based on patients with prostate cancer who underwent iodine-125 (I-125) seed implantation.

PATIENTS AND METHODS

Seventy-five patients underwent I-125 seed implantation for prostate cancer. We modeled the severity of lower urinary tract symptoms (LUTS) to be estimated using a linear model, which is formulated as an inner product between the dose distribution D and voxel-wise radiosensitivity B inside the prostate. For the estimation, tensor regression based on a low-rank decomposition with generalized fused lasso penalty was applied.

RESULTS

The spatial distribution of B was visually assessed. Positive parameters appeared dominantly in the region close to the urethra and the prostate base.

CONCLUSION

Our tensor regression-based model can predict intra-organ radiosensitivity in a data-driven manner, providing a compelling parameter distribution associated with the development of LUTS after I-125 seed implantation for prostate cancer.

Dynamic Changes in Bladder Morphology Over Time in Cervical Cancer Patients

Objectives:

Continuous surveillance of bladder volume (BV) is beneficial during the treatment of various urogenital diseases because the bladder is always changing its position, size and even shape at different filling phases. For this purpose, we quantified the motion of the urinary bladder.

Methods:

Daily ultrasound measurements and weekly cone-beam computed tomography scans were obtained from 89 patients in the supine position. BV, bladder centroid positions, and triaxial lengths in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions were compared across different time points.

Results:

BV linearly increased over time, and the mean urinary filling rate (v_tot) was correlated with the patients’ age and water consumption. The greatest bladder centroid motion occurred longitudinally, with less movement observed laterally. The maximum bladder centroid movement was 18.8 ± 2.2 mm inferiorly and 1.8 ± 0.9 mm posteriorly for every 10% decrease in BV. The rates of changes in triaxial lengths differed across the 4 filling phases. The rate was the largest at a BV range of 10-80 mL, especially in the LR direction, with values of 5.9 ± 1.0, 3.6 ± 1.0, and 3.9 ± 1.0 mm per every 10-mL BV increase for LR, AP, and SI, respectively. With bladder filling (<80 mL), the maximum increase in triaxial length was observed in the SI direction and the rates of all changes considerably decreased, especially at BV > 600 mL.

Conclusion:

The v_tot could be used to evaluate the temporal changes in the bladder. The spatial changes should be assessed according to different filling phases based on the centroid position and triaxial lengths.

Acute and late side-effects after low dose-rate brachytherapy for prostate cancer; incidence, management and technical considerations

PURPOSE

To review common reported side effects and complications after primary LDR-BT (monotherapy) and discuss some of the technical aspects that could impact the treatment outcomes.

METHODS AND MATERIALS

A literature search was undertaken using medical subject headings (MeSH) complemented by the authors' personal and institutional expertise.

RESULTS

The reported incidence of acute and late grade 2 or above urinary, bowel and sexual side effects is very variable across the literature. The learning curve and the implant quality have a clear impact on the toxicity outcomes. Being aware of some of the technical challenges encountered during the procedure and ways to mitigate them could decrease the incidence of side effects. Careful planning of seed placement and seed deposition allow sparing of the organs at risk and a lower incidence of urinary and gastro-intestinal toxicity.

CONCLUSIONS

Low dose-rate brachytherapy remains a standard monotherapy treatment in the setting of favorable-risk prostate cancer. High disease control and low long-term toxicities are achievable in expert hands with a good technique.

Analysis of radioactive implant migration in patients treated with iodine-125 seeds for permanent prostate brachytherapy with MRI-classified median lobe hyperplasia

Purpose

Prostate cancer with median lobe hyperplasia (MLH) is a relative contraindication for permanent prostate brachytherapy (PPB) because of an increased risk of post-implant dysuria and technical difficulties associated with achieving stability while implanting within the intravesical tissue. We examined treatment outcome, seed migration, and urination disorders after treatment in MLH patients in order to determine to what degree MLH implants could be stabilized.

Material and methods

Between March 2007 and December 2016, 32 patients had MLH identified radiologically on magnetic resonance imaging, and 193 patients did not have MLH (non-MLH). All patients were treated with loose seeds. In this study, seed migration was defined as a seed distant from the target (≥ 1.5 cm) and/or with no dosimetric contribution to the target. The MLH patients were divided into 2 MLH groups of mild (< 10 mm) and severe (≥ 10 mm) MLH by measuring the distance between the posterior transitional zone and the prostatic tissue protruding into the bladder. We retrospectively analyzed seed migration, dose-volume histograms (DVH), and genitourinary toxicity.

Results

MLH was classified as mild in 24 patients and severe in 8. Seed migration occurred in 61 (31.6%) of 193 non-MLH patients and 10 (31.5%) of 32 MLH patients. Implant seed migration and low-dose level of median lobe tended to be high in severe MLH cases. International Prostate Symptom Score (IPSS) peaked one month after implantation, but then resolved slowly and returned to around the pre-treatment level after one year. There were no severe complications.

Conclusions

MLH does not appear to be a strong contraindication for low-dose-rate brachytherapy. However, we found that the seed migration and degree of cold spots tended to be higher in severe MLH cases than in others; therefore, close attention when treating severe MLH cases must be paid.

Simulation of an HDR "Boost" with Stereotactic Proton versus Photon Therapy in Prostate Cancer: A Dosimetric Feasibility Study

Purpose/Objectives

To compare the dose escalation potential of stereotactic body proton therapy (SBPT) versus stereotactic body photon therapy (SBXT) using high-dose rate prostate brachytherapy (HDR-B) dose-prescription metrics.

Patients and Methods

Twenty-five patients previously treated with radiation for prostate cancer were identified and stratified by prostate size (≤ 50cc; n = 13, > 50cc; n = 12). Initial CT simulation scans were re-planned using SBXT and SBPT modalities using a prescription dose of 19Gy in 2 fractions. Target coverage goals were designed to mimic the dose distributions of HDR-B and maximized to the upper limit constraint for the rectum and urethra. Dosimetric parameters between SBPT and SBXT were compared using the signed-rank test and again after stratification for prostate size (≤ 50cm³ and >50cm³) using the Wilcoxon rank test.

Results

Prostate volume receiving 100% of the dose (V100) was significantly greater for SBXT (99%) versus SBPT (96%) (P ≤ 0.01), whereas the median V125 (82% vs. 73%, P < 0.01) and V200 (12% vs. 2%, P < 0.01) was significantly greater for SBPT compared to SBXT. Median V150 was 49% for both cohorts (P = 0.92). V125 and V200 were significantly correlated with prostate size. For prostates > 50cm³, V200 was significantly greater with SBPT compared to SBXT (14.5% vs. 1%, P = 0.005), but not for prostates 50cm³ (9% vs 4%, P = 0.11). Median dose to 2cm³ of the bladder neck was significantly lower with SBPT versus SBXT (9.6 Gy vs. 14 Gy, P < 0.01).

Conclusion

SBPT and SBXT can be used to simulate an HDR-B boost for locally advanced prostate cancer. SBPT demonstrated greater dose escalation potential than SBXT. These results are relevant for future trial design, particularly in patients with high risk prostate cancer who are not amenable to brachytherapy.

Complications and side effects of high-dose-rate prostate brachytherapy

PURPOSE

To describe technical challenges and complications encountered during and after high-dose-rate prostate brachytherapy (HDR-BT) and review management of these complications.

METHODS AND MATERIALS

The authors performed a systematic review of the literature on toxicities encountered after prostate HDR-BT +/- external beam radiotherapy. A total of 397 studies were identified, of which 64 were included. A focused review of literature regarding the management of acute and late toxicities also performed.

RESULTS

Most acute toxicities include grade 0-2 genitourinary and gastrointestinal toxicity. Overall, Grade 3+ Common Terminology Criteria for Adverse Events toxicity after HDR-BT was low [genitourinary: 0-1%; gastrointestinal 0-3%]. Rates of fistula formation were <1%, and radiation cystitis/proctitis were <14% and more commonly reported in cohorts treated with HDR-BT boost and external beam radiotherapy.

CONCLUSIONS

HDR-BT both as monotherapy or combined with external beam radiotherapy for prostate cancer is well tolerated. Serious complications are rare.

The impact of a rectal hydrogel spacer on dosimetric and toxicity outcomes among patients undergoing combination therapy with external beam radiotherapy and low-dose-rate brachytherapy

PURPOSE

Rectal hydrogel spacers have been shown to decrease rectal radiation dose and toxicity. In this study, we compared prostate and rectal dosimetry and acute toxicity outcomes in patients who had and had not received a rectal hydrogel spacer prior to combination therapy with external beam radiotherapy and low-dose-rate brachytherapy.

MATERIALS AND METHODS

All patients with intermediate-risk and high-risk prostate cancer who received combination therapy at our institution were identified between 2014 and 2019. Dosimetric outcomes of brachytherapy implants and quality of life (QOL) outcomes were compared between patients who had and had not received a hydrogel spacer.

RESULTS

A Total of 168 patients meeting our inclusion criteria were identified. Twenty-two patients had received a rectal hydrogel spacer, among whom the mean separation between the rectum and prostate was 7.5 mm, and the V100_rectum was reduced by 47% (0.09 cc vs. 0.17 cc, p = 0.04). There was no difference in the percentage of patients achieving a D90 of ≥100 Gy between those who had and had not received a spacer. The mean rate of change in I-PSS and SHIM scores did not differ between the two groups at 2 months after PID.

CONCLUSION

LDR brachytherapy appears feasible after the placement of a rectal hydrogel spacer. While there was a significantly reduced V100_rectum among patients who had received a hydrogel spacer, there was no statistically significant difference in patients achieving a D90_prostate of ≥100 Gy. Although there was no difference appreciated in QOL scores, the length of follow-up was limited in the rectal-spacer group.

Importance of the ICRU bladder point dose on incidence and persistence of urinary frequency and incontinence in locally advanced cervical cancer: An EMBRACE analysis

PURPOSE

To identify patient- and treatment-related risk factors and dose-effects for urinary frequency and incontinence in locally advanced cervical cancer (LACC) treated with radio(chemo)therapy and image-guided adaptive brachytherapy (IGABT).

MATERIAL AND METHODS

Physician-assessed (CTCAE) and patient-reported (EORTC) frequency and incontinence recorded in the EMBRACE-I study were analysed. Risk factors analysis was performed in patients without bladder infiltration and with baseline morbidity available. Cox regression was used for CTCAE grade (G) ≥ 3 and G ≥ 2 and for EORTC "very much" and "quite a bit" or worse. Logistic regression was used for late persistent morbidity defined when CTCAE G ≥ 1 or EORTC ≥ "quite a bit" were scored in at least half of follow-ups.

RESULTS

Longitudinal data on 1153 and 884 patients were available for CTCAE and EORTC analysis, respectively. Median follow-up was 48[3-120] months. Crude incidence rates of G≥2 were 13% and 11% for frequency and incontinence, respectively. Baseline morbidity and overweight-obesity were risk factors for both symptoms. Elderly patients were at higher risk for incontinence. Patients receiving conformal-radiotherapy were at higher risk for frequency. ICRU bladder point (ICRU-BP) dose was a stronger predictor for incontinence than bladder D_2cm3. The 5-year actuarial estimate of G ≥ 2 incontinence increased from 11% to 20% with ICRU-BP doses > 75 Gy compared to ≤ 65 Gy. Frequency showed weaker associations with dose.

CONCLUSION

ICRU-BP dose, in addition to clinical parameters, is a risk factor for urinary incontinence and shows a dose-effect after radio(chemo)therapy and IGABT. ICRU-BP dose should be monitored during treatment planning alongside volumetric parameters. Frequency seems associated with larger irradiated volumes.

Strict bladder filling and rectal emptying during prostate SBRT: Does it make a dosimetric or clinical difference?

Background

To evaluate inter-fractional variations in bladder and rectum during prostate stereotactic body radiation therapy (SBRT) and determine dosimetric and clinical consequences.

Methods

Eighty-five patients with 510 computed tomography (CT) images were analyzed. Median prescription dose was 40 Gy in 5 fractions. Patients were instructed to maintain a full bladder and empty rectum prior to simulation and each treatment. A single reviewer delineated organs at risk (OARs) on the simulation (Sim-CT) and Cone Beam CTs (CBCT) for analyses.

Results

Bladder and rectum volume reductions were observed throughout the course of SBRT, with largest mean reductions of 86.9 mL (19.0%) for bladder and 6.4 mL (8.7%) for rectum noted at fraction #5 compared to Sim-CT (P < 0.01). Higher initial Sim-CT bladder volumes were predictive for greater reduction in absolute bladder volume during treatment (ρ = − 0.69; P < 0.01). Over the course of SBRT, there was a small but significant increase in bladder mean dose (+ 4.5 ± 12.8%; P < 0.01) but no significant change in the D2cc (+ 0.8 ± 4.0%; P = 0.28). The mean bladder trigone displacement was in the anterior direction (+ 4.02 ± 6.59 mm) with a corresponding decrease in mean trigone dose (− 3.6 ± 9.6%; P < 0.01) and D2cc (− 6.2 ± 15.6%; P < 0.01). There was a small but significant increase in mean rectal dose (+ 7.0 ± 12.9%, P < 0.01) but a decrease in rectal D2cc (− 2.2 ± 10.1%; P = 0.04). No significant correlations were found between relative bladder volume changes, bladder trigone displacements, or rectum volume changes with rates of genitourinary or rectal toxicities.

Conclusions

Despite smaller than expected bladder and rectal volumes at the time of treatment compared to the planning scans, dosimetric impact was minimal and not predictive of detrimental clinical outcomes. These results cast doubt on the need for excessively strict bladder filling and rectal emptying protocols in the context of image guided prostate SBRT and prospective studies are needed to determine its necessity.

Analysis of outcomes after non-contour-based dose painting of dominant intra-epithelial lesion in intra-operative low-dose rate brachytherapy

Purpose

To compare the outcomes of patients with intermediate risk prostate cancer (IR-PCa) treated with low-dose rate I-125 seed brachytherapy (LDR-BT) and targeted dose painting of a histologic dominant intra-epithelial lesion (DIL) to those without a DIL.

Methods

455 patients with IR-PCa were treated at a single center with intra-operatively planned LDR-BT, each following the same in-house dose constraints. Patients with a DIL on pathology had hot spots localized to that region but no specific contouring during the procedure.

Results

396 (87%) patients had a DIL. Baseline tumor characteristics and overall prostate dosimetry were similar between patients with and without DIL except the median number of biopsy cores taken: 10 (10–12) vs 12 (10–12) (p = 0.002).

19 (5%) and 18 (5%) of patients with and 1 (2%) and 0 (0%) of those without DIL experienced CTCAE grade 2 and 3 toxicity respectively. Overall, toxicity grade did not significantly correlate with presence of DIL (p = 0.10).

Estimated 7-year freedom from biochemical failure (FFBF) was 84% (95% confidence interval: 79–89) and 70% (54–89) in patients with and without a DIL (log-rank p = 0.315). In DIL patients, cox regression revealed location of DIL (“Base” vs “Apex” HR: 1.03; 1.00–1.06; p = 0.03) and older age (70 vs 60 HR: 1.62; 1.06–2.49; p = 0.03) was associated with poor FFBF.

Conclusions

Targeting DIL through dose painting during intraoperatively planned LDR-BT provided no statistically significant change in FFBF. Patients with DILs in the prostate base had slightly lower FFBF despite DIL boost.

Assessment of Long-term Changes in Lower Urinary Tract Symptoms in Patients With Prostate Cancer Who Underwent Low-dose-rate Prostate Brachytherapy

OBJECTIVE

To investigate long-term changes in lower urinary tract symptoms in patients with prostate cancer (PCa) who underwent low-dose-rate brachytherapy with iodine-125 (LDR-BT).

PATIENTS AND METHODS

In this retrospective study, 313 patients with localized PCa underwent LDR-BT at Gifu University hospital between August 2004 and December 2013. The International Prostate Symptom Score (IPSS), Overactive Bladder Symptom Score (OABSS), and quality of life due to urinary symptoms (IPSS-QOL) were measured before LDR-BT; at 1, 3, 6, 9, 12, 24, 36, 48, and 60 months after LDR-BT; and annually thereafter. Study endpoints were chronological changes in IPSS, OABSS, and IPSS-QOL compared to pretreatment values. A multivariable nonlinear regression model with robust sandwich estimator evaluated association between outcomes and time with adjustment for covariates.

RESULTS

All scores worsened immediately after LDR-BT compared to preoperative scores. However, symptoms improved with time and returned to baseline in 18-36 months. After a 5-year follow-up after LDR-BT, OABSS significantly worsened in almost all patients compared to baseline although there were gradual improvements in less than 5 years after LDR-BT.

CONCLUSIONS

Our results may be of clinical importance in selecting treatment modalities for patients with localized PCa and long-term survival after definitive therapy.

DNA repair gene polymorphisms, tumor control, and treatment toxicity in prostate cancer patients treated with permanent implant prostate brachytherapy

BACKGROUND

Radiotherapy and brachytherapy are common treatments for localized prostate cancer (PCa). However, very few studies evaluated the association of variations in DNA damage response genes and treatment outcomes and toxicity in brachytherapy-treated patients.

PURPOSE

To evaluate the association of inherited germline variations in DNA repair-associated genes with tumor control and treatment toxicity in patients treated with low-dose-rate prostate brachytherapy (LDRB).

MATERIAL AND METHODS

The cohort consists of 475 I-125 LDRB patients with a median follow-up of 51 months after seed implantation. Patients were genotyped for 215 haplotype tagging single nucleotide variations (htSNPs) in 29 candidate genes of DNA damage response and repair pathways. Their association with biochemical recurrence (BCR) was assessed using Cox regression models and Kaplan-Meier survival curves. Linear regressions and analysis of covariance (ANCOVA) between early and late International Prostate Symptom Score (IPSS) with htSNPs were used to evaluate the association with urinary toxicity.

RESULTS

After adjustment for the established risk factors, six htSNPs in five genes were found to be significantly associated with an altered risk of BCR, with adjusted hazard ratios (HR_adj. ) ranging between 3.6 and 11.1 (P < .05). Compared to carriers of the ERCC3 rs4150499C allele, patients homozygous for the T allele (n = 22) had a significant higher risk of BCR with a HR of 11.13 (IC₉₅  = 3.9-32.0; P < .0001; q < 0.001). The Kaplan-Meier survival curve revealed a mean BCR-free survival time reduced from 213 ± 7 to 99 ± 12 months (log-rank P < .0001) for homozygous T carriers compare to noncarriers. For late IPSS (>6 months after treatment), htSNP rs6544990 from MSH2 showed a statistically significant b-coefficient of 1.85 ± 0.52 (P < .001; q < 0.1). Homozygous carriers of the MSH2 rs6544990C allele (n = 62) had a mean late IPSS 3.6 points higher than patients homozygous for the A allele (n = 132). This difference was significant when tested by ANCOVA using pretreatment IPSS as a covariate (P < .01).

CONCLUSIONS

This study suggests an association of the intronic variants of the DNA nucleotide excision repair ERCC3 and DNA mismatch repair MSH2 genes with elevated risk of BCR and late urinary toxicity respectively after LDRB. Further validation is required before translational clinical advances.

Evaluation of the urethral α/β ratio and tissue repair half-time for iodine-125 prostate brachytherapy with or without supplemental external beam radiotherapy

PURPOSE

To assess the correlation between postimplant dosimetric quantifiers and the genitourinary (GU) toxicity of low-dose rate brachytherapy for prostate cancer.

METHODS AND MATERIALS

The minimum urethral dose (UD10, 30, and 90) and the percent volume of the urethra receiving the prescription dose (V100, V150) were calculated from the postimplant dose-volume histograms of 182 patients. We then calculated various urethral biologically equivalent doses (uBEDs) using different values of the α/β ratio and tissue repair half-time (t1/2) and examined the correlations with GU toxicity.

RESULTS

Common dosimetric quantifiers, such as UD90 (brachytherapy) + UD50 (external beam radiotherapy), showed no correlation with Grade ≥ 2 GU toxicity. There was a significant correlation between Grade ≥2 GU toxicity and uBED when the α/β value was 0.5 or 1 Gy and t1/2 was 0.5-2.5 h. An uBED (α/β = 1.0, t1/2 = 0.5) had the largest hazard ratio for GU toxicity, and it was also significantly correlated with Grade ≥ 2 GU toxicity according to multivariate analysis.

CONCLUSIONS

We observed a significant correlation of uBED with GU toxicity when α/β was 0.5 or 1.0 Gy and t1/2 was 0.5-2.5 h. As the simple formula we used has not been verified in basic experiments, more data are needed to validate our results.

A Population-based Statistical Model for Investigating Heterogeneous Intraprostatic Sensitivity to Radiation Toxicity After 125I Seed Implantation

AIM

To develop a population-based statistical model in order to find a spatial pattern of dose distribution which is related to lower urinary tract symptoms (LUTS) after iodine-125 (¹²⁵I) seed implantation for prostate cancer.

PATIENTS AND METHODS

A total of 75 patients underwent ¹²⁵I seed implantation for prostate cancer. Principal component analysis was applied to the standardized dose array and for each patient dose distribution was uniquely characterized by a combination of weighted eigenvectors. The correlation between eigenvectors and the severity of LUTS was investigated with linear regression analysis.

RESULTS

Eight eigenvectors were identified as being significantly associated with the severity of LUTS (p<0.05). Multivariate regression model identified that intraprostatic parameters, which were positively associated with the severity of LUTS, were distributed around a portion of the urethral base and a peripheral region of the prostate.

CONCLUSION

We established a population-based statistical model that may indicate a significant dose pattern associated with the severity of radiation toxicity.

Prostate brachytherapy procedural training: incorporation of related procedures in resident training and competency assessment

Purpose

Inadequate procedural training is of increasing concern in resident training, especially in prostate brachytherapy (PB). Transperineal rectal spacer placement (TRSP) requires many of the same proficiencies as PB. This work describes the assessment of teaching techniques focusing on developing critical competencies for PB using related clinical procedures (TRSP).

Material and methods

For PB and TRSP, key competencies were identified: 9 for PB and 7 for TRSP; 4 are shared between PB and TRSP. "Comfort level" with these procedures was assessed prior to and following participation in TRSP.

Results

8 of 12 trainees at our institution participated in TRSP procedures. 2 of these trainees had prior experience with PB or related procedures and were excluded. Trainees self-reported "comfort levels" between 0 and 3 for four competency domains. Initial median comfort (MC) level for competency domains relevant to PB included: patient positioning (median 1, range 0-2), transrectal ultrasound imaging (median 1, range 0-1), fiducial placement (median 1, range 0-1), and hydrodissection (median 0, range 0-1). Median number of TRSP procedures performed by assessed trainees during the analysis period was 4 (range 1-6). Following TRSP procedure training, MC level increased: 2 points for patient positioning (median 3, range 1-3; p < 0.01), 1.5 points for transrectal ultrasound imaging (median 2.5, range 1.3, p < 0.001); 1 point for fiducial placement (median score 2, range 1-3; p < 0.001); and 1.5 points for hydrodissection (median score 2, range 1-3; p < 0.001).

Conclusions

Increasing trainee involvement in related procedures to develop core competencies may help facilitate increased comfort with common skills critical to the independent performance of PB.

A Phase 2 Randomized Pilot Study Comparing High-Dose-Rate Brachytherapy and Low-Dose-Rate Brachytherapy as Monotherapy in Localized Prostate Cancer

Purpose

To compare health-related quality of life (HRQOL) of high-dose-rate brachytherapy (HDRB) versus low dose-rate brachytherapy (LDRB) for localized prostate cancer in a multi-institutional phase 2 randomized trial.

Methods and Materials

Men with favorable-risk prostate cancer were randomized between monotherapy brachytherapy with either Iodine-125 LDRB to 144 Gy or single-fraction Iridium-192 HDRB to 19 Gy. HRQOL and urinary toxicity were recorded at baseline and at 1, 3, 6, and 12 months using the Expanded Prostate Cancer Index Composite (EPIC)-26 scoring and the International Prostate Symptom Score (IPSS). Independent samples t test and mixed effects modeling were performed for continuous variables. Time to IPSS resolution, defined as return to its baseline score ±5 points, was calculated using Kaplan-Meier estimator curves with the log-rank test. A multiple-comparison adjusted P value of ≤.05 was considered significant.

Results

LDRB and HDRB were performed in 15 and 16 patients, respectively, for a total of 31 patients. At 3 months, patients treated with LDRB had a higher IPSS score (mean, 15.5 vs 6.0, respectively; P = .003) and lower EPIC urinary irritative score (mean, 69.2 vs 85.3, respectively; P = .037) compared with those who received HDRB. On repeated measures at 1, 3, 6, and 12 months, the IPSS (P = .003) and EPIC urinary irritative scores (P = .019) were significantly better in the HDR arm, translating into a lower urinary toxicity profile. There were no significant differences in the EPIC urinary incontinence, sexual, or bowel habit scores between the 2 groups at any measured time point. Time to IPSS resolution was significantly shorter in the HDRB group (mean, 2.0 months) compared with the LDRB group (mean, 6.0 months; P = .028).

Conclusions

HDRB monotherapy is a promising modality associated with a lower urinary toxicity profile and higher HRQOL in the first 12 months compared with LDRB.

Safety of Prostate Stereotactic Body Radiation Therapy after Transurethral Resection of Prostate (TURP): A Propensity Score Matched Pair Analysis

PURPOSE

To determine the genitourinary (GU) toxicity outcomes in prostate cancer patients treated with stereotactic body radiation therapy (SBRT) who have undergone a prior transurethral resection of prostate (TURP) and compare it to a similar non-TURP cohort.

MATERIALS AND METHODS

Fifty prostate cancer patients who had undergone a single TURP, had a good baseline urinary function, and had been subsequently treated with SBRT were chosen from a prospectively maintained database. These were propensity score matched to a similar non-TURP cohort treated during the same period. Matching was done for diabetes mellitus and volume of radiation therapy. Acute GU and late GU toxicity were scored using the Radiation Therapy Oncology Group (RTOG) criteria. Stricture and incontinence were scored using Common Terminology for Common Adverse Events version 4.0.

RESULTS

Median follow-up for the entire cohort was 26 months (non-TURP vs TURP, 30 months vs 22 months, P = .34). The median duration between TURP and start of SBRT was 10 months. There was no significant difference between non-TURP versus TURP cohort in terms of RTOG acute GU toxicities grade ≥2 (8% vs 6%, P = .45), RTOG late GU toxicities grade ≥2 (8% vs 12%, P = .10), stricture rates (4% vs 6%, P = .64), and incontinence rates (0% vs 4%, P = .15). The median duration of time to late toxicity was 16 months vs 10 months (P = .12) in non-TURP and TURP cohort, respectively.

CONCLUSIONS

Although modestly increased as compared with non-TURP patients, GU toxicities remains low with SBRT in post-TURP patients. SBRT can be safely performed in carefully selected post-TURP prostate cancer patients.

The value of a bladder-filling protocol for patients with prostate cancer who receive post-operative radiation: results from a prospective clinical trial

BACKGROUND AND PURPOSE

This study compares two different strategies for maintaining a constant bladder volume during a course of postoperative radiotherapy in prostate cancer. In addition, we studied how changes in bladder filling affect the clinical target volume (CTV) and the coverage hereof.

MATERIAL AND METHODS

Twenty-nine patients with PSA-relapse after radical prostatectomy were divided into two groups: voiding and drinking 300 ml 1 hour before treatment (Group 1); and maintained a comfortably filled bladder (Group 2). The bladder volumes were calculated based on the planning CT (pCT) and a weekly Cone Beam CT (CBCT) during the treatment period. Furthermore, the variability of bladder extension was analyzed and correlated to the volume of the bladder covered with the 95% of the dose (V_95%,bladder).

RESULTS

The estimated median bladder volumes were 120 ml (95% CI: (93, 154)) and 123 ml (95% CI: (98, 155)) in groups 1 and 2, respectively. The intra-individual variation in bladder volume, assessed as the standard deviation, was 64 ml (95% CI: (46, 105)) in Group 1 and 61 (95% CI: (45, 94)) ml in Group 2. Increasing the bladder volume extended the bladder cranially while the caudal extension was almost constant. The correlation between bladder volume and V_95%,bladder was 3.5 ml per 100 ml in group 1 and 1.2 ml per 100 ml in group 2 with no significant difference.

CONCLUSIONS

The intention to maintain a constant volume for the bladder is not fulfilled with either of the protocols in this study, and changes in bladder volumes does not seem to affect the position, or the coverage of the CTV.

Acute and late toxicities in localized prostate cancer patients treated with low-dose 125I brachytherapy (110 Gy) in combination with external beam radiation therapy versus brachytherapy alone (160 Gy)

Purpose

The aim of this analysis was to compare acute and late toxicities between low-dose-rate brachytherapy (LDR-BT) (110 Gy) in combination with 45 Gy in 25 fractions external beam radiation therapy (EBRT) and LDR-BT (160 Gy) alone for localized prostate cancer.

Material and methods

One hundred five consecutive patients with localized prostate cancer treated from May 2014 to May 2017 were included in this retrospective analysis. Sixty patients received combination therapy and 45 patients received BT monotherapy. The LDR-BT procedure was performed using ¹²⁵I seeds.

Results

The median follow-up time was 28 months in both groups. Three-year effect rates were overall survival: 100% in both groups. The biochemical failure rate was 2.3% in the combination group and 0% in the monotherapy group (p = 0.373). No patients died during the study period. In both groups, almost all the patients experienced acute urethritis. There was a significant difference between the combination therapy group (8.3%) and BT monotherapy group (11.1%) in late genitourinary (GU) toxicities ≥ grade 2 (p = 0.035). Only 2 patients (3.3%) in the combination therapy group developed late ≥ grade 2 rectal hemorrhage. There were no significant differences between two groups in hematuria ≥ grade 2 (p = 0.068) or rectal hemorrhage ≥ grade 2 (p = 0.206).

Conclusions

To our knowledge, this is the first report to compare the GU and gastrointestinal toxicities between the combination therapy and BT monotherapy (160 Gy) for localized prostate cancer. Unexpectedly, there were more late GU toxicities (except for hematuria) in the BT monotherapy group.

Initial toxicity, quality-of-life outcomes, and dosimetric impact in a randomized phase 3 trial of hypofractionated versus standard fractionated proton therapy for low-risk prostate cancer

Purpose

Randomized evidence for extreme hypofractionation in prostate cancer is lacking. We aimed to identify differences in toxicity and quality-of-life outcomes between standard fractionation and extreme hypofractionated radiation in a phase 3 randomized trial.

Methods and materials

We analyzed the results of the first 75 patients in our phase 3 trial, comparing 38 Gy relative biologic effectiveness (RBE) in 5 fractions (n = 46) versus 79.2 Gy RBE in 44 fractions (n = 29). Patients received proton radiation using fiducials and daily image guidance. We evaluated American Urological Association Symptom Index (AUASI), adverse events (AEs), and Expanded Prostate Index Composite (EPIC) domains. The primary endpoint of this interim analysis was the cumulative incidence of grade 2 (G2) or higher AEs. The randomized patient allocation scheme was a 2:1 ratio favoring the 38 Gy RBE arm.

Results

The median follow-up was 36 months; 30% of patients reached 48-month follow-up. AUASI scores differed <5 points (4.4 vs 8.6; P = .002) at 1 year, favoring the 79.2 Gy arm. Differences in AUASI were not significant at ≥18 months. EPIC urinary symptoms favored the 79.2 Gy arm at 1 year (92.3 vs 84.5; P = .009) and 18 months (92.3 vs 85.3; P = .03); bother scores were not significant at other time points. Cumulative ≥G2 genitourinary toxicity was similar between the 79.2 Gy and 38 Gy arms (34.5% vs 30.4%; P = .80). We found no differences in the EPIC domains of bowel symptoms, sexual symptoms, or bowel ≥G2 toxicities. Bladder V80 (79.2 Gy arm; P = .04) and V39 (38 Gy arm; P = .05) were predictive for cumulative G2 genitourinary AEs.

Conclusions

Low AE rates were seen in both study arms. Early temporary differences in genitourinary scores disappeared over time. Bladder constraints were associated with genitourinary AEs.

An Investigation of Dosimetric Correlates of Acute Toxicity in Prostate Stereotactic Body Radiotherapy: Dose to Urinary Trigone is Associated with Acute Urinary Toxicity

AIMS

There are limited data on dosimetric correlates of toxicity in stereotactic body radiotherapy (SBRT) for prostate cancer. We aimed to identify potential relationships between dose and toxicity using conventional dose-volume histograms (DVHs) and dose-surface maps (DSMs).

MATERIALS AND METHODS

Urinary bladder trigone and rectum DSMs were produced for a single-institution service evaluation cohort of 50 patients receiving SBRT for localised prostate cancer, together with conventional DVHs for bladder and rectum. Patients had been prospectively recruited to this cohort and treated according to a pre-defined protocol to a dose of 36.25 Gy in five fractions. Radiation Therapy Oncology Group (RTOG) and International Prostate Symptom Score (IPSS) toxicity data were recorded prospectively. Logistic regression was used to identify dosimetric predictors of acute IPSS+10 (rise of 10 points or more above baseline) and grade 2+ RTOG toxicity.

RESULTS

On univariate analysis, trigone area receiving 40 Gy and trigone Dmax were associated with IPSS+10 (odds ratio 1.06 [1.02-1.11], P = 0.007 and odds ratio 1.54 [1.06-2.25], P = 0.024, respectively). These two variables were highly correlated. In a multivariate model, including all baseline variables, trigone Dmax remained associated with IPSS+10 (odds ratio 1.91 [1.13-3.22], P = 0.016). These findings were not significant with Holm-Bonferroni correction for multiple testing (corrected P value threshold 0.006). No associations were seen between rectal toxicity and DVH or DSM parameters.

CONCLUSIONS

Our study suggests a potential relationship between high doses to the urinary bladder trigone and patient-reported urinary toxicity in prostate SBRT, and is consistent with previous studies in conventionally fractionated radiotherapy, justifying further evaluation in larger cohorts.

Development of a prediction model for late urinary incontinence, hematuria, pain and voiding frequency among irradiated prostate cancer patients

BACKGROUND AND PURPOSE

Incontinence, hematuria, voiding frequency and pain during voiding are possible side effects of radiotherapy among patients treated for prostate cancer. The objective of this study was to develop multivariable NTCP models for these side effects.

MATERIAL AND METHODS

This prospective cohort study was composed of 243 patients with localized or locally advanced prostate cancer (stage T1-3). Genito-urinary (GU) toxicity was assessed using a standardized follow-up program. The GU toxicity endpoints were scored using the Common Terminology Criteria for Adverse Events version 3.0 (CTCAE 3.0) scoring system. The full bladder and different anatomical subregions within the bladder were delineated. A least absolute shrinkage and selection operator (LASSO) logistic regression analysis was used to analyze dose volume effects on the four individual endpoints.

RESULTS

In the univariable analysis, urinary incontinence was significantly associated with dose distributions in the trigone (V55-V75, mean). Hematuria was significantly associated with the bladder wall dose (V40-V75, mean), bladder dose (V70-V75), cardiovascular disease and anticoagulants use. Pain during urinating was associated with the dose to the trigone (V50-V75, mean) and with trans transurethral resection of the prostate (TURP). In the final multivariable model urinary incontinence was associated with the mean dose of the trigone. Hematuria was associated with bladder wall dose (V75) and cardiovascular disease, while pain during urinating was associated with trigone dose (V75) and TURP. No significant associations were found for increase in voiding frequency.

CONCLUSIONS

Radiation-induced urinary side effects are associated with dose distributions to different organs as risk. Given the dose effect relationships found, decreasing the dose to the trigone and bladder wall may reduce the incidence of incontinence, pain during voiding and hematuria, respectively.

Changes in prostate orientation due to removal of a Foley catheter

PURPOSE

Investigate the impact on prostate orientation caused by use and removal of a Foley catheter, and the dosimetric impact on men prospectively treated with prostate stereotactic body radiotherapy (SBRT).

METHODS

Twenty-two men underwent a CT simulation with a Foley in place (FCT), followed immediately by a second treatment planning simulation without the Foley (TPCT). The change in prostate orientation was determined by rigid registration of three implanted transponders between FCT and TPCT and compared to measured orientation changes during treatment. The impact on treatment planning and delivery was investigated by analyzing the measured rotations during treatment relative to both CT scans, and introducing rotations of ±15° in the treatment plan to determine the maximum impact of allowed rotations.

RESULTS

Removing the Foley caused a statistically significant prostate rotation (P < 0.0028) compared to normal biological motion in 60% of patients. The largest change in rotation due to removing a Foley occurs about the left-right axis (tilt) which has a standard deviation two to five times larger than changes in rotation about the Sup-Inf (roll) and Ant-Post (yaw) axes. The change in tilt due to removing a Foley for prone and supine patients was -1.1° ± 6.0° and 0.3° ± 7.4°, showing no strong directional bias. The average tilt during treatment was -1.6° ± 7.1° compared to the TPCT and would have been -2.0° ± 7.1° had the FCT been used as the reference. The TPCT was a better or equivalent representation of prostate tilt in 82% of patients, vs 50% had the FCT been used for treatment planning. However, 92.7% of fractions would still have been within the ±15° rotation limit if only the FCT were used for treatment planning. When rotated ±15°, urethra V_{105% = 38.85Gy}  < 20% was exceeded in 27% of the instances, and prostate (CTV) coverage was maintained above D_95%  > 37 Gy in all but one instance.

CONCLUSIONS

Removing a Foley catheter can cause large prostate rotations. There does not appear to be a clear dosimetric benefit to obtaining the CT scan with a Foley catheter to define the urethra given the changes in urethral position from removing the Foley catheter. If urethral sparing is desired without the use of a Foley, utilization of an MRI to define the urethra may be necessary, or a pseudo-urethral planning organ at risk volume (PRV) may be used to limit dosimetric hot spots.

Reductions in prostatic doses are associated with less acute morbidity in patients undergoing Pd-103 brachytherapy: Substantiation of the rationale for focal therapy

PURPOSE

Interest in prostate dose reduction or focal treatment exists due to expected reductions in treatment morbidity. Prior analyses have not generally corroborated relationships between prostate or urethral dose and urinary toxicity after brachytherapy, but such analyses have been performed on cohorts all receiving the same prescribed dose. We analyzed patients treated to differing prescription doses to assess acute urinary morbidity with dose reduction.

METHODS AND MATERIALS

Patients treated with Pd-103 to either 125 Gy or 90-100 Gy were compared using the International Prostate Symptom Score (IPSS) at 1-month postimplant. Patients in the 90-100 Gy cohort began external beam radiation therapy after their 1-month assessment; thus, toxicities were measured before contribution from external beam radiation therapy. Patient/treatment characteristics were compared to verify subgroup homogeneity. Dose and change in IPSS 1 month after treatment were assessed using a multivariate linear regression model.

RESULTS

One hundred ninety-one and 41 patients were treated with 125 Gy versus 90-100 Gy, respectively. Preimplant and postimplant prostate volumes and initial IPSS were similar between groups. Higher prescription dose and increased pretreatment IPSS were independent predictors of increased 1-month IPSS. In addition, every 10 percentage point additional prostate volume receiving a given dose was associated with increase in IPSS after treatment for the same level of pretreatment IPSS.

CONCLUSION

Lower prescription dose and decreased volume of high-dose regions to the prostate correlated with reduced acute urinary morbidity after brachytherapy. Our findings suggest that focal treatment approaches with modest dose reductions to subregions of the prostate may reduce acute morbidity and potentially expand the number of patients eligible for brachytherapy.

Comparison of prostate distortion by inflatable and rigid endorectal MRI coils in permanent prostate brachytherapy imaging

PURPOSE

To study the deformation of the prostate by a rigid reusable endorectal coil and a balloon-type endorectal coil (BTC) during MRI of the prostate in brachytherapy imaging.

METHODS AND MATERIALS

The prostate gland was contoured on 157 MRI scans from 52 prostate cancer patients undergoing brachytherapy. The curvature of the posterior prostate surface deformation was computed as a measure of prostate distortion and compared between scans with a BTC, rigid endorectal coil (REC), or no endorectal coil. For the nine patients who had MRIs with all three endorectal scenarios, a mean prostate deformation vector was also calculated between scenarios using deformable image registration. These measures of prostate distortion were compared with the prostate anterior-to-posterior to left-to-right ratio (AP/LR) on the largest prostate axial slice.

RESULTS

Significant differences in prostate curvature were found between scans without an endorectal coil versus a REC versus a BTC (p < 0.001). The mean prostate deformation was 3.9 mm due to the BTC and 2.0 mm for the REC (p = 0.012). The mean AP/LR ratio was 0.62 with a BTC versus 0.76 without a coil or 0.73 with a REC (p < 0.001), but no difference existed between scans with a REC versus no coil (p = 0.7). The AP/LR ratio showed moderate correlation with prostate curvature (r = 0.48), and with mean prostate deformation (r = -0.64 to 0.68).

CONCLUSIONS

The REC caused minimal deformation of the prostate compared with a BTC with adequate MR image quality, and calculation of the cross-sectional AP/LR ratio on the largest axial prostate slice can serve as a simple measure of prostate distortion.

[Therapeutic innovations in radiation oncology for localized prostate cancer]

Intensity-modulated radiation therapy, image-guided radiation therapy with fiducial markers and prostate brachytherapy allow the delivery of dose escalation for localized prostate cancer with very low rates of long-term toxicity and sequelae. Nowadays, modern radiotherapy techniques make it possible to shorten treatment time with hypofractionation, to better protect surrounding healthy tissues and to escalate the dose even further. Advances in radiotherapy are closely linked to advances in magnetic resonance imaging (MRI) and/or PET imaging. Functional imaging makes it possible to deliver personalised pelvic nodal radiotherapy, targeting the nodal areas at higher risk of microscopic involvement. In patients with an index lesion at baseline or at failure, MR-based focal therapy or focal dose escalation with brachytherapy or stereotactic body radiation therapy is also currently investigated. MR-based adaptive radiotherapy, which makes it possible to track prostate shifts during radiation delivery, is another step forward in the integration of MR imaging in radiation delivery.

Stereotactic Body Radiation Therapy for Localized Prostate Cancer

Stereotactic body radiation therapy (SBRT) has become a viable treatment option for the many patients who receive a diagnosis of localized prostate cancer each year. Technological advancements have led to tight target conformality, allowing for high-dose-per-fraction delivery without untoward normal tissue toxicity. Biochemical control, now reported up to 5 years, appears to compare favorably with dose-escalated conventionally fractionated radiotherapy. Moreover, toxicity and quality of life follow-up data indicate genitourinary and gastrointestinal toxicities are likewise comparable to conventional radiation therapy. Nevertheless, because of the long natural history of prostate cancer, extended follow-up will be necessary to confirm these impressive initial results. Within this prostate SBRT review, we explore the detailed rationale for SBRT treatment, the diverse SBRT techniques utilized and their unique technical considerations, and finally data for SBRT clinical efficacy and treatment-related toxicity.

Association of bladder dose with late urinary side effects in cervical cancer high-dose-rate brachytherapy

PURPOSE

The purpose of this work was to study the association between specific urinary sequelae and locally accumulated dose to the bladder wall and bladder neck in the treatment of cervical cancer with multifraction high-dose-rate (HDR) brachytherapy.

METHODS AND MATERIALS

A cohort of 60 cervical cancer patients, treated with both external beam and five HDR brachytherapy insertions between 2008 and 2014 at the BC Cancer Agency, was identified. The accumulated dose received over five brachytherapy sessions was evaluated for the bladder wall and bladder neck of each patient using dosimetric parameters calculated from deformably registered image data sets. These parameters were examined as potential predictors of urinary sequelae including hematuria, frequency, urgency, incontinence, stream, nocturia, and dysuria. Two different dichotomization schemes were evaluated for grouping patients into Case and Control groups. The two-sample Student's t test was used for normally distributed samples and the Mann-Whitney nonparametric U test for non-normal distributions.

RESULTS

A strong association between dose to the bladder neck and incontinence was found (p = 0.001). A statistically significant association (p < 0.05) was also observed between urgency and certain bladder-wall parameters.

CONCLUSIONS

Localized dose to the bladder neck is a potential predictor of urinary incontinence, whereas weaker associations were observed between urgency and some bladder-wall parameters.