Dosimetric outcomes in prostate brachytherapy: Is downsizing the prostate with androgen deprivation necessary?

ObjectivesA large prostate volume has historically been a relative contraindication to prostate brachytherapy (PB) because of concerns of toxicity and potential pubic arch interference. Common practice has been to downsize large prostates with androgen deprivation therapy (ADT) before proceeding with brachytherapy. The present study compares postimplant dosimetry in patients with prostate volumes >50 cc with those with prostate volumes ≤50 cc.MethodsA review of all patients who underwent PB at our institution from 2001 to 2006 was performed. Postimplant dosimetry was obtained approximately 4 weeks after brachytherapy.ResultsOne-hundred forty-five out of a total of 148 patients had available dosimetry. In the 113 patients with prostate volumes ≤50 cc (mean, 35.4 cc, range, 14.2–49.7 cc); the mean D₉₀ (dose which covers 90% of the prostate), V₁₀₀ (volume of prostate receiving 100% of the prescribed dose), V₁₅₀ (volume of prostate receiving 150% of the prescribed dose), and V₂₀₀ (volume of prostate receiving 200% of the prescribed dose) was 128.9%, 95.6%, 73.9%, and 51.2%, respectively. In the 32 patients with prostate volumes >50 cc (mean 58.1 cc, range 50.2–86.0 cc); the mean D₉₀, V₁₀₀, V₁₅₀, and V₂₀₀ was 125.1%, 95.2%, 68.2%, and 41.7%, respectively. The rectal V₁₀₀ was 1.0 cc for both cohorts. There was no statistically significant difference between the cohorts with respect to postimplant dosimetry for D₉₀, V₁₀₀, and V₁₅₀. The V₂₀₀ for prostate volumes >50 cc was significantly lower (p < 0.05).ConclusionsIn the present study, patients with prostate volumes >50 cc have postimplant dosimetry parameters similar to patients with prostate volumes ≤50 cc for D₉₀, V₁₀₀, and V₁₅₀; and significantly lower values for V₂₀₀. These results suggest that patients with large prostate volumes may not need to be routinely placed on hormonal therapy; sparing patients the side effects of hormonal therapy, and sparing the health care system the costs of luteinizing hormone-releasing hormone agonist injections.     

Overcoming pubic arch interference with free-hand needle placement in men undergoing prostate brachytherapy

PurposeThe present study evaluates the postimplant dosimetry when free-hand needles were placed to overcome interference from the pubic arch.Methods and MaterialsA review of all patients who underwent prostate brachytherapy at our institution from 2001 to 2006 was performed. Postimplant dosimetry in men requiring free-hand needle placement was compared with postimplant dosimetry in men not requiring free-hand needle placement.ResultsOf the 145 patients who underwent prostate brachytherapy, 8 patients required free-hand needle placement. The mean prostate volume in the free-hand needle cohort was 46.0 cc with a mean of 3.4 free-hand needles placed. In the 137 patients not requiring free-hand needle placement, the mean volume was 39.7 cc. The mean D₉₀, V₁₀₀, V₁₅₀, and rectal V₁₀₀ for the free-hand cohort was 129.5%, 96.3%, 81.6%, and 1.45 cc, respectively. The mean D₉₀, V₁₀₀, V₁₅₀, and rectal V₁₀₀ in men not requiring free-hand needle placement was 126.8%, 97.1%, 78.7%, and 1.03 cc, respectively.ConclusionThe present study finds that adequate postimplant dosimetry can be obtained if free-hand needles are required due to pubic arch interference.     

Differences between intraoperative ultrasound-based dosimetry and postoperative computed tomography-based dosimetry for permanent interstitial prostate brachytherapy

PurposeTo compare the results of intraoperative ultrasound (US)-based dosimetry with those of postimplant computed tomography (CT)-based dosimetry after ¹²⁵I prostate brachytherapy.Methods and MaterialsSubjects comprised 160 patients who underwent prostate brachytherapy using ¹²⁵I seed implants. Prescribed dose was set as 145 Gy to the periphery of the prostate. Implantation was performed using an intraoperative interactive technique. Postimplant dosimetry was performed on Days 1 and 30 after implantation using CT. Dosimetric results for the prostate, urethra, and rectum were compared among intraoperative US and CT on Day 1 (CT₁) and Day 30 (CT₃₀).ResultsMean minimal dose received by 90% of prostate volume was 133.7%, 115.6%, and 125.8% of the prescribed dose on US, CT₁, and CT₃₀, respectively: This value temporarily decreased on Day 1 and increased on Day 30. Other parameters for the prostate and urethra showed similar trends. Conversely, mean rectal volume receiving 100% of the prescribed dose was 0.69, 0.46, and 1.02 mL on US, CT₁, and CT₃₀, respectively. Rectal parameters tended to be underestimated on US relative to CT₃₀-based dosimetry. A positive linear relationship was identified between US and CT observations for every prostate parameter and the dose covering 30% of the urethra.ConclusionsOur results demonstrate significant differences between dosimetric parameters obtained by US, CT₁, and CT₃₀. However, significant correlations also exist between US and CT, at least in prostate and urethral parameters. Clarification of the degrees of difference might make US planning more feasible.     

Improving prostate brachytherapy quality assurance with MRI–CT fusion–based sector analysis in a phase II prospective trial of men with intermediate-risk prostate cancer

PurposeWe combined sector analysis with MRI–CT fusion to comprehensively assess postimplant dosimetry after prostate brachytherapy.Methods and MaterialsSubjects were 50 men with intermediate-risk prostate cancer treated with ¹²⁵I brachytherapy in a prospective phase II clinical trial. On Day 30 after the implantation, dosimetry was evaluated in the prostate base, midgland, and apex regions on fused MRI–CT scans and CT scans. Volumes of each sector receiving 100% of the prescribed dose (V₁₀₀) and doses to 90% of each sector (D₉₀) were also calculated on the ultrasonogram used for treatment planning and compared with values derived from CT and fused MRI–CT scans.ResultsFused MRI–CT scans revealed lower-than-expected doses for the whole prostate (V₁₀₀ = 91.3%, D₉₀ = 152.9 Gy) compared with CT scans (98.5% and 183.6 Gy, p < 0.0001) and lower doses to the prostate base (V₁₀₀ = 79%, D₉₀ = 130 Gy) vs. CT (96% and 170 Gy, p < 0.0001). However, lower doses to the prostate base did not adversely affect biochemical outcomes in men with biopsy-proven disease at the base. At a median followup time of 42 months, the mean prostate-specific antigen level for all patients was 0.3 ng/mL, and no patient had experienced biochemical or clinical progression or recurrence.ConclusionsMRI–CT fusion–based sector analysis was feasible and revealed significantly lower doses to the prostate base than doses estimated from CT alone, although this did not affect biochemical outcomes. MRI–CT fusion–based sector analysis may be useful for developing MRI-based dosimetric markers to predict disease outcomes and treatment-related morbidity.     

Impact of MRI-based postimplant dosimetric assessment in prostate brachytherapy using contrast-enhanced T1-weighted images

PurposeTo compare contrast-enhanced T1-weighted (CE-T1WI) magnetic resonance imaging (MRI) with computed tomography (CT) for postimplant dosimetry and seed recognition in prostate brachytherapy.Methods and MaterialsA total of 245 patients who received ¹²⁵I prostate brachytherapy with or without external beam radiotherapy were enrolled. For postimplant analysis, CT and MRI scans were obtained at 1 month after seed implantation. For MRI-based dosimetry, T2-weighted images were fused with the CE-T1WI; the prostate was delineated on the T2-weighted images, and the seed detection was performed manually on the CE-T1WI. In CT-based dosimetry, the seed detection was essentially performed automatically. The dosimetric results obtained by MRI-based and CT-based dosimetry were compared.ResultsThe mean prostate D₉₀ (the minimum dose received by 90% of the prostate volume) estimated by MRI-based and CT-based dosimetry were 113% and 115%, respectively, with no significant difference. The mean prostate V₁₀₀ (the percent volume of the postimplant prostate receiving 100% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 95.2% and 95.8%, respectively, again with no significant difference. The mean prostate V₁₅₀ (the percent volume of the postimplant prostate receiving 150% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 52.8% and 57.0%, respectively (p < 0.01). In all of the 35 patients (14%) in whom the MRI-based V₁₅₀ were at least 10% lower than the CT-based results, the seed detection by CT-based dosimetry was overestimated in highly seed-clustered areas or in the areas close to calcifications because of reconstruction artifacts in CT images.ConclusionsMRI-based dosimetry using CE-T1WI appears to be acceptable. Our results suggest that MRI-based dosimetry is a practical method for estimation of the higher dose distribution, especially if seeds are clustered together or when they are close to calcifications.     

First report on the use of a thinner 125I radioactive seed within 20-gauge needles for permanent radioactive seed prostate brachytherapy: Evaluation of postimplant dosimetry and acute toxicity

PurposeTo compare postoperative dosimetry and acute toxicity of new 0.5-mm ¹²⁵I seeds in 20-gauge (20G) diameter prostate brachytherapy (PB) needles with standard 0.8-mm seeds in 18G needles.Methods and MaterialsPostoperative dosimetry was performed on 100 consecutive PB patients treated with ThinSeeds in 20G needles and compared with 100 consecutively treated PB patients using standard-sized seeds and needles (18G). Dosimetry was performed on postoperative Day 1 CT scans. Acute urinary retention was also compared between these two groups. Acute toxicity was evaluated in 22 consecutively treated patients with thinner seeds/needles and compared with 22 consecutive concurrent patients treated with standard seeds and needles. All patients were evaluated by pre- and post-PB self-administered surveys, physical examinations on post-PB Day 1, and telephone surveys on Day 7. Endpoints included dysuria, acute urinary retention, hematuria, perineal pain/bruising, and International Prostate Symptom Score.ResultsPost-PB dosimetric comparison demonstrated that the V₁₀₀ (95% vs. 91%), D₉₀ (161 Gy vs.149 Gy), V₁₅₀ (55% vs. 45%), and RV₁₀₀ (0.43 cc vs. 0.30 cc) were significantly (p < 0.0004) higher in the 20G group. Urinary retention rates were 8% and 7% and median catheter-dependent durations were 7 and 14 days for the 20G and 18G groups, respectively. No significant differences were found for dysuria, hematuria, or International Prostate Symptom Score. Post-PB Day 1 perineal bruising and pain scores on Days 1 and 7 were significantly less (p < 0.04) in 20G cohort.ConclusionsSmaller diameter needles and seeds resulted in improved post-PB Day 1 V₁₀₀ and D₉₀ dosimetry, and significantly less acute perineal pain and bruising.     

Live implant dosimetry may be an effective replacement for postimplant computed tomography in localized prostate cancer patients receiving low dose rate brachytherapy

PurposeTo determine if Live Implant Dosimetry (LIDO) utilizing intraoperative transrectal ultrasound (TRUS) is equivalent to postimplant CT dosimetry (either day 0 or day 30) in patients with localized prostate cancer (PC) treated with low dose rate (LDR) prostate seed brachytherapy.Methods and MaterialsThe treated population consisted of 628 men with localized (T1-T2) PC. All d'Amico risk categories (low, intermediate, and high) were included, and 437 patients were treated with monotherapy (160 Gy) [low and low tier intermediate], and the remainder (191) [high tier intermediate and high risk] with an implant boost (106 Gy) post external beam radiation, to a volume including the prostate and seminal vesicles (46 Gy). LIDO with intraoperative TRUS, postimplant CT (day 0 and day 30) were performed in all cases. Prostate volumes (V), V₁₀₀ (prostate) and dose (D) D₉₀ (prostate), D₃₀ (urethra), and Rectum D_2cc, were recorded. No urinary catheter was used on Day 30 CT.ResultsMore than 91.33% of monotherapy patients reached the target D₉₀ according to LIDO while only 82.99% of Day 0 CT and 92.82% of Day 30 CT achieved target D₉₀. When considering V₁₀₀, monotherapy patients recorded target dosimetry in 90.93%, 82.31%, and 92.02% of cases assessed by LIDO, Day 0 CT and Day 30 CT, respectively. Strong correlations are observed in D₉₀, Rectum D_2cc and Urethra D₃₀ across imaging modalities but V₁₀₀ and V₁₅₀ were poorly correlated due to the relative quantification of this parameter and high degree of error in measurement. Of all monotherapy patients with satisfactory dosimetry on LIDO, 94.82% reached target D₉₀ at day 30 CT and 94.19% reached target V₁₀₀.ConclusionsLIDO and CT are both effective tools for assessing postimplant dosimetry. Patients with satisfactory LIDO dosimetry are highly likely to have equivalent dosimetry on CT at follow-up, indicating that postimplant CT may be eliminated in PC a patients implanted with this technique.     

Prostate brachytherapy intraoperative dosimetry using a combination of radiographic seed localization with a C-arm and deformed ultrasound prostate contours

PurposeThe purpose of the study was to assess the feasibility of performing intraoperative dosimetry for permanent prostate brachytherapy by combining transrectal ultrasound (TRUS) and fluoroscopy/cone beam CT [CBCT] images and accounting for the effect of prostate deformation.Methods and Materials13 patients underwent TRUS and multiview two-dimensional fluoroscopic imaging partway through the implant, as well as repeat fluoroscopic imaging with the TRUS probe inserted and retracted, and finally three-dimensional CBCT imaging at the end of the implant. The locations of all the implanted seeds were obtained from the fluoroscopy/CBCT images and were registered to prostate contours delineated on the TRUS images based on a common subset of seeds identified on both image sets. Prostate contours were also deformed, using a finite-element model, to take into account the effect of the TRUS probe pressure. Prostate dosimetry parameters were obtained for fluoroscopic and CBCT-dosimetry approaches and compared with the standard-of-care Day-0 postimplant CT dosimetry.ResultsHigh linear correlation (R² > 0.8) was observed in the measured values of prostate D_90%, V_100%, and V_150%, between the two intraoperative dosimetry approaches. The prostate D_90% and V_100% obtained from intraoperative dosimetry methods were in agreement with the postimplant CT dosimetry. Only the prostate V_150% was on average 4.1% (p-value <0.05) higher in the CBCT-dosimetry approach and 6.7% (p-value <0.05) higher in postimplant CT dosimetry compared with the fluoroscopic dosimetry approach. Deformation of the prostate by the ultrasound probe appeared to have a minimal effect on prostate dosimetry.ConclusionsThe results of this study have shown that both of the proposed dosimetric evaluation approaches have potential for real-time intraoperative dosimetry.     

Relationship between Day 0 dosimetric parameters and biochemical relapse-free survival in patients treated with transperineal permanent prostate interstitial brachytherapy with 125I seeds

ObjectivesTo determine the relationship between dosimetric parameters obtained on postimplantation Day 0 and biochemical relapse-free survival (bRFS) in patients treated with ¹²⁵I transperineal interstitial permanent prostate brachytherapy (TIPPB).MethodsTwo-hundred twenty men with low-risk (n = 155, 70.4%), low-volume intermediate-risk (n = 63, 28.7%), or high-risk (n = 2, 0.9%) prostate cancer were treated with TIPPB between December 2000 and June 2006. Seventy-four (33.6%) patients received short-term (3–6 months) androgen suppression therapy before TIPPB. The median followup for patients free of biochemical failure was of 37.9 months (range, 24.0–84.5 months).ResultsThe receiver operating characteristic (ROC) analysis established a best-fit cutoff value for the quantifiers D₉₀ and V₁₀₀ of 147 Gy and 92%, respectively. The Kaplan–Meier analysis of bRFS at the cutoff value of D₉₀ = 147 Gy using the ASTRO, nadir + 2, and combined (ASTRO and nadir + 2) definitions showed a trend toward statistical significance for the ASTRO (p = 0.076) and nadir + 2 (p = 0.064) definitions and a statistically significant correlation for the combined definition (p = 0.033). The corresponding 7-year bRFS for the D₉₀ >147 Gy and D₉₀ ≤147 Gy subsets using the ASTRO, nadir + 2, and combined definitions were 96.5% vs. 89.7% (ASTRO, p = 0.076); 93.7% vs. 70.5% (nadir + 2, p = 0.064); and 94.4 vs. 75.5% (combined, p = 0.033). The V₁₀₀ (%) cutoff value of 92% predicted by the ROC analysis was not significant. Among other cutoff values, only D₉₀ = 140 Gy (p = 0.050) and D₉₀ = 160 Gy (p = 0.098) showed a trend toward statistical significance when the nadir + 2 and the ASTRO definitions were used. The rest of dosimetric, tumor, and patient parameters did not show statistical correlation with bRFS in the Kaplan–Meier analysis.ConclusionsThe cutoff value of D₉₀ = 147 Gy obtained on postimplantation Day 0 showed a trend toward significant correlation with bRFS when the standard ASTRO and nadir + 2 definitions were used and a weak but statistically significant correlation with bRFS as per the nonstandard combined definition in a series of patients with predominantly low-risk disease (70.4%) treated at high radiation doses (median D₉₀ = 152.9 Gy, median V₁₀₀ = 92.5%).     

Is there any advantage to three-dimensional planning for vaginal cuff brachytherapy?

PurposeTo evaluate whether the three-dimensional (3D) CT-based high-dose rate planning for vaginal cuff brachytherapy offers any advantage over the 2D orthogonal film-based library plans for adjuvant treatment of endometrial cancers.Methods and MaterialsEighty-four consecutive postoperative patients with endometrial cancers treated with vaginal brachytherapy as an adjuvant treatment were analyzed. Patients had CT imaging-based plans. Clinical target volume (CTV) was defined by expanding the upper 2.5 cm of the cylinder by 5 mm in all directions and editing to exclude any bladder and rectum. The dose prescribed was 7 Gy with three fractions at 5 mm depth with a goal of D₉₀ ≥100% for CTV. All dosimetric parameters were compared with library-based plans.ResultsBoth the 2D- and 3D-based plans allowed sufficient dosage to the CTV (D₉₀ for CTV ≥95%). The doses of 0.1, 1, and 2 cc to rectum and bladder were significantly higher for 2D-based plans (p ≤ 0.001 in each parameter). D_{2 cc} with 2D plan for rectum and bladder was >100% (range: 103–116%) in 7 (8%) and 6 (7%) patients, respectively. In contrast, no patients had D_{2 cc} >100% with 3D planning for both organs.ConclusionThree-dimensional CT-based planning for high-dose rate vaginal cuff brachytherapy helps to decrease dose to critical organs without compromising coverage of CTV by customizing the dosimetry according to individual patient anatomy.     

Dosimetric effect of interfractional needle displacement in prostate high-dose-rate brachytherapy

PurposeTo quantify the dosimetric deviations that would arise from delivering subsequent prostate high-dose-rate fractions with only needle readjustment and no replanning after the first fraction.Methods and MaterialsPatients were treated with either two implant sessions (two 9.5-Gy fractions per session) separated by 2–4 weeks or with one implant session and external beam radiotherapy. After needle placement, needle positions were adjusted under CT guidance, after which dosimetric planning was performed before each fraction. To evaluate the consequence of not replanning before the second fraction, we analyzed the dosimetric parameters of 45 consecutive implants (26 patients). Needles with optimized dwell positions from the first fraction were transferred to the needle positions in the second fraction. Needle displacement between fractions was assessed as well as changes in plan metrics.ResultsAfter adjustment, the mean interfractional needle displacement was 3.5 mm. If replanned, the probability of planning target volume D_90% ≥95% is 100%, prostate V_100% ≥95% is 87%, and urethra V₁₁₅% ≤10% is 78%. If treated without replanning, the probability of planning target volume D_90% ≥95% is 82%, prostate V_100% ≥95% is 53%, and urethra V_115% ≤10% is 69%. Even for implants with minimal needle displacement (<3 mm) and minimal prostate volume change (<3 cc), the dosimetric consequence of not replanning the second fraction would result in 46% of cases with a prostate V_100% <95%.ConclusionThe dosimetric consequences of not replanning the second fraction for prostate high-dose-rate implants results in significantly inferior plan metrics.     

Comparison of low and intermediate source strengths for 125I prostate brachytherapy implants

PurposeTo compare the implant quality and clinical outcomes for patients treated with low and intermediate strength ¹²⁵I seeds in prostate brachytherapy implants.Methods and MaterialsThis retrospective review included 390 consecutive patients treated with prostate brachytherapy from 1999 to 2006. The first 142 patients were implanted with source strengths lower than 0.415 U (0.327 mCi), with the subsequent 248 patients implanted with source strengths higher than 0.493 U (0.388 mCi). Clinical, dosimetric, toxicity, and outcome data were compared between these two cohorts of patients.ResultsDespite having similar prostate volumes, fewer sources (median, 95 vs. 113; p < 0.0001) and fewer needles (median, 23 vs. 29; p < 0.0001) were implanted in the intermediate strength cohort. The postimplant dosimetry demonstrated better quality implants in patients treated with intermediate strength sources (median D₉₀, 160.0 Gy vs. 139.6 Gy; p < 0.0001), with greater dose inhomogeneity identified in the intermediate strength cohort of patients. A higher incidence of late rectal toxicity was identified in patients treated with intermediate strength sources despite lower rectal doses in this cohort. The biochemical relapse-free survival, prostate cancer survival, and overall survival were not significantly different between the two cohorts.ConclusionsThe transition from low to intermediate strength sources has led to fewer resources being used and improved postoperative dosimetry. Although there were more rectal complications identified in the intermediate strength cohort of patients in this analysis, there were no other significantly worse clinical or biochemical outcomes for patients implanted with intermediate strength sources.     

Prostate cancer control and survival in Vietnam veterans exposed to Agent Orange

BackgroundIn this study, we evaluated the impact of Agent Orange exposure on survival in Vietnam Veterans undergoing prostate brachytherapy.Methods and MaterialFrom May 1995 to January 2005, 81 Vietnam veterans (29 with Agent Orange exposure and 52 without) and 433 nonveterans of comparable age (mean age, 58 years) underwent prostate brachytherapy. The mean follow-up was 5.0 years. Biochemical progression-free survival (bPFS) was defined as a prostate-specific antigen (PSA) ≤ 0.40 ng/mL after nadir. Patients with metastatic prostate cancer or hormone refractory disease without obvious metastases who died of any cause were classified as died of prostate cancer. All other deaths were attributed to the immediate cause of death. Multiple parameters were evaluated for impact on survival.ResultsAt 9 years, Agent Orange–exposed men were least likely to remain biochemically controlled (89.5%, 100%, and 97.2% in Agent Orange–exposed, nonexposed veterans, and nonveterans, respectively, p = 0.012). No significant differences in cause-specific (CSS) (p = 0.832) or overall survival (OS) (p = 0.363) were discerned. In multivariate analysis, CSS was best predicted by Gleason Score and day 0 D₉₀, whereas Gleason Score, % positive biopsies, and D₉₀ predicted for bPFS. None of the evaluated parameters predicted for OS, however, a trend was identified for better OS in younger patients and those with a higher D₉₀. In addition, Agent Orange exposure did not predict for any of the survival parameters. To date, 22 patients have died (metastatic prostate cancer two, second malignancies nine, cardiovascular disease eight, trauma two, and pulmonary one).ConclusionsIn this cohort of prostate brachytherapy patients, Agent Orange exposure did not statistically impact survival in multivariate analysis.     

Biochemical and clinical experience with real-time intraoperatively planned permanent prostate brachytherapy

PurposeTo evaluate patient characteristics and dosimetric parameters that predict biochemical failure (BCF) after real-time planned low-dose-rate prostate brachytherapy.MethodsFrom 1998 to 2008, a low-risk cohort by National Comprehensive Cancer Network criteria of 341 men with a median followup of 41.6 months was analyzed. This cohort had a median age of 65.1 years, prostate volume of 35.8 cc, and pretreatment prostate-specific antigen of 5.6 ng/mL. Patients had predominately Gleason 6 (95.9%) and T1c (81.3%) disease. About 3.6% of the patients received androgen deprivation therapy. Kaplan–Meier and Cox proportional hazards survival analysis methods were used to analyze predictors of BCF (Phoenix definition).ResultsAt 72 months, freedom from BCF was 91.1% (95% confidence interval = 85.0–94.8). The median D₉₀ was 145.9 Gy, and the median V₁₀₀ was 90.3%. Because of infrequent BCF, the following prostate volume groups were examined: 15–<25, 25–<35, 35–<45, and 45+ cc. Of all possible predictors, only small prostate volume (15–<25 cc group) was significantly associated with BCF (hazard ratio = 8.44, 95% confidence interval = 1.82–39.14, p = 0.007). Using Kaplan–Meier analysis, time to BCF was also significantly increased in the lowest prostate volume 15–<25 cc group with 24.1% failing at 48 months compared with 1.6–5.1% among the other groups.ConclusionsReal-time planned low-dose-rate prostate brachytherapy provides excellent biochemical control as a single-agent treatment for low-risk prostate cancer with 91.1% freedom from BCF at 72 months. Only prostate volume less than 25 cc was an independent predictor of BCF.