Prostate-Specific Antigen 5 Years following Stereotactic Body Radiation Therapy for Low- and Intermediate-Risk Prostate Cancer: An Ablative Procedure?

Independent association between prostate-specific antigen nadir and PSA progression-free survival in first-line abiraterone acetate treatment in castration-resistant prostate cancer patients: a pilot study

Background

There is limited evidence regarding the correlation between prostate-specific antigen (PSA) kinetics and clinical outcomes. Therefore, after regulating other covariates, we studied patients with castration-resistant prostate cancer who received abiraterone acetate as the first-line treatment. In this study, we investigated whether time to PSA nadir was independently associated with PSA progression-free survival (PFS).

Methods

As a retrospective cohort study, this study contained a total of 77 castration-resistant prostate cancer patients who received abiraterone acetate from October 2015 to April 2021 in a Chinese hospital. The dependent variable was PSA-PFS. The objective independent variable was time to PSA nadir (TTPN). Covariates involved in this study included age, duration of androgen deprivation therapy (ADT), PSA level at baseline, time of 50% PSA decline, time of PSA decline to nadir, Gleason score, bone metastasis, previous treatment, PSA decline <50% in 3 months, PSA to nadir in 3 months, PSA decline <90%, PSA decline <0.2 ng/mL, and PSA flare.

Results

For the 77 subjects, their mean age was 72.70 ± 8.08 years. Fully calibrated linear regression findings indicated that PSA decline and kinetics were positively associated with PFS (months) after adjusting confounders (β = 0.77, 95% CI: 0.11-1.44). A non-linear relationship was not detected between PSA decline or PSA kinetics and progression-free survival.

Conclusion

According to the data of this study, there was a correlation between early PSA changes and patients treated with abiraterone acetate.

Photon vs proton hypofractionation in prostate cancer: A systematic review and meta-analysis

BACKGROUND

High-level evidence on hypofractionated proton therapy (PT) for localized and locally advanced prostate cancer (PCa) patients is currently missing. The aim of this study is to provide a systematic literature review to compare the toxicity and effectiveness of curative radiotherapy with photon therapy (XRT) or PT in PCa.

METHODS

PubMed, Embase, and the Cochrane Library databases were systematically searched up to April 2022. Men with a diagnosis of PCa who underwent curative hypofractionated RT treatment (PT or XRT) were included. Risk of grade (G) ≥ 2 acute and late genitourinary (GU) OR gastrointestinal (GI) toxicity were the primary outcomes of interest. Secondary outcomes were five-year biochemical relapse-free survival (b-RFS), clinical relapse-free, distant metastasis-free, and prostate cancer-specific survival. Heterogeneity between study-specific estimates was assessed using Chi-square statistics and measured with the I2 index (heterogeneity measure across studies).

RESULTS

A total of 230 studies matched inclusion criteria and, due to overlapped populations, 160 were included in the present analysis. Significant lower rates of G ≥ 2 acute GI incidence (2 % vs 7 %) and improved 5-year biochemical relapse-free survival (95 % vs 91 %) were observed in the PT arm compared to XRT. PT benefits in 5-year biochemical relapse-free survival were maintained for the moderate hypofractionated arm (p-value 0.0122) and among patients in intermediate and low-risk classes (p-values < 0.0001 and 0.0368, respectively). No statistically relevant differences were found for the other considered outcomes.

CONCLUSION

The present study supports that PT is safe and effective for localized PCa treatment, however, more data from RCTs are needed to draw solid evidence in this setting and further effort must be made to identify the patient subgroups that could benefit the most from PT.

Disease control outcomes of stereotactic body radiation therapy or moderate hypo-fractionation for prostate cancer: Real-world experience at two Canadian centers

BACKGROUND

Advantages of using stereotactic body radiation therapy to treat prostate cancer include short treatment times, decreased costs, and limited toxicity. Randomized trial outcomes comparing 5-fraction stereotactic body radiation therapy to conventionally fractionated radiotherapy or hypo-fractionated radiation therapy are pending.

OBJECTIVE

We report the 10-year experience with 5-fraction stereotactic body radiation therapy and hypo-fractionated radiation therapy at two Canadian centers.

MATERIAL AND METHODS

Patients with low- or intermediate-risk prostate cancer treated with stereotactic body radiation therapy alone (35-40 Gy in 5 fractions) or hypo-fractionated radiation therapy alone (60-62 Gy in 20 fractions) in the period of July 2010 and June 2020. The biochemical relapse-free survival, PSA nadir, interval time to PSA nadir, time to biochemical recurrence (2 ng/ml above PSA nadir) and overall survival were reviewed. Outcomes between treatment groups were compared after propensity-matching by patient baseline characteristics. Kaplan-Meier curves were used to assess biochemical relapse-free survival and overall survival.

RESULTS

We identified 205 and 513 patients with low or intermediate-risk prostate cancer who were treated with stereotactic body radiation therapy or hypo-fractionation, respectively. Intermediate-risk category composed 81% and 95% of the stereotactic body radiation therapy and hypo-fractionated radiation therapy cohorts, respectively. After a median follow up of 58.6 months for the stereotactic body radiation therapy cohort and 45.0 months for the hypo-fractionated cohort, biochemical relapse-free survival and overall survival were not significantly different between treatment groups. The 5-year biochemical relapse-free survival rates were 92.1% and 93.6% and overall survival rates were 96.4% and 95.0% for the stereotactic body radiation therapy and hypo-fractionated cohorts, respectively, after propensity-matching. Stereotactic body radiation therapy resulted in a significantly lower PSA nadir (0.18 ng/ml) compared to hypo-fractionated radiation therapy (0.48 ng/ml) in patients with low-risk prostate cancer. Mean time to biochemical recurrence was not different between treatment groups.

CONCLUSIONS

Stereotactic body radiation therapy is an effective treatment option for low and intermediate-risk prostate cancer with encouraging biochemical relapse-free survival and overall survival rates comparable with hypo-fractionated radiation therapy.

The march toward single-fraction stereotactic body radiotherapy for localized prostate cancer-Quo Vadimus?

PURPOSE

Stereotactic body radiotherapy (SBRT) is an emerging treatment option for localized prostate cancer. There is increasing interest to reduce the number of fractions for prostate SBRT.

METHODS

We provide a narrative review and summary of prospective trials of different fractionation schedules for prostate SBRT, focusing on efficacy, toxicities, and quality of life outcomes.

RESULTS

There are two randomized phase 3 trials comparing standard external beam radiotherapy with ultra-hypofractionated radiotherapy. HYPO-RT-PC compared 78 Gy in 39 fractions vs 42.7 Gy in 7 fractions (3D-CRT or IMRT) showing non-inferiority in 5-year biochemical recurrence-free survival and equivalent tolerability. PACE-B trial compared 78 Gy in 39-fraction or 62 Gy in 20-fraction vs 36.25 Gy in 5-fraction prostate SBRT, with no significant differences in toxicity outcomes at 2 years. Five-year efficacy data for PACE-B are expected in 2024. Five-fraction prostate SBRT is currently the most common and well-established fractionation schedule with multiple prospective phase 2 trials published to date. There is more limited data on 1-4 fraction prostate SBRT. All fractionation schedules had acceptable toxicity outcomes. Experience from a high-dose-rate brachytherapy randomized trial showed inferior efficacy with single-fraction compared to two-fraction brachytherapy. Hence, caution should be applied in adopting single-fraction prostate SBRT.

CONCLUSION

Two-fraction SBRT is likely the shortest fractionation schedule that maintains the therapeutic ratio. Several randomized trials currently recruiting will likely provide us with more definite answers about whether two-fraction prostate SBRT should become a standard-of-care option. Enrollment of eligible patients into these trials should be encouraged.

High Dose “HDR-Like” Prostate SBRT: PSA 10-Year Results From a Mature, Multi-Institutional Clinical Trial

Purpose/Objective(s)

Although ample intermediate-term prostate stereotactic body radiotherapy (SBRT) outcomes have been reported, 10-year results remain relatively sparse.

Materials/Methods

Eighteen institutions enrolled 259 low- and intermediate-risk patients. Median follow-up is 5.5 years, with 66 patients followed ≥ 10 years. This SBRT regimen specifically emulated an existing HDR brachytherapy dose schedule and isodose morphology, prescribed to 38 Gy/4 fractions, delivered daily by robotic SBRT, mandating > 150% dose escalation in the peripheral zone. Androgen deprivation therapy was not allowed, and a hydrogel spacer was not available at that time.

Results

Median pre-SBRT PSA 5.12 ng/mL decreased to 0.1 ng/mL by 3.5 years, with further decrease to a nadir of < 0.1 ng/mL by 7 years, maintained through 10 years. Ten-year freedom from biochemical recurrence measured 100% for low-risk, 84.3% for favorable intermediate risk (FIR), and 68.4% for unfavorable intermediate (UIR) cases. Multivariable analysis revealed that the UIR group bifurcated into two distinct prognostic subgroups. Those so classified by having Gleason score 4 + 3 and/or clinical stage T2 (versus T1b/T1c) had a significantly poorer 10 year freedom from biochemical recurrence rate, 54.8% if either or both factors were present, while UIR patients without these specific factors had a 94.4% 10-year freedom from biochemical recurrence rate. The cumulative incidence of grade 2 GU toxicity modestly increased over time – 16.3% at 5 years increased to 19.2% at 10 years-- while the incidence of grade 3+ GU and GI toxicity remained low and stable to 10 years - 2.6% and 0%, respectively. The grade 2 GI toxicity incidence also remained low and stable to 10 years – 4.1% with no further events after year 5.

Conclusion

This HDR-like SBRT regimen prescribing 38 Gy/4 fractions but delivering much higher intraprostatic doses on a daily basis is safe and effective. This treatment achieves a median PSA nadir of <0.1 ng/mL and provides high long-term disease control rates without ADT except for a subgroup of unfavorable intermediate-risk patients.

Early PSA kinetics for low- and intermediate-risk prostate cancer treated with definitive radiation therapy

PURPOSE

This study uses a patient-specific model to characterize and compare ideal PSA kinetics for low- and intermediate-risk prostate cancer following definitive radiation treatment with conventionally fractionated (CFRT), hypofractionated (HFRT), stereotactic body radiation therapy (SbRT), or brachytherapy, both high-dose-rate (HDR) and low-dose-rate (LDR).

METHODS AND MATERIALS

This retrospective analysis includes low- and intermediate-risk prostate cancer patients treated between 1998 and 2018 at an NCI-designated Comprehensive Cancer Center. Demographics and treatment characteristics were prospectively collected. Patients had at least two PSA measurements within 24-months of treatment and were free from biochemical recurrence. The incidence of, time to, and risk factors for PSA nadir (nPSA) and bounce (bPSA) were analyzed at 24-months following radiotherapy. Ideal PSA kinetics were characterized for each modality and compared.

RESULTS

Of 1,042 patients, 45% had low-risk cancer, 37% favorable intermediate-risk, and 19% unfavorable intermediate-risk. nPSA were higher for ablative modalities, both as absolute nPSA and relative to initial PSA (iPSA). Median time to nPSA ranged from 14.8 to 17.1 months. Over 50% treated with non-ablative therapy (CFRT, HFRT, and LDR) reached an nPSA threshold of ≤0.5 ng/mL compared to 23% of SbRT and 33% of HDR cohorts. The incidence of bPSA was 13.3% and not affected by treatment modality, Gleason Score, or prostate volume. PSA decay rate was faster for ablative therapies in the 6-24 month period.

CONCLUSIONS

Analysis of PSA within 24-months following radiation therapy revealed ablative therapies are associated with a latent PSA response and higher nPSA. Multivariable logistics modeling revealed younger age, iPSA above the median, presence of bPSA, and ablative therapy as predictors for not achieving nPSA ≤0.5 ng/mL. PSA decay rate appears to be faster in ablative therapies following a latent period. Understanding the different PSA kinetic profiles is necessary to assess treatment response and survey for disease recurrence.

Ten-Year Single Institutional Analysis of Geographic and Demographic Characteristics of Patients Treated With Stereotactic Body Radiation Therapy for Localized Prostate Cancer

Objectives

Stereotactic Body Radiation Therapy (SBRT) offers definitive treatment for localized prostate cancer with comparable efficacy and toxicity to conventionally fractionated radiotherapy. Decreasing the number of treatment visits from over 40 to five may ease treatment burden and increase accessibility for logistically challenged patients. Travel distance is one factor that affects a patient’s access to treatment and is often related to geographic location and socioeconomic status. In this study, we review the demographic and geographic factors of patients treated with SBRT for prostate cancer for a single institution with over a decade of experience.

Methods

Patient zip codes from one thousand and thirty-five patients were derived from a large, prospectively maintained quality of life database for patients treated for prostate cancer with SBRT from 2008 to 2017. The geospatial distance between the centroid of each zip code to our institution was calculated using the R package Geosphere. Characteristics for seven hundred and twenty-one patients were evaluated at the time of analysis including: race, age, and insurance status. To assess the geographic reach of our institution, we evaluated the demographic features of each zip code using US Census data. Statistical comparisons for these features and their relation to distance traveled for treatment was performed using the Mann-Whitney U test. Finally, an unsupervised learning algorithm was performed to identify distinct clusters of patients with respect to median income, racial makeup, educational level, and rural residency.

Results

Patients traveled from 246 distinct zip codes at a median distance of 11.35 miles. Forty percent of patients were African American, 6.9% resided in a rural region, and 22% were over the age of 75. Using K-means cluster analysis, four distinct patient zip-code groups were identified based on the aforementioned demographic features: Suburban/high-income (45%), Urban (30%), Suburban/low-income (17%), and Rural (8%). For each of the clusters, the average travel distance for SBRT was significantly different at 11.17, 9.26, 11.75, and 40.2 miles, respectively (p-value: <0.001).

Conclusions

Distinct demographic features are related to travel distance for prostate SBRT. In our large cohort, travel distance did not prevent uptake of prostate SBRT in African American, elderly or rural patient populations. Prostate SBRT offers a diverse population modern treatment for their localized prostate cancer and particularly for those who live significant distances from a treatment center.

Biochemical Control and Toxicity Outcomes of Stereotactic Body Radiation Therapy Versus Low-Dose-Rate Brachytherapy in the Treatment of Low- and Intermediate-Risk Prostate Cancer

PURPOSE

Low-dose-rate (LDR) brachytherapy and stereotactic body radiation therapy (SBRT) have both shown acceptable outcomes in the treatment of low- and intermediate-risk prostate cancer. Minimal data have been published directly comparing rates of biochemical control and toxicity with these 2 modalities. We hypothesize that LDR and SBRT will provide similar rates of biochemical control.

METHODS AND MATERIALS

All low- and intermediate-risk patients with prostate cancer treated definitively with SBRT or LDR between 2010 and 2018 were captured. Phoenix definition was used for biochemical failure. Independent t tests were used to compare baseline characteristics, and repeated measure analysis of variance test was used to compare American Urologic Association (AUA) and the Expanded Prostate Cancer Index Composite (EPIC) scores between treatment arms over time. Biochemical control was estimated using the Kaplan-Meier method. Differences in acute and late toxicity were assessed via Pearson χ².

RESULTS

In the study, 219 and 118 patients were treated with LDR and SBRT. Median follow-up was 4.3 years (interquartile range, 3.1-6.1). All patients treated with LDR received 125.0 Gy in a single fraction. SBRT consisted of 42.5 Gy in 5 fractions. Five-year biochemical control for LDR versus SBRT was 91.6% versus 97.6% (P = .108). LDR patients had a larger increase in mean AUA scores at 1 month (17.2 vs 10.3, P < .001) and 3 months posttreatment (14.0 vs 9.7, P < .001), and in mean EPIC scores at 1 month (15.7 vs 13.8, P < .001). There was no significant difference between LDR and SBRT in late grade 3 genitourinary toxicity (0.9% vs 2.5%, P = .238); however, LDR had lower rates of late grade 3 gastrointestinal toxicity (0.0% vs 2.5%, P = .018).

CONCLUSIONS

Our data show similar biochemical control and genitourinary toxicity rates at 5 years for both SBRT and LDR, with slightly higher gastrointestinal toxicity with SBRT and higher AUA and EPIC scores with LDR.

Prostate SBRT: Comparison the Efficacy and Toxicity of Two Different Dose Fractionation Schedules

Background: CyberKnife SBRT is capable of producing dosimetry comparable to that created by HDR brachytherapy. Our original CyberKnife prostate SBRT schedule of 3,800 cGy/4 fractions (“high dose”) was based upon favorable published prostate HDR brachytherapy experience. Subsequently, our trial was modified to allow a lower dose of 3,400 cGy/5 fractions (“moderate dose”) in selected cases.

Methods: Two hundred eighty-nine low and intermediate-risk patients were treated to either high dose (178 pts) or moderate dose (111 pts). The dose selection was individualized; high dose more commonly used in younger, intermediate-risk patients, and moderate dose more commonly used in older, low-risk patients.

Results: Median PSA reached 5-year nadir levels of 0.034 ng/mL in the high dose, vs. 0.1 ng/mL in the moderate dose groups, respectively (p = 0.044 by year 4), with 62 vs. 44% reaching an ablation PSA nadir (<0.1 ng/mL) by year 5, respectively. Five year biochemical relapse free survival rates measured 98.3% for moderate dose and 94.3% for high dose groups, respectively (p = 0.1946). Five-year actuarial grade 2 genitourinary (GU) toxicity rates measured 11.6 vs. 8.7% for high dose vs. moderate dose groups, respectively, with a far lower incidence of grade ≥3 GU and grade ≥2 GI toxicity rates in both groups.

Conclusions: Both regimens are efficacious in their respective, selected groups. Both arms have low grade ≥3 GU toxicity and ≥grade 2 GI toxicity. In favor of the original high dose regimen, it has longer follow-up, produces a lower PSA nadir value and is more likely to eventually produce an ablation PSA nadir (<0.1 ng/mL). In favor of the lower dose regimen, it also produces a low PSA nadir, and does so with a slightly lower grade 2 GU toxicity rate. As a lower PSA nadir could be the initial predictor a lower clinical relapse rate far beyond 5 years, even if no difference is apparent within that time frame, a practical strategy could be to more strongly consider the high dose regimen in those with the greatest potential longevity, while for those with a more limited longevity, particularly if they have minimal negative prognostic factors, the moderate dose regimen could be more attractive.

Results of 15 Gy HDR-BT boost plus EBRT in intermediate-risk prostate cancer: Analysis of over 500 patients

PURPOSE/OBJECTIVE

To report biochemical control associated with single fraction 15 Gy high-dose-rate brachytherapy (HDR-BT) boost followed by external beam radiation (EBRT) in patients with intermediate-risk prostate cancer.

MATERIALS AND METHODS

A retrospective chart review of all patients with intermediate-risk disease treated with a real-time ultrasound-based 15 Gy HDR-BT boost followed by EBRT between 2009 and 2016 at a single quaternary cancer center was performed. Freedom from biochemical failure (FFBF), cumulative incidence of androgen deprivation therapy use for biochemical or clinical failure post-treatment (CI of ADT) and metastasis-free survival (MFS) outcomes were measured.

RESULTS

518 patients met the inclusion criteria for this study. Median age at HDR-BT was 67 years (IQR 61-72). 506 (98%) had complete pathologic information available. Of these, 146 (28%) had favorable (FIR) and 360 (69%) had unfavorable (UIR) intermediate-risk disease. 83 (16%) received short course hormones with EBRT + HDR. Median overall follow-up was 5.2 years. FFBF was 91 (88-94)% at 5 years. Five-year FFBF was 94 (89-99)% and 89 (85-94)% in FIR and UIR patients, respectively (p = 0.045). CI of ADT was 4 (2-6)% at 5 years. Five-year CI of ADT was 1 (0-3)% and 5 (2-8)% in FIR and UIR patients, respectively (p = 0.085). MFS was 97 (95-98)% at 5 years. Five-year MFS was 100 (N/A-100)% and 95 (92-98)% in FIR and UIR patients, respectively (p = 0.020).

CONCLUSION

In this large cohort of intermediate-risk prostate cancer patients, 15 Gy HDR-BT boost plus EBRT results in durable biochemical control and low rates of ADT use for biochemical failure.

Stereotactic body radiotherapy with periprostatic hydrogel spacer for localized prostate cancer: toxicity profile and early oncologic outcomes

Background

Multiple phase I-II clinical trials have reported on the efficacy and safety of prostate stereotactic body radiotherapy (SBRT) for the treatment of prostate cancer. However, few have reported outcomes for prostate SBRT using periprostatic hydrogel spacer (SpaceOAR; Augmenix). Herein, we report safety and efficacy outcomes from our institutional prostate SBRT experience with SpaceOAR placement.

Methods

Fifty men with low- or intermediate-risk prostate cancer treated at a single institution with linear accelerator-based SBRT to 3625 cGy in 5 fractions, with or without androgen deprivation therapy (ADT) were included. All patients underwent SpaceOAR and fiducial marker placement followed by pre-treatment MRI. Toxicity assessments were conducted at least weekly while on treatment, 1 month after treatment, and every follow-up visit thereafter. Post-treatment PSA measurements were obtained 4 months after SBRT, followed by every 3–6 months thereafter. Acute toxicity was documented per RTOG criteria.

Results

Median follow up time was 20 (range 4–44) months. Median PSA at time of diagnosis was 7.4 (2.7–19.5) ng/ml. Eighteen men received 6 months of ADT for unfavorable intermediate risk disease. No PSA failures were recorded. Median PSA was 0.9 ng/mL at 20 months; 0.08 and 1.32 ng/mL in men who did and did not receive ADT, respectively. Mean prostate-rectum separation achieved with SpaceOAR was 9.6 ± 4 mm at the prostate midgland.

No grade ≥ 3 GU or GI toxicity was recorded. During treatment, 30% of men developed new grade 2 GU toxicity (urgency or dysuria). These symptoms were present in 30% of men at 1 month and in 12% of men at 1 year post-treatment. During treatment, GI toxicity was limited to grade 1 symptoms (16%), although 4% of men developed grade 2 symptoms during the first 4 weeks after SBRT. All GI symptoms were resolving by the 1 month post-treatment assessment and no acute or late rectal toxicity was reported > 1 month after treatment.

Conclusions

Periprostatic hydrogel placement followed by prostate SBRT resulted in minimal GI toxicity, and favorable early oncologic outcomes. These results indicate that SBRT with periprostatic spacer is a well-tolerated, safe, and convenient treatment option for localized prostate cancer.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1346-5) contains supplementary material, which is available to authorized users.

Hypofractionated Radiotherapy for Localized Prostate Cancer: When and for Whom?

PURPOSE OF REVIEW

To summarize recent evidence concerning the use of moderately hypofractionated external beam radiotherapy, defined as 2.4-3.4 Gy per fraction, and ultrahypofractionated external beam radiotherapy (also known as stereotactic body radiotherapy [SBRT]), defined as at least 5 Gy per fraction, in men with localized prostate cancer.

RECENT FINDINGS

Taken together, a number of recently completed randomized trials show that moderately hypofractionated radiotherapy confers similar biochemical control compared to conventionally fractionated radiotherapy without increasing late toxicity. These effects appear to extend across all baseline clinical risk groups. Several single-arm phase II studies, as well as a recently published large-scale randomized trial comparing SBRT with conventional fractionation, show very promising biochemical control and favorable acute and late treatment-related morbidity with the use of SBRT in predominantly low- and intermediate-risk prostate cancer. As it is associated with similar prostate cancer control and toxicity while improving patient convenience and reducing cost, moderate hypofractionation is a preferred alternative to conventional fractionation in a majority of men with localized prostate cancer choosing radiotherapy as their primary treatment modality. To date, studies conducted largely in low- and intermediate-risk prostate cancer report encouraging oncologic outcomes and acceptable toxicity with SBRT. Mature results of phase III trials evaluating five-fraction SBRT regimens are eagerly awaited.

Multi-Institutional Analysis of Prostate-Specific Antigen Kinetics After Stereotactic Body Radiation Therapy

PURPOSE

Understanding prostate-specific antigen (PSA) kinetics after radiation therapy plays a large role in the management of patients with prostate cancer (PCa). This is particularly true in establishing expectations regarding PSA nadir (nPSA) and PSA bounces, which can be disconcerting. As increasingly more patients are being treated with stereotactic body radiation therapy (SBRT) for low- and intermediate-risk PCa, it is imperative to understand the PSA response to SBRT.

METHODS AND MATERIALS

PSA data from 5 institutions were retrospectively analyzed for patients with localized PCa treated definitively with SBRT alone from 2004 to 2016. Patients received 35 to 40 Gy in 5 fractions, per institutional standards. Patients who had less than 12 months of PSA data or received androgen deprivation therapy were excluded from this study. Linear and logistic multivariable analysis were performed to identify predictors of nPSA, bounce, and biochemical recurrence, and joint latent class models were developed to identify significant predictors of time to biochemical failure.

RESULTS

A total of 1062 patients were included in this study. Median follow-up was 66 months (interquartile range [IQR], 36.4-89.9 months). Biochemical failure per the Phoenix criteria occurred in 4% of patients. Median nPSA was 0.2 ng/mL, median time to nPSA was 40 months, 84% of patients had an nPSA ≤0.5 ng/mL, and 54% of patients had an nPSA ≤0.2 ng/mL. On multivariable analysis, nPSA was a significant predictor of biochemical failure. Benign PSA bounce was noted in 26% of patients. The median magnitude of PSA bounce was 0.52 ng/mL (IQR, 0.3-1.0 ng/mL). Median time to PSA bounce was 18.1 months (IQR, 12.0-31.1 months). On multivariable analysis, age and radiation dose were significantly associated with a lower incidence of bounce. Joint latent class models modeling found that nPSA and radiation dose were significantly associated with longer time to biochemical failure.

CONCLUSIONS

In this multi-institutional cohort of patients with long-term follow-up, we found that SBRT led to low nPSAs. In turn, lower nPSAs are associated with reduced incidence of, and longer time to, biochemical failure. Benign PSA bounces occurred in a quarter of patients, as late as several years after treatment. Further studies are needed to directly compare the PSA response of patients who receive SBRT versus other treatment modalities.

Long-term Outcomes of Stereotactic Body Radiotherapy for Low-Risk and Intermediate-Risk Prostate Cancer

Importance

Stereotactic body radiotherapy harnesses improvements in technology to allow the completion of a course of external beam radiotherapy treatment for prostate cancer in the span of 4 to 5 treatment sessions. Although mounting short-term data support this approach, long-term outcomes have been sparsely reported.

Objective

To assess long-term outcomes after stereotactic body radiotherapy for low-risk and intermediate-risk prostate cancer.

Design, Setting, and Participants

This cohort study analyzed individual patient data from 2142 men enrolled in 10 single-institution phase 2 trials and 2 multi-institutional phase 2 trials of stereotactic body radiotherapy for low-risk and intermediate-risk prostate cancer between January 1, 2000, and December 31, 2012. Statistical analysis was performed based on follow-up from January 1, 2013, to May 1, 2018.

Main Outcomes and Measures

The cumulative incidence of biochemical recurrence was estimated using a competing risk framework. Physician-scored genitourinary and gastrointestinal toxic event outcomes were defined per each individual study, generally by Radiation Therapy Oncology Group or Common Terminology Criteria for Adverse Events scoring systems. After central review, cumulative incidences of late grade 3 or higher toxic events were estimated using a Kaplan-Meier method.

Results

A total of 2142 men (mean [SD] age, 67.9 [9.5] years) were eligible for analysis, of whom 1185 (55.3%) had low-risk disease, 692 (32.3%) had favorable intermediate-risk disease, and 265 (12.4%) had unfavorable intermediate-risk disease. The median follow-up period was 6.9 years (interquartile range, 4.9-8.1 years). Seven-year cumulative rates of biochemical recurrence were 4.5% (95% CI, 3.2%-5.8%) for low-risk disease, 8.6% (95% CI, 6.2%-11.0%) for favorable intermediate-risk disease, 14.9% (95% CI, 9.5%-20.2%) for unfavorable intermediate-risk disease, and 10.2% (95% CI, 8.0%-12.5%) for all intermediate-risk disease. The crude incidence of acute grade 3 or higher genitourinary toxic events was 0.60% (n = 13) and of gastrointestinal toxic events was 0.09% (n = 2), and the 7-year cumulative incidence of late grade 3 or higher genitourinary toxic events was 2.4% (95% CI, 1.8%-3.2%) and of late grade 3 or higher gastrointestinal toxic events was 0.4% (95% CI, 0.2%-0.8%).

Conclusions and Relevance

In this study, stereotactic body radiotherapy for low-risk and intermediate-risk disease was associated with low rates of severe toxic events and high rates of biochemical control. These data suggest that stereotactic body radiotherapy is an appropriate definitive treatment modality for low-risk and intermediate-risk prostate cancer.

Stereotactic Ablative Radiotherapy for Prostate Cancer-The Treatment Results of 500 Patients and Analysis of Failures

OBJECTIVE

Stereotactic ablative radiotherapy is a very promising approach for the treatment of patients with prostate cancer. The aim of this study was to evaluate the clinical tolerance, effectiveness, patterns of failure, and attempt to define predictive factors based on our experience.

METHODS

The cohort consists of 264 low-risk and 236 intermediate-risk consecutive patients treated at one institution. Prostate-specific antigen (PSA), adverse effects, and androgen deprivation therapy (ADT) usage were noted.

RESULTS

Median follow-up was 31.3 months. Over 90% of the patients reported no gastrointestinal toxicity. There were 4 occurrences of G3+ sequelae. 75% patients had no genitourinary toxicity at first month, and up to 90% during the rest of follow-up, with only 1 case of G3 adverse event. The toxicity was more pronounced in patients with higher PSA concentrations. Prior to stereotactic ablative radiotherapy, the mean PSA was 7.59 and 277 patients used ADT. The PSA decreased for up to 20 months before reaching a plateau. The decline was slower, and PSA levels were higher in patients without ADT. A total of 15 treatment failures occured in a median time of 19.9 months. Higher PSA concentrations were connected with higher failure rates, even in the first month and prior to reaching Phoenix criterion.

CONCLUSION

CyberKnife-based stereotactic ablative radiotherapy of low-risk and intermediate-risk prostate cancer patients is an effective and well-tolerated modality of treatment. PSA is the most important predictive factor. The evolution of PSA concentration in a particular subgroup of patients suggests that ADT in intermediate-risk cases could improve long-term results.

Risk factors for biochemical recurrence after a tissue-ablative prostate-specific antigen <0.2 ng/mL

PURPOSE

A prostate-specific antigen (PSA) nadir <0.2 ng/mL is generally considered as tissue ablative and at low risk for recurrence. After attaining such a low PSA nadir, we analyzed risk factors for recurrence.

METHODS AND MATERIALS

We identified patients from our institutionalized database with either D'Amico low- or intermediate-risk prostate cancer that was treated with either low-dose-rate prostate brachytherapy or external beam radiotherapy as monotherapy. We compared patients who attained a nadir <0.2 ng/mL and subsequently developed biochemical failure to patients who did not experience biochemical failure by using χ² test and Student t test. Survival analysis was performed using the Kaplan-Meier method (log-rank test).

RESULTS

Of 892 patients, 560 (63%) achieved a nadir <0.2 ng/mL. Only 23 (4.1%) later developed a biochemical recurrence. The 7-year Kaplan-Meier biochemical recurrence-free survival after a PSA nadir of <0.2 ng/mL was 96%. Patients who later experienced biochemical recurrence were more likely to have Cancer of the Prostate Risk Assessment Score intermediate- or high-risk cancer: (74% vs. 40%, p < 0.001). Patients were more likely to have a diagnostic PSA >6.0 ng/mL: (66% vs. 43% p < 0.001) and have a Gleason score ≥ 3  + 4: (52% vs. 34%, p = 0.005). They were also more likely to be older (p = 0.003): mean (SD) 70.3 (6.4) vs. 66.2 (6.5) and have a time to PSA nadir that was significantly shorter (p = 0.013): mean (SD) 51.8 (29.6) vs. 65.2 (25.1).

CONCLUSIONS

Biochemical recurrence after attaining a PSA nadir <0.2 ng/mL is rare and more frequent in patients with intermediate risk cancer and older patients. These patients can benefit from a prolonged followup with specialized physicians.