|Year : 2016 | Volume
| Issue : 1 | Page : 406-410
Feasibility of brachytherapy as monotherapy for high-volume, low-risk prostate cancer
Arti Parekh1, Paul L Nguyen2, Laura J West2, Catherine Duarte2, Powell L Graham2, Dennis R Larock3, Vincent Yeung4, Mark D Hurwitz4
1 Department of Radiation Oncology, Johns Hopkins Hospital, Baltimore, MD, USA
2 Department of Radiation Oncology, Dana-Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, USA
3 Department of Urology, Saint Anne's Hospital, Fall River, MA, USA
4 Department of Radiation Oncology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA
|Date of Web Publication||13-Apr-2016|
Mark D Hurwitz
Bodine Center, Suite G-301, 111 South 11th Street, Philadelphia, PA 19107
Source of Support: None, Conflict of Interest: None
Background: We sought to determine whether patients with high-volume, low-risk prostate cancer are suitable candidates for ultrasound-guided brachytherapy, monotherapy alone, without supplemental external beam radiation.
Materials and Methods: The study cohort comprised 200 consecutive patients who received ultrasound.guided monotherapy from November 02, 1998 to March 26, 2010. Real.time intraoperative treatment planning was performed for all patients. 145. Gy with I125 was prescribed to the prostate with no margin. The primary endpoint was time to prostate-specific antigen. (PSA) failure using the phoenix definition. Cox multivariable regression analysis was used to determine the factors significantly associated with time to PSA failure.
Results: Median follow-up was 59 months (range 1.2–146.8 months). The median PSA was 5.0 ng/ml. For the overall cohort, both 5- and 8-year PSA failure-free survival was 92.3% (95% confidence interval [95% CI]: 86.5–95.7%). Low-risk patients per the NCCN criteria had 5- and 8-year PSA failure-free survival of 93.6%. On cox multivariable analysis, only baseline PSA (adjusted hazard ratio: 1.29 [95% CI: 1.02–1.65], P = 0.036) was associated with outcome. Among patients with <33% cores positive, 33–<50% cores positive, and ≥50% cores positive, the 5-year PSA failure-free survival was 92.3% (95% CI: 85.1–96.1%), 91.0% (95% CI: 68.5–97.6%), and 93.3% (95% CI: 61.2–99.0%), respectively.
Conclusions: Our analysis indicates that patients with a high number of cores positive for cancer can be adequately treated with modern brachytherapy as monotherapy and be spared the additional morbidity and cost of supplemental external beam radiation or androgen deprivation therapy.
Keywords: Brachytherapy, percent positive cores, prognostic factors, prostate, prostate-specific antigen
|How to cite this article:|
Parekh A, Nguyen PL, West LJ, Duarte C, Graham PL, Larock DR, Yeung V, Hurwitz MD. Feasibility of brachytherapy as monotherapy for high-volume, low-risk prostate cancer. J Can Res Ther 2016;12:406-10
|How to cite this URL:|
Parekh A, Nguyen PL, West LJ, Duarte C, Graham PL, Larock DR, Yeung V, Hurwitz MD. Feasibility of brachytherapy as monotherapy for high-volume, low-risk prostate cancer. J Can Res Ther [serial online] 2016 [cited 2020 Jul 7];12:406-10. Available from: http://www.cancerjournal.net/text.asp?2016/12/1/406/180083
| > Introduction|| |
Current guidelines state that men with low-risk prostate cancer based on having clinical T1c or T2a, Gleason ≤6, and prostate-specific antigen (PSA) <10 diseases are suitable candidates for brachytherapy monotherapy., However, based on prior data that men with a high number of cores positive for cancer, face a greater risk of adverse prostate cancer outcomes, many practitioners are reluctant to offer brachytherapy monotherapy for patients with ≥50% cores., We sought to determine whether modern brachytherapy monotherapy, as delivered in a community setting, could be a feasible treatment option for men with low-risk but high-volume prostate cancer.
| > Materials and Methods|| |
The study was approved by our Institutional Review Board.
The study cohort consisted of 200 consecutive patients who were treated with ultrasound-guided transperineal permanent prostate brachytherapy monotherapy from November 02, 1998 to March 26, 2010. All implants were performed by a radiation oncologist and urologist. Real-time intraoperative treatment planning was performed for all patients. Biplanar ultrasound and fluoroscopic guidance were used to assist with needle placement. 145 Gy with I 125 was prescribed to the prostate with no margin, thus restricting the planning target volume to the clinical target volume.
Endpoints and statistical analysis
The primary endpoint of our study was time to PSA failure. Biochemical failure was defined using the phoenix definition (i.e., nadir + 2 or initiation of salvage androgen deprivation therapy [ADT]).
Univariable and multivariable cox regression was used to determine factors that are associated with PSA failure. Continuous variables in the analysis included time to failure and baseline PSA. Categorical variables included Gleason score, and whether percent positive cores were <33%, 33–<50%, or ≥50%.
For the multivariable analysis, we were not able to include T-category because there were no events among the patients with T2a disease. Adjusted hazard ratios and 95% confidence intervals (95% CIs) were reported for the covariates, and P < 0.05 was used as a cut-off to indicate significance. For the purpose of illustration, Kaplan–Meier analysis was used to estimate the PSA failure-free survival, stratified by variables of interest.
Intercooled Stata 8.0, StataCorp, College Station, TX, the USA, for Windows was used to perform all statistical analyses.
| > Results|| |
Patient baseline characteristics
Median follow-up was 59 months (range 1.2–146.8 months). The median PSA was 5.0 ng/ml. The cohort included 3% of patients who were Gleason <6, 90% Gleason 6, and 7% Gleason 3 + 4 = 7. There were 163 and 37 patients classified as T1c and T2a, respectively [Table 1]. One hundred eighty-one patients (90.5%) and 19 patients (9.5%) of patients were classified as low- and intermediate-risk respectively, per NCCN guidelines.
Prostate-specific antigen failure-free survival
For the overall cohort, 5-year PSA failure-free survival was 92.3% (95% CI: 86.5–95.7%), and 8-year was 92.3% (95% CI: 86.5–95.7%). Two additional failures were noted with longer-term follow-up beyond 8 years however most failures occurred within 5 years. One patient who was scored as a treatment failure per the phoenix definition had a peak PSA level of 2.7 ng/ml, with subsequent decline in PSA which stabilized under 1 ng/ml, with 2 years of additional follow-up.
Factors associated with outcome
On univariable analysis, only baseline PSA was significantly associated with outcome (hazard ratio 1.29 [95% CI: 1.02–1.65], P = 0.031). Patients with a PSA ≤10 had a 5- and 8-year PSA failure-free survival rate of 93.6% (95% CI: 87.9–96.6%), as compared to 55.5% (95% CI: 73.4–87.6%) at 5- and 8-year for those with a PSA <10 at baseline [Figure 1]. Those with low-risk prostate cancer had 5- and 8-year PSA failure-free survival rates of 93.6% (95% CI: 87.6–96.8%), whereas those with intermediate-risk disease, had PSA failure-free survival rates of 80.8% (95% CI: 50.5–93.5%).
Of note, percent of cores positive was not significantly associated with outcome. Specifically, among patients with <33% cores positive (n = 159), 33–<50% cores positive (n = 26), and ≥0% cores positive (n = 15), the 5-year PSA failure-free survival was 92.3% (95% CI: 85.1–96.1%), 91.0% (95% CI: 68.5–97.6%), and 93.3% (95% CI: 61.2–99.0%), respectively as illustrated in [Figure 2].
On Cox multivariable analysis, only baseline PSA was significantly associated with failure rates [Table 2]. The percentage of positive cores and Gleason score were not associated with failure rate. In addition, patients with 33–<50% cores and ≥50% cores positive did not have significantly higher failure rates compared to those with <33% positive biopsies (hazard ratio for 33–<50% cores vs. <33% = 1.02 [95% CI: 0.22–473], P = 0.97; hazard ratio for ≥50% vs. <33% = 0.868 [95% CI: 0.10–6.89], P = 0.109).
| > Discussion|| |
In this analysis, we assessed results of brachytherapy monotherapy in a community setting to determine whether percent of positive cores should be used as selection criteria for men considering monotherapy. We found that in this cohort of men with mainly low- and favorable-intermediate-risk disease receiving modern brachytherapy, only baseline PSA was associated with outcome, and percentage of cores positive for cancer was not a significant adverse prognostic factor. Specifically, the 5-year PSA failure-free survival for men with <33% cores positive, 33–<50% cores positive, and ≥50% cores positive was 92.3%, 91.0%, and 93.3%, respectively. Our data suggest that for men with low or favorable intermediate-risk prostate cancer, modern brachytherapy monotherapy provides an effective treatment regardless of the percentage of cores positive for tumor.
Currently, both the NCCN guidelines and the American Brachytherapy Society guidelines state that brachytherapy monotherapy is appropriate for all men with low-risk prostate cancer (i.e., cT1c or T2a, PSA <10, and Gleason 6), but in practice, it is common for practitioners to add additional therapy for men with a high percentage of cores positive (e.g., <50%) out of concern that this portends high-volume disease that may not be curable with brachytherapy alone., An additional concern is that due to dose heterogeneity in the prostate, “cold spots” due to suboptimal brachytherapy seed placement may increase the risk of local recurrence in men with extensive disease within the prostate. A physician survey conducted by Frank et al. on patterns of care with respect to brachytherapy found that expert genitourinary radiation oncologists were hesitant to use brachytherapy alone with high-volume disease. For example, the survey found that up to 90% of physicians would add external beam radiation therapy (EBRT) to brachytherapy implants in patients with 50% biopsy cores positive and either Gleason 7 (3 + 4) or serum PSA between 10 and 20 ng/ml.
The weight that practitioners place on percent positive cores as a prognostic factor is illustrated in a current clinical trial RTOG 0924, which assesses the role of ADT and pelvic radiation for unfavorable intermediate-risk or high-risk patients. In addition, to the risk of lymph node involvement and other intermediate or high-risk factors, patients with Gleason score 6+ >50% biopsies are eligible. Our results suggest that patients with Gleason 6 and <50% positive cores may not require such extensive treatment and could do well with high-quality brachytherapy implants to the prostate alone, thereby avoiding the additional morbidity of ADT and supplemental external beam radiation as well as significantly lowering the cost of therapy.,,,, This finding is plausible for a number of reasons. First, patients with low-grade prostate cancer rarely develop metastases; therefore, Gleason 6 tumors with a high number of cores positive likely represent high-volume localized disease. With modern attention to treatment planning and postoperative dosimetry, brachytherapy can provide excellent coverage to the entire prostate, often with ≥150% of the dose going to areas of known tumor in the peripheral zone, which may be more than adequate to eliminate high-volume localized disease. In addition, Davis et al. have shown that men with low-risk prostate cancer typically have at most 3 mm of extracapsular extension at prostatectomy, and brachytherapy can often deliver tumoricidal doses to about 5 mm beyond the capsule.
The presence of controversy regarding the predictive value of percent positive cores; however, must be acknowledged. Many studies have investigated the use of percent positive cores in predicting PSA failure-free survival in EBRT ,,,, and brachytherapy ,, with some studies demonstrating prognostic significance while others do not.
Similar to our findings, in a study done by Merrick et al. there was no clinical significance found to percent positive cores with regards to 5-year biochemical free survival. No significant difference was found in failure rate between those with <34%, 34–50%, or <50% positive cores, and they concluded that this was a result of dose escalation achieved with seed implants not easily achieved with other radiation modalities. Merrick et al. also found in a randomized controlled trial of 20 versus 44 Gy supplemental EBRT for intermediate to high-risk disease following brachytherapy that overall survival was equivalent. This suggests that high-quality brachytherapy makes supplemental EBRT less important, even for unfavorable risk disease.
On the other hand, Guzzo et al. for example, retrospectively evaluated patients who received brachytherapy for factors that predicted biochemical failure, including prebrachytherapy PSA, percent positive prostate needle biopsies, and biopsy Gleason score. They found a significant association between biochemical failure and percent positive biopsies above the median, 27%. Of note, dichotomization using the Guzzo cutoff of 27% positive biopsies was neither significant in our cohort nor dichotomization using our median percent positive biopsies of 16.7%. Additional studies will be needed to help resolve this controversy.
The lack of consensus regarding the predictive value of percent positive cores is similar to the diversity of practice seen with perineural invasion (PNI). Although the association between PNI and biochemical failure after EBRT has been demonstrated in some studies, the prognostic role of PNI in the context of brachytherapy is less clear.,, Piña et al. reported excellent biochemical control in men treated with I 125 interstitial implants, with a 5-year actuarial rate of 92.9%, and the authors suggest that a biopsy positive for PNI should not preclude the possibility of brachytherapy for treatment, again potentially reflecting the ability of brachytherapy monotherapy to deliver very high tumorical doses to within the prostate and a few millimeters beyond it. On the other hand, Ding et al. demonstrated a 6 times increase in biochemical failure in PNI positive patients treated with permanent seed prostate brachytherapy, suggesting a benefit of EBRT in these patients., This controversy remains to be delineated in larger studies.
There are some points however that deserve consideration in our study. Our findings are based on a patient population in which few had high-volume disease. Out of our cohort of 200 patients, only 20% of the patients had 33% or more of their cores positive, which somewhat limits the ability to detect a difference due to the percent of cores positive. Furthermore, the median follow-up was 59 months, and it is possible that greater differences in outcome may emerge over time although most failures occurred within 5 years. A study that includes a larger percentage of patients with high-volume and low-risk disease as well as longer follow-up will add value to the current literature and help elucidate the prognostic value of percent positive cores on biopsy even further.
| > Conclusions|| |
In summary, our study suggests that with a high-quality implant and escalated-dose achievable with brachytherapy, there was no association between percent positive cores on biopsy and biochemical failure. Thus, it demonstrates that contrary to conventional practice by many physicians, patients with high-volume disease may be successfully implanted with brachytherapy alone. If these results are validated in larger series, men with high-volume, low-risk disease can be treated with brachytherapy monotherapy and can avoid the morbidity and cost of supplemental therapies that may not be needed. In addition, it is important to consider the emerging data that continues to support the use of high-dose rate (HDR) monotherapy, with the theoretical advantage of more consistent implant quality and lower acute and late toxicity. However, longer follow-up is needed to fully define the role of HDR monotherapy.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]