Abstract
PurposeLong-term data regarding the disease control outcomes of proton beam therapy (PBT) for patients with favorable risk intact prostate cancer (PC) are limited. Herein, we report our institution's long-term disease control outcomes in PC patients with clinically localized disease who received PBT as primary treatment.MethodsOne hundred sixty-six favorable risk PC patients who received definitive PBT to the prostate gland at our institution from 2010 to 2012 were retrospectively assessed. The outcomes studied were biochemical failure-free survival (BFFS), biochemical failure, local failure, regional failure, distant failure, PC-specific survival, and overall survival. Patterns of failure were also analyzed. Multivariate Cox proportional hazards modeling was used to estimate independent predictors of BFFS.ResultsThe median length of follow-up was 8.3 years (range, 1.2–10.5 years). The majority of patients had low-risk disease (58%, n = 96), with a median age of 64 years at the onset of treatment. Of 166 treated men, 13 (7.8%), 8 (4.8%), 2 (1.2%) patient(s) experienced biochemical failure, local failure, regional failure, respectively. Regional failure was seen in an obturator lymph node in 1 patient and the external iliac lymph nodes in the other. None of the patients experienced distant failure. There were 5 (3.0%) deaths, none of which were due to PC. The 5- and 8-year BFFS rate were 97% and 92%, respectively. None of the clinical disease characteristics or treatment-related factors assessed were associated with BFFS on multivariate Cox proportional hazards modeling (all P > .05).ConclusionDisease control rates reported in our assessment of PBT were similar to those reported in previous clinically localized intact PC analyses, which used intensity-modulated radiotherapy, three-dimensional conformal radiotherapy, or radical prostatectomy as definitive therapy. In addition, BFFS rates were similar, if not improved, to previous PBT studies.
Highlights
Despite the controversy and subsequent changes in prostate-specific antigen (PSA) screening recommendations, prostate cancer (PC) remains the most common nonskin cancer diagnosis for males in the United States [1]
A subset of these patients can be further stratified into very-low risk disease, which the National Comprehensive Cancer Network defines as having clinical stage T1c, grade group 1, PSA less than 10 ng/mL, fewer than 3 prostate biopsy fragments/cores positive, less than 50% cancer in each fragment/core, and PSA density less than 0.15 ng/mL/ kg [4]
The survival outcomes were improved in the very low-risk (VLR) cohort (5- and 8-year biochemical failure-free survival (BFFS) of 98% [95% CI 96%–100%] and 95% [95% CI 91%–100%], respectively) compared with the LR (5- and 8-year BFFS of 97% [95% CI 94%–100%] and 92% [95% CI 87%-100%], respectively) and favorable intermediate risk (FIR) (5- and 8-year BFFS of 96% [95% CI 93%–100%] and 92% [95% CI 85%-100%] cohort, respectively)
Summary
Despite the controversy and subsequent changes in prostate-specific antigen (PSA) screening recommendations, prostate cancer (PC) remains the most common nonskin cancer diagnosis for males in the United States [1]. 40% of newly diagnosed patients present with low-risk disease, which is defined as grade group 1, PSA less than 10 ng/mL, and clinical stage T1c to T2a [2, 3]. A subset of these patients can be further stratified into very-low risk disease, which the National Comprehensive Cancer Network defines as having clinical stage T1c, grade group 1, PSA less than 10 ng/mL, fewer than 3 prostate biopsy fragments/cores positive, less than 50% cancer in each fragment/core, and PSA density less than 0.15 ng/mL/ kg [4]. Other established treatment options for favorable risk PC include radical prostatectomy (RP) and brachytherapy, but a significant portion of patients are not clinically suitable, or wish to avoid, these invasive procedures
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