Proton Beam Therapy Alone for Intermediate- or High-Risk Prostate Cancer: An Institutional Prospective Cohort Study

Abstract

The role of proton beam therapy (PBT) as monotherapy for localized prostate cancer (PCa) remains unclear. The purpose of this study was to evaluate the efficacy and adverse events of PBT alone for these patients. Between January 2011 and July 2014, 218 patients with intermediate- and high-risk PCa who declined androgen deprivation therapy (ADT) were enrolled to the study and were treated with PBT following one of the following protocols: 74 Gray (GyE) with 37 fractions (fr) (74 GyE/37 fr), 78 GyE/39 fr, and 70 GyE/28 fr. The 5-year progression-free survival rate in the intermediate- and high-risk groups was 97% and 83%, respectively (p = 0.002). The rate of grade 2 or higher late gastrointestinal toxicity was 3.9%, and a significant increased incidence was noted in those who received the 78 GyE/39 fr protocol (p < 0.05). Grade 2 or higher acute and late genitourinary toxicities were observed in 23.5% and 3.4% of patients, respectively. Our results indicated that PBT monotherapy can be a beneficial treatment for localized PCa. Furthermore, it can preserve the quality of life of these patients. We believe that this study provides crucial hypotheses for further study and for establishing new treatment strategies.

A Literature Review of Proton Beam Therapy for Prostate Cancer in Japan

“…Arimura et al conducted a prospective cohort study, which includes 218 individuals, from January 2011–July 2014. 78 Gy, 74 Gy, and 70 Gy were irradiated depending on the risk status of the patient and the cumulative incidence of GU toxicities were as follows: 28.1%, 27.9%, and 13.1% for acute, and 3.4%, 3.5%, and 3.3% for late toxicities [27].…”

“…Data also showed that scores were at their lowest three years after the treatment, followed by a slight recovery. Thus, patient age can be a big factor in measuring EPIC scores after PBT [27].…”

“…Overall, biochemical relapse free survival was at 97%, 91.1%, and 83.1% for low, intermediate, and high risk patients, while overall survival was 98.4%, 96.8%, and 95.2%. Another study determined the five-year progression free survival rate for intermediate and high risk patients were 97% and 83%, respectively, and overall survival rates measured 96% and 98% [27]. Univariate analysis showed several factors associated with biochemical relapse free survival such as NCCN classification, age, performance status, operability, T stage, Gleason score, PSA value, and ADT.…”

“…Acute GU incidence was noted to be accounted more on the total dose delivered rather than the dose per fraction. Low incidence of GI toxicity associated with PBT is possibly due to the conformation of the lateral beams during dose delivery producing the characteristic dose distribution of proton beams to the target [27]. Grade 3 late GI and GU toxicities were noted to be of very low incidence, not only in the study conducted by Takagi et al, but also from prior results presented by Mendenhall et al and Bryant et al Furthermore, late gastrointestinal studies from previous reports of Zelefsky et al, Pollack et al, Michalski et al, Ryu et al, and Slater et al [42,43,44,45,46,47] were also comparable with the results stated in the study of Nihei et al [18].…”

Assessment of Polyethylene Glycol Hydrogel Spacer and Its Effect on Rectal Radiation Dose in Prostate Cancer Patients Receiving Proton Beam Radiation Therapy

“…Large series of PBRT patients without hydrogel has variable reported rectal toxicity rates ranging from 0% to 64%. 6,25 The pivotal randomized controlled trial that led to FDA approval of PEG hydrogel in photon EBRT demonstrated no difference in acute toxicity rates (<3 months after therapy) with 23% and 28% in hydrogel and control groups, respectively. However, at late follow-up (>3 months), there was a significant reduction in rectal toxicity (grade 2) in those who had hydrogel placement of 7% versus 2%.…”