Five-year outcomes from a prospective trial of image-guided accelerated hypofractionated proton therapy for prostate cancer

Dosimetric Features of Ultra-Hypofractionated Intensity Modulated Proton Therapy for Prostate Cancer

Purpose

To report clinical and dosimetric characteristics of 5-fraction stereotactic ablative radiotherapy (SABR) using intensity modulated proton therapy (IMPT) for localized prostate cancer.

Materials and Methods

All patients receiving IMPT SABR from 2017 to 2021 for localized prostate cancer at our institution were included. Five fractions were delivered every other day to the prostate +/- seminal vesicles [clinical target volume (CTV)] with 3 mm/3% robustness. A 4-field arrangement with 2 anterior oblique and 2 opposed lateral beams was used in most patients (97%), and most (99%) had a retroprostatic hydrogel spacer.

Results

A total of 534 patients with low (14%), favorable intermediate (45%), unfavorable intermediate (36%), high (4.0%), or very high-risk (0.6%) disease are evaluated. Prescription dose was 36.25 Gy (31%), 38 Gy (38%), or 40 Gy (31%) was prescribed. Median volume percentage of CTV receiving at least 100% of prescription dose [V100% (%)] was 100% [interquartile range: 99.99-100]. Rectum V50% (%), V80% (%), and V90% (%) were significantly lower in patients who had spacer, with a mean difference of -9.70%, -6.59%, and -4.42%, respectively, compared to those who did not have spacer. Femoral head dose was lower with a 4-field arrangement. Mean differences in left and right femoral head V40% (%) were -6.99% and -10.74%, respectively.

Conclusion

We provide a large, novel report of patients treated with IMPT SABR for localized prostate cancer. Four-field IMPT with hydrogel spacer provides significant sparing of rectum and femoral heads without compromising target coverage.

Differences in Patterns of Care and Referral Between Proton and Photon Therapy

Purpose

To report demographic and clinical characteristics of patients who were more likely to receive proton beam therapy (PBT) than photon therapy from facilities with access to proton centers.

Materials and Methods

We utilized the national cancer database to identify the facilities with access to PBT between 2004 and 2015 and compared the relative usage of photons and PBT for demographic and clinical scenarios in breast, prostate, and nonsmall cell cancer.

Results

In total, 231 facilities with access to proton centers accounted for 168 323 breast, 39 975 lung, and 77 297 prostate cancer patients treated definitively. Proton beam therapy was used in 0.5%, 1.5%, and 8.9% of breast, lung, and prostate cases. Proton beam therapy was correlated with a farther distance traveled and longer start time from diagnosis for each site (P < .05).For breast, demographic correlates of PBT were treatment in the west coast (odds ratio [OR] = 4.81), age <60 (OR = 1.25), white race (OR = 1.94), and metropolitan area (OR = 1.58). Left-sided cancers (OR = 1.28), N2 (OR = 1.71), non-ER+/PR+/Her2Neu- cancers (OR = 1.24), accelerated partial breast irradiation (OR = 1.98), and hypofractionation (OR = 2.35) were predictors of PBT.For nonsmall cell cancer, demographic correlates of PBT were treatment in the south (OR = 2.6), metropolitan area (OR = 1.72), and Medicare insurance (OR = 1.64). Higher comorbid score (OR = 1.36), later year treated (OR = 3.16), and hypofractionation (not SBRT) (OR = 3.7) were predictors of PBT.For prostate, correlates of PBT were treatment in the west coast (OR = 2.48), age <70 (OR = 1.19), white race (OR = 1.41), metropolitan area (OR = 1.25), higher income/education (OR = 1.25), and treatment at an academic center (OR = 33.94). Lower comorbidity score (OR = 1.42), later year treated (OR = 1.37), low-risk disease (OR = 1.45), definitive compared to postoperative (OR = 6.10), and conventional fractionation (OR = 1.64) were predictors of PBT.

Conclusion

Even for facilities with established referrals to proton centers, PBT utilization was low; socioeconomic status was potentially a factor. Proton beam therapy was more often used with left-sided breast and low-risk prostate cancers, without a clear clinical pattern in lung cancer.

A pooled patient-reported outcomes analysis of moderately hypofractionated proton beam therapy and photon-based intensity modulated radiation therapy for low- or intermediate-risk prostate cancer

BACKGROUND

We sought to characterize and compare late patient-reported outcomes (PROs) after moderately hypofractionated intensity modulated radiation therapy (IMRT) and proton beam therapy (PBT) for localized prostate cancer (PC).

METHODS

This multi-institutional analysis included low- or intermediate-risk group PC patients treated with moderately hypofractionated radiation to an intact prostate stratified by treatment modality: IMRT or PBT. The primary outcomes were prospectively collected patient-reported late gastrointestinal (GI) and genitourinary (GU) toxicity assessed by International Prostate Symptom Score (IPSS) and Expanded PC Index Composite (EPIC). Multivariable regression analysis (MVA) controlling for age, race, and risk group tested the effect of time, treatment, and their interaction.

RESULTS

287 IMRT and 485 PBT patients were included. Intermediate risk group (81.2 vs. 68.2%; p < 0.001) and median age at diagnosis (70 vs. 67 years; p < 0.001) were higher in the IMRT group. On MVA, there was no significant difference between modalities. PBT IPSS did not differ from IMRT IPSS at 12 months (odds ratio [OR], 1.19; p = 0.08) or 24 months (OR, 0.99; p = 0.94). PBT EPIC overall GI function at 12 months (OR, 3.68; p = 0.085) and 24 months (OR 2.78; p = 0.26) did not differ from IMRT EPIC overall GI function. At 24 months, urinary frequency was no different between PBT and IMRT groups (OR 0.35; p = 0.096).

CONCLUSIONS

This multi-institutional analysis of low- or intermediate-risk PC treated with moderately hypofractionated PBT and IMRT demonstrated low rates of late patient-reported GI and GU toxicities. After covariate adjustment, late GI and GU PROs were not significantly different between PBT or IMRT cohorts.

5-Years Analysis of Effectivity and Toxicity of Ultra-Hypofractionated Proton Radiotherapy in the Treatment of Low- and Intermediate-Risk Prostate Cancer-A Retrospective Analysis

BACKGROUND

We retrospectively analyzed the 5-year biochemical disease-free survival (bDFS) and occurrence of late toxicity in prostate cancer patients treated with pencil beam scanning (PBS) proton radiotherapy.

METHODOLOGY

In the period from January 2013 to June 2018, 853 patients with prostate cancer were treated with an ultra-hypofractionated schedule (36.25 GyE/five fractions). The mean PSA value was 6.7 (0.7-19.7) µg/L. There were 318 (37.3%), 314 (36.8%), and 221 (25.9%) patients at low (LR), favorable intermediate (F-IR), and unfavorable intermediate risk (U-IR), respectively. Neoadjuvant hormonal therapy was administered to 197 (23.1%) patients, and 7 (0.8%) patients had adjuvant hormonal therapy. The whole group of patients reached median follow-up time at 62.7 months, and their mean age was 64.8 (40.0-85.7) years. The bDFS rates and late toxicity profile were evaluated.

RESULTS

Median treatment time was 10 (7-38) days. Estimated 5-year bDFS rates were 96.5%, 93.7%, and 91.2% for low-, favorable intermediate-, and unfavorable intermediate-risk groups, respectively. Cumulative late toxicity (CTCAE v4.0) of G2+ was as follows: gastrointestinal (GI)-G2: 9.1%; G3: 0.5%; genitourinary (GU)-G2: 4.3%, and no G3 toxicity was observed. PSA relapse was observed in 58 (6.8%) patients: 16 local, 22 lymph node, 4 bone recurrences, and 10 combined sites of relapse were detected. Throughout the follow-up period, 40 patients (4.7%) died, though none due to prostate cancer.

CONCLUSION

Ultra-hypofractionated proton beam radiotherapy is an effective treatment for low- and favorable intermediate-risk prostate cancer, with long-term bDFS rates comparable to other techniques. It is promising for unfavorable intermediate-risk prostate cancer and has acceptable long-term GI and favorable GU toxicity.

Hypofractionated Radiotherapy in Localized, Low-Intermediate-Risk Prostate Cancer: Current and Future Prospectives

At the time of diagnosis, the vast majority of prostate carcinoma patients have a clinically localized form of the disease, with most of them presenting with low- or intermediate-risk prostate cancer. In this setting, various curative-intent alternatives are available, including surgery, external beam radiotherapy and brachytherapy. Randomized clinical trials have demonstrated that moderate hypofractionated radiotherapy can be considered as a valid alternative strategy for localized prostate cancer. High-dose-rate brachytherapy can be administered according to different schedules. Proton beam radiotherapy represents a promising strategy, but further studies are needed to make it more affordable and accessible. At the moment, new technologies such as MRI-guided radiotherapy remain in early stages, but their potential abilities are very promising.

A Phase II prospective study of hypofractionated proton therapy of prostate and pelvic lymph nodes: Acute effects on patient-reported quality of life

BACKGROUND

The objective of this study was to report acute changes in patient-reported quality of life (PRQOL) using the 26-item Expanded Prostate Index Composite (EPIC-26) questionnaire in a prospective study using hypofractionated intensity-modulated proton beam therapy (H-IMPT) targeting the prostate and the pelvic lymph nodes for high-risk or unfavorable intermediate-risk prostate cancer.

METHODS

Fifty-five patients were enrolled. H-IMPT consisted of 45 GyE to the pelvic lymph nodes and 67.5 GyE to the prostate and seminal vesicles in 25 fractions. PRQOL was assessed with the urinary incontinence (UI), urinary irritative/obstructive symptoms (UO), and bowel function (BF) domains of EPIC-26 questionnaire. Mean changes in domain scores were analyzed from pretreatment to the end of treatment and 3 months posttreatment. A clinically meaningful change (or minimum important change) was defined as a score change > 50% of the baseline standard deviation.

RESULTS

The mean scores of UO, UI, and BF at baseline were 84.6, 91.1, and 95.3, respectively. At the end of treatment, there were statistically significant and clinically meaningful declines in UO and BF scores (-13.5 and -2.3, respectively), while the decline in UI score was statistically significant but not clinically meaningful (-13.7). A clinically meaningful decline in UO, UI, and BF scores occurred in 53.5%, 22.7%, and 73.2% of the patients, respectively. At 3 months posttreatment, all three mean scores showed an improvement, with fewer patients having a clinically meaningful decline in UO, UI, and BF scores (18.4%, 20.5%, and 45.0%, respectively). There was no significant reduction in the mean UO and UI scores compared to baseline, although the mean BF score remained lower than baseline and the difference was clinically meaningful.

CONCLUSIONS

UO, UI, and BF scores of PRQOL declined at the end of H-IMPT. UO and UI scores showed improvement at 3 months posttreatment and were similar to the baseline scores. However, BF score remained lower at 3 months posttreatment with a clinically meaningful decline.

The Role of Hypofractionation in Proton Therapy

Hypofractionated radiotherapy is an attractive approach for minimizing patient burden and treatment cost. Technological advancements in external beam radiotherapy (EBRT) delivery and image guidance have resulted in improved targeting and conformality of the absorbed dose to the disease and a reduction in dose to healthy tissue. These advances in EBRT have led to an increasing adoption and interest in hypofractionation. Furthermore, for many treatment sites, proton beam therapy (PBT) provides an improved absorbed dose distribution compared to X-ray (photon) EBRT. In the past 10 years there has been a notable increase in reported clinical data involving hypofractionation with PBT, reflecting the interest in this treatment approach. This review will discuss the reported clinical data and radiobiology of hypofractionated PBT. Over 50 published manuscripts reporting clinical results involving hypofractionation and PBT were included in this review, ~90% of which were published since 2010. The most common treatment regions reported were prostate, lung and liver, making over 70% of the reported results. Many of the reported clinical data indicate that hypofractionated PBT can be well tolerated, however future clinical trials are still needed to determine the optimal fractionation regime.

Prostate Cancer Treatment with Pencil Beam Proton Therapy Using Rectal Spacers sans Endorectal Balloons

Purpose

Proton beam radiotherapy (PBT) has been used for the definitive treatment of localized prostate cancer with low rates of high-grade toxicity and excellent patient-reported quality-of-life metrics. Technological advances such as pencil beam scanning (PBS), Monte Carlo dose calculations, and polyethylene glycol gel rectal spacers have optimized prostate proton therapy. Here, we report the early clinical outcomes of patients treated for localized prostate cancer using modern PBS–PBT with hydrogel rectal spacing and fiducial tracking without the use of endorectal balloons.

Materials and Methods

This is a single institutional review of consecutive patients treated with histologically confirmed localized prostate cancer. Prior to treatment, all patients underwent placement of fiducials into the prostate and insertion of a hydrogel rectal spacer. Patients were typically given a prescription dose of 7920 cGy at 180 cGy per fraction using a Monte Carlo dose calculation algorithm. Acute and late toxicity were evaluated using the Common Terminology Criteria for Adverse Events (CTCAE), version 5. Biochemical failure was defined using the Phoenix definition.

Results

From July 2018 to April 2020, 33 patients were treated (median age, 75 years). No severe acute toxicities were observed. The most common acute toxicity was urinary frequency. With a median follow-up of 18 months, there were no high-grade genitourinary late toxicities; however, one grade 3 gastrointestinal toxicity was observed. Late erectile dysfunction was common. One treatment failure was observed at 21 months in a patient treated for high-risk prostate cancer.

Conclusion

Early clinical outcomes of patients treated with PBS–PBT using Monte Carlo–based planning, fiducial placement, and rectal spacers sans endorectal balloons demonstrate minimal treatment-related toxicity with good oncologic outcomes. Rectal spacer stabilization without the use of endorectal balloons is feasible for the use of PBS–PBT.

Five- and seven-year outcomes for image-guided moderately accelerated hypofractionated proton therapy for prostate cancer

BACKGROUND

To report 5- and 7-year outcomes after image-guided moderately accelerated hypofractionated proton therapy (AHPT) for prostate cancer.

MATERIAL AND METHODS

We reviewed the first 582 prostate cancer patients enrolled on prospective outcomes tracking trial and treated with double-scattered moderately AHPT between 2008 and 2015. 269 patients had low-risk (LR) and 313 had intermediate-risk (IR) disease, including 149 with favorable intermediate-risk (FIR) and 164 with unfavorable intermediate-risk (UIR) disease. LR patients received a median 70.0GyRBE (2.5GyRBE/fraction) and IR patients received a median of 72.5 GyRBE. Seventeen patients (UIR, n = 12) received androgen deprivation therapy (ADT) for a median of 6 months. Toxicities were graded per the CTCAE, v4.0, and patient-reported quality-of-life data were reviewed.

RESULTS

Median follow-up was 8.0 years (0.9-12.2). The 5- and 7-year rates of freedom from biochemical progression (FFBP) overall and in the LR and IR subsets, respectively, were 96.8/95.2%, 98.8/98.8%, and 95.0/91.9%. For the FIR and UIR subsets, they were 97.2/95.2% and 93.1/88.8%. Actuarial 5- and 7-year rates of late CTCAE, v4.0, grade 2 gastrointestinal (GI), grade 3 GI, and grade 3 genitourinary (GU) toxicities were 9.9%/11.2%, 1.4/1.4% and 1.3/2.1%, respectively. No grade ≥4 GI or GU toxicities occurred. The mean (standard deviation, SD) IPSS and EPIC Composite bowel function and bother scores were 7 (SD = 5), 97 (SD = 7), and 94 (SD = 6), respectively at baseline, 7 (SD = 5), 92 (SD = 13), and 92 (SD = 9) at the 5-year follow-up, and 7 (SD = 5), 93 (SD = 12), and 92 (SD = 10) at the 7-year follow-up.

CONCLUSION

Image-guided AHPT 5- and 7-year outcomes show high efficacy, minimal physician-assessed toxicity, and excellent patient-reported outcomes in this cohort.

Proton therapy for prostate cancer: current state and future perspectives

OBJECTIVE

Localized prostate cancer can be treated with several radiotherapeutic approaches. Proton therapy (PT) can precisely target tumors, thus sparing normal tissues and reducing side-effects without sacrificing cancer control. However, PT is a costly treatment compared with conventional photon radiotherapy, which may undermine its overall efficacy. In this review, we summarize current data on the dosimetric rationale, clinical benefits, and cost of PT for prostate cancer.

METHODS

An extensive literature review of PT for prostate cancer was performed with emphasis on studies investigating dosimetric advantage, clinical outcomes, cost-effective strategies, and novel technology trends.

RESULTS

PT is safe, and its efficacy is comparable to that of standard photon-based therapy or brachytherapy. Data on gastrointestinal, genitourinary, and sexual function toxicity profiles are conflicting; however, PT is associated with a low risk of second cancer and has no effects on testosterone levels. Regarding cost-effectiveness, PT is suboptimal, although evolving trends in radiation delivery and construction of PT centers may help reduce the cost.

CONCLUSION

PT has several advantages over conventional photon radiotherapy, and novel approaches may increase its efficacy and safety. Large prospective randomized trials comparing photon therapy with proton-based treatments are ongoing and may provide data on the differences in efficacy, toxicity profile, and quality of life between proton- and photon-based treatments for prostate cancer in the modern era.

ADVANCES IN KNOWLEDGE

PT provides excellent physical advantages and has a superior dose profile compared with X-ray radiotherapy. Further evidence from clinical trials and research studies will clarify the role of PT in the treatment of prostate cancer, and facilitate the implementation of PT in a more accessible, affordable, efficient, and safe way.

Patient-Reported Quality of Life Outcomes after Moderately Hypofractionated and Normofractionated Proton Therapy for Localized Prostate Cancer

We retrospectively evaluated the three-year patient-reported quality of life (QOL) after moderately hypofractionated proton therapy (MHPT) for localized prostate cancer in comparison with that after normofractionated PT (NFPT) using the Expanded Prostate Cancer Index Composite-50. Patients who received MHPT (60-63 Gy (relative biological effectiveness equivalents; RBE)/20-21 fractions) (n = 343) or NFPT (74-78 Gy (RBE)/37-39 fractions) (n = 296) between 2013 and 2016 were analyzed. The minimum clinically important difference (MCID) threshold was defined as one-half of a standard deviation of the baseline value. The median follow-up was 56 months and 83% completed questionnaires at 36 months. Clinically meaningful score deterioration was observed in the urinary domain at 1 month in both groups and in the sexual domain at 6-36 months in the NFPT group, but not observed in the bowel domain. At 36 months, the mean score change for urinary summary was -0.3 (MHPT) and -1.6 points (NFPT), and that for bowel summary was +0.1 and -2.0 points; the proportion of patients with MCID was 21% and 24% for urinary summary and 18% and 29% for bowel summary. Overall, MHPT had small negative impacts on QOL over three years, and the QOL after MHPT and NFPT was similar.

Clinical Efficacy and Safety of Proton and Carbon Ion Radiotherapy for Prostate Cancer: A Systematic Review and Meta-Analysis

BACKGROUND

Carbon ion radiotherapy (CIRT) and proton beam therapy (PBT) are promising methods for prostate cancer, however, the consensus of an increasing number of studies has not been reached. We aimed to provide systematic evidence for evaluating the efficacy and safety of CIRT and PBT for prostate cancer by comparing photon radiotherapy.

MATERIALS AND METHODS

We searched for studies focusing on CIRT and PBT for prostate cancer in four online databases until July 2021. Two independent reviewers assessed the quality of included studies and used the GRADE approach to rate the quality of evidence. R 4.0.2 software was used to conduct the meta-analysis. A meta-regression test was performed based on the study design and tumor stage of each study.

RESULTS

A total of 33 studies including 13 CIRT- and 20 PBT-related publications, involving 54,101, participants were included. The quality of the included studies was found to be either low or moderate quality. Random model single-arm meta-analysis showed that both the CIRT and PBT have favorable efficacy and safety, with similar 5-year overall survival (OS) (94 vs 92%), the incidence of grade 2 or greater acute genitourinary (AGU) toxicity (5 vs 13%), late genitourinary (LGU) toxicity (4 vs 5%), acute gastrointestinal (AGI) toxicity (1 vs 1%), and late gastrointestinal (LGI) toxicity (2 vs 4%). However, compared with CIRT and PBT, photon radiotherapy was associated with lower 5-year OS (72-73%) and a higher incidence of grade 2 or greater AGU (28-29%), LGU (13-14%), AGI (14-19%), and LGI toxicity (8-10%). The meta-analysis showed the 3-, 4-, and 5-year local control rate (LCR) of CIRT for prostate cancer was 98, 97, and 99%; the 3-, 4-, 5-, and 8-year biochemical relapse-free rate (BRF) was 92, 91, 89, and 79%. GRADE assessment results indicated that the certainty of the evidence was very low. Meta-regression results did not show a significant relationship based on the variables studied (P<0.05).

CONCLUSIONS

Currently available evidence demonstrated that the efficacy and safety of CIRT and PBT for prostate cancer were similar, and they may significantly improve the OS, LCR, and reduce the incidence of GU and GI toxicity compared with photon radiotherapy. However, the quantity and quality of the available evidence are insufficient. More high-quality controlled studies are needed in the future.

Ultrahypofractionated Proton Radiation Therapy in the Treatment of Low and Intermediate-Risk Prostate Cancer-5-Year Outcomes

PURPOSE

To analyze the 5-year biochemical disease-free survival (bDFS) and late toxicity profile in patients with prostate cancer treated with pencil beam scanning (PBS) proton radiation therapy.

METHODS AND MATERIALS

Between January 2013 and March 2016, 284 patients with prostate cancer were treated using intensity modulated proton therapy (IMPT), with an ultrahypofractionated schedule (36.25 GyE in 5 fractions). Five patients were immediately lost from follow-up and thus were excluded from analysis. Data for 279 patients were prospectively collected and analyzed with a median follow-up time of 56.5 (range, 3.4-87.5) months. The mean age at time of treatment was 64.5 (40.1-85.7) years, and the median prostate-specific antigen (PSA) value was 6.35 μg/L (0.67-17.3 μg/L). A total of 121 (43.4%) patients had low-risk, 125 patients (44.8%) had favorable, and 33 (11.8%) unfavorable intermediate-risk cancer. In addition, 49 (17.6%) patients underwent neoadjuvant hormonal therapy, and no patients had adjuvant hormonal therapy. bDFS and late toxicity profiles were evaluated.

RESULTS

The median treatment time was 9 days (range, 7-18 days). The 5-year bDFS was 96.9%, 91.7%, and 83.5% for the low-, favorable, and unfavorable intermediate-risk group, respectively. Late toxicity (Common Terminology Criteria for Adverse Events v.4) was as follows: gastrointestinal: grade 1, 62 patients (22%), grade 2, 20 patients (7.2%), and grade 3, 1 patient (0.36%); genitourinary: grade 1, 80 patients (28.7%), grade 2, 14 patients (5%), and grade 3, 0 patients. PSA relapse was observed in 17 patients (6.1%), and lymph node or bone recurrence was detected in 11 patients. Four (1.4%) local recurrences were detected. Nine patients (3.2%) died of causes unrelated to prostate cancer. No deaths related to prostate cancer were reported.

CONCLUSION

Ultrahypofractionated proton beam radiation therapy for prostate cancer is effective with long-term bDFS comparable with other fractionation schedules and with minimal serious long-term GI and GU toxicity.

A Pooled Toxicity Analysis of Moderately Hypofractionated Proton Beam Therapy and Intensity Modulated Radiation Therapy in Early-Stage Prostate Cancer Patients

PURPOSE

Data comparing moderately hypofractionated intensity modulated radiation therapy (IMRT) and proton beam therapy (PBT) are lacking. We aim to compare late toxicity profiles of patients with early-stage prostate cancer treated with moderately hypofractionated PBT and IMRT.

METHODS AND MATERIALS

This multi-institutional analysis included patients with low- or intermediate-risk biopsy-proven prostate adenocarcinoma from 7 tertiary referral centers treated from 1998 to 2018. All patients were treated with moderately hypofractionated radiation, defined as 250 to 300 cGy per daily fraction given for 4 to 6 weeks, and stratified by use of IMRT or PBT. Primary outcomes were late genitourinary (GU) and gastrointestinal (GI) toxicity. Adjusted toxicity rates were calculated using inverse probability of treatment weighting, accounting for race, National Comprehensive Cancer Network risk group, age, pretreatment International Prostate Symptom Score (GU only), and anticoagulant use (GI only).

RESULTS

A total of 1850 patients were included: 1282 IMRT (median follow-up 80.0 months) and 568 PBT (median follow-up 43.9 months). Overall toxicity rates were low, with the majority of patients experiencing no late GU (56.6%, n = 1048) or late GI (74.4%, n = 1377) toxicity. No difference was seen in the rates of late toxicity between the groups, with late grade 3+ GU toxicity of 2.0% versus 3.9% (odds ratio [OR] 0.47; 95% confidence interval 0.17-1.28) and late grade 2+ GI toxicity of 14.6% versus 4.7% (OR 2.69; confidence interval 0.80-9.05) for the PBT and IMRT cohorts, respectively. On multivariable analysis, no factors were significantly predictive of GU toxicity, and only anticoagulant use was significantly predictive of GI toxicity (OR 1.90; P = .008).

CONCLUSIONS

In this large, multi-institutional analysis of 1850 patients with early-stage prostate cancer, treatment with moderately hypofractionated IMRT and PBT resulted in low rates of toxicity. No difference was seen in late GI and GU toxicity between the modalities during long-term follow-up. Both treatments are safe and well tolerated.

Consensus Statement on Proton Therapy for Prostate Cancer

Proton therapy is a promising but controversial treatment in the management of prostate cancer. Despite its dosimetric advantages when compared with photon radiation therapy, its increased cost to patients and insurers has raised questions regarding its value. Multiple prospective and retrospective studies have been published documenting the efficacy and safety of proton therapy for patients with localized prostate cancer and for patients requiring adjuvant or salvage pelvic radiation after surgery. The Particle Therapy Co-Operative Group (PTCOG) Genitourinary Subcommittee intends to address current proton therapy indications, advantages, disadvantages, and cost effectiveness. We will also discuss the current landscape of clinical trials. This consensus report can be used to guide clinical practice and research directions.

Overall Survival After Treatment of Localized Prostate Cancer With Proton Beam Therapy, External-Beam Photon Therapy, or Brachytherapy

With limited high-level evidence, we carried out a comparative effectiveness study for the effect of proton beam therapy (PBT) on overall survival compared to external-beam radiotherapy (EBRT) and brachytherapy (BT) among patients with localized prostate cancer using a national database. PBT was associated with a significant overall survival benefit compared to EBRT and had a similar performance as BT.

Extreme hypofractionated proton radiotherapy for prostate cancer using pencil beam scanning: Dosimetry, acute toxicity and preliminary results

INTRODUCTION

Extreme hypofractionated radiotherapy for prostate cancer is a common modality in photon therapy. Pencil beam scanning (PBS) in similar fractionation allows better dose distribution and makes proton therapy more available for such patients. The purpose of this study is the feasibility of extreme proton hypofractionated radiotherapy and publication of early clinical results.

METHODS

Two hundred patients with early-stage prostate cancer were treated with IMPT (intensity-modulated proton therapy), extreme hypofractionated schedule (36.25 GyE in five fractions) between February 2013 and December 2015. Mean age of the patients was 64.3 years, and the mean value of prostate-specific antigen (PSA) before treatment was 6.83 μg/L (0.6-17.3 μg/L). Ninety-three patients (46.5%) were in the low-risk group. One hundred and seven patients (53.5%) were in the intermediate-risk group. Twenty-nine patients (14.5%) had neoadjuvant hormonal therapy, and no patients had adjuvant hormonal therapy. Acute toxicity, late toxicity and short-term results were evaluated.

RESULTS

All patients finished radiotherapy without interruptions. The median follow-up time was 36 months. The mean treatment time was 9.5 days (median 9 days). Acute toxicity according to Common Terminology Criteria for Adverse Events (CTCAE) v 4.0 was (gastrointestinal toxicity) GI (grade) G1-17%, G2-3.5%; (genitourinary toxicity) GU G1-40%, G2-19%; and no G3 toxicity was observed. Late toxicity was GI G1-19%, G2-5.5%; GU G1-17%, G2-4%; and no G3 toxicity was observed. PSA relapse was observed in one patient (1.08%) in the low-risk group (pelvic lymph node involvement was detected) and in seven patients (6.5%) in the intermediate-risk group (three lymph node metastases, two lymph node and bone metastases, two PSA relapses). No patient died of prostate cancer, and three patients died from other reasons. No local recurrence of cancer in the prostate was observed.

CONCLUSIONS

Proton beam radiotherapy for prostate cancer is feasible with a low rate of acute toxicity and promising late toxicity and effectivity.

Hypofractionated Proton Therapy in Early Prostate Cancer: Results of a Phase I/II Trial at Loma Linda University

Purpose

To determine whether a hypofractionated proton therapy regimen will control early-stage disease and maintain low rates of side effects similar to results obtained using standard-fraction proton therapy at our institution.

Materials and Methods

A cohort of 146 patients with low-risk prostate cancer according to National Comprehensive Cancer Network guidelines (Gleason score <7, prostate-specific antigen [PSA] <10, tumor stage of T1-T2a) received 60 Gy (cobalt Gy equivalent) of proton therapy (20 fractions of 3.0 Gy per fraction) in 4 weeks, a dose biologically equivalent to standard fractionation (44-45 fractions of 1.8 Gy to a total of 79.2 to 81 Gy in 0 weeks). Patients were evaluated at least weekly during treatment, at which time documentation of treatment tolerance and acute reactions was obtained. Follow-up visits were conducted every 3 months for the first 1 years, every 6 months for the next 3 years, then annually. Follow-up visits consisted of history and physical examination, PSA measurements, and evaluation of toxicity.

Results

The median follow-up time was 42 months (range, 3-96 months). Acute grade 2 urinary toxicity occurred in 16% (20/120) of the patients; acute grade 2 or higher gastrointestinal toxicity was seen in 1.7% (2/120). At 9 months, 1 patient had late grade 3 urinary toxicity, which resolved by 12 months; no grade 3 gastrointestinal toxicities occurred. The 3-year biochemical survival rate was 99.3% (144/145). The median time to PSA nadir was 30 months.

Conclusion

Hypofractionated proton therapy of 60 Gy in 20 fractions was safe and effective for patients with low-risk prostate cancer.

Four-Year Outcomes From a Prospective Phase II Clinical Trial of Moderately Hypofractionated Proton Therapy for Localized Prostate Cancer

PURPOSE

Moderately hypofractionated radiation therapy represents an effective treatment for localized prostate cancer (PC). Although large randomized trials have reported the efficacy of photon-based hypofractionated therapy, hypofractionated proton therapy (HFPT) has not been extensively studied. This study was performed to determine the clinical and patient-reported outcomes for patients with PC treated with HFPT.

METHODS AND MATERIALS

Between 2010 and 2017, 184 men were enrolled on a trial of 70 Gy in 28 fractions of HFPT for low- to intermediate-risk PC. Acute and late toxicity was evaluated using National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. Patient-reported outcomes were measured by International Prostate Symptom Score, International Index of Erectile Function Questionnaire, and Expanded Prostate Cancer Index Composite scores.

RESULTS

Median follow-up was 49.2 months. Enrolled patients had low-risk (n = 18), favorable intermediate-risk (n = 78), and unfavorable intermediate-risk (n = 88) PC. Four-year rates of biochemical-clinical failure-free survival were 93.5% (95% confidence interval, 89%-98%), 94.4% (89%-100%), 92.5% (86%-100%), and 93.8% (88%-100%) in the overall group and the low-risk, favorable intermediate-risk, and unfavorable intermediate-risk cohorts, respectively (log-rank P > .4). The incidence of acute grade 2 or higher gastrointestinal (GI) and urologic toxicities were 3.8% and 12.5%, respectively. The 4-year incidence of late grade 2 or higher urologic and GI toxicity was 7.6% (4%-13%) and 13.6% (9%-20%), respectively. One late grade 3 GI toxicity was reported. All late toxicities were transient. Patient-reported International Prostate Symptom, International Index of Erectile Function, and Expanded Prostate Cancer Index Composite scores had no significant long-term changes after completion of HFPT (Supplementary Table 1, available at https://doi.org/10.1016/j.ijrobp.2019.05.069).

CONCLUSIONS

HFPT is associated with low rates of toxicity and does not appear to negatively affect 4-year patient reported urinary and bowel health. Further comparative analyses are warranted to better understand differences between proton and photon HFRT.

Serum Testosterone 60 Months after Passive-Scatter Proton Therapy for Localized Prostate Cancer

Studies demonstrate a decline of ∼10% in serum testosterone (ST) level after X-ray radiotherapy for prostate cancer. We evaluated changes in ST for patients with low- and intermediate-risk prostate cancer receiving 70-82Gy(RBE) using passive-scatter proton therapy (PT). ST was checked at baseline (n = 358) and at 60+ months after PT (n = 166). The median baseline ST was 363.3 ng/dl (range, 82.0-974.0). The median ST 5 years after PT was 391.5 ng/dl (range, 108.0-1061.0). The difference was not statistically significant (p = 0.9341). Passive-scatter PT was not associated with testosterone suppression at 5 years, suggesting that protons may cause less out-of-field scatter radiation than X-rays.

Patient-Reported Sexual Survivorship Following High-Dose Image-Guided Proton Therapy for Prostate Cancer

OBJECTIVE

To help guide individualized treatment, we sought to identify baseline predictive factors that impact long-term erectile function following high-dose image-guided radiotherapy (HD-IGRT).

METHODS

Potent men with localized prostate cancer treated with radiotherapy alone were enrolled in an institutional review board-approved prospective cohort study. Men received HD-IGRT as primary treatment of prostate cancer. Patient-reported inventories were used to assess erectile function at baseline, 6 months, 2 years, and 5 years after treatment. Long-term potency rates were compared to validated models, and baseline factors were used to create a novel, internally validated nomogram for predicting long-term function.

RESULTS

1,159 men were treated with HD-IGRT. Among 676 men who were potent at baseline and did not receive hormone therapy, the potency rates at 6 months, 2 years, and 5 years were 81%, 68%, and 61%. Recursive partitioning categorized patients into 3 groups based on two factors: baseline response to EPIC Q57 (ability to have an erection) and pre-existing heart disease. At 5 years, the most favorable group reported "very good" on Q57 and had an 80% potency rate (n = 137; p = 0.83); the intermediate group reported "good" on Q57 and had no baseline cardiac disease with a 62% potency rate (n = 145; p = 0.86); and the remaining poor risk group had a 37% potency rate (n = 117; p = 0.19).

CONCLUSIONS

Patient-reported pretreatment sexual function and comorbidities enables stratification and prediction of erectile function. EPIC subset questions with baseline comorbidities may potentially serve as a quick and practical clinical tool for predicting sexual survivorship.

Proton beam therapy for cancer in the era of precision medicine

Precision radiotherapy, which accurately delivers the dose on a tumor and confers little or no irradiation to the surrounding normal tissue and organs, results in maximum tumor control and decreases the toxicity to the utmost extent. Proton beam therapy (PBT) provides superior dose distributions and has a dosimetric advantage over photon beam therapy. Initially, the clinical practice and study of proton beam therapy focused on ocular tumor, skull base, paraspinal tumors (chondrosarcoma and chordoma), and unresectable sarcomas, which responded poorly when treated with photon radiotherapy. Then, it is widely regarded as an ideal mode for reirradiation and pediatrics due to reducing unwanted side effects by lessening the dose to normal tissue. During the past decade, the application of PBT has been rapidly increasing worldwide and gradually expanding for the treatment of various malignancies. However, to date, the role of PBT in clinical settings is still controversial, and there are considerable challenges in its application. We systematically review the latest advances of PBT and the challenges for patient treatment in the era of precision medicine.

Minimal toxicity after proton beam therapy for prostate and pelvic nodal irradiation: results from the proton collaborative group REG001-09 trial

BACKGROUND

Proton beam therapy (PBT) reduces normal organ dose compared to intensity modulated radiation therapy (IMXT) for prostate cancer patients who receive pelvic radiation therapy. It is not known whether this dosimetric advantage results in less gastrointestinal (GI) and genitourinary (GU) toxicity than would be expected from IMXT.

MATERIAL AND METHODS

We evaluated treatment parameters and toxicity outcomes for non-metastatic prostate cancer patients who received pelvic radiation therapy and enrolled on the PCG REG001-09 trial. Patients who received X-ray therapy and/or brachytherapy were excluded. Of 3210 total enrolled prostate cancer patients, 85 received prostate and pelvic radiation therapy exclusively with PBT. Most had clinically and radiographically negative lymph nodes although 6 had pelvic nodal disease and one also had para-aortic involvement. Pelvic radiation therapy was delivered using either 2 fields (opposed laterals) or 3 fields (opposed laterals and a posterior beam). Median pelvic dose was 46.9 GyE (range 39.7-56) in 25 fractions (range 24-30). Median boost dose to the prostate +/- seminal vesicles was 30 GyE (range 20-41.4) in 16 fractions (range 10-24).

RESULTS

Median follow-up was 14.5 months (range 2.8-49.2). Acute grade 1, 2, and 3 GI toxicity rates were 16.4, 2.4, 0%, respectively. Acute grade 1, 2, and 3 GU toxicity rates were 60, 34.1, 0%, respectively.

CONCLUSIONS

Prostate cancer patients who receive pelvic radiation therapy using PBT experience significantly less acute GI toxicity than is expected using IMXT. Further investigation is warranted to confirm whether this favorable acute GI toxicity profile is related to small bowel sparing from PBT.

Long-term outcomes of proton therapy for prostate cancer in Japan: a multi-institutional survey of the Japanese Radiation Oncology Study Group

This is the first multi‐institutional retrospective survey of the long‐term outcomes of proton therapy (PT) for prostate cancer in Japan. This retrospective analysis comprised prostate cancer patients treated with PT at seven centers between January 2008 and December 2011 and was approved by each Institutional Review Board. The NCCN classification was used. Biochemical relapse was based on the Phoenix definition (nadir + 2.0 ng/mL). Toxicities were evaluated with the Common Terminology Criteria for Adverse Events version 4.0. There were 215, 520, and 556 patients in the low‐risk, intermediate‐risk, and high‐risk groups, respectively. The median follow‐up period of surviving patients was 69 months (range: 7–107). Among all patients, 98.8% were treated using a conventional fractionation schedule and 1.2% with a hypofractionation schedule; 58.5% and 21.5% received neoadjuvant and adjuvant androgen deprivation therapy, respectively. The 5‐year biochemical relapse‐free survival (bRFS) and overall survival rates in the low‐risk, intermediate‐risk, and high‐risk groups were 97.0%, 91.1%, and 83.1%, and 98.4%, 96.8%, and 95.2%, respectively. In the multivariate analysis, the NCCN classification was a significant prognostic factor for bRFS, but not overall survival. The incidence rates of grade 2 or more severe late gastrointestinal and genitourinary toxicities were 4.1% and 4.0%, retrospectively. This retrospective analysis of a multi‐institutional survey suggested that PT is effective and well‐tolerated for prostate cancer. Based on this result, a multi‐institutional prospective clinical trial (UMIN000025453) on PT for prostate cancer has just been initiated in order to define its role in Japan.