What is the ideal radiotherapy dose to treat prostate cancer? A meta-analysis of biologically equivalent dose escalation

Revolutionizing localized prostate cancer treatment: Stereotactic radiotherapy "Moroccan experience"

INTRODUCTION

Prostate cancer is the most common urological cancer, and its incidence  is increasing. Radical prostatectomy and radiotherapy are theprimary treatments for localized forms. Stereotactic Body RadioTherapy (SBRT), a new and innovative therapy, has been validated for some cancer localizations but not yet for localized prostate cancer. Our study aims to report the efficacy and tolerance results of SBRT for localized prostate cancer.

MATERIALS AND METHODS

This is a retrospective study of 27 patients with localized prostate cancer (CaP) who were treated with SBRT in our department from 2017 to 2021 using transponders for tumor tracking. The dose was 36.25 Gy delivered in five fractions of 7.25 Gy. The delineation and doses of organs at risk were determined based on the recommendations of the SFRO and the TG101 report of medical physics. All patients were treated using a latest-generation linear accelerator (True Beam STXÒ).

RESULTS

Acute toxicities were observed in 33.3% of cases, with 22.2% grade 1 or 2 genitourinary (GU) and no grade 3 while 11.1% gastrointestinal (GI) toxicities were reported as grade 1-2 (7.4%) and one case grade 3 (3.7%). Late grade 1 or 2 GU toxicity was observed in 14.84% of cases, with no reports of late GI toxicity. After a 26-month follow-up period, the biochemical failure-free survival rate was 92.6%.

CONCLUSIONS

The results of our study are consistent with the existing literature and support the safety and effectiveness of SBRT as a treatment option for localized prostate cancer (CaP). In the United States, both ASTRO and the NCCN recognize SBRT as a valid treatment option for localized CaP. Ongoing phase III trials are being conducted to further substantiate these long-term results and to establish SBRT as the future standard of care for localized CaP.

Toxicity and Patient-Reported Quality-of-Life Outcomes After Prostate Stereotactic Body Radiation Therapy With Focal Boost to Magnetic Resonance Imaging-Identified Prostate Cancer Lesions: Results of a Phase 2 Trial

PURPOSE

In this prospective phase 2 trial, we investigated the toxicity and patient-reported quality-of-life outcomes in patients treated with stereotactic body radiation therapy (SBRT) to the prostate gland and a simultaneous focal boost to magnetic resonance imaging (MRI)-identified intraprostatic lesions while also de-escalating dose to the adjacent organs at risk.

METHODS AND MATERIALS

Eligible patients included low- or intermediate-risk prostate cancer (Gleason score ≤7, prostate specific antigen ≤20, T stage ≤2b). SBRT was prescribed to 40 Gy in 5 fractions delivered every other day to the prostate, with any areas of high disease burden (MRI-identified prostate imaging reporting and data system 4 or 5 lesions) simultaneously escalated to 42.5 to 45 Gy and areas overlapping organs at risk (within 2 mm of urethra, rectum, and bladder) constrained to 36.25 Gy (n = 100). Patients without a pretreatment MRI or without MRI-identified lesions were treated to dose of 37.5 Gy with no focal boost (n = 14).

RESULTS

From 2015 to 2022, a total of 114 patients were enrolled with a median follow-up of 42 months. No acute or late grade 3+ gastrointestinal (GI) toxicity was observed. One patient developed late grade 3 genitourinary (GU) toxicity at 16 months. In patients treated with focal boost (n = 100), acute grade 2 GU and GI toxicity was seen in 38% and 4% of patients, respectively. Cumulative late grade 2+ GU and GI toxicities at 24 months were 13% and 5% respectively. Patient-reported outcomes showed no significant long-term change from baseline in urinary, bowel, hormonal, or sexual quality-of-life scores after treatment.

CONCLUSIONS

SBRT to a dose of 40 Gy to the prostate gland with a simultaneous focal boost up to 45 Gy is well tolerated with similar rates of acute and late grade 2+ GI and GU toxicity as seen in other SBRT regimens without intraprostatic boost. Moreover, no significant long-term changes were seen in patient-reported urinary, bowel, or sexual outcomes from pretreatment baseline.

A pilot study of stereotactic body radiotherapy combined with pelvic radiotherapy and GTVp boost based on multiparameter magnetic resonance image in patients with high-risk prostate cancer

This pilot study aimed to explore the preliminary effects and safety of stereotactic body radiotherapy (SBRT) combined with preventive pelvic radiotherapy and primary gross tumor volumes (GTVp) boost in patients with high-risk prostate cancer based on multiparameter magnetic resonance image (mpMRI). Tumors were contoured as GTVp based on mpMRI. The prostate and proximal seminal vesicles were considered as the clinical target volume1. The pelvic lymphatic drainage area constituted clinical target volume 2. Radiation doses were 40Gy or 45Gy/5fractions to planning target volume of primary tumor, 37.5Gy/5f to prostate, seminal vesicle, and positive pelvic lymph nodes, and 25Gy/5f to pelvic synchronously. The treatment was delivered 3 times per week. Volumetric modulated arc radiotherapy and intensity-modulated radiotherapy were used to complete SBRT. The genitourinary (GU) and gastrointestinal (GI) toxicities were evaluated. Quality of life data was also captured. A total of 15 patients were enrolled in this study with a median age of 78 (56-87) from 2017 to 2020. All patients received SBRT. At 3 months after radiotherapy, the proportion of PSA < 0.006 ng/mL was 66.7% (10/15). The 2-year biochemical relapse-free survival was 93.3%. The incidence of grade 1 acute GU side effects was 80% (12/15); the incidence of acute grade 1 GI toxicity was 66.7% (10/15); and no grade 2 or higher acute GU and GI side effects was observed. Two patients presented with temporary late grade 2 GI toxicity. International Prostatic System Score increased rapidly after a transient increase at 1 week (P = .001). There were no significant differences in EORTC quality of life scores in all domains except global health status. In this pilot study, it was revealed that SBRT combined with preventive pelvic radiotherapy and GTVp boost based on mpMRI image was effective and well tolerated for patients with high-risk prostate cancer.

Direct Comparison of Two Different Definitions with Biochemical Recurrence after Low-Dose-Rate Brachytherapy for Prostate Cancer

We aimed to determine whether biochemical recurrence-free survival (BRFS) of patients with prostate cancer (PCa) who received low-dose-rate brachytherapy (LDR-BT) differed according to the definition of biochemical recurrence (BCR) after radical prostatectomy (RP) and the definition given by the Japanese Prostate Cancer Outcome Study of Permanent Iodine-125 Seed Implantation (J-POPS). We reviewed the clinical records of 476 consecutive patients with PCa who received LDR-BT at the Gifu University Hospital. The primary endpoint of this study was the difference in BRFS between the two aforementioned definitions. When the follow-up period ended, 74 (15.5%) and 20 (4.2%) patients had BCR according to the RP and J-POPS definitions, respectively. The 5-year BRFS rates were 85.0% and 96.9% for the RP and J-POPS definitions, respectively (p < 0.005). According to the RP definition, the 5-year BRFS rates were 80.6% in the group aged <63 years and 86.6% in those aged ≥63 years (p = 0.050). According to the J-POPS definition, the 5-year BRFS rates were 94.1% and 97.8% in the groups aged <63 years and ≥63 years, respectively (p = 0.005). The definition of recurrence in LDR-BT may need to be reconsidered.

Ten‐year outcomes of whole‐pelvic intensity‐modulated radiation therapy for prostate cancer with regional lymph node metastasis

BACKGROUND

Management of pelvic node-positive prostate cancer has been challenging and controversial. We conducted a study to evaluate the outcomes of whole-pelvic (WP) simultaneous integrated boost (SIB) intensity-modulated radiation therapy (IMRT) combined with androgen deprivation therapy (ADT).

METHODS

A total of 67 consecutive patients with cT1c-4N1M0 prostate cancer were definitively treated by WP SIB-IMRT. Neoadjuvant ADT (median: 8.3 months) was administered in all cases. WP SIB-IMRT was designed to simultaneously deliver 78, 66.3, and 58.5 Gy in 39 fractions to the prostate plus seminal vesicles, metastatic lymph nodes (LNs), and the pelvic LN region, respectively. Adjuvant ADT (median: 24.7 months) was administered in 66 patients.

RESULTS

The median follow-up period was 81.6 months (range: 30.5-160.7). Biochemical relapse-free, overall, and prostate cancer-specific survival rates at 10 years were 59.8%, 79.6%, and 86.3%, respectively. Loco-regional recurrence was not observed. Being in International Society of Urological Pathology grade group 5 and having a posttreatment detectable nadir prostate-specific antigen (PSA) level (≥0.010 ng/ml) were significantly associated with worse prostate cancer-specific survival and progression of castration resistance. The 10-year cumulative incidence rates of grade 2 and 3 late toxicities were, respectively, 1.5% and 0% for genitourinary, 0% and 1.5% for gastrointestinal events. No grade 4 acute or late toxicities were observed.

CONCLUSIONS

WP SIB-IMRT can be safely administered to patients with pelvic node-positive prostate cancer. Since grade group 5 and detectable nadir PSA levels are risks for castration resistance, we may need to increase the intensity of treatment for such cases.

Comparison of AUA and phoenix definitions of biochemical failure following permanent brachytherapy for prostate cancer

PURPOSE

To compare biochemical recurrence free survival (BCRFS) and cancer-specific survival (CSS) after brachytherapy using the AUA and the Phoenix definitions.

METHODS AND MATERIALS

2634 men with T1-T4N0M0 prostate cancer were treated with brachytherapy with or without neoadjuvant hormonal therapy or external beam radiation therapy. Five, 10, and 15- year BCRFS and CSS were estimated with Kaplan-Meier estimates with log rank. Multivariate analysis of survival was performed with Cox regression analysis.

RESULTS

Median age was 66, follow-up was 8.6 years, and prostate specific antigen was 6.9. Overall, 11.1% (n = 293) of patients experienced Phoenix BCR and 17.48% (n = 457) experienced AUA BCR. The rates of AUA BCR and Phoenix BCR were significantly different at 5 and 10-years but not at 15 years. Patients treated with BED ≤ 200 Gy were more likely to experience AUA BCR (22.5% vs. 12.4%, OR 1.44, p < 0.001) and Phoenix BCR (14.3% and 8.3%, OR 1.37, p < 0.001) than patients treated with a BED > 200 Gy.

CONCLUSIONS

Compared to the Phoenix definition, the AUA definition of BCR after brachytherapy is associated with significantly worse BCRFS for the first 15 years after treatment. Receiving a BED > 200, which cannot be achieved without the addition of brachytherapy, is associated with better BCRFS and CSS. Our findings reaffirm the importance of dose in the management of prostate cancer.

Integrating external beam and prostate seed implant dosimetry for intermediate and high-risk prostate cancer using biologically effective dose: Impact of image registration technique

PURPOSE

Combining external beam radiation therapy (EBRT) and prostate seed implant (PSI) is efficacious in treating intermediate- and high-risk prostate cancer at the cost of increased genitourinary toxicity. Accurate combined dosimetry remains elusive due to lack of registration between treatment plans and different biological effect. The current work proposes a method to convert physical dose to biological effective dose (BED) and spatially register the dose distributions for more accurate combined dosimetry.

METHODS AND MATERIALS

A PSI phantom was CT scanned with and without seeds under rigid and deformed transformations. The resulting CTs were registered using image-based rigid registration (RI), fiducial-based rigid registration (RF), or b-spline deformable image registration (DIR) to determine which was most accurate. Physical EBRT and PSI dose distributions from a sample of 91 previously-treated combined-modality prostate cancer patients were converted to BED and registered using RI, RF, and DIR. Forty-eight (48) previously-treated patients whose PSI occurred before EBRT were included as a "control" group due to inherent registration. Dose-volume histogram (DVH) parameters were compared for RI, RF, DIR, DICOM, and scalar addition of DVH parameters using ANOVA or independent Student's t tests (α = 0.05).

RESULTS

In the phantom study, DIR was the most accurate registration algorithm, especially in the case of deformation. In the patient study, dosimetry from RI was significantly different than the other registration algorithms, including the control group. Dosimetry from RF and DIR were not significantly different from the control group or each other.

CONCLUSIONS

Combined dosimetry with BED and image registration is feasible. Future work will utilize this method to correlate dosimetry with clinical outcomes.

Predicting Local Failure after Partial Prostate Re-Irradiation Using a Dosiomic-Based Machine Learning Model

The aim of this study is to predict local failure after partial prostate re-irradiation for the treatment of isolated locally recurrent prostate cancer by using a machine learning classifier based on radiomic features from pre-treatment computed tomography (CT), positron-emission tomography (PET) and biological effective dose distribution (BED) of the radiotherapy plan. The analysis was conducted on a monocentric dataset of 43 patients with evidence of isolated intraprostatic recurrence of prostate cancer after primary external beam radiotherapy. All patients received partial prostate re-irradiation delivered by volumetric modulated arc therapy. The gross tumor volume (GTV) of each patient was manually contoured from planning CT, choline-PET and dose maps. An ensemble machine learning pipeline including unbalanced data correction and feature selection was trained using the radiomic and dosiomic features as input for predicting occurrence of local failure. The model performance was assessed using sensitivity, specificity, accuracy and area under receiver operating characteristic curves of the score function in 10-fold cross validation repeated 100 times. Local failure was observed in 13 patients (30%), with a median time to recurrence of 36.7 months (range = 6.1–102.4 months). A four variables ensemble machine learning model resulted in accuracy of 0.62 and AUC 0.65. According to our results, a dosiomic machine learning classifier can predict local failure after partial prostate re-irradiation.

Phase III randomised controlled trial on PSMA PET/CT guided hypofractionated salvage prostate bed radiotherapy of biochemical failure after radical prostatectomy for prostate cancer (PERYTON-trial): study protocol

Background

Salvage external beam radiotherapy (sEBRT) for patients with a biochemical recurrence (BCR) after radical prostatectomy provides a 5-year biochemical progression-free survival up to 60%. Multiple studies have shown that dose escalation to the primary prostate tumour improves treatment outcome. However, data is lacking on the role of dose escalation in the recurrent salvage setting. The main objective of the PERYTON-trial is to investigate whether treatment outcome of sEBRT for patients with a BCR after prostatectomy can be improved by increasing the biological effective radiation dose using hypofractionation. Moreover, patients will be staged using the PSMA PET/CT scan, which is superior to conventional imaging modalities in detecting oligometastases.

Methods

The PERYTON-study is a prospective multicentre open phase III randomised controlled trial. We aim to include 538 participants (269 participants per treatment arm) with a BCR after prostatectomy, a PSA-value of < 1.0 ng/mL and a recent negative PSMA PET/CT scan. Participants will be randomised in a 1:1 ratio between the conventional fractionated treatment arm (35 × 2 Gy) and the experimental hypofractionated treatment arm (20 × 3 Gy). The primary endpoint is the 5-year progression-free survival after treatment. The secondary endpoints include toxicity, quality of life and disease specific survival.

Discussion

Firstly, the high rate of BCR after sEBRT may be due to the presence of oligometastases, for which local sEBRT is inappropriate. With the use of the PSMA PET/CT before sEBRT, patients with oligometastases will be excluded from intensive local treatment to avoid unnecessary toxicity. Secondly, the currently applied radiation dose for sEBRT may be too low to achieve adequate local control, which may offer opportunity to enhance treatment outcome of sEBRT by increasing the biologically effective radiotherapy dose to the prostate bed.

Trial registration

This study is registered at ClinicalTrials.gov (Identifier: NCT04642027). Registered on 24 November 2020 – Retrospectively registered. The study protocol was approved by the accredited Medical Ethical Committee (METc) of all participating hospitals (date METc review: 23-06-2020, METc registration number: 202000239). Written informed consent will be obtained from all participants.

• This is the first PSMA PET/CT based study addressing the role of hypofractionation in salvage external beam radiation therapy (sEBRT);

• Participants will be randomised 1:1 to conventional fractionated sEBRT (35 × 2 Gy) or hypofractionated sEBRT (20 × 3 Gy);

• The PSMA PET/CT-scan will be used for staging of all participants at baseline;

• The primary endpoint is 5-year progression-free survival after treatment;

• All participants will receive early sEBRT (PSA < 1.0 ng/mL) without the use of androgen deprivation therapy;

• A quality assurance program was undertaken, to ensure protocol compliance within the PERYTON-trial;

• An interim analysis will be performed after the inclusion of 25% (n = 135) of the total number of required participants, to identify any early signs of excessive (unexpected) acute toxicity.

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.

SAbR for High-Risk Prostate Cancer-A Prospective Multilevel MRI-Based Dose Escalation Trial

PURPOSE

Radiation dose intensification improves outcome in men with high-risk prostate cancer (HR-PCa). A prospective trial was conducted to determine safety, feasibility, and maximal tolerated dose of multilevel magnetic resonance imaging (MRI)-based 5-fraction SAbR in patients with HR-PCa.

METHODS AND MATERIALS

This phase I clinical trial enrolled patients with HR-PCa with grade group ≥4, prostate-specific antigen (PSA) ≥20 ng/mL, or radiographic ≥T3, and well-defined prostatic lesions on multiparametric MRI (mpMRI) into 4 dose-escalation cohorts. The initial cohort received 47.5 Gy to the prostate, 50 Gy to mpMRI-defined intraprostatic lesion(s), and 22.5 Gy to pelvic lymph nodes in 5 fractions. Radiation doses were escalated for pelvic nodes to 25 Gy and mpMRI lesion(s) to 52.5 Gy and then 55 Gy. Escalation was performed sequentially according to rule-based trial design with 7 to 15 patients per cohort and a 90-day observation period. All men received peri-rectal hydrogel spacer, intraprostatic fiducial placement, and 2 years of androgen deprivation. The primary endpoint was maximal tolerated dose according to a 90-day acute dose-limiting toxicity (DLT) rate <33%. DLT was defined as National Cancer Institute Common Toxicity Criteria for Adverse Events ≥grade 3 treatment-related toxicity. Secondary outcomes included acute and delayed gastrointestinal (GI)/genitourinary (GU) toxicity graded with Common Toxicity Criteria for Adverse Events.

RESULTS

Fifty-five of the 62 enrolled patients were included in the analysis. Dose was escalated through all 4 cohorts without observing any DLTs. Median overall follow-up was 18 months, with a median follow-up of 42, 24, 12, and 7.5 months for cohorts 1 to 4 respectively. Acute and late grade 2 GU toxicities were 25% and 20%, while GI were 13% and 7%, respectively. Late grade 3 GU and GI toxicities were 2% and 0%, respectively.

CONCLUSIONS

SAbR dose for HR-PCa was safely escalated with multilevel dose painting of 47.5 Gy to prostate, 55 Gy to mpMRI-defined intraprostatic lesions, and 25 Gy to pelvic nodal region in 5 fractions. Longer and ongoing follow-up will be required to assess late toxicity.

Salvage therapy for prostate cancer after radical prostatectomy

More than 40% of men with intermediate-risk or high-risk prostate cancer will experience a biochemical recurrence after radical prostatectomy. Clinical guidelines for the management of these patients largely focus on the use of salvage radiotherapy with or without systemic therapy. However, not all patients with biochemical recurrence will go on to develop metastases or die from their disease. The optimal pre-salvage therapy investigational workup for patients who experience biochemical recurrence should, therefore, include novel techniques such as PET imaging and genomic analysis of radical prostatectomy specimen tissue, as well as consideration of more traditional clinical variables such as PSA value, PSA kinetics, Gleason score and pathological stage of disease. In patients without metastatic disease, the only known curative intervention is salvage radiotherapy but, given the therapeutic burden of this treatment, importance must be placed on accurate timing of treatment, radiation dose, fractionation and field size. Systemic therapy also has a role in the salvage setting, both concurrently with radiotherapy and as salvage monotherapy.

Gantry-Based 5-Fraction Elective Nodal Irradiation in Unfavorable-Risk Prostate Cancer: Outcomes From 2 Prospective Studies Comparing SABR Boost With MR Dose-Painted HDR Brachytherapy Boost

PURPOSE

Guidelines from the American Society of Clinical Oncology and Cancer Care Ontario recommend brachytherapy boost for patients with intermediate-risk or high-risk prostate cancer. SABR is an emerging technique for prostate cancer, but its use in high-risk disease is limited. Efficacy, toxic effects, and quality of life (QoL) were compared in patients treated on 2 prospective protocols that used SABR boost or magnetic resonance-guided high-dose-rate brachytherapy (HDR-BT) boost with 6 to 18 months of androgen deprivation therapy (ADT).

METHODS AND MATERIALS

In SATURN study (study 1), patients received 40 Gy to the prostate and 25 Gy to the pelvis in 5 weekly fractions. In SPARE (study 2), patients received HDR-BT (15 Gy × 1) to the prostate and ≤22.5 Gy to the magnetic resonance imaging nodule, followed by 25 Gy in 5 weekly fractions to the pelvis. All patients received between 6 and 18 months of ADT.

RESULTS

Thirty patients (7% unfavorable intermediate risk and 93% high risk, per National Comprehensive Cancer Network [NCCN] criteria) completed study 1, and 31 patients (3% favorable intermediate risk, 47% unfavorable intermediate risk, and 50% high risk) completed treatment as per study 2. The median follow-up times were 72 and 62 months, respectively. In study 2, 6 patients had biochemical failure, and all 6 developed metastatic disease. Actuarial 5-year biochemical failure was 0% for study 1 and 18.2% for study 2 (P = .005). There was no significant difference in the worst acute or late gastrointestinal or genitourinary toxicity. Grade 3 late genitourinary toxicity was noted in 3% of the patients in study 2 (HDR-BT boost). There was either no significant difference or minimal clinically important change in QoL.

CONCLUSIONS

In the context of 5-fraction pelvic radiation therapy and ADT, there did not appear to be a significant difference in toxicity or QoL between SABR and HDR-BT boost. Although efficacy favored the SABR boost cohort, this should be viewed in the context of limitations and biases associated with comparing 2 sequential phase 2 studies.

Stereotactic Body Radiation Therapy (SBRT) for prostate cancer: Preliminary results of toxicity

To the Editor, Prostate cancer is the second most common cancer in men in Morocco after lung cancer. External radiotherapy (RTE) is a curative therapeutic option for localized prostate cancer, However the conventional RTE remains a long treatment (7- 8 weeks, 5 days a week) which is demanding for patients and make difficult to manage the waiting lists. The development of imaging and irradiation techniques over the last decades has allowed a high precision in the delivery of the dose to the target organ and a better protection of the organs at risk (OAR), which has encouraged the hypo fractionated irradiation of localized prostate cancer, especially after the results of radiobiology studies that suggested a low report a/b for the prostate.

Biologically Effective Dose and Rectal Bleeding in Definitive Proton Therapy for Prostate Cancer

Purpose and Objectives

With increasing use of hypofractionation and extreme hypofractionation for prostate cancer, rectal dose-volume histogram (DVH) parameters that apply across dose fractionations may be helpful for treatment planning in clinical practice. We present an exploratory analysis of biologically effective rectal dose (BED) and equivalent rectal dose in 2 Gy fractions (EQD2) for rectal bleeding in patients treated with proton therapy across dose fractionations.

Materials and Methods

From 2016 to 2018, 243 patients with prostate cancer were treated with definitive proton therapy. Rectal DVH parameters were obtained from treatment plans, and rectal bleeding events were recorded. The BED and EQD2 transformations were applied to each rectal DVH parameter. Univariate analysis using logistic regression was used to determine DVH parameters that were significant predictors of grade ≥ 2 rectal bleeding. Youden index was used to determine optimum cutoffs for clinically meaningful DVH constraints. Stepwise model-selection criteria were then applied to fit a “best” multivariate logistic model for predicting Common Terminology Criteria for Adverse Events grade ≥ 2 rectal bleeding.

Results

Conventional fractionation, hypofractionation, and extreme hypofractionation were prescribed to 117 (48%), 84 (34%), and 42 (17.3%) patients, respectively. With a median follow-up of 20 (2.5-40) months, 10 (4.1%) patients experienced rectal bleeding. On univariate analysis, multiple rectal DVH parameters were significantly associated with rectal bleeding across BED, EQD2, and nominal doses. The BED volume receiving 55 Gy > 13.91% was found to be statistically and clinically significant. The BED volume receiving 55 Gy remained statistically significant for an association with rectal bleeding in the multivariate model (odds ratio, 9.81; 95% confidence interval, 2.4-40.5; P = .002).

Conclusion

In patients undergoing definitive proton therapy for prostate cancer, dose to the rectum and volume of the rectum receiving the dose were significantly associated with rectal bleeding across conventional fractionation, hypofractionation, and extreme hypofractionation when using BED and EQD2 transformations.

Treatment Strategies for High-Risk Localized and Locally Advanced and Oligometastatic Prostate Cancer

Simple Summary

The definitions of locally advanced and oligometastatic prostate cancer are ambiguous, and there are no standard treatments for these. Although multidisciplinary treatment combining systemic and local treatment may be effective, there are many unresolved issues such as the choice of local treatment, use of new endocrine agents and chemotherapy, and selection of optimal patients. The present article discusses the definitions, diagnoses, and treatment of very high-risk prostate cancer and oligometastatic prostate cancer.

Abstract

Despite the significant advances in the treatment of high-risk prostate cancer, patients with very high-risk features such as being locally advanced (clinical stage T3–4 or minimal nodal involvement), having a high Gleason pattern, or with oligometastasis may still have a poor prognosis despite aggressive treatment. Multidisciplinary treatment with both local and systemic therapies is thought to be effective, however, unfortunately, there is still no standard treatment. However, in recent years, local definitive therapy using a combination of radiotherapy and androgen deprivation is being supported by several randomized clinical trials. This study reviews the current literature with a focus on the definition of very high-risk prostate cancer, the role of modern imaging, and its treatment options.

Radiation therapy with curative intention in men with de novo metastatic prostate carcinoma: shoot'em all!

BACKGROUND

About 5% of prostate cancer cases are metastatic at diagnoses. Radiotherapy of both primary tumor and secondary lesions can be, in addition to systemic treatments, a radical alternative for selected patients.

MATERIALS AND METHODS

Patients with de novo prostate carcinoma with bone or lymph node metastases were retrospectively reviewed. All patients received moderate hypofractionated IMRT/VMAT up to 63 Gy in 21 daily fractions of 3 Gy to prostate and metastases with neoadjuvant and concurrent androgen deprivation therapy (ADT). According to known advances some patients also received abiraterone, enzalutamide, or docetaxel.

RESULTS

Between 2015-2020, we attended 26 prostate cancer patients (median age 69.5 years, range 52-84) with simultaneous oligometastases [mean 2.1 metastases, median 1.5 metastases (range 1-6)]. Eighteen patients (69%) presented lymph node metastases, 4 (15.5%) bone metastases and 4 (15.5%) both lymph node and bone metastases. With a median follow-up of 15.5 months (range 3-65 months), 16 patients (62%) are alive and tumor free while 10 (38%) are alive with tumor. Four patients (17%) developed tumor progression, out of irradiated area in all cases, with a median time to progression of 43.5 months (range 27-56 months). Actuarial progression-free survival (PFS) rates at 12 and 24 months were 94.1% and 84.7%, respectively. No grade > 2 acute or late complications were recorded.

CONCLUSIONS

Simultaneous directed radical hypofractionated radiation therapy for prostate and metastases is feasible, well tolerated and achieves an acceptable PFS rate. However, further studies with longer follow-up are necessary to definitively address these observations.

Highly hypofractionated intensity-modulated radiation therapy for nonmetastatic prostate cancer with a simultaneous integrated boost to intraprostatic lesions: a planning study

PURPOSE

The purpose of this planning study was to develop an acceptable technique for highly hypofractionated intensity-modulated radiation therapy using simultaneous integrated boost technique (SIB-hHF-RT) for nonmetastatic National Comprehensive Cancer Network high-risk prostate cancer.

MATERIALS AND METHODS

We created SIB-hHF-RT plans for 14 nonmetastatic prostate cancer patients with MRI-detectable intraprostatic lesions (IPLs) and without intestines locating close to the seminal vesicle and prostate. We prescribed 57 Gy for IPLs and 54 Gy for the remainder of planning target volume (PTV) in 15 fractions. The IPLs were contoured based on magnetic resonance imaging, and PTV was generated by adding 6-8-mm margins to the clinical target volume. For the dose-volume constraints of organs at risk (OARs), the same constraints as 54 Gy plans were used so as not to increase the toxicity.

RESULTS

All created plans fulfilled the dose-volume constraints of all targets and OARs. The median estimated beam-on time was 108.5 s. For patient-specific quality assurance, the global gamma passing rates (3%/2 mm) with 10% dose threshold criteria were greater than 93% in all cases and greater than 95% in 11 cases.

CONCLUSION

SIB-hHF-RT plans were developed that fulfill the acceptable dose-volume constraints and pass patient-specific quality assurance. We believe these plans can be applied to selected patients with nonmetastatic prostate cancer.

Dosimetric comparison of MR-linac-based IMRT and conventional VMAT treatment plans for prostate cancer

Background

The aim of this study was to evaluate and compare the performance of intensity modulated radiation therapy (IMRT) plans, planned for low-field strength magnetic resonance (MR) guided linear accelerator (linac) delivery (labelled IMRT MRL plans), and clinical conventional volumetric modulated arc therapy (VMAT) plans, for the treatment of prostate cancer (PCa). Both plans used the original planning target volume (PTV) margins. Additionally, the potential dosimetric benefits of MR-guidance were estimated, by creating IMRT MRL plans using smaller PTV margins.

Materials and methods

20 PCa patients previously treated with conventional VMAT were considered. For each patient, two different IMRT MRL plans using the low-field MR-linac treatment planning system were created: one with original (orig.) PTV margins and the other with reduced (red.) PTV margins. Dose indices related to target coverage, as well as dose-volume histogram (DVH) parameters for the target and organs at risk (OAR) were compared. Additionally, the estimated treatment delivery times and the number of monitor units (MU) of each plan were evaluated.

Results

The dose distribution in the high dose region and the target volume DVH parameters (D_98%, D_50%, D_2% and V_95%) were similar for all three types of treatment plans, with deviations below 1% in most cases. Both IMRT MRL plans (orig. and red. PTV margins) showed similar homogeneity indices (HI), however worse values for the conformity index (CI) were also found when compared to VMAT. The IMRT MRL plans showed similar OAR sparing when the orig. PTV margins were used but a significantly better sparing was feasible when red. PTV margins were applied. Higher number of MU and longer predicted treatment delivery times were seen for both IMRT MRL plans.

Conclusions

A comparable plan quality between VMAT and IMRT MRL plans was achieved, when applying the same PTV margin. However, online MR-guided adaptive radiotherapy allows for a reduction of PTV margins. With a red. PTV margin, better sparing of the surrounding tissues can be achieved, while maintaining adequate target coverage. Nonetheless, longer treatment delivery times, characteristic for the IMRT technique, have to be expected.

Dosimetric Analysis of the Short-Ranged Particle Emitter 161Tb for Radionuclide Therapy of Metastatic Prostate Cancer

Simple Summary

A tremendous effort and rapid development of the prostate-specific membrane antigen (PSMA)-targeting radio ligands for radionuclide therapy has resulted in encouraging response rates for advanced prostate cancer. Different radionuclides have been utilized or suggested as suitable candidates. In this study, a dynamic model of metastatic progress was developed and utilized to estimate a radiopharmaceutical’s potential of obtaining metastatic control of advanced prostate cancer. The simulations performed demonstrated the advantage of utilizing radionuclides with short-range particle emission, i.e., alpha-emitters and low-energy electrons. The recently-proposed beta-emitting radionuclide terbium-161 demonstrates great potential of being a future candidate towards targeted radionuclide therapy of advanced prostate cancer. This is in line with recent encouraging preclinical results and development of upscaling the product quality. Recently, the first in-human application with a [¹⁶¹Tb]Tb-DOTATOC also demonstrated good SPECT image quality, which can enable dosimetry calculations for new ¹⁶¹Tb-based radiopharmaceuticals.

Abstract

The aim of this study was to analyze the required absorbed doses to detectable metastases (D_req) when using radionuclides with prostate specific membrane antigen (PSMA)-targeting radioligands to achieve a high probability for metastatic control. The Monte Carlo based analysis was performed for the clinically-used radionuclides yttrium-90, iodine-131, lutetium-177, and actinium-225, and the newly-proposed low-energy electron emitter terbium-161. It was demonstrated that metastatic formation rate highly influenced the metastatic distribution. Lower values generated few large detectable metastases, as in the case with oligo metastases, while high values generated a distribution of multiple small detectable metastases, as observed in patients with diffused visualized metastases. With equal number of detectable metastases, the total metastatic volume burden was 4–6 times higher in the oligo metastatic scenario compared to the diffusely visualized scenario. The D_req was around 30% higher for the situations with 20 detectable metastases compared to one detectable metastasis. The D_req for iodine-131 and yttrium-90 was high (920–3300 Gy). The D_req for lutetium-177 was between 560 and 780 Gy and considerably lower D_req were obtained for actinium-225 and terbium-161, with 240–330 Gy and 210–280 Gy, respectively. In conclusion, the simulations demonstrated that terbium-161 has the potential for being a more effective targeted radionuclide therapy for metastases using PSMA ligands.

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.

Degarelix as a neoadjuvant hormonal therapy for acute urinary tract toxicity associated with external beam radiotherapy for intermediate- and high-risk prostate cancer: a propensity score matched analysis

BACKGROUND

In prostate cancer treatment, lower urinary tract symptoms significantly improve with luteinizing hormone-releasing hormone antagonists use compared with agonists. However, it is unclear whether luteinizing hormone-releasing hormone antagonists can decrease acute urinary tract toxicity during external beam radiotherapy. This study aimed to assess whether luteinizing hormone-releasing hormone antagonists used as neoadjuvant therapy reduced acute urinary tract toxicity during external beam radiotherapy compared with luteinizing hormone-releasing hormone agonists.

METHODS

The study included 78 patients who underwent intensity-modulated radiation therapy for intermediate- and high-risk prostate cancer between April 2013 and January 2020. Irradiation was initiated after 3-6 months of neoadjuvant therapy. Androgen deprivation therapy was given to the intermediate-risk group for 6 months and the high-risk group for 2-3 years. The European Organization for Research and Treatment of Cancer/Radiation Therapy Oncology Group toxicity grading scale was used to evaluate the urinary tract system toxicity. Relevant clinical factors were used in matching patients based on propensity scores to enable comparison between the groups.

RESULTS

Each group had 27 matched patients. There was no reduction in urinary tract toxicity with the use of luteinizing hormone-releasing hormon antagonists (P = 0.624). For patients with an International Prostate Symptom Score of ≥11 at the start of treatment, 18 patients in each group were matched. Significantly lower scores were observed in the luteinizing hormone-releasing hormon antagonist group (P = 0.041).

CONCLUSIONS

Luteinizing hormone-releasing hormon antagonists may reduce acute urinary tract toxicity during prostate cancer external beam radiotherapy compared with luteinizing hormone-releasing hormon agonists, in particular in patients with moderate to severe symptoms at the start of treatment.

Five-year outcomes from a prospective comparative effectiveness study evaluating external-beam radiotherapy with or without low-dose-rate brachytherapy boost for localized prostate cancer

BACKGROUND

To inform patients who are in the process of selecting prostate cancer treatment, the authors compared disease-specific function after external-beam radiotherapy (EBRT) alone versus EBRT plus a low-dose-rate (LDR) brachytherapy boost (EBRT-LDR).

METHODS

For this prospective study, men who had localized prostate cancer in 2011 and 2012 were enrolled. Assessments at baseline, 0.5, 1, 3, and 5 years included the patient-reported Expanded Prostate Index Composite, the 36-item Medical Outcomes Study Short-Form Health Survey, and treatment-related regret. Regression models were adjusted for baseline function and for patient and treatment characteristics. The minimum clinically important difference in scores on the Expanded Prostate Index Composite 26-item instrument was from 5 to 7 for urinary irritation and from 4 to 6 for bowel function.

RESULTS

Six-hundred ninety-five men met inclusion criteria and received either EBRT (n = 583) or EBRT-LDR (n = 112). Patients in the EBRT-LDR group were younger (median age, 66 years [interquartile range [IQR], 60-71 years] vs 69 years [IQR, 64-74 years]; P < .001), were less likely to receive pelvic radiotherapy (10% vs 18%; P = .040), and had higher baseline 36-item Medical Outcomes Study Short-Form Health Survey physical function scores (median score, 95 [IQR, 86-100] vs 90 [IQR, 70-100]; P < .001). Over a 3-year period, compared with EBRT, EBRT-LDR was associated with worse urinary irritative scores (adjusted mean difference at 3 years, -5.4; 95% CI, -9.3, -1.6) and bowel function scores (-4.1; 95% CI, -7.6, -0.5). The differences were no longer clinically meaningful at 5 years (difference in urinary irritative scores: -4.5; 95% CI, -8.4, -0.5; difference in bowel function scores: -2.1; 95% CI, -5.7, -1.4). However, men who received EBRT-LDR were more likely to report moderate or big problems with urinary function bother (adjusted odds ratio, 3.5; 95% CI, 1.5-8.2) and frequent urination (adjusted odds ratio, 2.6; 95% CI, 1.2-5.6) through 5 years. There were no differences in survival or treatment-related regret between treatment groups.

CONCLUSIONS

Compared with EBRT alone, EBRT-LDR was associated with clinically meaningful worse urinary irritative and bowel function over 3 years after treatment and more urinary bother at 5 years.

LAY SUMMARY

In men with prostate cancer who received external-beam radiation therapy (EBRT) with or without a brachytherapy boost (EBRT-LDR), EBRT-LDR was associated with clinically worse urinary irritation and bowel function through 3 years but resolved after 5 years. Men who received EBRT-LDR continued to report moderate-to-big problems with urinary function bother and frequent urination through 5 years. There was no difference in treatment-related regret or survival between patients who received EBRT and those who received EBRT-LDR. These intermediate-term estimates of function may facilitate counseling for men who are selecting treatment.

Use of deformable image registration techniques to estimate dose to organs at risk following prostate external beam radiation therapy and high-dose-rate brachytherapy

PURPOSE

The purpose of this investigation was to examine differences in estimates of accumulated rectal dose when using deformable image registration (DIR) compared with rigid image registration (RIR) methods, and parameter addition methods for combined transrectal ultrasound (TRUS)-based high-dose-rate brachytherapy (HDR-BT) and external beam radiation therapy (EBRT) treatments of prostate cancer.

MATERIAL AND METHODS

In this retrospective study, data from 10 patients who had previously received HDR-BT in one 15 Gy fraction, followed by 46 Gy EBRT in twenty-three fractions were used. To estimate total combined dose to the rectum, dose accumulation using both DIR and RIR methods were compared with parameter addition methods, which assume the same region of rectal anatomy receives the maximum dose from both treatment modalities. For both rigid and deformable image registration techniques, the quality of image registration was evaluated through metrics, including mean distance to agreement and dice similarity coefficient of prostate contours. Total D1cc and D2cc for the rectum was calculated and compared using each method.

RESULTS

The parameter addition methods predicted the highest accumulated dose to the rectum. On average, the predicted D2cc dose was higher than that calculated by the DIR method by 6.59 Gy EQD2 (range, -3.03 to 13.68 Gy EQD2) for partial parameter addition (PPA), and 4.88 Gy EQD2 (range, -3.41 to 11.97 Gy EQD2) for the full parameter addition (FPA) methods. Similarly, RIR predicted higher average doses compared with DIR, with a difference of 3.46 Gy EQD2 (range, -5.50 to 7.90 Gy EQD2). The results showed a significant difference between DIR and parameter addition methods for dose estimation.

CONCLUSIONS

This retrospective study demonstrates significant differences in accumulated rectal dose prediction using different image registration methods. Each method has limitations in its application, and when used with real-time HDR-BT dose planning, awareness of these limitations is essential.

Phase I/II Study of Extreme Hypofractionated Stereotactic Body Radiation Therapy Boost to Prostate for Locally Advanced, Node-Positive and Oligometastatic Cancer

Introduction: Stereotactic body radiation therapy (SBRT) is increasingly being utilized to deliver escalated radiation doses for improving outcomes in various malignancies. We analyzed our cohort of locally advanced, node-positive, and bone oligometastatic prostate cancer patients, that were treated with a combination of pelvic RT using conventional fractionation (CF) and SBRT boost to prostate using extreme hypofractionation (EH), along with hormone therapy (HT).

Materials and Methods: Outcomes of 44 prospectively treated patients were analyzed. Volumetric modulated arc therapy (VMAT) was utilized to deliver a dose of 45 Gy to pelvic nodal region, 50 Gy to prostate, and 54-56 Gy to gross nodes in 25 fractions. EH boost 18 Gy in three fractions was delivered to the prostate using CyberKnife (Accuray, Sunnyvale, CA, USA) SBRT. Bone oligometastasis, if any, were treated to a dose of 16 Gy in two fractions, delivered on weekends. Serum prostate-specific antigen (PSA), multi-parametric magnetic resonance imaging (MRI) of pelvis, and prostate-specific membrane antigen-positron emission tomography (PSMA-PET) were used for response assessment during follow-up. HT was given as per standard guidelines.

Results: There were 33 (75%) locally advanced, nine (20.5%) node-positive, and two (4.5%) oligometastatic cases. At a median follow-up of 63.5 months, the five-year progression-free survival (PFS) was 88.2%, biochemical PFS (bPFS) was 91.4% and overall survival (OS) was 96.9%. Grade III or greater acute genitourinary and gastrointestinal toxicity was 2.3% each, and late toxicity was 4.5% and 0%, respectively.

Conclusion: Excellent five-year outcomes can be attained even for locally advanced, node-positive and bone oligometastatic prostate cancer, by means of dose-escalation using EH-SBRT boost to the prostate.

Imputing radiobiological parameters of the linear-quadratic dose-response model from a radiotherapy fractionation plan

The objective in cancer radiotherapy is to maximize tumor-kill while limiting toxic effects of radiation dose on nearby organs-at-risk (OAR). Given a fixed number of treatment sessions, planners thus face the problem of finding a dosing sequence that achieves this goal. This is called the fractionation problem, and has received steady attention over a long history in the clinical literature. Mathematical formulations of the resulting optimization problem utilize the linear-quadratic (LQ) framework to characterize radiation dose-response of tumors and OAR. This yields a nonconvex quadratically constrained quadratic program. The optimal dosing plan in this forward problem crucially depends on the parameters of the LQ model. Unfortunately, these parameters are difficult to estimate via in vitro or in vivo studies, and as such, their values are unknown to treatment planners. The clinical literature is thus replete with debates about what parameter values will make specific dosing plans effective. This paper formulates this as an inverse optimization problem. The LQ dose-response parameters appear in the objective function, the left hand side, and the right hand side of the forward problem, and none of the existing generic methods can provide an exact solution of the inverse problem. This paper exploits the structure of the problem and identifies all possible parameter values that render the given dosing plan optimal, in closed-form. This closed-form formula is applied to dosing-plans from three clinical studies published within the last two years.

Management of Isolated Local Failures Following Stereotactic Body Radiation Therapy for Low to Intermediate Risk Prostate Cancer

Background: Stereotactic body radiation therapy (SBRT) is a safe and effective treatment option for patients with low to intermediate risk prostate cancer (1). SBRT results in very low PSA nadirs secondary to the delivery of high biologically effective doses. Studies reporting on the diagnosis, confirmation, and management of salvageable isolated local failures (ILF) are limited. This study aims to determine the incidence and management approach of ILF after SBRT in a large single institution cohort. Method: All patients with low or intermediate risk localized prostate cancer treated with SBRT at Georgetown University Hospital were eligible for this study. Treatment was delivered using robotic SBRT with doses of 35-36.25 Gy in five fractions. ILF were diagnosed using multiparametric MRI and/or biopsy prompted by rising PSA levels after achieving long-term nadir. Patient's characteristics were extracted from a prospective institutional quality of life trial (IRB 2009-510). Type of salvage therapy and post-salvage PSA were determined on subsequent follow-up and chart review. Results: Between December 2008 to August 2018, 998 men with low to intermediate risk prostate cancer were eligible for inclusion in this analysis. Twenty-four patients (low risk, n = 5; intermediate risk, n = 19) were found to have ILF within the prostate on either MRI (n = 19) and/or biopsy (n = 20). Median pre-treatment PSA was 7.55 ng/ml. Median time to diagnosis of ILF was 72 months (24-110 months) with median PSA at the time of ILF of 2.8 ng/ml (0.7-33 ng/ml). Median PSA doubling time was 17 months (5-47 months). Thirteen patients with biopsy proven ILF proceeded with salvage therapy (cryotherapy n = 12, HIFU n = 1). Of 12 patients who underwent cryotherapy, 7 had a post-treatment PSA of <0.1 ng/ml. One patient experienced a urethral-cutaneous fistula (grade 3 toxicity). Conclusion: The incidence of isolated local recurrence is rare in our cohort. Diagnosis and management of isolated local failures post-SBRT continues to evolve. Our report highlights the importance of early utilization of MRI and confirmatory biopsy at relatively low PSA levels and long PSA doubling time (1). Additionally, undetectable PSA levels after salvage therapy supports the role of early treatment in ILF (1). Further research is needed to determine appropriate patient selection and salvage modality in this population.

Patient-specific radiotherapy quality assurance for estimating actual treatment dose

This study aimed to evaluate the optimal method for planning computed tomography (CT) for prostate cancer radiotherapy to avoid a dose difference of ≥3% between the actual and planned treatments using multiple acquisition planning CT (MPCT). We calculated the 3-dimensional (3D) displacement error between the pelvic bone and matching fiducial marker on MPCT and cone-beam CT scans of 25 patients who underwent prostate volumetric-modulated arc therapy for prostate cancer. The correlation of the 3D displacement error and the dose difference between planned and actual treatments was calculated using least squares second-order polynomial model. The 3D displacement error showed a moderate correlation with differences between planned and accumulated treatment doses (r = 0.587, p < 0.0001). Moreover, the improvement rate of the minimum 3D displacement error showed a strong correlation with the relative error between each MPCT image (r = 0.793, p < 0.0001). Significant differences were observed between planned and actual treatment doses (p < 0.0001) in the relative 3D displacement errors of <1 mm, 1 to 3 mm, and >3 mm. The 3D displacement error on MPCT (as the selection estimation index for optimal planning CT) is useful for monitoring patient-specific intensity-modulated radiation therapy quality assurance. This new method allows to estimate dose differences from the planned dose before commencing treatment, thereby ensuring high-quality therapy. As radiotherapy quality is critical for patient outcome, these findings may contribute to better management of prostate cancer.

Apoptotic and predictive factors by Bax, Caspases 3/9, Bcl-2, p53 and Ki-67 in prostate cancer after 12 Gy single-dose

Radio-induced apoptosis is mediated by the activation of tumor protein p53, Bax and caspases. The purpose of this study was to investigate the early activation of this pathway in men receiving in vivo irradiation immediately before radical prostatectomy for locally advanced prostate cancer. We also investigated cell proliferation index (Ki-67), proto-oncogene (p53) and anti-apoptotic protein (Bcl-2) levels as potential predictive factors. We selected a homogeneous sample of 20 patients with locally advanced prostate cancer and candidate to radical prostatectomy. To assess the apoptotic pathways, Bax, is studied through immunofluorescence assay, before and after 12 Gy single dose intraoperative radiotherapy (IORT) to the prostate, on bioptic samples and on surgical specimens. Moreover, before and after IORT, Bcl-2, p53, and Ki-67 were also detected through immunohistochemistry. A count of positive Bax spots for immunofluorescence was performed on tumor cells, prostatic intraepithelial neoplasia (PIN), and healthy tissue areas before and after IORT. We also analyzed Caspases 3 and 9 expressions after IORT. Before IORT, Bcl-2 mean value in neoplastic cells was 2.23% ± 1.95, mean Ki-67 in neoplastic area was 4.5% ± 3.8, and p53 was 22.5% ± 6.8. After IORT, Bcl-2 mean value in neoplastic cells was 8.85 ± 8.92%, Ki-67 in neoplastic area was 7.8 ± 6.09%, and p53 was 24.9 ± 26.4%. After the irradiation, healthy areas expressed significantly lower levels of Bax (2.81 ± 1.69%) with respect to neoplastic cells (p < 0.0001), while in PIN areas, Bax positive cells were significantly more present than in neoplastic areas (p = 0.0001). At statistical analysis, it was observed that cancer cells with Ki-67 ≥ 8% had a trend toward greater expression of Bax (p = 0.0641). We observed an increase of Bcl-2 expression after IORT in neoplastic areas (p = 0.0041). Biopsy specimens with p53 ≥ 18% and Ki-67 ≥ 8% had worse post-operative staging with extracapsular invasion (p = 0.04 for both parameters) and nodal positivity (p = 0.04 for p53 and p = 0.0001 at pathology for ki-67). No correlation between IORT and Caspases activation was noted. In conclusion, after 12 Gy IORT, Bax was overexpressed in tumor and PIN cells. Pre-operative Ki-67 and p53 definition could be used in future studies to predict patients with worse pathological stage, while Bcl-2 activation after IORT might be a predictive factor for loco-regional failure.

A radiobiological study of the schemes with a low number of fractions in high-dose-rate brachytherapy as monotherapy for prostate cancer

Purpose

Schemes with high doses per fraction and small number of fractions are commonly used in high-dose-rate brachytherapy (HDR-BT) for prostate cancer. Our aim was to analyze the differences between published clinical results and the predictions of radiobiological models for absorbed dose required in a single fraction monotherapy HDR-BT.

Material and methods

Published HDR-BT clinical results for low- and intermediate-risk patients with prostate cancer were revised. For 13 clinical studies with 16 fractionation schedules between 1 and 9 fractions, a dose-response relation in terms of the biochemical control probability (BC) was established using Monte Carlo-based statistical methods.

Results

We obtained a value of α/β = 22.8 Gy (15.1-60.2 Gy) (95% CI) much larger than the values in the range 1.5-3.0 Gy that are usually considered to compare the results of different fractionation schemes in prostate cancer radiotherapy using doses per fraction below 6 Gy. The doses in a single fraction producing BC = 90% and 95% were 22.3 Gy (21.5-24.2 Gy) and 24.3 Gy (23.0-27.9 Gy), respectively.

Conclusions

The α/β obtained in our analysis of 22.8 Gy for a range of dose per fraction between 6 and 20.5 Gy was much greater than the one currently estimated for prostate cancer using low doses per fraction. This high value of α/β explains reasonably well the data available in the region of high doses per fraction considered.

Interstitial high-dose-rate brachytherapy as a boost in synchronous prostate and rectal cancer treatment: case report and literature review

PURPOSE

Prostate and colorectal cancers are the first and the third most popular malignancies in male population, in which some patients may develop these tumors metachronously or synchronously. At present, there are no standard recommendations, and oncologists need to provide an optimal management for two different cancers with an acceptable risk of possible treatment of adverse effects.

MATERIAL AND METHODS

This case report presents the treatment of a 61-year-old patient suffering from synchronous prostate and rectal cancer. Both malignancies were locally advanced, histologically proven, and defined as cT2cN0M0 stage prostate and cT3N2M0 stage rectal adenocarcinoma.

RESULTS

Multidisciplinary treatment team decided on synchronous radical treatment of both malignancies. The patient was qualified to long-term androgen deprivation therapy (ADT) and preoperative chemoradiation, with a total dose of 50.4 Gy in 28 fractions delivered with intensity modulated radiation therapy/image-guided radiation therapy (IMRT/IGRT) to a proper prostatic and rectal gross and nodal clinical target volume (CTV) with concurrent 5-fluorouracil. Additional dose of 15 Gy in a single fraction was delivered to prostate with interstitial HDR brachytherapy within a week after external beam radiotherapy (EBRT). After 8 weeks, the patient underwent sphincter-sparing surgery, with total mesorectal excision. Treatment tolerance was good, and genitourinary toxicity was not observed until now. At present, the patient is 45 months after completion of chemoradiation and surgery. Current prostate specific antigen (PSA) level is < 0.003 ng/ml, with no evidence of locoregional recurrence or distant metastases. Patient completed long-term ADT.

CONCLUSIONS

High-dose-rate (HDR) brachytherapy as a boost seems to be well-tolerated and effective option for delivering proper treatment dose to prostate in case of simultaneous treatment of rectal and prostate cancer.

Kilovoltage intrafraction monitoring during normofractionated prostate cancer radiotherapy

PURPOSE

During radiotherapy (RT) for prostate cancer (PCa), interfraction and intrafraction movements can lead to decreased target dose coverage and unnecessary over-exposure of organs at risk. New image-guided RT techniques accuracy allows planning target volume (PTV) margins reduction. We aim to assess the feasibility of a kilovoltage intrafraction monitoring (KIM) to track the prostate during RT.

METHODS AND MATERIALS

Between November 2017 and April 2018, 44 consecutive patients with PCa were included in an intrafraction prostate motion study using the Truebeam Auto Beam Hold® tracking system (Varian Medical Systems, United State) triggered by gold fiducials localization on kilovoltage (kV) imaging. A 5-mm PTV was considered. A significant gating event (SGE) was defined as the occurrence of an automatic beam interruption requiring patient repositioning following the detection of one fiducial outside a 5-mm target area around the marker during more than 45seconds.

RESULTS

Six patients could not benefit from the KIM because of technical issues (loss of one fiducial marker=1, hip prosthesis=4, morbid obesity causing table movements=1). The mean rate of SGE per patient was 14±19%, and the fraction average delivery time was increased by 146±86seconds. For a plan of 39 fractions of 2Gy, the additional radiation dose increased by 0.13±0.09Gy. The mean rates of SGE were 2% and 18% (P=0.002) in patients with planned fraction<90 and>90seconds respectively, showing that duration of the session strongly interfered with prostate intrafraction movements. No other significant clinical and technical parameter was correlated with the occurrence of SGE.

CONCLUSION

Automated intrafraction kV imaging can effectively perform autobeam holds due to intrafraction movement of the prostate in the large majority of patients. The additional radiation dose and delivery time are acceptable. This technique may be a cost-effective alternative to electromagnetic transponder guidance.

Multi-atlas-based auto-segmentation for prostatic urethra using novel prediction of deformable image registration accuracy

PURPOSE

Accurate identification of the prostatic urethra and bladder can help determine dosing and evaluate urinary toxicity during intensity-modulated radiation therapy (IMRT) planning in patients with localized prostate cancer. However, it is challenging to locate the prostatic urethra in planning computed tomography (pCT). In the present study, we developed a multiatlas-based auto-segmentation method for prostatic urethra identification using deformable image registration accuracy prediction with machine learning (ML) and assessed its feasibility.

METHODS

We examined 120 patients with prostate cancer treated with IMRT. All patients underwent temporary urinary catheter placement for identification and contouring of the prostatic urethra in pCT images (ground truth). Our method comprises the following three steps: (a) select four atlas datasets from the atlas datasets using the deformable image registration (DIR) accuracy prediction model, (b) deform them by structure-based DIR, (3) and propagate urethra contour using displacement vector field calculated by the DIR. In (a), for identifying suitable datasets, we used the trained support vector machine regression (SVR) model and five feature descriptors (e.g., prostate volume) to increase DIR accuracy. This method was trained/validated using 100 patients and performance was evaluated within an independent test set of 20 patients. Fivefold cross-validation was used to optimize the hype parameters of the DIR accuracy prediction model. We assessed the accuracy of our method by comparing it with those of two others: Acostas method-based patient selection (previous study method, by Acosta et al.), and the Waterman's method (defines the prostatic urethra based on the center of the prostate, by Waterman et al.). We used the centerlines distance (CLD) between the ground truth and the predicted prostatic urethra as the evaluation index.

RESULTS

The CLD in the entire prostatic urethra was 2.09 ± 0.89 mm (our proposed method), 2.77 ± 0.99 mm (Acosta et al., P = 0.022), and 3.47 ± 1.19 mm (Waterman et al., P < 0.001); our proposed method showed the highest accuracy. In segmented CLD, CLD in the top 1/3 segment was highly improved from that of Waterman et.al. and was slightly improved from that of Acosta et.al., with results of 2.49 ± 1.78 mm (our proposed method), 2.95 ± 1.75 mm (Acosta et al., P = 0.42), and 5.76 ± 3.09 mm (Waterman et al., P < 0.001).

CONCLUSIONS

We developed a DIR accuracy prediction model-based multiatlas-based auto-segmentation method for prostatic urethra identification. Our method identified prostatic urethra with mean error of 2.09 mm, likely due to combined effects of SVR model employment in patient selection, modified atlas dataset characteristics and DIR algorithm. Our method has potential utility in prostate cancer IMRT and can replace use of temporary indwelling urinary catheters.

A phase IB clinical trial of 15 Gy HDR brachytherapy followed by hypofractionated/SBRT in the management of intermediate-risk prostate cancer

PURPOSE

High dose-rate (HDR) brachytherapy is commonly administered as a boost to external beam radiation therapy (EBRT). Our purpose was to compare toxicity with increasingly hypofractionated EBRT in combination with a single 15 Gy HDR boost for men with intermediate-risk prostate cancer.

METHODS AND MATERIALS

Forty-two men were enrolled on this phase IB clinical trial to one of three EBRT dose cohorts: 10 fractions, seven fractions, or five fractions. Patients were followed prospectively for safety, efficacy, and health-related quality of life (Expanded Prostate Index Composite). Efficacy was assessed biochemically using the Phoenix definition.

RESULTS

With a median follow up of 36 months, the biochemical disease-free survival was 95.5%. One man developed metastatic disease at 5 years. There was no significant minimally important difference in EPIC PRO for either urinary, bowel, or sexual domains. There was one acute Grade 3 GI and GU toxicity, but no late Grade 3 GU or GI toxicities.

CONCLUSION

Fifteen gray HDR brachytherapy followed by a five fraction SBRT approach results in high disease control rates and low toxicity similar to previously reported HDR protocols with significant improvement in patient convenience and resource savings. While mature results with longer follow up are awaited, this treatment approach may be considered a safe and effective option for men with intermediate-risk disease.

Ten-Year Update of a Randomized, Prospective Trial of Conventional Fractionated Versus Moderate Hypofractionated Radiation Therapy for Localized Prostate Cancer

PURPOSE

The previously published single institution randomized prospective trial failed to show superiority in the 5-year biochemical and/or clinical disease failure (BCDF) rate with moderate hypofractionated intensity-modulated radiation therapy (H-IMRT) versus conventionally fractionated IMRT (C-IMRT). We now present 10-year disease outcomes using updated risk groups and definitions of biochemical failure.

METHODS

Men with protocol-defined intermediate- and high-risk prostate adenocarcinoma were randomly assigned to receive C-IMRT (76 Gy in 38 fractions) or H-IMRT (70.2 Gy in 26 fractions). Men with high-risk disease were all prescribed 24 months of androgen deprivation therapy (ADT) and had lymph node irradiation. Men with intermediate risk were prescribed 4 months of ADT at the discretion of the treating physician. The primary endpoint was cumulative incidence of BCDF. We compared disease outcomes and overall mortality by treatment arm, with sensitivity analyses for National Comprehensive Cancer Network (NCCN) risk group adjustment.

RESULTS

Overall, 303 assessable men were randomly assigned to C-IMRT or H-IMRT. The median follow-up was 122.9 months. Per updated NCCN risk classification, there were 28 patients (9.2%) with low-risk, 189 (62.4%) with intermediate-risk, and 86 (28.4%) with high-risk prostate cancer. The arms were equally balanced for clinicopathologic factors, except that there were more black patients in the C-IMRT arm (17.8% v 7.3%; P = .02). There was no difference in ADT use (P = .56). The 10-year cumulative incidence of BCDF was 25.9% in the C-IMRT arm and was 30.6% in the H-IMRT arm (hazard ratio, 1.31; 95% CI, 0.82 to 2.11). The two arms also had similar cumulative 10-year rates of biochemical failure, prostate cancer-specific mortality, and overall mortality; however, the 10-year cumulative incidence of distant metastases was higher in the H-IMRT arm (rate difference, 7.8%; 95% CI, 0.7% to 15.1%).

CONCLUSION

H-IMRT failed to demonstrate superiority compared with C-IMRT in long-term disease outcomes.

Phase I Trial of MRI-Guided Prostate Cancer Lattice Extreme Ablative Dose (LEAD) Boost Radiation Therapy

PURPOSE

A phase I clinical trial was designed to test the feasibility and toxicity of administering high-dose spatially fractionated radiation therapy to magnetic resonance imaging (MRI)-defined prostate tumor volumes, in addition to standard treatment.

METHODS AND MATERIALS

We enrolled 25 men with favorable to high-risk prostate cancer and 1 to 3 suspicious multiparametric MRI (mpMRI) gross tumor volumes (GTVs). The mpMRI-GTVs were treated on day 1 with 12 to 14 Gy via dose cylinders using a lattice extreme ablative dose technique. The entire prostate, along with the proximal seminal vesicles, was then treated to 76 Gy at 2 Gy/fraction. For some high-risk patients, the distal seminal vesicles and pelvic lymph nodes received 56 Gy at 1.47 Gy/fraction concurrently in 38 fractions. The total dose to the lattice extreme ablative dose cylinder volume(s) was 88 to 90 Gy (112-123 Gy in 2.0 Gy equivalents, assuming an α-to-β ratio of 3).

RESULTS

Dosimetric parameters were satisfactorily met. Median follow-up was 66 months. There were no grade 3 acute/subacute genitourinary or gastrointestinal adverse events. Maximum late genitourinary toxicity was grade 1 in 15 (60%), grade 2 in 4 (16%), and grade 4 in 1 (4%; sepsis after a posttreatment transurethral resection). Maximum late gastrointestinal toxicity was grade 1 in 11 (44%) and grade 2 in 4 (16%). Two patients experienced biochemical failure.

CONCLUSIONS

External beam radiation therapy delivered with an upfront spatially fractionated, stereotactic high-dose mpMRI-GTV boost is feasible and was not associated with any unexpected events. The technique is now part of a follow-up phase II randomized trial.

Longitudinal model-based meta-analysis for survival probabilities in patients with castration-resistant prostate cancer

PURPOSE

The aims of this longitudinal model-based meta-analysis (MBMA) were to indirectly compare the time courses of survival probabilities and to identify corresponding potential significant covariates across approved drugs in patients with castration-resistant prostate cancer (CRPC).

METHODS

A systematic literature review for monotherapy studies in patients with CRPC was conducted up to August 8, 2018. The time courses of progression-free survival (PFS) and overall survival (OS) were fitted with parametric survival models. Covariate analyses were performed to determine the impact of treatment drugs, dosing regimens, and patient characteristics on the survival probabilities. Simulations were carried out to quantify the magnitude of covariate effects.

RESULTS

A total of 146 studies including clinical trials and real-world data on longitudinal survival probabilities in 20,712 patients with CRPC were included in our meta-database. The time courses of PFS and OS probabilities were best described by the log-logistic model. There was no significant difference in median OS and PFS between docetaxel, cabazitaxel, abiraterone acetate, and enzalutamide. There was no significant dose-response relationship in PFS or OS for docetaxel at 50 to 120 mg/m² every 3 weeks (Q3W) and cabazitaxel at 20 to 25 mg/m² Q3W. Model-based simulations indicated that PFS probability was associated with chemotherapy, Gleason score, and baseline prostate-specific antigen (BLPSA), while OS probability was associated with chemotherapy, Gleason score, visceral metastasis, Eastern Cooperative Oncology Group performance status, and BLPSA.

CONCLUSION

Our modeling and simulation framework can be applied to support indirect comparison, dose selection, and go/no-go decision-making for new agents targeting CRPC.

A Randomized Phase II Trial of Prostate Boost Irradiation With Stereotactic Body Radiotherapy (SBRT) or Conventional Fractionation (CF) External Beam Radiotherapy (EBRT) in Locally Advanced Prostate Cancer: The PBS Trial (NCT03380806)

Standard therapy for high-risk (HR) prostate cancer (PrCa) involves androgen deprivation therapy (ADT) and pelvic conventional fractionation (CF) external beam radiotherapy (EBRT) followed by boost CF-EBRT treatment to prostate for a total of 78 to 80 Gy in 39 to 40 fractions. This is a long and inconvenient treatment for patients. Brachytherapy boost treatment studies indicate that escalation of biological dose of radiotherapy (RT) can improve outcomes in HR-PrCa. However, brachytherapy is an invasive treatment associated with increased toxicity and requires specialized resources. Stereotactic body radiotherapy (SBRT) is a promising, non-invasive alternative to brachytherapy. However, its impact on patient quality of life (QoL) and RT-associated toxicity has not been investigated in a randomized setting. In this study, we investigate SBRT as a boost treatment, following pelvic CF-EBRT, in patients with HR-PrCa treated with ADT. One hundred patients with locally advanced PrCa will be randomized to receive daily CF-EBRT of 45 to 46 Gy in 23 to 25 fractions followed by either daily CF-EBRT of 32 to 33 Gy in 15 to 16 fractions (control arm) or SBRT boost treatment of 19.5 to 21 Gy in 3 fractions (1 fraction per week) (experimental arm). The primary objective of the PBS trial is early bowel and urinary QoL (expanded prostate index composite [EPIC], up to 6 months after RT). This phase II randomized study (PBS) provides an appropriate setting to investigate effectively the impact of SBRT boost on QoL and toxicity in patients with HR-PrCa, before this modality can be compared against the current standard of care in larger phase III protocols.

Low incidence of late recurrence in patients with intermediate-risk prostate cancer treated by intensity-modulated radiation therapy plus short-term androgen deprivation therapy

OBJECTIVES

This study evaluated the long-term outcomes of intensity-modulated radiation therapy (IMRT) combined with short-term neoadjuvant androgen deprivation therapy (ADT) in patients with intermediate-risk (IR) prostate cancer (PCa).

MATERIALS AND METHODS

Patients with IR PCa treated with IMRT at our institution between September 2000 and November 2010 were analyzed retrospectively. The treatment consisted of IMRT (70-78 Gy in 35-39 fractions) combined with 6 months of neoadjuvant ADT. Salvage ADT was initiated when the prostate-specific antigen level was > 4.0 ng/mL RESULTS: In total, 106 consecutive patients with IR PCa (median age: 70 years old) were analyzed. The median follow-up period was 8.0 years. The overall survival, PCa-specific survival, biochemical failure, and clinical failure rates were 99.0%, 100.0%, 6.8%, and 1.9% at 5 years and 89.1%, 100.0%, 11.3%, and 2.9% at 10 years, respectively. Late recurrence (> 5 years) was observed in three cases (2.8%). The cumulative incidence rates of genitourinary (GU) and gastrointestinal (GI) toxicities (grade 2/3) were 10.5% and 5.8% at 5 years, and 14.7% and 5.8% at 10 years, respectively. No patient developed grade 4/5 GU toxicities or grade 3-5 GI toxicities.

CONCLUSION

IMRT at a dose up to 78 Gy combined with short-term neoadjuvant ADT resulted in excellent long-term disease-free outcomes with acceptable morbidities among patients with IR PCa. In addition, the incidence of late recurrence was very low. Further investigation is warranted to confirm our findings.

Dose Escalation in Stereotactic Body Radiation Therapy for Pancreatic Cancer: A Meta-Analysis

OBJECTIVE

To determine whether increasing biologically effective dose (BED) with stereotactic body radiation therapy (SBRT) is associated with improved local control (LC) or toxicities in patients with locally advanced pancreatic cancer.

METHODS

A PICOS/PRISMA/MOOSE selection protocol was used to identify 15 studies across 12 institutions in 5 countries where patients received definitive SBRT for nonmetastatic disease. Biologically equivalent doses were calculated with an α/β of 10 (ie, BED10) for LC and acute toxicity and 3 (ie, BED3) for late toxicity. Fixed and random effects models were used to characterize LC and grade 3/4 toxicities by BED.

RESULTS

There were 508 patients included with a median follow-up time of 9.1 months. The median dose was 30 Gy, and the most common regimen was 30 Gy/5 fractions. There was no significant difference in LC rates at 1 year between the BED10<70 Gy versus ≥70 Gy groups, with an estimate of 0.60 (95% confidence interval [CI], 0.36-0.81) versus 0.83 (95% CI, 0.63-0.97), respectively. There was no significant difference in acute toxicity rates between the BED10<70 Gy versus ≥70 Gy groups, with an estimate of 0.02 (95% CI, 0.00-0.08) versus 0.05 (95% CI, 0.00-0.22), respectively. Given the dose distribution across studies, 3 intervals were used to characterize BED3. There were no significant differences in late toxicity among those receiving BED3<100, 100 to 200, or >200 Gy.

CONCLUSIONS

SBRT for pancreatic cancer results in LC rates of 60% to 83% and clinically significant toxicity of <7%. Increasing BED10 beyond 70 Gy was not associated with increased rates of 1-year LC or acute toxicity. Increasing BED3 beyond 100 Gy was not associated with increased rates of late toxicity.

Performance evaluation of a newly developed three-dimensional model-based global-to-local registration in prostate cancer

We evaluated the performance of a newly developed three-dimensional (3D) model-based global-to-local registration of multiple organs, by comparing it with a 3D model-based global registration in the prostate region. This study included 220 prostate cancer patients who underwent intensity-modulated radiotherapy or volumetric-modulated arc therapy. Our registration proceeded sequentially, i.e. global registration including affine and piece-wise affine transformation followed by local registration. As a local registration, Laplacian-based and finite element method-based registration was implemented in Algorithm A and B, respectively. Algorithm C was for global registration alone. The template models for the prostate, seminal vesicles, rectum and bladder were constructed from the first 20 patients, and then three different registrations were performed on these organs for the remaining 200 patients, to assess registration accuracy. The 75th percentile Hausdorff distance was <1 mm in Algorithm A; it was >1 mm in Algorithm B, except for the prostate; and 3.9 mm for the prostate and >7.8 mm for other organs in Algorithm C. The median computation time to complete registration was <101, 30 and 16 s in Algorithms A, B and C, respectively. Analysis of variance revealed significant differences among Algorithms A-C in the Hausdorff distance and computation time. In addition, no significant difference was observed in the difference of Hausdorff distance between Algorithm A and B with Tukey's multiple comparison test. The 3D model-based global-to-local registration, especially that implementing Laplacian-based registration, completed surface registration rapidly and provided sufficient registration accuracy in the prostate region.

A comparison of outcomes for patients with intermediate and high risk prostate cancer treated with low dose rate and high dose rate brachytherapy in combination with external beam radiotherapy

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Superior biochemical progression free survival for LDR in combination with EBRT.

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On multivariable analysis, HDR and EBRT and Gleason ≥8 predicted for progression.

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Low cumulative incidence of ≥grade 3 GU and GI toxicities.

Introduction

There is evidence to support use of external beam radiotherapy (EBRT) in combination with both low dose rate brachytherapy (LDR–EBRT) and high dose rate brachytherapy (HDR–EBRT) to treat intermediate and high risk prostate cancer.

Methods

Men with intermediate and high risk prostate cancer treated using LDR–EBRT (treated between 1996 and 2007) and HDR–EBRT (treated between 2007 and 2012) were identified from an institutional database. Multivariable analysis was performed to evaluate the relationship between patient, disease and treatment factors with biochemical progression free survival (bPFS).

Results

116 men were treated with LDR-EBRT and 171 were treated with HDR–EBRT. At 5 years, bPFS was estimated to be 90.5% for the LDR–EBRT cohort and 77.6% for the HDR–EBRT cohort. On multivariable analysis, patients treated with HDR–EBRT were more than twice as likely to experience biochemical progression compared with LDR–EBRT (HR 2.33, 95% CI 1.12–4.07). Patients with Gleason ≥8 disease were more than five times more likely to experience biochemical progression compared with Gleason 6 disease (HR 5.47, 95% CI 1.26–23.64). Cumulative incidence of ≥grade 3 genitourinary and gastrointestinal toxicities for the LDR–EBRT and HDR–EBRT cohorts were 8% versus 4% and 5% versus 1% respectively, although these differences did not reach statistical significance.

Conclusion

LDR–EBRT may provide more effective PSA control at 5 years compared with HDR–EBRT. Direct comparison of these treatments through randomised trials are recommended to investigate this hypothesis further.

Particle therapy for prostate cancer: The past, present and future

Although prostate cancer control using radiotherapy is dose‐dependent, dose–volume effects on late toxicities in organs at risk, such as the rectum and bladder, have been observed. Both protons and carbon ions offer advantageous physical properties for radiotherapy, and create favorable dose distributions using fewer portals compared with photon‐based radiotherapy. Thus, particle beam therapy using protons and carbon ions theoretically seems suitable for dose escalation and reduced risk of toxicity. However, it is difficult to evaluate the superiority of particle beam radiotherapy over photon beam radiotherapy for prostate cancer, as no clinical trials have directly compared the outcomes between the two types of therapy due to the limited number of facilities using particle beam therapy. The Japanese Society for Radiation Oncology organized a joint effort among research groups to establish standardized treatment policies and indications for particle beam therapy according to disease, and multicenter prospective studies have been planned for several common cancers. Clinical trials of proton beam therapy for intermediate‐risk prostate cancer and carbon‐ion therapy for high‐risk prostate cancer have already begun. As particle beam therapy for prostate cancer is covered by the Japanese national health insurance system as of April 2018, and the number of facilities practicing particle beam therapy has increased recently, the number of prostate cancer patients treated with particle beam therapy in Japan is expected to increase drastically. Here, we review the results from studies of particle beam therapy for prostate cancer and discuss future developments in this field.

Ten-year outcomes of high-dose intensity-modulated radiation therapy for nonmetastatic prostate cancer with unfavorable risk: early initiation of salvage therapy may replace long-term adjuvant androgen deprivation

Background

The optimal timing of salvage androgen deprivation therapy (ADT) following definitive radiation therapy for prostate cancer (PCa) is unknown. This study evaluated the efficacy of early initiation of salvage-ADT (S-ADT) based on predetermined timing among patients with unfavorable PCa treated with high-dose intensity-modulated radiation therapy (IMRT).

Materials and methods

High-risk (HR) and very-high-risk (VHR) PCa patients treated with IMRT at our institution between September 2000 and December 2010 were analyzed retrospectively. Treatment consisted of high-dose IMRT (78 Gy/39 fractions) combined with 6 months of neoadjuvant-ADT (NA-ADT). S-ADT was initiated when prostate-specific antigen levels exceeded 4.0 ng/mL.

Results

In total, 268 (184 HR and 84 VHR) patients were analyzed. The median follow-up period was 114.4 months. The 10-year overall survival (OS), PCa-specific survival (PCSS), biochemical failure (BF), and clinical failure (CF) rates were 82.8%, 97.1%, 27.3%, and 12.8% among the HR PCa patients and 79.4%, 87.9%, 56.2%, and 26.7% among the VHR PCa patients (p = 0.839, = 0.0377, < 0.001, and < 0.001), respectively. The 10-year cumulative incidence rates of urinary and rectal (grades 2–3) toxicities were 22.6% and 5.8%, respectively. No grade 4 or higher toxicities were observed.

Conclusion

High-dose IMRT combined with short-term NA-ADT resulted in long-term disease-free status, with acceptable morbidity among approximately three-fourths of the HR PCa patients and nearly half of the VHR PCa patients. Moreover, excellent survival outcomes were achieved by the early S-ADT initiation. This approach may be a promising alternative to uniform provision of long-term ADT.

Impact of Radiation Therapy Dose Escalation on Prostate Cancer Outcomes and Toxicities

OBJECTIVES

Freedom from biochemical failure (FFBF) is a common primary outcome of randomized-controlled trials of prostate cancer (PCa). We aimed to determine how increasing the PCa biologically equivalent dose (BED) of external radiation therapy (RT) is correlated with FFBF and overall patient outcomes: overall survival (OS), distant metastasis (DM), and cancer-specific mortality (CSM); as well as genitourinary (GU), and gastrointestinal toxicities.

MATERIALS AND METHODS

We performed a meta-analysis of 6884 PCa patients from 12 randomized-controlled trials of external beam RT. Mixed effects regression models were used to estimate weighted linear relationships between BED and observed percentages of 5- and 10-year outcomes. For toxicities, a subset analysis of using 3-dimensional conformal RT (3D-CRT) versus intensity-modulated RT (IMRT) was performed.

RESULTS

Increasing BED correlated with improved FFBF: 10-year absolute improvement of 9.6% and 7.2% for low-risk and intermediate-risk patients, respectively (P<0.05); but not with improvement of OS, DM, or CSM at either time point. BED escalation was not correlated with increased acute toxicities; it was correlated with increased late gastrointestinal toxicities in patients treated with 3D-CRT (1.5% increase over BED range, P<0.01). IMRT patients had significantly fewer late toxicities, despite being treated at higher BED.

CONCLUSIONS

RT BED escalation has resulted in significantly improved PCa FFBF at up to 10 years; but not with improvement in OS, DM, or CSM. Thus, FFBF is a poor surrogate of overall patient outcomes for trials of RT. Late toxicities were less frequent with IMRT than with 3D-CRT, even at higher BED.

A Pooled Analysis of Biochemical Failure in Intermediate-risk Prostate Cancer Following Definitive Stereotactic Body Radiotherapy (SBRT) or High-Dose-Rate Brachytherapy (HDR-B) Monotherapy

OBJECTIVES

To investigate biochemical relapse-free survival (BRFS) in men with National Comprehensive Cancer Network-defined intermediate-risk prostate cancer (PC) treated with either stereotactic body radiotherapy (SBRT) or high-dose-rate brachytherapy (HDR-B) monotherapy.

MATERIALS AND METHODS

A retrospective, multi-institutional analysis of 437 patients with intermediate-risk PC treated with SBRT (N=300) or HDR-B (N=137) was performed. Men who underwent SBRT were treated to 35 to 40 Gy in 4 to 5 fractions. A total of 95.6% who underwent HDR-B were treated to 42 Gy in 6 fractions. Baseline patient characteristics were compared using a T test for continuous variables and the Mantel-Haenszel χ metric or Fisher exact test for categorical variables. Kaplan-Meier curves were generated to estimate 5-year actuarial BRFS. Multivariate analysis using a Cox proportional-hazards model was used to evaluate factors associated with biochemical failure.

RESULTS

The mean age at diagnosis was 68.4 (SD±7.8) years. T-category was T1 in 63.6% and T2 in 36.4%. Mean initial prostate-specific antigen was 7.4 (SD±3.4) ng/mL. Biopsy Gleason score was ≤3+4 in 82.8% and 4+3 in 17.2%. At a median of 4.1 years of follow-up, the BRFS rate (Phoenix definition) was 96.3%, with no difference when stratifying by treatment modality or biologically equivalent dose (BED1.5). On multivariate analysis, age (hazard ratio 1.08, P=0.04) and biopsy Gleason score (hazard ratio 2.48, P=0.03) were significant predictors of BRFS.

CONCLUSIONS

With a median follow-up period of 4 years, SBRT and HDR-B monotherapy provide excellent BRFS in intermediate-risk PC. Longer-term follow-up is necessary to determine the ultimate efficacy of these hypofractionated approaches, but they appear promising relative to standard fractionation outcomes.

Variations in patterns of concurrent androgen deprivation therapy use based on dose escalation with external beam radiotherapy vs. brachytherapy boost for prostate cancer

PURPOSE

Retrospective data suggest less benefit from androgen deprivation therapy (ADT) in the setting of dose-escalated definitive radiation for prostate cancer, especially when a combination of external beam radiotherapy (EBRT) and brachytherapy approaches are used. This study aimed to test the hypothesis that patients with prostate cancer with intermediate- or high-risk disease undergoing extreme dose escalation with a brachytherapy boost are less likely to receive ADT.

METHODS AND MATERIALS

Data from the National Cancer Database were extracted for men aged 40-90 years diagnosed with node-negative, non-metastatic prostate cancer from 2004 to 2015. Only patients with intermediate- or high-risk disease who were treated with definitive radiotherapy were included. The association and patterns of care between dose escalated radiotherapy and ADT receipt were assessed using multivariable logistic regression.

RESULTS

Patients with unfavorable intermediate- and high-risk prostate cancer were significantly less likely to receive ADT if they underwent dose escalation with a combination of EBRT and brachytherapy (odds ratio 0.67, p < 0.0001). Over time, this decrease in ADT utilization has widened for patients with unfavorable intermediate-risk disease. There was no difference in ADT utilization when comparing patients treated with non-dose-escalated EBRT to those treated with dose-escalated EBRT (without brachytherapy).

CONCLUSION

In this large national database, patients with unfavorable intermediate- and high-risk prostate cancer were significantly less likely to receive guideline-indicated ADT if they underwent extreme dose escalation with combined radiation modalities. As we await prospective data guiding the utility of ADT with dose escalated radiation, these findings suggest potential underutilization of ADT in patients at higher risk of advanced disease.

A pilot study of highly hypofractionated intensity-modulated radiation therapy over 3 weeks for localized prostate cancer

The purpose of this pilot study was to evaluate the feasibility of highly hypofractionated intensity-modulated radiation therapy (IMRT) in 15 fractions over 3 weeks for treating localized prostate cancer based on prostate position-based image-guided radiation therapy. Twenty-five patients with National Comprehensive Cancer Network (NCCN) very low- to unfavorable intermediate-risk prostate cancer were enrolled in this study from April 2014 to September 2015 to receive highly hypofractionated IMRT (without intraprostatic fiducial markers) delivering 54 Gy in 15 fractions over 3 weeks. Patients with intermediate-risk disease underwent neoadjuvant androgen suppression for 4-8 months. Twenty-four patients were treated with highly hypofractionated IMRT, and one was treated with conventionally fractionated IMRT because the dose constraint of the small bowel seemed difficult to achieve during the simulation. Seventeen percent had very low- or low-risk, 42% had favorable intermediate-risk, and 42% had unfavorable intermediate-risk disease according to NCCN guidelines. The median follow-up period was 31 months (range, 24-42 months). No Grade ≥3 acute toxicity was observed, and the incidence rates of Grade 2 acute genitourinary and gastrointestinal toxicities were 21% and 4%, respectively. No Grade ≥2 late toxicity was observed. Biochemical relapse was observed in one patient at 15 months, and the biochemical relapse-free survival rate was 95.8% at 2 years. A prostate-specific antigen bounce of ≥0.4 ng/ml was observed in 11 patients (46%). The highly hypofractionated IMRT regimen is feasible in patients with localized prostate cancer and is more convenient than conventionally fractionated schedules for patients and health-care providers.

The experience of a developing country using an electronic portal imaging device for the verification of patient positioning and dosimetry in radiotherapy for prostate cancer

Purpose

This is a retrospective study to evaluate the efficacy and safety of routine use of electronic portal imaging device (EPID) in intensity-modulated radiation therapy for localised prostate cancer.

Materials and methods

Data from 20 patients with localised prostate cancer treated by radical radiotherapy using intensity-modulated technique in Habib Bourguiba Hospital were analysed to define the action levels for pretreatment planer dose distribution of 100 treatment fields and the set-up errors of 418 portal imaging. Pretreatment planar dose distribution was measured with the EPID. The additional dose from repeated portal imaging was determined with treatment planning system.

Results

For all 100 fields, the predicted and the measured planar dose distribution agrees well with mean±standard deviation value for γmax=2·31±0·57, γavg=0·36±0·07 and γ%≤1=98·94%±0·71%, respectively. For the evaluation of set-up errors, the mean total errors with 1 SD in the lateral, longitudinal and vertical directions were 0·11±0·44 cm; 0·02±0·37 cm and −0·02±0·21 cm, respectively. The imaging additional dose was evaluated as 1 cGy per monitor unit.

Conclusion

EPID is a useful tool to verify pretreatment dose distribution and to assess the correct field position without a significant increase in the absorbed dose due to the repetition of portal imaging.