Standard whole prostate gland radiotherapy with and without lesion boost in prostate cancer: Toxicity in the FLAME randomized controlled trial

Photon vs proton hypofractionation in prostate cancer: A systematic review and meta-analysis

BACKGROUND

High-level evidence on hypofractionated proton therapy (PT) for localized and locally advanced prostate cancer (PCa) patients is currently missing. The aim of this study is to provide a systematic literature review to compare the toxicity and effectiveness of curative radiotherapy with photon therapy (XRT) or PT in PCa.

METHODS

PubMed, Embase, and the Cochrane Library databases were systematically searched up to April 2022. Men with a diagnosis of PCa who underwent curative hypofractionated RT treatment (PT or XRT) were included. Risk of grade (G) ≥ 2 acute and late genitourinary (GU) OR gastrointestinal (GI) toxicity were the primary outcomes of interest. Secondary outcomes were five-year biochemical relapse-free survival (b-RFS), clinical relapse-free, distant metastasis-free, and prostate cancer-specific survival. Heterogeneity between study-specific estimates was assessed using Chi-square statistics and measured with the I2 index (heterogeneity measure across studies).

RESULTS

A total of 230 studies matched inclusion criteria and, due to overlapped populations, 160 were included in the present analysis. Significant lower rates of G ≥ 2 acute GI incidence (2 % vs 7 %) and improved 5-year biochemical relapse-free survival (95 % vs 91 %) were observed in the PT arm compared to XRT. PT benefits in 5-year biochemical relapse-free survival were maintained for the moderate hypofractionated arm (p-value 0.0122) and among patients in intermediate and low-risk classes (p-values < 0.0001 and 0.0368, respectively). No statistically relevant differences were found for the other considered outcomes.

CONCLUSION

The present study supports that PT is safe and effective for localized PCa treatment, however, more data from RCTs are needed to draw solid evidence in this setting and further effort must be made to identify the patient subgroups that could benefit the most from PT.

Commissioning and implementing a Quality Assurance program for dedicated radiation oncology MRI scanners

PURPOSE

ACR and AAPM task group's guidelines addressing commissioning for dedicated MR simulators were recently published. The goal of the current paper is to present the authors' 2-year experience regarding the commissioning and introduction of a QA program based on these guidelines and an associated automated workflow.

METHODS

All mandatory commissioning tests suggested by AAPM report 284 were performed and results are reported for two MRI scanners (MAGNETOM Sola and Aera). Visual inspection, vendor clinical or service platform, third-party software, or in-house python-based code were used. Automated QA and data analysis was performed via vendor, in-house or third-party software. QATrack+ was used for QA data logging and storage. 3D geometric distortion, B0 inhomogeneity, EPI, and parallel imaging performance were evaluated.

RESULTS

Contrasting with AAPM report 284 recommendations, homogeneity and RF tests were performed monthly. The QA program allowed us to detect major failures over time (shimming, gradient calibration and RF interference). Automated QA, data analysis, and logging allowed fast ACR analysis daily and monthly QA to be performed in 3 h. On the Sola, the average distortion is 1 mm for imaging radii of 250 mm or less. For radii of up to 200 mm, the maximum, average (standard deviation) distortion is 1.2  and 0.4 mm (0.3 mm). Aera values are roughly double the Sola for radii up to 200 mm. EPI geometric distortion, ghosting ratio, and long-term stability were found to be under the maximum recommended values. Parallel imaging SNR ratio was stable and close to the theoretical value (ideal g-factor). No major failures were detected during commissioning.

CONCLUSION

An automated workflow and enhanced QA program allowed to automatically track machine and environmental changes over time and to detect periodic failures and errors that might otherwise have gone unnoticed. The Sola is more geometrically accurate, with a more homogenous B0 field than the Aera.

Focal Boost in Prostate Cancer Radiotherapy: A Review of Planning Studies and Clinical Trials

BACKGROUND

Focal boost radiotherapy was developed to deliver elevated doses to functional sub-volumes within a target. Such a technique was hypothesized to improve treatment outcomes without increasing toxicity in prostate cancer treatment.

PURPOSE

To summarize and evaluate the efficacy and variability of focal boost radiotherapy by reviewing focal boost planning studies and clinical trials that have been published in the last ten years.

METHODS

Published reports of focal boost radiotherapy, that specifically incorporate dose escalation to intra-prostatic lesions (IPLs), were reviewed and summarized. Correlations between acute/late ≥G2 genitourinary (GU) or gastrointestinal (GI) toxicity and clinical factors were determined by a meta-analysis.

RESULTS

By reviewing and summarizing 34 planning studies and 35 trials, a significant dose escalation to the GTV and thus higher tumor control of focal boost radiotherapy were reported consistently by all reviewed studies. Reviewed trials reported a not significant difference in toxicity between focal boost and conventional radiotherapy. Acute ≥G2 GU and late ≥G2 GI toxicities were reported the most and least prevalent, respectively, and a negative correlation was found between the rate of toxicity and proportion of low-risk or intermediate-risk patients in the cohort.

CONCLUSION

Focal boost prostate cancer radiotherapy has the potential to be a new standard of care.

From once-weekly to semi-weekly whole prostate gland stereotactic radiotherapy with focal boosting: Primary endpoint analysis of the multicenter phase II hypo-FLAME 2.0 trial

BACKGROUND AND PURPOSE

The hypo-FLAME trial showed that once-weekly (QW) focal boosted prostate stereotactic body radiotherapy (SBRT) is associated with acceptable acute genitourinary (GU) and gastrointestinal (GI) toxicity. Currently, we investigated the safety of reducing the overall treatment time (OTT) of focal boosted prostate SBRT from 29 to 15 days.

MATERIAL AND METHODS

Patients with intermediate- and high-risk prostate cancer were treated with SBRT delivering 35 Gy in 5 fractions to the whole prostate gland with an iso-toxic boost up to 50 Gy to the intraprostatic lesion(s) in a semi-weekly (BIW) schedule. The primary endpoint was radiation-induced acute toxicity (CTCAE v5.0). Changes in quality of life (QoL) were examined in terms of proportions achieving a minimal clinically important change (MCIC). Finally, acute toxicity and QoL scores of the BIW schedule were compared with the results of the prior QW hypo-FLAME schedule (n = 100).

RESULTS

Between August 2020 and February 2022, 124 patients were enrolled and treated BIW. No grade ≥3 GU or GI toxicity was observed. The 90-days cumulative incidence of grade 2 GU and GI toxicity rates were 47.5% and 7.4%, respectively. Patients treated QW scored significant less grade 2 GU toxicity (34.0%, p = 0.01). No significant differences in acute GI toxicity were observed. Furthermore, patients treated QW had a superior acute bowel and urinary QoL.

CONCLUSION

Semi-weekly prostate SBRT with iso-toxic focal boosting is associated with acceptable acute GU and GI toxicity. Based on the comparison between the QW and BIW schedule, patients should be counselled regarding the short-term advantages of a more protracted schedule. Registration number ClinicalTrials.gov: NCT04045717.

Tolerability of concurrent external beam radiotherapy and [177Lu]Lu-PSMA-617 for node-positive prostate cancer in treatment naïve patients, phase I study (PROQURE-I trial)

BACKGROUND

Prostate cancer patients with locoregional lymph node disease at diagnosis (N1M0) still have a limited prognosis despite the improvements provided by aggressive curative intent multimodal locoregional external beam radiation therapy (EBRT) with systemic androgen deprivation therapy (ADT). Although some patients can be cured and the majority of patients have a long survival, the 5-year biochemical failure rate is currently 29-47%. [¹⁷⁷Lu]Lu-PSMA-617 has shown impressive clinical and biochemical responses with low toxicity in salvage setting in metastatic castration-resistant prostate cancer. This study aims to explore the combination of standard EBRT and ADT complemented with a single administration of [¹⁷⁷Lu]Lu-PSMA-617 in curative intent treatment for N1M0 prostate cancer. Hypothetically, this combined approach will enhance EBRT to better control macroscopic tumour localizations, and treat undetected microscopic disease locations inside and outside EBRT fields.

METHODS

The PROQURE-I study is a multicenter prospective phase I study investigating standard of care treatment (7 weeks EBRT and 3 years ADT) complemented with one concurrent cycle (three, six, or nine GBq) of systemic [¹⁷⁷Lu]Lu-PSMA-617 administered in week two of EBRT. A maximum of 18 patients with PSMA-positive N1M0 prostate cancer will be included. The tolerability of adding [¹⁷⁷Lu]Lu-PSMA-617 will be evaluated using a Bayesian Optimal Interval (BOIN) dose-escalation design. The primary objective is to determine the maximum tolerated dose (MTD) of a single cycle [¹⁷⁷Lu]Lu-PSMA-617 when given concurrent with EBRT + ADT, defined as the occurrence of Common Terminology Criteria for Adverse Events (CTCAE) v 5.0 grade three or higher acute toxicity. Secondary objectives include: late toxicity at 6 months, dosimetric assessment, preliminary biochemical efficacy at 6 months, quality of life questionnaires, and pharmacokinetic modelling of [¹⁷⁷Lu]Lu-PSMA-617.

DISCUSSION

This is the first prospective study to combine EBRT and ADT with [¹⁷⁷Lu]Lu-PSMA-617 in treatment naïve men with N1M0 prostate cancer, and thereby explores the novel application of [¹⁷⁷Lu]Lu-PSMA-617 in curative intent treatment. It is considered likely that this study will confirm tolerability as the combined toxicity of these treatments is expected to be limited. Increased efficacy is considered likely since both individual treatments have proven high anti-tumour effect as mono-treatments.

TRIAL REGISTRATION

ClinicalTrials, NCT05162573 . Registered 7 October 2021.

Retreatment Plan Success through Patient Health Awareness, Health Behavior, and Access to Doctor after a Focal Therapy Procedure for Prostate Cancer

Objective: The research aimed to investigate the retreatment plan success through patient health awareness, health behavior, and access to a doctor when patients have in-field or outfield recurrence after a focal therapy procedure for prostate cancer. This research is initiated because many men are victims of prostate cancer. Methods: The research collected data from patient's focal therapy clinics for their treatment of prostate cancer. The data for this research was collected with a longitudinal design because a complete procedure of patient treatment was required in this study. Results: The findings disclosed that prostate cancer patients' retreatment can be a success when they have health awareness and access to a doctor for focal therapy. The model developed in this research is a significant contribution to the literature on patient satisfaction and prostate cancer treatment. The research has contributed remarkable implications to the theory by presenting a newly developed relationship with empirical evidence based on patients' responses. Conclusion: The study has presented a roadmap for the practical treatment of prostate cancer patients and treatment success for the patient's treatment in the future. Some future recommendations are also reported for future investigation and work on prostate cancer and retreatment success.

Standard and Hypofractionated Dose Escalation to Intraprostatic Tumor Nodules in Localized Prostate Cancer: 5-Year Efficacy and Toxicity in the DELINEATE Trial

PURPOSE

Our purpose was to report 5-year efficacy and toxicity of intraprostatic lesion boosting using standard and hypofractionated radiation therapy.

METHODS AND MATERIALS

DELINEATE (ISRCTN 04483921) is a single center phase 2 multicohort study including standardly fractionated (cohort A: 74 Gy/37F to prostate and seminal vesicles [PSV]; cohort C 74 Gy/37F to PSV plus 60 Gy/37F to pelvic lymph nodes) and moderately hypofractionated (cohort B: 60 Gy/20F to PSV) prostate intensity-modulated radiation therapy patients with National Comprehensive Cancer Network intermediate/high-risk disease. Patients received an integrated boost of 82 Gy (cohorts A and C) or 67 Gy (cohort B) to multiparametric magnetic resonance imaging identified lesion(s). Primary endpoint was late Radiation Therapy Oncology Group (RTOG) gastrointestinal (GI) toxicity at 1 year. Secondary endpoints were acute and late toxicity (clinician and patient reported) and freedom from biochemical/clinical failure at 5 years.

RESULTS

Two hundred and sixty-five men were recruited and 256 were treated (55 cohort A, 153 cohort B, and 48 cohort C). Median follow-up for each cohort was >5 years. Cumulative late RTOG grade 2+ GI toxicity at 1 year was 3.6% (95% confidence interval [CI], 0.9%-13.8%) (cohort A), 7.2% (95% CI, 4%-12.6%) (cohort B), and 8.4% (95% CI, 3.2%-20.8%) (cohort C). Cumulative late RTOG grade 2+ GI toxicity to 5 years was 12.8% (95% CI, 6.3%-25.1%) (cohort A), 14.6% (95% CI, 9.9%-21.4%) (cohort B), and 20.7% (95% CI, 11.2%-36.2%) (cohort C). Cumulative RTOG grade 2+ genitourinary toxicity to 5 years was 12.9% (95% CI, 6.4%-25.2%) (cohort A), 18.2% (95% CI, 12.8%-25.4%) (cohort B), and 18.2% (95% CI, 9.5%-33.2%) (cohort C). Five-year freedom from biochemical/clinical failure was 98.2% (95% CI, 87.8%-99.7%) (cohort A), 96.7% (95% CI, 91.3%- 98.8%) (cohort B), and 95.1% (95% CI, 81.6-98.7%) (cohort C).

CONCLUSIONS

The DELINEATE trial has shown safety, tolerability, and feasibility of focal boosting in 20 or 37 fractions. Efficacy results indicate a low chance of prostate cancer recurrence 5 years after radiation therapy. Evidence from ongoing phase 3 randomized trials is awaited.

SBRT focal dose intensification using an MR-Linac adaptive planning for intermediate-risk prostate cancer: An analysis of the dosimetric impact of intra-fractional organ changes

INTRODUCTION

Using an magnetic resonance linear accelerator (MR-Linac) may improve the precision of visible tumor boosting with ultra-hypofractionation by accounting for daily positional changes in the target and organs at risk (OAR).

PATIENTS AND METHODS

Fifteen patients with prostate cancer and an MR-detected dominant lesion were treated on the MR-Linac with stereotactic body radiation (SBRT) to 40 Gy in 5 fractions, boosting the gross tumor volume (GTV) to 45 Gy with daily adaptive planning. Imaging was acquired again after initial planning (verification scan), and immediately after treatment (post-treatment scan). Prior to beam-on, additional adjustments were made on the verification scan. Contours were retrospectively adjusted on verification and post-treatment scans, and the daily plan recalculated on these scans to estimate the true dose delivered.

RESULTS

The median prostate D95% for plan 1, 2 and 3 was 40.3 Gy, 40.5 Gy and 40.3 Gy and DIL D95% was 45.7 Gy, 45.2 Gy and 44.6 Gy, respectively. Bladder filling was associated with reduced GTV coverage (p = 0.03, plan 1 vs 2) and prostate coverage (p = 0.03, plan 2 vs 3). The D0.035 cc constraint was exceeded on verification and post-treatment plans in 24 % and 33 % of fractions for the urethra, 31 % and 45 % for the bladder, and 35 % and 25 % for the rectum, respectively.

CONCLUSION

MR-Linac guided, daily adaptive SBRT with focal boosting of the GTV yields acceptable planned and delivered dosimetry. Adaptive planning with a MR-Linac may reliably deliver the prescribed dose to the intended tumor target.

Management of men with lower urinary tract symptoms referred for prostate radiotherapy

Objective:

To report on the experience of the management of lower urinary tract symptoms (LUTS) in men referred for prostate radiotherapy (RT) in a large tertiary referral centre.

Methods:

Between February and November 2018, 156 men referred for radiotherapy were seen and assessed according to their LUTS history: International Prostate Symptom Score (IPSS), flow rate (FR) and post-void residual (PVR). Patients with LUTS were offered management options depending on severity including lifestyle advice, oral medication or surgery. A subset of patients ( n = 102) were reassessed post-RT, and univariate and multivariate logistic regression was performed to predict symptoms improvement.

Results:

Prior to referral for RT and assessment at our dedicated LUTS clinic, 65% of men had a documented history of LUTS, 14% had completed an IPSS questionnaire and only 13% had a urinary FR; 17% (27/156) had prior treatment in the form of medication or surgery. In our assessment, 77/156 (49%) had mild, 66/156 (42%) moderate and 13/156 (8%) severe LUTS determined by IPSS. Out of 156, 71 (46%) had a quality-of-life score >3. Of the men, 81% were offered lifestyle advice, 47 patients were started on alpha blockers and 20 (12.8%) went onto Transurethral Resection of the Prostate prior to RT; 6 weeks following RT, 61 (50%) patients had higher IPSS scores. Patients who were started on alpha blockers ( p = 0.022) or had TURP ( p = 0.015) were less likely to have an increase in IPSS score on multivariate analysis.

Conclusion:

Men undergoing RT for prostate cancer often have co-existing LUTS. Consideration and evaluation of their LUTS and offer of treatment either medication or surgery could improve urinary symptoms in men undergoing prostate radiotherapy in the short term. Longer term data are still needed to understand the full long-term impact on patient’s symptoms and quality of life. We recommend that patients have formal LUTS assessment pre-RT.

Level of evidence:

Not applicable.

Cost effectiveness of treatment strategies for high risk prostate cancer

BACKGROUND

Patients with high-risk prostate cancer (HRPC) have multiple accepted treatment options. Because there is no overall survival benefit of one option over another, appropriate treatment must consider patient life expectancy, quality of life, and cost.

METHODS

The authors compared quality-adjusted life years (QALYs) and cost effectiveness among treatment options for HRPC using a Markov model with three treatment arms: (1) external-beam radiotherapy (EBRT) delivered with 20 fractions, (2) EBRT with 23 fractions followed by low-dose-rate (LDR) brachytherapy boost, or (3) radical prostatectomy alone. An exploratory analysis considered a simultaneous integrated boost according to the FLAME trial (ClinicalTrials.gov identifier NCT01168479).

RESULTS

Treatment strategies were compared using the incremental cost-effectiveness ratio (ICER). EBRT with LDR brachytherapy boost was a cost-effective strategy (ICER, $20,929 per QALY gained). These results were most sensitive to variations in the biochemical failure rate. However, the results still demonstrated cost effectiveness for the brachytherapy boost paradigm, regardless of any tested parameter ranges. Probabilistic sensitivity analysis demonstrated that EBRT with LDR brachytherapy was favored in 52% of 100,000 Monte Carlo iterations. In an exploratory analysis, EBRT with a simultaneous integrated boost was also a cost-effective strategy, resulting in an ICER of $62,607 per QALY gained; however, it was not cost effective compared with EBRT plus LDR brachytherapy boost.

CONCLUSIONS

EBRT with LDR brachytherapy boost may be a cost-effective treatment strategy compared with EBRT alone and radical prostatectomy for HRPC, demonstrating high-value care. The current analysis suggests that a reduction in biochemical failure alone can result in cost-effective care, despite no change in overall survival.

High Dose “HDR-Like” Prostate SBRT: PSA 10-Year Results From a Mature, Multi-Institutional Clinical Trial

Purpose/Objective(s)

Although ample intermediate-term prostate stereotactic body radiotherapy (SBRT) outcomes have been reported, 10-year results remain relatively sparse.

Materials/Methods

Eighteen institutions enrolled 259 low- and intermediate-risk patients. Median follow-up is 5.5 years, with 66 patients followed ≥ 10 years. This SBRT regimen specifically emulated an existing HDR brachytherapy dose schedule and isodose morphology, prescribed to 38 Gy/4 fractions, delivered daily by robotic SBRT, mandating > 150% dose escalation in the peripheral zone. Androgen deprivation therapy was not allowed, and a hydrogel spacer was not available at that time.

Results

Median pre-SBRT PSA 5.12 ng/mL decreased to 0.1 ng/mL by 3.5 years, with further decrease to a nadir of < 0.1 ng/mL by 7 years, maintained through 10 years. Ten-year freedom from biochemical recurrence measured 100% for low-risk, 84.3% for favorable intermediate risk (FIR), and 68.4% for unfavorable intermediate (UIR) cases. Multivariable analysis revealed that the UIR group bifurcated into two distinct prognostic subgroups. Those so classified by having Gleason score 4 + 3 and/or clinical stage T2 (versus T1b/T1c) had a significantly poorer 10 year freedom from biochemical recurrence rate, 54.8% if either or both factors were present, while UIR patients without these specific factors had a 94.4% 10-year freedom from biochemical recurrence rate. The cumulative incidence of grade 2 GU toxicity modestly increased over time – 16.3% at 5 years increased to 19.2% at 10 years-- while the incidence of grade 3+ GU and GI toxicity remained low and stable to 10 years - 2.6% and 0%, respectively. The grade 2 GI toxicity incidence also remained low and stable to 10 years – 4.1% with no further events after year 5.

Conclusion

This HDR-like SBRT regimen prescribing 38 Gy/4 fractions but delivering much higher intraprostatic doses on a daily basis is safe and effective. This treatment achieves a median PSA nadir of <0.1 ng/mL and provides high long-term disease control rates without ADT except for a subgroup of unfavorable intermediate-risk patients.

Imaging Biomarkers in Prostate Stereotactic Body Radiotherapy: A Review and Clinical Trial Protocol

Advances in imaging have changed prostate radiotherapy through improved biochemical control from focal boost and improved detection of recurrence. These advances are reviewed in the context of prostate stereotactic body radiation therapy (SBRT) and the ARGOS/CLIMBER trial protocol. ARGOS/CLIMBER will evaluate 1) the safety and feasibility of SBRT with focal boost guided by multiparametric MRI (mpMRI) and ¹⁸F-PSMA-1007 PET and 2) imaging and laboratory biomarkers for response to SBRT. To date, response to prostate SBRT is most commonly evaluated using the Phoenix Criteria for biochemical failure. The drawbacks of this approach include lack of lesion identification, a high false-positive rate, and delay in identifying treatment failure. Patients in ARGOS/CLIMBER will receive dynamic ¹⁸F-PSMA-1007 PET and mpMRI prior to SBRT for treatment planning and at 6 and 24 months after SBRT to assess response. Imaging findings will be correlated with prostate-specific antigen (PSA) and biopsy results, with the goal of early, non-invasive, and accurate identification of treatment failure.

Rationale for Utilization of Hydrogel Rectal Spacers in Dose Escalated SBRT for the Treatment of Unfavorable Risk Prostate Cancer

In this review we outline the current evidence for the use of hydrogel rectal spacers in the treatment paradigm for prostate cancer with external beam radiation therapy. We review their development, summarize clinical evidence, risk of adverse events, best practices for placement, treatment planning considerations and finally we outline a framework and rationale for the utilization of rectal spacers when treating unfavorable risk prostate cancer with dose escalated Stereotactic Body Radiation Therapy (SBRT).

Brachytherapy focal dose escalation using ultrasound based tissue characterization by patients with non-metastatic prostate cancer: Five-year results from single-center phase 2 trial

PURPOSE

This prospective trial investigates side effects and efficacy of focal dose escalation with brachytherapy for patients with prostate cancer.

METHODS AND MATERIALS

In the Phase II, monocentric prospective trial 101 patients with low-/intermediate- and high-risk prostate cancer were enrolled between 2011 and 2013. Patients received either PDR-/HDR-brachytherapy alone with 86-90 Gy (EQD2, α/β = 3 Gy) or PDR-/HDR-brachytherapy as boost after external beam radiation therapy up to a total dose of 91-96 Gy (EQD2, α/β = 3 Gy). Taking place brachytherapy all patients received the simultaneous integrated focal boost to the intra-prostatic tumor lesions visible in computer-aided ultrasonography (HistoScanning™) - up to a total dose of 108-119 Gy (EQD2, α/β = 3 Gy). The primary endpoint was toxicity. Secondary endpoints were cumulative freedom from local recurrence, PSA-free survival, distant metastases-free survival, and overall survival. This trial is registered with ClinicalTrials.gov, number NCT01409876.

RESULTS

Median follow-up was 65 months. Late toxicity was generally low with only four patients scoring urinary grade 3 toxicity (4/101, 4%). Occurrence of any grade of late rectal toxicities was very low. We did not register any grade ≥2 of late rectal toxicities. The cumulative 5 years local recurrence rate (LRR) for all patients was 1%. Five years- biochemical disease-free survival estimates according Kaplan-Meier were 98,1% and 81,3% for low-/intermediate-risk and high-risk patients, respectively. Five years metastases-free survival estimates according Kaplan-Meier were 98,0% and 83,3% for all patients, low-/intermediate-risk and high-risk patients, respectively.

CONCLUSIONS

The 5 years-results from this Phase II Trial show that focal dose escalation with computer-aided ultrasonography and brachytherapy for patients with non-metastatic prostate cancer is safe and effective.

A Comparison between Patient- and Physician-Reported Late Radiation Toxicity in Long-Term Prostate Cancer Survivors

Simple Summary

Radiotherapy is widely used as treatment for localized prostate cancer. Due to a high incidence and a good survival after treatment, a large number of prostate cancer survivors are at risk of developing late radiation toxicity. Symptoms may significantly affect quality of life; therefore, the monitoring of toxicities and evaluating their impact are increasingly important matters. Toxicities have always been assessed by physicians, but there is a growing interest in the use of questionnaires to be completed by patients themselves, so-called patient-reported outcome measures. The aim of this study was to compare both outcomes in long-term prostate cancer survivors, and to determine which outcome correlates best with a biological predictor of late radiation toxicity. In symptomatic patients, we found a low agreement; patients assigned greater severity to symptoms than the trial physician assistant did. Neither outcome correlated with the biological predictor. Consideration of both perspectives seems warranted to provide the best care.

Abstract

Patient-reported outcome measures (PROMs) are advocated for the monitoring of toxicity after radiotherapy. However, studies comparing physician- and patient-reported toxicity show low concordance. In this study, we compared physician- and patient-reported toxicity in long-term prostate cancer survivors after radiotherapy, and we determined the correlation with a presumable risk factor for late toxicity: γ-H2AX foci decay ratio (FDR). Patients formerly included in a prospective study were invited to participate in this new study, comprising one questionnaire and one call with a trial physician assistant. Concordance was calculated for seven symptoms. Gamma-H2AX FDRs were determined in ex vivo irradiated lymphocytes in a previous analysis. Associations between FDR and long-term prevalence of toxicity were assessed using univariable logistic regression analyses. The 101 participants had a median follow-up period of 9 years. Outcomes were discordant in 71% of symptomatic patients; in 21%, the physician-assessed toxicity (using CTCAE) was higher, and, in 50%, the patients reported higher toxicity. We did not find a correlation between presence of toxicity at long-term follow-up and FDR. In conclusion, patients assigned greater severity to symptoms than the trial physician assistant did. Consideration of both perspectives may be warranted to provide the best care.

Neural-network dose-prediction for rectal spacer stratification in dose-escalated prostate radiotherapy

Purpose

To develop a knowledge‐based decision‐support system capable of stratifying patients for rectal spacer (RS) insertion based on neural network predicted rectal dose, reducing the need for time‐ and resource‐intensive radiotherapy (RT) planning.

Methods

Forty‐four patients treated for prostate cancer were enrolled into a clinical trial (NCT03238170). Dose‐escalated prostate RT plans were manually created for 30 patients with simulated boost volumes using a conventional treatment planning system (TPS) and used to train a hierarchically dense 3D convolutional neural network to rapidly predict RT dose distributions. The network was used to predict rectal doses for 14 unseen test patients, with associated toxicity risks calculated according to published data. All metrics obtained using the network were compared to conventionally planned values.

Results

The neural network stratified patients with an accuracy of 100% based on optimal rectal dose–volume histogram constraints and 78.6% based on mandatory constraints. The network predicted dose‐derived grade 2 rectal bleeding risk within 95% confidence limits of ‐1.9% to +1.7% of conventional risk estimates (risk range 3.5%–9.9%) and late grade 2 fecal incontinence risk within ‐0.8% to +1.5% (risk range 2.3%–5.7%). Prediction of high‐resolution 3D dose distributions took 0.7 s.

Conclusions

The feasibility of using a neural network to provide rapid decision support for RS insertion prior to RT has been demonstrated, and the potential for time and resource savings highlighted. Directly after target and healthy tissue delineation, the network is able to (i) risk stratify most patients with a high degree of accuracy to prioritize which patients would likely derive greatest benefit from RS insertion and (ii) identify patients close to the stratification threshold who would require conventional planning.

Simultaneous integrated boost (SIB) to dominant intra-prostatic lesions during extreme hypofractionation for prostate cancer: the impact of rectal spacers

Purpose

Boosting dominant intra-prostatic lesions (DILs) has the potential to increase the therapeutic ratio in prostate cancer radiotherapy. In this study, employing 5-fraction stereotactic ablative radiotherapy (SABR) volumetric modulated arc therapy (VMAT) to deliver 40 Gy to the prostate clinical target volume (CTV) while boosting the DIL up to 50 Gy was evaluated for patients before and after rectal spacer insertion.

Materials and methods

24 Computed Tomography (CT) scans of 12 prostate cancer patients with unfavourable intermediate or high risk prostate cancer were employed in this study. At least two treatment plans were generated for each patient to compare pre- and post-spacer insertion plans. Plans were evaluated for target coverage, organs-at-risk doses, and the achievable boost dose level.

Results

The CTV coverage was significantly better in plans with a spacer, V40Gy 98.4% versus 97.0% (p = 0.012). Using spacers significantly reduced rectal dose in all 12 patients in this study. It was possible to boost DIL to 50 Gy to without violating dose constraints in 6 of 12 patients and to 47.5 Gy in 3 patients post-spacer insertion. For 3 patients (25%) it was not possible to boost DIL above 45 Gy even with a spacer in situ. Without a spacer, for 6 patient (50%) clinically acceptable plan were only achieved when the DIL dose was lowered to 45 Gy. In five of these 6 patients the dose limiting structure was the urethra (urethra planning risk volume V45Gy [cc] ≤ 0.1 cc constraint).

Conclusions

Clinically acceptable plans for 5 fraction SABR, 40 Gy to the prostate CTV, with a SIB to DIL (45–50 Gy) were achieved. The boost dose achieved was DIL location dependent and primarily affected by DIL’s proximity to the urethra. Compared to plans before spacer insertion, higher DIL dose were achieved with spacer in situ for 25% of the patients. Moreover, significant reduction in rectal dose and better target coverage were also achieved for all patients with spacers in situ.

A narrative review of MRI acquisition for MR-guided-radiotherapy in prostate cancer

Magnetic resonance guided radiotherapy (MRgRT), enabled by the clinical introduction of the integrated MRI and linear accelerator (MR-LINAC), is a novel technique for prostate cancer (PCa) treatment, promising to further improve clinical outcome and reduce toxicity. The role of prostate MRI has been greatly expanded from the traditional PCa diagnosis to also PCa screening, treatment and surveillance. Diagnostic prostate MRI has been relatively familiar in the community, particularly with the development of Prostate Imaging - Reporting and Data System (PI-RADS). But, on the other hand, the use of MRI in the emerging clinical practice of PCa MRgRT, which is substantially different from that in PCa diagnosis, has been so far sparsely presented in the medical literature. This review attempts to give a comprehensive overview of MRI acquisition techniques currently used in the clinical workflows of PCa MRgRT, from treatment planning to online treatment guidance, in order to promote MRI practice and research for PCa MRgRT. In particular, the major differences in the MRI acquisition of PCa MRgRT from that of diagnostic prostate MRI are demonstrated and explained. Limitations in the current MRI acquisition for PCa MRgRT are analyzed. The future developments of MRI in the PCa MRgRT are also discussed.

Radiation therapy for prostate cancer: What's the best in 2021

Radiotherapy is highly involved in the management of prostate cancer. Its features and potential applications experienced a radical evolution over last decades, as they are associated to the continuous evolution of available technology and current oncological innovations. Some application of radiotherapy like brachytherapy have been recently enriched by innovative features and multidisciplinary dedications. In this report we aim to put some questions regarding the following issues regarding multiple aspects of modern application of radiation oncology: the current application of radiation oncology; the modern role of stereotactic body radiotherapy (SBRT) for both the management of primary lesions and for lymph-nodal recurrence; the management of the oligometastatic presentations; the role of brachytherapy; the aid played by the application of the organ at risk spacer (spacer OAR), fiducial markers, electromagnetic tracking systems and on-line Magnetic Resonance guided radiotherapy (MRgRT), and the role of the new opportunity represented by radiomic analysis.

Positron emission tomography guided dose painting by numbers of lung cancer: Alanine dosimetry in an anthropomorphic phantom

•

DPBN was delivered to a phantom based on the anatomy of a lung cancer patient examined by FDG PET/CT prior to radiotherapy.

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Alanine dosimetry showed that DPBN can be delivered with high accuracy to the tumour in the anthropomorphic phantom.

•

For regions outside the tumour, high correspondence between planned and delivered doses were also found.

•

Positioning errors can lead to large deviations and potentially sub-optimal tumor doses.

Background and purpose

Dose painting by numbers (DPBN) require a high degree of dose modulation to fulfill the image-based voxel wise dose prescription. The aim of this study was to assess the dosimetric accuracy of ¹⁸F-fluoro-2-deoxy-glucose positron emission tomography(¹⁸F-FDG-PET)-based DPBN in an anthropomorphic lung phantom using alanine dosimetry.

Materials and methods

A linear dose prescription based on ¹⁸F-FDG-PET image intensities within the gross tumor volume (GTV) of a lung cancer patient was employed. One DPBN scheme with low dose modulation (Scheme A; minimum/maximum fraction dose to the GTV 2.92/4.26 Gy) and one with a high modulation (Scheme B; 2.81/4.52 Gy) were generated. The plans were transferred to a computed tomograpy (CT) scan of a thorax phantom based on CT images of the patient. Using volumetric modulated arc therapy (VMAT), DPBN was delivered to the phantom with embedded alanine dosimeters. A plan was also delivered to an intentionally misaligned phantom. Absorbed doses at various points in the phantom were measured by alanine dosimetry.

Results

A pointwise comparison between GTV doses from prescription, treatment plan calculation and VMAT delivery showed high correspondence, with a mean and maximum dose difference of <0.1 Gy and 0.3 Gy, respectively. No difference was found in dosimetric accuracy between scheme A and B. The misalignment caused deviations up to 1 Gy between prescription and delivery.

Conclusion

DPBN can be delivered with high accuracy, showing that the treatment may be applied correctly from a dosimetric perspective. Still, misalignment may cause considerable dosimetric erros, indicating the need for patient immobilization and monitoring.

A statistical, voxelised model of prostate cancer for biologically optimised radiotherapy

Background and purpose

Radiation therapy (RT) is commonly indicated for treatment of prostate cancer (PC). Biologicallyoptimised RT for PC may improve disease-free survival. This requires accurate spatial localisation and characterisation of tumour lesions. We aimed to generate a statistical, voxelised biological model to complement in vivomultiparametric MRI data to facilitate biologically-optimised RT.

Material and methods

Ex vivo prostate MRI and histopathological imaging were acquired for 63 PC patients. These data were co-registered to derive three-dimensional distributions of graded tumour lesions and cell density. Novel registration processes were used to map these data to a common reference geometry. Voxelised statistical models of tumour probability and cell density were generated to create the PC biological atlas. Cell density models were analysed using the Kullback–Leibler divergence to compare normal vs. lognormal approximations to empirical data.

Results

A reference geometry was constructed using ex vivo MRI space, patient data were deformably registered using a novel anatomy-guided process. Substructure correspondence was maintained using peripheral zone definitions to address spatial variability in prostate anatomy between patients. Three distinct approaches to interpolation were designed to map contours, tumour annotations and cell density maps from histology into ex vivo MRI space. Analysis suggests a log-normal model provides a more consistent representation of cell density when compared to a linear-normal model.

Conclusion

A biological model has been created that combines spatial distributions of tumour characteristics from a population into three-dimensional, voxelised, statistical models. This tool will be used to aid the development of biologically-optimised RT for PC patients.

Urethral and bladder dose-effect relations for late genitourinary toxicity following external beam radiotherapy for prostate cancer in the FLAME trial

PURPOSE

or objectives The FLAME trial (NCT01168479) showed that by adding a focal boost to conventional fractionated EBRT in the treatment of localized prostate cancer, the five-year biochemical disease-free survival increased, without significantly increasing toxicity. The aim of the present study was to investigate the association between radiation dose to the bladder and urethra and genitourinary (GU) toxicity grade ≥2 in the entire cohort.

MATERIAL AND METHODS

The dose-effect relations of the urethra and bladder dose, separately, and GU toxicity grade ≥2 (CTCAE 3.0) up to five years after treatment were assessed. A mixed model analysis for repeated measurements was used, adjusting for age, diabetes mellitus, T-stage, baseline GU toxicity grade ≥1 and institute. Additionally, the association between the dose and separate GU toxicity subdomains were investigated.

RESULTS

Dose-effect relations were observed for the dose (Gy) to the bladder D2cm³ and urethra D0.1cm³, with adjusted odds ratios of 1.14 (95% CI 1.12-1.16, p<0.0001) and 1.12 (95% CI 1.11-1.14, p<0.0001), respectively. Additionally, associations between the dose to the urethra and bladder and the subdomains urinary frequency, urinary retention and urinary incontinence were observed.

CONCLUSION

Further increasing the dose to the bladder and urethra will result in a significant increase in GU toxicity following EBRT. Focal boost treatment plans should incorporate a urethral dose-constraint. Further treatment optimization to increase the focal boost dose without increasing the dose to the urethra and other organs at risk should be a focus for future research, as we have shown that a focal boost is beneficial in the treatment of prostate cancer.

Patterns of Failure Following External Beam Radiotherapy With or Without an Additional Focal Boost in the Randomized Controlled FLAME Trial for Localized Prostate Cancer

BACKGROUND

Focal dose escalation in external beam radiotherapy (EBRT) showed an increase in 5-yr biochemical disease-free survival in the Focal Lesion Ablative Microboost in Prostate Cancer (FLAME) trial.

OBJECTIVE

To analyze the effect of a focal boost to intraprostatic lesions on local failure-free survival (LFS) and regional + distant metastasis-free survival (rdMFS).

DESIGN, SETTING, AND PARTICIPANTS

Patients with intermediate- or high-risk localized prostate cancer were included in FLAME, a phase 3, multicenter, randomized controlled trial.

INTERVENTION

Standard treatment of 77 Gy to the entire prostate in 35 fractions was compared to an additional boost to the macroscopic tumor of up to 95 Gy during EBRT.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

LFS and rdMFS, measured via any type of imaging, were compared between the treatment arms using Kaplan-Meier and Cox regression analyses. Dose-response curves were created for local failure (LF) and regional + distant metastatic failure (rdMF) using logistic regression.

RESULTS AND LIMITATIONS

A total of 571 patients were included in the FLAME trial. Over median follow-up of 72 mo (interquartile range 58-86), focal boosting decreased LF (hazard ratio [HR] 0.33, 95% confidence interval [CI] 0.14-0.78) and rdMF (HR 0.58, 95% CI 0.35-0.93). Dose-response curves showed that a greater dose to the tumor resulted in lower LF and rdMF rates.

CONCLUSIONS

A clear dose-response relation for LF and rdMF was observed, suggesting that adequate focal dose escalation to intraprostatic lesions prevents undertreatment of the primary tumor, resulting in an improvement rdMF.

PATIENT SUMMARY

Radiotherapy is a treatment option for high-risk prostate cancer. The FLAME trial has shown that a high dose specifically targeted at the tumor within the prostate will result in better disease outcome, with less likelihood of regional and distant disease spread. The FLAME trial is registered on ClinicalTrials.gov as NCT01168479.

Dosimetric Uncertainties in Dominant Intraprostatic Lesion Simultaneous Boost Using Intensity Modulated Proton Therapy

Purpose

While intensity modulated proton therapy can deliver simultaneous integrated boost (SIB) to the dominant intraprostatic lesion (DIL) with high precision, it is sensitive to anatomic changes. We investigated the dosimetric effects from these changes based on pretreatment cone-beam computed tomographic (CBCT) images and identified the most important factors using a multilayer perceptron neural network (MLPNN).

Methods and Materials

DILs were contoured based on coregistered multiparametric magnetic resonance images for 25 previously treated prostate cancer patients. SIB plans were created with (1) prostate clinical target volume − V70 Gy = 98%; (2) DIL − V98 Gy > 95%; and (3) all organs at risk (OARs)"?> within clinical constraints. SIB plans were applied to daily CBCT-based deformed planning computed tomography (CT)"?>. DIL − V98 Gy, bladder/rectum maximum dose (Dmax) and volume changes, femur shifts, and the distance from DIL to organs at riskOARs"?> in both planning computed tomogramsCT"?> and CBCT were calculated. Wilcoxon signed-ranks tests were used to compare the changes. MLPNNs were used to model the change in ΔDIL − V98 Gy > 10% and bladder/rectum Dmax > 80 Gy, and the relative importance factors for the model were provided. The performances of the models were evaluated with receiver operating characteristic curves.

Results

Comparing initial plan to the average from evaluation plans, respectively, DIL − V98 Gy was 89.3% ± 19.9% versus 86.2% ± 21.3% (P = .151); bladder Dmax 71.9 ± 0.6 Gy versus 74.5 ± 2.9 Gy (P < .001); and rectum Dmax 70.1 ± 2.4 Gy versus 74.9 ± 9.1Gy (P = .007). Bladder and rectal volumes were 99.6% ± 39.5% and 112.8% ± 27.2%, respectively, of their initial volume. The femur shift was 3.16 ± 2.52 mm. In the modeling of ΔDIL V98 Gy > 10%, DIL to rectum distance changes, DIL to bladder distance changes, and rectum volume changes ratio are the 3 most important factors. The areas under the receiver operating characteristic curves were 0.89, 1.00, and 0.99 for the modeling of ΔDIL − V98 Gy > 10%, and bladder and rectum Dmax > 80 Gy, respectively.

Conclusions

Dosimetric changes in DIL SIB with intensity modulated proton therapy can be modeled and classified based on anatomic changes on pretreatment images by an MLPNN.

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.

Short-duration dynamic [18F]DCFPyL PET and CT perfusion imaging to localize dominant intraprostatic lesions in prostate cancer: validation against digital histopathology and comparison to [18F]DCFPyL PET/MR at 120 minutes

Purpose

Localized prostate cancer (PCa) in patients is characterized by a dominant focus in the gland (dominant intraprostatic lesion, DIL). Accurate DIL identification may enable more accurate diagnosis and therapy through more precise targeting of biopsy, radiotherapy and focal ablative therapies. The goal of this study is to validate the performance of [¹⁸F]DCFPyL PET and CT perfusion (CTP) for detecting and localizing DIL against digital histopathological images.

Methods

Multi-modality image sets: in vivo T2-weighted (T2w)-MRI, 22-min dynamic [¹⁸F]DCFPyL PET/CT, CTP, and 2-h post-injection PET/MR were acquired in patients prior to radical prostatectomy. The explanted gland with implanted fiducial markers was imaged with T2w-MRI. All images were co-registered to the pathologist-annotated digital images of whole-mount mid-gland histology sections using fiducial markers and anatomical landmarks. Regions of interest encompassing DIL and non-DIL tissue were drawn on the digital histopathological images and superimposed on PET and CTP parametric maps. Logistic regression with backward elimination of parameters was used to select the most sensitive parameter set to distinguish DIL from non-DIL voxels. Leave-one-patient-out cross-validation was performed to determine diagnostic performance.

Results

[¹⁸F]DCFPyL PET and CTP parametric maps of 15 patients were analyzed. SUV_Late and a model combining K_i and k₄ of [¹⁸F]DCFPyL achieved the most accurate performance distinguishing DIL from non-DIL voxels. Both detection models achieved an AUC of 0.90 and an error rate of < 10%. Compared to digital histopathology, the detected DILs had a mean dice similarity coefficient of 0.8 for the K_i and k₄ model and 0.7 for SUV_Late.

Conclusions

We have validated using co-registered digital histopathological images that parameters from kinetic analysis of 22-min dynamic [¹⁸F]DCFPyL PET can accurately localize DILs in PCa for targeting of biopsy, radiotherapy, and focal ablative therapies. Short-duration dynamic [¹⁸F]DCFPyL PET was not inferior to SUV_Late in this diagnostic task.

Clinical trial registration number: NCT04009174 (ClinicalTrials.gov).

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.

Proton vs. photon radiotherapy for MR-guided dose escalation of intraprostatic lesions

BACKGROUND

Dose escalation has been associated with improved biochemical control for prostate cancer. Focusing the high dose on the MRI-defined intraprostatic lesions (IL) could spare the surrounding organs at risk and hence allow further escalation. We compare treatment efficacy between state-of-the-art focally-boosted proton and photon-based radiotherapy, and investigate possible predictive guidelines regarding individualized treatment prescriptions.

MATERIAL AND METHODS

Ten prostate cancer patients with well-defined ILs were selected. Multiparametric MRI was used to delineate ILs, which were transferred to the planning CT via image registration. Pencil beam scanning proton therapy and volumetric modulated arc therapy treatment plans, were created for each patient. Each modality featured 6 plans: (1) moderately hypofractionated dose: 70 Gy to the prostate in 28 fractions, (2)-(6) plan 1 plus additional simultaneous-integrated-boost to ILs to 75.6, 81.2, 86.6, 98 and 112 Gy in 28 fractions. Equivalent dose to 2 Gy-per-fraction (EqD2) was used to calculate tumor control (TCP) and normal tissue complication probabilities (NTCP) for ILs and organs-at-risk.

RESULTS

For both modalities, the maximum necessary dose to achieve TCP > 99% was 98 Gy for very high-risk ILs. For lower risk ILs lower doses were sufficient. NTCP was <25% and 35% for protons and photons at the maximum dose escalation, respectively. For the cases and beam characteristics considered, proton therapy was dosimetrically superior when IL was >4 cc or located <2.5 mm from the rectum.

CONCLUSION

This work demonstrated the potential role for proton therapy in the setting of prostate focal dose escalation. We propose that anatomical characteristic could be used as criteria to identify patients who would benefit from proton treatment.

Value of 18F-fluorocholine PET/CT in predicting response to radical radiotherapy in patients with localized prostate cancer

PURPOSE

This study aims to establish whether metabolic parameters obtainable from FCH PET/CT can predict long-term response to radical radiotherapy (rRT) in patients with localized prostate cancer (PCa).

METHODS

Drawing on a single-center database, we retrospectively reviewed the pre-treatment FCH PET/CT scans of 50 patients who underwent rRT between 2012 and 2017. Patients were enrolled if they had a follow-up of at least 3 years after rRT. Various metabolic parameters were considered for each PET/CT, including FCH multifocality. rRT was administered to all patients for a total equivalent dose of 76-80 Gy, using a standard or hypofractionated schedule. Patients were classified as disease-free (DF) if their PSA levels after rRT rose by <2 ng/mL vis-à-vis their PSA nadir, or as not disease free (NDF) if their PSA levels rose by more than 2 ng/ml.

RESULTS

A multifocal FCH uptake in the prostate gland was identified in 27 patients (54%). At 3-year follow-up, 37 patients (74%) were judged DF, and 13 (26%) were NDF. The SUVmax and SUVmean, and the sum of the two values in all FCH foci in the prostate gland were significantly higher for NDF patients than for DF patients (all p < 0.005). The sum of the TLCKA levels in all FCH foci was likewise significantly higher in patients who were NDF than in those found DF (median 54.5 vs. 29.4; p < 0.05). At univariate analysis, the most of PET-metrics and Gleason Score were predictors of biochemical relapse after 3-year follow-up (all p < 0.05).

CONCLUSION

Higher SUVs seems predict a worse outcome for patients with multifocal intraprostatic lesions who are candidates for rRT.

Gamma-H2AX Foci Decay Ratio as a Stronger Predictive Factor of Late Radiation Toxicity Than Dose-Volume Parameters in a Prospective Cohort of Prostate Cancer Patients

PURPOSE

Late radiation toxicity is a major dose-limiting factor in curative cancer radiation therapy. Previous studies identified several risk factors for late radiation toxicity, including both dose-volume factors and genetic predisposition. Herein, we investigated the contribution of genetic predisposition, particularly compared with dose-volume factors, to the risk of late radiation toxicity in patients treated with highly conformal radiation therapy.

METHODS AND MATERIALS

We included 179 patients with prostate cancer who underwent treatment with curative external beam radiation therapy between 2009 and 2013. Toxicity was graded according to the Common Terminology Criteria for Adverse Events version 4.0. Transcriptional responsiveness of homologous recombination repair genes and γ-H2AX foci decay ratios (FDRs) were determined in ex vivo irradiated lymphocytes in a previous analysis. Dose-volume parameters were retrieved by delineating the organs at risk (OARs) on CT planning images. Associations between risk factors and grade ≥2 urinary and bowel late radiation toxicities were assessed using univariable and multivariable logistic regression analyses. The analyses were performed using the highest toxicity grade recorded during the follow-up per patient.

RESULTS

The median follow-up period was 31 months. One hundred and one patients (56%) developed grade ≥2 late radiation toxicity. Cumulative rates for urinary and bowel grade ≥2 late toxicities were 46% and 17%, respectively. In the multivariable analysis, factors significantly associated with grade ≥2 late toxicity were transurethral resection of the prostate (P = .013), γ-H2AX FDR <3.41 (P = .008), and rectum V70 >11.52% (P = .017).

CONCLUSIONS

Our results suggest that impaired DNA double-strand break repair in lymphocytes, as quantified by γ-H2AX FDR, is the most critical determining factor of late radiation toxicity. The limited influence of dose-volume parameters could be due to the use of increasingly conformal techniques, leading to improved dose-volume parameters of the organs at risk.

68Ga-PSMA-11 PET, 18F-PSMA-1007 PET, and MRI for Gross Tumor Volume Delineation in Primary Prostate Cancer: Intermodality and Intertracer Variability

PURPOSE

To assess the intermodality and intertracer variability of gallium-68 (⁶⁸Ga)- or fluorine-18 (¹⁸F)-labeled prostate-specific membrane antigen (PSMA) positron emission tomography (PET) and biparametric magnetic resonance imaging (bpMRI)-based gross tumor volume (GTV) delineation for focal boosting in primary prostate cancer.

METHODS

Nineteen prospectively enrolled patients with prostate cancer underwent a PSMA PET/MRI scan, divided into a 1:1 ratio between ⁶⁸Ga-PSMA-11 and ¹⁸F-PSMA-1007, before radical prostatectomy (IWT140193). Four delineation teams performed manual contouring of the GTV based on bpMRI and PSMA PET imaging, separately. Index lesion coverage (overlap%) and interobserver variability were assessed. Furthermore, the distribution of the voxelwise normalized standardized uptake values (SUV%) was determined for the majority-voted (>50%) GTV (GTV^majority) and whole prostate gland to investigate intertracer variability. The median patientwise SUV% contrast ratio (SUV%-CR, calculated as median GTV^majority SUV% / median prostate gland without GTV^majority SUV%) was calculated according to the tracer used.

RESULTS

A significant difference in overlap% favoring PSMA PET compared with bpMRI was found in the ¹⁸F subgroup (median, 63.0% vs 53.1%; P = .004) but was not present in the ⁶⁸Ga subgroup (32.5% vs 50.6%; P = .100). Regarding interobserver variability, measured Sørensen-Dice coefficients (0.58 vs 0.72) and calculated mean distances to agreement (2.44 mm vs 1.22 mm) were statistically significantly lower and higher, respectively, for the ¹⁸F cohort compared with the ⁶⁸Ga cohort. For the bpMRI-based delineations, the median Sørensen-Dice coefficient and mean distance to agreement were 0.63 and 1.76 mm, respectively. Median patientwise SUV%-CRs of 1.8 (interquartile range [IQR], 1.6-2.7) for ¹⁸F-PSMA and 3.3 (IQR, 2.7-5.9) for ⁶⁸Ga-PSMA PET images were found.

CONCLUSIONS

Both MRI and PSMA PET provided consistent intraprostatic GTV lesion detection. However, the PSMA tracer seems to have a major influence on the contour characteristics, owing to an apparent difference in SUV% distribution in the prostate gland.

Pilot study comparing dominant intraprostatic lesion volume using Ga-68 prostate-specific membrane antigen PET-computed tomography and multiparametric MRI

PURPOSE

The standard imaging used for delineation of dominant intraprostatic lesion (DIL) is multiparametric MRI (mpMRI). The use of biologic imaging such as Ga-68 prostate-specific membrane antigen (PSMA) PET-computed tomography (PET-CT) for this purpose is being explored in view of increased sensitivity of this modality and the associated ease of delineation.

MATERIALS AND METHODS

The primary objective of the study was to compare the autogenerated volumes of the DIL in Ga-68 PSMA PET-CT with the standard volume delineated in mpMRI. Twenty patients with biopsy-proven untreated prostatic adenocarcinoma were included. Multiple percentages of the maximum standardized uptake value (%SUVmax) were used to autogenerate DIL volumes in Ga-68 PSMA PET-CT and these volumes were numerically matched with the consensus DIL volume in mpMRI. PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) were also calculated for each lesion.

RESULTS

Median volume of DIL in mpMRI was 4 cm (interquartile range, IQR = 2.5-7.6 cm). The IQR for interobserver variability was 0.5-2.5 cm. Median SUVmax of the DIL was 14.1 (IQR = 10.2-22.3). Median %SUVmax corresponding to mpMRI volume was 41% of SUVmax (IQR = 34-55%). There was a strong negative correlation between MRI volume and %SUVmax (r = -0.829, P < 0.001). There was a significant correlation between TL-PSMA and prostate-specific antigen (r = 0.609, P = 0.004).

CONCLUSIONS

The median DIL volume was 4 cm and median %SUVmax corresponding to MR volume of DIL was 41%. A strong inverse relationship is found between mpMRI-defined DIL volume and the %SUVmax which generates similar volume in Ga-68 PSMA PET-CT. TL-PSMA could be a quantitative biomarker for tumor load and prognosis.

Automated treatment planning of prostate stereotactic body radiotherapy with focal boosting on a fast-rotating O-ring linac: Plan quality comparison with C-arm linacs

Purpose

The integration of auto‐segmentation and automated treatment planning methods on a fast‐rotating O‐ring linac may improve the time efficiency of online adaptive radiotherapy workflows. This study investigates whether automated treatment planning of prostate SBRT with focal boosting on the O‐ring linac could generate plans that are of similar quality as those obtained through manual planning on clinical C‐arm linacs.

Methods

For 20 men with prostate cancer, reference treatment plans were generated on a TrueBeam STx C‐arm linac with HD120 MLC and a TrueBeam C‐arm linac with Millennium 120 MLC using 6 MV flattened dual arc VMAT. Manual planning on the Halcyon fast‐rotating O‐ring linac was performed using 6 MV FFF dual arc VMAT (HA2‐DL10) and triple arc VMAT (HA3‐DL10) to investigate the performance of the dual‐layer MLC system. Automated planning was performed for triple arc VMAT on the Halcyon linac (ET3‐DL10) using the automated planning algorithms of Ethos Treatment Planning. The prescribed dose was 35 Gy to the prostate and 30 Gy to the seminal vesicles in five fractions. The iso‐toxic focal boost to the intraprostatic tumor nodule(s) was aimed to receive up to 50 Gy. Plan deliverability was verified using portal image dosimetry measurements.

Results

Compared to the C‐arm linacs, ET3‐DL10 shows increased seminal vesicles PTV coverage (D_99%) and reduced high‐dose spillage to the bladder (V_37Gy) and urethra (D_0.035cc) but this came at the cost of increased high‐dose spillage to the rectum (V_38Gy) and a higher intermediate dose spillage (D2cm). No statistically significant differences were found when benchmarking HA2‐DL10 and HA3‐DL10 with the C‐arm linacs. All plans passed the patient‐specific QA tolerance limit.

Conclusions

Automated planning of prostate SBRT with focal boosting on the fast‐rotating O‐ring linac is feasible and achieves similar plan quality as those obtained on clinical C‐arm linacs using manual planning.

Contemporary radiotherapy: present and future

Oncology care is increasingly a multidisciplinary endeavour, and radiation therapy continues to have a key role across the disease spectrum in nearly every cancer. However, the field of radiation oncology is still one of the most poorly understood of the cancer disciplines. In this Review, we attempt to summarise and contextualise developments within the field of radiation oncology for the non-radiation oncologist. We discuss advancements in treatment technologies and imaging, followed by an overview of the interplay with advancements in systemic therapy and surgical techniques. Finally, we review new frontiers in radiation oncology, including advances within the metastatic disease continuum, reirradiation, and emerging types of radiation therapy.

Stereotactic pelvic radiotherapy with HDR boost for dose escalation in intermediate and high-risk prostate cancer (SPARE): Efficacy, toxicity and quality of life

BACKGROUND

The ASCO/CCO guidelines recommend brachytherapy (BT) boost for eligible intermediate- (IR) or high-risk (HR) prostate cancer (PCa) patients. We present efficacy, toxicity and quality-of-life (QoL) outcomes in patients treated on a prospective protocol of MRI dose-painted high-dose-rate BT boost (HDR-BT) followed by 5-fraction pelvic radiotherapy (RT) and 6-18 months of androgen deprivation therapy (ADT).

METHODS

In this phase I/II study, IR or HR PCa patients received HDR-BT 15 Gy × 1 to prostate and up to 22.5 Gy to MRI nodule, followed by 25 Gy in 5, weekly fractions to pelvis. Toxicity was assessed using CTCAEv3.0, and QoL was captured using EPIC questionnaire. Biochemical failure (BF; nadir + 2.0), and proportion of patients with PSA < 0.4 ng/ml at 4-years (4yPSARR) were evaluated. A minimally clinically important change (MCIC) was recorded if QoL score decreased >0.5 standard deviation of baseline scores.

RESULTS

Thirty-one patients (NCCN 3.2% favorable IR, 48.4% unfavorable IR and 48.4% HR) completed treatment with a median follow-up of 61 months. Median D90 to MR nodule was 19.0 Gy and median prostate V100% was 96.5%. The actuarial 5-year BF rate was 18.2%, and the 4yPSARR was 71%. One patient died of PCa. Acute grade 2 and 3 toxicities: GU: 50%, 7%, and GI: 3%, none, respectively. Late grade 2 and 3 toxicities were: GU: 23%, 3%, and GI: 7%, none, respectively. Proportion of patients with MCIC was 7.7% for urinary domain and 32.0% for bowel domain.

CONCLUSIONS

This novel treatment protocol incorporating MRI dose-painted HDR-BT boost and 5-fraction pelvic RT with ADT is well tolerated.

Reproducibility and accuracy of a target motion mitigation technique for dose-escalated prostate stereotactic body radiotherapy

BACKGROUND AND PURPOSE

To quantitate the accuracy, reproducibility and prostate motion mitigation efficacy rendered by a target immobilization method used in an intermediate-risk prostate cancer dose-escalated 5×9Gy SBRT study.

MATERIAL AND METHODS

An air-inflated (150 cm³) endorectal balloon and Foley catheter with three electromagnetic beacon transponders (EBT) were used to mitigate and track intra-fractional target motion. A 2 mm margin was used for PTV expansion, reduced to 0 mm at the interface with critical OARs. EBT-detected ≥ 2 mm/5 s motions mandated treatment interruption and target realignment prior to completion of planned dose delivery. Geometrical uncertainties were measured with an in-house ESAPI script.

RESULTS

Quantitative data were obtained in 886 sessions from 189 patients. Mean PTV dose was 45.8 ± 0.4 Gy (D95 = 40.5 ± 0.4 Gy). A mean of 3.7 ± 1.7 CBCTs were acquired to reach reference position. Mean treatment time was 19.5 ± 12 min, 14.1 ± 11 and 5.4 ± 5.9 min for preparation and treatment delivery, respectively. Target motion of 0, 1-2 and >2 mm/10 min were observed in 59%, 30% and 11% of sessions, respectively. Temporary beam-on hold occurred in 7.4% of sessions, while in 6% a new reference CBCT was required to correct deviations. Hence, all sessions were completed with application of the planned dose. Treatment preparation time > 15 min was significantly associated with the need of a second reference CBCT. Overall systematic and random geometrical errors were in the order of 1 mm.

CONCLUSION

The prostate immobilization technique explored here affords excellent accuracy and reproducibility, enabling normal tissue dose sculpting with tight PTV margins.

First experimental evaluation of multi-target multileaf collimator tracking during volumetric modulated arc therapy for locally advanced prostate cancer

PURPOSE

Locally advanced and oligometastatic cancer patients require radiotherapy treatment to multiple independently moving targets. There is no existing commercial solution that can simultaneously track and treat multiple targets. This study experimentally implemented and evaluated a real-time multi-target tracking system for locally advanced prostate cancer.

METHODS

Real-time multi-target MLC tracking was integrated with 3D x-ray image guidance on a standard linac. Three locally advanced prostate cancer treatment plans were delivered to a static lymph node phantom and dynamic prostate phantom that reproduced three prostate trajectories. Treatments were delivered using multi-target MLC tracking, single-target MLC tracking, and no tracking. Doses were measured using Gafchromic film placed in the dynamic and static phantoms. Dosimetric error was quantified by the 2%/2 mm gamma failure rate. Geometric error was evaluated as the misalignment between target and aperture positions. The multi-target tracking system latency was measured.

RESULTS

The mean (range) gamma failure rates for the prostate and lymph nodes, were 18.6% (5.2%, 28.5%) and 7.5% (1.1%, 13.7%) with multi-target tracking, 7.9% (0.7%, 15.4%) and 37.8% (18.0%, 57.9%) with single-target tracking, and 38.1% (0.6%, 75.3%) and 37.2% (29%, 45.3%) without tracking. Multi-target tracking had the lowest geometric error with means and standard deviations within 0.2 ± 1.5 for the prostate and 0.0 ± 0.3 mm for the lymph nodes. The latency was 730 ± 20 ms.

CONCLUSION

This study presented the first experimental implementation of multi-target tracking to independently track prostate and lymph node displacement during VMAT. Multi-target tracking reduced dosimetric and geometric errors compared to single-target tracking and no tracking.

IPEM Topical Report: an international IPEM survey of MRI use for external beam radiotherapy treatment planning

Introduction/Background. Despite growing interest in magnetic resonance imaging (MRI), integration in external beam radiotherapy (EBRT) treatment planning uptake varies globally. In order to understand the current international landscape of MRI in EBRT a survey has been performed in 11 countries. This work reports on differences and common themes identified.Methods. A multi-disciplinary Institute of Physics and Engineering in Medicine working party modified a survey previously used in the UK to understand current practice using MRI for EBRT treatment planning, investigate how MRI is currently used and managed as well as identify knowledge gaps. It was distributed electronically within 11 countries: Australia, Belgium, Denmark, Finland, France, Italy, the Netherlands, New Zealand, Sweden, the UK and the USA.Results. The survey response rate within the USA was <1% and hence these results omitted from the analysis. In the other 10 countries the survey had a median response rate of 77% per country. Direct MRI access, defined as either having a dedicated MRI scanner for radiotherapy (RT) or access to a radiology MRI scanner, varied between countries. France, Italy and the UK reported the lowest direct MRI access rates and all other countries reported direct access in ≥82% of centres. Whilst ≥83% of centres in Denmark and Sweden reported having dedicated MRI scanners for EBRT, all other countries reported ≤29%. Anatomical sites receiving MRI for EBRT varied between countries with brain, prostate, head and neck being most common. Commissioning and QA of image registration and MRI scanners varied greatly, as did MRI sequences performed, staffing models and training given to different staff groups. The lack of financial reimbursement for MR was a consistent barrier for MRI implementation for RT for all countries and MR access was a reported important barrier for all countries except Sweden and Denmark.Conclusion. No country has a comprehensive approach for MR in EBRT adoption and financial barriers are present worldwide. Variations between countries in practice, equipment, staffing models, training, QA and MRI sequences have been identified, and are likely to be due to differences in funding as well as a lack of consensus or guidelines in the literature. Access to dedicated MR for EBRT is limited in all but Sweden and Denmark, but in all countries there are financial challenges with ongoing per patient costs. Despite these challenges, significant interest exists in increasing MR guided EBRT planning over the next 5 years.

[Modern radiation therapy planning and image-guided radiotherapy using the example of prostate cancer]

CLINICAL/METHODICAL ISSUE

Optimizing radiotherapy demands precise delineation of the target structure, not only before but also during the course of radiotherapy.

STANDARD RADIOLOGICAL METHODS

For many years, planning of external radiation treatment planning has been based on computer tomography data.

METHODOLOGICAL INNOVATIONS

With the advent of image-guided radiotherapy (IGRT), magnetic resonance imaging (MRI) and functional hybrid imaging are increasingly being integrated into radiation treatment planning. The development of the MR-linac can be seen as an innovation.

PERFORMANCE

The integration of MRI and hybrid imaging (positron emission tomography [PET]/CT, PET/MRI) in the treatment planning process enables more precise treatment planning due to the better morphological and functional information. The integration of MRI data on the MR-linac in daily position control enables adaptation of the irradiation plan to the current conditions.

ACHIEVEMENTS

Technical innovation such as the MR-linac as well as increasing use of hybrid imaging contribute to the objective of further individualization within (radio)oncology.

PRACTICAL RECOMMENDATIONS

Using the example of prostate cancer, the application of prostate-specific membrane antigen (PSMA) ligands and hybrid imaging offers great potential for individualized strategic treatment decisions. The MR-linac appears to be particularly suitable for radiation therapy of prostate cancer. Special attention must be paid to the technical aspects of positioning and data acquisition for the purpose of radiation treatment planning.

Predictors for post-treatment biopsy outcomes after prostate stereotactic body radiotherapy

PURPOSE

To investigate predictors associated with post-treatment biopsy outcomes after stereotactic body radiotherapy (SBRT) for localized prostate cancer.

MATERIALS AND METHODS

257 patients treated with prostate SBRT to dose levels of 32.5 Gy to >40 Gy in 5-6 fractions underwent a post-treatment biopsy performed approximately two years after treatment to evaluate local control status. 73 had% intermediate-risk disease (n = 187) and the remaining 17% (n = 43) and 10% (n = 27) had low-risk and high-risk disease, respectively.

RESULTS

The incidence of positive, negative, and treatment-effect post-treatment biopsies were 15.6%, 57.6%, and 26.8%, respectively. The incidence of a positive biopsy according to dose was 37.5% (n = 9/24), 21.4% (n = 6/28), 19.4% (n = 6/31), and 10.9% (n = 19/174) for 32.5 Gy, 35 Gy, 37.5 Gy, and >40 Gy, respectively. In a multivariable model, patients treated with SBRT doses of <40 Gy and those with unfavorable-intermediate-risk or high-risk disease had higher likelihood of a positive post-treatment biopsy. A positive post-SBRT biopsy was associated with a significantly higher likelihood of subsequent PSA relapse at five years (Positive biopsy: 57%, 95% CI: 29-77% compared to negative biopsy: 7%, 95% CI: 3-14%; p < 0.001).

CONCLUSION

Based on two-year post-SBRT biopsies, excellent tumor control was achieved when dose levels of 40 Gy or higher were used. Standard SBRT dose levels of 35-37.5 Gy were associated with a higher likelihood of a positive post-treatment biopsy. Two-year positive post-treatment biopsies pre-dated the development of PSA failure in the majority of patients.

Robust treatment planning of dose painting for prostate cancer based on ADC-to-Gleason score mappings - what is the potential to increase the tumor control probability?

BACKGROUND AND PURPOSE

The aim of this study was to evaluate the potential to increase the tumor control probability (TCP) with 'dose painting by numbers' (DPBN) plans optimized in a treatment planning system (TPS) compared to uniform dose plans. The DPBN optimization was based on our earlier published formalism for prostate cancer that is driven by dose-responses of Gleason scores mapped from apparent diffusion coefficients (ADC).

MATERIAL AND METHODS

For 17 included patients, a set of DPBN plans were optimized in a TPS by maximizing the TCP for an equal average dose to the prostate volume (CTVT) as for a conventional uniform dose treatment. For the plan optimizations we applied different photon energies, different precisions for the ADC-to-Gleason mappings, and different CTVT positioning uncertainties. The TCP increasing potential was evaluated by the DPBN efficiency, defined as the ratio of TCP increases for DPBN plans by TCP increases for ideal DPBN prescriptions (optimized without considering radiation transport phenomena, uncertainties of the CTVT positioning, and uncertainties of the ADC-to-Gleason mapping).

RESULTS

The median DPBN efficiency for the most conservative planning scenario optimized with a low precision ADC-to-Gleason mapping, and a positioning uncertainty of 0.6 cm was 10%, meaning that more than half of the patients had a TCP gain of at least 10% of the TCP for an ideal DPBN prescription. By increasing the precision of the ADC-to-Gleason mapping, and decreasing the positioning uncertainty the median DPBN efficiency increased by up to 40%.

CONCLUSIONS

TCP increases with DPBN plans optimized in a TPS were found more likely with a high precision mapping of image data into dose-responses and a high certainty of the tumor positioning. These findings motivate further development to ensure precise mappings of image data into dose-responses and to ensure a high spatial certainty of the tumor positioning when implementing DPBN clinically.

Focal Boost to the Intraprostatic Tumor in External Beam Radiotherapy for Patients With Localized Prostate Cancer: Results From the FLAME Randomized Phase III Trial

PURPOSE

This study investigates whether focal boosting of the macroscopic visible tumor with external beam radiotherapy increases biochemical disease-free survival (bDFS) in patients with localized prostate cancer.

PATIENTS AND METHODS

In the phase III, multicenter, randomized controlled Focal Lesion Ablative Microboost in Prostate Cancer trial, 571 patients with intermediate- and high-risk prostate cancer were enrolled between 2009 and 2015. Patients assigned to standard treatment received 77 Gy (fractions of 2.2 Gy) to the entire prostate. The focal boost arm received an additional simultaneous integrated focal boost up to 95 Gy (fractions up to 2.7 Gy) to the intraprostatic lesion visible on multiparametric magnetic resonance imaging. Organ at risk constraints were prioritized over the focal boost dose. The primary end point was 5-year bDFS. Secondary end points were disease-free survival (DFS), distant metastases-free survival, prostate cancer-specific survival, overall survival, toxicity, and health-related quality of life.

RESULTS

Median follow-up was 72 months. Biochemical DFS was significantly higher in the focal boost compared with the standard arm (hazard ratio 0.45, 95% CI, 0.28 to 0.71, P < .001). At 5-year follow-up bDFS was 92% and 85%, respectively. We did not observe differences in prostate cancer-specific survival (P = .49) and overall survival (P = .50). The cumulative incidence of late genitourinary and GI toxicity grade ≥ 2 was 23% and 12% in the standard arm versus 28% and 13% in the focal boost arm, respectively. Both for late toxicity as health-related quality of life, differences were small and not statistically significant.

CONCLUSION

The addition of a focal boost to the intraprostatic lesion improved bDFS for patients with localized intermediate- and high-risk prostate cancer without impacting toxicity and quality of life. The Focal Lesion Ablative Microboost in Prostate Cancer study shows that a high focal boost strategy to improve tumor control while respecting organ at risk dose constraints is effective and safe.

Feasibility of MR-guided ultrahypofractionated radiotherapy in 5, 2 or 1 fractions for prostate cancer

The drive towards hypofractionated prostate radiotherapy is motivated by a low alpha/beta ratio for prostate cancer (1 to 3 Gy) compared to surrounding organs at risk, implying an improved therapeutic ratio with increasing dose per fraction. Early evidence from studies of ultrahypofractionated (UHF) prostate HDR brachytherapy has shown good tolerability in terms of normal tissue toxicities and clinical outcomes similar to conventional fractionation schedules. MR-guided stereotactic body radiotherapy (SBRT) with online plan adaptation and real-time tumour imaging may enable UHF doses to be delivered to the prostate safely, without the invasiveness of brachytherapy. The feasibility of UHF prostate treatment planning for the Unity MR-Linac (MRL, Elekta AB, Stockholm) was investigated for target prescriptions and planning constraints derived from the HDR brachytherapy and SBRT literature. Monaco 5.40 (Elekta) was used to generate MRL step-and-shoot IMRT plans for three dose fractionation protocols (5, 2 and 1 fractions), for ten randomly selected previously treated prostate cancer patients. Of the ten plans per UHF scheme, all clinical goals were met in all cases for 5 fractions, and in six cases for both 2 and 1 fraction schemes. PTV D95% was compromised by up to 6.4% and 3.9% of the associated target dose for 2 and 1 fraction plans respectively. There were two cases of PTV D95% compromise greater than a 5% dose decrease for the 2 fraction plans. The study suggests feasibility of the UHF treatment planning approaches if combined with real-time motion mitigation strategies.

Prospective evaluation of probabilistic dose-escalated IMRT in prostate cancer

BACKGROUND

Cure- and toxicity rates after intensity-modulated radiotherapy (IMRT) of prostate cancer are dose-and volume dependent. We prospectively studied the potential for organ at risk (OAR) sparing and compensation of tumor movement with the coverage probability (CovP) concept.

PATIENTS AND METHODS

Twenty-eight prostate cancer patients (median age 70) with localized disease (cT1c-2c, N0, M0) and intermediate risk features (prostate-specific antigen [PSA] < 20, Gleason score ≤ 7b) were treated in a prospective study with the CovP concept. Planning-CTs were performed on three subsequent days to capture form changes and movement of prostate and OARs. The clinical target volume (CTV) prostate and the OARs (bladder and rectum) were contoured in each CT. The union of CTV1-3 was encompassed by an isotropic margin of 7 mm to define the internal target volume (ITV). Dose prescription/escalation depended on coverage of all CTVs within the ITV. IMRT was given in 39 fractions to 78 Gy using the Monte-Carlo algorithm. Short-term androgen deprivation was recommended and given in 78.6% of patients.

RESULTS

Long-term toxicity was evaluated in 26/28 patients after a median follow-up of 7.1 years. At last follow-up, late bladder toxicity (Radiation Therapy Oncology Group, RTOG) G1 was observed in 14.3% of patients and late rectal toxicities (RTOG) of G1 (7.1%) and of G2 (3.6%) were observed. No higher graded toxicity occurred. After 7.1 years, biochemical control (biochemically no evidence of disease, bNED) was 95.5%, prostate cancer-specific survival and the distant metastasis-free survival after 7.1 years were 100% each.

CONCLUSIONS

CovP-based IMRT was feasible in a clinical study. Dose escalation with the CovP concept was associated by a low rate of toxicity and a high efficacy regarding local and distant control.

MR-Guided Radiotherapy for Prostate Cancer

External beam radiotherapy remains the primary treatment modality for localized prostate cancer. The radiobiology of prostate carcinoma lends itself to hypofractionation, with recent studies showing good outcomes with shorter treatment schedules. However, the ability to accurately deliver hypofractionated treatment is limited by current image-guided techniques. Magnetic resonance imaging is the main diagnostic tool for localized prostate cancer and its use in the therapeutic setting offers anatomical information to improve organ delineation. MR-guided radiotherapy, with daily re-planning, has shown early promise in the accurate delivery of radiotherapy. In this article, we discuss the shortcomings of current image-guidance strategies and the potential benefits and limitations of MR-guided treatment for prostate cancer. We also recount present experiences of MR-linac workflow and the opportunities afforded by this technology.

Comparison of Manual and Semi-Automatic [18F]PSMA-1007 PET Based Contouring Techniques for Intraprostatic Tumor Delineation in Patients With Primary Prostate Cancer and Validation With Histopathology as Standard of Reference

PURPOSE

Accurate contouring of intraprostatic gross tumor volume (GTV) is pivotal for successful delivery of focal therapies and for biopsy guidance in patients with primary prostate cancer (PCa). Contouring of GTVs, using 18-Fluor labeled tracer prostate specific membrane antigen positron emission tomography ([18F]PSMA-1007/PET) has not been examined yet.

PATIENTS AND METHODS

Ten Patients with primary PCa who underwent [18F]PSMA-1007 PET followed by radical prostatectomy were prospectively enrolled. Coregistered histopathological gross tumor volume (GTV-Histo) was used as standard of reference. PSMA-PET images were contoured on two ways: (1) manual contouring with PET scaling SUVmin-max: 0-10 was performed by three teams with different levels of experience. Team 1 repeated contouring at a different time point, resulting in n = 4 manual contours. (2) Semi-automatic contouring approaches using SUVmax thresholds of 20-50% were performed. Interobserver agreement was assessed for manual contouring by calculating the Dice Similarity Coefficient (DSC) and for all approaches sensitivity, specificity were calculated by dividing the prostate in each CT slice into four equal quadrants under consideration of histopathology as standard of reference.

RESULTS

Manual contouring yielded an excellent interobserver agreement with a median DSC of 0.90 (range 0.87-0.94). Volumes derived from scaling SUVmin-max 0-10 showed no statistically significant difference from GTV-Histo and high sensitivities (median 87%, range 84-90%) and specificities (median 96%, range 96-100%). GTVs using semi-automatic segmentation applying a threshold of 20-40% of SUVmax showed no significant difference in absolute volumes to GTV-Histo, GTV-SUV50% was significantly smaller. Best performing semi-automatic contour (GTV-SUV20%) achieved high sensitivity (median 93%) and specificity (median 96%). There was no statistically significant difference to SUVmin-max 0-10.

CONCLUSION

Manual contouring with PET scaling SUVmin-max 0-10 and semi-automatic contouring applying a threshold of 20% of SUVmax achieved high sensitivities and very high specificities and are recommended for [18F]PSMA-1007 PET based focal therapy approaches. Providing high specificities, semi-automatic approaches applying thresholds of 30-40% of SUVmax are recommend for biopsy guidance.

Isotropic Expansion of the Intraprostatic Gross Tumor Volume of Primary Prostate Cancer Patients Defined in MRI-A Correlation Study With Whole Mount Histopathological Information as Reference

Introduction

An accurate delineation of the intraprostatic gross tumor volume (GTV) is of importance for focal treatment in patients with primary prostate cancer (PCa). Multiparametric MRI (mpMRI) is the standard of care for lesion detection but has been shown to underestimate GTV. This study investigated how far the GTV has to be expanded in MRI in order to reach concordance with the histopathological reference and whether this strategy is practicable in clinical routine.

Patients and Methods

Twenty-two patients with planned prostatectomy and preceded 3 Tesla mpMRI were prospectively examined. After surgery, PCa contours delineated on histopathological slides (GTV-Histo) were superimposed on MRI using ex-vivo imaging as support for co-registration. According to the PI-RADSv2 classification, GTV was manually delineated in MRI (GTV-MRI) by two experts in consensus. For volumetric analysis, we compared GTV-MRI and GTV-Histo. Subsequently, we isotropically enlarged GTV-MRI in 1 mm increments within the prostate and also compared those with GTV-Histo regarding the absolute volumes. For evaluating the spatial accuracy, we considered the coverage ratio of GTV-Histo, the Sørensen–Dice coefficient (DSC), as well as the contact with the urethra.

Results

In 19 of 22 patients MRI underestimated the intraprostatic tumor volume compared to histopathological reference: median GTV-Histo (4.7 cm³, IQR: 2.5–18.8) was significantly (p<0.001) lager than median GTV-MRI (2.6 cm³, IQR: 1.2–6.9). A median expansion of 1 mm (range: 0–4 mm) adjusted the initial GTV-MRI to at least the volume of GTV-Histo (GTV^exp-MRI). Original GTV-MRI and expansion with 1, 2, 3, and 4 mm covered in median 39% (IQR: 2%–78%), 62% (10%–91%), 70% (15%–95%), 80% (21–100), 87% (25%–100%) of GTV-Histo, respectively. Best DSC (median: 0.54) between GTV-Histo and GTV-MRI was achieved by median expansion of 2 mm. The urethra was covered by initial GTVs-MRI in eight patients (36%). After applying an expansion with 2 mm the urethra was covered in one more patient by GTV-MRI.

Conclusion

Using histopathology as reference, we demonstrated that MRI underestimates intraprostatic tumor volume. A 2 mm–expansion may improve accurate GTV-delineation while respecting the balance between histological tumor coverage and overtreatment.