Two-fraction stereotactic ablative radiotherapy (SABR) versus two-fraction high dose rate (HDR) brachytherapy for localized prostate cancer: Does dose heterogeneity matter?

Radiotherapy in localized prostate cancer: a multicenter analysis evaluating tumor control and late toxicity after brachytherapy and external beam radiotherapy in 1293 patients

BACKGROUND AND PURPOSE

Comparing oncological outcomes and toxicity after primary treatment of localized prostate cancer using HDR- or LDR-mono-brachytherapy (BT), or conventionally (CF) or moderately hypofractionated (HF) external beam radiotherapy.

MATERIALS AND METHODS

Retrospectively, patients with low- (LR) or favorable intermediate-risk (IR) prostate cancer treated between 03/2000 and 09/2022 in two centers were included. Treatment was performed using either CF with total doses between 74 and 78 Gy, HF with 2.4-2.6 Gy per fraction in 30 fractions, or LDR- or HDR-BT. Biochemical control (BC) according to the Phoenix criteria, and late gastrointestinal (GI), and genitourinary (GU) toxicity according to RTOG/EORTC criteria were assessed.

RESULTS

We identified 1293 patients, 697 with LR and 596 with IR prostate cancer. Of these, 470, 182, 480, and 161 were treated with CF, HF, LDR-BT, and HDR-BT, respectively. For BC, we did not find a significant difference between treatments in LR and IR (p = 0.31 and 0.72). The 5‑year BC for LR was between 93 and 95% for all treatment types. For IR, BC was between 88% in the CF and 94% in the HF group. For CF and HF, maximum GI and GU toxicity grade ≥ 2 was between 22 and 27%. For LDR-BT, we observed 67% grade ≥ 2 GU toxicity. Maximum GI grade ≥ 2 toxicity was 9%. For HDR-BT, we observed 1% GI grade ≥ 2 toxicity and 19% GU grade ≥ 2 toxicity.

CONCLUSION

All types of therapy were effective and well received. HDR-BT caused the least late toxicities, especially GI.

Predictive value of magnetic resonance imaging diffusion parameters using artificial intelligence in low-and intermediate-risk prostate cancer patients treated with stereotactic ablative radiotherapy: A pilot study

INTRODUCTION

To investigate the predictive value of the pre-treatment diffusion parameters of diffusion-weighted magnetic resonance imaging (DW-MRI) using artificial intelligence (AI) for prostate-specific antigen (PSA) response in patients with low- and intermediate-risk prostate cancer (PCa) treated with stereotactic ablative radiotherapy (SABR).

METHODS

Retrospective evaluation was performed for 30 patients using pre-treatment multi-parametric MR image datasets between 2017 and 2021. MR-based mean- and minimum apparent diffusion coefficients (ADCmean, ADCmin) were calculated for the intraprostatic dominant lesion. Therapeutic response was assessed using PSA levels. Predictive performance was assessed by the receiver operating characteristic (ROC) analysis. Statistics performed with a significance level of p ≤ 0.05.

RESULTS

No biochemical relapse was detected after a median follow-up of twenty-three months (range: 3-50), with a median PSA of 0.01 ng/ml (range: 0.006-2.8) at the last examination. Significant differences were observed between the pre-treatment ADCmean, ADCmin parameters, and the group averages of patients with low and high 1-year-PSA measurements (p < 0.0001, p < 0.0001). In prediction, the random forest (RF) model outperformed the decision tree (DT) and support vector machine (SVM) models by yielding area under the curves (AUC), with 0.722, 0.685, and 0.5, respectively.

CONCLUSION

Our findings suggest that pre-treatment MR diffusion data may predict therapeutic response using the novel approach of machine learning in PCa patients treated with SABR.

IMPLICATIONS FOR PRACTICE

Clinicians shall measure and implement the evaluation of the suggested parameters (ADCmin, ADCmean) to provide the most accurate therapy for the patient.

The march toward single-fraction stereotactic body radiotherapy for localized prostate cancer-Quo Vadimus?

PURPOSE

Stereotactic body radiotherapy (SBRT) is an emerging treatment option for localized prostate cancer. There is increasing interest to reduce the number of fractions for prostate SBRT.

METHODS

We provide a narrative review and summary of prospective trials of different fractionation schedules for prostate SBRT, focusing on efficacy, toxicities, and quality of life outcomes.

RESULTS

There are two randomized phase 3 trials comparing standard external beam radiotherapy with ultra-hypofractionated radiotherapy. HYPO-RT-PC compared 78 Gy in 39 fractions vs 42.7 Gy in 7 fractions (3D-CRT or IMRT) showing non-inferiority in 5-year biochemical recurrence-free survival and equivalent tolerability. PACE-B trial compared 78 Gy in 39-fraction or 62 Gy in 20-fraction vs 36.25 Gy in 5-fraction prostate SBRT, with no significant differences in toxicity outcomes at 2 years. Five-year efficacy data for PACE-B are expected in 2024. Five-fraction prostate SBRT is currently the most common and well-established fractionation schedule with multiple prospective phase 2 trials published to date. There is more limited data on 1-4 fraction prostate SBRT. All fractionation schedules had acceptable toxicity outcomes. Experience from a high-dose-rate brachytherapy randomized trial showed inferior efficacy with single-fraction compared to two-fraction brachytherapy. Hence, caution should be applied in adopting single-fraction prostate SBRT.

CONCLUSION

Two-fraction SBRT is likely the shortest fractionation schedule that maintains the therapeutic ratio. Several randomized trials currently recruiting will likely provide us with more definite answers about whether two-fraction prostate SBRT should become a standard-of-care option. Enrollment of eligible patients into these trials should be encouraged.

Long-term outcomes of ultra-hypofractionated 2 fractions single day HDR brachytherapy in localized prostate cancer

INTRODUCTION AND OBJECTIVES

We previously published the toxicity and initial results of a prospective cohort of patients treated with 2 fractions HDR-BRT administered in a single day. In the present analysis we report the long-term cancer control results of our prospective trial and investigate the relationship between PSA nadir and biochemical control.

MATERIAL AND METHODS

A total of 120 patients were treated with HDR Brachytherapy monotherapy administered in two fractions in a single day. Between November 2010 and February 2016, 84 patients with low-risk and 36 patients with intermediate-risk prostate cancer in accordance with the NCCN practice guidelines.

RESULTS

Median age was 66 years (range 45-84) and median PSA was 7.5 ng/ml (range 0.01-16 ng/ml). Overall, 84.2% had Gleason score 6 and 15.8% Gleason 7. Thirty-one percent of patients received ADT.After a median follow-up of the cohort was 123 months. Actuarial rates of no biochemical evidence of disease (bNED), overall survival, local control and metastasis-free survival for all patients were 93.3%, 86.7%, 95.2% and 96.1%, respectively.The median time to achieve PSA nadir was 80.5 months. Patients who attained a PSA Nadir ≤ 0.20 ng/mL exhibited a 10-year bNED survival rate of 96.9%, whereas thosewho failed to reach this PSA level had a survival rate of only 40%.

CONCLUSIONS

In patients with favorable localized prostate cancer, 2 fractions HDR-BT monotherapy is a highly curative radiation technique that attains PSA nadir levels < 0.2 ng/mL in 95% of cases.

Treatment planning comparison of high-dose-rate brachytherapy vs. robotic and conventional stereotactic body radiotherapy for ultrahypofractionated treatment of prostate cancer

Background and purpose

Ultrahypofractionated radiation therapy is increasingly used in the treatment of prostate cancer. High-dose-rate brachytherapy (HDR-BT) and stereotactic body radiotherapy (SBRT) are representative methods of ultrahypofractionation. This study was performed to compare clinically applied treatment plans for patients who had been treated using HDR-BT vs. conventional or robotic SBRT.

Materials and methods

Calculated dose-volume indices between HDR-BT without a perirectal spacer (n = 20), robotic SBRT without a spacer (n = 40), and conventional (non-robotic) SBRT with a spacer (n = 40) were compared. Percentages against the prescription dose regarding the planning target volume (PTV), bladder, rectum, and urethra were statistically compared.

Results

The D50% of the PTV with HDR-BT (140.5% ± 4.9%) was significantly higher than that with robotic or conventional SBRT (116.2% ± 1.6%, 101.0% ± 0.4%, p < 0.01). The D2cm³ of the bladder with HDR-BT (65.6% ± 6.4%) was significantly lower than those with SBRT (105.3% ± 2.9%, 98.0% ± 1.3%, p < 0.01). The D2cm³ of the rectum with HDR-BT (60.6% ± 6.2%) was also significantly lower than those with SBRT (85.1% ± 8.8%, 70.4% ± 9.6%, p < 0.01). By contrast, the D0.1cm³ of the urethra with HDR-BT (117.1% ± 3.6%) was significantly higher than those with SBRT (100.2% ± 0.7%, 104.5% ± 0.6%, p < 0.01).

Conclusions

HDR-BT could administer a higher dose to the PTV and a lower dose to the bladder and rectum, at the cost of a slightly higher dose to the urethra compared with SBRT.

Two-fraction stereotactic ablative radiotherapy with simultaneous boost to MRI-defined dominant intra-prostatic lesion - Results from the 2SMART phase 2 trial

PURPOSE

This is the first report of the 2SMART Phase II trial evaluating the safety of two-fraction stereotactic ablative radiotherapy (SABR) with focal boost to magnetic resonance imaging (MRI) defined dominant intra-prostatic lesion (DIL) for localised prostate cancer.

MATERIALS AND METHODS

Men with low or intermediate risk prostate cancer were eligible for the study. The gross tumour volume (GTV) was MRI-defined DIL, and the clinical target volume (CTV) was entire prostate gland. The planning target volume (PTV) was a 2 mm expansion anteroposterior and lateral, and 2.5 mm superoinferior. The prescribed dose was 32 Gy to GTV, and 26 Gy to CTV. Primary endpoint was minimal clinically important change (MCIC) in quality of life (QOL) within 3-months of SABR, assessed using the EPIC-26 questionnaire. Secondary endpoints were acute and late toxicities (assessed using CTCAEv4), PSA nadir, and biochemical failure (based on Phoenix criteria).

RESULTS

Thirty men were enrolled in the study - 2 (7%) had low-risk and 28 (93%) had intermediate risk prostate cancer. The median follow-up was 44 months (range:39-49 months). The median PSA nadir was 0.25 ng/mL, with median time to nadir of 37 months. One patient (3%) had biochemical failure at 44 months post-treatment. Ten (33%), six (20%), and three (10%) men had acute MCIC in urinary, bowel, and sexual QOL domains respectively. No acute or late grade ≥ 3 urinary or bowel toxicities were observed.

CONCLUSION

This novel protocol of two-fraction prostate SABR with MRI-defined DIL boost is a safe approach for dose-escalation, with minimal impact on acute QOL and no grade ≥ 3 toxicities.