Simultaneous Focal Boost With Stereotactic Radiation Therapy for Localized Intermediate- to High-Risk Prostate Cancer: Primary Outcomes of the SPARC Phase 2 Trial

Hypofractionation/Ultra-hypofractionation for Prostate Cancer Radiotherapy

Prostate cancer is the most commonly diagnosed cancer in men worldwide. Radiotherapy is an integral component for the treatment of localized prostate cancer. Radiobiologically, prostate cancer is sensitive to an increased dose of radiotherapy delivered per fraction, called "hypofractionation", due to intrinsic differences in the rate of cancer cell growth and repair of DNA damage. Hypofractionation delivers planned treatment over fewer radiotherapy sessions compared to conventional fractionation and has been shown to be noninferior to conventional fractionation with an acceptable toxicity profile. Ultra-hypofractionation, often delivered via stereotactic body radiotherapy (SBRT), further reduces the number of treatments by using even larger doses per fraction and has shown promising results with high biochemical control rates and low rates of late toxicity. The adoption of hypofractionated and ultra-hypofractionated schedules improves resource utilization in radiation oncology without compromising patient safety or efficacy. Ongoing research continues to refine patient selection, fractionation schemes, and incorporates advanced imaging, precise treatment planning, and motion management techniques to help mitigate toxicity and optimize outcomes in localized intermediate and high-risk disease.

Risk-adapted intensification therapy in high-risk prostate cancer: how relevant is the role of radiation dose

BACKGROUND/PURPOSE

Dose escalation has demonstrated a significant improvement in biochemical recurrence in high-risk prostate cancer (HRPCa). We evaluated the impact on overall survival (OS) of dose intensification with external beam radiation therapy (EBRT) in a cohort of HRPCa patients treated in a single institution.

METHODS AND MATERIALS

Between January 1997 and January 2024, a total of 1451 consecutive localized PCa patients were treated with primary EBRT alone as part of a prospective institutional program for risk-adapted dose-intensification radiotherapy. For the present analysis, we specifically selected a cohort of 424 consecutive HRPCa patients with a minimum follow-up (FU) of 5 years. The median RT dose was 79.2 Gy (interquartile range [IQR] 74.9-80.3). Short and long-term hormones were administered in 56 (13%) and 350 (83%) of patients respectively. Kaplan-Meier curves were used to calculate overall survival (OS). Cumulative incidence of distant metastasis (DM), and cause specific survival (CSS) were estimated using competing risk regression.

RESULTS

Median patient age was 69 years (IQR 65-72) and median FU was 118 months (IQR 88.0-135.0). At the time of analysis, 54 of 424 patients (13%) had died. The leading cause of death was cardiovascular disease in 16/54 patients (4%), followed by PCa in 15 patients (3%). At 10 and 15 years, the KM estimated OS rates were 91% (95% CI 87-93) and 71% (95% CI 61-79), respectively. The corresponding rates for MFS were 87% (95% CI 83-90) and 60% (95% CI 49-68), and for CSS were 97% (95% CI 95-99) and 90% (95% CI 49-81), respectively. In multivariate analysis, when adjusted for patient age, T stage, Gleason/ISUP group, PSA and length of hormone-therapy, higher radiation dose remained significantly associated with an improved OS (HR 0.89; 95% CI 0.84-0.94), MFS (HR 0.94; 95% CI 0.90-0.98) and CSS (HR 0.89; 95% CI 0.84-0.94).

CONCLUSIONS

The present study confirms that radiation dose intensification is paramount in the treatment of HRPCa with independence of duration of ADT.

Propensity Score Matched Analysis of External Beam Radiotherapy With or Without Focal Boost to Intraprostatic Lesions in Prostate Cancer

BACKGROUND

This study evaluated the impact of radiotherapy (RT) with or without a simultaneous integrated boost (SIB) to intraprostatic lesions on survival, recurrence, and toxicity in localized prostate cancer (PCa). Key prognostic and predictive factors were also analyzed.

MATERIALS AND METHODS

A retrospective analysis included 712 intermediate- and high-risk PCa patients treated with external beam RT at 78 Gy, with or without SIB (up to 86 Gy), between 2010 and 2018. Propensity score matching (PSM) was used to ensure comparability. Outcomes assessed included biochemical disease-free survival (bDFS), prostate cancer-specific survival (PCSS), local recurrence (LR), distant metastasis (DM), and treatment-related toxicities.

RESULTS

After PSM, 417 patients were analyzed (208 with SIB, 209 without). Over a median follow-up of 8.6 years, the SIB group showed higher 8-year bDFS (93.8% vs. 83.5%; p = 0.006) and lower rates of DM (6.1% vs. 13.0%; p = 0.003) and LR (1.8% vs. 6.9%; p = 0.03). PCSS was similar between groups (95.7% vs. 92.3%; p = 0.38). Advanced T stage and absence of SIB were predictors of worse bDFS, DM, and LR, while higher Gleason score were associated with poorer PCSS and DM in multivariable analysis. There were no significant differences in 8-year Grade ≥ 2 GU (10.1% vs. 10.5%; p = 0.98) or GI (7.8% vs. 6.5%; p = 0.64) toxicities between the SIB and non-SIB groups.

CONCLUSIONS

SIB with external beam RT significantly improves bDFS and reduces LR and DM in intermediate- and high-risk PCa, with no increase in significant toxicities. These findings emphasize the value of dose escalation in achieving better local control and long-term outcomes while maintaining patient safety.

HERMES: Randomised trial of 2-fraction or 5-fraction MRI-guided adaptive prostate radiotherapy

OBJECTIVE

To demonstrate safety and feasibility of 2-fraction stereotactic body radiotherapy (SBRT) for prostate cancer.

METHODS

This single centre, non-comparative, phase II/R-IDEAL2b trial randomised 46 patients with intermediate/lower high-risk prostate cancer with visible gross tumour volume (GTV) on multiparametric magnetic resonance imaging (MRI) to receive 36.25Gy in 5 fractions over 10 days or 24Gy in 2 fractions with a GTV boost up to 27Gy over 8 days. All treatment was delivered on an MR-linac with daily adaptive replanning. The primary endpoint was acute grade ≥2 (G2+) genitourinary (GU) toxicity (CTCAEv5). Secondary endpoints include gastrointestinal (GI) toxicity and patient reported outcomes.

RESULTS

G2+GU acute toxicity was observed in 6/22 (27.3%; 95% CI (0.11-0.50) of patients in the 2-fraction group and 7/24 (29.2%; 95% CI (0.13-0.50) in the 5-fraction group. There were no grade 3(G3) GU toxicities. G2+ urinary frequency rose from 4.5% (1/22) at week 2 to 13.6% (3/22) at week 4 in 2-fraction SBRT. G2+ urinary frequency peaked earlier in 5-fraction SBRT at 16.7% (4/24) in week 2, falling to 12.5% (3/24) at week 4. At 12 weeks, median EPIC-26 urinary-incontinence score was 85.5, IQR 75-100) for 2-fraction SBRT and 100, IQR 93.8-100) for 5-fraction SBRT. Urinary irritative-obstructive scores were higher at 12 weeks in the 2-fraction group (93.8, IQR 87.5-100) and 87.5, IQR 81.3-93.8 in the 5-fraction group. Peak IPSS score was lower in the 2-fraction group (8, IQR 4-11) and 13.5, IQR 10-17) in the 5-fraction group. G2+ GI acute toxicity occurred in 3/24 (6.8%) after 5-fraction SBRT, but none after 2-fraction SBRT.

CONCLUSIONS

Acceptable acute GU toxicity was seen after 2-fraction SBRT. Acute GI toxicity was low. Randomised trials are warranted to explore late toxicity and biochemical control.

Primary Analysis of (NCT03380806) a Phase II Randomized Trial of Stereotactic Body Radiotherapy Boost Versus Conventional Fractionation External Beam Radiotherapy Boost in Unfavorable-Intermediate and High-Risk Prostate Cancer

BACKGROUND

Standard treatment for unfavorable-intermediate and high-risk prostate cancer involves androgen deprivation therapy (ADT) in combination with pelvic conventional fractionation (CF) external beam radiotherapy (EBRT) and a CF-EBRT or brachytherapy boost to the prostate. This trial compared CF-EBRT boost with stereotactic body radiotherapy (SBRT) boost after pelvic CF-EBRT.

METHODS

Patients were randomized to receive a boost using either CF-EBRT (32-34 Gy in 15-17 fractions) or SBRT (19.5-21 Gy in three weekly fractions) following pelvic CF-EBRT (45-46 Gy in 23-25 fractions). The primary objective was to assess early (3-month post-radiotherapy) gastrointestinal (GI) and genitourinary (GU) quality of life (QoL), using the expanded prostate index composite (EPIC) score. Secondary objectives included long-term QoL, International Prostate Symptom Score (IPSS) changes, toxicity assessments, and long-term disease control outcomes. Linear regression and Fisher's exact test were used for analysis.

RESULTS

Of the 100 patients randomized, 53 received CF-EBRT, and 47 received SBRT. After a mean follow-up of 18.5 months, no significant differences were observed in EPIC score changes between CF-EBRT and SBRT at 3 months posttreatment for urinary (11.5 vs. 8.6, p = 0.23), bowel (5.2 vs. 6.4, p = 0.57), and overall QoL (8.3 vs. 7.5, p = 0.61). IPSS scores were similar (p = 0.11), and CTCAE v.5.0 toxicity rates were comparable, with an odds ratio of 0.90 (p > 0.99). Biochemical failure rates were under 5% for both groups.

CONCLUSIONS

This is the first randomized trial to report QoL outcomes after SBRT boost radiotherapy in patients with unfavorable-intermediate and high-risk prostate cancer. SBRT boost after pelvic CF-EBRT is well-tolerated and demonstrates comparable outcomes in QoL and toxicity to the CF-EBRT boost. Further follow-up is needed to assess the long-term effects on QoL, toxicity, and disease control.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03380806.

PSMA-PET Guided Intraprostatic Boost in Prostate SBRT (PROBE): A Phase 2 Trial

PURPOSE

To assess the safety of using combined Gallium68-prostate-specific membrane antigen (PSMA)-positron emission tomography (PET)/computed tomography (CT) (68Ga-PSMA-PET/CT) and multiparametric magnetic resonance imaging (mpMRI) for planning dominant intraprostatic lesion (DIL) boost in prostate stereotactic radiation therapy (SBRT) for dose escalation (PROBE).

METHODS AND MATERIALS

Patients with intermediate- or high-risk prostate adenocarcinoma with DIL identified on mpMRI and 68Ga-PSMA-PET/CT and suitable for SBRT were enrolled in this phase 2 trial. 68Ga-PSMA-PET/CT was fused with mpMRI for gross tumor volume (GTV) delineation. Semiautomatic contouring of DIL was performed using 20% to 90% of the maximum standardized uptake value (SUVmax) (DILx%). Concordance metrics were used to select the DILx% matching closest to GTVMRI (GTVPET). Prostate (36.25 Gy), pelvic nodes (25 Gy), GTVunion: GTVPET ∪ GTVMRI (40 Gy), and GTVoverlap: GTVPET ∩ GTVMRI (42.5 Gy) were planned for 5-fraction SBRT. All patients received androgen deprivation therapy (ADT) for 6 months. The primary endpoint for the present analysis was concordance (volumetric and spatial) between GTVMRI and GTVPET. Secondary endpoints included the percentage SUVmax threshold for GTVPET contouring (%SUVGTV-PET) and cumulative acute (≤90 days) urinary and gastrointestinal toxicity using Common Terminology Criteria for Adverse Event (CTCAE) v5.0.

RESULTS

Thirty patients (54% intermediate risk, 46% high risk) were enrolled. GTVMRI and GTVPET showed strong volumetric correlation (Spearman correlation coefficient ρ = 0.817, 95% CI, 0.64-0.91; P < .001). The median Dice similarity coefficient, Jaccard index, and the mean Hausdorff distance for PET and magnetic resonance imaging boost volumes were 0.56, 0.37, and 2.2, respectively. The median %SUVGTV-PET was 48% (IQR, 40%-58%). There was an inverse correlation between DIL SUVmax and %SUVGTV-PET (Spearman correlation coefficient ρ = -0.598, 95% CI lower -0.79, upper -0.29; P < 0.001). Cumulative grade 2 acute urinary and GI toxicity were 13.3% and 6.6%, respectively, with no grade ≥3 toxicities.

CONCLUSION

Boost volumes on 68Ga-PSMA-PET/CT and mpMRI were volumetrically similar, however, with poor spatial concordance. The %SUVmax threshold for GTVPET contouring correlated inversely with DIL SUVmax and was a median of 48%. Based on the favorable acute toxicity profile, PSMA-PET guided intraprostatic boost is likely to be safe for dose escalation in prostate SBRT.

Prognostic significance of the mEPE score in intermediate-risk prostate cancer patients undergoing ultrahypofractionated robotic SBRT

PURPOSE

This study aimed to evaluate the prognostic significance of magnetic resonance imaging (MRI) parameters on biochemical failure-free survival (BFS) in patients diagnosed with intermediate-risk prostate cancer and treated with robotic ultrahypofractionated stereotactic body radiotherapy (SBRT) without androgen deprivation therapy (ADT).

METHODS

A retrospective analysis was conducted in patients with intermediate-risk prostate cancer undergoing robotic SBRT delivered in five fractions with a total radiation dose of 35-36.25 Gy. The primary endpoint was biochemical failure as defined by the Phoenix criteria. Among other clinicopathological data, T stage, Prostate Imaging-Reporting and Data System (PI-RADS) score, and multiparametric magnetic resonance imaging-based extra-prostatic extension (mEPE) score were collected and analyzed using the log-rank test.

RESULTS

A total of 74 patients were eligible for analysis. Median age at treatment was 68.8 years and median prostate volume was 47.8 cm3. Fifty-four and 14 patients were diagnosed with Gleason scores 7a and 7b, respectively. In total, 40 patients were classified as having unfavorable intermediate-risk prostate cancer according to American Urological Association/American Society for Radiation Oncology/ Society of Urologic Oncology (AUA/ASTRO/SUO) guidelines. The median follow-up was 30 months (range: 4-91.2 months; interquartile range (IQR): 18.5-48 months). The 3‑year BFS was 92%. A total of 12 (16.2%) biochemical failures were reported. In univariate analysis, an mEPE score of 5, the delivered total radiation dose (35 Gy vs. 36.25 Gy), and a prostate-specific antigen (PSA) nadir >1 ng/ml were associated with lower BFS (mEPE-BFS: p < 0.001, total radiation dose-BFS: p = 0.04, PSA nadir-BFS: p =< 0.001).

CONCLUSION

Patients diagnosed with intermediate-risk prostate cancer with a high mEPE score are more likely to experience biochemical failure after SBRT. Treatment intensification measures, such as administration of concomitant ADT, should be considered.

Stereotactic body radiotherapy with a focal boost to the intraprostatic tumor for intermediate and high risk prostate cancer: 5-year efficacy and toxicity in the hypo-FLAME trial

BACKGROUND

The addition of an integrated focal boost to the intraprostatic lesion is associated with improved biochemical disease-free survival (bDFS) in patients with intermediate- and high-risk prostate cancer (PCa) in conventionally fractionated radiotherapy. Furthermore, whole gland stereotactic body radiotherapy (SBRT) demonstrated to be non-inferior to conventional radiotherapy for low- and intermediate-risk PCa. To investigate the combination of ultra-hypofractionated prostate SBRT with iso-toxic focal boosting for intermediate- and high-risk PCa, we performed the hypo-FLAME trial.

METHODS

Patients with intermediate- or high-risk PCa were enrolled in the phase II hypo-FLAME trial. All patients were treated with 35 Gy in 5 weekly fractions to the whole prostate gland with an iso-toxic integrated boost up to 50  Gy to the multiparametric MRI-defined tumor(s). If the dose constraints to the normal tissues would be exceeded, these were prioritised over the focal boost dose. The current analysis reports on the 5-year bDFS, late toxicity and health-related quality of life (HRQoL).

RESULTS

Between 2016 and 2018, 100 men were treated with a median follow-up of 61 months. The estimated 5-year bDFS (95 % CI) was 93 % (86 % to 97 %). At 5 years, the prevalence of grade 2 + genitourinary and gastrointestinal toxicity was 12 % and 4 %, respectively.

CONCLUSION

Ultra-hypofractionated focal boost SBRT is associated with encouraging biochemical control rates up to 5-year follow-up in patients with intermediate- and high-risk PCa. Furthermore, prostate SBRT with iso-toxic focal boosting is associated with acceptable late genitourinary and gastrointestinal toxicity rates.

In Curative Stereotactic Body Radiation Therapy for Prostate Cancer, There Is a High Possibility That 45 Gy in Five Fractions Will Not Be Tolerated without a Hydrogel Spacer

The purpose of this study was to determine the maximum tolerated dose (MTD) for stereotactic body radiation therapy (SBRT) in the treatment of non-metastatic prostate cancer. This study was a phase 1 dose escalation trial conducted in Japan. Patients with histologically proven prostate cancer without lymph nodes or distant metastases were enrolled. The prescribed doses were 42.5, 45, or 47.5 Gy in five fractions. Dose-limiting toxicity (DLT) was defined as grade (G) 3+ gastrointestinal or genitourinary toxicity within 180 days after SBRT completion, and a 6 plus 6 design was used as the method of dose escalation. A total of 16 patients were enrolled, with 6 in the 42.5 Gy group and 10 in the 45 Gy group. No DLT was observed in the 42.5 Gy group. In the 45 Gy group, one patient experienced G3 rectal hemorrhage, and another had G4 rectal perforation, leading to the determination of 42.5 Gy as the MTD. None of the patients experienced biochemical recurrence or death during the follow-up period. We concluded that SBRT for non-metastatic prostate cancer at 42.5 Gy in five fractions could be safely performed, but a total dose of 45 Gy increased severe toxicity.