Impact of Interfractional Bladder and Trigone Displacement and Deformation on Radiation Exposure and Subsequent Acute Genitourinary Toxicity: A Post Hoc Analysis of Patients Treated with Magnetic Resonance Imaging-Guided Prostate Stereotactic Body Radiation Therapy in a Phase 3 Randomized Trial

Patterns of Failure After Prostate-Only Radiotherapy in High-Risk Prostate Cancer: Implications for Refining Pelvic Nodal Contouring Guidelines

PURPOSE

To study prostate specific membrane antigen - positron emission tomography (Ga68PSMA-PETCT) based patterns of relapse at biochemical failure (BCF) after prostate-only radiotherapy (PORT) in high-risk (HR) prostate cancer and its implications on pelvic contouring recommendations.

METHODS AND MATERIALS

Patients with clinico-radiological high-risk node-negative prostate cancer treated with curative PORT and androgen deprivation therapy (ADT), either within the POP-RT randomised trial or off trial, who underwent a Ga68PSMA-PETCT upon BCF were included. Patterns of regional and distant recurrence on Ga68PSMA-PETCT were studied. Pelvic nodal recurrences were mapped with reference to the superior border of pubic symphysis. Pelvic lymph nodal caudal border (PLNcb) recommendations in the published contouring guidelines (RTOGcb, GETUGcb, PIVOTALcb, NRGcb, GFRUcb) were evaluated.

RESULTS

Of the total 262 patients screened, 68 eligible patients were included (POP-RT trial 35 patients; off-trial 33 patients). Median follow-up was 91 months (IQR, 72-117) and median time to BCF was 65 months (IQR, 49-83). Regional and distant recurrence was seen in 31 (46%) and 31 (46%) patients, respectively. Of the nodal recurrences, nearly half (46%, 14/31) had no distant metastases and 64% (20/31) had a failure in the common iliac nodal region. The lower-most nodal recurrence was 20 mm cranial to the top of pubic symphysis (RTOGcb, GETUGcb, GFRUcb) and 10 mm cranial to the PIVOTALcb. The PLNcb recommended by NRG guideline (NRGcb) had an inter-patient variability of 32 mm, ranging from 16 mm above to 16 mm below the top of pubic symphysis, and the lower most nodal recurrence ranged from 4 mm to 36 mm cranial to NRGcb.

CONCLUSION

Pelvic failures accounted for a major proportion of recurrences after prostate-only radiotherapy, with the caudal most nodal recurrence being 20 mm cranial to the top of pubic symphysis. This could have implications in defining the caudal border of contouring recommendations.

Treatment Optimization in Linac-Based SBRT for Localized Prostate Cancer: A Single-Arc versus Dual-Arc Plan Comparison

This study aimed to comprehensively present data on treatment optimization in linac-based SBRT for localized prostate cancer at a single institution. Moreover, the dosimetric quality and treatment efficiency of single-arc (SA) versus dual-arc (DA) VMAT planning and delivery approaches were compared. Re-optimization was performed on twenty low-to-intermediate-risk- (36.25 Gy in 5 fractions) and twenty high-risk (42.7 Gy in 7 fractions) prostate plans initially administered with the DA FFF-VMAT technique in 2021. An SA approach was adopted, incorporating new optimization parameters based on increased planning and clinical experience. Analysis included target coverage, organ-at-risk (OAR) sparing, treatment delivery time, and the pre-treatment verification's gamma analysis-passing ratio. The SA optimization technique has consistently produced superior plans. Rectum and bladder mean doses were significantly reduced, and comparable target coverage and homogeneity were achieved in order to maintain a urethra protection strategy. The mean SA treatment delivery time was reduced by 22%; the mean monitor units increased due to higher plan complexity; and dose measurements demonstrated optimal agreement with calculations. The substantial reduction in treatment delivery time decreased the probability of prostate motion beyond the applied margins, suggesting potential decrease in treatment-related toxicity and improved target coverage in prostate SBRT. Further investigations are warranted to assess the long-term clinical outcomes.