ASCO GU 2019: Stereotactic Body Radiotherapy Compared to Conventionally Fractionated or Moderately Hypofractionated External Beam Radiotherapy for Localized Prostate Cancer

San Francisco, CA ( External beam radiotherapy (EBRT) has been considered as a curative treatment for localized prostate cancer (LPCa). Large randomized controlled trials (RCTs) have shown moderately hypofractionated regimens (2.5–3 Gy/fraction(f)) as non-inferior to conventionally fractionated regimens (2 Gy/f). Compared to conventionally fractionated or moderately hypofractionated external beam radiotherapy (CFMHRT), stereotactic body radiotherapy (SBRT) reduces patient treatment duration but condensed overall treatment time may influence acute toxicity severity. PACE-B trial was developed to evaluate non-inferiority of SBRT compared to CFMHRT for biochemical or clinical failure.

During the general session on optimizing diagnosis and treatment of clinically significant nonmetastatic prostate cancer session at the Annual ASCO GU 2019 meeting in San Francisco, Nicholas Van As presented the results of PACE-B trial. This is a phase III open-label multiple-cohort RCT. He started by showing the schema for the trial design. Men with LPCa, stage T1-T2, ≤ Gleason 3 + 4, PSA ≤ 20 ng/mL, unsuitable for surgery or preferring EBRT, were eligible for the PACE-B cohort. Between August 2012- and January 2018, 874 pts (38 centers) were randomized (1:1) to SBRT or CFMHRT. SBRT dose was 36.25 Gy/5f in 1-2 weeks, CFMHRT as 78 Gy/39f over 7.5 weeks, or 62 Gy/20f in 4 wks. Androgen deprivation therapy was not allowed. The primary endpoints of this study were clinical and biochemical progression-free survival. The secondary endpoints were overall survival, prostate cancer-specific survival, clinician-reported acute toxicity, clinician-reported late toxicity, patient-reported outcomes and commencement of androgen deprivation therapy. The results reported were clinician reported acute toxicity which was assessed at baseline, 2-weekly during CFMHRT and at 2, 4, 8 and 12 weeks post-treatment. Key toxicity outcomes were worst grade 2+ Radiation Therapy Oncology Group (RTOG) genitourinary (GU) and gastrointestinal (GI) acute toxicities. Fiducial markers were not mandated, but image guidance was mandated.

Nicholas Van As then presented the results from this study which showed that by per protocol analysis n=430 received CFMHRT, n=414 received SBRT. Key demographic and clinical variables were comparable between the CFMHRT and SBRT groups respectively; Mean age: 69.5 vs 69.3 years; T-stage ≥T2b: 51.8% vs 56.6%; Gleason Score 3+4: 80.2% vs 85.0%; PSA 10-20 ng/mL: 30.9% vs 31.6%; Use of fiducial markers: 57% vs 73%. RTOG G2+ toxicity was not significantly different for GI events (CMFHRT 52/430 (12.1%) vs SBRT 42/414 (10.1%), p=0.368), nor GU events (CFMHRT 117/430 (27.2%) vs SBRT 96/414 (23.2%), p=0.179). The graphs were also summarized which showed that toxicity appears slightly earlier in SBRT arm compared to CMFHRT arm for G1 toxicity but there is complete overlap of G2+ toxicities between the two arms.

Nicholas Van as summarized that despite an accelerated treatment schedule, RTOG assessments show similar rates of acute GI and GU toxicity for SBRT and CFHFRT. Patient follow-up in PACE-B is continuing, and the results of late toxicity and biochemical/clinical failure are awaited.

Presented by: Nicholas John Van As, MBBCH, MRCP, FRCR, MD(res), Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London

Written by: Abhishek Srivastava, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center, Fox Chase Cancer Center, Philadelphia, PA. Twitter: @shekabhishek at the 2019 American Society of Clinical Oncology Genitourinary Cancers Symposium, (ASCO GU) #GU19, February 14-16, 2019 - San Francisco, CA
email news signup