ESTRO 2023 - Abstract Book

S702

Monday 15 May 2023

ESTRO 2023

Purpose or Objective Different techniques exist for the delivery of accelerated partial breast irradiation (APBI) for appropriately selected patients with early breast cancer after breast-conserving surgery (BCS). The long-term 10y.-results of a Phase 3 trial evaluating the non-inferiority of APBI using multicatheter brachytherapy compared to whole-breast irradiation (WBI) are presented. Materials and Methods We randomized patients aged ≥ 40 years with low risk invasive breast cancer and ductal carcinoma in-situ after BCS to receive either 50 Gy WBI with tumor bed boost of 10 Gy or APBI using multicatheter brachytherapy. The primary endpoint was local recurrence rate in the “as-treated” population. Secondary endpoints were overall survival, disease-free survival, cumulative incidence of regional recurrence and distant metastasis, incidence and severity of acute and late side effects, cosmesis. The trial is registered with ClinicalTrials.gov, NCT00402519. Results Between 2004 and 2009, 1184 participants with early stage breast cancer were randomly assigned to receive either WBI with boost or APBI using interstitial multicatheter brachytherapy. Median follow-up of patients was 10.4 years. The cumulative incidence of local recurrence at 10 years was 1.58% (95% CI: 0.37; 2.8%) in the WBI and 3.51% (95% CI: 1.99; 5.03%) in the APBI arm (difference 1.93% (95% CI: -0.018; 3.87, p=0.074). 10-year disease-free survival was 87.95% (95%CI: 85.1 – 90.91%) with WBI and 84.89% (95%CI: 81.97 – 87.91%) with APBI (difference -3.06%, 95% CI: -7.22;1.09%; p=0.18). 10- year overall survival was 89.5% (95% CI: 86.9–92.2%) in WBI-treated and 90.5% (95% CI: 88.1–92.9%) in APBI-treated patients (difference 1 · 95% CI: -2 · 66–4 · 56; p=0 · 5). Finally, the patients in APBI arm showed significantly lower incidence of treatment-related late-side events > grade 2 (p=0.021). Conclusion The efficacy of adjuvant APBI using multicatheter brachytherapy after breast conserving surgery for early breast cancer is similar to adjuvant WBI with tumor bed boost and is associated with lower incidence of late side effects. OC-0831 Standard vs dose reduced chemoradiotherapy in anal cancer: short-term results of the PLATO-ACT4 RCT A. Gilbert 1 , J. Webster 2 , S. Brown 2 , J. Copeland 2 , S. Ruddock 2 , D. Gilbert 3 , M. Hawkins 4 , R. Muirhead 5 , A. Renehan 6 , R. Adams 7 , M. Harrison 8 , D. Sebag-Montefiore 1 1 University of Leeds, Leeds Cancer Centre, Leeds, United Kingdom; 2 University of Leeds, Leeds Institute of Clinical Trials Research, Leeds, United Kingdom; 3 Royal Sussex County Hospital, Sussex Cancer Centre, Brighton, United Kingdom; 4 University College London, Dept of Medical Physics & Biomedical Engineering, London, United Kingdom; 5 Oxford University Hospitals NHS Trust, Department of Oncology, Churchill Hospital, Oxford, United Kingdom; 6 Manchester Cancer Research Centre, NIHR Manchester Biomedical Research Centre, Manchester, United Kingdom; 7 Cardiff University, Centre for Trials Research, Cardiff, United Kingdom; 8 Mount Vernon Centre for Cancer Treatment, Mount Vernon Hospital, London, United Kingdom Purpose or Objective Localised squamous cell carcinoma of the anus is treated with radical chemoradiotherapy. Cure rates are high but treatment can result in significant long-term morbidity. Materials and Methods ACT 4 is a phase II prospective, multi-centre, 2-arm RCT, embedded within the PLATO platform; investigating dose reduced intensity modulated radiotherapy (dr-IMRT) with chemotherapy in patients (pts) with T1-2( ≤ 4cm)N0 anal cancer. The primary outcome is 3-year locoregional control; with the aim of reducing acute and late toxicity. We report on the planned 6-month endpoint analysis – radiological complete clinical response rates (cRR), acute toxicity (CTCAEv5), treatment compliance, and patient reported outcomes (PROs; EORTC-QLQ C30 and ANL27). Pts with T1-2( ≤ 4cm)N0M0 squamous cancer of the anus were randomised 1:2 to standard dose IMRT (sd-IMRT; 50.4Gy in 28F; elective nodal irradiation 40Gy in 28F) or dr-IMRT (41.4Gy in 23F; elective nodal irradiation 34.5Gy in 23F) with concurrent mitomycin 12mg/m2 day (D)1 and capecitabine (CAP) 825mg/m2 twice daily on days of RT. 123 pts were required to demonstrate dr-IMRT does not produce efficacy rates <80% and reaches efficacy rates of ≥ 90%. The sample was inflated to 162 for analysis of p16+ genotype outcomes. Results 160 pts were recruited from 28 UK sites (sd-IMRT n=55; dr-IMRT n=105) between Jan 2017 and Dec 2020. 3 pts randomised to reduced dose IMRT were excluded for the modified intention to treat analysis. See Table 1 for pt characteristics. For pts with MRI at 6 months, 90.0% sd-IMRT (n=45/50) and 92.4% dr-IMRT (n=85/92) had a TRG grade 1 or 2 (complete or fibrosis only) (see Table 2). 99% received planned RT; 1 pt (sd-IMRT) withdrew due to toxicity and 1 pt (dr-IMRT) withdrew consent from the trial at D17. One pt (dr-IMRT) received 50.4Gy after stopping CAP on D2 due to toxicity. 25.5% (sd-IMRT; n=14) and 15.2% (dr-IMRT; n=16) experienced at least one RT interruption; 32% due to toxicity, 68% logistical. Chemotherapy modifications (sd-IMRT n=32, 58.2%; dr-IMRT n=50, 47.6%) were in the majority of cases due to toxicity (65-80%). ≥ G3 acute toxicity was reported in 45.5% sd-IMRT (n=25) versus 35.2% dr-IMRT (n=37; see Table 1). Overall for PROs, there was a large to moderate deterioration in pain, fatigue, overall bowel function, quality of life, physical, role and social function at the end of CRT which resolved to baseline by either 6 weeks or 6 months in both arms. Sexual function improved to baseline levels by 6 weeks for men and 6 months for women in dr-IMRT, but poorer sexual function was maintained to 6 months in sd-IMRT for both men and women.