S732
Clinical – Lower GI
ESTRO 2026
remain challenging [1]. Another approach to reduce toxicity is a reduction in radiotherapy volume. Recent NORDIC Group guidance suggested the routine exclusion of external iliac nodes and highlighted the potential for exclusion of the inguinal nodes for early- stage tumours [2]. The prospective, multi-centre PLATO clinical trial platform (ISRCTN88455282) incorporates 3 distinct trials with common threads between them. We aim to compare acute side effects and compliance in involved-field radiotherapy and whole pelvic radiotherapy, using the relevant cohorts within different trials in PLATO. Material/Methods: ACT3 is a phase II non-randomised trial in early-stage anal cancer. After local excision of T1N0M0, patients with ≤ 1mm margins received involved-field radiotherapy to the tumour alone with 41.4Gy in 23fractions with Mitomycin C 12mg/ m2 D1 and Capecitabine 825mg/m2 bd weekdays. ACT4 is a phase II, non-comparative randomised-controlled trial, investigating reduced-dose IMRT for T1/2N0M0 tumours. The reduced dose arm received 34.5Gy to the prophylactic nodes in the pelvis with a simultaneous integrated boost to tumour of 41·4Gy in 23fractions with identical chemotherapy doses. We compare acute compliance, toxicity (CTCAE v5) and PROs (EORTC QLQ-C30/ANL27) up to 6-months. Results: 44 patients underwent local excision followed by involved field CRT (ACT3). 105 patients underwent reduced-dose CRT to whole pelvis (ACT4). All ACT3 patients were T1; in ACT4 there were 19.0% (20/105) T1 patients and 81.0% (85/105) T2 patients. Mean age in ACT3 and ACT4 were 60.5 (S.D 11.00) and 65.2 (S.D. 9.81) respectively. G3+ adverse effects were reported in 18.6% (8/43) in ACT3 and 35.2% (37/105) in ACT4. Respectively in ACT3 and ACT4: radiotherapy interruptions due to toxicity were 0 and 3.8% (4/105); chemotherapy modifications for toxicity were 15.9% (7/44) and 24.8% (26/105); the number of patients requiring an extension in overall treatment time >3 days due to toxicity was 0 and 1% (1/105).PRO scores for both cohorts were broadly similar over all domains at baseline, last week of treatment and 6-months; PRO scores deteriorated at the end of CRT and returning to baseline levels by 6-months.
Conclusion: Despite different populations, it appears compliance and acute toxicity are improved in the involved field radiotherapy cohort compared to whole pelvis cohort. 3-year PROs for both cohorts will offer further insight into the impact on longer term toxicity. References: [1] Gilbert et al. Lancet Oncol 2025;26:707-18[2] Nilsson et al. Acta Oncol 2023;62:897-906 Keywords: anal, ACT3, PLATO, trial, compliance, toxicity Personalising Radiotherapy Dose in Anal Cancer (PLATO) Platform: 6-month patient reported outcomes across ACT3, ACT4 and ACT5 trials Alexandra Gilbert 1,2 , Chloe Gaul 2 , Joanne Webster 2 , Sarah R Brown 2 , Joanne Copeland 2 , Sharon Ruddock 2 , Duncan Gilbert 3 , Maria A Hawkins 4 , Rebecca Muirhead 5 , Andrew Renehan 6,7 , Natalie Abbott 8,9 , Lindy Berkman 10 , Matthew Norris 2 , Rob Glynne-Jones 11 , Vicky Goh 12 , Sheela Rao 13 , Susan D Richman 1 , Alexandra Smith 2 , Richard Adams 14 , Mark Harrison 11 , Nathalie Casanova 15 , Stephen Falk 16 , Alexandra Stewart 17,18 , David Sebag-Montefiore 1,2 1 Leeds Institute of Medical Research at St James’s, University of Leeds, Leeds, United Kingdom. 2 Leeds Cancer Research UK Clinical Trials Unit, Leeds Institute of Clinical Trials Research, University of Leeds, Leeds, Proffered Paper 3983
Made with FlippingBook - Share PDF online