ESTRO 2025 - Abstract Book

S4330

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

3. Green H et al. PO-1970 Primary renal cell cancer SBRT: a dosimetric evaluation of VMAT, Cyberknife and proton beam therapy. Radiotherapy and Oncology. 2023;182:S1737-S8. 4. Correa RJM et al. The Emerging Role of Stereotactic Ablative Radiotherapy for Primary Renal Cell Carcinoma: A Systematic Review and Meta-Analysis. Eur Urol Focus. 2019;5(6):958-69. 5. Benjamini Y et al. Adaptive linear step-up procedures that control the false discovery rate. Biometrika. 2006;93(3):491-507.

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Digital Poster The role of PET/CT in radiotherapy planning for anal squamous cell carcinoma (SCC): changes in staging and pathway timeliness. Joanna Meng 1 , Glen Blackman 1 , Thomas Richards 1 , Maria Hawkins 1,2 , Douglas Brand 1,2 1 Department of Radiotherapy, UCLH, London, United Kingdom. 2 Department of Medical physics and Biochemical Engineering, UCL, London, United Kingdom Purpose/Objective: Concurrent chemo-radiation (CRT) is the standard of care treatment for most patients with non-metastatic anal SCC. Current ESMO Anal cancer guidelines mandate CT-Chest/Abdo/Pelvis and MRI-Pelvis for staging, but limit PET to a recommended approach(Rao, 2021). Our department routinely utilises PET/CT for radiotherapy (RT) planning, acting simultaneously to stage the disease and aid tumour delineation. Using PET/CT for RT planning may speed up the pathway, avoiding a wait for staging PET/CT results before a planning scan is arranged. Material/Methods: 125 patients with anal SCC treated with CRT between January 2013 to February 2024 were identified from the electronic health record. The stage determined by CT/MRI-Pelvis was compared with the stage determined by PET/CT. Time from diagnosis to commencing RT was compared between those who had a staging-PET versus planning-PET. Statistical significance was calculated using the Mann-Whitney-U test. Results: Out of 125 patients, 121 (97%) had a PET/CT, 109 (90%) were specifically done for RT planning. Figure 1 summarises the patients’ baseline characteristics. PET/CT led to change in staging for 19 patients (15%) who were initially staged with conventional CT and MRI-Pelvis. 8 patients (6%) with nodes detected on staging CT were found to be non-FDG avid on PET/CT, resulting in down staging. In 10 patients (8%), PET/CT revealed new FDG avid nodes or distant metastases not previously seen on initial staging scans. In one patient, PET/CT found new liver metastases, which resulted in a change in treatment intent to palliative. Overall, mean time from diagnosis to commencing RT was 41 days (95% CI: 39-44). Figure 2 shows a pathway breakdown for patients who had a PET. For those who had a planning-PET, mean days from diagnosis to commencing RT was 40 days (95% CI: 38-43). This was 49 days (95% CI: 39-60) for those who had a staging-PET followed by another planning scan. The difference was not statistically significant (p>0.05).