ESTRO 2024 - Abstract Book

S60 ESTRO 2024 Online intra-fraction adaptation: not only inter-fraction, but also intra-fraction variations may occur, requiring a dedicated strategy for online treatment adaptation. Dose accumulation and image deformable registration as well as a robust intra-fraction planning strategy are the main challenges to be faced in this scenario. Online Plan QA: ensuring the quality and accuracy of the online adapted treatment plans in real time is critical for successful online adaptive radiotherapy. Online log-file analysis and AI based approaches are the most interesting solution to solve this problem. Online ART holds great promise for advancing cancer treatment, particularly in the field of proton therapy. Using real patient data and simulations, it has been gained valuable insights into the challenges and opportunities associated with this innovative approach based on the experience of photon therapy. Taking into account the pitfalls and clinical practice experienced with photon therapy, several advantages could be beneficial for the clinical implementation of online adaptive proton therapy workflow. First, the ability to evaluate the previous pitfalls and considerations using real patient data from the MR-LINAC system, would allow to simulate online adaptive proton therapy. Secondly, the sharing of errors or near misses experienced in the photon environment could allow them to be anticipated in the proton therapy setting. In addition, select and optimise resources as well as identify dedicated tools to make the entire online adaptive workflow faster, more robust, reproducible and operator independent. Finally, the need for a model to support the clinical decision to adapt or not to adapt: will this be the question? Invited Speaker Jennifer Ward 1,2,3 , H. Miles Prince 4,5 , Chris McCormac 6,5 , Stephen Lade 7 , Odette Buelens 4 , Carrie Van Der Weyden 4 , Friyana Bhabha 6 , Belinda A. Campbell 1,5 1 Peter MacCallum Cancer Centre, Department of Radiation Oncology, Melbourne, Australia. 2 Royal College of Surgeons, Depertment of Medicine, Dublin, Ireland. 3 Royal Australian and New Zealand College of Radiologists, Department of Radiation Oncology, Victoria, Australia. 4 Peter MacCallum Cancer Centre, Department of Haematology, Melbourne, Australia. 5 University of Melbourne, The Sir Peter MacCallum Department of Oncology, Melbourne, Australia. 6 Peter MacCallum Cancer Centre, Department of Surgical Oncology, Melbourne, Australia. 7 Peter MacCallum Cancer Centre, Department of Pathology, Melbourne, Australia Background and Purpose: Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder (PCSMLPD) is a benign behaving condition, typically manifesting as solitary head or neck papules, frequently creating cosmetic concerns. Optimal management of this rare disease is unclear. Herein, patterns of care, treatment responses, acute toxicities, relapse rates and survival outcomes are described, with particular focus on low-dose RT. Materials and Methods: Eligibility required biopsy-proven PCSMLPD on central pathology review, diagnosed between 2007–2022. Patterns of care, treatment responses and relapse patterns were assessed. Freedom-from-progression (FFP) was compared between RT and surgery. Results: 41 patients were eligible. First-line treatments were: RT, 19 (46.3 %); surgery, 17 (41.5 %) (3 received adjuvant RT); watchful waiting, 5 (12.2 %). Median follow-up was 37.7 months. Overall, 24 patients received RT (19 definitive first-line, 3 adjuvant, 2 second-line). 10 (42 %) received 4 Gy in 2 fractions (with no acute toxicities); 14 (58 %) received 20–40 Gy. Complete response rate was 100 %. No post-RT relapses were observed. After first-line surgery alone (n = 14, 3 with positive margins), 4 (28.5 %) experienced relapse (2 local, 2 distant). Watchful-waiting (n = 5) led to partial Abstract: 3377 Low-dose radiotherapy in primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder