ESTRO 2025 - Abstract Book

S3494

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

[5] Lund CM et al . AAPM 64th Annual Meeting & Exhibition. 10-14 July 2022. [6] Perl J et al . Med Phys. 2012; 39(11):6818-37. [7] IBA Beam Data Library. 2019. Github repository, https://gitlab.com/openmcsquare/MCsquare/- /tree/master/BDL. [8] Titt U et al. Phys Med Biol. 7 Dec 2010;55(23):7097-106. [9] Trofimov A, Bortfeld T. Technol Cancer Res Treat. Oct 2003;2(5):437-44.

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Digital Poster Clinical Acceptability of the Next Generation in Modulated Arc Therapy for Nasopharyngeal Carcinoma Kenton Thompson 1,2 , Catherine Laferlita 1 , Tsien Fua 1,2 , Christopher Daniels 1 , Vanessa Panettieri 1,2 , Nicholas Hardcastle 1,2 , Thomas Devereux 1,2 , Tomas Kron 1,2 , Pauline Lim 1 , Katrina Woodford 1,2 , Sandro Porceddu 1,2 1 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. 2 Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia Purpose/Objective: For advanced stage curative nonmetastatic nasopharyngeal carcinoma (NPC) dose coverage is often compromised due to proximity of critical structures, resulting in a lowering of tumour control probability. 1 Both IMRT and VMAT have dosimetric advantages, but hybrid optimisation and delivery is currently not an integrated process. 2,3 RapidArc Dynamic solution (RAD) (Varian Medical Systems, Palo Alto, USA) uniquely leverages dynamic collimation and combines IMRT and VMAT in a single continuous delivery. This comparative study aims to evaluate the clinical acceptability of RAD planning to conventional VMAT for a cohort of curative NPC cases treated at our institution. Material/Methods: Eligibility for evaluation consisted of T3-4, any N, M0 NPC patients treated with curative intent between 1 July 2019 and 1 July 2023. Twenty patients formed the cohort. Two RAD approaches were developed and optimised: 1. Single arc with 5 STatic Angle Modulated Ports (STAMP) - RAD1 2. 2 arcs with 4 STAMPs per arc - RAD2 Target, OARs and complexity metrics were compared. Statistical differences were determined by a Wilcoxon signed rank test (p ≤ 0.05). To determine the clinical acceptability of the treatment plans, the RAD plans and the approved clinical VMAT plans were presented to two practicing radiation oncologists specialising in head and neck for blinded review. The reviewers were given a clinic summary (age, gender, TNM, EBV status, agreed treatment plan (RT alone, chemoRT +/- induction), prescribed dose) and asked to confirm that each plan was acceptable (Y/N), rank the plans from 1 (best) to 3 (worst) and provide reason for the highest ranked plan. Results: Compared with the clinical plans, RAD1 increased D98% of GTVp_7000 (mean increase 0.82Gy, p=0.01) and PTV_7000 (mean increase 0.42Gy, p=0.14). Compared with the clinical plans, the RAD2 increased D98% of GTVp_7000 (mean increase 0.87Gy, p=0.01) and PTV_7000 (mean increase 0.71Gy, p=0.01). For both approaches dose constraints to critical neurological structures were maintained. Table 1. summarises the key plan metrics. The number of accepted plans was different between the blinded reviewers. When combining reviews, more RAD plans were assessed acceptable and ranked higher. RAD1 and RAD2 approaches were both assessed as acceptable 32/40 compared to only 20/40 clinical plans, and 32/40 highest ranked plans were one of the two RAD approaches. Table 2. summarises the scoring of the reviewers.