ESTRO 2024 - Abstract Book

S4005

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

References:

1. Versteijne E, Dam van JL, Suker M, Janssen QP, Groothuis K, et al. Neoadjuvant chemoradiotherapy versus upfront surgery for resectable and borderline resectable pancreatic cancer: long-term results of the Dutch randomized PREOPANC trial. J Clinical Oncol 2022;40(11):1220-1230

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Poster Discussion

Implementing plan of the day for cervix cancer: which contouring method and margins to use

Lei Wang 1,2 , Jonathan Mohajer 1 , Helen McNair 1,2 , Emma Harris 2 , Susan Lalondrelle 1,2

1 Royal Marsden Hospital, Radiotherapy and Imaging, Sutton, United Kingdom. 2 Institute of Cancer Research, Radiotherapy and Imaging, Sutton, United Kingdom

Purpose/Objective:

Due to substantial interfraction motion in cervix cancer, interest has been growing in Plan-of-the-Day (PotD) solutions [1]. However, implementation has been variable, partly due to uncertainty over optimum methodology for contouring the planning target volumes (PTVs). No evidence-based guidelines exist. Published methods vary but cannot be compared due to differences in patient population and reporting metrics. We assessed published methodologies against our own data.

Material/Methods:

Forty cervical cancer patients were treated with 25 daily fractions of radiotherapy. Each had planning CT with full bladder (CT-FB) and empty bladder (CT-EB), planning MRI with half-full bladder and daily cone beam CTs (CBCTs). From the daily CBCTs for each patient, 5-11 examples were selected to represent interfraction motion. All planning scans (120) and selected CBCTs (239) had targets and organs at risk (OARs) contoured following EMBRACE-II guidelines [2]. The low-risk clinical target volume (CTV LR ) included the tumour, cervix, uterus, upper vagina and parametria. The high-risk clinical target volume (CTV HR ) comprised the tumour and uninvolved cervix. A literature search for studies reporting cervix PotD methodology identified 30 adaptive and non-adaptive solutions to PTV generation which were applied to our patients. Coverage of the daily CTV LR was assessed on 239 treatment fractions. Mean PTV size was recorded as a surrogate for OAR dosimetry. For each PotD strategy, the optimum PTV was selected to maximise CTV LR and CTV HR coverage while minimising OAR coverage; the coverage and size of selected PTVs were recorded. For 11 patients treated prospectively with PotD, an alternative clinician-derived solution was investigated alongside the simulated PTVs; clinician PTVs were subjectively edited and extrapolated based on estimation of pelvic organ motion.