ESTRO 2024 - Abstract Book

S3724

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

the LyProX database. Finally, a unilateral plan (UnilatP) was generated from which the whole contralateral region of the CTVe was omitted. UnilatPs were only generated for patients with no presence of N+ contralateral, no midline extension and no central tumour. Patients who did not fulfil the inclusion criteria of neither SelectP nor UnilatP were excluded from the study. All CTVs were expanded with a 3 mm isotropic CTV-to-PTV margin, and prescribed doses were 68Gy, 60Gy, and 50Gy for PTV1, PTV2, and PTV3, respectively. Each TP underwent quality assessment by an experienced medical physicist. Mean dose to OARs (esophagus, glottic larynx, subglottic larynx, lips, oral cavity, left & right parotid, lower, middle & upper pharyngeal constrictor muscle (PCM), left & right submandibular, and thyroid) were reported. Normal tissue complication probabilities (NTCP) were calculated to evaluate the probability of moderate to severe xerostomia and dysphagia according to the LENSTSOMA scale. Finally, to assess the spill-over dose, the remaining volume at risk receiving more than 30Gy (V 30Gy RVR) was calculated. Eight patients were excluded as they did not fulfil the inclusion criteria, leaving a total of twelve patients for further analysis. Seven of the twelve patients qualified for UnilatP. An overview of the omitted lymph node levels is reported in table 1. The quality of all included TPs was approved according to the study criteria. Mean doses to OAR are reported in figure 1. When comparing the BaseP and UnilatP, the mean dose to OAR were substantially lower for the glottic larynx, contralateral parotid, lower PCM, contralateral submandibular, and thyroid. Hence, UnilatP shows substantial reductions in mean doses to OAR, while SelectP only shows little to no observable reduction when compared to BaseP. The NTCPs, as reported in figure 2, show minimal variation in probability of xerostomia and dysphagia between BaseP and SelectP. Nevertheless, there is a noteworthy decrease for both xerostomia (mean 3.2%) and dysphagia (mean 5.7%) when comparing BaseP and UnilatP. Hence, UnilatPs result in a lower probability that a patient would experience xerostomia and/or dysphagia in contrast to both BasePs and SelectPs. Finally, a substantial decrease of V 30Gy RVRs was observed between BaseP and UnilatP (32.8% [21.4%; 44.5%]), whereas only a small reduction was seen between BaseP and SelectP (9.8% [-3.9%; 28.4%]). Results: