ESTRO 2022 - Abstract Book

S346

Abstract book

ESTRO 2022

Results For the primary target, d r was 1.7 mm and 1.86 mm for pCTV and dirCTV, respectively (see Figure 2). For the elective target, d r was 1.29 mm and 1.51 mm for pCTV and dirCTV, respectively. Furthermore, minor non relevant differences were noted for the mean DSC for all patients between the pCTV and dirCTV for both primary and elective targets ( Δ DSC mean < 3%). Conclusion Smaller setup uncertainty settings of <2 mm are feasible when using online CBCT guided proton therapy with 6D correction. A larger study cohort would be required to see if robust planning using a 2 mm setup uncertainty setting or smaller is possible. The feasibility of using the auto-propagated CTVs instead of physician corrected CTVs to analyse the errors for a larger HNC patient population is further demonstrated.

PD-0404 Evaluating pharyngeal constrictors for adaptive radiotherapy intervention to reduce dysphagia

O. Paetkau 1 , S. Weppler 1 , J. Kwok 2 , H. Quon 2 , W. Smith 1

1 Tom Baker Cancer Center, Medical Physics, Calgary, Canada; 2 Tom Baker Cancer Center, Radiation Oncology, Calgary, Canada Purpose or Objective This study evaluates pharyngeal constrictors as a target for adaptive radiotherapy (ART) in head and neck cancer treatment to reduce patient reported dysphagia. Suitable ART targets exhibit anatomical changes resulting in systematic dose changes larger than 5% throughout treatment. Materials and Methods A dataset of 66 oropharyngeal or nasopharyngeal patients treated with curative chemo-radiotherapy (70Gy in 33 fractions; 34 with dysphagia and 32 without) were retrospectively studied. A summary score greater than 40 on the MD Anderson Dysphagia Inventory survey identified patients with moderate-to-severe dysphagia. Weekly cone beam CT (CBCT) and patient-reported outcomes at one-year post-RT were collected. We propagated the dose and clinical contours to weekly CBCTs using Velocity, Version 3.2.02. Dose accumulation was performed by weighting dose-volume histogram metrics by time between CBCTs. The pharyngeal constrictor mean volume and dose were calculated for each available CBCT.