ESTRO 2021 Abstract Book

S604

ESTRO 2021

Purpose or Objective To investigate the potential of diffusion-weighted MRI (DW-MRI) changes during radiotherapy (RT) for head and neck cancer (HNC) in the detection and prediction of dysphagia. Materials and Methods Patients enrolled in a prospective, IRB-approved study with MRI scans before and during RT (week 4–7) were included in this analysis. Dynamic Imaging Grade of Swallowing Toxicity (DIGEST; scores of 0–3) and MD Anderson symptom inventory (MDASI; 0–10) were used to determine dysphagia before, mid-treatment (MDASI) and 12 months post-RT (DIGEST, MDASI). 17 swallowing-related structures were manually delineated on pre- and mid T2 MRI and propagated to the co-registered (deformable) DW-MRI sequences: the superior (SPC), middle (MPC), and inferior (IPC) pharyngeal constrictor, ipsi- and contralateral M. masseter (MM), ant. digastric muscle (ADM), genioglossus (GG), geniohyoid (GH), mylohyoid (MH), ipsi- and contralateral medial and lateral pterygoideus, soft palate (SP), base of tongue (BOT), oral tongue, and epiglottis. All visible tumor on T2 and T1 post contrast MRI was subtracted from the structures. Mean apparent diffusion coefficient (ADC) values were extracted, percentage change from baseline to mid-treatment calculated and correlated with absolute change in DIGEST and MDASI scores. Results 46 HNC patients were included in this analysis (89% male, median age 59 years). The majority of primary tumors was located in the oropharynx (n=34, 74%) and the oral cavity (n=5, 11%). 29 patients (63%) received intensity modulated radiotherapy (IMRT), 15 (33%) pencil beam scanning proton therapy, and 2 (4%) a combination of both. Prescribed dose to the high dose planning target volume (PTV) was 60–70 Gy in 30–35 fractions. MDASI scores for swallowing difficulties significantly increased from baseline (mean: 1.00) to mid- treatment (mean: 5.90; p<0.001) and 12 months post-RT (mean: 2.20; p=0.002), and mean DIGEST scores from 0.22 at baseline to 0.69 12 months post-RT (p=0.005). The mean ADC values increased from pre- to mid- treatment by 6–27% in the ipsilateral muscles and midline structures (0–1% in the contralateral muscles) with significant changes in the SPC, SP, and epiglottis (p<0.001), the MPC (p<0.01), BOT, IPC, GH, ADM, and GG (p<0.05). The change in ADC value from baseline to mid-treatment of the SPC was significantly correlated with the change in MDASI score mid-treatment (p=0.026). No significant correlation could be found in percentage ADC change of any of the muscles with the change in MDASI and DIGEST scores 12 months post-treatment. Conclusion DW-MRI is able to detect radiation-associated changes in the swallowing structures during RT. The change of ADC value from pre- to mid-treatment in the SPC was significantly correlated with patient reported swallowing difficulties mid-treatment and might serve as a biomarker for dysphagia. No predictive value was found for any swallowing structure in DW-MRI for late dysphagia. PD-0773 Update of the results of single vocal cord irradiation for early-stage glottic cancer L. Tans 1 , M. Dorr 2 , A. Al-Mamgani 3 , S.L. Kwa 1 , A. Sewnaik 4 , F. Keskin-Cambay 1 , R. Nout 1 , W. Heemsbergen 5 1 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiation Oncology, Rotterdam, The Netherlands; 2 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Otolaryngology and Head and Neck Surgery, Rotterdam, The Netherlands; 3 Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Department of Radiation Oncology, Amsterdam, The Netherlands; 4 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Otolaryngology and Head and Neck Surgery, Rotterdam, The Netherlands; 5 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, The Netherlands A novel radiation technique was developed in our institute in 2011; Single Vocal Cord Irradiation, (SVCI) for selected patients with T1a laryngeal cancer. The rationale is to irradiate smaller volumes and therefore reduce toxicity, with the radiobiological advantage of a shorter overall treatment time, and a reduction of the burden for patients and their families with fewer treatment visits. Earlier results showed excellent tumor control and a favorable toxicity profile. The aim of the current study is to validate these results in an expanded cohort of patients with longer follow-up time. Between February 2011 and January 2020, 111 consecutive patients with early-stage glottic cancer were treated with IMRT-SVCI on a standard Linac using a schedule of 58.08 Gy, given in 16 fractions of 3.63Gy. The CTV was the involved cord. The PTV was generated using a margin to the CTV of 3, 5, and 3 mm for the left- right, cranial-caudal, and anterior-posterior directions, respectively. Setup verification was done by means of an online correction protocol using daily cone-beam CT prior to each fraction. As in the proof-of-concept study, the endpoints were local control (LC), overall survival (OS), grade ≥3 acute and late toxicity (CTCAE) and voice quality assessment using voice handicap index questionnaires. Results After a median follow-up of 38 months, two patients developed in-field local failure after 7 and 41 months. The 3- and 5-years LC rates were 99.1% (0.9%1SE) and 97.1% (2.1%1SE), respectively. The ultimate local control rates at 5-years was 99% as both patients with local failure were successfully salvaged by means of total laryngectomy. However, one patient died because of second local recurrence. The 5-years OS was 80.6% and the laryngectomy-free survival was 98.1%. All patients finished the treatment without any interruption. No patients developed acute grade ≥3 toxicity. One-hundred and eight patients were evaluable for late toxicity (≥6 months of follow-up). Late grade ≥3 toxicity was reported in 7 patients (6.5%, all were G3); 2 because of severe hoarseness and 5 patient because of laryngeal radionecrosis 5 to 25 month post-SVCI of which two received tracheostomy because of severe laryngeal edema. The VHI score improved over time, as only 22% of Materials and Methods Materials and methods: Purpose or Objective Background and purpose: