ESTRO 2020 Abstract book

S495 ESTRO 2020

be an effective option. The aim of this study is to evaluate the preliminary results of CyberKnife (CK) SRT for localized EACAs. Material and Methods Four cases (four females, 84 to 98 years old) of EACC of N0M0 (=no lymph node involvement and no distant metastasis) were treated. All four tumors (0.30 - 11.1 ml) were diagnosed as squamous cell carcinoma histologically. Total dose of 24 – 33 Gy in 3 - 5 fractions (D95 [dose delivered to 95% of the target volume]=100% dose) was delivered by CK-SRT. Results All four cases were alive at the end of the follow-up period of 19 to 106 months. In three cases (tumor volume, 0.3 – 3.5 ml) of four the treated tumors regressed or disappeared at the end of the follow-up period of 106, 28, and 19 months. In the other one case the treated tumor (11.1 ml) regrew and cervical lymph node metastasis occurred and both were treated with CK-SRT again 6 months and 20 months after the initial CK-SRT respectively. The tumors had been stable until 39 months after the initial CK-SRT. Conclusion In three of three cases of small tumors were regressed or disappeared without lymph node involvement or distant metastasis. In the other case additional SRT was performed for recurrent tumors and the patient condition was stable. SRT may be an effective option for early-stage EACCs. PO-0833 Prognostic value of tumor volume for outcomes of locally advanced laryngeal cancer treatment I. Albitskiy 1 , N. Nassar 2 , S. Billan 1 1 Rambam Medical Center, radiation oncology, Haifa, Israel ; 2 Technion, Medical School, Haifa, Israel Purpose or Objective Laryngeal carcinoma is the second most common tumor in the head & neck area after skin tumors. This type of malignancy accounts for 1-2% of all malignancies. Squamous cell carcinoma of larynx is the most common histologic type and accounts for more than 90% of cases. In advanced stages including T3N0 and T1-3N1-3M0 combined chemoradiotherapy is the accepted approach. In addition to the known prognostic factors including disease stage, vocal fixation, continued smoking during treatment, very few works have investigated the significance of tumor volume. The working hypothesis is that there is a positive correlation between tumor volume and treatment failure in patients with stage T3-4 laryngeal cancer. Material and Methods A retrospective study that included 49 T3-T4 cases treated at the Rambam Human Health Medical Center from 2010- In whom we were able to calculate tumor volume (GTV) according to planning CT, performed at the same diagnostic CT protocol. Mean age was 64 years, of which 42 were men and 7 women, mean tumor volume was 15.02 ml. All of them received radiotherapy 70Gy/56Gy concurrent with chemotherapy or in according to contraindications – cetuximab. The variables analyzed included demographics, smoking (pre-treatment; post- treatment), alcohol drinking, staging (TNM), treatment schedule, tumor volume-GTV (gross tumor volume), overall survival, disease-free survival, Disease-specific survival, and recurrence of the disease. Results After a mean follow-up of 68.6 months, the overall five- year survival was 31.9%, the five-year disease-free survival was 31.8%, the five-year specific non-mortal survival was 40.8%. In a univariate analysis of prognostic measures of survival, the volume of GTV in the group of survivors was 11.74 ± 8.26 ml vs 16.20 ± 20.78 ml in the failures (non statistically significant). In the group of patients that did not die as a result of the disease, the average tumor

PO-0831 IMRT for recurrent nasopharyngeal cancer: OAR tolerance and acute toxicity D. Aissaoui 1 , K. Mahjoubi 1 , A. Essadok 1 , R. Abidi 1 , C. Nasr 1 1 Salah Azaiz Institute, Radiation Oncology, Tunis, Tunisia of nasopharyngeal carcinoma (NPC) and progress in radiotherapy techniques, local control of primary NPC has been optimized and the patients’ quality of life has been enhancing. However, local failure still remains a concern, especially in locally advanced disease. In these cases, re irradiation with intensity modulated radiotherapy (IMRT) remains the most effective method for patients with recurrent NPC. The aim of our study was to evaluate the doses to organs at risk and treatment-related acute toxicities after reirradiation with IMRT for recurrent NPC. Material and Methods We recorded data from 10 patients reirradiated between January 2014 and June 2019 for local recurrence of NPC. Patients were followed weekly during treatment to determine the acute toxicities which were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) v.4. Results There were 7 men and 3 women. The average age at diagnosis was 45.8 years old (range 17-67 years). The initial tumor was a carcinoma undifferentiated (UCNT) in 8 cases and poorly differentiated carcinoma in 2 cases. Four patients had locally advanced tumor (T3-T4). For the primary tumor, 6 patients had neoadjuvant chemotherapy followed by radiotherapy +- concurrent chemotherapy, 3 patients had concurrent chemo-RT and one patient had radiotherapy. The average time interval from primary treatment and the relapse was 13.9 years (ranged from 2 to 34 years). Recurrence was confirmed histologically with nasopharyngeal biopsie +- adenectomy. Reirraadiation was delivered with IMRT. The dose was 60 Gy in 30 fractions for all the patients with concurrent cisplatin. GTVs were delineated using MRI images in 7 patients. The average Dmax (maximum doses) for the brain stem and for the spinal cord were respectively 13.9 Gy (range: 12.5-17.8 Gy) and 9.3 Gy (range: 7.5-11.1 Gy). For the ocular structures, the mean Dmax was 4.5 Gy (range: 1.5- 15 Gy) for the chiasma, 3.4 Gy for the right optical nerve (range 1.1-8.9 Gy ) and 6.05 Gy for the left optical nerve (range 1.3-15 Gy). Mean doses were 20.3 Gy (range 4.9-38.9 Gy) and 22.7 Gy (range 11.8-49.8 Gy) for right and left parotid, respectively. During treatment, all patients had developed acute mucitus grade I or II. Four patients had feeding diffuculties. No severe neurological toxicity has been observed. One patient had asymptomatic temporal necrosis. Conclusion The IMRT for recurrent NPC was rather well tolerated. It offers major dosimetric benefits, to deliver sufficient doses at the target volume while protecting risky organs already irradiated. Monitoring during treatment is essentiel to record consequent complications. PO-0832 Stereotactic radiotherapy for localized external auditory canal carcinoma Y. Mori 1 , S. Mizumatsu 2 , M. Hatano 2 1 Shin-Yurigaoka General Hospital, Center for Advanced IGRT, Kawasaki, Japan ; 2 Aoyama General Hospital, CyberKnife Center, Toyokawa- Aichi, Japan Purpose or Objective External auditory canal carcinoma (EACC) sometimes diagnosed in an early stage, because it arises superficially in the ear canal and may cause ear obstruction symptoms in the early phase. In addition, in the early stage of EACCs involvement into lymph nodes or distant metastases are reported less frequent. So that, stereotactic radiotherapy (SRT) concentrating high-dose radiation on the target may Purpose or Objective with contemporary standard management