ESTRO 2023 - Abstract Book

S993

Digital Posters

ESTRO 2023

Purpose or Objective We aimed to explore a potential individualized elective prophylactic neck irradiation (iEPNI) to optimize the current strategy by investigating the distribution of metastatic lymph nodes (LNs) in nasopharyngeal carcinoma (NPC). Materials and Methods Magnetic resonance imaging (MRI) and clinical data of 870 non-metastatic NPC patients admitted to the Hunan Cancer Hospital between January 2019 and December 2019 were reviewed. All patients were staged using the 8th TNM staging system, and the LN location was assigned based on the 2013 guidelines. According to the distribution patterns of the LNs in NPC, the intra-regional lymphatic drainage levels were categorized into the following three stations: Station 1 of level VIIa and II; Station 2 of level III and Va; and Station 3 of level IV, Vb, and Vc. Other levels were defined as extra-regional areas. Results The incidence of LN metastasis was 822/870 (94.5%), including 198 cases of unilateral metastasis and 624 cases of bilateral metastasis. Among the 870 patients, the most frequently involved intra-regional lymphatic drainage was level II (89.3%), followed by level VIIa (80.0%), II (59.5%), Va (30.6%), IV (21.3%), Vb (8.9%), and Vc (1.1%). In the extra-regional areas, the detailed LN distribution was: level Ia (0.2%), level Ib (7.7%), level VI (0.1%), level VIIb (5.6%), level VIII (5.5%), level IX (0.3%), and level X (0.2%). The rate of LN metastasis in Station 1, Station 2, and Station 3 was 820/870 (94.3%), 532/870 (61.1%), and 199/870 (22.9%), respectively. Only four patients were considered to be skipping metastasis among the three stations (4/870, 0.5%). Additionally, in 203 patients with unilateral Station 1 LN metastasis, there were 86 (42.4%) and 37 (18.2%) patients with ipsilateral Station 2 and Station 3 metastasis, respectively, and 3 (1.5%) and 1 (0.5%) patients with contralateral Station 2 and Station 3 LN metastasis, respectively. Conclusion LN spread in an organized manner from Station 1 to Station 3 with rare skipping metastasis. A potential iEPNI strategy of prophylactical neck irradiation to the ipsilateral latter node-negative station might be feasible, which is detailed as follows: irradiation to Station 1 in patients with no LN metastasis, irradiation to Station 2 in patients with only Station 1 metastasis, and irradiation to Station 3 in patients with Station 2 metastasis but without Station 3 metastasis. Further prospective investigations are expected to validate the strategy. Purpose or Objective Previous studies on radiation dose escalation have shown mixed results, and it is not established how to select the subgroup of head and neck cancer patients that would benefit from dose escalated radiotherapy. In this study we retrospectively analysed treatment outcome and side effects in patients with oropharyngeal cancer treated with dose escalated radiotherapy compared to a matched cohort treated with standard dose radiotherapy. Materials and Methods We identified 244 patients treated with >72 Gy (EQD2, α / β = 10 Gy) and 332 treated with 68 Gy for oropharyngeal squamous cell carcinoma between 2011 and 2018 at our institution. A matched cohort was selected for analysis, including 215 patients from each dose level. Data on treatment outcome and side effects (osteoradionecrosis (ORN), skin, mucosa, larynx, trismus, salivary glands and dysphagia) were collected from a local quality registry and supplemented with a review of medical records. Results Clinical characteristics of the two subgroups are listed in Table 1. The 5-year overall survival (OS) was 77.8% (95% CI 72.4 91.6) and 73.7% (67.8-80.1) in the high dose and control group respectively (p=0.24). A subgroup analysis stratified by T stage showed no significant differences in OS in patients with T1 or T2 tumours. By contrast, advanced primary tumours fared better in the high-dose subgroup with a 5-year OS in T3-tumours being 65.7% (54.3-79.5) and 42.8% (27.1-67.6) in the high-dose and control group respectively (p=0.03) and OS in T4-tumours being 79.1% (69.6-89.9) and 44.4% (24.6-80.5) in the high-dose and control group respectively (p<0.001). In accordance with this, no significant differences was seen in progression free survival (PFS) between the two groups in T1- and T2-tumours; while patients with advanced primary tumours in the high-dose group fared better with a 5-year PFS in T3-tumours of 66.6% (55.1-80.5), compared to 43.1% (27.4 67.8) in the control group (p=0.04), and similarly for T4-tumours with 71.4% (61.0-83.4) and 44.4% (24.6-80.5) in the high dose and control groups, respectively (p=0.02). Grade ≥ 3 ORN and dysphagia were more common in the dose-escalated group compared to the control group, with 19 (8.8%) vs. 4 (1.9%) patients developing grade ≥ 3 ORN in the high-dose and control group, respectively (p=0.003), and 37 (17.2%) vs. 21 (9.8%) patients developing grade ≥ 3 dysphagia in the high-dose and control groups, respectively (p=0.04). There were no other significant differences in the investigated grade ≥ 3 side effects. Median follow up was 78.1 months in the dose-escalated cohort and 60.2 months in the control group. PO-1240 Large primary tumours of oropharyngeal cancer may benefit from radiation dose escalation A. Embring 1 , E. Onjukka 1 , C. Mercke 1 , I. Lax 1 , A. Berglund 2 , S. Friesland 1 1 Karolinska Institutet, Department of Oncology-Pathology, Stockholm, Sweden; 2 Epistat, Epistat, Uppsala, Sweden