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Radiation-induced ocular complications are frequent during head and neck radiotherapy (HNRT). Someone are benign and others can be very serious leading to vision loss The damage of lacrimal gland (LG) is one of the most underestimated complications in HNRT. The purpose of this study is to evaluate the cumulative doses in the LG during radiotherapy (RT) for nasopharyngeal carcinoma (NPC) with a clinical toxicities correlation.

This is a retrospective study analyzing the dosimetric plans of 50 patients with NPC (82% stage III and IVa) treated between august 2020 and June 2022. All patients received neoadjuvant chemotherapy then RT at a total dose of 69.96Gy in 33 daily fractions with concomitant weekly cisplatin. The treatment plan was carried out with volumetric modulated arc therapy for 27 patients and Intensity Modulated Radiation Therapy for 23 patients. The right LG (RLG) and the left one (LLG) were delineated separately and the following variables were recorded: maximum dose (Dmax), mean dose (Dmean), volume of the planning target volume (PTV), cranio-caudal distance between the PTV receiving a dose of 60 Gy (PTV60) and LG (d). Ocular toxicity was assessed using the RTOG radiation morbidity criteria. Clinical assessment was performed at the end of the RT sessions, 6 and 12 months later.

The median of Dmax in the RLG and LLG was of 5.6Gy [2.6–38] and 6.2 [2.6-27] respectively. The median Dmean in the RLG and LLG was 3.6 Gy [2.2-14.8] and 3.8 Gy [2.2-12]. The mean PTV volume was of 320 cc. The mean “d” was of 12 mm [0-24] (table1).

Table 1: Data of the cumulative doses in the lacrimal glands:

After a median follow up of 17 moths, no patients had G3 or G4 ocular toxicities. Nine (18%) and 2 (4%) patients developed G1 and G2 dry eye respectively. For those patients, the mean PTV volume was of 412 cc [334-683], the mean “d” was of 7 mm [0-9] and tumors were classified as T3-T4 for six patients. However, Dmean were below to 25 Gy in all these cases. In addition, the Q3 of Dmax in the RLG and LLG was of 29.7Gy [6.6-38 Gy] and 17.8 Gy [4.5-27 Gy] respectively. The Q3 of Dmean in the RLG and LLG was 10.5 Gy [3.9-14.8 Gy] and 8.6 Gy [3.8-12.2 Gy].

Although dry eye is not a common radiation-induced complication for NPC RT, we propose the delineation of the LG as an organ at risk in case of closely advanced NPC as well as stricter dose constraints in the absence of radiation-induced dry eye prevention. The results of this study show that these constraints could be reasonable to respect during dosimetric optimization: Dmean ≤11 Gy and Dmax ≤30Gy.These results should to be confirmed by larger prospective series with clinical assessement.