Dosimetric Investigation Of Radiotherapy-Related Trigeminal Nerve Toxicity In Oral Cavity And Oropharynx Cancer

Abstract

Trigeminal nerve (TGN) damage due to radiotherapy (RT) is an expected complication in head and neck cancer because of its anatomic location. In this study, in oral cavity and oropharyngeal cancer patients we aimed to investigate the dosimetric relationship between RT and TGN toxicity, that was previously observed in our study in parotid tumor patients. Nineteen patients treated with adjuvant or definitive RT between 2013 and 2019 were retrospectively evaluated. TGN including ophthalmic, maxillary and mandibulary branches was contoured subsequently on RT planning tomography scans by using the contouring guideline for TGN and its branches in head and neck cancer published in 2018. The dose volume histogram over total dose was generated in order to determine the maximum dose (Dmax) for TGN, max dose for remaining TGN extracted from PTV (PTV-TGN Dmax), the dose for specified volumes such as 0.1 cm3 (D0.1), 0.2 cm3 (D0.2) ), 0.5 cm3 (D0.5), 1 cm3 (D1) and 2 cm3 (D2) volumes and then the reflection of these doses on toxicity. TGN late toxicity was graded according to CTCAE v5.0. The median age was 64 years (range 24-85 years) and the mean follow-up was 50 months (range 35-65 months). Of the 19 patients, 13 patients (68%) developed grad I-III TGN toxicity distributed as grade I in 9 patients, grade II in 3 patients and grade III in 1 patient. The median duration of toxicity was 16 months after RT. TGN damage manifested itself as difficulty in jaw movements in 4 (30%), loss of sensation in 1 (8%), paresthesia in 5 (38%) and pain in 3 (23%) patients. The characteristics of patients are summarized in Table 1. The only clinical factor related with TGN toxicity was found to be the type of treatment (definitive CRT vs adjuvant CRT vs adjuvant RT (p = 0.034). The dosimetric parameters related with toxicity were total RT dose (p = 0.004), TGN Dmax (p = 0.002), PTV-TGN Dmax (p = 0.028), D2 (p = 0.001), D1 (p = 0.007), D0.5 (with p = 0.005), D0.2 (p = 0.001), and D0.1 (p = 0.001) doses respectively. In terms of TGN toxicity, threshold values for TGN Dmax, PTV-TGN Dmax, D0.1, D0.2, D0.5, D1 and D2 were detected to be as 67.5 Gy, 66.7 Gy, 64.9 Gy, 64 Gy, 63 Gy and 59.3 Gy, respectively. TGN late toxicity is an important complication of RT that has not been yet clearly defined in head and neck cancer. During RT planning, taking into account of cut off values which has correlated with our previous study may play a remarkable role.Abstract 3965; TableParametern (%)Gender Female Male8(42) 11(58)Tumor location5(26)Tongue2(11)Lower Lip2(11)Retromolar Trigon2(11)Hard Palate2(11)Buccal Mucosa1(5)Gingiva1(5)Base of mouth3(15)Tonsil1(5)Oropharynx undefinedStage I II III IVA IVB3(16) 3(16) 4(21) 8(42) 1(5)Histology SCC Mucoepithelial Carcinoma Adenoid Cystic Carcinoma16(84) 2(11) 1(5)LVI Positive Negative Unknown1(5) 14(74) 4(21)PNI Positive Negative Unknown5(26) 11(58) 3(16)Surgery margin Positive Close Negative13(68) 8(42) 1(5) 4(21)Treatment Procedure Definitive CRT Surgery + RT Surgery + CRT6(32) 5(26) 8(41) Open table in a new tab