Toxicity of Simultaneous Integrated Boost Intensity Modulated Radiation Therapy in Post-Operative Oral Cavity Cancer

Abstract

To assess the acute toxicity of Simultaneous integrated boost intensity modulated radiation therapy (SIB-IMRT) in postoperative oral cavity cancers with intermediate risk features was the primary objective of this study. The secondary objectives were to assess late toxicity and efficacy. This was a prospective, interventional study conducted at a single center. Patient accrual was done from November 2017 to August 2018 and data was analyzed in November 2019. Patients of oral cavity carcinoma who underwent surgery and had at least one risk factor on histopathological evaluation i.e., T3/T4 stage, node positive without extra capsular extension, lymphovascular invasion (LVI), perineural invasion (PNI), close margin (<5 mm), depth of invasion ≥3 mm for tongue and ≥7 mm for buccal mucosa were included. All patients had indication for adjuvant RT alone without concurrent chemotherapy. Post-operative RT was delivered with SIB-IMRT technique using 6 MV X-rays on a Linear accelerator. A dose of 63.6 Gray (Gy) in 30 fractions was delivered to high risk clinical target volume (CTV), 54 Gy in 30 fractions to intermediate risk CTV and 51 Gy in 30 fractions to low risk CTV. Dose constraints for the spinal cord was Dmax ≤ 42Gy, PRV cord Dmax ≤ 48Gy, brainstem Dmax ≤50.4 Gy, each parotid Dmean ≤ 26 Gy. Weekly assessment was done during RT and acute radiation toxicities were recorded as per Radiation Therapy Oncology Group (RTOG) acute toxicity criteria in terms of oral mucositis (OM), skin toxicity and dysphagia. Subsequent visits were monthly for the first 3 months, 2 monthly for the next 6 months and 3 monthly thereafter. Clinical examination with an assessment of the late toxicity was done as per RTOG late morbidity scoring schema. Radiological imaging (CECT or MRI) was done at 3 months post RT. Statistical analysis was performed using statistical package for sciences (SPSS version 20.0). Survival analysis was done by Kaplan-Meier method with log rank test. A total of 30 patients were included in the study with a median age of 48.5 years (range 33-75 year). The frequency N (%) of primary site involved was tongue 13(43.33), buccal mucosa 12(40), alveolus 4 (13.33) and retromolar trigone 1 (3.33). All patients completed RT and the median duration of RT was 42 days [mean days 42.3±0.93]. Maximum acute grade ≤2 vs grade 3 oral mucositis was 46.67% vs 53.33%, skin toxicity was 86.67% vs 13.33 %, dysphagia was 66.67% vs 33.33% respectively. No patients had grade 4 or 5 acute toxicity. At a median follow up of 11 months [range 6-18 month], grade 1 late toxicities were 53.33% (subcutaneous toxicity) and 33.33% (xerostomia). Loco regional control was 96.67%. IMRT-SIB is safe in terms of acute toxicity however the short follow up duration limits assessment of late toxicity and locoregional control rates in post-operative oral cavity cancers with intermediate risk.Abstract 3966; TableRisk factor for adjuvant RTN (%)>pT316(53.33)p N+9(30)PNI+11(36.67)LVI+5(16.67)Close margin1(3.33)DOI20(66.67) Open table in a new tab