Proton therapy & oral mucositis in oral&oropharyngeal cancers: outcomes, dosimetric&NTCP benefit

Abstract Introduction – Radiation Induced oral mucositis (RIOM), is a common, debilitating, acute side effect of radiotherapy for oral cavity (OC) and oropharyngeal (OPx) cancers; technical innovations for reducing it are seldom discussed. Intensity modulated proton therapy (IMPT) has been reported extensively for treating OPx cancers,and less frequently for OC cancers. We aim to quantify the reduction in the likelihood of RIOM in treating these 2 subsites with IMPT compared to Helical Tomotherapy. Material and methods – We report with acute toxicities and early outcomes of 22 consecutive patients of OC and OPx cancers treated with IMPT, and compare dosimetry and normal tissue complication probability (NTCP) of ≥ grade 3 mucositis for IMPT and HT. Results – Twenty two patients, 77% males, 41% elderly and 73% OC subsite, were reviewed. With comparable target coverage, IMPT reduced mean dose and D32, D39, D45, D50 significantly, for both oral mucosa (OM) and spared oral mucosa (sOM). With IMPT, there was a 7% absolute and 16.5% relative reduction in NTCP for grade 3 mucositis for OM, compared to HT. IMPT further reduced NTCP for sOM and the benefit was maintained in OC, OPx subsites and elderly subgroup. Acute toxicities, grade III dermatitis and mucositis, were noted in 50% and 45.5% patients, respectively, while 22.7% patients had grade 3 dysphagia. Compared with published data, hospital admission rate, median weight loss, feeding tube insertion, unplanned treatment gaps are less with IMPT. At median follow-up of 15 months, 81.8% are alive; 72.7%, alive without disease and 9%, alive with disease. Conclusion: The dosimetric benefit of IMPT translates into NTCP reduction for Grade 3 mucositis compared to Helical Tomotherapy, for OPx and OC cancers and encourages the use of IMPT in their management.