3571 - Propensity Score-Matched Comparison of Dosimetry and Outcomes of Mucosal-Sparing IMPT and IMRT In South Asian Oral and Oropharyngeal Cancer Patients
Presenter(s)
S. Nangia1, N. Burela1, G. Singh2, T. Anusha1, S. Gayen2, G. Aishwarya2, N. Hedne3, A. D'Cruz4, and D. S. Sharma2; 1Department of Radiation Oncology, Apollo Proton Cancer Centre, Chennai, India, 2Department of Medical Physics, Apollo Proton Cancer Centre, Chennai, India, 3Department of Head Neck Surgical Oncology, Apollo Proton Cancer Centre, Chennai, India, 4Department of Head Neck Surgical Oncology, Indraprastha Apollo Hospital, New Delhi, India
Purpose/Objective(s):
The hypothesis is that mucosal-sparing intensity modulated proton therapy (MS-IMPT) improves locoregional control (LRC) and reduces treatment-related adverse effects compared with mucosal-sparing intensity modulated radiation therapy (MS-IMRT) in South Asian patients with oral cavity (OC) and oropharyngeal (OPx) squamous cell carcinoma (SCC). The primary endpoint was 2-year LRC.Materials/Methods:
We retrospectively analysed 106 consecutive patients with OC-OPx SCC treated, as per a previously published mucosal sparing protocol, between July 2019 and July 2025 (53 MS-IMPT, 53 MS-IMRT) identified from a prospectively maintained institutional database. Patients were matched 1:1 using propensity scores based on age, subsite, stage, margins, extranodal extension, and perineural invasion (caliper 0.2 SD). Definitive RT dose was 70 Gy in 35 fractions; postoperative RT dose was 60–66 Gy in 30–33 fractions. Dosimetric parameters, acute =Grade 3 toxicities, weight loss >10%, and survival outcomes, including LRC, progression-free survival (PFS), and overall survival (OS) were compared. Survival was estimated using Kaplan–Meier methodology and compared with log-rank testing.Results:
Thirty-nine OC and 14 OPx patients were included in each cohort. The median age was 54 (IMPT) and 55 (IMRT) years; 89% & 90% had stage III–IV disease, and 62% & 64% received concurrent systemic therapy, respectively. The median prescribed dose was 64 Gy in the MS-IMPT arm and 60 Gy in the MS-IMRT arm. Bilateral nodal irradiation was delivered in 94% and 77% of patients, respectively (p=0.012). All evaluated organs at risk (OARs) except the mandible demonstrated significantly lower doses with MS-IMPT (Table 1). At a median follow-up of 20.4 months, 2-year LRC was 88% with MS-IMPT versus 75% with MS-IMRT (p=0.007), and 2-year OS was 87% versus 72% (p=0.017). No failures occurred in the unirradiated neck. No significant differences were observed in acute =Grade 3 mucosal or skin reactions or reactive feeding tube placement. Weight loss >10% was significantly lower with MS-IMPT (6% vs 19%). Table 1: Median and Interquartile range (IQR) of OAR doses for MS-IMPT and MS-IMRT patientsConclusion: In this propensity-matched South Asian cohort, MS-IMPT was associated with improved OAR sparing and superior 2-year LRC and OS compared to MS-IMRT without increased acute reactions. Findings are limited by the retrospective design and warrant prospective validation.
| OAR | IMPT | IMRT | p-value | ||
| Median (Gy) | IQR (Gy) | Median (Gy) | IQR (Gy) | ||
| Mean Dose – Spared Pharyngeal Constrictors | 27.1 | 24.9-32.7 | 36.1 | 31-43 | <0.05 |
| Mean Dose – Larynx | 34.7 | 28.3-38.3 | 40.4 | 37.2-45.9 | <0.05 |
| Mean Dose – Spared Oral Mucosa | 14.9 | 10.8-20.3 | 33.1 | 28.3-37.9 | <0.05 |
| Mean Dose – Contralateral Parotid | 20.5 | 16.9-24.1 | 23.7 | 12.6-29.8 | 0.05 |
| Maximum Dose – Spinal Cord | 24.1 | 19-26 | 36.9 | 34.5-39.4 | <0.05 |
| Mean Dose – Contralateral Cochlea | 2.9 | 1.1-10.1 | 15.5 | 9.8-18.3 | <0.05 |
| Mandible_V50Gy (%) | 31.8 | 23.5-43.6 | 33.4 | 26.3-45.9 | 0.09 |