Correlation between Target Volume and Organs at Risk Doses in Stage Ii-Iva Nasopharyngeal Carcinoma Patients Treated With Helical Tomotherapy: A Prospective Single Institution Study from Northeast India

Abstract

Background: Nasopharyngeal carcinoma (NPC) is a relatively rare head and neck cancer globally, accounting for only about 0.7% of all cancers The peak incidence arises between 15 and 25 years of age, with the second peak of 50 and 59 years of age. The majority of patients present with locally advanced disease (stage II–IVA) requiring combined modality therapy .The aim of the study is to examine the relationship between target volume and organ-at-risk (OAR) doses in nasopharyngeal carcinoma (NPC) patients treated with image-guided helical tomotherapy.

Material and Methods: In this prospective single-institutional study, 30 patients with histologically confirmed stage II–IVA NPC were treated with helical tomotherapy  to a dose of 70 Gy in 35 fractions with concurrent Cisplatin chemotherapy. The target volumes and key Organs at Risk (spinal cord, brainstem, bilateral cochlea, parotids, larynx, oral cavity) were delineated. Dose–volume histogram parameters (maximum dose Dmax, mean dose Dmean, and V50Gy for selected structures) were recorded. Pearson correlation coefficients (r) between GTVp and OAR dose metrics were computed and a p value <0.05 was considered significant.

Results: The GTVp volume ranged between 10–210 cm³ (mean ~78 cm³). Larger GTVp was significantly associated with higher doses to the right cochlea and oral cavity. Specifically, GTVp had a positive correlation with right cochlea Dmax (r≈0.77, p=0.005) and Dmean (r≈0.84, p=0.004), and with oral cavity mean dose (r≈0.68, p=0.030) .No other OAR parameters showed significant correlations (all p>0.05).

Conclusions: Thus in Nasopharyngeal Cancer treated  with helical tomotherapy, increasing tumor volume was linked to higher doses to the right cochlea and oral cavity. These findings underscore the impact of tumor extent on OAR exposure and highlight the need for careful dose optimization, especially to auditory and mucosal structures, in patients with large GTVs.