Intensity-modulated Radiotherapy Versus Volumetric Modulated Arc Therapy in Head and Neck Cancers: A Comparative Analysis of Compliance, Toxicities and Dosimetric Parameters.

Introduction Intensity-modulated radiotherapy (IMRT) is now a standard technique to treat head and neck cancers. Another advanced technique - volumetric-modulated arc therapy (VMAT) - is gaining popularity due to rapid treatment delivery, which allows patient comfort and reduced intrafraction motion. The present study aims to compare the compliance, dosimetric parameters and acute toxicities between both techniques in head and neck cancer patients. Materials and methods One hundred de-novo patients of head and neck cancers presenting to our department and planned to be treated by definite chemoradiation either due to medical inoperability, patient preference or anatomical inaccessibility for surgery were selected. Patients were assigned to one of the treatment groups quasi-randomly in a 1:1 ratio, with odd-number participants planned to be treated by IMRT (Group I) and the even-number patients planned to be treated by VMAT (Group II). Contrast-enhanced computed tomography (CECT) scan of the head and neck region was used for simulation and radiotherapy planning, and target volumes were delineated along with organs at risk (OARs). The dose prescription was at 70 Gy in 35 fractions at 2 Gy/fraction for five days a week, delivered with concurrent chemotherapy (injection Cisplatin @35 mg/m weekly). Concurrent chemotherapy was avoided in septuagenarian patients, those with Cisplatin ineligibility or in early glottic cancer patients. Planning target volume (PTV) dosimetric parameters calculated were: V66.5Gy (%), D2% (Gy), D50% (Gy), D98% (Gy), Dmax (Gy), Dmean (Gy), homogeneity index, conformity index and monitor units (MUs). Dose constraints to OARs given were Dmax (Gy) to planning organ at risk volume (PRV) brainstem, PRV spine, optic chiasma, optic nerve, lens and mandible; Dmean (Gy) to both parotids, cochlea, PseudoOAR and lips. Though brachial plexus and dysphagia aspiration-related structures (DARS) were prospectively contoured, they were not included in the dose planning.  Patients were assessed weekly during the treatment for oral mucositis, radiation-induced dermatitis and haematological toxicity and were followed up at least for six months from the day of the completion of treatment. Statistical analysis was performed using IBM SPSS version 22, and p-value <0.05 was considered significant. Results Amongst PTV parameters for IMRT vs VMAT, D2 (71.9±0.58 vs 73.2±0.66 p=0.02), Dmax (74.09±0.6 vs 74.5±1.11; p=0.04) and MUs (2002.4 vs 604.78, p=0.0002) showed statistical significance, contributing to decreased beam on time during treatment delivery, which was better in the VMAT arm. OAR dosimetry was lower in VMAT for right cochlea (20.6 vs 15.97, p=0.07), right lens (2.69 vs 2.01, p=0.04), left optic nerve (6.05 vs 3.21, p=0.04) and lips (19.05 vs 14.88, p=0.004) but statistically significant. Other dosimetric parameters and dosimetry of OARs did not show any statistical difference. The RTOG grade 3-4 skin reactions between IMRT and VMAT were found to be comparable (p=0.82), but not statistically significant. The RTOG grade 3-4 oral mucositis between IMRT and VMAT were also found to be comparable (p=0.63), but not statistically significant. Conclusion VMAT is better than IMRT in terms of lesser MUs delivered but with comparable PTV, OAR dosimetry and acceptable acute toxicities. The long-term follow-up in terms of secondary malignancies needs to be evaluated.