Correlation of tumour and treatment characteristics to dose received by cochlea in volumetric arc therapy

Purpose This is a radiation field simulation study using CT images designed to see the cochlear dosimetry and its correlation with tumour and treatment characteristics during radiotherapy for head and neck cancers (HNC) for identifying the factors associated with a higher dose delivered to the cochlea. Methods From 2018 to 2020, 80 patients with HNC underwent volumetric arc therapy (VMAT) to a dose of 66–70 Gy at 2 Gy per fraction with bilateral cochlea contoured for VMAT optimization as an organ at risk. Minimum, mean and maximum planned radiation dose to the cochlea based on tumour and treatment characteristics and dose-volume histogram variables of VMAT plans were analysed. Results Mean (standard deviation, SD) cochlear volume was 0.14 (0.06) cm 3 with maximum and mean planned doses of 10.3 (SD = 11.6) Gy and 8.5 (SD = 9.8) Gy, respectively. We found a statistically significant correlation between mean dose received by bilateral cochlea ( P —0.000, r r ight —0.84, r left —0.78, r midline —0.92). Tumours of the paranasal sinuses, and the parotids and more advanced T stages were associated with a higher mean dose to cochlea but was not significant statistically. The dose received by the 95% target nodal volume (D 95% ) showed a significant correlation with the cochlear mean dose ( P —0.000, r right —0.85, r left —0.77, r midline —0.93) Conclusion With VMAT we have achieved a better sparing of cochlea. The mean dose to the cochlea of one side significantly differed from the other side in patients with lateralized cancers. D 95% of nodal volume also showed a significant correlation with the cochlear mean dose.