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) cm3 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, rright-0.84, rleft-0.78, rmidline-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 (D95%) showed a significant correlation with the cochlear mean dose (P-0.000, rright-0.85, rleft-0.77, rmidline-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. D95% of nodal volume also showed a significant correlation with the cochlear mean dose.

Relative contributions of radiation and cisplatin-based chemotherapy to sensorineural hearing loss in head-and-neck cancer patients.

BACKGROUND: One of the debilitating complications of head and neck cancer radiotherapy is hearing loss. OBJECTIVE: To quantify the magnitude of sensory neural hearing loss (SNHL) in the head and neck cancer patients undergoing chemoradiation therapy. DESIGN AND METHODS: This is a prospective study. Eighty patients with head and neck cancers and undergoing volumetric arc therapy were taken up for the study. Regular audiological evaluation was done. The changes in audiological parameters from baseline are correlated with cochlear dose. RESULTS: Cochlea received maximum doses of up to 28.52 Gy without causing SNHL in the absence of chemotherapy. But in concurrent chemoradiotherapy, hearing loss was found at least dose of 9 Gy at frequency range of 4 KHz-8 KHz. The risk of SNHL is independent of cumulative doses of Cisplatin. In 106 ears receiving concurrent chemoradiation, 82.1% and 74.5% ears had sensorineural hearing loss at 4 KHz and 8 KHz respectively, following the completion of treatment. Otoacoustic emissions in the chemoradiation group showed a significant change at the completion of treatment. CONCLUSION AND SIGNIFICANCE: Volumetric arc therapy have facilitated sparing of cochlea (< 40 Gy). This has resulted in better clinical outcome in terms of SNHL. The inclusion of concurrent cisplatin chemotherapy is a significant risk factor for the development of SNHL at higher frequencies.