Comparision of lens doses using volumetric modulated arc therapy and field in field radiotherapy planning techniques in whole brain irradiation of patients with brain metastases

The aim of this study is to compare lens doses using volumetric modulated arc therapy (VMAT) and field in field (FIF) radiotherapy planning techniques in the treatment of whole brain radiotherapy of patients with brain metastases. Whole brain, lenses, optic nerves and orbitas are contoured on the tomography images of 20 patients with brain metastases. Target volume was irradiated for fractional dose 3 Gray (Gy) and total dose 30 Gy, using 6 MV photon energy for palliative purposes. The priority is increasing the quality of life in palliation purposes whole brain radiotherapy, so lens doses are of great importance in this sense. For this reason, the lenses were tried to be protected as much as possible while plannings were done. Whole brain, lenses and other critical organs's dose value, conformity index (CI), homogeneity index (HI) and monitor unit (MU) values which are obtained by the treatment planning system (TPS) were evaluated dosimetrically and statistically. When the averages of the minimum, mean and maximum doses of whole brain tissue were statistically analyzed, p values respectively were found as 0.003, 0.024 and 0.003 and the FIF technique was found to be superior.When the averages of the maximum doses of the right and left lenses were statistically analyzed in terms of two techniques, p values were found to be 0.001 and it was noticed that lenses are better protected with the FIF technique. Both planning techniques are clinically feasible. However, our study also showed that when critical volumes which is affecting the quality of life of the patient are mentioned, FIF technique gives better results in whole brain radiotherapy.