The Comparison of Brain and Lens Doses in Whole Brain Radiotherapy With Different Treatment Plannings

Abstract

The aim of study was to evaluate the effects ontarget volume (brain) and lens doses with different treatment plannings in patients who received whole brain radiotherapy because of brain metastases. The system tomography scans of 14 patients at 0.5 cm intervals, were transferred to three-dimensional treatment planning computer and the normal tissues and target volumes were outlined. Seven different treatment plannings were done for each patient. Plan I: Angled blocked plan; Plan II: Non-angled blocked plan; Plan III: Helmet plan; Plan IV: Blocked plan with the inferior border at the inferior orbital ridge; Plan V: Angled unblocked plan; Plan VI: Non-angled unblocked plan; Plan VII: Conventially planned non-angled unblocked plan. Brain and lens minimum, maximum and mean doses and brain V95 and D95 doses were recorded for each plan using dose-volume histograms. When the plans were compared according to the brain minimum, mean, V95 and D95 doses, it was observed that the doses in Plan VII were lower than the others (mean 1171.57 cGy, mean 3294.64 cGy, 97.48% and mean 2990.57 cGy respectively, p < 0.05). When the plans were compared according to the lens doses, the minimum, maximum and mean doses were higher in the unblocked plans (p < 0.05). It was seen that with the angling of beams five degrees to the posterior the lens doses decreased (p < 0.05). This study shows that using 3 dimensional treatment planning, brain minimum doses increases and the dose inhomogenity decreases, and lens doses decreases using customized blocks and angling of beams five degrees posteriorly.