Parotid gland dose reduction in the hippocampus avoidance whole-brain radiotherapy using helical tomotherapy.

The present study aimed to reduce the parotid gland dose in the hippocampus avoidance with whole-brain radiotherapy (HA-WBRT) using the helical tomotherapy (HT). Ten patients who had previously undergone WBRT were randomly selected and enrolled in this study. During the treatment planning, two different techniques to the jaw were applied for each patient, namely, 1.0 cm fixed jaw and 2.5 cm dynamic jaw. To efficiently reduce the dose in the bilateral parotid glands, directional block (DB) mode was set. The DB is a function of a treatment planning system for the dose reduction in organs at risk. The standard HA-WBRT plan which did not reduce the parotid gland dose was also designed to compare the plan quality. Compared with the standard HA-WBRT plan, the parotid gland dose could be reduced by approximately 70% without extending the delivery time by adding the parotid gland on the DB mode to the dose constraint. In addition, the differences in dosimetric parameters observed between the plans employing the 1.0 cm fixed jaw and 2.5 cm dynamic jaw were almost negligible. Moreover, delivery time in the 2.5 cm dynamic jaw could be greatly reduced by 60% compared with that in the 1.0 cm fixed jaw.