Whole lung irradiation in pediatric patients using helical tomotherapy to minimize cardiac, breast, and thyroid dose

Abstract

The purpose of this study is to determine whether the use of helical tomotherapy can reduce dose to the heart, breast tissue, and thyroid gland in children receiving whole lung irradiation (WLI). Computed tomography simulation scans from nine pediatric patients previously treated with WLI were used for this dosimetry study. Each scan was alternatively planned using helical tomotherapy to minimize dose to surrounding critical structures. The clinical target volume (CTV) included both lungs. The ribs and spine in proximity to the lungs were included in the CTV to minimize bone asymmetry resulting from partial irradiation. The planning target volume (PTV) included the CTV with a 0.8-cm margin. The following structures were contoured: right atrium, left atrium, right ventricle, left ventricle, right and left breast, thyroid gland, and the humeral heads. Median dose (D med), minimum dose (D min), and maximum dose (D max) for the PTV, CTV, heart chambers, thyroid gland, right and left breast as well as right and left humeral heads were also obtained. The median PTV receiving the prescription dose was 97 %, with PTVs ranging from 95 to 99 %. The average D med for each of the four chambers of the heart ranged from 37 to 55 % of the prescription dose. The average D med for the breasts ranged from 88 to 95 % while for the thyroid gland was 10 % of the prescription dose. Helical tomotherapy can minimize the radiation dose delivered to nontarget organs such as the heart, breasts, and thyroid gland.