Cardiac-Sparing Whole Lung Intensity Modulated Radiation Therapy in Children With Wilms Tumor: Final Report on Technique and Abdominal Field Matching to Maximize Normal Tissue Protection

Purpose: Cardiac-sparing whole lung intensity modulated radiation therapy (WL IMRT) has been shown to improve cardiac protection and lung volume dose coverage compared with standard anteroposterior techniques. This dosimetry study had 2 aims: To determine the dosimetric advantages of a modified WL IMRT (M-WL IMRT) technique, designed to reduce radiation exposure to the thyroid gland and breast tissues, compared with standard WL IMRT (S-WL IMRT) and to determine the dosimetric advantages of M-WL IMRT and dosimetrically matched abdomen and flank radiation therapy (RT) fields designed to reduce normal tissue exposure compared with standard field matching techniques. Methods and materials: Computed tomography scans of the chest and abdomen that were obtained during computed tomography simulation of 10 female children were used. For Aim 1, for S-WL IMRT, the planning target volume (PTV) was obtained with a 1-cm expansion of the 4-dimensional lung volume (internal target volume). For M-WL IMRT, the PTV was reduced around the breast and thyroid gland to facilitate thyroid and breast sparing. For Aim 2, standard matching techniques for 3-dimensional anterior/posterior-posterior/anteriorwhole lung and abdominal RT fields were compared with a new dosimetric matching technique for WL IMRT and abdomen and flank fields. For both aims, the dose coverage of the lungs and radiation exposure to normal tissues (heart, thyroid, breasts) were statistically compared. Results: Compared with S-WL IMRT, the M-WL IMRT technique provided similar lung PTV dose coverage and a significantly superior reduction in mean breast and thyroid doses, without compromising cardiac protection. The M-WL IMRT technique combined with a dosimetrically matched abdomen and flank fields showed significantly superior normal tissue protection compared with standard matched anterior/posterior-posterior/anteriorlung and abdomen and flank RT fields. Conclusions: This study has shown that the M-WL IMRT technique can reduce radiation exposure to the thyroid gland and breast tissue without compromising cardiac protection and 4-dimensional lung volume dose coverage. This report also describes a new dosimetric matching technique between WL IMRT and abdomen and flank fields that will improve normal tissue sparing compared with standard techniques.