Adaptive radiation therapy for pediatric head and neck malignancies: Dosimetric implications

Abstract

Purpose: This study was designed to evaluate the role of adaptive radiation therapy for children receiving curative radiation therapy to the head and neck region.

Methods and materials: Ten children receiving definitive, conformal radiation therapy to the head and neck region were prospectively evaluated for anatomic changes during the course of radiation therapy. Images were acquired midway through the number of planned radiation therapy fractions during the planned course of radiation therapy. Body contours, target volumes, and organs at risk were redrawn on the new set of images. Two sets of additional treatment plans were generated: (1) a nonoptimized plan (plan 2), that is, an overlay of the original plan (plan 1) on the new set of contours, and (2) an optimized plan (plan 3) with the new set of contours. These 3 sets of plans were then compared for dosimetric differences.

Results: Five children had nasopharynx carcinoma, whereas the other 5 had embryonal rhabdomyosarcoma. The average reduction in gross tumor volume was 40% (mean volume, 41.87 mL; P = .005). The average changes in right and left parotid volumes were 2.72 and 1.92 mL, respectively. With nonoptimized plans, the average increase in maximum dose to the spinal cord was 15% (79.99%-94.99%; P = .013). With reoptimization, the maximum dose to the spinal cord decreased from 94.99% to 85.26% (mean difference, -9.73%; P = .02). Average D99 for the planning target volume (dose received by 99% of the target volume) was 88.66% and 86.89% with the original and reoptimized plans, respectively (P = .50). For the entire group, the mean conformation number index with nonoptimized plans was reduced from 0.734 to 0.628 (P = .013). This improved with reoptimization (P = .114). The homogeneity index improved with reoptimization from a mean value of 0.113 to 0.098 (P = 0.28). For nonoptimized plans, the average integral dose increased from 74.66 to 76.27 L-Gy (P = .486) compared with the original plans. Reoptimization resulted in a 5% average reduction in the integral dose, from 76.27 to 72.28 L-Gy (P = .007).

Conclusions: This study demonstrates the usefulness of adaptive radiation therapy for children receiving radiation therapy to the head and neck region.