SU-E-J-38: Rotational Setup Errors in Pediatric Patients Receiving Radiation Therapy for Intracranial Tumors

We have clinically observed that larger rotational setup errors are more prominent in pediatric patients who received radiation therapy for brain tumors. In this work, we quantitatively evaluated the daily setup corrections in pitch, roll, and yaw axes for children who received intracranial radiation therapy under x-ray image guidance.

Daily localization data of 43 patients between the ages of 10 months and 21.9 years were analyzed in this study. Patients were immobilized with thermoplastic mask during treatments, and 2D orthogonal x-ray images wereacquired for setup corrections before each treatment. Rotational setup corrections in pitch, roll, and yaw axes were extracted from 873 treatment fractions, and were analyzed for the whole group of patients and for two age groups: < 5 and = 5 years old.

The mean values for the pitch corrections were 1.91° and 1.65° (p:0.02), roll corrections were 1.37° and 1° (p<0.001), and yaw corrections were 1.93° and 1.47° (p<0.001), respectively. For patients < 5 years, 21.7% of treatments had pitch corrections more than 3°, versus 15.6% of treatments required pitch corrections more than 3° for patients >= 5 years. Similarly, 10.6% of roll corrections and 20.9% of yaw corrections were more than 3° for patients < 5 years. On the other hand, 2.1% of roll and 13.8% of yaw corrections were more than 3° for patients = 5 years old.

Data indicate that children less than 5 years old are more prone to rotational setup errors during intracranial radiation therapy. This can be attributed to reduced efficacy of immobilization devices due to smaller and rounder anatomicalfeatures of pediatric patients, and challenges in setup while the patient is under anesthesia. The role of daily image guidance and rotational setup corrections becomes important to ensure target coverage, especially for children < 5 years old.