Author: Chang Heon Choi, Minjae Choi, Yoonsuk Huh, Jin Jegal, Jung-in Kim, So-Yeon Park 👨🔬
Affiliation: Department of Radiation Oncology, Veterans Health Service Medical Center, Department of Radiation Oncology, Seoul National University Hospital 🌍
Purpose: Total Body Irradiation (TBI) aims to achieve a uniform dose distribution across the entire body. However, in conventional TBI setups that use extended source-to-surface distance (SSD) and lead compensators, the compensator thickness is calculated based on a representative value for segmented body regions, which fails to accurately account for sophisticated and curved body contours. To address this limitation, we developed a patient-specific lead ball compensator (LBC) using 3D printing technology.
Methods: To evaluate the attenuation factor and dose uniformity of lead ball filled sheets, lead balls with various diameters ranging from 0.3 mm to 2 mm were analyzed. The optimal diameter, 0.3 mm, was identified, and the attenuation factor of the 0.3 mm lead ball sheet was used as a scaling factor to adjust the RANDO phantom CT images, enabling the fabrication of a patient-specific compensator using a 3D printer. Dose uniformity and point doses in RANDO phantom were assessed using EBT4 films and OSLDs and the results were compared with conventional TBI treatment methods utilizing the conventional compensator (CC).
Results: The 0.3 mm lead ball sheet exhibited the lowest dose fluctuation, with a 21.8% reduction in the InterQuartile Range of standard deviation compared to a 3 mm thickness lead sheet, demonstrating the highest dose uniformity. The attenuation factor of the 0.3 mm lead ball was measured as 0.891, which is equivalent to approximately 2.5 mm thickness lead sheet. Compared to CC, the LBC reduced the standard deviation by 23.5% in the head and 26.7% in the neck, while maintaining similar dose uniformity in other regions. The dose at depth showed comparable results to those achieved with the CC.
Conclusion: Lead balls are reusable, making them a practical material for filling 3D compensators. Patient-specific lead ball compensators effectively reflect curved body contours, ensuring uniform dose distribution during TBI.