Room: ePoster Forums
Purpose: Total Body Irradiation (TBI) is typically performed at extended source-to-skin distance (SSD), and the treatment planning is done by simple point dose calculation based on measurement data. The goal of this study is to validate the use of a computerized treatment planning system (TPS, Eclipse) in TBI planning. Typical TPS is commissioned with beam data collected at standard SSD of 100 cm. Extrapolation is required when planning treatments at extended SSDs beyond 400 cm. This requires comprehensive validation.
Methods: Rectangular water phantoms of different sizes were created in Eclipse. Various dosimetric factors including absolute output at extended SAD, phantom scatter factors, off-axis ratios, TMRs, spoiler factors, and compensator transmission factors were calculated in Eclipse using Analytical Anisotropic Algorithm (AAA, V10) and compared with the TBI commissioning measurements at the same geometry. Homogeneous patient phantoms approximating patient body sizes were created with MATLAB and imported into Eclipse. Dose distributions were calculated in Eclipse, and representative point doses were compared with measurements obtained during treatment and those from standard manual calculation.
Results: Dosimetric factors calculated in Eclipse showed good agreement with TBI commissioning measurements. The differences were all within 2% in the range of clinical situations, with most of them within 1%. When comparing in vivo dose measurements and Eclipse calculations, umbilicus (central axis) dose showed better agreement than lung. Along the midline, doses at head and umbilicus agreed better with prescribed dose than doses at neck, lung, and lower legs.
Conclusion: This work demonstrates that Eclipse can be used for TBI planning at extended SSD with beam data from standard SSD. The Eclipse provides not only dose at certain points, but also full 3D dose distributions that allow more detailed evaluation of the patient treatment plan, hence reducing the need for time-consuming in vivo dose measurements.