Motion effects in stereotactic body radiotherapy (SBRT) dosimetry of bone metastases: Case study using homogeneous and inhomogeneous CIRS phantoms

The Stereotactic Body Radiotherapy (SBRT) for bone metastases has been implemented in radiotherapy center in Indonesia. In this study, we simulated and explored the effect of target motion in SBRT on bone metastases using the homogeneous (002 H9K) and inhomogeneous (002 LFC) CIRS phantom to simulate the presence of inhomogeneous medium near the target, with the holder for chamber. Both phantoms have the interchangeable rod for ionisation chamber, while for TLD and gafchromic EBT3, a holder was devised using Teflon material. In order to evaluate the impact of target motion, the measurements were performed in static and superior-inferior motion with the amplitude of 5, 10, and 20 mm. The measurement in the static condition has the standard deviation of <1.5 for gafchromic film EBT3 and <0.2 for PTW N30013. For the measurement of superior-inferior dynamic motion, we obtained a decrease in the dose of the target volume with increasing amplitudes of the movements. In addition, the standard deviation of dynamic measurement results was in the range of 1.13 to 11.7, 9.5 to 28.6, and 0.05 to 7.21 for gafchromic film EBT3, exradin A16 and PTW N30013, respectively.