Evaluation of Accuracy of Stereotactic Body Radiotherapy Using 3D Moving Phantom

The objective of the present study was to use original data on respiration and tumor location coordinates saved during treatment period of patients who underwent body Radiotherpay to operate a 3D phantom for backward verification of the accuracy of stereotactic body radiotherapy.

The present study acquired original treatment data of 20 patients who underwent CyberKnife radiotherapy. Radiation was irradiated on the 3D phantom after applying external respiratory coordinates and tumor movement coordinate, which were original data from actual patients. The irradiated radiochemical film was scanned 24 hour later and assessment was made by γ-index values based on comparison of 2D dose distribution and radiotherapy plan.

The mean correlation error of entire treatment process of 20 patients was 1.26±073 (range: 0.47–1.98). The mean respiratory cycle of the patients during the entire treatment period was 3.77 sec (range: 1.90 5.39 sec). As an indicator of regularity of patient respiratory cycle, standard deviation of respiration during the entire treatment period was measured, the results of which showed minimum of 0.35 and maximum of 1.65. When the respiration and internal tumor movement of entire process after completion of treatment in 20 patients were applied to the 3D phantom for comparative analysis against the treatment plan, the mean pass rate of gamma-index values was 95.20±4.35% (range: 81.87%-99.92%). Since the mean pass rate was ≥ 95%, accuracy of radiotherapy was confirmed by backward verification

The significance of the present study can be found in the fact that it performed backward dose verification by reproducing respiratory and tumor coordinate after radiotherapy, using the same condition as before radiotherapy.