Investigation of Radiation Isocenter Accuracy of Linear Accelerator - New Approach of Comprehensive Evaluation of Gantry, Couch, and Collimator Isocenters.

Objective: For stereotactic machines, recommendations demand stringent localization and precise delivery, as reflected by isocenter verification. Determining and analyzing the radiation isocenter for all clinical combinations of gantry, collimator, and couch are crucial for the quality of radiation therapy delivered. Although several radiation isocenter verification devices exist, there is no time-efficient system available for verifying the combined radiation isocenter. This paper presents a newly patented approach for the combined accuracy verification of the gantry, collimator, and couch radiation isocenter.

Methods: The novel combined radiation isocenter verification tool is used to expose a star test pattern on the dosimetric film at various angular combinations of the gantry, collimator, and couch. The exposed dosimetric film was evaluated using Radiochromic.com's standard third-party film analysis software.

Results: According to the results, the combined radiation isocenter for unit 1 is 0.74 mm dia (0.37 mm radius), and for unit 2, it is 0.62 mm dia (0.31 mm radius). These results are in good agreement with the requirements for three-dimensional conformal radiotherapy, intensity-modulated radiation therapy, volumetric-modulated arc therapy, stereotactic radiosurgery, and stereotactic body radiotherapy techniques.

Conclusion: This combined radiation isocenter verification tool aids in comprehensive evaluation of gantry, couch and collimator isocenters using radiographic film. It is easier to implement and faster to analyse compared to existing techniques, using a PC-based program that minimizes human error and increases measurement accuracy. This new approach can be used for routine quality assurance checks.