Positional Consistency of Radiation Isocenter of a Single Energy Medical Linear Accelerator after Use of Fourteen Years for Cancer Treatment - Abstract
The position of radiation isocenter is an important part in quality assurance checks of a medical linear accelerator (Linac). All radiotherapy treatment planning’s and their delivery are done by taking radiation isocenter as a reference point. This isocenter can shift when the gantry, collimator and patient couch do not move symmetrically with each other. In our study, the radiation isocenter verification was done by using a special therapeutic film with digital image processing by using special software. Image acquisition was done using scanning of radiation exposed film by 6 MV photon beam with star shot method. This star shaped beam was designed by the rotation of the collimator, gantry and couch individually. The consistency of position of radiation isocenter was checked five times within last one year randomly by rotation of gantry, collimator to the couch of the medical Linac which is being used since fourteen years for cancer treatment. The mean value throughout the year shows that the size (diameter) for rotational gantry is 0.46 mm, collimator is 0.42 mm and 0.48 mm for the couch. As per AAPM report 40, the size of the Linac radiation isocenter diameter used in this study is still in good agreement because the value of the radiation isocenter is less than 2 mm diameter.