Purpose: The in-room laser which is used for patient positioning in radiotherapy is generally projected on the radiation isocenter determined by the Winston-Lutz test and so on. In this study, a couch-mounted verification device was developed that could evaluate all in-room lasers' alignment including the horizontality and verticality at one time. The device has the function to perform the light/radiation field coincidence test and the Winston-Lutz test at the same time. The aim of this report was to introduce the verification procedure for two tests, using the newly developed software and device, and to present the tuning flow of the in-room laser. Moreover, the analysis accuracy of the developed software was evaluated in comparison with commercial software.
Methods: First, the light/radiation field was evaluated by using tungsten markers on the central surface of the device. Next, after aligning the long-carved lines on the front and sides of the device with the in-room lasers, the Winston-Lutz test was carried out by using the tungsten sphere in the center of the device. The acquired images were collectively analyzed using the developed software equipped with the reporting function. Additionally, the result of this Winston-Lutz test was compared with the result from commercial software.
Results: A series of the light/radiation field coincidence test and the Winston-Lutz test were analyzed using the developed device and software. The results could be easily confirmed using the reporting function of the software. Regarding the result of the Winston-Lutz test, most of the analysis differences between the developed software and commercially available software were within the pixel size (0.22 mm).
Discussions: Since the accuracy of the radiation field affects the result of the Winston-Lutz test, the presented procedure of performing the light/radiation coincidence field test in advance facilitates the interpretation of the error of the Winston-Lutz test. Based on the results of the Winston-Lutz test, we were able to demonstrate the tuning flow of all in-room lasers including the horizontality and verticality by using the developed device.
Conclusions: We have developed a couch-mounted verification device and software that can evaluate the light/radiation coincidence field test and the alignment including the horizontality and verticality of the in-room laser used for patient positioning in radiotherapy, and reported its usefulness. The analysis accuracy of the developed software was comparable to that of commercially available software. The use of this device and the developed software would contribute to not only the efficiency of adjusting all in-room lasers' alignment including the horizontality and verticality but also reflect accurately the result of the Winston-Lutz test.
Keywords: laser, Winston-Lutz test; light field; quality control; radiation field.