Analysis of Utilization of Intrafraction Imaging on a Petlinac
Abstract
Purpose
Intrafraction imaging is a useful tool to provide information within the fraction on the patient positioning. It allows for adjustment for any movement that may occur during treatment. The novel PETLINAC is equipped with superior kV CT imaging providing accurate localization. This tool may be overused especially with the combination of standard margins and veer from the as low as reasonably achievable principle.
Methods
For lung stereotactic body radiation therapy on this LINAC, the clinic protocol is to take a kV CT halfway through the treatment. Analysis of five patients’ entire treatment courses was performed to observe if there were any shifts during these intrafraction images.
Results
Patient 1 had no shifts. Patient 2 had shifts in 2 of 3 fractions. The maximum shifts were in the magnitude of -3.1 for y and -3.3 for z. Patient 3 had shifts for 4 of 8 fractions with maximum deviations being in the y direction (1mm) and z direction (-4mm). The fourth patient had shifts for 1 of 4 fractions which were with max shifts in x (0.8mm) and z directions (-3.1mm). The fifth patient had shifts for 1 of 5 fractions which all surpassed 1mm and were -3.3mm, 1.2mm, 1.4mm for x, y, and z respectively.
Conclusion
It’s evident that a majority of intrafraction images result in no shift and are solely used for verification. When there are adjustments, they too are minimal and in most cases could be neglected. With more patients this trend is sure to hold and confirm the need to reduce the amount of intrafraction imaging to reduce dose to the patient, reduce the amount of time on the table, and reduce the instances of interlocks that occur directly resulting from intrafraction imaging.