Poster - Thur Eve - 43: Is faster always better? An evaluation of frame rate effects on continuous acquisition mode...

As radiotherapy moves towards intensity modulated arc therapy (arc-IMRT), there is a need for electronic portal imaging (EPID) to move towards continuous acquisition (cine) mode for dosimetric verification purposes. However, as the EPID resolution and frame rate (fps) increase, so does the computational burden of image processing. We investigated the reliability of cine mode EPID imaging in IMRT as a function of frame rate.

We acquired EPID images continuously while running an IMRT plan (6MV photons, 150MU, dose rate = 300MU/min) with frame rates ranging from 1-12 fps, as well as a single integrated mode image. Each cine dataset was then averaged to form a single image, which was compared with the integrated mode image by means of a pixel-by-pixel absolute value subtraction.

Although a greater frame rate gave better agreement with the integrated mode image in all cases, the relative benefit diminished with increasing frame rate. In particular, for the IMRT plan delivered, there was little benefit of imaging faster than 6 fps, and virtually no benefit in increasing from 9 to 12 fps. In contrast, 12 fps produces twice the number of images as 6 fps which significantly increases the image processing and data storage burdens.

Increasing frame rate in cine mode EPID imaging may be beneficial in some cases, but there is likely a threshold level above which no relevant additional information is obtained. Further research to determine the ideal frame rate for any particular IMRT or arc-IMRT plan is warranted.