Room: AAPM ePoster Library
Purpose: The current Varian RPM (Real-time Positioning Management) software allows for the use of the traditional 2 marker infrared block or the 4 marker block (trueBEAM block). The accuracy of each block was measured by comparing the software measured amplitude of each block to the calculated block amplitude on an angular/elevation platform.
Method and Materials: A platform supported by three independent legs was constructed to allow for various elevations (up to 3 cm) and angulations of the marker block position. The location of the two marker blocks on the platform were positioned such that they are meant to measure the same amplitude according to the manufacture’s recommendation. The displacement of this point is measured by the software for each block and that is compared to the calculated amplitude based on 3D geometry and the known leg heights.
Results: Elevation changes of any of the posts by 1 cm, with or without tilt, caused a less than 1 mm amplitude difference for both blocks. As the tilt angle increased, so did the amplitude difference between calculated amplitude and software detected amplitude for both marker blocks. At larger tilt, the 2-reflector block showed a slightly better response when tilted towards the camera, but worse than the trueBEAM block when tilted away from camera. The trueBEAM block also showed less tracking variability in most tilt scenarios. When the platform was raised with no tilt, there was small difference between calculated amplitude and software detected amplitude for both marker blocks.
Conclusion: We demonstrated that the trueBEAM block responded similarly to the 2-reflector marker block using existing RPM software. The trueBEAM block can provide better accuracy and consistency at larger tilt when placed on a curved body contour. Clinics should be able to implement the trueBEAM block for all existing units using RPM.