AbstractID: 9189 Title: Multi-leaf collimator phantom: A quality assurance tool for radiation therapy
planning systems and CT simulators
The evolution of 3-D conformal radiation treatment has lead to the increasing use of multi-leaf collimators (MLCs). Intensity
modulated radiation therapy, as well as other modern radiation treatment techniques, use MLCs to create irregular field shapes that are
incorporated into the patient treatment plan. A quality assurance (QA) phantom has been designed and built to handle irregular field
shapes created by MLCs and micro-MLCs, based on the basic elements of a previously designed phantom. The redesigned phantom
allows for the assessment of fields produced by MLCs and micro-MLCs from several manufacturers, and is therefore relevant to most
radiation therapy institutions to assess the display of these fields in a treatment planning environment. With computed tomography
(CT) scans of the phantom, QA assessments can be made of the field edge display for a variety of shapes and orientations on both the
RTPS and CT simulators. The dimensions of the phantom were verified to be physically correct within an error range of 0 to 0.7 mm.
In a multiple observer test it was found that errors in leaf placement larger than 1 mm, with respect to the phantom geometry, were
identified 100% of the time. The phantom has already proven useful, identifying a display error in a RTPS. The MLC geometry
phantom is a useful tool in the QA of radiation therapy with application to RTPS and CT simulators, especially those with MLC
display capabilities. The phantom is marketed by Modus Medical Devices Inc.