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Phone: (800) 795-5226
Fax: (440) 729-8238
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IMRT QA Equipment :
MapCHECK™
The MapCHECK™ is a 2-dimensional therapy beam measurement system intended for quick and precise verification of the dose distribution resulting from an IMRT plan. Beam measurement is accomplished using a grid of 445 diode detectors that are housed between two sheets of solid acrylic. The MapCHECK™ measures the integrated ABSOLUTE dose at all detector locations, each of which has been corrected to the central detector sensitivity. This measured dose map is then automatically normalized and compared to a normalized imported treatment plan dose map, all in less than one minute.
Plan Verification & MLC Misalignment
Using this approach for IMRT plan verification, a 5-field case, from measurement to analysis, should take approximately 15 minutes. This is for verification of each field, rather than a composite, which can allow errors to creep into the plan and go unnoticed. It is widely accepted that field specific verification is a more stringent test of the plan than composite measurements. However MapCHECK™ will measure composite dose when it is delivered at zero degree gantry angle if desired. Either method is faster than film verification techniques.
The MapCHECK™ has been shown to detect MLC misalignments as fine as 1mm; therefore film and EPID are no longer the only detector medium capable of this. Additionally, the MapCHECK™’s diode detectors exhibit better dose agreement with ionization chambers than film. Also, the high spatial resolution (0.8 x 0.8mm) of the MapCHECK™’s detectors make them ideal for high dose-gradient analysis.
Analysis Functions
The MapCHECK™ employs three user-defined analysis functions for measured/plan comparison:
1 - Percent Difference
– This is the percent difference between a measured point and it’s mirrored planned point. This is the first comparison test. Typically this is set to 3% difference, and is user adjustable on the fly. If this comparison does not “pass”, then…
2 - Distance to Agreement (D2A)
– The measured point now becomes the midpoint of a circle. The radius of the circle is the D2A distance defined by the user, typically 3mm. All planned points within 3mm of the measured midpoint are evaluated for an EXACT match with the measured midpoint. This is done in either of the following ways:
An exact matching planned point is found
Two points are found, one of which is higher, and one of which is lower than the measured point, indicating that somewhere between the two is a point that equals the measured point
3 - Threshold
– This is the portion of the measured dose map that is analyzed. Typically, all measured points that are greater than or equal to 10% of the normalized dose map are evaluated. This prevents evaluation of detectors outside of the field which have experienced scatter dose. Threshold also is a user definable setting.
Click Here to Download a Printable Information Sheet. (.PDF format)
PH 1-800-795-5226
FAX 440-729-8238
P.O. Box 666 Chesterland, OH 44026
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