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COMPASS is used for quality assurance and plan verification in external beam radiation therapy for multileaf collimated fields and intensity modulated fields. It computes dose (energy per volume deposited by ionizing radiation) three-dimensionally in a geometrical representation of a patient or a phantom. The calculation is based on read-in treatment plans, and additionally on online or offline measurements of radiation fields with radiation-transparent or non-transparent, 2 dimensional multi-element ionization chamber arrays.

The system is intended to be used with intensity modulated radiation therapy, delivered with high energy x-ray beams from an isocentric gantry linear accelerator. The modulation of these beams shall be accomplished by means of MLCs and Jaws. The aim is to measure the fluences of the applied fields by means of electronic 2D devices, including transmission detector which can be used during patient irradiation. Alternatively the fluences can be calculated from a computation independent from the original TPS, using segmentation data from the TPS or a delivery log file. Furthermore, the intention of the system is to recalculate the resulting dose distribution in a phantom or, using patient anatomy data, in a patient. Moreover, the system allows performing QA tests on the radiation delivery system. When the system is used together with electronic 2D devices, preferably with transmission detector, it can also provide sensitivity calibration and performance tests on EPID systems. Finally, the system will provide online information about the quality of the delivery, both on a delivery system level (e.g. leaf positioning accuracy, dose per segment accuracy) as on the patient level (resulting dose distribution). In case of discrepancies, corrective action (adjusted plan for further fractions) shall be proposed.