What is film gamma in IMRT dosimetry?

Film gamma in IMRT (Intensity-Modulated Radiation Therapy) dosimetry is a method used to evaluate the accuracy of radiation dose delivery by comparing the planned dose distribution to the actual dose measured using radiographic film. The gamma index combines both the dose difference and the spatial agreement between the two distributions into a single metric, typically expressed as a percentage. A gamma value of 1.0 or lower indicates acceptable agreement, while values greater than 1.0 suggest discrepancies that may need to be addressed. This technique is crucial for ensuring quality assurance in radiation therapy treatments.