D7 Diagnostic and therapy equipment (QA)

Topic

Quality control for radiotherapy equipment is the discipline that ensures the dose prescribed by the radiation oncologist effectively reaches the tumor volume with the precision and accuracy needed to maximize the likelihood of tumor control while minimizing the risk of treatment-related complications in healthy tissue.

An error involving the linear accelerator can manifest in two distinct ways, each with its own consequences: if the error results in an underdose to the tumor, the probability of controlling the tumor decreases while the risk of recurrence rises; conversely, if the error results in an overdose to healthy tissue, the likelihood of complications in that tissue increases, thereby raising the toxicity experienced by the patient.

To prevent both types of errors, the quality control program operates at three different time intervals: daily quality control, which verifies before each treatment session that the equipment's fundamental parameters remain constant; monthly quality control, which conducts a more comprehensive review of the equipment's dosimetric and geometric parameters; and annual quality control, which subjects the equipment to full commissioning, verifying dose variation with depth in the body, dose profiles, field factors, and the dose calculation algorithm.

Quality control is not limited to the linear accelerator; it also encompasses all imaging equipment used to guide treatment—such as cone-beam computed tomography, kilovoltage imaging, and electronic portal imaging devices—as well as brachytherapy systems. In all cases, quality control for radiotherapy equipment serves the same purpose: ensuring that the dose actually received by the patient matches the dose prescribed by the radiation oncologist—neither more nor less—and is delivered to the exact intended location.

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