D8 Clinical dosimetry

Topic

Clinical dosimetry is the branch of medical physics that measures, calculates, and verifies the radiation dose actually absorbed by a patient's tissues during radiotherapy; it acts as the bridge connecting the physics of radiation-matter interaction with the clinical prescription made by the radiation oncologist.

Clinical dosimetry ensures that the dose prescribed by the radiation oncologist—measured in Grays and calculated to achieve a specific probability of tumor control—is precisely the dose the patient's tumor actually absorbs: nothing more, nothing less.

To guarantee this, clinical dosimetry relies on a chain of steps, each calibrated against the preceding one: the process begins with a national primary standard maintained at a national metrology laboratory; this national primary standard is used to calibrate the medical physicist's detector—an ionization chamber; this calibrated ionization chamber is then used to calibrate the linear accelerator that will treat the patient; and finally, the calibrated linear accelerator delivers the dose to the patient in accordance with a treatment plan calculated using the dosimetric model.

This chain of calibrations—extending step-by-step from the national primary standard to the patient—is known as metrological traceability. It is precisely this traceability that gives real physical meaning to a value like sixty Grays when prescribed for a tumor; without this complete chain, the value would be merely an arbitrary figure. Clinical dosimetry ensures that, instead, it represents a verifiable physical measurement from start to finish.

ID:2331