In vivo dosimetry and patient-specific quality assurance

Radiotherapy accidents, though rare, have come from wrong plans, wrong patients and machine faults. Patient-specific quality assurance checks each complex plan on a phantom before the first treatment, and in vivo dosimetry measures the dose during treatment with diodes, thermoluminescent detectors or, increasingly, the electronic portal imaging device behind the patient, which reconstructs the delivered dose in three dimensions. Several countries require in vivo dosimetry by regulation; it is also central to safe FLASH and ultra-high-dose-rate research.