TLD Audit in Radiotherapy in the Czech Republic

The National Radiation Protection Institute in Prague organises the TLD audit. The aim of the audit is to provide a basic control of clinical dosimetry in the Czech Republic for purposes of state supervision in radiotherapy. The TLD audit covers absorbed dose measurements under reference conditions for 60 Co and 137 Cs beams, high energy X ray and electron beams of linear accelerators and betatrons. Absorbed dose measured by TLD is compared with absorbed dose stated by the radiotherapy centre. Encapsulated LiF:Mg,Ti powder is used for the measurement. A deviation of ±3% between the stated and TLD measured dose is considered acceptable. The first TLD audit was in 1997. A total of 110 beams were checked. Seven major deviations (more than ±6%) were found, which were investigated in depth. Medical physicists from these departments reported a set-up error. However, at most of those hospitals with major deviations, an in situ audit in detail was carried out soon after the TLD audit. Discrepancies were found in clinical dosimetry but some of the irradiation units were poor, technically. Regular TLD audit seems to be a good way of eliminating errors in basic clinical dosimetry.