The Role Of The National Physical Laboratory In Monitoring And Improving Dosimetry In UK Radiotherapy

The National Physical Laboratory, in collaboration with the Institute for Physics and Engineering in Medicine [IPEM] operates an audit programme to ensure national consistency in radiotherapy dosimetry in the UK. The present programme covers dosimetry of megavoltage photons, electrons (3-22 MeV) and low and medium energy (10-300 kV) photons. The aim of each audit is to verify the local measurement of absorbed dose at the radiotherapy centre. The audit measurements – principally beam quality and linac output – are made following the same protocol as the clinic but using different equipment. The audit is not an absolute measurement of the absorbed dose but amounts to a check that the equipment used by the centre is operating as expected and that the Code of Practice is being implemented correctly. The protocols used in the UK are IPSM 1990 [1] for high-energy photons, IPEM 2003 [2] for electrons and IPEMB 1996 [3] and IPEM 2005 [4] for low energy photons. For the purpose of these audits, NPL maintains a set of calibrated ionisation chambers.