Small field dosimetry: What have we learnt?

Small field x-ray beam dosimetry is difficult due to a number of challenges that include a lack of lateral electronic equilibrium, source occlusion, high dose gradients, and detector volume averaging. This has become more apparent with a rapid increase in the number of treatment machines that deliver small x-ray fields which are used for precision radiotherapy techniques such as stereotactic radiosurgery (SRS) and SBRT. A large body of literature is now available for dosimetry in small fields, but with a lot of contradiction. There is also a large collection of micro-detectors that are being advocated for dosimetry. This review provides an update on small field dosimetry, recommendations for measurements and updates on recent commercial detectors on the market. It is recommended that detectors that are small volume and tissue equivalent are best suited for small field dosimetry which are plastic scintillators, synthetic diamond detectors and possibly Gafchromic films.