Dec 10, 2010
IPEM report examines small field dosimetry
The Institute of Physics and Engineering in Medicine (IPEM) has published a new report entitled Small Field MV Photon Dosimetry. Compiled by IPEM's Small Field Working Party, the report discusses the difficulties and challenges associated with treatment fields smaller than 4 cm.
Accurate dosimetry in small photon fields is currently a hot topic in radiotherapy, with sessions at many of the major conferences dedicated to the unique challenges posed by such fields. The IPEM report is, to date, the only comprehensive report published in this area.
The 196-page report is presented in 12 chapters. The authors explain the physics of small fields and discuss the potential for treatment error in delivering small fields. Challenges in absolute, reference and relative dosimetry are addressed in detail, as well as the difficulties in making small field measurements.
The report examines potential errors in dose models, including a discussion on the necessary elements in fluence and dose calculation methods that are needed to model small collimator settings in order to achieve acceptable computational accuracy. Attention is drawn to relevant aspects of quality assurance for the treatment machine and collimating jaws. The characteristics of commercially available detectors for small field applications are also summarized.
The majority of the report presents established or newly proposed methodologies on the determination of dosimetric parameters (profiles, depth functions and output factors) for single narrow collimated fields. Recommendations for good working practice – to be consulted and used alongside the clinical experience, scientific judgement and existing expertise – are also provided. Finally, the report suggests future directions and future work required to reduce uncertainty in the determination of dose in small MV photon fields.
• The report Small Field MV Photon Dosimetry is available from IPEM, priced at £35.00 (IPEM members) or £50.00 (non-members).