Testing of Code of Practice on Small Field Dosimetry

Recent trends in radiotherapy techniques have increased substantially the use of small radiation fields. A key step in the radiotherapy process is the requirement for consistent reference dosimetry traceable to metrological primary standards and to enable common procedures within a country to be followed for reference dosimetry.  For conventional radiotherapy this has been achieved by Codes of Practice such as IAEA TRS 398 (IAEA, Vienna, 2000). However these Codes of Practice are all based on the use of a reference 10 cm x 10 cm field that may not be achievable using some modern specialized machines. So the developments in small field techniques have increased the uncertainty of clinical dosimetry and its link to reference dosimetry protocols. A joint working group between the IAEA and AAPM (American Association of Medical Physics) was established to prepare an International Code of Practice for small static photon fields. The aim is to harmonize the dosimetry of small fields in a similar way that IAEA TRS 398 has achieved for conventional radiotherapy. A CRP will be needed to test the procedures recommended in the new Code of Practice for different types of radiation beams and dosimeters used in special radiotherapy techniques such as various forms of Stereotactic Radiotherapy (SRT), Stereotactic Body Radiotherapy (SBRT) Stereotactic Radiosurgery (SRS) and Intensity Modulated Radiation Therapy (IMRT). Under the framework of the CRP, participants are expected to (i) contribute to the coordinated research activities, designed to test the small field Code of Practice and (ii) conduct measurements using their own radiotherapy beams and detectors, (iii) analyse and report the results of their measurements. The review of all results and discussions during RCMs will help identify implementation challenges and propose possible changes to the Code to ensure its smooth implementation in the clinic. The results of the CRP will be published in a Human Health Report to support implementation of the new Code of Practice in Member States.