Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions Review


Authors: Das, I. J.; Francescon, P.; Moran, J. M.; Ahnesjö, A.; Aspradakis, M. M.; Cheng, C. W.; Ding, G. X.; Fenwick, J. D.; Saiful Huq, M.; Oldham, M.; Reft, C. S.; Sauer, O. A.
Review Title: Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions
Abstract: Small-field dosimetry used in advance treatment technologies poses challenges due to loss of lateral charged particle equilibrium (LCPE), occlusion of the primary photon source, and the limited choice of suitable radiation detectors. These challenges greatly influence dosimetric accuracy. Many high-profile radiation incidents have demonstrated a poor understanding of appropriate methodology for small-field dosimetry. These incidents are a cause for concern because the use of small fields in various specialized radiation treatment techniques continues to grow rapidly. Reference and relative dosimetry in small and composite fields are the subject of the International Atomic Energy Agency (IAEA) dosimetry code of practice that has been published as TRS-483 and an AAPM summary publication (IAEA TRS 483; Dosimetry of small static fields used in external beam radiotherapy: An IAEA/AAPM International Code of Practice for reference and relative dose determination, Technical Report Series No. 483; Palmans et al., Med Phys 45(11):e1123, 2018). The charge of AAPM task group 155 (TG-155) is to summarize current knowledge on small-field dosimetry and to provide recommendations of best practices for relative dose determination in small megavoltage photon beams. An overview of the issue of LCPE and the changes in photon beam perturbations with decreasing field size is provided. Recommendations are included on appropriate detector systems and measurement methodologies. Existing published data on dosimetric parameters in small photon fields (e.g., percentage depth dose, tissue phantom ratio/tissue maximum ratio, off-axis ratios, and field output factors) together with the necessary perturbation corrections for various detectors are reviewed. A discussion on errors and an uncertainty analysis in measurements is provided. The design of beam models in treatment planning systems to simulate small fields necessitates special attention on the influence of the primary beam source and collimating devices in the computation of energy fluence and dose. The general requirements for fluence and dose calculation engines suitable for modeling dose in small fields are reviewed. Implementations in commercial treatment planning systems vary widely, and the aims of this report are to provide insight for the medical physicist and guidance to developers of beams models for radiotherapy treatment planning systems. © 2021 American Association of Physicists in Medicine
Keywords: treatment planning; note; radiation dose; diagnostic accuracy; accuracy; radiotherapy; dosimetry; photon; radiation field; dose calculation; radiation detection; thermoluminescence dosimetry; data processing; solid state; relative dosimetry; treatment modalities; detector correction factors; non-equilibrium dosimetry; photon dose modeling; small field; polyacrylamide gel
Journal Title: Medical Physics
Volume: 48
Issue: 10
ISSN: 0094-2405
Publisher: American Association of Physicists in Medicine  
Date Published: 2021-10-01
Start Page: e886
End Page: e921
Language: English
DOI: 10.1002/mp.15030
PUBMED: 34101836
PROVIDER: scopus
DOI/URL:
Notes: Note -- Export Date: 1 December 2021 -- Source: Scopus
Altmetric
Citation Impact
BMJ Impact Analytics
MSK Authors
  1. Jean Marie Moran
    53 Moran