title: Postal dosimetry audit test for small photon beams.
abstract: OBJECTIVE
  Small radiation beams (<4 cm width) are being increasingly used in the delivery of advanced techniques as Intensity Modulated Radiotherapy (IMRT) and Stereotactic Radiosurgery (SRS). Dose measurements in small beams present challenges not encountered for larger beams. A postal audit with Thermoluminiscent Dosimeters (TLD) was developed to check the doses in small photon beams. A validation test in real conditions was carried out in fourteen centres.
  
  
  METHODS
  The TLD postal audit employs very small chips (1×1×1 mm(3)) of TLD-100 inserted at 5 and 10 cm of depth in a cylindrical PMMA phantom designed for this purpose. This experimental system is mailed to the audited centres to be irradiated with beams of 1 and 3 cm of side or diameter. The prescribeddose is 1.5 Gy at 10 cm. The properties of this system were studied experimentally and by Monte Carlo (MC) simulation, before the external test.
  
  
  RESULTS
  Deviations between the prescribed and measured absorbed doses are below 5% for 69% (1×1 cm(2) beam) and 64% (3×3 cm(2) beam) of the audited centres. When deviations are above 5%, their causes have been investigated and led to corrections.
  
  
  CONCLUSIONS
  The developed postal audit is suitable to verify the absorbed doses in small photon beams with an accuracy of 2.9% (1 s).
authors: Hospital Universitario Puerta de Hierro Majadahonda, Madrid, Spain.
authors: María del Mar
authors: Mdel M
authors: Espinosa
authors: Luis
authors: L
authors: Núñez
authors: José Luis
authors: JL
authors: Muñiz
authors: Juan Ignacio
authors: JI
authors: Lagares
authors: Miguel
authors: M
authors: Embid
authors: José María
authors: JM
authors: Gómez-Ros
mesh_terms: D006801:Humans; D008485:Medical Audit; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons; D011177:Postal Service; D011874:Radiometry; D011878:Radiotherapy / Q000592:standards*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D013030:Spain; D013819:Thermoluminescent Dosimetry