title: On the suitability of ultrathin detectors for absorbed dose assessment in the presence of high-density heterogeneities.
abstract: OBJECTIVE
  The aim of this study was to evaluate the suitability of several detectors for the determination of absorbed dose in bone.
  
  
  METHODS
  Three types of ultrathin LiF-based thermoluminescent dosimeters (TLDs)-two LiF:Mg,Cu,P-based (MCP-Ns and TLD-2000F) and a (7)Li-enriched LiF:Mg,Ti-based (MTS-7s)-as well as EBT2 Gafchromic films were used to measure percentage depth-dose distributions (PDDs) in a water-equivalent phantom with a bone-equivalent heterogeneity for 6 and 18 MV and a set of field sizes ranging from 5 x 5 cm2 to 20 x 20 cm2. MCP-Ns, TLD-2000F, MTS-7s, and EBT2 have active layers of 50, 20, 50, and 30 μm, respectively. Monte Carlo (MC) dose calculations (PENELOPE code) were used as the reference and helped to understand the experimental results and to evaluate the potential perturbation of the fluence in bone caused by the presence of the detectors. The energy dependence and linearity of the TLDs' response was evaluated.
  
  
  RESULTS
  TLDs exhibited flat energy responses (within 2.5%) and linearity with dose (within 1.1%) within the range of interest for the selected beams. The results revealed that all considered detectors perturb the electron fluence with respect to the energy inside the bone-equivalent material. MCP-Ns and MTS-7s underestimated the absorbed dose in bone by 4%-5%. EBT2 exhibited comparable accuracy to MTS-7s and MCP-Ns. TLD-2000F was able to determine the dose within 2% accuracy. No dependence on the beam energy or field size was observed. The MC calculations showed that a[Formula: see text] thick detector can provide reliable dose estimations in bone regardless of whether it is made of LiF, water or EBT's active layer material.
  
  
  CONCLUSIONS
  TLD-2000F was found to be suitable for providing reliable absorbed dose measurements in the presence of bone for high-energy x-ray beams.
authors.affiliation: Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, 08028 Barcelona, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Bueno
authors.affiliation: Servei de Radiofísica i Radioprotecció, Hospital de la Santa Creu i de Sant Pau, 08025 Barcelona, Spain.
authors.forename: P
authors.initials: P
authors.lastname: Carrasco
authors.affiliation: Servei de Radiofísica i Radioprotecció, Hospital de la Santa Creu i de Sant Pau, 08025 Barcelona, Spain.
authors.forename: N
authors.initials: N
authors.lastname: Jornet
authors.affiliation: Servei de Física Mèdica i Protecció Radiològica, Institut Català d'Oncologia-Girona, 17007 Girona, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Muñoz-Montplet
authors.affiliation: Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, 08028 Barcelona, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Duch
mesh_terms: D040761:Biomimetic Materials / Q000528:radiation effects; D001842:Bone and Bones / Q000528:radiation effects*; D002138:Calibration; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D004867:Equipment Design; D005459:Fluorides; D016014:Linear Models; D018020:Lithium Compounds; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D014867:Water; D014965:X-Rays
chemical_list: D018020:Lithium Compounds; D014867:Water; C027651:lithium fluoride; D005459:Fluorides