title: Effect of electron contamination on in vivo dosimetry for lung block shielding during TBI.
abstract: Our institution performs in vivo verification measurement for each of our total body irradiation (TBI) patients with optically stimulated luminescent dosimeters (OSLD). The lung block verification measurements were commonly higher than expected. The aim of this work is to understand this discrepancy and improve the accuracy of these lung block verification measurements. Initially, the thickness of the lung block was increased to provide adequate lung sparing. Further tests revealed the increase was due to electron contamination dose emanating from the lung block. The thickness of the bolus material covering the OSLD behind the lung block was increased to offset the electron contamination. In addition, the distance from the lung block to the dosimeter was evaluated for its effect on the OSLD reading and found to be clinically insignificant over the range of variability in our clinic. The results show that the improved TBI treatment technique provides for better accuracy of measured dose in vivo and consistency of patient setup.
authors.affiliation: University of Texas Health Science Center at San Antonio; University of Arkansas for Medical Sciences. nganesh76@hotmail.com.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Narayanasamy
authors.forename: Wilbert
authors.initials: W
authors.lastname: Cruz
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Saenz
authors.forename: Sotirios
authors.initials: S
authors.lastname: Stathakis
authors.forename: Niko
authors.initials: N
authors.lastname: Papanikolaou
authors.forename: Neil
authors.initials: N
authors.lastname: Kirby
mesh_terms: D004583:Electrons; D004866:Equipment Contamination; D006801:Humans; D000072231:In Vivo Dosimetry / Q000379:methods*; D008168:Lung / Q000528:radiation effects*; D011829:Radiation Dosage; D011835:Radiation Protection; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D013819:Thermoluminescent Dosimetry; D014916:Whole-Body Irradiation