title: Estimating dose to implantable cardioverter-defibrillator outside the treatment fields using a skin QED diode, optically stimulated luminescent dosimeters, and LiF thermoluminescent dosimeters.
abstract: The purpose of this work was to determine the relative sensitivity of skin QED diodes, optically stimulated luminescent dosimeters (OSLDs) (microStar™ DOT, Landauer), and LiF thermoluminescent dosimeters (TLDs) as a function of distance from a photon beam field edge when applied to measure dose at out-of-field points. These detectors have been used to estimate radiation dose to patients' implantable cardioverter-defibrillators (ICDs) located outside the treatment field. The ICDs have a thin outer case made of 0.4- to 0.6-mm-thick titanium (∼2.4-mm tissue equivalent). A 5-mm bolus, being the equivalent depth of the devices under the patient's skin, was placed over the ICDs. Response per unit absorbed dose-to-water was measured for each of the dosimeters with and without bolus on the beam central axis (CAX) and at a distance up to 20 cm from the CAX. Doses were measured with an ionization chamber at various depths for 6- and 15-MV x-rays on a Varian Clinac-iX linear accelerator. Relative sensitivity of the detectors was determined as the ratio of the sensitivity at each off-axis distance to that at the CAX. The detector sensitivity as a function of the distance from the field edge changed by ± 3% (1-11%) for LiF TLD-700, decreased by 10% (5-21%) for OSLD, and increased by 16% (11-19%) for the skin QED diode (Sun Nuclear Corp.) at the equivalent depth of 5 mm for 6- or 15-MV photon energies. Our results showed that the use of bolus with proper thickness (i.e., ∼d(max) of the photon energy) on the top of the ICD would reduce the scattered dose to a lower level. Dosimeters should be calibrated out-of-field and preferably with bolus equal in thickness to the depth of interest. This can be readily performed in clinic.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: Maria F
authors.initials: MF
authors.lastname: Chan
authors.forename: Yulin
authors.initials: Y
authors.lastname: Song
authors.forename: Lawrence T
authors.initials: LT
authors.lastname: Dauer
authors.forename: Jingdong
authors.initials: J
authors.lastname: Li
authors.forename: David
authors.initials: D
authors.lastname: Huang
authors.forename: Chandra
authors.initials: C
authors.lastname: Burman
mesh_terms: D017147:Defibrillators, Implantable; D004867:Equipment Design; D019544:Equipment Failure Analysis; D062791:Optically Stimulated Luminescence Dosimetry / Q000295:instrumentation*; D011829:Radiation Dosage; D020266:Radiotherapy, Conformal; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity; D012879:Skin Physiological Phenomena; D013819:Thermoluminescent Dosimetry / Q000295:instrumentation*