Impact of source position on high-dose-rate skin surface applicator dosimetry Journal Article

Authors: Jeong, J.; Barker, C. A.; Zaider, M.; Cohen, G. N.
Article Title: Impact of source position on high-dose-rate skin surface applicator dosimetry
Abstract: Purpose Skin surface dosimetric discrepancies between measured and treatment planning system predicted values were traced to source position sag inside the applicator and to source transit time. We quantified their dosimetric impact and propose corrections for clinical use. Methods and Materials We measured the dose profiles from the Varian Leipzig-style high-dose-rate (HDR) skin applicator, using EBT3 film, photon diode, and optically stimulated luminescence dosimeter for three different GammaMedplus HDR afterloaders. The measured dose profiles at several depths were compared with BrachyVision Acuros calculated profiles. To assess the impact of the source sag, two different applicator orientations were considered. The dose contribution during source transit was assessed by comparing diode measurements using an HDR timer and an electrometer timer. Results Depth doses measured using the three dosimeters were in good agreement, but were consistently higher than the Acuros dose calculations. Measurements with the applicator face up were significantly (exceeding 10%) lower than those in the face down position, due to source sag inside the applicator. Based on the inverse square law, the effective source sag was evaluated to be about 0.5 mm from the planned position. The additional dose during source transit was evaluated to be about 2.8% for 30 seconds of treatment with a 40700 U (10 Ci) source. Conclusion With a very short source-to-surface distance, the small source sag inside the applicator has a significant dosimetric impact. This effect is unaccounted for in the vendor's treatment planning template and should be considered before the clinical use of the applicator. Further investigation of other applicators with large source lumen diameter may be warranted. © 2016 American Brachytherapy Society
Keywords: skin cancer; dosimetry; hdr brachytherapy; leipzig skin-applicator; dwell position uncertainty; source transit dose
Journal Title: Brachytherapy
Volume: 15
Issue: 5
ISSN: 1538-4721
Publisher: Elsevier Science, Inc.  
Date Published: 2016-09-01
Start Page: 650
End Page: 660
Language: English
DOI: 10.1016/j.brachy.2016.04.389
PROVIDER: scopus
PUBMED: 27263059
PMCID: PMC5499667
Notes: Article -- Export Date: 6 December 2016 -- Source: Scopus
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MSK Authors
  1. Gilad N Cohen
    139 Cohen
  2. Christopher Barker
    126 Barker
  3. Marco Zaider
    169 Zaider
  4. Jeho Jeong
    27 Jeong