SU‐E‐T‐336: Quantification of the 3D Dose Distributions Around Small Metal Objects Using Polymer Gel Dosimeter

L. Warmington, Y. Watanabe

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Purpose: Patients are increasingly undergoing radiotherapy procedures, in which small metals are implanted in the body for target localization in IGRT or dose enhancement. The purpose of this study is to investigate the feasibility of 3D dose measurements in the vicinity of a thin metallic objects using a polymer‐gel dosimeter. Methods: A MAGIC gel dosimeter was manufactured in‐house. The gel was poured into 20‐ml glass vials, then, it was cooled in a refrigerator for about 30 mins until the gel had a high viscosity. Tweezers were used to carefully insert lead, gold, or aluminum foils (1cm × 1cm × ∼0.5mm) into the gel with minimal disturbance to the surrounding area. Finally, the gels were returned to the refrigerator and allowed to solidify for at least 24 hours. The samples were irradiated with 18MV and 250kVp photon beams such that the foils were perpendicular to the beam direction. T2‐weighted images were acquired after 24 hours with a 3T‐MRI scanner using a turbo spin‐echo sequence. Imaging parameters were as follows: field‐of‐view = 180mm × 180mm, pixel‐size = 0.35mm × 0.35mm, and slice‐thickness = 5mm. Dose distributions were calculated by using a two‐point method from the MR images taken at two echo times (20 and 101 ms). Results: There was no signal from the metal foil allowing ease of identification. All 18MV samples and the 250kVp aluminum sample did not show any appreciable change in the dose distribution. The 250kVp samples for lead and gold, however, had a significant decrease in absorbed dose downstream of the foil. The dose profiles along the beam direction revealed dose reductions of 18% and 16% for lead and gold, respectively. Conclusion: We demonstrated that polymer‐gel dosimetry can be used to measure the fine dosimetric structures around a small metallic object although its accuracy still must be assessed.

Original languageEnglish (US)
Pages (from-to)3564-3565
Number of pages2
JournalMedical Physics
Volume38
Issue number6
DOIs
StatePublished - Jun 2011

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