Faculty, Staff and Student Publications

Language

English

Publication Date

12-1-2025

Journal

Precision Radiation Oncology

DOI

10.1002/pro6.70033

PMID

41477297

PMCID

PMC12750306

PubMedCentral® Posted Date

11-28-2025

PubMedCentral® Full Text Version

Post-print

Abstract

Purpose: To characterize the newly released GafChromicTM EBT4 film for transit dose measurement in high-dose rate brachytherapy (HDR-BT) surface applicators and to systematically investigate the relationship between transit dose and 192Ir source activity.

Methods: EBT4 film was used to measure dose at 3 mm depth from a horizontally oriented Leipzig-style surface applicator connected to a 192Ir HDR-BT remote afterloading unit. Transit dose was systematically characterized across eight different source activities ranging from 3.372 to 9.716 Ci (13,724 U to 39,544 U) using measurements with seven nominal dwell times (5-100 seconds, scaled to 10 Ci (40,700 U)). Transit dose was derived from linear extrapolation to zero dwell time and compared with dose calculated (10-Ci source with 100-s nominal dwell time, excluding transit contributions) using the treatment planning system (TPS) Eclipse (Version 16.1).

Results: EBT4 film demonstrated excellent dose-response linearity with nominal dwell time (adjusted R2 > 0.99) across all source activities, confirming its suitability for transit dose measurement. Transit dose contributions ranged from 0.3% to 4.3% of TPS dose (100-s nominal dwell time at 10 Ci), with maximum contribution from the 9.543 Ci source (0.225±0.040 Gy) and minimum from the 5.502 Ci source (0.017±0.025 Gy). Transit dose showed poor linear correlation with source activity (adjusted R2 = 0.497), indicating that factors beyond source activity influence transit dose magnitude.

Conclusions: This study validates EBT4 film as a reliable tool for transit dose measurement in surface brachytherapy. The observed non-linear relationship between transit dose and source activity reveals the critical influence of experimental setup variables, particularly source guide tube geometry, which affects the source-to-target distance during transit. These findings demonstrate that transit dose is impacted by multiple interdependent factors including source activity, guide tube configuration, and setup geometry. For clinical applications, this highlights the importance of standardized setup protocols and empirical measurement for accurate transit dose assessment.

Keywords

High‐dose‐rate brachytherapy, Leipzig surface applicator, radiochromic film, transit dose

Published Open-Access

yes

Download

Share

COinS
 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.