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.
| [1] |
Rivard MJ, Coursey BM, DeWerd LA, et al., Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations, Med Phys 2004:31:633–674.
|
| [2] |
Perez-Calatayud J, Ballester F, Das RK, et al.Dose calculation for photon-emitting brachytherapy sources with average energy higher than 50 keV: report of the AAPM and ESTRO, Medical physics 2012;39:2904–2929.
|
| [3] |
Wong TP, Fernando W, Johnston PN, et al., Transit dose of an Ir-192 high dose rate brachytherapy stepping source, Physics in Medicine & Biology 2001;46:323.
|
| [4] |
Sahoo N, Measurement of transit time of a remote after-loading high dose rate brachytherapy source, Medical physics 2001;28:1786–1790.
|
| [5] |
Fonseca G, Landry G, Reniers B, et al., The contribution from transit dose for 192Ir HDR brachytherapy treatments, Physics in Medicine & Biology 2014;59:1831.
|
| [6] |
Bastin KT, Podgorsak MB, Thomadsen BR, et al., The transit dose component of high dose rate brachytherapy: direct measurements and clinical implications, Int J Radiat Oncol Biol Phys. 1993;26:695–702.
|
| [7] |
Fonseca G, Rubo R, Minamisawa R, et al., Determination of transit dose profile for a 192Ir HDR source, Medical Physics 2013;40:051717.
|
| [8] |
Supe S, Shwetha B, Bijina T, et al., Measurement of transit time of a Gammamed-Plus remote afterloading high dose rate brachytherapy source, Polish Journal of Medical Physics and Engineering 2007;13:55–63.
|
| [9] |
Jeong J, Barker CA, Zaider M, et al., Impact of source position on high-dose-rate skin surface applicator dosimetry, Brachytherapy 2016;15:650–660.
|
| [10] |
Aldelaijan S, Mohammed H, Tomic N, et al., Radiochromic film dosimetry of HDR 192Ir source radiation fields, Medical physics 2011;38:6074–6083.
|
| [11] |
Tien CJ, Pinkham DW, Chen ZJ, et al., Feasibility of using multiple-dwell positions in 192Ir Leipzig-style brachytherapy surface applicators to expand target coverage and clinical application, Brachytherapy 2020;19:532–543.
|
| [12] |
Draeger E, Pinkham DW, Chen ZJ, et al., Clinically-implementable template plans for multidwell treatments using Leipzig-style applicators in 192Ir surface brachytherapy, Brachytherapy 2021;20:401–409.
|
| [13] |
Palmer AL, Bradley D, Nisbet A, Evaluation and implementation of triple-channel radiochromic film dosimetry in brachytherapy, Journal of applied clinical medical physics 2014;15:280–296.
|
| [14] |
Li X, Su F-C, Sarkar V, Zhao H, et al., Impact of detector selection on commissioning of Leipzig surface applicators with improving immobilization in high-dose-rate brachytherapy, Brachytherapy 2022;21:511–519.
|
| [15] |
Fulkerson RK, Perez-Calatayud J, Ballester F, et al., Surface brachytherapy: joint report of the AAPM and the GEC-ESTRO Task Group No. 253, Medical Physics 2020;47:e951-e987.
|
| [16] |
Guan F, Chen H, Draeger E, et al., Characterization of GafchromicTM EBT4 film with clinical kV/MV photons and MeV electrons, Precision Radiation Oncology 20237:84–91.
|
| [17] |
Massillon-JL G, Chiu-Tsao S-T, Domingo-Munoz I, et al., Energy dependence of the new Gafchromic EBT3 film: dose response curves for 50 kV, 6 and 15 MV X-ray beams, International Journal of Medical Physics, Clinical Engineering and Radiation Oncology 2012;1:60–65.
|
| [18] |
Iftimia I, McKee AB, Halvorsen PH, Varian HDR surface applicators—commissioning and clinical implementation, Journal of applied clinical medical physics 2016;17:231–248.
|
| [19] |
Guan F, Wang X, Yang M, et al., Dosimetric response of Gafchromic™ EBT-XD film to therapeutic protons, Precision radiation oncology 2023;7:15–26.
|
| [20] |
Draeger E, Guan F, Lee MY, et al., Clinical use of Gafchromic EBT4 film for in vivo dosimetry for total body irradiation, Journal of applied clinical medical physics 2025;26:e14574.
|
| [21] |
Howard ME, Herman MG, Grams MP, Methodology for radiochromic film analysis using FilmQA Pro and ImageJ, PLoS One 2020;15:e0233562.
|
RIGHTS & PERMISSIONS
2025 The Author(s). Precision Radiation Oncology published by John Wiley & Sons Australia, Ltd on behalf of Shandong Cancer Hospital & Institute.
PDF
