Prog Med Phys.  2017 Mar;28(1):16-21. 10.14316/pmp.2017.28.1.16.

Evaluation of Dual-channel Compound Method for EBT3 Film Dosimetry

• Kang SW
• Chung JB
• Kim KH
• Eom KY
• Song C
• Lee JW
• Cho W
• Suh TS

• KMID: 2382800
• DOI: http://doi.org/10.14316/pmp.2017.28.1.16

Abstract

This study assessed the feasibility of a dual-channel (DC) compound method for film dosimetry. The red channel (RC) is usually used to ensure dosimetric quality using a conventional fraction dose because the RC is more accurate at low doses within 3 Gy than is the green channel (GC). However, the RC is prone to rapid degradation of sensitivity at high doses, while degradation of the GC is slow. In this study, the DC compound method combining the RC and GC was explored as a means of providing accurate film dosimetry for high doses. The DC compound method was evaluated at various dose distributions using EBT3 film inserted in a solid-water phantom. Measurements with 10×20 cm² radiation field and 60° dynamic-wedge were done. Dose distributions acquired using the RC and GC were analyzed with root-mean-squares-error (RMSE) and gamma analyses. The DC compound method was used based on the RC after correcting the GC for high doses in the gamma analysis. The RC and GC produced comparatively more accurate RMSE values for low and high doses, respectively. Gamma passing rates with an acceptance criterion of 3%/3 mm revealed that the RC provided rapid reduction in the high dose region, while the GC displayed a gradual decrease. In the whole dose range, the DC compound method had the highest agreement (93%) compared with single channel method using either the RC (80%) or GC (85%). The findings indicate that the use of DC compound method is more appropriate in dosimetric quality assurance for radiotherapy using high doses.

Keyword

Gafchromic EBT3 film; Film dosimetry; Dual-channel compound; Gamma analysis

MeSH Terms

Film Dosimetry*
Methods*
Radiotherapy

Figure

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  Fig. 1. Calibration net optical-density (netOD) curves for the red and green channel.

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  Fig. 2. EBT film showing a mimic image irradiated radiation for analyzing cross- (red dot line) and in-line (blue dot line) profiles.

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  Fig. 3. The dose profiles ((a) cross-line and (b) in-line) obtained in DRC and DGC compared to DCalc. The cross-line profile was measured in central-axis for dose distribution and the in-line profiles were measured in five positions of d1, d2, d3, d4, and d5, respectively.

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  Fig. 4. Gamma distributions of analysis for (a) red, (b) green channel, (c) dual-channel compound method, and (d) the converted gamma distribution of green channel.

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  Fig. 5. Comparison of the gamma passing rates in dose distributions using the red channel, green channel, and dual-channel compound method with increasing doses.

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