ESTRO 2024 - Abstract Book

S3211

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

McGill University, Medical Physics, Montreal, Canada

Purpose/Objective:

Dose response and energy dependence of the latest EBT4 GafChromic film model was compared to its predecessor EBT3 model in a dose rage up to 10 Gy for two beam qualities: 6 MV and 120 kVp photon beams.

Material/Methods:

Six pieces of both EBT3 and EBT4 models GafChromic films were irradiated using 6 MV and 120 kVp (4.19 mm Al HVL) photon beams with following doses: 0, 2, 4, 6, 8, and 10 Gy. Films were cut into 2” by 3” pieces in size, with longer edge cut along longer edge of the film sheet and positioned along longer edge of scanning bed, and scanned 24 hours post irradiation with Epson Expression 11000 document scanner. Output of the 6 MV beam (Varian TrueBeam STX linac) was established using the AAPM TG-51 while the output of the 120 kVp beam (Xstrahl orthovoltage unit) was based on the AAPM TH-61 reference dosimetry protocols. Film response was calculated as normalized pixel values, (PVunexposed/PVexposed)-1 [1], from green color channel of scanned RGB TIFF images.

Results:

Figure 1.a and Figure 1.b show dose response curves to 6 MV and 120 kVp photon beams, respectively. Figure 1.c and Figure 1.d depicts energy dependent dose response of EBT3 and EBT4 film models, respectively. The new film model has lower sensitivity than its predecessor and exhibits similar energy dependent response [2]. However, it is apparent that the EBT4 film model demonstrates improved linear dose response when compared to the EBT3 film model.

Conclusion:

Sensitivity of the latest EBT4 GafChromic film model appears to be lower than its predecessor, the EBT3 film as well as similar energy dependent dose response. The sensitivity being lower, similar to the EBT-XD film model [3], makes the latest EBT4 film model suitable for high radiation dose measurements in radiation therapy. In addition, the other advantage is that, dose response of the novel film model has better linearity than its predecessor when normalized pixel value of the green color channel from the scanned RGB TIFF images is used.

Keywords: Gafchromic film, dosimetry, sensitivity curve

References:

1. Saad Aldelaijan and Slobodan Devic, “Comparison of dose response functions for EBT3 model GafChromic (TM) film dosimetry system,” Physica Medica 49, (2018) 121-126.

2. H. Bekerat, S. Devic, F. DeBlois, K. Singh, A. Sarfehnia, J. Seuntjens, Shelley Shih, Xiang Yu, D. Lewis, “Improving the Energy Response of External Beam Therapy (EBT) GafChromicTM Dosimetry Films at Low Energies (≤100 keV),” Med. Phys. 41, 022101 (2014); doi: 10.1118/1.4860157