Energy Dependence of the New Gafchromic EBT3 Film:Dose Response Curves for 50 KV, 6 and 15 MV X-Ray Beams

Guerda Massillon-JL, Sou-Tung Chiu-Tsao, Ivan Domingo-Munoz, Maria F. Chan

Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, USA.
Instituto de Física, Universidad Nacional Autónoma de México, A.P. 20-364, 01000 DF, México.
Quality MediPhys LLC, 17 Jade Lane, Denville, NJ, USA.

DOI: 10.4236/ijmpcero.2012.12008                

Abstract

Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6 MV, 15 MV, and 50 kV) at 7 dose values (50-3200 cGy). Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2 × 2 cm² at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average net optical density (netOD) and its associated uncertainty were determined. The Student’s t-test was performed to evaluate the statistical differences between the net OD/dose values of the three energy modalities, with different color channels and spatial resolutions. Results and Discussion: The dose response curves for the three energy modalities were compared in three color channels. Weak energy dependence was found. For doses above 100 cGy, no statistical differences were observed between 6 and 15 MV beams, regardless of spatial resolution and color channel. However, statistical differences were observed between 50 kV and the megavoltage beams. The degree of energy dependence (from MV to 50 kV) was found to be a function of color channel, dose level, and spatial resolution. Conclusions: The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6 MV to 15 MV. For very low energy photon (e.g. 50 kV), variation of more than 11% due to the energy-dependence is observed, depending on the absorbed dose, spatial resolution and color channel used.

Keywords

Radiochromic Film; EBT3 Film; Dose Response Curve; Quality Assurance; Low-Energy Photons

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	M. Fuss, E. Sturtewagen, C. De Wagter, and D. Georg, “Dosimetric characterization of GafChromic EBT film and its implication on film dosimetry quality assurance,” Phys. Med. Biol. 52 4211–4225 (2007).
[2]	L. Richley, A. C. John, H. Coomber and S. Fletcher, “Evaluation and optimization of the new EBT2 radiochromic film dosimetry system for patient dose verification in radiotherapy,” Phys. Med. Biol. 55, 2601–2617 (2010).
[3]	G. Massillon-JL and L. Zú?iga-Meneses, “The response of the new MD-V2-55 radiochromic film exposed to 60Co gamma rays,” Phys. Med. Biol. 55, 5437–5449 (2010).
[4]	S. Devic, J. Seuntjens, E. Sham, E. Podgorsak, C. R. Schmidtlein, A. S. Kilrov, and C. G. Soares, “Precise radiochromic film dosimetry using a flat-bed scanner,” Med. Phys. 32, 2245–2253 (2005).
[5]	M. J. Butson, T. Cheung, and P. K. N. Yu, “Absorption spectra variations of EBT radiochromic film from radiation exposure,” Phys. Med. Biol. 50, N135–N140 (2005).
[6]	T. Cheung, M. J. Butson, and P. K. N. Yu, “Post-irradiation colouration of Gafchromic EBT radiochromic film,” Phys. Med. Biol. 50, N281–N285 (2005).
[7]	L. J. van Battum, D. Hoffmans, H. Piersma, and S. Heukelom, “Accurate dosimetry with GafChromic? EBT film of a 6 MV photon beam in water: What level is achievable?” Med. Phys. 35, 704–716 (2008).
[8]	M. Marti?íková, B. Ackermann, and O. J?kel, “Analysis of uncertainties in Gafchromic? EBT film dosimetry of photon beams,” Phys. Med. Biol. 53, 7013–7027 (2008).
[9]	B. C. Ferreira, M. C. Lopes, and M. Capela, “Evaluation of an Epson flatbed scanner to read Gafchromic EBT films for radiation dosimetry,” Phys. Med. Biol. 54, 1073–1085 (2009).
[10]	B. Hartmann, M. Marti?íková, and O. J?kel, “Homogene-ity of Gafchromic EBT2 Film,” Med. Phys. 37, 1753–1756 (2010).
[11]	A. Micke, D. F. Lewis, and Xiang Yu “Multichannel film dosimetry with nonuniformity correction,” Med. Phys. 38, 2523–2534 (2011).
[12]	D. F. Lewis “Practical Guide to Radiochromic Film EBT2/EBT3”, available at http://www.filmqapro.com/Documents/Lewis%20-%20Europe%2011-2011.pdf (April 2012).
[13]	M. J. Butson, P. K. N.Yu, TsangCheung, Hani Alnawaf, “Energy response of the new EBT2 radiochromic film to x-ray radiation,” Radiat. Meas. 45, 836-839 (2010).
[14]	B. Arjomandy, R. Tailor, A. Anand, N. Sahoo, M. Gillin, K. Prado, and M. Vicic, “Energy dependence and dose response of Gafchromic EBT2 film over a wide range of photon, electron, and proton beam energies,” Med. Phys. 37, 1942-1947 (2010).
[15]	P. Lindsay, A. Rink, M. Ruschin, and D. Jaffray, “Investigation of energy dependence of EBT and EBT-2 Gaf-chromic film,” Med. Phys. 37, 571-576 (2010).
[16]	J. G. H. Sutherland and D. W. O. Rogers, “Monte Carlo calculated absorbed-dose energy dependence of EBT and EBT2 film,” Med. Phys. 37, 1110-1116 (2010).
[17]	P. R. Almond, P. J. Biggs, B. M. Coursey, W. F. Hanson, M. S. Huq, R. Nath, D. W. O. Rogers, “AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams,” Med. Phys. 26, 1847-1870 (1999).
[18]	J. H. Hubbell and S. M. Seltzer, NIST X-ray Attenuation Databases http://www.nist.gov/pml/data/xraycoef/index.cfm (accessed May 2012).
[19]	H. Alva, H. Mercado-Uribe, M. Rodríguez-Villafuerte and M. E. Brandan, “The use of a reflective scanner to study radiochromic film response,” Phys .Med. Biol. 47, 2925-2933 (2002).
[20]	Engineering Statistic Handbooks, available at http://itl.nist.gov/div898/handbook/eda/section3/eda3672.htm accessed January 2012.
[21]	M. G. Natrella, Experimental Statistics, NBS Handbook 91 National Bureau Standards Washington DC 1963; re-printed 1966.
[22]	R. F. Mould, Introductory medical statistics, 2nd ed. Bristol and Philadelphia: Institute of Physics, 1995.