Derivation of TMR from PDD in Absence of Scatter Factors

Document Type : Original Article

Authors

Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

Abstract

Background and Objective: There are some complications for TMR(Tissue Maximum Ratio) calculation in radiotherapy treatment planning system. For example in TMR calculation from PDD(Percentage depth dose), BSF(Back Scatter Factor) or measurement is difficult and inaccurate. The goal of this study was to calculate TMR from PDD in absence of scatter factors and its conversion to a computer software for promotion of treatment planning system(TPS) in radiotherapy departments.
Subjects and Methods: Measurements of PDD was performed using Varian and Siemens accelerators at Ahvaz Golestan Hospital radiotherapy department, by ionization chamber CC13 and scanditronix water phantom, for both 6 and 18 MV therapeutic energies. Then an analytical equation for TMR calculation from PDD was defined. By this equation TMR values for square fields in different depths for 2-50MV therapeutic energies were determined. Finally we employed MATLAB software to produce a computer program to be used in TPS software.
Result: There was a good agreement between TMR values calculated by presented analytical equation and TMR values in the BJR(British Journal of Radiology) report. In most energies for therapeutic fields, the difference between analytical and BJR values was less than 2% for depths up to 10 cm, and less than 4% for depths  up to 20cm .
Conclusion: The presented analytical equation can quick calculate and quantify

Keywords


1-Agarwal SK, Scheele  RV, Wakley J. Tissue maximum-dose ratio (TMR) for 8 MV xrays. American Journal of Roentgenology 1971; 112(4): 797-802.
2-Khan FM, The physics of radiation therapy. Lippincott Williams & Wilkins; 2009. P.158-174.
3-Khan FM, Williamson JF, Sewchand W, Kim TH. Basic data for dosage calculation and compensation. J Radiation Oncology Biol Phys 1980; 6(6): 745-751.
4-Wysocka A, Maciszewski W. The photon beam characteristics of linear accelerator equipped with additional narrow beam collimator 2000: 2563-2565.
5-Isa M, Iqbal K, Afzal  M, Buzdar S, Chow J. Poster-Thur Eve-23:Statistical analysis and verification of the percentage depth dose calculation based on the tissue maximum ratio in external beam radiotherapy. Medical Physics 2012; 39(7): 4628-4629.
6-Linthout N, Verellen D, Acker SV, Storme Guy. A simple theoretical verification of monitor unit calculation for intensity modulated beams using dynamic mini-multileaf collimation. Radiotherapy and Oncology. 2004; 71(2004): 235-241.
7-Gibbons JP, Reft CS. Monitor unit calculations for external photon and electron beams. Medical physics 2002; 29: 106.
8-Ando S, Yi B, Sun M, Sarfaraz M, Yu C. SU-FF-T-424: The Measurement of MovingTissue Maximum Ratio for Dynamic MLC Based Total Body Irradiation. Medical Physics 2006; 33: 2143.
9-Gotoh S, Ochi M, Hayashi N, MatsushimaS, Uchida T, Obata S, ‘et al’. Narrow photon beam dosimetry for linear accelerator radiosurgery. Radiotherapy and oncology. 1996; 41(3): 221-224.
10-Ron Zhu X, Josef Allen J, Shi J. Tottal scatter factors and tissue maximum ratios for small radiosurgery fields:comparison of diode detectors,a parallel-plate ion chamber, and radiographic film. Medical Pysics 2000; 27(3): 472-477.
11-Cheng CW, Cho SH, Taylor M. Determination of zero-field size percent depth doses and tissue maximum ratios for stereotactic radiosurgery and IMRT dosimetry: Comparison between experimental measurements and Monte Carlo simulation. Medical Physics 2007; 34(8): 3149-3157.
12-Thomadsen BR, Kubsad SS, Paliwal BR, Shahabi S, Mackie R. On the cause of the variation in tissue-maximum ratio values with source-to-detector distance. Medical Physics 1993; 20(3): 723-727.
13-Khan FM, Sewchand W, Lee J, Jeffrey JF.  Revision of tissue-maximum ratio and scatter-maximum ratio concepts for cobalt 60 and higher energy x-ray beams. Medical Physics. 1980; 7(3): 230-237.
14-Bedford JL, Hansen VN, Webb S. The derivation of tissue-maximum ratio from percentadepth dose requires peak scatter factor to be considered a function of source-to-surface distance. British journal of radiology 1998; 71(848): 876-881.
15-Sharma SD, Kumar S, Dagaonkar SS, Bisht G, Dayanand S, Devi R, ‘et al’. Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems. Journal of Medical Physics/Association of Medical Physicists of India  2007; 32(1): 18-23.
16-Kinsey E, Guerrero M, Prado K, Yi B. Are the Calculation Methods for Determining tissue-Maximum Ratios from Percent Depth Dose Valid for Flattening Filter-Free Photon Beams?.  Medical Physics  2012; 39(6): 3711.
17-Frye DMD, Paliwal BR, Thomadsen BR, Jursinic P. Intercomparison of normalized head-scatter factor measurement techniques. Medical Physics 1995; 22(2): 249-252.
18-Chen L, Chen LX, Sun HQ, Huang SM, Sun WZ, Gao XW, ‘et al’. Measurements and comparisons for data of small beams of linear accelerators. Chinese Journal of Cancer 2009; 28(3): 272-276.
19-Garcia-Garduno OA, Larraga-Gutierrez GM, Rodriguez –Villafuerte M, Martinez-Davalos A, Celis MA. Small photon beam measurements using radiochromic film and Monte Carlo simulations in a water phantom. Radiotherapy and Oncology 2010; 96(2010): 250-253.
20-Apostolidis G, Stankovic J, Radosevic-Jelic L. Dosimetric characteristic of large photon fields(Varian, Clinac 2100, X-6MV) by using standard measurement approach. Oncology and Radiology  2002; 10(1): 25-28.
21-BJR(British Institute of Radiology) & Institution of Physics and Engineering in Medicine and Biology. Central axis depth dose data for use in radiotherapy. Br J Radiat 1996; 25: 168-181.