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1. P. Andreo, D. Burns, K. Hohlfeld, M. Huq, T. Kanai, F. Laitano, V. Smyth, and S. Vynckier, “Absorbed dose determination in external beam radiotherapy,” IAEA Technical Reports Series No. 398 (IAEA, Vienna, 2000).
2. P. R. Almond, P. J. Biggs, B. M. Coursey, W. F. Hanson, M. S. Huq, R. Nath, and D. W. O. Rogers, “AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams,” Med. Phys. 26, 18471870 (1999).
3. R. Alfonso, P. Andreo, R. Capote, M. S. Huq, W. Kilby, P. Kjall, T. R. Mackie, H. Palmans, K. Rosser, J. Seuntjens, W. Ullrich, and S. Vatnitsky, “A new formalism for reference dosimetry of small and nonstandard fields,” Med. Phys. 35, 51795186 (2008).
4. E. Pantelis, A. Moutsatsos, K. Zourari, L. Petrokokkinos, L. Sakelliou, W. Kilby, C. Antypas, P. Papagiannis, P. Karaiskos, E. Georgiou, and I. Seimenis, “On the output factor measurements of the cyberknife iris collimator small fields: Experimental determination of the correction factors for microchamber and diode detectors,” Med. Phys. 39, 48754885 (2012).
5. P. Francescon, S. Cora, and N. Satariano, “Calculation of for several small detectors and for two linear accelerators using Monte Carlo simulations,” Med. Phys. 38, 65136527 (2011).
6. E. Sterpin, T. R. Mackie, and S. Vynckier, “Monte Carlo computed machine-specific correction factors for reference dosimetry of TomoTherapy static beam for several ion chambers,” Med. Phys. 39, 40664072 (2012).
7. G. Cranmer-Sargison, S. Weston, J. A. Evans, N. P. Sidhu, and D. I. Thwaites, “Monte carlo modelling of diode detectors for small field mv photon dosimetry: Detector model simplification and the sensitivity of correction factors to source parameterization,” Phys. Med. Biol. 57, 51415153 (2012).
8. P. Francescon, W. Kilby, N. Satariano, and S. Cora, “Monte Carlo simulated correction factors for machine specific reference field dose calibration and output factor measurement using fixed and iris collimators on the CyberKnife system,” Phys. Med. Biol. 57, 37413758 (2012).
9. A. J. D. Scott, S. Kumar, A. E. Nahum, and J. D. Fenwick, “Characterizing the influence of detector density on dosimeter response in non-equilibrium small photon fields,” Phys. Med. Biol. 57, 44614476 (2012).
10. H. Bouchard and J. Seuntjens, “Ionization chamber-based reference dosimetry of intensity modulated radiation beams,” Med. Phys. 31, 24542465 (2004).
11. D. M. Gonzalez-Castano, L. B. Gonzalez, M. A. Gago-Arias, J. Pardo-Montero, F. Gomez, V. Luna-Vega, M. Sanchez, and R. Lobato, “A convolution model for obtaining the response of an ionization chamber in static non standard fields,” Med. Phys. 39, 482491 (2012).
12. A. Djouguela, D. Harder, R. Kollhoff, A. Rhmann, K. Willborn, and B. Poppe, “The dose-area product, a new parameter for the dosimetry of narrow photon beams,” Z. Med. Phys. 16, 217227 (2006).
13. J. Fan, K. Paskalev, L. Wang, L. Jin, J. Li, A. Eldeeb, and C. Ma, “Determination of output factors for stereotactic radiosurgery beams,” Med. Phys. 36, 52925300 (2009).
14. B. Hundertmark, E. Sterpin, and T. Mackie, “A robust procedure for verifying tomotherapy hi-art source models for small fields,” Phys. Med. Biol. 56, 36853699 (2011).
15. E. Chung, H. Bouchard, and J. Seuntjens, “Investigation of three radiation detectors for accurate measurement of absorbed dose in nonstandard fields,” Med. Phys. 37, 24042413 (2010).
16. D. W. O. Rogers, B. Walters, and I. Kawrakow, “BEAMnrc users manual,” Technical Report No. PIRS 509 rev L (NRC, Ottawa, 2011).
17. B. R. B. Walters, I. Kawrakow, and D. W. O. Rogers, “DOSXYZnrc users manual,” Technical Report No. PIRS 794 rev B (NRC, Ottawa, 2005).
18. J. Wulff, K. Zink, and I. Kawrakow, “Efficiency improvements for ion chamber calculations in high energy photon beams,” Med. Phys. 35, 13281336 (2008).
19. International Commission on Radiation Units and Measurements, “Stopping powers for electrons and positrons,” ICRU Report No. 37 (ICRU, Bethesda, 1984).
20. H. Bouchard, J. Seuntjens, J.-F. Carrier, and I. Kawrakow, “Ionization chamber gradient effects in nonstandard beam configurations,” Med. Phys. 36, 46544663 (2009).
21. I. Kawrakow, E. Mainegra-Hing, and D. W. O. Rogers, “EGSnrcMP: The multi-platform environment for EGSnrc,” Technical Report No. PIRS-877 (NRC, Ottawa, 2006).
23. C. Coles and J. Yarnold, “The IMPORT trials are launched (September 2006),” Clin. Oncol. 18, 587590 (2006).
24. D. A. Low, W. B. Harms, S. Mutic, and J. A. Purdy, “A technique for the quantitative evaluation of dose distributions,” Med. Phys. 25, 656661 (1998).
25. F. Crop, N. Reynaert, G. Pittomvils, L. Paelinck, C. De Wagter, L. Vakaet, and H. Thierens, “The influence of small field sizes, penumbra, spot size and measurement depth on perturbation factors for microionization chambers,” Phys. Med. Biol. 54, 29512969 (2009).
26. F. Lacroix, M. Guillot, M. McEwen, L. Gingras, and L. Beaulieu, “Extraction of depth-dependent perturbation factors for silicon diodes using a plastic scintillation detector,” Med. Phys. 38, 54415447 (2011).
27. F. Sánchez-Doblado, G. Hartmann, J. Pena, J. Roselló, G. Russiello, and D. Gonzalez-Castano, “A new method for output factor determination in mlc shaped narrow beams,” Phys. Medica 23, 5866 (2007).

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TheAlfonso et al. [Med. Phys.35, 5179–5186 (2008)] formalism for small field dosimetry proposes a set of correction factors ( ) which account for differences between the detector response in nonstandard (clinical) and machine-specific-reference fields. In this study, the Monte Carlo method was used to investigate the viability of such small field correction factors for four different detectors irradiated under a variety of conditions. Because values for single detector position measurements are influenced by several factors, a new theoretical formalism for integrated-detector-position [dose area product (DAP)] measurements is also presented and was tested using Monte Carlo simulations.

A BEAMnrc linac model was built and validated for a Varian Clinac iX accelerator. Using the egs++ geometry package, detailed virtual models were built for four different detectors: a PTW 60012 unshielded diode, a PTW 60003 Diamond detector, a PTW 31006 PinPoint (ionization chamber), and a PTW 31018 MicroLion (liquid-filled ionization chamber). The egs_chamber code was used to investigate the variation of with detector type, detector construction, field size, off-axis position, and the azimuthal angle between the detector and beam axis. Simulations were also used to consider the DAP obtained by each detector: virtual detectors and water voxels were scanned through high resolution grids of positions extending far beyond the boundaries of the fields under consideration.

For each detector, the correction factor ( ) was shown to depend strongly on detector off-axis position and detector azimuthal angle in addition to field size. In line with previous studies, substantial interdetector variation was also observed. However, it was demonstrated that by considering DAPs rather than single-detector-position dose measurements the high level of interdetector variation could be eliminated. Under small field conditions, mass density was found to be the principal determinant of water equivalence. Additionally, the mass densities of components outside the sensitive volumes were found to influence the detector response.

values for existing detector designs depend on a host of variables and their calculation typically relies on the use of time-intensive Monte Carlo methods. Future moves toward density-compensated detector designs or DAP based protocols may simplify the methodology of small field dosimetry.


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