Skip to main content
banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
The full text of this article is not currently available.
1.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(9), 18471869 (1999).
2.P. Andreo, D. T. Burns, K. Hohfield, M. S. Huq, T. Kanai, F. Laitano, V. Smyth, and S. Vynckier, “Absorbed dose determination in external beam radiotherapy: An international code of practice for dosimetry based on standards of absorbed dose to water,” Technical Report TRS-398, International Atomic Energy Agency, Vienna, Austria, 2001.
3.R. Alfonso, P. Andreo, R. Capote, S. M. Huq, W. Kilby, P. Kjäll, 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(11), 51795186 (2008).
4.K. M. Langen, N. Papanikolaou, J. Balog, R. Crilly, D. Followill, S. M. Goddu, W. Grant III, G. Olivera, C. R. Ramsey, and C. Shi, “QA for helical tomotherapy: Report of the AAPM Task Group 148,” Med. Phys. 37(9), 48174853 (2010).
5.S. J. Thomas, M. M. Aspradakis, J. P. Byrne, G. Chalmers, S. Duane, J. Rogers, R. A. S. Thomas, G. S. J. Tudor, and N. Twyman, “Reference dosimetry on TomoTherapy: An addendum to the 1990 UK MV dosimetry code of practice,” Phys. Med. Biol. 59, 13391352 (2014).
6.X. A. Li, M. Soubra, J. Szanto, and L. H. Gerig, “Lateral electron equilibrium and electron contamination in measurements of head scatter factors using miniphantoms and brass caps,” Med. Phys. 22, 11671170 (1995).
7.P. Francescon, S. Cora, C. Cavedon, P. Scalchi, S. Reccanello, and F. Colombo, “Use of a new type of radiochromic film, a new parallel-plate micro-chamber, MOSFETs, and TLD 800 microcubes in the dosimetry of small beams,” Med. Phys. 25(4), 503511 (1998).
8.H. Bouchard and J. P. Seuntjens, “Ionization chamber-based reference dosimetry of intensity modulated radiation beams,” Med. Phys. 31(9), 24542465 (2004).
9.R. Capote, F. Sánchez-Doblado, A. Leal, J. Ignacio Lagares, R. Arráns, and G. H. Hartmann, “An EGSnrc Monte Carlo study of the microionization chamber for reference dosimetry of narrow irregular IMRT beamlets,” Med. Phys. 31(9), 24162422 (2004).
10.F. Sánchez-Doblado, R. Capote, J. V. Roselló, A. Leal, J. I. Lagares, R. Arráns, and G. H. Hartmanne, “Micro ionization chamber dosimetry in IMRT verification: Clinical implications of dosimetric errors in the PTV,” Radiother. Oncol. 75(3), 342348 (2005).
11.F. Araki, “Monte Carlo study of a Cyberknife stereotactic radiosurgery system,” Med. Phys. 33(8), 29552963 (2006).
12.O. A. Sauer and J. Wilbert, “Measurement of output factors for small photon beams,” Med. Phys. 34(6), 19831988 (2007).
13.A. J. D. Scott, A. E. Nahum, and J. D. Fenwick, “Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields,” Med. Phys. 35(10), 46714684 (2008).
14.I. J. Das, G. X. Ding, and A. Ahnesjö, “Small fields: Nonequilibrium radiation dosimetry,” Med. Phys. 35(1), 206215 (2008).
15.P. Francescon, S. Cora, and C. Cavedon, “Total scatter factors of small beams: A multidetector and Monte Carlo study,” Med. Phys. 35(2), 504513 (2008).
16.H. Bouchard, J. P. Seuntjens, J. Carrier, and I. Kawrakow, “Ionization chamber gradient effects in nonstandard beams,” Med. Phys. 36(10), 46544663 (2009).
17.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(12), 65136527 (2011).
18.A. Gago-Ariasa, R. Rodriguez-Romero, P. Sanchez-Rubio, D. Miguel Gonzalez-Castaño, F. Gomez, L. Nunez, H. Palmans, P. Sharpe, and J. Pardo-Montero, “Correction factors for A1SL ionization chamber dosimetry in TomoTherapy: Machine-specific, plan-class, and clinical fields,” Med. Phys. 39(4), 19641970 (2012).
19.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(12), 37413758 (2012).
20.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(7), 40664072 (2012).
21.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(16), 51415153 (2012).
22.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(14), 44614476 (2012).
23.T. S. A. Underwood, H. C. Winter, M. A. Hill, and J. D. Fenwick, “Mass-density compensation can improve the performance of a range of different detectors under non-equilibrium conditions,” Phys. Med. Biol. 58(23), 82958310 (2013).
24.T. S. A. Underwood, H. C. Winter, M. A. Hill, and J. D. Fenwick, “Detector density and small field dosimetry: Integral versus point dose measurement schemes,” Med. Phys. 40(8), 082102 (16pp.) (2013).
25.D. Czarnecki and K. Zink, “Monte Carlo calculated correction factors for diodes and ion chambers in small photon fields,” Phys. Med. Biol. 58(8), 24312444 (2013).
26.J. D. Fenwick, S. Kumar, A. J. D. Scott, and A. E. Nahum, “Using cavity theory to describe the dependence on detector density of dosimeter response in non-equilibrium small fields,” Phys. Med. Biol. 58(9), 29012923 (2013).
27.P. Francescon, W. Kilby, and N. Satariano, “Monte Carlo simulated correction factors for output factor measurement with the CyberKnife system-results for new detectors and correction factor dependence on measurement distance and detector orientation,” Phys. Med. Biol. 59(6), N11N17 (2014).
28.H. Benmakhlouf, J. Sempau, and P. Andreo, “Output correction factors for nine small field detectors in 6 MV radiation therapy photon beams: A penelope Monte Carlo study,” Med. Phys. 41(4), 041711 (12pp.) (2014).
29.Y. Kamio and H. Bouchard, “Correction-less dosimetry of nonstandard photon fields: A new criterion to determine the usability of radiation detectors,” Phys. Med. Biol. 59, 46735002 (2014).
30.P. Francescon, S. Beddar, N. Satariano, and I. J. Das, “Variation of for the small-field dosimetric parameters percentage depth dose, tissue-maximum ratio, and off-axis ratio,” Med. Phys. 41(10), 101708 (14pp.) (2014).
31.P. Papaconstadopoulos, F. Tessier, and J. Seuntjens, “On the correction, perturbation and modification of small field detectors in relative dosimetry,” Phys. Med. Biol. 59(19), 59375952 (2014).
32.H. Benmakhlouf, J. Johansson, I. Paddick, and P. Andreo, “Monte Carlo calculated and experimentally determined output correction factors for small field detectors in Leksell Gamma Knife Perfexion beams,” Phys. Med. Biol. 60(10), 39593973 (2015).
33.IPEM, “Small field MV photon dosimetry,” Technical Report 103, Institute of Physics in Engineering and Medicine, York, 2010.
34.A. E. Nahum, “Cavity theory, stopping power ratios, correction factors,” in Clinical Dosimetry Measurements in Radiotherapy, AAPM summer school (Medical Physics Publishing), 91–136 (2009).
35.D. W. O. Rogers, “General characteristics of radiation dosimeters and a terminology to describe them,” in Clinical Dosimetry Measurements in Radiotherapy, edited by D. W. O. Rogers and J. E. Cygler (Medical Physics, Madison, WI, 2009).
36.L. H. Gray, “An ionization method for the absolute measurement of gamma ray energy,” Proc. R. Soc. A 156, 578596 (1936).
37.G. C. Laurence, “The measurement of extra hard x-rays and gamma-rays in roentgens,” Can. J. Res. 15a, 6778 (1937).
38.P. R. Burch, “Cavity ion chamber theory,” Radiat. Res. 3, 361378 (1955).
39.P. R. Burch, “Comment on recent cavity ionization theories,” Radiat. Res. 6, 7984 (1957).
40.T. E. Burlin, “A general theory of cavity ionisation,” Br. J. Radiol. 39, 727734 (1966).
41.A. Janssens, G. Eggermont, R. Jacobs, and G. Thielens, “Spectrum perturbation and energy deposition models for stopping power ratio calculations in general cavity theory,” Phys. Med. Biol. 19, 619630 (1974).
42.L. Zheng-Ming, “An electron transport theory of cavity ionization,” Radiat. Res. 84, 115 (1980).
43.A. Janssens, “Modified energy-deposition model, for the computation of the stopping-power ratio for small cavity sizes,” Phys. Rev. A 23, 11641173 (1981).
44.A. F. Bielajew, “Ionisation cavity theory: A formal derivation of perturbation factors for thick-walled ion chambers in photon beams,” Phys. Med. Biol. 31(2), 161170 (1986).
45.I. Kawrakow, “Stopping power ratios,” Technical Report Lecture notes, National Research Council of Canada, Ottawa, Canada, 1998.
46.H. Bouchard, “A theoretical re-examination of Spencer-Attix cavity theory,” Phys. Med. Biol. 57(11), 33333358 (2012).
47.L. V. Spencer and F. H. Attix, “A theory of cavity ionization,” Radiat. Res. 3(3), 239254 (1955).
48.A. E. Nahum, “Water/air mass stopping power ratios for megavoltage photons and electrons beams,” Phys. Med. Biol. 23(1), 2438 (1978).
49.Task Group 21 Radiation Therapy Committee (AAPM), “A protocol for the determination of absorbed dose from high-energy photon and electron beams,” Med. Phys. 10(6), 741771 (1983).
50.International Commission on Radiation Units and Measurements, “Radiation dosimetry: Electrons with initial energies between 1 and 50 MeV,” Technical Report No. 35, International Commission on Radiation Units and Measurements, Washington, D.C., 1984.
51.International Atomic Energy Agency, “Absorbed dose determination in photon and electron beams: An international code of practice,” Technical Report TRS-277, International Atomic Energy Agency, Vienna, Austria, 1987.
52.S. Olsson and E. S. Bergstrand, Calibration of alanine dosimeters, 2001.
53.S. Olsson, E. S. Bergstrand, Å. K. Carlsson, E. O. Hole, and E. Lund, “Radiation dose measurements with alanine/agarose gel and thin alanine films around a 192ir brachytherapy source, using ESR spectroscopy,” Phys. Med. Biol. 47(8), 13331356 (2002).
54.E. Kearsley, “A new general cavity theory,” Phys. Med. Biol. 29(10), 11791187 (1984).
55.D. W. O. Rogers, “Fundamentals of dosimetry based on absorbed-dose standards,” in Teletherapy Physics, Present and Future, AAPM summer school (Palta, JR, Mackie, TR, ed.), AAPM, 319–356 (1996).
56.P. Andreo, D. T. Burns, and M. S. Huq, “Review of the data in the international code of practice IAEA TRS-398 (2000). Comparison with other dosimetry protocols,” inRecent Developments in Accurate Radiation Dosimetry (Proc. Int. Workshop Montreal, 2001), edited by J. P. Seuntjens and P. N. Mobit (Medical Physics, Madison, WI, 2002), Vol. 29.
57.L. A. Buckley and D. W. O. Rogers, “Wall correction factors, pwall, for thimble ionization chambers,” Med. Phys. 33(2), 455464 (2006).
58.J. Wulff, J. T. Heverhagen, and K. Zink, “Monte-Carlo-based perturbation and beam quality correction factors for thimble ionization chambers in high-energy photon beams,” Phys. Med. Biol. 53(11), 28232836 (2008).
59.L. L. W. Wang and D. W. O. Rogers, “Calculation of the replacement correction factors for ion chambers in megavoltage beams by Monte Carlo simulation,” Med. Phys. 35(5), 17471755 (2008).
60.L. L. W. Wang and D. W. O. Rogers, “The replacement correction factors for cylindrical chambers in high-energy photon beams,” Phys. Med. Biol. 54(6), 16091620 (2009).
61.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(9), 29512969 (2009).
62.A. E. Nahum, “Perturbation effects in dosimetry: Part I. Kilovoltage x-rays and electrons,” Phys. Med. Biol. 41(9), 15311580 (1996).
63.L. V. Spencer and U. Fano, “Energy spectrum resulting from electron slowing down,” Phys. Rev. 93(6), 11721181 (1954).
64.J. R. Cunningham and R. J. Schulz, “On the selection of stopping-power and mass energy-absorption coefficient ratios for high-energy x-ray dosimetry,” Med. Phys. 11(5), 618623 (1983).
65.P. Andreo and A. Brahme, “Stopping power data for high-energy photon beam,” Phys. Med. Biol. 31, 839858 (1986).
66.A. Kosunen and D. W. O. Rogers, “Beam quality specification for photon beam dosimetry,” Med. Phys. 20(4), 11811188 (1993).
67.P. Andreo, “Improved calculations of stopping-power ratios and their correlation with the quality of therapeutic photon beams,” in Measurement Assurance in Dosimetry (Proc Symp. Vienna, 1993) (IAEA, Vienna, 1994), pp. 335359.
68.D. W. Rogers and C. L. Yang, “Corrected relationship between %dd(10)x and stopping-power ratios,” Med. Phys. 26(4), 538540 (1999).
69.H. Bouchard and J. Seuntjens, “Applications of Monte Carlo to radiation dosimetry,” inMonte Carlo Techniques in Radiation Therapy, edited by J. Seco and F. Verhaegen (CRC, Taylor and Francis Group, Boca Raton, FL, 2013), Chap. 4.
70.F. Sánchez-Doblado, P. Andreo, R. Capote, A. Leal, M. Perucha, R. Arráns, L. Núñez, E. Mainegra, J. I. Lagares, and E. Carrasco, “Ionization chamber dosimetry of small photon fields: A Monte Carlo study on stopping-power ratios for radiosurgery and IMRT beams,” Phys. Med. Biol. 48(14), 20812099 (2003).
71.K. Eklund and A. Ahnesjö, “Fast modelling of spectra and stopping-power ratios using differentiated fluence pencil kernels,” Phys. Med. Biol. 53, 42314247 (2008).
72.U. Fano, “Note on the Bragg-Gray cavity principle for measuring energy dissipation,” Radiat. Res. 1(3), 237240 (1954).
73.H. Bouchard, J. Seuntjens, and H. Palmans, “On charged particle equilibrium violation in external photon fields,” Med. Phys. 39(1), 14731480 (2012).
74.H. E. Johns and J. R. Cunningham, “The Physics of Radiology,” 4th ed. (Thomas, Springfield, IL, 1983).
75.A. F. Bielajew, “An analytic theory of the point-source nonuniformity correction factor for thick-walled ionisation chambers in photon beams,” Phys. Med. Biol. 35(4), 517538 (1990).
76.A. F. Bielajew, “Correction factors for thick-walled ionisation chambers in point-source photon beams,” Phys. Med. Biol. 35(4), 501516 (1990).
77.I. Kawrakow, “Accurate condensed history Monte Carlo simulation of electron transport. II. Application to ion chamber response simulations,” Med. Phys. 27(3), 499513 (2000).
78.J. Sempau and P. Andreo, “Configuration of the electron transport algorithm of penelope to simulate ion chambers,” Phys. Med. Biol. 51, 35333548 (2006).
79.E. Sterpin, J. Sorriaux, K. Souris, S. Vynckier, and H. Bouchard, “A Fano cavity test for Monte Carlo proton transport algorithms,” Med. Phys. 41(1), 011706 (10pp.) (2014).
80.I. Kawrakow and D. W. O. Rogers, “The EGSnrc code system,” NRC Report PIRS-701, NRC, Ottawa, 2000.
81.H. W. Lewis, “Multiple scattering in an infinite medium,” Phys. Rev. 78(5), 526529 (1950).
82.M. J. Berger, “Monte Carlo calculation of the penetration and diffusion of fast charged particles,” Methods Comput. Phys. 1, 135215 (1963).
83.H. K. Looe, T. S. Stelljes, S. Foschepoth, D. Harder, K. Willborn, and B. Poppe, “The dose response functions of ionization chambers in photon dosimetry- Gaussian or non-Gaussian?,” Z. Med. Phys. 23, 129143 (2013).
84.P. H. Charles, G. Cranmer-Sargison, D. I. Thwaites, S. B. Crowe, T. Kairn, R. T. Knight, J. Kenny, C. M. Langton, and J. V. Trapp, “A practical and theoretical definition of very small field size for radiotherapy output factor measurements,” Med. Phys. 41(4), 041707 (8pp.) (2014).
85.B. R. Muir and D. W. O. Rogers, “Monte Carlo calculations of kQ, the beam quality conversion factor,” Med. Phys. 37(11), 59395950 (2010).
86.International Commission on Radiation Units and Measurements, “Stopping powers for electrons and positions,” Technical Report No. 37, International Commission on Radiation Units and Measurements, Washington, D.C., 1984.
87.M. J. Berger, J. H. Hubbell, S. M. Seltzer, J. Chang, J. S. Coursey, R. Sukumar, D. S. Zucker, and K. Olsen, “XCOM: Photon cross section database,” Technical Report, National Institute of Standards and Technology, Gaithersburg, MD, 2010.
88.M. J. Berger, J. S. Coursey, M. A. Zucker, and J. Chang, “ESTAR, PSTAR, and ASTAR: Computer programs for calculating stopping-power and range tables for electrons, protons, and helium ions,” Technical Report, National Institute of Standards and Technology, Gaithersburg, MD, 2005.
89.P. H. Charles, S. B. Crowe, T. Kairn, R. T. Knight, B. Hill, J. Kenny, C. M. Langton, and J. V. Trapp, “Monte Carlo-based diode design for correction-less small field dosimetry,” Phys. Med. Biol. 58(13), 45014512 (2013).
90.P. H. Charles, G. Cranmer-Sargison, D. I. Thwaites, T. Kairn, S. B. Crowe, G. Pedrazzini, T. Aland, J. Kenny, C. M. Langton, and J. V. Trapp, “Design and experimental testing of air slab caps which convert commercial electron diodes into dual purpose, correction-free diodes for small field dosimetry,” Med. Phys. 41(10), 101701 (9pp.) (2014).
91.International Commission on Radiation Units and Measurements, “Fundamental quantities and units for ionizing radiation: Report no. 85,” J. ICRU 11(1a), 133 (2011).
92.H. Bouchard, Y. Kamio, H. Palmans, J. Seuntjens, and S. Duane, “Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects,” Med. Phys. 42, 60486061 (2015).

Data & Media loading...


Article metrics loading...



To explain the reasons for significant quality correction factors in megavoltage small photon fields and clarify the underlying concepts relevant to dosimetry under such conditions.

The validity of cavity theory and the requirement of charged particle equilibrium (CPE) are addressed from a theoretical point of view in the context of nonstandard beams. Perturbation effects are described into four main subeffects, explaining their nature and pointing out their relative importance in small photon fields.

It is demonstrated that the failure to meet classical cavity theory requirements, such as CPE, is not the reason for significant quality correction factors. On the contrary, it is shown that the lack of CPE alone cannot explain these corrections and that what matters most, apart from volume averaging effects, is the relationship between the lack of CPE in the small field itself and the density of the detector cavity. The density perturbation effect is explained based on Fano’s theorem, describing the compensating effect of two main contributions to cavity absorbed dose. Using the same approach, perturbation effects arising from the difference in atomic properties of the cavity medium and the presence of extracameral components are explained. Volume averaging effects are also discussed in detail.

Quality correction factors of small megavoltage photon fields are mainly due to differences in electron density between water and the detector medium and to volume averaging over the detector cavity. Other effects, such as the presence of extracameral components and differences in atomic properties of the detection medium with respect to water, can also play an accentuated role in small photon fields compared to standard beams.


Full text loading...


Access Key

  • FFree Content
  • OAOpen Access Content
  • SSubscribed Content
  • TFree Trial Content
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd