An approximation of central-axis absorbed dose in narrow photon beams.

In narrow photon beams of therapeutic energy range, the absorbed dose derived from experimental measurements is subject to a significant error. The error stems from high dose gradients characteristic to small radiation fields and from finite probe dimensions. In this study, a simple model for the narrow-beam absorbed dose is described. It is shown that broad-beam dose data are sufficient to predict a narrow-beam dose. The dose is calculated as a sum of primary and scatter components given in the form of respective analytical functions. For both functions, numerical coefficients are determined in broad-beam geometry. The model is evaluated by comparing calculated dose values with the Monte Carlo simulated narrow-beam dose data for 6 and 15 MV x rays.

[1]  B. Bjärngard,et al.  Attenuation in high-energy x-ray beams. , 1994, Medical physics.

[2]  J. H. Hubbell,et al.  Tables of X-Ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 keV to 20 MeV for Elements Z = 1 to 92 and 48 Additional Substances of Dosimetric Interest , 1995 .

[3]  T. Zhu,et al.  X-ray source and the output factor. , 1995, Medical physics.

[4]  B. Bjärngard,et al.  Analysis of central-axis doses for high-energy x rays. , 1995, Medical physics.

[5]  A. Iwasaki.  Two types of phantom scatter correction factors (Sp) for high-energy photons. , 1996, Physics in medicine and biology.

[6]  David W. O. Rogers,et al.  Presta: The parameter reduced electron-step transport algorithm for electron monte carlo transport , 1986 .

[7]  B. Bjärngard,et al.  Doses on the central axes of narrow 6-MV x-ray beams. , 1990, Medical physics.

[8]  T C Zhu,et al.  Experimental determination of the dose kernel in high-energy x-ray beams. , 1996, Medical physics.

[9]  P. Nizin.  Electronic equilibrium and primary dose in collimated photon beams. , 1993, Medical physics.

[10]  P S Nizin,et al.  Primary dose in photon beams with lateral electron disequilibrium. , 1991, Medical physics.

[11]  R Mohan,et al.  Energy and angular distributions of photons from medical linear accelerators. , 1985, Medical physics.

[12]  A. Ahnesjö,et al.  A pencil beam model for photon dose calculation. , 1992, Medical physics.

[13]  H. Rashid,et al.  "Zero-field" dose data for 60Co and other high-energy photon beams in water. , 1993, Medical physics.

[14]  B. Bjärngard,et al.  Description of the scatter component in photon-beam data. , 1988, Physics in medicine and biology.

[15]  E. El-Khatib,et al.  Differential scatter integration in regions of electronic non-equilibrium. , 1995, Physics in medicine and biology.

[16]  D. Bellezza,et al.  The elements of tissue-air ratio and systematic error. , 1996, Medical physics.

[17]  P. Nizin.  Geometrical aspects of scatter-to-primary ratio and primary dose. , 1991, Medical physics.

[18]  R L Siddon,et al.  A note on equivalent circles, squares, and rectangles. , 1982, Medical physics.

[19]  R. Sloboda,et al.  Linear accelerator photon beam quality at off-axis points. , 1997, Medical physics.