Translate this page into:
Dose prediction accuracy of anisotropic analytical algorithm and pencil beam convolution algorithm beyond high density heterogeneity interface
*Corresponding author: Mr. Suresh B. Rana. suresh.rana@gmail.com
This article was originally published by Thieme Medical and Scientific Publishers Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Purpose: It is well known that photon beam radiation therapy requires dose calculation algorithms. The objective of this study was to measure and assess the ability of pencil beam convolution (PBC) and anisotropic analytical algorithm (AAA) to predict doses beyond high density heterogeneity. Materials and Methods: An inhomogeneous phantom of five layers was created in Eclipse planning system (version 8.6.15). Each layer of phantom was assigned in terms of water (first or top), air (second), water (third), bone (fourth), and water (fifth or bottom) medium. Depth doses in water (bottom medium) were calculated for 100 monitor units (MUs) with 6 Megavoltage (MV) photon beam for different field sizes using AAA and PBC with heterogeneity correction. Combinations of solid water, Poly Vinyl Chloride (PVC), and Styrofoam were then manufactured to mimic phantoms and doses for 100 MUs were acquired with cylindrical ionization chamber at selected depths beyond high density heterogeneity interface. The measured and calculated depth doses were then compared. Results: AAA′s values had better agreement with measurements at all measured depths. Dose overestimation by AAA (up to 5.3%) and by PBC (up to 6.7%) was found to be higher in proximity to the high-density heterogeneity interface, and the dose discrepancies were more pronounced for larger field sizes. The errors in dose estimation by AAA and PBC may be due to improper beam modeling of primary beam attenuation or lateral scatter contributions or combination of both in heterogeneous media that include low and high density materials. Conclusions: AAA is more accurate than PBC for dose calculations in treating deep-seated tumor beyond high-density heterogeneity interface.
Keywords
Acknowledgment
The author would like to thank Kevin Rogers at Arizona Center for Cancer Care for his support during the course of this project.
References
- Fraassa B. Quality assurance for clinical radiotherapy treatment planning. AAPM Report No. 62; Task Group No. 53, 1998.
- Papanikolaou N, Battista J, Mackie T, Kappas C, Boyer A. Tissue inhomogeneity corrections for megavoltage photon beams. AAPM Report No 85; Task Group No. 65, 2004.
- Robinson D. Inhomogeneity correction and the analytic anisotropic algorithm. J Appl Clin Med Phys 2008;9:112-22.
- Wong T, Metcalfe P, Kron T, Emeleus T. Radiotherapy x-ray dose distribution beyond air cavities. Australas Phys Eng Sci Med 1992;15:138-46.
- Plessis F, Willemse C, Lotter M, Goedhals L. Comparison of the Batho, ETAR and Monte Carlo dose calculation methods in CT based patient models. Med Phys 2001;28:582-9.
- Ding W, Johnston P, Wong T, Bubb I. Investigation of photon beam models in heterogeneous media of modern radiotherapy. Australas Phys Eng Sci Med 2004;27:39-48.
- Carrasco P, Jornet N, Duch M, Weber L, Ginjaume M, Eudaldo T, et al. Comparison of dose calculation algorithms in phantoms with lung equivalent heterogeneities under conditions of lateral electronic disequilibrium. Med Phys 2004;31:2899-911.
- Van Esch A, Tillikainen L, Pyykkonen J, Tenhunen M, Helminen H, Siljam äki S, et al. Testing of the analytical anisotropic algorithm for photon dose calculation. Med Phys 2006;33:4130-48.
- Breitman K, Rathee S, Newcomb C, Murray B, Robinson D, Field C, et al. Experimental validation of the eclipse AAA Algorithm. J Appl Clin Med Phys 2007;2:76-92.
- Storchi P, Van Battum L, Woudstra E. Calculation of a pencil beam kernel from measured photon beam data. Phys Med Biol 1999;44:2917-28.
- Mohan R, Chui C, Lidofsky L. Differential pencil beam dose computation model for photons. Med Phys 1986;13:64-73.
- Gray A, Oliver L, Johnson P. The accuracy of the pencil beam convolution and anisotropic analytical algorithms in predicting the dose effects due to the attenuation from immobilization devices and large air gaps. Med Phys 2009;36:3181-91.
- Hurkmans C, Knoos T, Nilsson P, Svahn-Tapper G, Danielsson H. Limitations of a Pencil Beam approach to photon dose calculations in the head and neck region. Radiother Oncol 1995;37:74-80.
- Sontag M, Cunningham J. Corrections to absorbed dose calculations for tissue inhomogeneities. Med Phys 1977;4:431-6.
- Storchi P, Woudstra E. Calculation of the absorbed dose distribution due to irregularly shaped photon beams using pencil beam kernels derived from basic beam data. Phys Med Biol 1996;41:637-56.