Experimental verification of convolution/superposition photon dose calculations for radiotherapy treatment planning

This work describes an experimental verification of the two-photon dose calculation engines available on the Helax-TMS (version 6.1) commercial radiotherapy treatment planning system. The performance of the pencil beam convolution and the collapsed cone superposition algorithms was examined for 4, 6...

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Bibliographic Details
Published in:	Physics in medicine & biology Vol. 48; no. 17; p. 2873
Main Authors:	Aspradakis, Maria M, Morrison, Rachel H, Richmond, Neil D, Steele, Alasdair
Format:	Journal Article
Language:	English
Published:	England 07-09-2003
Subjects:	Algorithms Computer Simulation Linear Energy Transfer Models, Biological Neoplasms - physiopathology Neoplasms - radiotherapy Photons - therapeutic use Practice Patterns, Physicians Quality Control Radiation Protection - methods Radiometry - methods Radiotherapy Dosage Radiotherapy Planning, Computer-Assisted - methods Radiotherapy, Conformal - methods Reproducibility of Results Sensitivity and Specificity Statistics as Topic
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Summary:	This work describes an experimental verification of the two-photon dose calculation engines available on the Helax-TMS (version 6.1) commercial radiotherapy treatment planning system. The performance of the pencil beam convolution and the collapsed cone superposition algorithms was examined for 4, 6, 15 MV beams, under a range of clinically relevant irradiation geometries. Comparisons against measurements were carried out in terms of absolute dose, thus assessment of the accuracy of monitor unit (MU) calculations was also carried out. Results show that both algorithms agree with measurement to acceptable tolerance levels in most cases in homogeneous water-equivalent media irradiated under full scatter conditions. The collapsed cone algorithm slightly overestimates the penumbra width and this is mainly due to discretization effects of the fluence matrix. The accuracy of this algorithm strongly depends on the resolution of the patient density matrix. It is recommended that the density matrix voxel size used for dose calculations is less than 5 x 5 x 5 mm3. The dose in media irradiated under missing tissue geometry, or in the presence of low or high-density heterogeneities, is modelled best with the collapsed cone algorithm. This is of particular clinical interest in treatment planning of the breast and of the thorax. For these treatment sites, a retrospective study of treatment plans indicated in certain cases significant overestimation of the dose to the planning target volume when using the pencil beam convolution model.
ISSN:	0031-9155
DOI:	10.1088/0031-9155/48/17/309