<abstract xmlns="http://www.w3.org/1999/xhtml"><bold>Background.</bold> Penumbra characteristics play a significant role in dose delivery accuracy for radiation therapy. For treatment planning, penumbra width and radiation field offset strongly influence target dose conformity and organ at risk sparing.<bold>Methods.</bold> In this study, we present an analytical and numerical approach for evaluation of the rounded leaf end effect on penumbra characteristics. Based on the rule of half-value layer, algorithms for leaf position calculation and radiation field offset correction were developed, which were advantageous particularly in dealing with large radius leaf end. Computer simulation was performed based on the Monte Carlo codes of EGSnrc/BEAMnrc, with groups of leaf end radii and source sizes. Data processing technique of curve fitting was employed for deriving penumbra width and radiation field offset.<bold>Results.</bold> Results showed that penumbra width increased with source size. Penumbra width curves for large radius leaf end were U-shaped. This observation was probably related to the fact that radiation beams penetrated through the proximal and distal leaf sides. In contrast, source size had negligible impact on radiation field offset. Radiation field offsets were found to be constant both for analytical method and numerical simulation. However, the overall resulting values of radiation field offset obtained by analytical method were slightly smaller compared with Monte Carlo simulation.<bold>Conclusions.</bold> The method we proposed could provide insight into the investigation of rounded leaf end effects on penumbra characteristics. Penumbra width and radiation field offset calibration should be carefully performed to commission multileaf collimator for intensity modulated radiotherapy.</abstract>

Background. Penumbra characteristics play a significant role in dose delivery accuracy for radiation therapy. For treatment planning, penumbra width and radiation field offset strongly influence target dose conformity and organ at risk sparing.Methods. In this study, we present an analytical and numerical approach for evaluation of the rounded leaf end effect on penumbra characteristics. Based on the rule of half-value layer, algorithms for leaf position calculation and radiation field offset correction were developed, which were advantageous particularly in dealing with large radius leaf end. Computer simulation was performed based on the Monte Carlo codes of EGSnrc/BEAMnrc, with groups of leaf end radii and source sizes. Data processing technique of curve fitting was employed for deriving penumbra width and radiation field offset.Results. Results showed that penumbra width increased with source size. Penumbra width curves for large radius leaf end were U-shaped. This observation was probably related to the fact that radiation beams penetrated through the proximal and distal leaf sides. In contrast, source size had negligible impact on radiation field offset. Radiation field offsets were found to be constant both for analytical method and numerical simulation. However, the overall resulting values of radiation field offset obtained by analytical method were slightly smaller compared with Monte Carlo simulation.Conclusions. The method we proposed could provide insight into the investigation of rounded leaf end effects on penumbra characteristics. Penumbra width and radiation field offset calibration should be carefully performed to commission multileaf collimator for intensity modulated radiotherapy.

Rounded leaf end effect of multileaf collimator on penumbra width and radiation field offset: an analytical and numerical study

Department of Mechanical Engineering, Tsinghua University, Beijing, China

Radiology and Oncology

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Background. Penumbra characteristics play a significant role in dose delivery accuracy for radiation therapy. For treatment planning, penumbra width and...

Rounded leaf end effect of multileaf collimator on penumbra width and radiation field offset: an analytical and numerical study

Published Online: Aug 21, 2015

Page range: 299 - 306

Received: Feb 01, 2015

Accepted: Mar 22, 2015

DOI: https://doi.org/10.1515/raon-2015-0023

Keywords
multileaf collimator, rounded leaf end effect, penumbra width, radiation field offset, Monte Carlo simulation

© 2015 Dong Zhou et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Rounded leaf end effect of multileaf collimator on penumbra width and radiation field offset: an analytical and numerical study

Published Online: Aug 21, 2015

Page range: 299 - 306

Received: Feb 01, 2015

Accepted: Mar 22, 2015

DOI: https://doi.org/10.1515/raon-2015-0023

Keywordsmultileaf collimator, rounded leaf end effect, penumbra width, radiation field offset, Monte Carlo simulation

© 2015 Dong Zhou et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
multileaf collimator, rounded leaf end effect, penumbra width, radiation field offset, Monte Carlo simulation