Two-step intensity modulated arc therapy (2-step IMAT) with segment weight and width optimization

• Main Authors: Meyer Juergen, Chew Theam, Sun Jidi
• Format: Article
• Language: English
• Published: BMC 2011-06-01
• Series: Radiation Oncology
• Online Access: http://www.ro-journal.com/content/6/1/57
• ISSN: 1748-717X

<p>Abstract</p> <p>Background</p> <p>2-step intensity modulated arc therapy (IMAT) is a simplified IMAT technique which delivers the treatment over typically two continuous gantry rotations. The aim of this work was to implement the technique into a computerized treatment planning system and to develop an approach to optimize the segment weights and widths.</p> <p>Methods</p> <p>2-step IMAT was implemented into the Prism treatment planning system. A graphical user interface was developed to generate the plan segments automatically based on the anatomy in the beam's-eye-view. The segment weights and widths of 2-step IMAT plans were subsequently determined in Matlab using a dose-volume based optimization process. The implementation was tested on a geometric phantom with a horseshoe shaped target volume and then applied to a clinical paraspinal tumour case.</p> <p>Results</p> <p>The phantom study verified the correctness of the implementation and showed a considerable improvement over a non-modulated arc. Further improvements in the target dose uniformity after the optimization of 2-step IMAT plans were observed for both the phantom and clinical cases. For the clinical case, optimizing the segment weights and widths reduced the maximum dose from 114% of the prescribed dose to 107% and increased the minimum dose from 87% to 97%. This resulted in an improvement in the homogeneity index of the target dose for the clinical case from 1.31 to 1.11. Additionally, the high dose volume V₁₀₅was reduced from 57% to 7% while the maximum dose in the organ-at-risk was decreased by 2%.</p> <p>Conclusions</p> <p>The intuitive and automatic planning process implemented in this study increases the prospect of the practical use of 2-step IMAT. This work has shown that 2-step IMAT is a viable technique able to achieve highly conformal plans for concave target volumes with the optimization of the segment weights and widths. Future work will include planning comparisons of the 2-step IMAT implementation with fixed gantry intensity modulated radiotherapy (IMRT) and commercial IMAT implementations.</p>