(Saturday, 4/7/2018)
Room: Foyer
Purpose: This study compared the dose blurring of three types of radiotherapy plans due to the setup error for the left-sided breast cancer; 3D conformal radiotherapy (3D-CRT), forward intensity-modulated radiotherapy (FIMRT), and volumetric modulated arc therapy (VMAT).
Methods: Four patients with left-sided breast cancer with breast conserving surgery were chosen. The prescription dose was 50.4 Gy in 28 fractions. The target volume was limited with the clinical target volume (622.46±200.75cm3). For 3D-CRT, conventional tangential fields using dynamic wedges between 15° and 20° were used. For FIMRT, multi-leaf collimators (MLCs) were used instead of the wedges under the same gantry angle in the 3D-CRT. For VMAT, two fields (clockwise and counterclockwise) were used with the similar tangential fields. Skin flash technique was not adopted with VMAT. The plans with setup error, where iso-center was shifted by ±3mm along the x or y-axis in the beam’s eye view, were obtained from each optimized plan with the same monitor units (MUs). We compared homogeneous index (HI), D2 (the dose received by the 2% of the target volume), and conformity index (CI) for the target coverage, and compared mean doses to ipsilateral lung, contralateral lung, heart and LAD coronary artery.
Results: While HI, D2, and CI of VMAT were significantly better than both those of 3D-CRT and those of FIMRT, the variations of HI, D2, and CI of VMAT were much larger than others. However, blurred target doses for VMAT were still better than others, and mean doses to normal organ for VMAT were also not affected with comparison to those for other techniques.
Conclusion: For radiotherapy plans for the left-sided breast cancer VMAT is not only the most useful technique for the target coverage, but also the most reliable for the setup error. More patients will be analyzed in the upcoming poster presentation.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT & Future Planning(No. 2013M2A2A7038291)
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