| Autor: |
Karl Otto, T Teke, Brenda G. Clark |
| Rok vydání: |
2006 |
| Předmět: |
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| Zdroj: |
International Journal of Radiation Oncology*Biology*Physics. 66:S71-S75 |
| ISSN: |
0360-3016 |
| DOI: |
10.1016/j.ijrobp.2005.10.035 |
| Popis: |
Purpose: This study compares the width of the penumbra obtained from two small-leaf multileaf collimators (MLCs) recommended for use in small field shaping for such techniques as stereotactic radiosurgery. Methods and Materials: High-resolution film dosimetry measurements were taken to characterize two MLCs with 3-mm and 5-mm leaf width at isocenter. The differences observed between leaf tip and leaf edge penumbra measured between 80% and 20% of maximum were explained using a simple model calculating transmission through the leaf tip geometry. Results: Substantial differences were found between the 80% to 20% penumbra for the two MLCs. The 3-mm MLC designed for a maximum field size of 9.8 cm × 9.8 cm showed 80% to 20% penumbra values of 2.4 ± 0.1 mm in both the directions perpendicular and parallel to the leaf motion. The 5-mm MLC designed for field sizes up to 40 cm × 40 cm showed comparable 80% to 20% penumbra in the direction perpendicular to leaf motion and 3.2 ± 0.1 mm in the direction parallel to leaf motion. The transmission modeling illustrated that this difference is largely due to the curvature of the leaf tip. It was found that to accommodate larger field sizes the leaf tip must have greater curvature, resulting in a larger penumbra. Conclusions: The results of this study show a difference in the leaf penumbra parallel to the direction of leaf motion between two MLCs designed for precision radiation therapy. This difference may be attributed to the leaf tip design and is determined by the maximum field size of the MLC. This difference is currently not modeled by all treatment planning systems and should be taken into account as part of any procurement assessment of a system for precision radiation therapy in the same way that the width of the leaf at isocenter would be considered. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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