Program Information
Semi-Automatic Fluence Modification Method to Reduce Hot Spots for Electronic Irregular Surface Compensation
S Sugimoto*, H Watanabe, T Kawabata, Juntendo University, Tokyo, Japan
Presentations
SU-E-FS2-7 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: Four Seasons 2
Purpose: To propose a semi-automatic fluence modification method to reduce hot spots for electronic irregular surface compensation.
Methods: Optimized fluence for each beam to compensate an irregular surface was obtained using the Irregular Surface Compensator algorithm in the Eclipse treatment planning system (version 13.6) (Varian Medical Systems, Palo Alto, CA). The fluences were converted to dynamic multileaf collimator motions and the 3D dose distribution was calculated using the AAA algorithm in Eclipse. Hot spots, where the doses were above a threshold were identified. A dose reduction factor at each hot-spot point for each beam was calculated to reduce the dose below the threshold and was converted to a fluence reduction factor. The dose reduction factor for each beam was determined to be proportional to the dose from the beam at the hot-spot point. The reduced fluences were imported to the original treatment plan and the volume dose was recalculated. The algorithm was implemented using Eclipse Scripting API. As an example, a treatment plan using opposed tangential beams was made to intend to give a uniform dose on the edge region of a cubic phantom (40x40x40 cm³) to simulate a whole breast irradiation case. The threshold was set to 107% of the prescribed dose of 2 Gy at the isocenter.
Results: By using the fluence reduction method, the maximum dose decreased from 114.4% to 108.9% of the prescribed dose in the example case. The volume of the hot spot region receiving more than the threshold dose was reduced by 87.8%, while the volumes of the 100% and 95% doses was changed by less than 0.5%.
Conclusion: The fluence modification method for electronic irregular surface compensation was feasible to reduce hot spot regions semi-automatically. It can be used for realizing an automatic treatment planning method for whole breast irradiation.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by JSPS KAKENHI Grant Number JP15K08702.
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