Optimizing the Dose Distribution in Stereotactic Body Radiotherapy with Standard Multileaf Collimator(MLC) ： A Planning Study

导读：体部立体定向放射治疗（SBRT）可实现靶区剂量的集中、精准和生物有效性，同时避开重要的正常器官。它在当今放疗世界扮演着越来越重要的地位。为了得到更好的剂量优化，目前有很多关于定位、处方剂量技术的研究，运用IMRT可实现SBRT的剂量优化，但各个放疗中心的结果却不尽相同，尚未完全统一。

Purpose： To evaluate in stereotactic body radiotherapy （SBRT） setting the impact of the spatial relationship between the target volume and main organ at risk （mOAR） using different target-multi-leaf collimator （ MLC ） block margins with or without fluence intensity modulation （ IMRT technique）. Methods/Patients： Dosimetric evaluation of 3 scenarios was performed. In the first one, the target and the main organ at risk （mOAR） had a partial overlap. In the second, the target was completely surrounded by the mOAR and in the third the target was near without touching the mOAR. Results and Conclusions： Maximal mOAR sparing was obtained with 6 mm （patients 1 and 3） and 4mm （patient 2） block margins. Concerning irradiation technique, IMRT plans showed a significant mOAR sparing in patients 1 and 3. In conclusion, a 5mm standard block margin can be proposed as optimal. Moreover, the use of IMRT in the SBRT setting may carry out a potential benefit, except when the mOAR surrounds the target.