独立准直器位置精度对半野联合处剂量的影响

目的:介绍在乳腺癌和鼻咽癌放射治疗中的单一等中心半野联合放疗技术,并对独立准直器位置精度对半野联合处剂量的影响进行研究,提出对策.方法:用带独立准直器的直线加速器,以一个等中心,上下半野技术照射体模,用胶片剂量仪分析半野衔接处剂量分布情况,并将研究结果应用于乳腺癌和鼻咽癌病人的放射治疗.结果:受加速器独立准直器位置精度的影响,半野衔接处可能存在最大不超过2mm的过剂量区或欠剂量区.如果消除该系统误差的影响,则半野衔接处可得到均匀的剂量分布.结论:单一等中心半野联合照射,半野衔接处处于照射靶区,必须重视独立准直器位置精度对衔接处剂量的影响,并加以修正.

Dosimetry Effect Upon the Junction Plane of Beam-split Fields Caused by the Location Accuracy of Asymmetric Jaws

Objective: To present a mono isocentric no-coplane irradiation technique used in brest and nasopharyngeal carcinoma radiotherapy, and study the dosimetry effect upon the junction plane of beam-split fields caused by the location accuracy of asymmetric jaws, then give the solving methods. Methods: Mono isocentric and beam-split fields irradiation technique was used to irradiation of the phantom with Siemens Linear Accelerator equipped with dual asymmetric jaws. Dose distribution at the plane of junction was measured with film dosimeter. Results: There is no more than 2 mm higher or lower dose area at the junction plane of two beam-split fields caused by the location accuracy of asymmetric jaws, and this error belongs to systematic error. An ideal dose distribution at the junction will be acquired once the systematic error corrected. Conclusion: The systematic error caused by the location accuracy of asymmetric jaws must be attached great importance to and must be corrected since the junction is located on the irradiation target while a mono isocentric no-coplane irradiation technique is used.