Eclipse放疗计划系统内非均匀组织深度剂量特性研究

Study on the Depth-Dose Characteristics in Eclipse Radiotherapy Treatment Planning System for Inhomogeneous Tissues

目的探讨Eclipse放射治疗计划系统内非均匀组织深度的剂量特性。方法在Eclipse计划系统里创建30 cm×30 cm×30 cm的水体模及3 cm深度处设立厚度为3 cm的肺组织或骨组织的非均匀介质,并赋予组织材料CT值;将源皮距设置为100 cm,射野面积大小分别取5 cm×5 cm、10 cm×10 cm、15 cm×15 cm、20 cm×20 cm;使用6 MV X射线照射,剂量大小为100 cGy,以蒙特卡洛结果为依据,采用AXB算法,获取体模中心轴上横向和纵向的剂量曲线。结果随着深度增加,纵向深度剂量呈先增大后减小的趋势,且射野面积越大,相对剂量越大;含肺或骨组织模体在与水组织交界处出现二次剂量建成。水-肺-水非均匀组织纵向深度剂量曲线上,在3 cm深度处,由水进入肺组织,由于没有反向散射剂量迅速减小;射束在穿透肺部时,由于缺乏散射,肺部剂量会比经过水组织低,在6 cm深度处剂量增大,最大增加2.28%。水-骨-水非均匀组织纵向深度剂量曲线上,在3 cm深度处,由水进入骨组织,剂量减小平稳。20 cm×20 cm射野下横向中心轴水-肺-水和水-骨-水等剂量曲线有明显差异,由水进入肺组织,横向深度剂量降低10.78%,由肺进入水组织,横向深度剂量增大10.61%;在水-骨-水组织中非均匀组织影响较小。结论Eclipse放疗计划系统AXB算法更适合非均匀组织计算,在非均匀组织界面处会形成二次剂量建成效应,因此放疗计划设计者应重视非均匀介质界面上的剂量变化。

Objective To explore the depth-dose characteristics in Eclipse radiotherapy treatment planning system for inhomogeneous tissues.Methods In the Eclipse treatment planning system,a water phantom of 30 cm×30 cm×30 cm and an inhomogeneous medium of lung tissue or bone tissue with a thickness of 3 cm was set up at a depth of 3 cm,and CT value was assigned to the tissue materials.The source skin distance was set to 100 cm while the field size were set as 5 cm×5 cm,10 cm×10 cm,15 cm×15 cm,20 cm×20 cm.The dose size was 100 cGy,and 6 MV X-ray irradiation was used,and the AXB algorithm was selected based on the Monte Carlo results to obtain the horizontal and vertical dose curves on the central axis of the phantom.Results The longitudinal depth dose increased first and then decreased with the increase of depth,and the larger the field area,the greater the relative dose;a second dose build-up was established at the junction of the lung or bone tissue phantom and the water tissue.In the longitudinal depth dose curve of water-lung-water inhomogeneous tissue,at a depth of 3 cm,water entered the lung tissue.Duo to the lack of backscatter,the dose decreased rapidly.When the beam penetrated the lungs,due to lack of scattering,the dose was lower than that through the water tissue,and the dose increased at a depth of 6 cm,with a maximum increase of 2.28%.In the longitudinal depth dose curve of water-bone-water non-uniform tissue,at a depth of 3 cm,water entered the bone tissue,and the dose decreased steadily.There was significant difference in the horizontal central axis water-lung-water and water-bone-water isodose curves under a 20 cm×20 cm field.The transverse depth dose decreased by 10.78%when entering lung tissue from water,and increased by 10.61%when entering water tissue from lung.The inhomogeneous tissue in the water-bone-water tissue had little effect.Conclusion The AXB algorithm of the Eclipse radiotherapy planning system is more suitable for the dose calculations of inhomogeneous tissue.A secondary build-up effect will occur.The radiotherapy plan designer should pay attention to the dose on the inhomogeneous medium interface.