Abstract：
Purpose.The aim of this study is to determine the planar dose distribution of irregularly-shaped electron beams at their maximum dose depth (zmax) using the modied lateral build-up ratio (LBR) and curve-fitting methods.Methods.Circular and irregular cutouts were created using Cerrobend alloy for a 14 × 14 cm2applicator. Percentage depth dose (PDD) at the standard source-surface-distance (SSD = 100 cm) and point dose at different SSD were measured for each cutout. Orthogonal profiles of the cutouts were measured atzmax. Data were collected for 6, 9, 12, and 15 MeV electron beam energies on a VERSA HDTMLINAC using the IBA Blue Phantom23D water phantom system. The planar dose distributions of the cutouts were also measured atzmaxin solid water using EDR2 films.Results.The measured PDD curves were normalized to a normalization depth (d0) of 1 mm. The lateral-buildup-ratio (LBR), lateral spread parameter (σR(z)), and effective SSD (SSDeff) for each cutout were calculated using the PDD of the open applicator as the reference field. The modified LBR method was then employed to calculate the planar dose distribution of the irregular cutouts within the field at least 5 mm from the edge. A simple curve-fitting model was developed based on the profile shapes of the circular cutouts around the field edge. This model was used to calculate the planar dose distribution of the irregular cutouts in the region from 3 mm outside to 5 mm inside the field edge. Finally, the calculated planar dose distribution was compared with the film measurement.Conclusions.The planar dose distribution of electron therapy for irregular cutouts atzmaxwas calculated using the improved LBR method and a simple curve-fitting model. The calculated profiles were within 3% of the measured values. The gamma passing rate with a 3%/3 mm and 10% dose threshold was more than 96%.
摘要：
目的：
本研究的目的是使用修正横向累积比（LBR）和曲线拟合方法计算不规则形状电子束在其最大剂量深度（zmax）的平面剂量分布。
方法:
圆形和不规则的切口使用Cerrobend合金用于14×14cm2的施加器。对于每个切口，测量标准源-表面距离（SSD=100cm）处的深度百分比剂量（PDD）和不同SSD处的点剂量。在zmax处测量切口的正交曲线。使用ibaBluePhantom23D水模系统在VERSAHDTMLINAC上收集了6、9、12和15MeV电子束能量的数据。使用EDR2films，在固体水中zmax处也测量了切口的平面剂量分布。
结果:
将测量的PDD曲线归一化至Imm的归一化深度(d0)。每个切口的横向堆积比(LBR)，横向扩展参数(σR(z))，和有效SSD（SSDeff）是使用开放式涂抹器的PDD作为参考字段来计算的。然后使用改进的LBR方法来计算距边缘至少5mm的场内部的不规则切口的平面剂量分布。基于场边缘周围圆形切口的轮廓形状，开发了一个简单的曲线拟合模型。该模型用于计算从外部3mm到区域边缘内部5mm的不规则切口的平面剂量分布。最后,将计算的剂量分布与胶片测量值进行比较。＆＃xD;结论：＆＃xD;使用改进的LBR方法和简单的曲线拟合模型计算了zmax下不规则切口的电子治疗的平面剂量分布。计算的曲线在测量值的3%以内。3%/3mm的γ通过率为96%以上。
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