Technical and Dosimetric Study of Four Facio-cervical Fields Conformal Radiotherapy for Nasopharyngeal Carcinoma

Objective: The aim of this study is to establish the methods of four facio-cervical field's conformal radiotherapy(4F-CRT) for nasopharyngeal carcinoma(NPC), and to optimize the methods for clinical practice. Materials and Methods:40 patients with untreated NPC of T1-T4(1997 AJCC Staging System) were rolled into this study.Conventional and four facio-cervical fields conform plans were designed for each patient using Pinnacle 8.0 three-dimension treatment planning system(3D-TPS)as follows: 1. Improved plan, four facio-cervical field's conform plan, anterior, posterior facio-cervical and two lateral opposing facio-cervical fields; 2. Conventional plan, two lateral opposing facio-cervical fields delivered to the target in each plan, only with the same dose dose volume histograms(DVHs) of the targets and normal organs, brain stem,spinal cord, parotid glands, and temporal mandibular joints(TMJs) were compared and the dose distribution were evaluated. Results: 1.The dose distribution of the improved plan could meet the requirements for the target volume. 2. There was not any significant difference in the dose of spinal cord between the two plans.The mean doses of Dmaxfor brain stem in conventional plan were much lower than those in the improved plan,though both were within safety limits. 3. Compared with the conventional plans, the improved plan significantly decreased the hotspot areas in the target volume and had better parotid glands and temporal mandibular joints sparing effect. Conclusion:Compared with the conventional plan, the improved plan provides satisfactory dose coverage to the tumor volume and better sparing of the parotid gland, TMJs and other normal tissues in external beam radiotherapy of NPC.     

鼻咽癌调强放疗靶区剂量学研究及近期疗效观察

目的:分析鼻咽癌调强放疗和常规放疗中靶区和周围组织器官的剂量分布,观察鼻咽癌调强放疗的效果和副作用.方法:对63例初治鼻咽癌采用CT模拟定位,为每例患者制定2套放疗计划,即调强放疗计划和半开准直器常规放疗计划.63例患者非随机分为2组,调强组28例进行调强放射治疗,常规组35例进行常规放射治疗.结果:在IMRT和常规计划中,对肿瘤区(GTV)的靶区覆盖率(V95)分别为99.55%和98.41%,差异无显著性(P>0.05);对于临床靶区(CTV1)的靶区覆盖率(V95)分别为98.51%和87.26%,差异有显著性(P<0.05);颈淋巴结靶区的靶区(CTV2)覆盖率(V95)分别为98.71%和77.63%,差异有显著性(P<0.05),临床靶区(CTV1)和颈淋巴结靶区(CTV2)IMRT的V95优于常规放疗.对串联器官IMRT计划和常规计划均能比较好的保护脊髓、脑干和视交叉,对并联器官IMRT计划中腮腺和下颌骨受照剂量显著低于常规计划.调强组与常规组近期有效率分别为96.4%和97.1%,差异无显著性(P>0.05),放疗6个月后调强组口干症状明显轻于常规组.结论:调强放疗可以使各个靶区得到足够、均匀的剂量分布,周围正常组织得到较好的保护.     

Effect of Perpendicular Shear Force on the Interfacial Morphology of Reactive Polymer Bilayer

We investigated the effect of shear forces perpendicular to the interface on the interfacial morphology of a reactive bilayer. It was observed that the perpendicular shear force greatly enhanced the roughness of the interface compared with parallel shear force. The main role of in situ formed graft copolymers is not to increase greatly the roughness of the interface, but to stabilize the interfacial morphology. We also observed that microemuslsions were observed at both the PMMA and PS layers, which is distinctly different from the situation obtained under parallel shear force (or without shear) that the microemlusions were seen in only the PMMA layer.

     

Dosimetric characteristics of the Elekta Beam Modulator

The dosimetric characteristics of a production pilot multi-leaf collimator (Elekta Beam Modulator, Elekta Oncology Systems, Crawley, UK) having a 4 mm leaf width (at isocentre) have been investigated. Characteristics explored included leaf bank set-up, penumbra width (80-20%) as a function of leaf position, leaf positioning reproducibility, interleaf leakage and leaf transmission. The penumbra values for leaf ends were measured to be between 4.2 and 4.8 mm for various large rectangular fields studied using Kodak X-omat V film at isocentre (1.5 cm deep). Similar films were taken with a standard 1 cm width multi-leaf collimator (MLC) and the penumbra for leaf ends was found to range from 4.3 to 5.2 mm. Other results showed that the rounded leaf tip provided tight control of the penumbra across the leaves' full range of travel. The positioning of the leaves was within a 0.5 mm range when approaching from the same direction. The maximum interleaf leakage was found to be 1.7% and the average leaf transmission less than 1.0%. No major differences were observed in leakage and transmission with changing gantry angle.     

Dosimetric effect of respiration-gated beam on IMRT delivery

Intensity modulated radiation therapy (IMRT) with a dynamic multileaf collimator (DMLC) requires synchronization of DMLC leaf motion with dose delivery. A delay in DMLC communication is known to cause leaf lag and lead to dosimetric errors. The errors may be exacerbated by gated operation. The purpose of this study was to investigate the effect of leaf lag on the accuracy of doses delivered in gated IMRT. We first determined the effective leaf delay time by measuring the dose in a stationary phantom delivered by wedge-shaped fields. The wedge fields were generated by a DMLC at various dose rates. The so determined delay varied from 88.3 to 90.5 ms. The dosimetric effect of this delay on gated IMRT was studied by delivering wedge-shaped and clinical IMRT fields to moving and stationary phantoms at dose rates ranging from 100 to 600 MU/min, with and without gating. Respiratory motion was simulated by a linear sinusoidal motion of the phantom. An ionization chamber and films were employed for absolute dose and 2-D dose distribution measurements. Discrepancies between gated and nongated delivery to the stationary phantom were observed in both absolute dose and 2-D dose distribution measurements. These discrepancies increased monotonically with dose rate and frequency of beam interruptions, and could reach 3.7% of the total dose delivered to a 0.6 cm3 ion chamber. Isodose lines could be shifted by as much as 3 mm. The results are consistent with the explanation that beam hold-offs in gated delivery allowed the lagging leaves to catch up with the delivered monitor units each time that the beam was interrupted. Low dose rates, slow leaf speeds and low frequencies of beam interruptions reduce the effect of this delay-and-catch-up cycle. For gated IMRT it is therefore important to find a good balance between the conflicting requirements of rapid dose delivery and delivery accuracy.     

Dosimetric effects on the penumbra region of irregular multi-leaf collimated fields

The dosimetric effect in the penumbra region for multi-leaf collimator (MLC) fields was studied using a Varian 21 EX linear accelerator. The beam profiles in the cross-line and in-line directions for MLC field configurations of varying lengths of protruded leaves, which are adjacent (on one or both sides) to the beam profile axes, were measured using a 6 MV photon beam. It was found that there is a decrease of dose in the 'edge' region of the protruded leaves' side in the cross-line profile, when the protruded leaves (upper and/or lower side) were moved out from 0.5 cm to 3 cm towards the central beam axis. When both the upper and lower portions of leaves were moved out forming a gap for the profile, the dose at the 'edge' region in the cross-line direction was decreased by about 20% and 6%, with the protruded length of leaves being 0.5 cm and 1 cm, respectively. The penumbra width of the cross-line profile increased with the protruded length of leaves when the gap width was 0.5 cm, and it was independent of the length when the width was increased larger than 1 cm. The Pinnacle treatment planning system could calculate the decrease of dose observed experimentally in the cross-line profile, but an underestimation of about 30% was found when using version 6.2b, which did not consider the leaf rounded end and tongue-and-groove effect. While the newly commissioned 7.4f, which considered the two aforementioned effects, made an improvement, it still underestimated the dose by 25% compared to the measurement. For the in-line profiles, both versions estimated the penumbra width well.     

极低频磁场对胞内钙振荡影响的机理分析

基于双钙库模型,本文以离子跨过细胞膜、细胞器膜迁移的几率作为细胞对电磁场的响应因子,来调制流过膜通道的离子的速率,进而影响细胞内钙离子的浓度。数值分析表明:在极低频磁场的作用下,一定能量因子下的频率条件或是一定频率因子下的能量条件可引起钙振荡形式的变化;窗效应是频率因子和能量因子共同作用的结果。     

磁疗用圆片永磁磁源空间磁场有限元分析

目的：研究圆片磁源空间磁场不同参数的量值和分布,为定量使用圆片磁源提供多参数计算依据。方法：采用有限元数值法计算得出的圆片磁源空间磁场的矢量磁位、磁感强度、磁场能量密度量值和空间分布图,并计算绘出磁感强度等值线和磁力线。结果：圆片磁源空间磁场的矢量磁位、磁感强度和磁场能量密度在磁源轴向（X轴）单调下降,在磁源极面径向（Y轴）由中心到半径处单调增加、过半径后单调下降,总体趋势随距磁源距离的增加而下降。磁感强度等值线和磁力线更直观地描述了磁场的变化。结论：多参数磁源空间磁场的计算,对于更准确地进行磁疗定量研究是非常必要的。     

Dosimetric accuracy of the ITP inverse treatment planning system

The dosimetric accuracy of the ITP system for intensity modulated radiation therapy was determined for 19 patient plans. Treatments were given with a Varian 2100C and a 120-leaf multileaf collimator using step and shoot delivery. Both absolute dose, determined by an ionization chamber, and relative dose, determined by film, were assessed. It was found that absolute dose agreement was within 0.1% +/- 1.5%, isodoses in the high dose-low gradient region were within 1.7% +/- 2%, and the distance to agreement for isodoses between 20% and 90% was 1.4 mm +/- 1 mm. This agreement is at least as good as that found for standard wedged fields in most treatment planning systems.