Measurement verification of dose distributions in pulsed-dose rate brachytherapy in breast cancer

Aim

The aim of the study was to verify the dose distribution optimisation method in pulsed brachytherapy.

Background

The pulsed-dose rate brachytherapy is a very important method of breast tumour treatment using a standard brachytheraphy equipment. The appropriate dose distribution round an implant is an important issue in treatment planning. Advanced computer systems of treatment planning are equipped with algorithms optimising dose distribution.

Materials and methods

The wax-paraffin phantom was constructed and seven applicators were placed within it. Two treatment plans (non-optimised, optimised) were prepared. The reference points were located at a distance of 5 mm from the applicators’ axis. Thermoluminescent detectors were placed in the phantom at suitable 35 chosen reference points.

Results

The dosimetry verification was carried out in 35 reference points for the plans before and after optimisation. Percentage difference for the plan without optimisation ranged from −8.5% to 1.4% and after optimisation from −8.3% to 0.01%. In 16 reference points, the calculated percentage difference was negative (from −8.5% to 1.3% for the plan without optimisation and from −8.3% to 0.8% for the optimised plan). In the remaining 19 points percentage difference was from 9.1% to 1.4% for the plan without optimisation and from 7.5% to 0.01% for the optimised plan.No statistically significant differences were found between calculated doses and doses measured at reference points in both dose distribution non-optimised treatment plans and optimised treatment plans.

Conclusions

No statistically significant differences were found in dose values at reference points between doses calculated by the treatment planning system and those measured by TLDs. This proves the consistency between the measurements and the calculations.     

Techniques for Processing Eyes Implanted With a Retinal Prosthesis for Localized Histopathological Analysis

With the recent development of retinal prostheses, it is important to develop reliable techniques for assessing the safety of these devices in preclinical studies. However, the standard fixation, preparation, and automated histology procedures are not ideal. Here we describe new procedures for evaluating the health of the retina directly adjacent to an implant. Retinal prostheses feature electrode arrays in contact with eye tissue. Previous methods have not been able to spatially localize the ocular tissue adjacent to individual electrodes within the array. In addition, standard histological processing often results in gross artifactual detachment of the retinal layers when assessing implanted eyes. Consequently, it has been difficult to assess localized damage, if present, caused by implantation and stimulation of an implanted electrode array. Therefore, we developed a method for identifying and localizing the ocular tissue adjacent to implanted electrodes using a (color-coded) dye marking scheme, and we modified an eye fixation technique to minimize artifactual retinal detachment. This method also rendered the sclera translucent, enabling localization of individual electrodes and specific parts of an implant. Finally, we used a matched control to increase the power of the histopathological assessments. In summary, this method enables reliable and efficient discrimination and assessment of the retinal cytoarchitecture in an implanted eye.     

Modelling external bone adaptation using evolutionary structural optimisation

External remodelling is significant in the bone healing process, and it is essential to predict the bone external shape in the design of artificial bone grafts. This paper demonstrates the effectiveness of the evolutionary structural optimisation (ESO) method for the simulation of bone morphology. A two-dimensional ESO strategy is developed which is capable of finding the modified bone topology beginning with any geometry under any loading conditions. The morphology of bone structure is described by the quantitative bone adaptation theory, which is integrated with the finite element method. The evolutionary topology optimisation process is introduced to find the bone shape. A rectangle, which occupies a larger space than the external shape of the bone structure, is specified as a design domain; the evolutionary process iteratively eliminates and redistributes material throughout the domain to obtain an optimum arrangement of bone materials. The technique has been tested on a wide range of examples. In this paper, the formation of trabecular bone architecture around an implant is studied; as another example, the growth of the coronal section of a vertebral body is predicted. The examples support the assertion that the external shape of bone structure can be successfully predicted by the proposed ESO procedure.     

氧化钛纳米管对即刻种植骨结合影响的实验研究

目的:评价氧化钛纳米管对犬即刻种植骨结合效果的影响。方法:犬拔牙后即刻将光滑表面(对照组)和氧化钛纳米管表面(实验组)种植体植入拔牙窝内,于12周后处死取材,进行显微CT扫描、组织学染色分析以及生物力学检测。结果:扫描电镜显示经过阳极氧化后,钛表面形成了直径为30-80纳米的纳米管状结构;12周后,显微CT扫描结果提示实验组骨体积分数(BV/TV)、骨小梁数目(Tb.N)、骨小梁厚度(Tb.Th)均显著高于对照组,骨小梁间隙(Tb.Sp)显著低于对照组,差异具有统计学意义(P0.05)。术后12周,实验组与对照组骨结合率分别为49.35±11.76%、31.79±13.07%,最大拔出力分别为105.28±27.87N、79.23±20.46N,实验组均显著高于对照组,差异均具有统计学意义(P0.05)。结论:氧化钛纳米管表面有利于促进即刻种植后骨结合的效果。     

Micromechanical evaluation of mineralized multilayers

The biomechanical stability of osseointegrated implants is of particular importance, especially the stability which is achieved from structural manipulation at the interface between the implant surface and the bone tissues. Nanoscale β-tricalcium phosphate-immobilized titanium was prepared by discharge into a physiological buffered saline solution. Compared with hydroxyapatite, it has been shown to be effective in generating a bone-like chemical structure on the surface by cooperative interaction between osteoblastic cells and the β-tricalcium phosphate. The present study, after cell cultivation, investigates the nanostructures and biomechanical property differences of a mineralized layer formed on two samples of nano-calcium phosphate-immobilized titanium. A scanning probe microscope study revealed that the mineralized tissue formed on the β-tricalcium phosphate samples after 1 week of cell culture showed significantly higher roughness, compared with hydroxyapatite samples. Nanoindentation micromechanical evaluation of the in vitro generated multilayered structures exhibited thicker bone-like mineralized layers on the β-tricalcium phosphate samples. A successful modification of titanium implants through the cooperative interaction between osteoblastic cells and nano β-tricalcium phosphate is anticipated.     

Numerical investigation of bone remodelling around immediately loaded dental implants using sika deer (Cervus nippon) antlers as implant bed

This study combines finite element method and animal studies, aiming to investigate tissue remodelling processes around dental implants inserted into sika deer antler and to develop an alternative animal consuming model for studying bone remodelling around implants. Implants were inserted in the antlers and loaded immediately via a self-developed loading device. After 3, 4, 5 and 6 weeks, implants and surrounding tissue were taken out. Specimens were scanned by μCT scanner and finite element models were generated. Immediate loading and osseointegration conditions were simulated at the implant-tissue interface. A vertical force of 10 N was applied on the implant. During the healing time, density and Young’s modulus of antler tissue around the implant increased significantly. For each time point, the values of displacement, stresses and strains in the osseointegration model were lower than those of the immediate loading model. As the healing time increased, the displacement of implants was reduced. The 3-week immediate loading model (9878 ± 1965 μstrain) illustrated the highest strains in the antler tissue. Antler tissue showed similar biomechanical properties as human bone in investigating the bone remodelling around implants, therefore the use of sika deer antler model is a promising alternative in implant biomechanical studies.     

医用硅橡胶长期肌肉内植入的方法学探讨

选用三种医用硅橡胶材料进行长期肉内植入试验。从方法学角对植入体形状,植入途径,包埋与切片方向,实验观察期,纤维包膜成分,评价指标等方面作了实验性探讨。     

慢性牙周炎对牙种植修复的疗效影响

目的:分析慢性牙周对种植义齿修复疗效的影响。方法:选择2013年7月至2015年6月在宝鸡市中医医院接受牙种植修复治疗的慢性牙周炎患者52例(70枚)作为观察组及同期接受牙种植的牙周健康患者49例(69枚),作为对照组。观察分析两组患者种植修复1、3、6、12个月的边缘骨吸收量(MBL)、改良菌斑指数(m PLI)、改良龈沟出血指数(m SBI)、探测深度(PD)以及种植体龈沟液IL-1、IL-6水平的变化情况。结果:种植1年后,对照组的种植成功率为97.10%(67/69),观察组的种植成功率为91.42%(64/70),两组比较差异无统计学意义(P0.05)。种植1个月及3个月后,两组的m PLI、m SBI、PD以及MBL比较无明显差异(P0.05);种植6个月后,观察组的m SBI、PD以及MBL显著高于对照组(P0.05),m PLI仍无明显变化。此外,种植1个月、3个月时,对照组的IL-1β未检出;6个月后,观察组的IL-1β显著高于对照组(P0.05);种植3个月后,观察组的IL-6显著高于对照组(P0.05)。结论:慢性牙周炎可降低牙种植修复治疗的疗效,可能与种植体周围炎的发生有关。     

Bone ingrowth on the surface of endosseous implants. Part 1: Mathematical model

Osseointegration, understood as an intimate apposition and interdigitation of bone to a biomaterial, is usually regarded as a major condition for the long-term clinical success of bone implants. Clearly, the anchorage of an implant to bone tissue critically relies on the formation of new bone between the implant and the surface of the old peri-implant bone and depends on factors such as the surface microtopography, chemical composition and geometry of the implant, the properties of the surrounding bone and the mechanical loading process. The main contribution of this work is the proposal of a new mathematical framework based on a set of reaction-diffusion equations that try to model the main biological interactions occurring at the surface of implants and is able to reproduce most of the above mentioned biological features of the osseointegration phenomenon. This is a two-part paper. In this first part, a brief biological overview is initially given, followed by the presentation and discussion of the model. In addition, two-dimensional finite element simulations of the bone-ingrowth process around a dental implant with two different surface properties are included to assess the validity of the model. Numerical solutions show the ability of the model to reproduce features such as contact/distance osteogenesis depending upon the specific surface microtopography. In Part 2 [Moreo, P., García-Aznar, J.M., Doblaré, M., 2008. Bone ingrowth on the surface of endosseous implants. Part 2: influence of mechanical stimulation, type of bone and geometry. J. Theor. Biol., submitted for publication], two simplified versions of the whole model are proposed. An analytical study of the stability of fixed points as well as the existence of travelling wave-type solutions has been done with both simplified models, providing a significant insight into the behaviour of the model and giving clues to interpret the effectiveness of recently proposed clinical therapies. Furthermore, we also show that, although the mechanical state of the tissue is not directly taken into account in the model equations, it is possible to analyse in detail the effect that mechanical stimulation would have on the predictions of the model. Finally, numerical simulations are also included in the second part of the paper, with the aim of looking into the influence of implant geometry on the osseointegration process.     

口腔种植体周围细菌感染病原菌分布特点及细菌感染的危险因素分析

摘要 目的：观察口腔种植体周围细菌感染病原菌分布特点,分析细菌感染的危险因素。方法：选择360例于2018年7月~2021年5月在我院行口腔种植术的患者。根据是否发生口腔种植体周围细菌感染将患者分为感染组和未感染组。分离鉴定感染组病原菌种类。收集患者的临床资料,引起口腔种植体周围细菌感染的影响因素采用单因素及多因素Logistic回归分析。结果：360例患者中共有35例发生口腔种植体周围细菌感染,发生率为9.72%。共分离出49株病原菌,其中需氧菌14株（28.57%）、厌氧菌32株（65.31%）、有益菌3株（6.12%）;厌氧菌中又以口腔链球菌11株（22.45%）、牙龈卟啉单胞菌9株（18.37%）、产黑色素普雷沃菌7株（14.29%）为主。单因素分析结果显示：口腔种植体周围细菌感染的发生与吸烟史、慢性牙周炎病史、饮酒史、是否合并糖尿病、种植体周围牙槽骨情况以及口腔健康习惯有关（P＜0.05）;多因素Logistic回归分析显示口腔种植体周围细菌感染的危险因素是口腔健康习惯不良、种植体周围牙槽骨不良、合并糖尿病、有饮酒史、有慢性牙周炎病史、有吸烟史（P＜0.05）。结论：口腔种植体周围细菌感染的病原菌以厌氧菌为主,种植体周围牙槽骨不良、有慢性牙周炎病史、有吸烟史、合并糖尿病、饮酒史、口腔健康习惯不良是感染发生的危险因素,应针对上述因素进行适当干预。