MICROSTRIP APPLICATOR FOR TREATMENT OF CERVICAL EROSION AND CERVICAL CONDYLOMA ACUMINATUM

1NTRODUCTIONChroniccervicalerosionisacommongynecologicaldisease'Thisdiseaseisobstinateanddifficulttobecuredandcandeteriorateintocancerofcervix'Atfirst,thefreezingtreatmentwasused,andtheeffectswerenotbad'Forthiskindoftreatment,liquidnitrogenwasrequired,andthetreattimewasabout20--30'minuteslong'Becauseofthegasificationofliquidnitrogen,itwasnoteasytoseeandcontrolthetreat-surface.Ifweusedmicrowavetreatment,alltheshortcomingsaboveareconquered'In1992,usingaspiralsegmentmicrostripapplicatorwith…     

Reconstruction of a ring applicator using CT imaging: impact of the reconstruction method and applicator orientation

The purpose of this study is to investigate whether the method of applicator reconstruction and/or the applicator orientation influence the dose calculation to points around the applicator for brachytherapy of cervical cancer with CT-based treatment planning. A phantom, containing a fixed ring applicator set and six lead pellets representing dose points, was used. The phantom was CT scanned with the ring applicator at four different angles related to the image plane. In each scan the applicator was reconstructed by three methods: (1) direct reconstruction in each image (DR), (2) reconstruction in multiplanar reconstructed images (MPR) and (3) library plans, using pre-defined applicator geometry (LIB). The doses to the lead pellets were calculated. The relative standard deviation (SD) for all reconstruction methods was less than 3.7% in the dose points. The relative SD for the LIB method was significantly lower (p < 0.05) than for the DR and MPR methods for all but two points. All applicator orientations had similar dose calculation reproducibility. Using library plans for applicator reconstruction gives the most reproducible dose calculation. However, with restrictive guidelines for applicator reconstruction the uncertainties for all methods are low compared to other factors influencing the accuracy of brachytherapy.     

固定型腔内后装施源器治疗宫颈癌的剂量分布特点

目的:研究固定型腔内后装施源器及标准腔内后装施源器的剂量分布特点,评价固定型腔内施源器是否符合临床剂量学要求。方法:比较固定型腔内后装施源器和标准型腔内施源器的等剂量曲线分布图,并根据腔内近距离放疗中剂量分布与距离平方成反比的剂量学特点,按照施源器材料中的指数衰减及吸收系数,计算出两种施源器x和y轴两个方向上的剂量比。结果:标准Ⅲ通腔内施源器和固定Ⅲ通腔内施源器等剂量曲线分布图通过TPS优化,图形基本一致:在冠状面上等剂量曲线呈扁梨行,宫颈、阴道剂量大于宫体剂量,在横断面上等剂量曲线呈扁椭圆形;且固定型扁平腔内施源器源中心到模表面距离为0.5 cm,而标准Ⅲ通腔内施源器从源中心到模表面距离为1 cm,通过计算可知当r=0.5 cm,l=1.0 cm时其剂量比大于l=1.5 cm时的剂量比,因此给予A点相同剂量所需要的时间较标准腔内后装施源器要短,由于治疗时间短,膀胱直肠所受剂量就小,通过优化,直肠剂量只有A点剂量的70%,而宫颈粘膜表面剂量比经典施源器剂量要高出45%。结论:固定型腔内后装施源器剂量分布符合临床剂量学要求,且优于标准施源器,同时由于使用简单方便,不用模拟机拍片,剂量计算模式也固定,更适合宫颈癌患者多的治疗中心使用。     

Leakage radiation from electron applicators on a medical accelerator

The leakage characteristics of electron applicators on our Clinac 2500 linear accelerator have been measured. The leakage radiation in the patient plane and at the surface of the electron applicators has been measured for applicator sizes from 6 cm X 6 cm to 25 cm X 25 cm and beam energies from 6 to 22 MeV. For certain applicator/energy combinations the leakage radiation was significant. The leakage radiation, relative to the central axis dose, was found to be up to 7% in the patient plane and up to 39% at the applicator surface. Reducing the collimator setting or adding lead at select locations on the applicator surface was effective in reducing the magnitude of the radiation leakage.     

Theoretical and experimental comparison of three types of electromagnetic hyperthermia applicator

There is evidence that heating of malignant tissue in the treatment of cancer may be beneficial and so the performance of different applicator designs needs to be established. A theoretical model of the dielectric loaded waveguide applicator is compared with models of two other applicators which depend on energy radiated from conductors carrying high frequency current. The latter are exemplified by the compact resonant patch applicator and the lightweight inductive current sheet applicator. It is shown that heating profiles and field penetration of each applicator are similar for equal radiating areas, and these results have been substantiated experimentally. Impedance match as a function of frequency and load is also compared for the three types of applicator.     

The importance of applicator design for intraluminal brachytherapy of rectal cancer

An important aspect of designing an applicator for radiation treatment of rectal cancer is the ability to minimize dose to the mucosa and noninvolved parts of the rectum wall. For this reason we investigated a construction of a flexible multichannel applicator with several channels placed along the periphery of a cylinder and a construction of a rigid cylinder with a central channel and interchangeable shields. Calculations of the dose gradient, dose homogeneity in the tumor, and shielding ability were performed for the two applicators in question. Furthermore, the influence on dose distribution around a flexible multichannel applicator from an unintended off-axis positioning of the source inside a bent channel was investigated by film measurements on a single bent catheter. Calculations showed that a single-channel applicator with interchangeable shields yields a higher degree of shielding and has a better dose homogeneity in the tumor volume than that of a multi-channel applicator. A single-channel applicator with interchangeable shields was manufactured, and the influence of different size of shield angle on dose rate in front of and behind the shields was measured. While dose rate in front of the shield and shielding ability are closely independent of the size of the shield angle when measured 1 cm from the applicator surface, dose rate in more distant volumes will to some extent be influenced by shield angle due to volume scatter conditions.     

Wedge-shaped applicator for additional light delivery and dosimetry in the diaphragmal sinus during photodynamic therapy for malignant pleural mesothelioma

In situ light dosimetry during photodynamic therapy (PDT) of malignant pleural mesothelioma (MPM) after tumour resection facilitates the delivery of a controlled light distribution to the inner thoracic surface. Illumination of the diaphragm-induced sinus, however, remains difficult. Our aim was to develop a wedge-shaped light applicator with incorporated light dosimetry to deliver an additional fluence limited to the sinus. The wedge-shaped applicator contains a cylindrical diffuser for light delivery and two isotropic detectors for simultaneous light dosimetry. These detectors were placed at strategic positions where the fluence rate is maximal or minimal (middle and edge). Prior to its clinical use, the performance of the sinus light applicator was tested in several optical tissue phantoms with different optical properties. The fluence rate distribution over the surface of the applicator showed little change when the wedge was submerged in four different optical phantoms. During clinical PDT of MPM the applicator had to be re-located manually four times in order to give an additional fluence of approximately 2 J cm(-2) to the entire sinus. The light applicator enables dosimetry-controlled light delivery for additional illumination of the sinus region that is often under-illuminated during thoracic integral illumination of MPM.     

A flattening filter for brachytherapy skin irradiation

Radioactive sources in close contact offer an alternative to superficial radiation in the treatment of skin lesions. A flattening filter was designed for a lead surface applicator to improve the skin dose distribution of a high dose rate (HDR) brachytherapy unit (Nucletron). At three heights from the opening (10, 15 and 25 mm) of the cylindrical applicator, the 192Ir source can be driven into the centre of the applicator. Thin sheets of lead foil (0.2 mm) were cut into circular shapes and placed in the opening to build a cylindrical cone that acts as a flattening filter. The shape of the cone was optimized in an iterative process using a spreadsheet and the resulting dose distribution under the applicator was determined using radiosensitive film. The use of the filter improved the dose distribution in a plane perpendicular to the beam axis to be within +/- 5% of the central axis dose. The present applicator and flattening filter together with an HDR brachytherapy unit offer an alternative for skin irradiation where a superficial unit is not available or will be replaced with a more flexible device. As the depth dose characteristics can be modified using different source-to-surface distances, the dose throughout the patient's skin can be shaped as desired by the radiation oncologist using a compensator design type approach.     

Attenuation of intracavitary applicators in 192Ir-HDR brachytherapy

Unlike the penetrating monoenergetic 662 keV gamma rays emitted by 137Cs LDR sources, the spectrum of 192Ir used in HDR brachytherapy contains low-energy components. Since these are selectively absorbed by the high-atomic number materials of which intracavitary applicators are made, the traditional neglect of applicator attenuation can lead to appreciable dose errors. We investigated the attenuation effects of a uterine applicator, and of a set of commonly used vaginal cylinders. The uterine applicator consists of a stainless steel source guide tube with a wall thickness of 0.5 mm and a density of 8.02 g/cm3, whereas the vaginal cylinders consist of the same stainless steel tube plus concentric polysulfone cylinders with a radius of 1 or 2 cm and a density of 1.40 g/cm3. Monte Carlo simulations were performed to compute dose distributions for a bare 192Ir-HDR source, and for the same source located within the applicators. Relative measurements of applicator attenuation using ion-chambers (0.125 cm3) confirmed the Monte Carlo results within 0.5%. We found that the neglect of the applicator attenuation overestimates the dose along the transverse plane by up to 3.5%. At oblique angles, the longer photon path within applicators worsens the error. We defined attenuation-corrected radial dose and anisotropy functions, and applied them to a treatment having multiple dwell positions inside a vaginal cylinder.     

微电脑微波手术仪的开发及临床应用

本文在介绍微电脑微波手术仪结构原理的基础上，重点讨论了微波功率自动检测控制方法，手术器温度场分布，腔内器官组织吸收功率分布，微波穿透深度计算等问题，最后对手术仪临床应用进行了分析总结。     

新型热疗宫颈癌微波辐射器的研制

介绍了用于宫颈癌腔内热疗的微波辐射器的设计方法和测试结果。这种辐射器与常规微波辐射器不同的是，其前部的内导体被一个带有反射罩的锥形螺旋天线所替代。在模拟肌肉组织中，我们证实这种辐射的热场分布向前端偏移，从而提高了该辐射器的临床应用价值。     

Scattered radiation from applicators in clinical electron beams

In radiotherapy with high-energy (4-25 MeV) electron beams, scattered radiation from the electron applicator influences the dose distribution in the patient. In most currently available treatment planning systems for radiotherapy this component is not explicitly included and handled only by a slight change of the intensity of the primary beam. The scattered radiation from an applicator changes with the field size and distance from the applicator. The amount of scattered radiation is dependent on the applicator design and on the formation of the electron beam in the treatment head. Electron applicators currently applied in most treatment machines are essentially a set of diaphragms, but still do produce scattered radiation. This paper investigates the present level of scattered dose from electron applicators, and as such provides an extensive set of measured data. The data provided could for instance serve as example input data or benchmark data for advanced treatment planning algorithms which employ a parametrized initial phase space to characterize the clinical electron beam. Central axis depth dose curves of the electron beams have been measured with and without applicators in place, for various applicator sizes and energies, for a Siemens Primus, a Varian 2300 C/D and an Elekta SLi accelerator. Scattered radiation generated by the applicator has been found by subtraction of the central axis depth dose curves, obtained with and without applicator. Scattered radiation from Siemens, Varian and Elekta electron applicators is still significant and cannot be neglected in advanced treatment planning. Scattered radiation at the surface of a water phantom can be as high as 12%. Scattered radiation decreases almost linearly with depth. Scattered radiation from Varian applicators shows clear dependence on beam energy. The Elekta applicators produce less scattered radiation than those of Varian and Siemens, but feature a higher effective angular variance. The scattered radiation decreases somewhat with increasing field size and is spread uniformly over the aperture. Experimental results comply with the results of simulations of the treatment head and electron applicator, using the BEAM Monte Carlo code, and Siemens, but feature a higher effective angular variance. The scattered radiation decreases somewhat with increasing field size and is spread uniformly over the aperture. Experimental results comply with the results of simulations of the treatment head and electron applicator, using the BEAM Monte Carlo code.     

Calibration of a scintillation dosemeter for beta rays using an extrapolation ionization chamber

A scintillation dosemeter is calibrated for 90Sr/90Y beta rays from an ophthalmic applicator, using an extrapolation ionization chamber as a reference instrument. The calibration factor for the scintillation dosemeter agrees with that given by the manufacturer of the dosemeter within ca. 2%. The estimated overall uncertainty of the present calibration is ca. 6% (2 sd). A calibrated beta-ray ophthalmic applicator can be used as a reference source for further calibrations performed in the laboratory or in the hospital.     

64-element intraluminal ultrasound cylindrical phased array for transesophageal thermal ablation under fast MR temperature mapping: an ex vivo study

This work was undertaken to investigate the feasibility of using a cylindrical phased array for transoesophaeal thermal ablation under magnetic resonance (MR) imaging guidance. Sixty-four transducers (0.45 mm wide by 15 mm tall), operating at 4.6 MHz, were spread around the periphery of a 10.6-mm-diam cylinder. The head of the applicator was covered with a 65-microm thick latex balloon attached using watertight seals. This envelope was inflated with degassed water to provide acoustic coupling between the transducer and the tissues. The underlying operating principle of this applicator is to rotate a plane ultrasound beam electronically. For this purpose, eight adjacent transducers were excited with appropriate delay times so as to generate a plane wave. The exposure direction was changed by exciting a different set of eight elements. Ex vivo experiments conducted on 47 samples of pig liver under MR temperature monitoring demonstrated the ability of this applicator to generate cylindrical or sector-based coagulation necroses at depths up to 19 mm with excellent angular precision by applying 20 W/cm2. MR thermometry was performed in "real-time" with segmented echo-planar imaging gradient echo sequences. The temporal resolution was approximately 3 s/ image. The average value for the temperature baseline in liver tissue close to the applicator was 0.3 degrees C (+/- 0.6 degrees C). The thermal dose delivered in tissues was computed on-line during temperature imaging. Excellent MR compatibility was demonstrated, all MR acquisitions were performed without susceptibility artifacts or radio-frequency interferences with the ultrasound device. Thermal lesions identified on post-treatment follow up showed good correlation with online MR thermometry data. The individual differences between measurements performed visually and using MRI thermal dose maps were about 11% of volume. This study demonstrated the feasibility of thermal ablation using a phased array intraluminal ultrasound applicator and on-line MR monitoring.     

The histological features of microwave coagulation therapy: an assessment of a new applicator design

Microwave ablation of tumours within the liver may become an adjunct or alternative to resection in patients with primary or secondary cancers. This technique combines the benefits of a large, localized coagulative effect with a single insertion of the applicator, in a significantly shorter time than comparable treatments. A new range of microwave applicators were developed and tested in animal models and both ex-vivo and in-vivo specimens of human liver at resection. At laparotomy, the applicator tip was inserted into normal liver parenchyma and tumours, with each specimen subjected to irradiation for 180 s or more and at varying power outputs. On sectioning an area of spherical blanching was observed around the applicator cavity. Microscopically a zone of coagulative necrosis was seen adjacent to the site of probe insertion. Damage to blood vessels and bile ducts occurred distal to the probe cavity suggesting the passage of heated fluid, a finding that was diminished by temporary occlusion of the hepatic vasculature (a Pringle manoeuvre). Ultra-structural damage was confirmed within the burn zone and selected liver enzymes were shown to be functioning beyond this region. We suggest this indicates the surrounding liver parenchyma is functioning normally and therefore the volume of microwave-induced damage is controllable. We are confident that the new applicator design will allow the effective treatment of larger tumours in a safe and controlled manner with a single application of energy.     

Feasibility of using interstitial ultrasound for intradiscal thermal therapy: a study in human cadaver lumbar discs

Application of heat in the spine using resistive wire heating devices is currently being used clinically for minimally invasive treatment of discogenic low back pain. In this study, interstitial ultrasound was evaluated for the potential to heat intradiscal tissue more precisely by directing energy towards the posterior annular wall while avoiding vertebral bodies. Two single-element directional applicator design configurations were tested: a 1.5 mm OD direct-coupled (DC) applicator which can be implanted directly within the disc, and a catheter-cooled (CC) applicator which is inserted in a 2.4 mm OD catheter with integrated water cooling and implanted within the disc. The transducers were sectored to produce 90 degrees spatial heating patterns for directional control. Both applicator configurations were evaluated in four human cadaver lumbar disc motion segments. Two heating protocols were employed in this study in which the temperature measured 5 mm away from the applicator was controlled to either T=52 degrees C, or T>70 degrees C for the treatment period. These temperatures (thermal doses) are representative of those required for thermal necrosis of in-growing nociceptor nerve fibres and disc cellularity alone, or with coagulation and restructuring of annular collagen in the high-temperature case. Steady-state temperature maps, and thermal doses (t43) were used to assess the thermal treatments. Results from these studies demonstrated the capability of controlling temperature distributions within selected regions of the disc and annular wall using interstitial ultrasound, with minimal vertebral end-plate heating. While directional heating was demonstrated with both applicator designs, the CC configuration had greater directional heating capabilities and offered better temperature control than the DC configuration, particularly during the high-temperature protocol. Further, ultrasound energy was capable of penetrating within the highly attenuating disc tissue to produce more extensive radial thermal penetration, lower maximum intradiscal temperature, and shorter treatment times than can be achieved with current clinical intradiscal heating technology. Thus, interstitial ultrasound offers potential as a more precise and faster heating modality for the clinical management of low back pain.     

The dosimetric properties of an intraoperative radiation therapy applicator system for a Mevatron-80

An applicator system for intraoperative radiation therapy has been fabricated which does not require physical docking with the accelerator. A dosimetric study has been completed which documents the properties of this system for a variety of electron beam energies, applicator sizes, collimator settings, both primary and secondary, and source-surface distance (SSD) settings. Sensitivity of the system to common misalignment errors was also determined. Results indicate (a) applicator leakage of less than 5%, (b) beam flatness to within plus or minus 5% at the dMAX with a single primary collimator setting, (c) smooth changes in output with cone size, beam energy and SSD, and (d) negligible changes in dose distributions within alignment errors permitted by the system.     

In vivo fluence rate measurements during Foscan-mediated photodynamic therapy of persistent and recurrent nasopharyngeal carcinomas using a dedicated light applicator

The objective of this study was to evaluate the performance of a dedicated light applicator for light delivery and fluence rate monitoring during Foscan-mediated photodynamic therapy of nasopharyngeal carcinoma in a clinical phase I/II study. We have developed a flexible silicone applicator that can be inserted through the mouth and fixed in the nasopharyngeal cavity. Three isotropic fibers, for measuring of the fluence (rate) during therapy, were located within the nasopharyngeal tumor target area and one was manually positioned to monitor structures at risk in the shielded area. A flexible black silicon patch tailored to the patient's anatomy is attached to the applicator to shield the soft palate and oral cavity from the 652-nm laser light. Fourteen patients were included in the study, resulting in 26 fluence rate measurements in the risk volume (two failures). We observed a systematic reduction in fluence rate during therapy in 20 out of 26 illuminations, which may be related to photodynamic therapy-induced increased blood content, decreased oxygenation, or reduced scattering. Our findings demonstrate that the applicator was easily inserted into the nasopharynx. The average light distribution in the target area was reasonably uniform over the length of the applicator, thus giving an acceptably homogeneous illumination throughout the cavity. Shielding of the risk area was adequate. Large interpatient variations in fluence rate stress the need for in vivo dosimetry. This enables corrections to be made for differences in optical properties and geometry resulting in comparable amounts of light available for Foscan absorption.     

电子束限束筒挡铅后的剂量学效应

本文探讨了挡船对电子束限束筒输出剂量的影响。采用标准水模及IONX2500／3型剂量仪,0.6cm^3电离室,对Philips SL75-14型直线加速器不同能量电子束固定限束筒、等效方野公式推算所得相应限束筒不规则野的吸收剂量进行了实测。结果分析：在限束筒上加空心铅块所获得的等效方野与该限束筒的吸收剂量无明显差别,但与等效方野公式推算所得相应限束筒的吸收剂量差别显著。因此我们认为：用不规则野电子束治疗时,应选用原限束筒的剂量学参数,不宜用等效方野公式推算所得相应限束筒的剂量学参数。     

驻留时间离差限制参数对三维后装计划的影响分析

目的:研究驻留时间离差限制（DTDC）参数对三维后装计划的影响。 方法:选取在中国医科大学附属第一医院治疗的30例妇科肿瘤患者计划,施源器为Fletcher单独宫腔管、全部三管和阴道施源器,每例患者治疗前扫描CT,并由医生勾画靶区和危及器官,以0.1步进修改DTDC参数,由DTDC=0到DTDC=1共制定11个计划,归一至DTDC=0时计划下相应的数值。比较CTV的V150、V200,膀胱、直肠的D2cc,驻留时间总和,计划调制指数,分析DTDC参数的修改对三维后装计划的影响。 结果:随着DTDC的增加,阴道施源器,Fletcher施源器单独宫腔管和全部三管使用时,CTV的V150和V200分别升高至105%和109%、102%和104%以及115%和120%,直肠和膀胱的D2cc分别至101%和102%、99%和99%以及115%和101%;总驻留时间分别达到DTDC=0时的96%、97%和104%。 结论:宫颈癌三维后装计划的制定针对不同的施源器应该选用合适的DTDC参数,给予患者更加合理治疗计划。