A technique for fractionated stereotactic radiotherapy in the treatment of intracranial tumors

PURPOSE: The excellent treatment results obtained with traditional radiosurgery have stimulated attempts to broaden the range of intracranial disorders treated with radiosurgical techniques. For major users of radiosurgery this resulted in a gradual shift from treating vascular diseases in a single session to treating small, well delineated primary tumors on a fractionated basis. In this paper we present the technique currently used in Montreal for the fractionated stereotactic radiotherapy of selected intracranial lesions. METHODS AND MATERIALS: The regimen of six fractions given every other day has been in use for "fractionated stereotactic radiotherapy" in our center for the past 5 years. Our current irradiation technique, however, evolved from our initial method of using the stereotactic frame for target localization and first treatment, and a "halo-ring" with tattoo skin marks for the subsequent treatments. Recently, we developed a more precise irradiation technique, based on an in-house-built stereotactic frame which is left attached to the patient's skull for the duration of the fractionated regimen. Patients are treated with the stereotactic dynamic rotation technique on a 10 MV linear accelerator (linac). RESULTS: In preparation for the first treatment, the stereotactic frame is attached to the patient's skull and the coordinates of the target center are determined. The dose distribution is then calculated, the target coordinates are marked onto a Lucite target localization box, and the patient is placed into the treatment position on the linac with the help of laser positioning devices. The Lucite target localization box is then removed, the target information is tattooed on the patient's skin, and the patient is given the first treatment. The tattoo marks in conjunction with the target information on the Lucite target localization box are used for patient set-up on the linac for the subsequent 5 treatments. The location of the target center is marked with radio-opaque markers on the target localization box and verified with a computerized tomography scanner prior to the second treatment. The same verification is done prior to other treatments when the target center indicated by the target localization box disagrees with that indicated by the tattoo marks. The new position of the target center is then determined and used for treatment positioning. CONCLUSION: The in-house-built frame is inexpensive and easily left attached to the patient's skull for the 12 day duration of the fractionated regimen. Positioning with the Lucite target localization box verified with tattoo marks ensures a high level of precision for individual fractionated treatments.     

MR image-guided portal verification for brain treatment field

PURPOSE: To investigate a method for the generation of digitally reconstructed radiographs directly from MR images (DRR-MRI) to guide a computerized portal verification procedure. METHODS AND MATERIALS: Several major steps were developed to perform an MR image-guided portal verification procedure. Initially, a wavelet-based multiresolution adaptive thresholding method was used to segment the skin slice-by-slice in MR brain axial images. Some selected anatomical structures, such as target volume and critical organs, were then manually identified and were reassigned to relatively higher intensities. Interslice information was interpolated with a directional method to achieve comparable display resolution in three dimensions. Next, a ray-tracing method was used to generate a DRR-MRI image at the planned treatment position, and the ray tracing was simply performed on summation of voxels along the ray. The skin and its relative positions were also projected to the DRR-MRI and were used to guide the search of similar features in the portal image. A Canny edge detector was used to enhance the brain contour in both portal and simulation images. The skin in the brain portal image was then extracted using a knowledge-based searching technique. Finally, a Chamfer matching technique was used to correlate features between DRR-MRI and portal image. RESULTS: The MR image-guided portal verification method was evaluated using a brain phantom case and a clinical patient case. Both DRR-CT and DRR-MRI were generated using CT and MR phantom images with the same beam orientation and then compared. The matching result indicated that the maximum deviation of internal structures was less than 1 mm. The segmented results for brain MR slice images indicated that a wavelet-based image segmentation technique provided a reasonable estimation for the brain skin. For the clinical patient case with a given portal field, the MR image-guided verification method provided an excellent match between features in both DRR-MRI and portal image. Moreover, target volume could be accurately visualized in the DRR-MRI and mapped over to the corresponding portal image for treatment verification. The accuracy of DRR-MRI was also examined by comparing it to the corresponding simulation image. The matching results indicated that the maximum deviation of anatomical features was less than 2.5 mm. CONCLUSION: A method for MR image-guided portal verification of brain treatment field was developed. Although the radiographic appearance in the DRR-MRI is different from that in the portal image, DRR-MRI provides essential anatomical features (landmarks and target volume) as well as their relative locations to be used as references for computerized portal verification.     

Organ preservation in the treatment of brain tumors

Within the many histological forms, the preservation of function in the central nervous system has always been predominant. However, the limited or null therapeutic interval for high grade gliomas enables organ preservation in small neoplasms only. In case of favorable histology (e.g. dysgerminoma, low grade small glioma), organ preservation is feasible with adequate techniques. When local control is predominant (e.g. neoplasms of eye) the techniques are long known but applied in very few Centers.     

A new technique for positioning tangential fields

PURPOSE: A technique that eliminates the use of a mechanical "breast-bridge" for positioning tangential fields for treatment of the intact breast or chest wall has been developed. METHODS AND MATERIALS: Treatment set-up parameters are determined using measuring capabilities (gantry angles and source-skin distances) available on a standard simulator unit. A programmable scientific calculator is used to determine field geometry from polar coordinates for various points on the patient's skin. The calculator program determines the field size, a depth and lateral shift from a skin reference point to the isocenter for the tangential fields, and the gantry angles. The program provides additional information which facilitates the simulation process: First, the coordinates of the isocenter for the tangential fields are expressed relative to couch coordinates for an initial arbitrary isocenter so that the "auto go to" capability available on some simulators can be used. Second, the coordinates of the medial and lateral entry points can be edited when the first set of tangents are not accepted. This part of the program allows quick and efficient adjustment of the fields to obtain adequate treatment volume coverage and a minimum of irradiated lung or heart. RESULTS: Simulation of more than 300 patients has shown the technique to be a practical and efficient method for positioning tangential fields for breast or chest wall irradiation. CONCLUSION: The technique described here takes full advantage of the capabilities of the new generation of computer controlled simulators, and offers an alternative to previous methods employing a mechanical "breast-bridge."     

Feasibility of ultrasound hyperthermia in the treatment of malignant brain tumors

In order to test the biological feasibility of using ultrasound-generated hyperthermia for the treatment of brain tumors, damage threshold studied and thermal dosimetry studies as a function of temperature were performed in 44 acute experiments in cats. Bilateral craniotomies were performed to expose the dural surface. Ultrasonic radiation was applied for 50 minutes at different intensities to generate temperatures up to 48 degrees C. Thermal fields were mapped using an electrode array of three triple-junction thermocouple probes. Each probe left a track easily identified histologically. Serial sections of each brain were cut and stained, allowing for precise correlation of histology and thermocouple location and temperature. At temperatures of less than 42 degrees C for 50 minutes, no evidence of damage could be detected in either gray or white matter. At 43 degrees C partial loss of neurons was seen in the brain adjacent to the probe, but at the same temperature in white matter, only edema was seen. At temperatures of 44-45 degrees C there was definite loss of both neurons in the gray matter and myelin tracts in the white matter. The lesions created by using ultrasound-generated hyperthermia were sharply marginated. This sharp demarcation histologically correlated well with the abrupt fall off in temperature as a function of distance from the lesion edge. The results of this study are important in two respects. First, it demonstrates that ultrasound can effectively heat the brain in an extremely controlled and precise manner. Second, the brain can withstand temperatures to 42 degrees C without showing histological evidence of damage, which is the temperature range at which neoplastic cells begin to show cytotoxic effects.     

A new,optical measuring technique for the determination of the vapour film thickness during film boiling

A non-contact measuring technique was developed and tested to determine the thickness of a vapour film during film boiling. The technique is based on the different optical properties of vapour and water admixed with a fluorescent substance. Pictures were taken of the surroundings of the vapour film using a long-distance microscope of high resolving power and a TV-camera; they were recorded with a video recorder. The pictures were evaluated using methods of digital image processing and by application of a model for the intensity distribution of fluorescence-radiation. The technique was tested on a steel sphere heated to 690°C and subsequently immersed into warm water of 55°C. The thickness of the vapour film directly after immersion was determined at 0.20 mm. The thickness decreased continuously during the cooling process and reached a thickness of 0.11 mm after 20 s, immediately before the collapse of the vapour film. The surface temperature of the steel sphere immediately before the collapse was about 420°C. The thicknesses of the vapour film calculated with a simple theoretical model were found to be about 50 % smaller than those measured.     

A rapid colour stabilization technique for radiochromic film dosimetry

Various forms of GAFChromic film have been used for several years as radiographic media for measuring dose distributions of brachytherapy sources and small radiation fields. Upon irradiation the film changes colour and darkens with time post-irradiation. The darkening is most rapid in the first 24 h, and it has been suggested that for accurate dosimetry a waiting period of 24 h should occur before any optical density (OD) measurements are taken. A more rapid colour stabilization (RCS) procedure has been developed and is evaluated. The procedure consists of heating the film post-irradiation for a period of 2 h at 45 degrees C. The RCS procedure is compared with a control group and the dose response is tested for linearity, stability and reproducibility using two densitometers with light sources at different wavelengths (632.8 nm and 671 nm). The rise in net optical density (NOD) for the period 3-168 h is less than 3% for the RCS group as compared with 12% for the controls. In the first 24 h, the increase in NOD for the RCS samples is less than 0.5%, as opposed to 6% for the control group.     

铁磁性金属材料电磁无损检测中优化磁化场设计的研究

利用电磁原理进行无损检测的方法在铁磁性金属材料的探伤中得到广泛应用.本文介绍了应用永久磁铁、电磁铁所形成的几种外加磁化场的特点,及其适用于不同检测要求的优化设计及合理使用的一般原则.     

场活化烧结中场特点、影响和作用

场活化烧结技术是一种在电场、应力场和温度场作用下实现快速致密化的粉末活化烧结技术.场活化烧结的特殊致密化过程和活化机理,源自于其特有的电场、应力场以及温度场作用.本文就各种场在场活化烧结过程中的特点、作用和影响的研究进展进行介绍.对于各种场在场活化烧结中的特点、作用和影响的认识,仍存在较多问题和分歧.各场间交互作用显著.从多场耦合的角度研究场活化烧结过程,有助于更准确、全面掌握各种场的特点、作用和影响,深入揭示场活化烧结的特殊致密化过程和活化机理.通过外加磁场提高场活化烧结的均匀性,进一步赋予材料特殊性能,具有良好的研究开发前景.     

Local treatment of tumors of the rectum with transanal endoscopic microsurgical technique

Nine patients were treated with transanal endoscopic microsurgery for rectal adenomas and three for incurable malignant disease of the rectum. The techniques are presented. One early complication was seen. In the median follow-up period of 6.5 months no recurrences were seen in the adenoma group. In the palliatively resected group of rectal cancers one patient has died and two patients are alive without stomas. It is concluded that the microsurgical technique is a safe treatment modality for some patients with rectal diseases.     

Optimizing interstitial delivery of BCNU from controlled release polymers for the treatment of brain tumors

OBJECTIVE: To determine quality of hip fracture services provided by "generalist" general surgeons (generalists) in Nova Scotia. DESIGN: Chart review and postoperative, blinded, random-ordered radiologic analysis. SETTING: Three community hospitals and 1 tertiary care hospital in Nova Scotia. PARTICIPANTS: Seven generalists who performed 120 hip fracture repairs and 7 orthopedic surgeons (specialists) who performed 135 hip fracture repairs. OUTCOME MEASURES: Patient demographics, preoperative, perioperative, postoperative and discharge information, technical quality of reduction as determined through postoperative radiologic assessment. RESULTS: There were no differences between patients treated by generalists and those treated by specialists with respect to age, sex, American Society of Anesthesiologists' class, level of function and fracture type. Intraoperatively, the patient groups were similar with respect to type of anesthesia, use of antibiotics, number of transfusions and surgical complications. Significant differences were noted in length of operation (54.4 v. 41.1 minutes), use of C-arm imaging (6.7% v. 85.9%) and management of Garden classes 1 and 2 subcapital fractures. Postoperatively, the 2 groups had similar numbers of medical complications, wound complications, reoperations, readmissions and deaths, and a similar level of function on discharge. Significant differences included the number of intensive care unit admissions (5.8% v. 15.6%) and length of stay there (5.7 v. 2.8 days) and of postoperative stay (14.5 v. 10.7 days). The assessment of radiographs did not demonstrate any significant difference in the quality of reduction. CONCLUSION: In Nova Scotia the outcomes of hip fracture surgery performed by generalists are comparable to those performed by specialists.     

Malignant brain tumors in the elderly

The increase in the incidence of primary brain tumors in the elderly over the last decade represents a serious problem because of the severe disability and risk of death associated with this disease. Surgery remains the mainstay of the management of malignant gliomas, and the magnitude of the resection correlates with the length of survival. The additional standard treatment modalities are reviewed. This article also discusses novel approaches being evaluated to treat both newly diagnosed and recurrent brain tumors.     

A new treatment for high grade gliomas of the brain

The data confirmed the fact that repeated administrations of iodine-125 labeled anti-epidermal growth factor receptor 425 is safe and may have benefited the management of primary high grade gliomas of the brain as well as recurrent astrocytomas. At present, a randomized control phase III trial is in the process of being initiated to evaluate the benefits that would accrue in a controlled environment.     

Immersion technique for brain removal in perinatal autopsies

Perinatal autopsies present forensic patholgists with a variety of challenges, not the least of which involves the removal and examination of very small and sometimes fragile organs. Removal of the immature brain can be particularly troublesome. Even if great care is taken during brain removal, one is often left with no more than a semifluid amorphous mass of softened tissue by the time the brain is ready to be fixed in formalin. We describe a method of perinatal brain removal which helps to preserve brain shape and integrity. By removing the brain while the head (and body) is totally immersed in water, we find that the brain is easier to remove and less apt to destruction. Subsequent fixation in formalin results in well-preserved, intact specimens, allowing for optimal examination and sectioning.     

蒸煮处理对覆膜铁用BOPET薄膜阻隔性能的影响

覆膜铁作为食品用罐包装用材,使用过程中需经高温蒸煮处理,为研究此过程对于覆膜铁用双向拉伸聚酯(BOPET)薄膜阻隔性能的影响,对经不同蒸煮时间处理的BOPET薄膜的水蒸气透过率、热效应、微观结构进行了探讨分析。研究结果表明,蒸煮处理有利于降低BOPET薄膜的水蒸气透过率;随着蒸煮处理时间的延长,薄膜的熔点和熔融热有一定程度的增加;同时蒸煮处理可以调整薄膜的微观结构,增加晶核数量的同时使结晶更致密,形成网络状结构有利于提升薄膜的阻隔性能。