Close radiographic landmarks for spinal cord localization in treatment of thoracic malignancy

BACKGROUND: On simulation radiographs of oblique fields, the spinal canal is estimated to be located on the deep surface of the tangential parts of the vertebral laminae within a width of the oblique diameter of the spinal canal. The aim of this study was to evaluate the accuracy of the estimated location of the spinal canal. MATERIALS AND METHODS: Beam's eye view digital simulation radiographs were produced using actual patient data from a computed tomography (CT) scanner. The spinal canal was projected onto the Beam's eye view image, and measurement of the distance between the tangential parts of the vertebral laminae and the anterior border of the spinal canal was performed. The oblique diameter on the axial CT image was compared to the measured distance. RESULTS: In all 10 patients, the tangential parts of the vertebral laminae were detectable on the Beam's eye view image. At all levels in all patients, the oblique diameter was slightly larger than or equal to the distance. With a gantry angle of 30 degrees the difference ranged from 0 to 2.5 mm (mean, 1.2 mm), from 0 to 1.0 mm (mean, 0.4 mm), and from 0 to 1.5 mm (mean, 0.4 mm) at levels T-1, T-4, and T-7, respectively. With a gantry angle of 45 degrees the difference ranged from 0 to 1.5 mm (mean, 0.8 mm), from 0 to 0.5 mm (mean, 0.3 mm), and from 0 to 1.0 mm (mean, 0.4 mm), respectively. CONCLUSION: The tangential parts of the vertebral laminae are useful landmarks, since the spinal canal location estimated using the tangential parts and measured oblique diameter of the spinal canal on the axial CT image is sufficiently accurate.     

Overlap detection and contour-tracking algorithms for critical organs--application to kidney

An auto-contouring technique has been developed for critical structures on transverse Computer Tomographic (CT) images with one or two overlap regions where object and background have similar CT values. In this technique, those regions are identified and skipped during contour tracking. The contours thus obtained are discontinuous which are corrected afterwards by suitable interpolations. The overlap detection criterion is never satisfied in a nonoverlapping environment and the contour, in this case, is essentially tracked on the basis of CT value threshold alone. The entire process can be initiated by minimal operator intervention. The method has been successfully tested for kidneys and several examples are furnished. The success and concomitant limitations of this technique are also discussed.     

Table-sag errors in CT treatment planning

It is common practice to utilize CT scans in place of patient contours for computerized treatment planning. Our experience, in particular with pelvic patients, is that setting up the patient for a CT scan using landmarks from a radiation therapy simulator does not always produce accurate field margins. In general, the treatment field center as produced by the CT scan is superior to the center as defined by the simulator film. We have determined this problem to be caused by simulator table sag as compared to the CT. We offer suggestions to correct the problem.     

Optimization of the primary collimator settings for fractionated IMRT stereotactic radiotherapy.

Advances in field-shaping techniques for stereotactic radiosurgery/radiotherapy have allowed dynamic adjustment of field shape with gantry rotation (dynamic conformal arc) in an effort to minimize dose to critical structures. Recent work evaluated the potential for increased sparing of dose to normal tissues when the primary collimator setting is optimized to only the size necessary to cover the largest shape of the dynamic micro multi leaf field. Intensity-modulated radiotherapy (IMRT) is now a treatment option for patients receiving stereotactic radiotherapy treatments. This multisegmentation of the dose delivered through multiple fixed treatment fields provides for delivery of uniform dose to the tumor volume while allowing sparing of critical structures, particularly for patients whose tumor volumes are less suited for rotational treatment. For these segmented fields, the total number of monitor units (MUs) delivered may be much greater than the number of MUs required if dose delivery occurred through an unmodulated treatment field. As a result, undesired dose delivered, as leakage through the leaves to tissues outside the area of interest, will be proportionally increased. This work will evaluate the role of optimization of the primary collimator setting for these IMRT treatment fields, and compare these results to treatment fields where the primary collimator settings have not been optimized.     

Evaluation of elastic matching system for anatomic (CT, MR) and functional (PET) cerebral images

To evaluate the performance of our elastic matching system, we have created a digitized atlas from the brain of a normal young man, using 135 myelin-stained sections at 700 microns spacing. Software was written to enter and edit regional anatomic contours, which were stacked and aligned to create a three-dimensional atlas. We then evaluated the matching system by comparing computer generated contours with expert defined contours for several subcortical structures, based on CT scans from six neurologically normal patients. The error in positioning, as defined by the distance between the centers of gravity, averaged 4.2 mm for the computer and 1.7 mm for the worst expert's reading, with the computer drawn region frequently inscribed within that of the expert. Comparison was also made for each structure by determining the volume of overlap and the volumes not overlapping. On average, the computer's agreement with the experts was approximately 20% less than the agreement among the experts. This was a preliminary test of the system using only subcortical structures. The results are promising, and techniques are being implemented to overcome the current deficiencies.     

Impact of CT information on the treatment planning for lung tumors

With CT information available today, the prevailing, though strong, argument for not applying lung corrections is that all clinical experience gathered so far applies to doses that were prescribed for uniform density throughout the treated volume. To ease the transition from not correcting, to the state of accounting for increased lung transmission, we have planned 10 patients: (a) in the conventional way with a wire contour obtained at simulation; target volume and critical structures were drawn in by the physician utilizing information gathered from diagnostic CT scans and X-ray films; no lung correction was applied for treatment planning. (b) For the same patients, a CT scan was obtained in treatment position and the target volume was outlined on the CT film utilizing the same information as in (a); a relative lung density of 0.3 was assigned for treatment planning. The geometric accuracy of patient outline and target volume obtained in both planning modalities is analyzed, and the intended and actually delivered tumor doses are compared when optimized treatment plans from either planning modality are selected for treatment.     

Intensity-modulated photon arc therapy for treatment of pleural mesothelioma

Radiotherapy plays a key role in the definitive or adjuvant management of patients with mesothelioma of the pleural surface. Many patients are referred for radiation with intact lung following biopsy or subtotal pleurectomy. Delivery of efficacious doses of radiation to the pleural lining while avoiding lung parenchyma toxicity has been a difficult technical challenge. Using opposed photon fields produce doses in lung that result in moderate-to-severe pulmonary toxicity in 100% of patients treated. Combined photon-electron beam treatment, at total doses of 4250 cGy to the pleural surface, results in two-thirds of the lung volume receiving over 2100 cGy. We have developed a technique using intensity-modulated photon arc therapy (IMRT) that significantly improves the dose distribution to the pleural surface with concomitant decrease in dose to lung parenchyma compared to traditional techniques. IMRT treatment of the pleural lining consists of segments of photon arcs that can be intensity modulated with varying beam weights and multileaf positions to produce a more uniform distribution to the pleural surface, while at the same time reducing the overall dose to the lung itself. Computed tomography (CT) simulation is critical for precise identification of target volumes as well as critical normal structures (lung and heart). Rotational arc trajectories and individual leaf positions and weightings are then defined for each CT plane within the patient. This paper will describe the proposed rotational IMRT technique and, using simulated isodose distributions, show the improved potential for sparing of dose to the critical structures of the lung, heart, and spinal cord.     

Clinical considerations in the use of missing tissue compensators for head and neck cases

The irregular shape or contour of the patient’s surface in the treatment field can alter the dose distribution resulting in non-uniformity of dose in the treatment volume. Missing tissue compensators have been most commonly used to improve this non-uniformity, especially in head & neck, breast, lung and supraclavicular regions. Two or three dimensional compensators have been typically designed to make the dose uniform at a specific depth. This compensation shifts the dose distribution within the treatment volume so that some structures may be under or over compensated. This study will examine how various sites in head and neck cases are affected by compensators. We have also analyzed the uncertainty in compensated dose due to the daily variations in patient repositioning. Computer isodose plans using Cobalt-60 gamma rays and 6 and 18 MV x-rays were generated using coronal contours. Results show that the dose uniformity is improved for the treatment sites, especially for the thinner sites, like the larynx and the anterior cervical neck nodes. Finally, patient movement or positioning errors of ±1.0 cm will cause a change in dose distribution.     

Clinical considerations in the use of missing tissue compensators for head and neck cases

The irregular shape or contour of the patient’s surface in the treatment field can alter the dose distribution resulting in non-uniformity of dose in the treatment volume. Missing tissue compensators have been most commonly used to improve this non-uniformity, especially in head & neck, breast, lung and supraclavicular regions. Two or three dimensional compensators have been typically designed to make the dose uniform at a specific depth. This compensation shifts the dose distribution within the treatment volume so that some structures may be under or over compensated. This study will examine how various sites in head and neck cases are affected by compensators. We have also analyzed the uncertainty in compensated dose due to the daily variations in patient repositioning. Computer isodose plans using Cobalt-60 gamma rays and 6 and 18 MV x-rays were generated using coronal contours. Results show that the dose uniformity is improved for the treatment sites, especially for the thinner sites, like the larynx and the anterior cervical neck nodes. Finally, patient movement or positioning errors of ±1.0 cm will cause a change in dose distribution.     

Detection of metastasis in cervical lymph nodes: CT and MR criteria and differential diagnosis.

Radiologists are frequently asked to evaluate cervical lymph nodes with CT or MR imaging to determine if metastases are present, how extensive the metastases are, and if they have spread from lymph nodes to critical adjacent structures such as the carotid artery and skull base. Accurate information of this type is essential if the most appropriate treatment is to be selected. The purpose of this report is to review the diagnostic criteria that are currently used with CT and MR imaging to diagnose metastases in cervical nodes by evaluating nodal size, shape, grouping, and necrosis and extranodal tumor spread. In addition, emphasis is placed on details that should be included in the CT and MR report, such as the location of the nodes, the presence of nodal calcification, and the presence of associated diseases such as parotid cysts that may suggest a specific diagnosis like HIV infection. Because optimal treatment planning depends on the combined information gleaned from the clinical evaluation and the imaging studies, it is essential that there be a close dialogue between clinicians and radiologists.     

Determination of ventricular volume following metrizamide CT ventriculography

Summary Volume averaging, relatively slight differences in the mean attenuation coefficients of CSF and white/grey matter, and the irregular contours of the human ventricular system have so far seriously limited the accuracy of CT estimation of ventricular volume. Taking advantage of the high attenuation of metrizamide-containing CSF, we have developed three methods for computing ventricular volume after metrizamide CT ventriculography; these methods depend upon computer analysis of X-ray absorption data obtained from contiguous CT brain slices. All three methods were validated by CT scanning a formalin-fixed cadaver brain containing an epoxy-resin cast of the ventricular system. Calculated ventricular volumes were compared with the actual measured volume of the ventricular cast.     

Dosimetric evaluation of a three-phase adaptive radiotherapy for nasopharyngeal carcinoma using helical tomotherapy

Adaptive radiotherapy (ART) has been introduced to correct the radiation-induced anatomic changes in head and neck cases during a treatment course. This study evaluated the potential dosimetric benefits of applying a 3-phase adaptive radiotherapy protocol in nasopharyngeal carcinoma (NPC) patients compared with the nonadaptive single-phase treatment protocol. Ten NPC patients previously treated with this 3-phase radiation protocol using Hi-Art Tomotherapy were recruited. Two new plans, PII-ART and PIII-ART, were generated based on the up-to-date computed tomography (CT) images and contours and were used for treatment in phase two (PII; after 25th fraction) and phase three (PIII; after 35th fraction), respectively. To simulate the situation of no replanning, 2 hybrid plans denoted as PII-NART and PIII-NART were generated using the original contours pasted on the PII- and PIII-CT sets by CT-CT fusion. Dosimetric comparisons were made between the NART plans and the corresponding ART plans. In both PII- and PIII-NART plans, the doses to 95% of all the target volumes (D₉₅) were increased with better dose uniformity, whereas the organs at risk (OARs) received higher doses compared with the corresponding ART plans. Without replanning, the total dose to 1% of brainstem and spinal cord (D₁) significantly increased 7.87 ± 7.26% and 10.69 ± 6.72%, respectively (P = 0.011 and 0.001, respectively), in which 3 patients would have these structures overdosed when compared with those with two replannings. The total maximum doses to the optic chiasm and pituitary gland and the mean doses to the left and right parotid glands were increased by 10.50 ± 10.51%, 8.59 ± 6.10%, 3.03 ± 4.48%, and 2.24 ± 3.11%, respectively (P = 0.014, 0.003, 0.053, and 0.046, respectively). The 3-phase radiotherapy protocol showed improved dosimetric results to the critical structures while keeping satisfactory target dose coverage, which demonstrated the advantages of ART in helical tomotherapy of NPC.     

A computerized three-dimensional treatment planning system utilizing interactive colour graphics.

A new computerized radiation treatment planning system has been developed to aid in three-dimensional treatment planning. Using interactive colour graphics in conjunction with a DPD 11/45 computer, the system can take multiple transverse contours and construct a perspective display of the treatment region showing organ surfaces as well as cross-sectional contours. With interactively selected orientations, the display allows easy perception of the relative positioning of the treatment volume and neighbouring anatomy. For external beam treatment planning, interactive computer simulation is used to select diaphragm sizes which best conform to the target area while avoiding sensitive structures. Dose calculations for the selected beams are carried out on multiple transverse planes. The calculational planes and surfaces are displayed in perspective with radiation dosage displayed in an interactively manipulated colour display. Altogether the system provides an easy assessment of the volume to be irradiated, interactive selection of optimal arrangements of treatment fields and a means for visualizing and evaluating the resulting dose distributions.     

Patología traumática de peñascos,un diagnóstico complejo. Claves para el informe

Fractures of the petrous part of the temporal bone are a common lesion of the base of the skull; most of these fractures result from high-energy trauma. In patients with multiple trauma, these injuries can be detected on CT scans of the head and neck, where the direct and indirect signs are usually sufficient to establish the diagnosis. It is important to these fractures because the temporal bone has critical structures and the complexity of this region increases the risk of error unless special care is taken. This article reviews the key anatomical points, the systematization of the imaging findings, and the classifications used for temporal bone fracture. We emphasize the usefulness of identifying and describing the findings in relation to important structures in this region, of looking for unseen fractures suspected through indirect signs, and of identifying anatomical structures that can simulate fractures. We point out that the classical classifications of these fractures are less useful, although they continue to be used for treatment decisions.     

Comparison of 2D conventional, 3D conformal, and intensity-modulated treatment planning techniques for patients with prostate cancer with regard to target-dose homogeneity and dose to critical, uninvolved structures

The purpose of this study was to compare 2-dimensional (2D), 3-dimensional (3D) and intensity-modulated radiation therapy (IMRT) techniques for external-beam radiation treatment for prostate cancer. Dose homogeneity within the target volume and doses to critical, uninvolved anatomic structures were evaluated. Computed tomography (CT) scans of 3 patients with localized prostate cancer (T2N0M0) were acquired and transferred to the treatment planning systems. The target volume and uninvolved structures were contoured on axial CT slices throughout the volume of interest. A comparison of the 3 treatment techniques was performed using isodose distributions, dose statistics, and dose-volume histograms. Dose homogeneity was found to be most uniform with the 2D technique; however, the 2D technique delivers unnecessary radiation doses to the rectum and bladder. The dose conformity observed with IMRT is increased compared with that observed with the 3D technique, as is the sparing of critical uninvolved structures; however, dose homogeneity appears to be worse with IMRT than with the 3D technique. Overall, of the 3 techniques, IMRT offers the most conformity in delivery of tumoricidal doses to the prostate while sparing dose to critical, uninvolved structures.     

Acute radiation toxicity assessment of a 3-D conformal head and neck radiation treatment technique

Patients undergoing radiation treatment for head and neck cancer have many critical structures within or adjacent to the treatment area. Avoiding these critical structures is more efficient and easier using 3-D conformal planning. At Sir Charles Gairdner Hospital an investigation into the acute radiation toxicity was undertaken when the head and neck treatment technique was changed from the conventional 2-D plan to the conformal 3-D plan. Although the primary target volume (PTV), fraction size and overall dose remain the same for the two techniques, differing beam configurations mean that treatment fields enter and exit through different parts of the head and neck. Ten patients were initially assessed to gain a baseline appearance of their head and neck region, and then graded weekly according to the toxicity criteria during treatment and at 4, 8 and 12 weeks after treatment. The results of the assessment indicate that there is no increase in toxicity as a result of treating using the conformal head and neck technique.     

基于Amira软件的小腿外侧供区皮瓣三维可视化设计

目的 利用个人电脑(PC),结合图像处理软件Amira 4.1对小腿外侧皮瓣进行三维重建,建立皮瓣动脉的可视化数字模型.方法 明胶-氧化铅混悬液灌注的新鲜成人标本1具,行下肢多排螺旋CT扫描,观测腓动脉的分布及彼此间的吻合情况,将数据输入个人PC,利用Amira软件,经剪切、分割、表面重建及体绘制等步骤,根据解剖结构特点,对皮肤及其血管进行三维重建,获得立体形态的动脉皮瓣结构.结果 重建了皮瓣主要构成,重建的三维结构可以多彩色、透明或任意组合显示,经不同角度观察,整体显示清晰、实体感强,皮肤、动脉的相互关系一目了然.在三维表面重建的图像中可清楚地观察各解剖结构的形态,特别是皮瓣动脉的分支及其体表投影得到了很好的显示.结论 小腿外侧皮瓣三维重建对基础研究、临床试验及手术规划具有重要价值,应用Amira软件可为三维建模提供基础.     

The utilization of a 3-dimensional noncoplanar treatment plan to avoid pacemaker complications.

Treatment planning of thoracic patients having upper lobe lesions and a pacemaker presents quite a challenge. It is necessary to avoid the pacemaker as well as other critical structures in order to deliver the prescribed dose for local control. This case demonstrates the utilization of noncoplanar beams and asymmetric fields to limit the radiation dose to the pacemaker. The dose to the pacemaker was quantified by the information represented in the dose-volume histogram (DVH) of the computerized tomography (CT)-based treatment plan. The delivered dose was verified utilizing thermoluminescent dosimeters (TLDs) placed on the patient. Measurements of the daily dose from all of the treatment fields to include the open jaws during portal imaging were taken to sum the total possible dose the pacemaker may receive. The allowable dose to the pacemaker is dependent upon individual manufacturers. It was found that with proper treatment planning and appropriate precautions, a patient is able to receive full-prescribed dose with no risks of interfering with the pacemaker function.