Radiotherapy treatment planning of basal meningiomas: improved tumor localization by correlation of CT and MR imaging data.

A localization technique, based on three-dimensional CT and MR imaging data for precision radiotherapy of basal meningiomas, is presented. Indications for radiotherapy included unresected tumors, gross disease remaining despite surgery, and recurrences. The patient's head was fixed in a stereotactic localization system which is usable at the CT, MR and the linear accelerator installations. The geometrical distortion of MR imaging data was evaluated in three dimensions by phantom measurements. The geometrical distortion was "corrected" (reducing displacements to the size of a pixel) by calculations based on modelling the distortion as a fourth order two-dimensional polynomial. The target volume was defined in three-dimensional MR imaging data after application of 0.1 mmol/kg b.w. Gd-DTPA solution and transferred precisely from MR onto CT data to provide a map of the radiation attenuation coefficient for dose calculation. The superior soft tissue contrast of MR showed an excellent tumor delineation especially when the bony base of the skull obscured the target in CT images. Target volume, calculated dose distribution, and critical structures could be transferred between CT and MR imaging data and displayed as three-dimensional shaded structures for better assessment for matching of target volume and dose distribution. With the described planning system a more precise target definition of basal meningiomas was possible by integration of the superior tumor delineation in MR compared with CT.     

Radiotherapy for tumors of the uterine cervix. Gross tumor volume and clinical target volume]

Treatment of carcinoma of the uterine cervix needs a multidisciplinary approach. External irradiation and brachytherapy are highly curative because of the tumor radiosensitivity. The main prognostic factors are tumoral volume and nodal involvement. Tumoral extent is evaluated by diagnostic MR imaging, and gynecological exam. Nodal involvement can be assessed, accurately by coelioscopic pelvic node sampling and by imaging modalities such as CT scan. The knowledge of these two factors helps to choose the treatment strategy. The use of imaging (MRI and CT) added to clinical findings allows to design external irradiation fields. 3D treatment planning in external irradiation and brachytherapy is based upon the use of imaging (CT and MRI). It leads to a better knowledge of dose distribution to the target and critical organs and allows more individualized and conformal treatment.     

Multimodalities imaging for target volume definition in radiotherapy

Modern radiotherapy delivery nowadays relies on tridimensional, conformal techniques. The aim is to better target the tumor while decreasing the dose administered to surrounding normal tissues. Gold standard imaging modality remains computed-tomography (CT) scanner. However, the intrinsic lack of contrast between soft tissues leads to high variabilities in target definition. The risks are : a geographical miss with tumor underirradiation on the one hand, and a tumor overestimation with undue normal tissues irradiation on the other hand. Alternative imaging modalities like magnetic resonance imaging and functional positron emission tomography could theoretically overcome the lack of soft tissues contrast of CT. However, the fusion of the different imaging modalities images requires the use of sophisticated computer algorithms. We will briefly review them. We will then review the different clinical results reported with multi-modalities imaging for tumors of the head, neck, lung, esophagus, cervix and lymphomas. Finally, we will briefly give practical recommendations for multi-modality imaging in radiotherapy treatment planning process.     

Apport de l’imagerie de spectroscopie de résonance magnétique du proton et des autres imageries métaboliques à la définition des volumes cibles de radiothérapie des tumeurs gliales de l’adulte et de l’enfant

Radiation therapy improves survival in high-grade gliomas but most patients relapse and usually within radiation fields. This may be due to uncertainties in target delineation and difficulties in identifying radioresistant regions for dose escalation. The use of T1 and T2-weighted magnetic resonance imaging (MRI) coregistration on the planning CT improves the target volume definition but magnetic resonance spectroscopic imaging (MRSI) and other types of metabolic and functional imaging (perfusion MRI, diffusion-weighted MRI, positron emission tomography (PET) imaging) may give useful additional information for target delineation. This article focuses on the potential of each imaging modality: assessment of response to treatment, detection of abnormalities not seen on MRI, predictive value for the site of local relapse. The incorporation of such techniques may improve target volume definition.     

Intérêt de la tomographie par émission de positons au [18F]-fluoro-2-désoxyglucose dans la détermination des volumes cibles de radiothérapie. Application à l''irradiation conformationnelle des cancers bronchiques non à petites cellules

Traditional radiation treatment planning relies on density imaging such as Computed Tomography for anatomic information of various structures of interest including target and normal tissues. However, the difficulties to distinguish malignant from normal tissue on CT slides often leads to inaccurate outlining of the GTV and/or to geographic misses. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) has shown an increase in both sensitivity and specificity over CT in locoregional staging of patients with non-small cell lung cancer (NSCLC). The co registration of FDG-PET images to the data of the CT planning offers the radiation oncologist the possibility to include functional information into the target outlining. For the treatment of patients with NSCLC, it has been shown that the use of FDG-PET images: 1) modified the shape and volume of radiation fields in 22-62% of cases, mainly due to a better nodal staging and distinction of atelectasis from tumor and; 2) significatively reduced the interobserver and intraobserver variability. This paper reviews the results reported in the literature. Challenges and proposed solutions are discussed.     

Biological imaging in radiation oncology

The goal of this study was to discuss the value of integrating biological imaging (PET, SPECT, MRS etc.) in radiation treatment planning and monitoring. Studies in patients with brain tumors have shown that, compared to CT and MRI alone, the image fusion of CT/MRI and amino acid SPECT or PET allows a more correct delineation of gross tumor volume (GTV) and planning target volume (PTV). For FDG-PET comparable results with different techniques are reported in the literature also for bronchial carcinoma, ear-nose-and-throat tumors, and cervical carcinoma, or, in the case of MRS, for prostate cancer. Imaging of hypoxia, cell proliferation, apoptosis, tumor angiogenesis, and gene expression leads to the identification of differently aggressive areas of a biologically inhomogeneous tumor mass that can be individually and more appropriately targeted using innovative IMRT. Thus, a biological, inhomogeneous dose distribution can be generated, the so-called dose painting. In addition, the biological imaging can play a significant role in the evaluation of the therapy response after radiochemotherapy. Clinical studies in ear-nose-and-throat tumors, bronchial carcinoma, esophagus carcinoma, and cervical carcinoma suggest that the sensitivity and specificity of FDG-PET for the therapy response are higher compared to anatomical imaging (CT and MRI). Clinical and experimental studies are required to define the real impact of these investigations in radiation treatment planning, and especially in the evaluation of therapy response.     

Adaptive biological image-guided IMRT with anatomic and functional imaging in pharyngo-laryngeal tumors: impact on target volume delineation and dose distribution using helical tomotherapy.

BACKGROUND AND PURPOSE: Adaptive image-guided IMRT appears to be a promising approach for dose escalation in pharyngo-laryngeal tumors. In this framework, we assessed in a proof of concept study the impact of anatomic and functional imaging modalities acquired prior and during radiotherapy on the target volume delineation and the dose distribution using helical tomotherapy. MATERIALS AND METHODS: Ten patients with pharyngo-laryngeal squamous cell carcinoma were treated by concomitant chemo-radiation delivered in 7 weeks. CT, T2-MRI, fat suppressed T2-MRI, and static and dynamic FDG-PET were acquired for each patient before the start of treatment and during radiotherapy, after mean prescribed doses of 14, 25, 35 and 45 Gy. GTVs were manually delineated on CT and MRI images while PET images were automatically segmented by means of a gradient-based method. From these volumes, CTVs and PTVs were derived using consistent guidelines. Simultaneous integrated boost IMRT planning was performed using helical tomotherapy. RESULTS: GTVs significantly decreased throughout the course of RT for all imaging modalities (p<0.001). Clinically non-significant differences and high correlations were found between GTVs delineated on CT and MRI, irrespective of the sequence used. By contrast, FDG-PET-based GTVs segmented from pre- and per-treatment images were significantly smaller compared to anatomical imaging modalities, without any difference existing between static and dynamic acquisition. These differences in GTVs translated into parallel reductions of both prophylactic and therapeutic CTVs and PTVs. Resulting FDG-PET-based and adaptive IMRT planning reduced the irradiated volumes by 15-40% compared to pre-treatment CT planning (V(90), V(95) and V(100)), but did marginally impact on doses to the OAR such as the spinal cord and the parotid glands. CONCLUSIONS: Adaptive IMRT with FDG-PET images has a significant impact on the delineation of TVs and on the dose distribution in pharyngo-laryngeal tumors. Such an approach might thus be considered for dose escalation strategies.     

Three-dimensional conformal radiation treatment planning and delivery for low- and intermediate-grade gliomas

Three-Dimensional conformal radiation treatment (3D-CRT) planning and delivery is an external beam radiation therapy modality that has the general goal of conforming the shape of a prescribed dose volume to the shape of a 3-dimensional target volume, simultaneously limiting dose to critical normal structures. 3-Dimensional conformal therapy should include at least one volumetric imaging study of the patient. This image should be obtained in the treatment position for visualizing the target and normal anatomic structures that are potentially within the irradiated volume. Most often, computed tomography (CT) and/or magnetic resonance imaging (MRI) are used; however, recently, other imaging modalities such as functional MRI, MR spectroscopy, and positron emission tomography (PET) scans have been used to visualize the clinically relevant volumes. This article will address the clinically relevant issues with regard to low- and intermediate-grade gliomas and the role of 3D-CRT planning. Specific issues that will be addressed will include normal tissue tolerance, target definition, treatment field design in regard to isodose curves and dose-volume histograms, and immobilization.     

基于头颈部千伏级锥形束CT的剂量计算研究

目的 探讨用机载千伏级锥形束CT (CBCT)对鼻咽癌患者治疗前扫描图像直接进行剂量计算的可行性.方法 选取治疗前行扇形束CT (FBCT)和CBCT扫描的11例鼻咽癌患者,将体位校正后重新扫描的CBCT图像传输至治疗计划系统中.在治疗计划系统中将FBCT和CBCT图像融合,将FBCT的计划移植至CBCT上.选择CBCT图像自己的HU-ED校正曲线重新进行剂量计算,与FBCT计划的靶区和正常器官的剂量体积直方图以及等中心层面剂量分布的γ通过率分析(阈值3%/3 mm)结果进行比较.结果 11例鼻咽癌患者中CBCT和FBCT计划的剂量体积直方图相似,等中心层面剂量分布中平均γ通过率为98.0%±1.33%.FBCT计划和CBCT计划的靶区受量差异都<1%,正常组织器官受量差异<2%.结论 治疗过程中得到的CBCT图像能用来进行剂量计算.

Abstract：

Objective To study the feasibility of dose calculation using kilovoltage X-ray cone-beam CT (KVCBCT) imaging for head-and-neck radiation therapy.Methods 11 patients with nasopharyngeal carcinoma were scanned with KVCBCT to adjust position before treatment, and rescanning images with KVCBCT after correction were input a treatment-planning system.The dose was recalculated by applying the patients′ treatment plans based on planning CT to the KVCBCT images.The dose distributions and dose volume histograms (DVH) of the tumor and critical structures were compared with the original treatment plan.Results The DVH and dose distribution of the plan based on the KVCBCT are compared with that of the planning CT, and they shows a good consistency for the 11 cases.The doses calculated from the planning CT and KVCBCT were compared on the isocenter planes.Using γ analysis with a criterion of 3%/3 mm, 98.0%±1.33% of the points on the isocenter planes in the planning CT and KVCBCT.The difference of the dose to target volume was<1% and to normal structure was<2%.Conclusions This study indicated that CBCT images can be used to make a treatment plan with its individual hounsfield unit-electron density calibration curve.     

A quantitative assessment of the addition of MRI to CT-based, 3-D treatment planning of brain tumors.

Quantitative 3-D volumetric comparisons were made of composite CT-MRI macroscopic and microscopic tumor and target volumes to their independently defined constituents. Volumetric comparisons were also made between volumes derived from coronal and axial MRI data sets, and between CT and MRI volumes redefined at a repeat session in comparison to their original definitions. The degree of 3-D dose coverage obtained from use of CT data only or MRI data only in terms of coverage of composite CT-MRI volumes was also analyzed. On average, MRI defined larger volumes as well as a greater share of composite CT-MRI volumes. On average, increases in block margin on the order of 0.5 cm would have ensured coverage of volumes derived from use of both imaging modalities had only MRI data been used. However, the degree of inter-observer variation in volume definition is on the order of the magnitude of differences in volume definition seen between the modalities, and the question of which imaging modality best describes tumor volumes remains unanswered until detailed histologic studies are performed. Given that tumor volumes independently apparent on CT and MRI have equal validity, composite CT-MRI input should be considered for planning to ensure precise dose coverage for conformal treatments.     

A comprehensive three-dimensional radiation treatment planning system

A comprehensive software system has been developed to allow 3-dimensional planning of radiation therapy treatments using the extensive anatomical information made available by imaging modalities such as CT and MR. Biological structures of interest and tumor volumes are defined by outlines drawn on a sequence of CT slices. Beam set-ups may then be determined in three dimensions by displaying the structure contours in a beam's eye view, or in two dimensions using a single CT cut. Each beam defined may be shaped by the specification of block aperture contours, and its intensity may be modified with the use of planar compensators. 3D dose calculation algorithms are discussed. To evaluate the calculation results, dose volume histograms are provided, as well as various types of displays in two and three dimensions, including dose on arbitrarily oriented planes, dose on the surface of anatomical objects, and isodose surfaces. Computer generated beam films are also available as an aid in patient set-up verification. These tools, and others, provide the basis for a comprehensive 3D system that can be used throughout the treatment planning process.     

CT模拟定位减少鼻咽癌放射治疗中的视神经剂量

目的：比较CT模拟定位治疗计划和常规普通模拟定位治疗计划治疗鼻咽癌时视神经的放射剂量。方法：对33例T1－T4期的鼻咽癌用Picker PQ5000螺旋CT及AcQPlan 4.1.1软件系统进行模拟定位。首先利用治疗计划系统上的数字重建的射线影像（DRR），根据患者的CT（或MRI）和临床检查结果，按照常规使用普通X射线模拟机拍摄定位片的定位方法设计出照射野。然后在所有CT层面逐层勾画出鼻咽肿瘤的大体肿瘤体积（GTV）、临床靶体积（CTV）和计划靶体积（PTV）。同时逐个勾画出周围重要顺官轮廓，特别小心勾画出眼球后视神经至视交叉的行程。根据肿瘤和周围重要器官之间在三维空间的相互关系设计合理的照射野。分别对两种治疗计划进行剂量计算，将靶中心剂量归一为100％，主要比较2种计划的肿瘤靶区、眼球和视神经最大放射剂量、平均剂量和中位剂量。同时比较2种计划放射野内视神经的长度。结果：不论是CT模拟计划还是常规模拟计划，鼻咽GTV和CTV均可有满意的剂量分布。但眼球、视神经和视交叉所接受的最大剂量、平均剂量和中位剂量都有显著差别。CT模拟计划中上述器官的受量明显低于常规计划。CT模拟计划可将更多的视神经保护在照射野外，避免不必要的照射。结论：CT模拟定位治疗计划减少了鼻咽癌放射治疗中视神经的放射剂量。     

Imaging-guided brachytherapy for locally advanced cervical cancer: the main process and common techniques

Brachytherapy (BT) delivers integrated boost doses to the central tumor while sparing the surrounding organs at risk (OARs) efficiently. It’s a mandatory treatment component for locally advanced cervical cancer (LACC) because it results in excellent overall survival and local control compared with other dose boosting modalities. Currently, BT is undergoing a transition from 2-dimensional (2D) to 3-dimensional (3D) treatment planning. Imaging-guided BT (IGBT) employing computed tomography (CT) or magnetic resonance imaging (MRI) can provide exact individual delineation of target and OARs meanwhile prescribe the dose to the target volume instead of “point A” for X-ray-based BT. There are three main techniques for BT: intracavitary (IC), interstitial (IS), and intracavitary/interstitial (IC/IS) combination. The applicator choice depends on the specific tumor extension. The real-time transabdominal ultrasound (US)-guided applicator placement technique is strongly recommended to ensure ideal applicator positioning. MRI is the ideal standard imaging for BT owing to its superior soft tissue visualization than CT. However, CT-based BT is more often performed because of the availability. In developing countries, US-based BT can be adopted. For treatment planning, the applicator reconstruction is easier on CT than on MRI, because the applicator image is more clearly visible. Individual treatment planning should be performed for every single applicator insertion to ensure dose accuracy. In this review article, we explain the main clinical process and common techniques, including the applicator choice and placement, imaging techniques, target delineation, and treatment planning; asthose will help to improve the efficiency of 3D BT.     

Four-dimensional proton treatment planning for lung tumors

PURPOSE: In proton radiotherapy, respiration-induced variations in density lead to changes in radiologic path lengths and will possibly result in geometric misses. We compared different treatment planning strategies for lung tumors that compensate for respiratory motion. METHODS AND MATERIALS: Particle-specific treatment planning margins were applied to standard helical computed tomography (CT) scans as well as to "representative" CT scans. Margins were incorporated beam specific laterally by aperture widening and longitudinally by compensator smearing. Furthermore, treatment plans using full time-resolved 4D-computed tomography data were generated. RESULTS: Four-dimensional treatment planning guaranteed target coverage throughout a respiratory cycle. Use of a standard helical CT data set resulted in underdosing the target volume to 36% of the prescribed dose. For CT data representing average target positions, coverage can be expected but not guaranteed. In comparison to this strategy, 4D planning decreased the mean lung dose by up to 16% and the lung volume receiving 20 Gy (prescribed target dose 72 Gy) by up to 15%. CONCLUSION: When the three planning strategies are compared, only 4D proton treatment planning guarantees delivery of the prescribed dose throughout a respiratory cycle. Furthermore, the 4D planning approach results in equal or reduced dose to critical structures; even the ipsilateral lung is spared.     

Correlation of neuropathologic findings,computerized tomographic and high-resolution ultrasound scans of canine avian sarcoma virus-induced brain tumors

The location, size, geometry and neuropathological findings of anaplastic astrocytomas (AA), gliosarcomas and sarcomas induced by the avian sarcoma virus (ASV) in dogs were compared with images generated using computerized tomography (CT) and real time high-resolution ultrasound (HRUS). Seven AA showed a wide range of findings on CT. Pre-contrast CT scans showed that the tumors could be hyper, hypo, or isodense. Three of seven AA had no contrast enhancement; two of these tumors were also isodense which resulted in a false-negative CT exam. Partial enhancement was seen in one tumor. This resulted in a sensitivity of detection of 72%. Real time HRUS was able to define tumor location, size and geometry of the AA missed or incompletely imaged by CT. All tumors were hyperechoic. Inhomogeneity of the echo pattern was due to hemorrhage, cyst formation, and necrosis within the tumors. Such secondary tumor characteristics were more accurately defined by HRUS compared to CT. Vasogenic edema in the brain surrounding tumors was of low density on CT and hypoechoic or indistinguishable from normal brain on US. Similar findings were seen in six gliosarcomas, two of which were not visualized by either pre- or post-contrast enhanced CT scans (sensitivity of 66%). Sarcomas differed in that they were either hyper or isodense; none were hypodense. The area of increased density matched the tumor geometry and correlated with dense cellularity and reticulin deposition. All 13 sarcomas showed contrast enhancement (100% sensitivity), but in two tumors, contrast enhanced CT underestimated the size of the tumor. Because of the large size and multiplicity of the sarcomas, HRUS imaging was not able to resolve the entire tumor volume because of limited imaging access. Intravenously injected horseradish peroxidase (HRP) crossed the tumor blood-brain barrier (BBB) only in those tumors in which contrast enhancement was seen. These studies suggest that intraoperative HRUS imaging may be useful in detecting and delineating human AA incompletely visualized by CT.     

鼻咽癌调强放疗中靶区和正常器官变化规律及临床意义探讨

目的探讨鼻咽癌调强放疗(IMRT)中靶区和正常器官变化规律。方法15例鼻咽癌初治患者接受全程IMRT,分别于计划设计前、治疗前、治疗25次时行3次CT扫描。第2、3次CT均和第1次CT行图像融合。3次CT图像的原发肿瘤(GTVnx)、GTVnx内气腔、腮腺、轮廓分别勾画,分析其变化规律。结果治疗计划完成时,有2例患者GTVnx增大。照射至25次时,GTVnx缩小0～10.39cm~3(即GTV内气腔容积);腮腺体积缩小0.13～23.80 cm~3;腮腺缩小程度与原体积大小有一定的相关性;腮腺外界向内侧移动,内界位置变化不大。头部轮廓横径均有不同程度缩小。结论鼻咽癌患者在接受IMRT过程中,原发肿瘤体积、腮腺结构、位置、轮廓横径在一定程度发生变化,这可能会影响IMRT剂量分布,降低靶区、增加正常组织剂量,值得临床进一步研究。     

Three-dimensional radiotherapy of head and neck and esophageal carcinomas: a monoisocentric treatment technique to achieve improved dose distributions

The specific aim of three-dimensional conformal radiotherapy is to deliver adequate therapeutic radiation dose to the target volume while concomitantly keeping the dose to surrounding and intervening normal tissues to a minimum. The objective of this study is to examine dose distributions produced by various radiotherapy techniques used in managing head and neck tumors when the upper part of the esophagus is also involved. Treatment planning was performed with a three-dimensional (3-D) treatment planning system. Computerized tomographic (CT) scans used by this system to generate isodose distributions and dose-volume histograms were obtained directly from the CT scanner, which is connected via ethernet cabling to the 3-D planning system. These are useful clinical tools for evaluating the dose distribution to the treatment volume, clinical target volume, gross tumor volume, and certain critical organs. Using 6 and 18 MV photon beams, different configurations of standard treatment techniques for head and neck and esophageal carcinoma were studied and the resulting dose distributions were analyzed. Film validation dosimetry in solid-water phantom was performed to assess the magnitude of dose inhomogeneity at the field junction. Real-time dose measurements on patients using diode dosimetry were made and compared with computed dose values. With regard to minimizing radiation dose to surrounding structures (i.e., lung, spinal cord, etc.), the monoisocentric technique gave the best isodose distributions in terms of dose uniformity. The mini-mantle anterior-posterior/posterior-anterior (AP/PA) technique produced grossly non-uniform dose distribution with excessive hot spots. The dose measured on the patient during the treatment agrees to within +/- 5 % with the computed dose. The protocols presented in this work for simulation, immobilization and treatment planning of patients with head and neck and esophageal tumors provide the optimum dose distributions in the target volume with reduced irradiation of surrounding non-target tissues, and can be routinely implemented in a radiation oncology department. The presence of a real-time dose-measuring system plays an important role in verifying the actual delivery of radiation dose.     

Open low-field magnetic resonance imaging in radiation therapy treatment planning

To evaluate the possibilities of an open low-field magnetic resonance imaging (MRI) scanner in external beam radiotherapy treatment (RT) planning.

A custom-made flat tabletop was constructed for the open MR, which was compatible with standard therapy positioning devices. To assess and correct image distortion in low-field MRI, a custom-made phantom was constructed and a software algorithm was developed. A total of 243 patients (43 patients with non-small-cell lung cancer, 155 patients with prostate cancer, and 45 patients with brain tumors) received low-field MR imaging in addition to computed tomographic (CT) planning imaging between January 1998 and September 2001 before the start of the irradiation.

Open low-field MRI provided adequate images for RT planning in nearly 95% of the examined patients. The mean and the maximal distortions 15 cm around the isocenter were reduced from 2.5 mm to 0.9 mm and from 6.1 mm to 2.1 mm respectively. The MRI-assisted planning led to better discrimination of tumor extent in two-thirds of the patients and to an optimization in lung cancer RT planning in one-third of the patients. In prostate cancer planning, low-field MRI resulted in significant reduction (40%) of organ volume and clinical target volume (CTV) compared with CT and to a reduction of the mean percentage of rectal dose of 15%. In brain tumors, low-field MR image quality was superior compared with CT in 39/45 patients for planning purposes.

The data presented here show that low-field MRI is feasible in RT treatment planning when image correction regarding system-induced distortions is performed and by selecting MR imaging protocol parameters with the emphasis on adequate images for RT planning.