MEDLINE Abstracts: New Imaging Techniques in Radiation Oncology
Stroom JC, Storchi PR
Physics in Medicine & Biology 42(4):745-55, 1997 Apr

Following the publication of ICRU Report 50, the concepts of GTV (gross tumour volume). CTV (clinical target volume) and PTV (planning target volume) are being used in radiotherapy planning with increasing frequency. In 3D planning, the GTV (or CTV) is normally outlined by the clinician in CT or MRI slices. The PTV is determined by adding margins to these volumes. Since manual drawing of an accurate 3D margin in a set of 2D slices is extremely time consuming, software has been developed to automate this step in the planning. The target volume is represented in a 3D matrix grid with voxel values one inside and zero outside the target volume. It is expanded by centering an ellipsoid at every matrix element within the volume. The shape of the ellipsoid reflects the size of the margins in the three main orthogonal directions. Finally, the PTV contours are determined from the 50% iso-value lines of the expanded volume. The software tool has been in clinical use since the end of 1994 and has mostly been applied to the planning of prostate irradiations. The accuracy is better than can be achieved manually and the workload has been reduced considerably (from 4 h manually to approximately 1 min automatically).









Khoo VS, Dearnaley DP, Finnigan DJ, Padhani A, Tanner SF, Leach MO
Radiotherapy & Oncology 42(1):1-15, 1997 Jan

The emerging utilisation of conformal radiotherapy (RT) planning requires sophisticated imaging modalities. Magnetic resonance imaging (MRI) has introduced several added imaging benefits that may confer an advantage over the use of computed tomography (CT) in RT planning such as improved soft tissue definition, unrestricted multiplannar and volumetric imaging as well as physiological and biochemical information with magnetic resonance (MR) angiography and spectroscopy. However, MRI has not yet seriously challenged CT for RT planning in most sites. The reasons for this include: (1) the poor imaging of bone and the lack of electron density information from MRI required for dosimetry calculations; (2) the presence of intrinsic system-related and object-induced MR image distortions; (3) the paucity of widely available computer software to accurately and reliably integrate and manipulate MR images within existing RT planning systems. In this review, the basic principals of MRI with its present potential and limitations for RT planning as well as possible solutions will be examined. Methods of MRI data acquisition and processing including image segmentation and registration to allow its application in RT planning will be discussed. Despite the difficulties listed, MRI has complemented CT-based RT planning and in some regions of the body especially the brain, it has been used alone with some success. Recent work with doped gel compounds allow the MRI mapping of dose distributions thus potentially providing a quality assurance tool and in a manner analogous to CT, the production of dose-response information in the form of dose volume histograms. However, despite the promise of MRI, much development research remains before its full potential and cost-effectiveness can be assessed.









Lichter AS, Ten Haken RK
Important Advances in Oncology :95-109, 1995

Three-dimensional treatment planning and conformal dose delivery have the potential to increase the effectiveness of radiation treatments. For the first time, it is possible to ensure that the intended target is being treated with the full, desired dose. By restricting the high dose region to conform more closely to the shape of the target, normal tissues receive a smaller percentage of the dose, allowing doses to be escalated to the target. New equipment, including multileaf collimators and computer-controlled treatment machines, along with faster and more sophisticated planning systems, are making 3-D planning and treatment delivery increasingly practical. The final impact of these new techniques on the ultimate outcome of a course of radiation will be ascertained through continuing clinical experience and through ongoing clinical trials.









Thomas FJ, Wood G
In Vivo 8(5):707-11, 1994 Nov-Dec

Despite advances in oncology, the local control of malignancies remains a formidable challenge. For the radiation oncologist, this challenge is approached by greater precision in the definition of the tumor and normal tissue with the intent of encompassing the former and excluding the latter from the high dose volume of treatment. Advances in diagnostic imaging have been incorporated into radiation therapy planning to achieve this goal. Recent developments in three dimensional treatment planning of CNS and pelvic malignancies illustrate the extent to which radiation oncology has come to rely on diagnostic imaging and the promise it offers for improvement in clinical care.









Ten Haken RK, Fraass BA, Kessler ML, McShan DL
Bulletin du Cancer 82 Suppl 5:592s-600s, 1995 Dec

Advances in computer technology have led to the availability of sophisticated three-dimensional treatment planning systems for use in many radiotherapy centers. However, additional complexity in both the planning and delivery of treatments has accompanied their use. Thus, even more computer-aided tools are beginning to appear to address these needs. Aspects of recent enhancements to 3-D treatment planning at the University of Michigan are presented.









Leichner PK, Koral KF, Jaszczak RJ, Green AJ, Chen GT, Roeske JC
Medical Physics 20(2 Pt 2):569-77, 1993 Mar-Apr

Planar and tomographic imaging techniques and methods of treatment planning in clinical radioimmunotherapy are reviewed. In clinical trials, the data needed for dosimetry and treatment planning are, in most cases, obtained from noninvasive imaging procedures. The required data include tumor and normal organ volumes, the activity of radiolabeled antibodies taken up in these volumes, and the pharmacokinetics of the administered activity of radiolabeled antibodies. Therefore, the topics addressed in this review include: (1) Volume determination of tumors and normal organs from x-ray-computed tomography and magnetic resonance imaging, (2) quantitation of the activity of radiolabeled antibodies in tumors and normal organs from planar gamma camera views, (3) quantitative single-photon emission computed tomography and positron emission tomography, (4) correlative image analysis, and (5) treatment planning in clinical radioimmunotherapy.