ISSN:0899-9457    

DOI:10.1002/ima.1850060102

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThis article presents personal view of an approach to the radiotherapy optimization problem using techniques of classical analysis. This, together with its limitations, can be seen in a broader context in the recent review by Brahme [3].

ISSN:0899-9457    

DOI:10.1002/ima.1850060103

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractModern photon radiotherapy optimization methods require the use of a number of nonuniform dose distributions incident on the tumor. From this point of view, radiotherapy optimization has strong similarities with the reconstruction problem in tomographic imaging. In general, the image reconstruction problem is simpler because in the absence of noise and with sufficiently many projections and exact solution always exists. However, it is in general impossible by external beam irradiation to produce an arbitrary desired dose distribution in the patient. This is primarily because the order of events from physical collection of projection data to reconstruction theory is reversed in therapy optimization, starting with the theory and ending with physical irradiation, where negative dose delivery is impossible. Despite this fundamental problem, many approximate image reconstruction methods work quite well for therapy optimization even though strict optimization requires radiobiological models and the finest external beam radiation tool available: the pencil beam.

ISSN:0899-9457    

DOI:10.1002/ima.1850060104

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractBy and large, radiation therapy is a noninvasive method of the treatment of cancer requiring knowledge of the precise location and extent of the disease to be destroyed and the organs to be protected from radiation damage. Images have always played a central role in providing the requisite information for this mode of cancer treatment. Different types of images, such as computed tomography (CT); magnetic resonance imaging (MRI), positron emission tomographic (PET), simulator, etc., are used to varying degrees depending upon their relevance to radiation oncology as well as their accessibility. It is often necessary to merge data from various types of images. The availability of three‐dimensional information from tomographic images has allowed the introduction of three‐dimensional conformal radiation therapy (3DCRT) methods. Images are employed for diagnosing and establishing the extent of the disease, planning and delivery treatments, and evaluating the effectiveness of the treatment in controlling the disease and assessing the damage to normal tissues. Each image type has a unique informational content of importance to radiation oncology. To extract the maximum information from images, it is necessary to employ various image processing tools. These tools allow us to perform such functions as (1) image enhancement; (2) image correlation to register information from various images; (3) segmentation of images to extract the surface outlines of the tumor volume and normal anatomic structures; and (4) two‐ and three dimensional data visualization. One important aspect of planning radiation treatments is the computation of dose distribution in the patient for a proposed configuration of radiation beams. This step requires tracing rays in a three‐dimensional CT image data set to compute radiologic path lengths through the patient's body. Although images are employed to a great advantage in radiation oncology, many problems still remain to be solved. Of the various 3DCRT tasks, the outlining of contours of the volume of intended treatment and normal anatomy on images is highly labor‐intensive and fraught with uncertainty. In addition, the integration of data from various imaging modalities is difficult and error prone because of distortions inherent in imaging and also because of the motion, deformation, and displacement of patients and their internal anatomy. Investigations are in progress to find solutions to these

ISSN:0899-9457    

DOI:10.1002/ima.1850060105

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractOver the last decade a large number of new treatment techniques have been developed to allow a true optimization of the delivered dose distribution in radiation therapy. The most important clinical requirement of most optimization techniques is to be able to deliver strongly nonuniform beams on the patient from arbitrary directions. For very complex tumors the number of beams required to eradicate the tumor without severe injury to normal tissues is quite high, to accurately make the three dimensional dose distribution conform to the target volume. For more simple target geometries fewer beams are sufficient, and in many cases with small tumors the classical uniform rectangular beams will do nicely. A number of new treatment techniques, from narrow beam robot mounted linear accelerators through fan beam devices using linear multileaf collimation in rotary gantries, to the most flexible external beam devices with scanned electron and photon beams and/or dynamic multileaf collimation available over the whole treatment field, are now rapidly coming into clinical use.

ISSN:0899-9457    

DOI:10.1002/ima.1850060106

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn contemporary radiotherapy dose optimization, radiation beams and beam modifiers are iteratively selected until the dose distribution is acceptable. Another approach, referred to as the “inverse problem,” is: Given the dose prescription, compute the optimal set of photon beams while preventing unphysical solutions such as negative beam weights, and iterate to achieve the prescription as closely as possible. This solution to this inverse problem, which uses image reconstruction mathematics, entails the delivery of large numbers of nonuniform beam intensities to produce uniform dose distributions. These dose distributions can be arranged to conform very closely to even complex target volumes, yet spare surrounding sensitive tissue. Alternatively, the dose distributions can be arranged to generously treat a regional field and “conformally avoid” overtreating sensitive volumes within the field. Multiple dose prescriptions can be delivered without additional effort. We propose that a practical way of delivering optimized dose distributions would be to intensity modulate a photon beam, using collimator leaves intersecting a slit field of radiation. Modulation is achieved by varying the time that the leaves are blocking the field. A practical geometry to deliver such a beam is a computed tomography‐like gantry configuration, which also lends itself to tomographic setup verification of dose delivered to the patient. We refer to such a delivery method as “tomotherapy.” Several types of tomotherapy simulations have been conducted. A fully three dimensional optimized treatment planning system using iterative filtered back‐projection have been developed. We will present examples of conformal plans for breast and prostate radiotherapy. We have constructed an experimental apparatus for simulating helical tomotherapy delivery by simultaneously rotating and longitudinally translating a phantom past an intensity‐modulated fan beam. A comparison between a computation and and experimentally realized plan is presented. A Monte Carlo simulation of the angular distribution and energy fluence spectrum of 10‐MV photons produced by a tungsten target have been used to estimate the optimized shape and mass of a primary shielding required to meet r

ISSN:0899-9457    

DOI:10.1002/ima.1850060107

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0899-9457    

DOI:10.1002/ima.1850060108

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mathematical problem of generating a desired dose distribution in a patient who has to undergo external beam radiotherapy is closely related to the problem of reconstructing an image from its projections. Under some simplifying assumptions the theory of the exponential Radon transform as developed for SPECT image reconstruction can be successfully applied to the field of radiotherapy. This results in a projection‐filtering algorithm for the calculation of optimal beam profiles. The method yields analytical solutions for circular and triangular dose distributions, and combinations thereof. Practical solutions for arbitrary cases can be found numerically. The problem of unphysical negative values in the calculated beam profiles is solved by a method combining “cutting off” and “sh

ISSN:0899-9457    

DOI:10.1002/ima.1850060109

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe role of simulated annealing in therapy planning is discussed from a historical, theoretical and practical viewpoint. The properties of the method are discussed in detail together with available options and specific implementations.

ISSN:0899-9457    

DOI:10.1002/ima.1850060110

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractConformal therapy offers considerable advantages over conventional radiotherapy treatment, because it has the potential for matchingalmost exactlythe delivered dose distribution to the prescribed dose distribution. Associated (inverse) treatment planning methods address a constrained linear optimization problem. In this article, a method based on maximizing the total entropy of the beam profiles is developed. Maximum entropy optimization constrains the computed dose to be within well‐defined tolerances of the prescribed dose, and has advantages of robustness, fast convergence, and high accuracy. For the work reported here, it is assessed using clinically prescribed irregular target dose volumes based on magnetic resonance imaging and computed tomography images. Results are shown for a two‐dimensional, homogeneous absorption, primary dose computation model, to illustrate the feasibility of the approach; however, the method may be extended to accommodate a more general three‐dimensional model, including inhomogeneities and scatter dose contributions. Optimization of beam offset for a regular angular displacement of beams is also considered, with particular regard to implications on total beam energy, entropy, and computation

ISSN:0899-9457    

DOI:10.1002/ima.1850060111

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY