Magnetic resonance imaging and high-resolution computed tomography in tumors of the lung and the mediastinum

CT for Predicting the Resectability of Lung Cancer

In order to assess the accuracy of CT in predicting the resectability of lung cancer, a prospective study was performed on 96 patients undergoing thoracotomy. The tumors were classified preoperatively according to the TNM classification and the new international staging system for lung cancer, and scored as being resectable by lobectomy or pulmectomy, potentially resectable by lobectomy or pulmectomy, or nonresectable. Of the tumors predicted to be resectable or potentially resectable, 86.6% and 63% were radically resected, respectively, and the need for lobectomy versus pulmectomy was correctly estimated in 81.3% of them. The insufficiency of CT for defining lymph node metastases and infiltrative tumor growth was considered a marked disadvantage of the method.

Design of MRI scan protocols for use in 3-D, CT-based treatment planning

MRI has the potential of providing the radiation therapy treatment planner with new insights into the definition of target and normal tissue volumes to augment CT in 3-D treatment planning. The current speed of MR scan sequences is not sufficient to enable the acquisition of both T1 and T2 weighted images in all three orthogonal planes in a reasonable period of time. Therefore, compromises must be made in the design of protocols specifically for use in radiotherapy planning which: (1) provide enough information to readily enable image registration; (2) preserve the three-dimensionality provided by image acquisition directly in coronal and sagittal planes; (3) yield tissue contrast as well as tumor specificity (where available); but (4) can be completed in a short enough span of time (or with enough checks) that the patient position is not compromised. Protocols designed for use in planning treatment of the brain, head and neck, lung, prostate, cervix, and sarcomas are presented.

State-of-the-art of external photon beam radiation treatment planning. Photon Treatment Planning Collaborative Working Group

A virtual revolution in computer capability has occurred in the last few years, largely based on rapidly decreasing costs and increasing reliability of digital memory and mass-storage capability. These developments have now made it possible to consider the application of both computer and display technologies to a much broader range of problems in radiation therapy, including planning of treatment, dose computation, and treatment verification. Several methods of three-dimensional dose computations in heterogeneous media capable of 3% accuracy are likely to be available, but significant work still remains, particularly for high energy x-rays where electron transport, and possibly pair production, need to be considered. Innovative display and planning techniques, as well as plan evaluation schemes, are emerging and show great promise for the future. No doubt these advances will lead to substantially improved treatment planning systems in the next few years. However, it must be emphasized that for many of these applications a tremendous software and hardware development effort is required.