We used a computerized microscopic image analysis system to directly measure the surface area of distal air spaces in methacrylate-embedded blocks randomly selected from inflation-fixed lobes that were resected from 45 patients as treatment of their peripheral lung tumors. In 28 of these patients, a preoperative computer tomography (CT) scan, at 6 and 10 cm below the sternal notch, was used to generate frequency histograms of CT numbers (measured as EMI units), a measure of lung density, in pixels from the lung or lobe that was subsequently resected. A similar CT number histogram was also derived from the lateral two fifths of the area of lobe/lung that was to be resected. The EMI unit that defined the lowest fifth percentile of this latter histogram correlated (n = 28, r = -0.77, p less than 0.001) with the mean value of the surface area of the walls of distal airspaces per unit lung volume (AWUV) in the five 1 mm x 1 mm microscopic fields with the lowest AWUV values, out of the 20 to 35 such fields examined in each patient. In the 34 of the 45 patients in whom we also measured volume-corrected diffusing capacity (DLCO/VA), this also correlated (n = 34, r = 0.84, p less than 0.001) with this value of AWUV, which measures the surface area of airspaces distal to the terminal bronchioles--reflecting an increase in airspace size, a defining characteristic of emphysema. However, a low DLCO/VA is nonspecific, whereas an abnormally low regional lung density is more likely to be specific for emphysema. In addition, highlighting those pixels of the CT display with low CT numbers (i.e., EMI units -500 [air] to -450, where zero = water) can locate areas of macroscopic emphysema, as shown by subsequent pathologic examination. Thus the quantitative CT scan can diagnose, quantitate, and locate mild to moderate emphysema, in humans, in life, noninvasively.

All subjects underwent CT scanning of the lungs and respiratory function testing within 2 days of each other. In five of the asthmatic patients a CT scan was performed on two occasions before and after treatment with nebulized bronchodilator. In a different group of five asthmatics these measurements were performed at the end of and 6 weeks after an exacerbation.The mean value of the lowest fifth percentile of the CT lung density in the patients with chronic obstructive pulmonary disease (COPD) was -942 (SD 36) Hounsfield units (HU), in the 17 asthmatic patients was -912 (34) HU, and in normal subjects was -880 (13). Despite a significant increase in peak expiratory flow rate from 266 (SD 102) to 406 (83) L·s -1 (p<0.02) following nebulized β 2 -agonist in five patients with chronic asthma, there was no significant change in CT lung density (p>0.05) Our study indicates that at least some patients with chronic, stable asthma develop a reduction in computed tomography lung density, similar to that in patients with emphysema.

No abstract

Previous attempts at optimization of radiotherapy planning are described and criticized, and consideration of these attempts has resulted in the development of a new technique using quadratic programming. Uniformity of tumour dose is selected as the most important feature of any plan, and this is achieved by minimizing the variance of the dose to preselected points within the tumour. The dose to vulnerable regions can be constrained not to exceed a given percentage of the mean tumour dose. Optimization of field weight and field type is possible. The operation of the system is described and some typical results are given.

No abstract