Calculation of 10 MV x-ray spectra emitted by a medical linear accelerator using the BFGS quasi-Newton method

To calculate photon spectra for a 10 MV x-ray beam emitted by a medical linear accelerator, we performed numerical analysis using the aluminium transmission data obtained along the central axis of the beam under the narrow beam condition corresponding to a 3x3 cm2 field at a 100 cm distance from the source. We used the BFGS quasi-Newton method based on a general nonlinear optimization technique for the numerical analysis. The attenuation coefficients, aluminium thicknesses and measured transmission data are necessary inputs for the numerical analysis. The calculated x-ray spectrum shape was smooth in the lower to higher energy regions without any angular components. The x-ray spectrum acquired by the employed method was evaluated by comparing the measurements along the central axis percentage depth dose in a water phantom and by a Monte Carlo simulation code, the electron gamma shower code. The values of the calculated percentage depth doses for a 10x10 cm2 field at a 100 cm source-to-surface distance in a water phantom were obtained using the same geometry settings as those of the water phantom measurement. The differences in the measured and calculated values were less than +/-1.0% for a broad region from the shallow part near the surface to deep parts of up to 25 cm in the water phantom.

Increase in the number of lymphocytes secreting IgG following blood transfusion

A sequential change in the number of circulating immunoglobulin (Ig) secreting cells of each Ig class following blood transfusion was studied using a reverse hemolytic plaque assay. The subjects studied were in two main groups, immunologically normal individuals and patients with malignant lymphoma or multiple myeloma who are, presumably, immune incompetent. A consistent increase in circulating IgG-secreting cells, along with either an earlier or simultaneous increase in IgM-secreting cells, was observed following blood transfusion in the immunologically normal individuals. An increase in IgA-secreting cells was also observed, but at a minimal magnitude. Such an increase was not apparent in patients with lymphoma or myeloma. The possible use of blood transfusion as a means of "challenging and checking" for the state of immune responsiveness in vivo is discussed.

Effects of corrective surgery on natural history of atrial septal defect of secundum type

Two hundred and seventy-eight patients with atrial septal defect of secundum type were operated on surgical closure of the defect. The patients were divided into 5 groups according to age at surgery, and preoperative complaints and laboratory findings were analyzed to evaluate natural history. As year passed, incidence of complaints increased. Cardiothoracic ratio (CTR), systolic pressure of the right ventricle (PRVS), end-diastolic pressure of the right ventricle (RVEDP), mean pressure of the right atrium (PRAm), ratio of pulmonary to systemic systolic pressure (PPA/PS), right ventricular dimension (RVD) and left atrial dimension (LAD) increased significantly, while frontal axis of the QRS complex, RV1, SV1 +RV5 and LVD decreased. No chronological changes were seen in ratio of pulmonary to systemic blood flow (QPA/QS) and ratio of pulmonary to systemic vascular resistance (RPA/RS). The first and second decades of life were considered to be stable stages of the disease. Postoperatively, changes in the above-mentioned parameters were compared in each age group, and effects of surgical repair on natural history were evaluated. Of 265 survivors, 168 were followed-up for more than one year, the longest period being 22 years. CTR, frontal axis, RV1, PRVS, RVEDP, PPA/PS and RVD decreased significantly, while SV1 + RV5, RPA/RS and LVD increased. No changes were seen in LAD. Surgical effects appeared most significantly in the first decade and least in the fifth or more. From these findings it would be concluded that corrective surgery should be best carried out in the first decade, at latest in the second, though not to be contraindicated by age alone. Otherwise, postoperative improvement of parameters delays or hemodynamical abnormalities may persist regardless of considerable clinical improvement.