[In vivo dosimetry and radiographic confirmation in radiotherapy of Hodgkin's lymphoma]. / Dosimetria in vivo e verifica radiografica nella radioterapia del linfoma di Hodgkin.

In September 1991 a protocol for quality control of large shaped irradiation fields was started in our department. In vivo dosimetry with semiconductor detectors was used to measure the absorbed dose and patient positioning was checked with portal films weekly. First, we set a computed dosimetric system yielding dosimetric values in real time and allowing their easy storage. Then, we calibrated the diodes and determined the correction factors for each of them outside standard conditions. Entrance dose, exit dose and midline dose were measured in 62 patients undergoing supradiaphragmatic radiation therapy for Hodgkin's lymphoma. The exist dose was measured weekly to assess treatment repeatability. High agreement was observed between measured and calculated doses; repeatability was also high, since only 6% of exit dose measurements exceeded 5% of the first determination. In 33 patients portal films were obtained in the first treatment session, and thereafter weekly, to assess mispositioning relative to simulation (reproducibility) and from one session to another (repeatability). A small systematic error was detected in both longitudinal (x = -3 mm; SD = 3.7 mm) and transverse (x = -2 mm; SD = 3.4 mm) directions. Statistically significant errors (> 6 mm) were observed in 14% of patients. Reproducibility was excellent. The protocol reported on in this paper not only helps avoid systematic dosimetric and/or positioning errors in the patients, but also helps identify the main causes of uncertainty and thus remove them.

Digital dynamic range expansion applied to X-ray densitometric analysis of total hip replacement.

Due to the presence of the stiff prosthetic stem fitted in the medullary canal during total hip replacement, the surrounding cortex of the femur changes its density over time. This bone remodelling takes place with every type of total hip prosthesis; however, its intensity may vary between prostheses and patients. In the worst cases this process can lead to the late failure of the implant. To monitor such bone density evolution, we are developing a tailored Computer-aided Densitometric Image Analysis system (the major part of this our system uses an 8-bit commercial hardware with 256 levels of grey). The equivalent dynamic range of an X-ray picture is about 10 bits. In this paper we present a method to overcome these hardware limitations by improving the software. Using a double-exposure acquisition it is possible to build a 9-bit image that is good enough for most applications involving bone density measurement.

133Xe regional lung perfusion and ventilation study with the computer-assisted gamma-camera.

A new method of studying regional lung functions using 133Xe and the computer-assisted scintillation camera is described. The method and the computer processing give details of the distribution of 133Xe during perfusion and ventilation and also measures of lung function. Some cases are described in detail, and the clinical significance of the method was confirmed in 45 cases.