Immune surveillance of mouse brain perivascular spaces by blood-borne macrophages.

Virchow-Robin's perivascular spaces lie between the basement membrane around pericytes and the basement membrane at the surface of the glia limitans of the brain vessels. They are directly connected to the subpial space and harbour a population of cells distinct from pericytes, perivascular microglia and other cells within perivascular spaces (e.g. T cells and mast cells) in their ability to quickly phagocytose particles from the cerebrospinal fluid (CSF). Morphology, function, and cell surface proteins of these perivascular cells suggest an origin from the monocyte/macrophage lineage. It is currently unclear to what extent these brain perivascular cells represent a resident population of histiocytes or undergo continuous supplementation from blood monocytes. Using transplants of green-fluorescent-protein (GFP)-transfected bone marrow cells, we therefore investigated the replacement of perivascular cells by blood-borne macrophages in adult mice. GFP-positive cells in the perivascular spaces were found as early as 2 weeks post transplantation. The substitution of host perivascular cells by donor-derived macrophages was then evaluated using immunocytochemistry and intraventricular injection of hydrophilic rhodamine-fluorescent tracers. Such tracers diffuse along perivascular spaces and are subsequently phagocytosed by perivascular cells leading to stable phagocytosis-dependent labelling. Thus, the population of newly immigrated macrophages could be related to the total number of perivascular macrophages. This approach revealed a continuous increase of donor-derived perivascular cells. At 14 weeks post transplantation, all perivascular cells were donor-derived. These data show that brain perivascular cells are a population of migratory macrophages and not resident histiocytes.

Time requirements in conformal radiotherapy treatment planning.

To investigate the influence of implementing three-dimensional treatment planning on staffing needs, valid questionnaire responses from 22 radiotherapy institutions have been evaluated. Average time requirements per plan rise from 213 to 439 min upon implementation, but with experience decrease to 317 min. No institution reports additional staff positions according to estimated requirements.

On the quality of treatment planning systems in radiation therapy.

PURPOSE: To assist in the design of quality assurance activities of 3D treatment planning systems (TPSs), a postal survey has been carried out, addressing TPS users on quality characteristics and their relative importance in clinical routine planning. MATERIAL AND METHODS: The approach as described in ISO/IEC 9126 has been used to analyze TPS quality. Both TPS quality characteristics and how these may be used to establish a quality model are included. A questionnaire on ranking of these TPS quality characteristics has been sent out to the German DEGRO members in February 1997. RESULTS: By the end of July 1997, 90 individual assessments (of 45 physicists, 35 physicians, and 10 radiographers) had been collected. On an importance scale from 1 (very important) to 6 (unimportant), weight factors of 1.71 (portability), 2.84 (maintainability), 3.18 (efficiency), 3.85 (usability), 4.52 (functionality) and 4.90 (reliability) have been determined from the data. From user satisfaction data also obtained from the questionnaire responses, baseline quality indices could be established from the quality model for the RTPs Cadplan, TMS Helax, and Voxelplan. CONCLUSION: The responses highlight the need for TPS quality assurance at the same time along the lines of safety-related, research-oriented, and interactive end-user software systems in radiotherapy treatment planning. Quality assurance activities must take this into account. Their effect can be monitored by using quality indices as derivable from the established quality model.