Reduction of downtime and improvement of the utility of a conventional radiotherapy simulator

The modifications made to a radiotherapy simulator that improve its functionality and minimize its downtime are described. Functionality was enhanced with some simple effective improvements. Decreasing the frequency and time spent on repairs reduced downtime. These “in‐house” improvements were made to a Varian Ximatron simulator at the Tom Baker Cancer Center. Now there is easier access to the field light and optical distance indicator (ODI). Projections of the field light and ODI are much brighter and ODI adjustment is more reproducible. A crosshair was etched onto the clear x‐ray exit window to optically overlap with the crosshair of the reticule. Now, the time required to replace a field light is up to seven times faster and the time to realign a reticule is reduced to the order of three times faster. Only one quality control (QC) check is required after these adjustments. Removal of excess heat within the gantry head has eliminated two major problems: (A) the metal rod supporting the mirror assembly for the field light no longer expands and contracts causing a misalignment of the field light projection, and (B) the damage to the bearing in the cooling fan assembly has been eliminated. The simulator is now more functional and these improvements have reduced downtime significantly, making repairs and adjustments much more convenient and efficient.

PACS number(s): 87.53.Vb, 87.53.Xd

Complexity of human immune response profiles for CD4+ T cell epitopes from the diabetes autoantigen GAD65

Complex protein antigens contain multiple potential T cell recognition epitopes, which are generated through a processing pathway involving partial antigen degradation via proteases, binding to MHC molecules, and display on the APC surface, followed by recognition via the T cell receptor. We have investigated recognition of the GAD65 protein, one of the well-characterized autoantigens in type I diabetes, among individuals carrying the HLA-DR4 haplotypes characteristic of susceptibility to IDDM. Using sets of 20-mer peptides spanning the GAD65 molecule, multiple immunostimulatory epitopes were identified, with diverse class II DR molecules functioning as the restriction element. The majority of T cell responses were restricted by DRB1 molecules; however, DRB4 restricted responses were also observed. Antigen-specific T cell clones and lines were derived from peripheral blood samples of pre-diabetic and IDDM patients and T cell recognition and response were measured. Highly variable proliferative and cytokine release profiles were observed, even among T cells specific for a single GAD65 epitope.

Modulation of T cell response to hGAD65 peptide epitopes

Human CD4 T cell responses to an epitope of hGAD65 (GAD = glutamic acid decarboxylase), residues 555-567, are modulated by interaction with an altered peptide ligand containing modifications at TCR contact residues. Using different HLA-DR4 molecules with polymorphisms at sites corresponding to peptide binding pockets p1 and p9, we tested the effect of additional modifications in the altered peptide ligand (APL) designed to increase the avidity of the MHC-peptide interaction and therefore the efficiency of TCR signaling. Modification of the peptide or the MHC molecule which enhanced the p1 interaction also enhanced the antagonist activity of the modified APL. In contrast, modifications at p9 led to a reversal in APL function, resulting in agonist activity. Molecular homology modeling of these MHC-peptide interactions suggests a structural basis for this functional dichotomy in which topographically remote variations lead to unique interaction effects.