Photon dose at the maze entrance door: The comparison of flattening filter and flattening filter free working modes.

In recent years, field flattening free accelerators have been introduced in therapy practice. One of the objective of these measurements was to establish if the maze door, designed for accelerators operating with flattening filter can provide adequate shielding in field flattening free mode of operation. Linac installed in this standard one band maze vault is equipped to operate at 6 MV with field flattening filter and in field flattening free mode of operation. Series of measurements of the photon dose at the maze door (with different jaws openings and gantry positions) were performed in both operation modes with and without water canister to mimic standard therapy conditions. In this paper results of photon dose measurements, performed at the maze door of the therapy linear accelerator vault are presented in order to compare photon dose in flattening filter and flattening filter free operation modes. It was obtained that in field flattening free mode of operation, the dose at the maze door is always lower than the dose measured in standard mode of operation with the field flattening filter. In the case when FFF therapy practice should start in some existing therapy vault, no additional shielding measures need to be added at the existing maze door.

The evaluation of the neutron dose equivalent in the two-bend maze.

The purpose of this study was to explore the effect of the second bend of the maze, on the neutron dose equivalent, in the 15MV linear accelerator vault, with two bend maze. These two bends of the maze were covered by 32 points where the neutron dose equivalent was measured. There is one available method for estimation of the neutron dose equivalent at the entrance door of the two bend maze which was tested using the results of the measurements. The results of this study show that the neutron equivalent dose at the door of the two bend maze was reduced almost three orders of magnitude. The measured TVD in the first bend (closer to the inner maze entrance) is about 5m. The measured TVD result is close to the TVD values usually used in the proposed models for estimation of neutron dose equivalent at the entrance door of the single bend maze. The results also determined that the TVD in the second bend (next to the maze entrance door) is significantly lower than the TVD values found in the first maze bend.

Schwann cell differentiation of modified myoepithelial cells within adenoid cystic carcinomas and polymorphous low-grade adenocarcinomas: clinicopathologic assessment of immunohistochemical staining.

Adenoid cystic carcinomas and polymorphous low-grade adenocarcinomas have a known propensity for perineural invasion. Although modified myoepithelial cells have been shown to possess characteristics of a variety of cell types, they have not yet been found to mimic nerve tissue. Histologic evidence of Schwann cell differentiation would suggest the pathophysiologic mechanism by which these tumours exhibit neurotropism. An archival study of 41 specimens was performed to evaluate the Schwann cell staining properties of adenoid cystic and polymorphous low-grade adenocarcinomas using antibodies to S-100 protein, GFAP, neuron-specific enolase, and using a solochrome stain. Charts were reviewed to assess correlations between immunohistochemical and histochemical staining properties and various clinical parameters. The findings strongly suggest that neuronal differentiation does occur within these tumours. Furthermore, it was determined that solochrome positivity confers a significantly less favourable disease-free interval in these neoplasms. This new finding was highly statistically significant and has potential implications in the determination of prognosis for patients with these tumours.

Intratympanic gentamicin therapy for Menière's disease: preliminary comparison of two regimens.

Selective chemical ablation of the vestibular endorgan using intratympanic gentamicin is an effective and safe treatment for incapacitating vertigo in patients with unilateral Menière's disease. A major risk of the treatment is sensorineural hearing loss. In this retrospective study, two different regimens of intratympanic gentamicin therapy are compared. In one group, multiple daily doses were administered in hospital over 4 consecutive days. The other group received single treatments at weekly intervals on an outpatient basis, following pretreatment audiometric and clinical assessment. We adopted the weekly protocol to theoretically reduce the incidence of treatment-related hearing loss by a more controlled titration of dosing. Preliminary results indicate that the weekly interval treatment offers equivalent efficacy with considerably less risk to hearing.