A consistency monitor for radiation therapy treatments

A thin, large area transparent transmission chamber mounted below the accessory tray is described and its suitability for daily treatment delivery consistency is investigated. The sensitivity of the detector to changes in monitor unit setting, field size, wedge size, missing blocks, and wedges is presented. Some of the other potential applications are also discussed.

Quality assurance tool for high dose rate brachytherapy

An insert for a well ionization chamber is described for quality assurance tests for high dose rate remote afterloaders. The use of this insert over time has shown its applicability for efficient QA tests for the high dose rate afterloader. The measurement results are six times greater than the uncertainties involved for the measurements. Checks on position can be made better than 1 mm and dwell times better than 1 s. The overall measurements can be done to better than 1.5%. QA checks can be accomplished in a shorter time period with as great or better accuracy than prior film techniques.

Evaluation of 3-[18F]fluoro-alpha-fluoromethyl-p-tyrosine as a tracer for striatal tyrosine hydroxylase activity

3-[18F]Fluoro-alpha-fluoromethyl-p-tyrosine (3-F-FMPT) was evaluated as a tracer for CNS tyrosine hydroxylase (TH) activity in rodents and in a rhesus monkey. Results of in vitro experiments using rat striatal homogenates showed that the introduction of fluorine into the 3-phenyl position did not significantly alter the ability of FMPT to act as a TH-activated L-aromatic amino acid decarboxylase (L-AAAD) inhibitor. These studies further showed that 3-F-FMPT-induced L-AAAD inhibition was dose-dependent. Furthermore, striatal homogenates prepared from rats pretreated with the potent TH inhibitor alpha-methyl-p-tyrosine was found to have diminished 3-F-FMPT-induced L-AAAD inhibition. However, despite these promising in vitro results, the biodistribution of this compound in mice showed low brain uptake and fast clearance through the kidneys. A PET study using a Rhesus monkey injected with 3-[18F]F-FMPT confirmed the results obtained in mice, i.e. negligible brain uptake but high localization in the bladder. We conclude that 3-[18F]F-FMPT would not be useful as a tracer for cerebral TH activity.

Alpha-interferon (Wellferon) as an adjunct to standard surgical therapy in the management of recurrent respiratory papillomatosis

Ten patients received lymphoblastoid alpha-interferon (Wellferon) in a crossover study so that Wellferon and standard microsurgical laryngeal laser therapy could be compared to laser therapy alone. Wellferon was administered initially at an intravenous high dose of 15 megaunits/m2 for 5 days followed by a daily dose of 2 megaunits/m2 subcutaneously for 6 months. Dosage was adjusted according to predefined toxicity. One patient was withdrawn from the study. Of the others, all but one received over 75% of the planned total dose. At follow-up of the nine assessable patients, complete remission was achieved in two of them, partial remission in four, and no response in the remainder. The two complete remissions were sustained for 2 years, but the four partial remissions were not sustained. Thus, a role for alpha-interferon in the kind of regimen used here remains to be established.

The actions of some esters of 4-hydroxyquinuclidine on guinea-pig ileum, atria and rat fundus strip

1 The acetyl, phenylacetyl, and diphenylacetyl esters of 4-hydroxyquinuclidine and their methiodides have been prepared.2 4-Diphenylacetoxyquinuclidine methiodide has higher affinity for muscarinic receptors than 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP methiodide) but it is less selective. At 30 degrees C its affinity for receptors in ileum is about 5 times that for receptors in atria, a difference similar to that found with diphenylacetoxytrophine methiodide. With 4-DAMP methiodide affinity for receptors in the ileum is over 10 times that for receptors in atria.3 4-Diphenylacetoxyquinuclidine methiodide has higher affinity for muscarinic receptors than 3-diphenylacetoxyquinuclidine hydrochloride or its methiodide.4 4-Acetoxyquinuclidine hydrochloride has less than one-hundredth of the activity of 3-acetoxyquinuclidine hydrochloride (acecyclidine) on guinea-pig ileum, atria, and rat fundus: however, 4-acetoxyquinuclidine methiodide is consistently more active than its 3-isomer, though it is only about 1/25 times as active as acecyclidine.5 4-Acetoxyquinuclidine hydrochloride is only a poor substrate for electric eel acetylcholinesterase: its affinity is similar to that of acecyclidine but it is greatly reduced by methylation.6 The relations between the structure and activity of the agonists are very different from the relations between the structure and affinity of the antagonists, which supports the view that agonists and antagonists bind to different conformations of the muscarinic receptor.