Monte carlo electron source model validation for an Elekta Precise linac.

PURPOSE: Electron radiation therapy is used frequently for the treatment of skin cancers and superficial tumors especially in the absence of kilovoltage treatment units. Head-and-neck treatment sites require accurate dose distribution calculation to minimize dose to critical structures, e.g., the eye, optic chiasm, nerves, and parotid gland. Monte Carlo simulations can be regarded as the dose calculation method of choice because it can simulate electron transport through any tissue and geometry. In order to use this technique, an accurate electron beam model should be used. METHODS: In this study, a two point-source electron beam model developed for an Elekta Precise linear accelerator was validated. Monte Carlo data were benchmarked against measured water tank data for a set of regular and circular fields and at 95, 100, and 110 cm source-to-skin-distance. EDR2 Film dose distribution data were also obtained for a paranasal sinus treatment case using a Rando phantom and compared with corresponding dose distribution data obtained from Monte Carlo simulations and a CMS XiO treatment planning system. A partially shielded electron field was also evaluated using a solid water phantom and EDR2 film measurements against Monte Carlo simulations using the developed source model. RESULTS: The major findings were that it could accurately replicate percentage depth dose and beam profile data for water measurements at source-to-skin-distances ranging between 95 and 110 cm over beam energies ranging from 4 to 15 MeV. This represents a stand-off between 0 and 15 cm. Most percentage depth dose and beam profile data (better than 95%) agreed within 2%/2 mm and nearly 100% of the data compared within 3%/3 mm. Calculated penumbra data were within 2 mm for the 20 x 20 cm2 field compared to water tank data at 95 cm source-to-skin-distance over the above energy range. Film data for the Rando phantom case showed gamma index map data that is similar in comparison with the treatment planning system and the Monte Carlo source model. The gamma index showed good agreement (2%/2 mm) between the Monte Carlo source model and the film data. CONCLUSIONS: Percentage depth dose and beam profile data were in most cases within a tolerance of 2%/2 mm. The biggest discrepancies were in most cases recorded in the first 6 mm of the water phantom. Circular fields showed local dose agreement within 3%/3mm. Good agreement was found between calculated dose distributions for a paranasal sinus case between Monte Carlo, film measurements and a CMS XiO treatment planning system. The electron beam model can be easily implemented in the BEAMnrc or DOSXYZnrc Monte Carlo codes enabling quick calculation of electron dose distributions in complex geometries.

Biomaterial-based technologies for brain anti-cancer therapeutics and imaging.

Treating malignant brain tumors represents one of the most formidable challenges in oncology. Contemporary treatment of brain tumors has been hampered by limited drug delivery across the blood-brain barrier (BBB) to the tumor bed. Biomaterials are playing an increasingly important role in developing more effective brain tumor treatments. In particular, polymer (nano)particles can provide prolonged drug delivery directly to the tumor following direct intracerebral injection, by making them physiochemically able to cross the BBB to the tumor, or by functionalizing the material surface with peptides and ligands allowing the drug-loaded material to be systemically administered but still specifically target the tumor endothelium or tumor cells themselves. Biomaterials can also serve as targeted delivery devices for novel therapies including gene therapy, photodynamic therapy, anti-angiogenic and thermotherapy. Nanoparticles also have the potential to play key roles in the diagnosis and imaging of brain tumors by revolutionizing both preoperative and intraoperative brain tumor detection, allowing early detection of pre-cancerous cells, and providing real-time, longitudinal, non-invasive monitoring/imaging of the effects of treatment. Additional efforts are focused on developing biomaterial systems that are uniquely capable of delivering tumor-associated antigens, immunotherapeutic agents or programming immune cells in situ to identify and facilitate immune-mediated tumor cell killing. The continued translation of current research into clinical practice will rely on solving challenges relating to the pharmacology of nanoparticles but it is envisioned that novel biomaterials will ultimately allow clinicians to target tumors and introduce multiple, pharmaceutically relevant entities for simultaneous targeting, imaging, and therapy in a unique and unprecedented manner.

Camel (Camelus dromedarius) contagious ecthyma in the Sudan. A case report.

The clinical and pathological features of the contagious ecthyma in camel calves in the Sudan were investigated. The animals were inappetant, emaciated and slightly anaemic. The disease was characterized by skin lesions around the lips and nostrils with occasional involvement of mucocutaneous junctions. The pathology includes vaculoar changes of the epithelial layers. Affected areas were ulcerated, haemorrhagic and with frequent secondary bacterial surinfection. Negative contrast electron microscopy has proven to be an extremely useful procedure for quick differential diagnosis.

Identity and lipase productivity of a mesophilic actinomycete isolated from Egyptian soil.

1. A mesophilic lipolytic actinomycete was isolated from Egyptian soil and was identified as a strain of Streptomyces flavogriseus. 2. Lipase(s) produced by S. flavogriseus is (at least partly) constitutive in its (their) nature and can be produced in the absence of lipids, however, its production is stimulated in their presence. 3. S. flavogriseus was unable to grow at 40 degrees C or higher temperatures. However, lipase(s) produced at lower temperatures (e.g. 20, 25, 30 and 35 degrees C) were more active at 45 and 55 degrees C. This is probably due to the presence of a heat sensitive lipase inhibitor in the culture filtrate. 4. Optimum conditions for lipase(s) production by S. flavoriseus are pH 6.8, incubation for 48-72 hours at 35 degrees C with 0.8% castor oil as the carbon source in Dox liquid medium supplemented with 0.3% yeast extract. 5. Factors supporting good growth were not always the same as those stimulating lipase(s) production.