Generalized model guides high dose radiotherapy
Conventional fractionated radiotherapy is planned using the linear-quadratic (LQ) equation to calculate radiation doses. However, the high-dose fractions used in newer techniques such as stereotactic radiosurgery, stereotactic body radiotherapy and high-dose-rate brachytherapy cannot be accurately calculated with this traditional model. To address this problem, researchers at Ohio State University (Columbus, OH) have developed a new mathematical equation: gLQ, the generalized form of the LQ equation, which is valid at both low and high doses (Sci. Transl. Med. 2 39ra48).
Irradiation is thought to cause two types of DNA damage: lethal lesions that result in immediate cell death, and sub-lethal lesions. The LQ equation does not account for the fact that at high radiation doses, there is less sub-lethal and more lethal DNA damage. The resulting error grows as the dose increases, potentially leading to inadequate treatments. The new equation can accurately calculate the amount of sub-lethal damage to cells. Comparisons with published studies – which measured the effects of different radiation doses on cells grown in vitro and in animals – confirmed that the gLQ model can accurately predict the killing effects of radiation through a wide dose range (up to 13.5 Gy).
Irradiating stem cell niche doubles glioblastoma survival
Patients with glioblastomas who received high doses of radiation to a part of the brain that harbours neural stem cells exhibited increased progression-free survival, according to a study from UCLA's Jonsson Comprehensive Cancer Center (Los Angeles, CA). The retrospective study examined 55 adults with grade 3 or grade 4 glioblastomas. Those who underwent irradiation of the specific neural stem cell site, known as the stem cell niche, experienced 15 months progression-free survival, while patients receiving lower or no dose to this region experienced 7.2 months of progression-free survival (BMC Cancer 10 384).
"Our study found that if you irradiated a part of the brain that was not necessarily part of the tumour, the patients did better," explained senior author Frank Pajonk. "We have been struggling for years to come up with new combinations of drugs and targeted therapies that would improve survival for patients with glioblastoma. It may be that by reshaping our radiation techniques we can extend survival for these patients." The study theorizes that the neural stem cell niche in the brain may harbour brain cancer stem cells. Irradiating the niche may damage or eliminate these cancer stem cells, improving patient survival. Pajonk notes that a prospective study is needed to confirm these results.
Low-temperature plasma delivers dental disinfection
Researchers from the University of Greifswald in Germany have investigated the use of low-temperature plasma devices as an alternative to chemical disinfection in dental practice. They examined the antifungal efficacy of an atmospheric pressure plasma jet and two dielectric barrier discharge (DBD) plasmas, as well as chlorhexidine digluconate and sodium hypochlorite antiseptic solutions, on Candida albicans biofilms grown on titanium discs. Candida albicans is a yeast that can cause oral infections, particularly in denture wearers (New J. Phys. 12 073039).
Treatment efficacy was determined by evaluating the number of colony-forming units (CFU ml–1, usually given logarithmically) on the discs before and after treatment. The DBD plasma treatments reduced the CFU significantly compared to chemical disinfectants. While ten minutes exposure to chlorhexidine digluconate or sodium hypochlorite led to a CFU log10 reduction factor of 1.5, the reduction factor of DBD plasma was up to five. Scanning electron microscopic images showed that plasma completely destroyed the yeast cells. "The possibility of using DBD plasma to treat a whole denture is ideal for denture cleaning. Plasma could also offer the opportunity to treat Candida infections directly, which is also important outside of dentistry," the authors write.
Vascular-targeted PDT tackles localized prostate cancer
NYU Langone Medical Center (New York, NY) has begun a Phase I/II clinical trial offering vascular-targeted photodynamic therapy (PDT) to patients with localized prostate cancer. The procedure involves intravenous administration of a photosensitizing drug called WST11. After 10 minutes, optical fibres positioned over the prostate deliver laser light for twenty minutes. Where the light activates the circulating drug, the blood vessels around the tumour are destroyed, shutting down the blood supply to the cancer. The study will investigate optimal dosage of the photosensitive drug and laser, and measure patient outcomes and long-term cancer control.
"This minimally invasive technique for localized prostate cancer offers the potential to destroy the cancer without making any incision or causing any potentially devastating sexual, urinary or reproductive side-effects," said Samir Taneja, director of the NYU Langone Medical Center's division of urologic oncology and principal investigator for the national, multi-centre trial testing this technology. "This procedure only treats the cancerous part of the prostate gland, similar to how a lumpectomy might be done for breast cancer."
Optimization workshop helped cut MDCT dose
A one-day dose optimization workshop helped radiology practices significantly reduce the radiation dose associated with multi-detector CT (MDCT) scans. Ten radiology practices in Queensland, Australia, participated in the study, in which a radiologist and medical imaging technologist from each site attended the feedback and optimization training workshop. Data from 1208 scans performed prior to the workshop were compared to data from 1153 scans performed afterwards. After the workshop, the average dose reduction was 46% for adult MDCT scans of the brain; 28% for adult MDCT pulmonary angiograms; 29% for adult MDCT lumbar spine scans; and 24% for adult MDCT urograms (J. Am. Coll. Radiol. 7 614).
"Although recent advances in CT technology may offer dose savings without the need to undertake an optimization process, recent work indicates that optimization is still required to deliver maximum dose savings while maintaining diagnostic image quality," said lead author Anthony Wallace, medical physicist at the Australian Radiation Protection and Nuclear Safety Agency. "Our study shows that small group teaching about optimization enabled clinically meaningful dose reduction for a variety of common adult scans. However, access to medical radiation physicists, assistance with time consuming data collection, and technical support from a medical imaging technologist, were critical to the success of the programme."