Image-enhancing nanoparticles traverse blood-brain barrier
The invasive nature of brain cancer means that there's often no clear boundary between the tumour and normal brain tissue, complicating surgical removal. Now, a team from the University of Washington (Seattle, WA) has used fluorescent nanoparticles to enhance visualization of this boundary. By attaching a tumour-targeting agent and a small fluorescent molecule to its surface, the researchers created a nanoparticle that can safely cross the blood-brain barrier and bind specifically to brain-tumour cells (Cancer Res. 69 6200).
Studies of a mouse model revealed that the particles remained in tumours for up to five days, with no evidence of damage to the blood-brain barrier. The injected particles improved the contrast in both MRI and optical imaging. The researchers predict that this nanoimaging could help with early detection of cancer, by improving the resolution of current diagnostic imaging techniques and enabling detection of smaller tumours. They also plan to evaluate the nanoparticle's potential for treating tumours.
Brain radiotherapy could reduce cognitive function
Even low doses of radiotherapy may contribute to progressive cognitive decline in patients treated for low-grade glioma (the most common brain cancer), according to research headed up at VU University Medical Center in the Netherlands. The study examined 65 patients with stable disease, 32 of whom had received radiotherapy. Patients were examined a mean of 12 years after treatment to assess attention, executive functioning, verbal memory, working memory, psychomotor functioning and information processing speed. In total, 27% of patients who did not have radiotherapy had cognitive disability, compared with 53% of those who received radiotherapy (Lancet Neurol. 8 810).
The authors note that these results indicate that radiation therapy is associated with long-term cognitive deterioration, and that all patients who had radiotherapy are at risk of developing attentional problems, not just those who received a high dose. They suggest that the risks associated with radiotherapy should be considered when planning treatment of low-grade glioma patients. An accompanying comment, however, points out the substantial improvements in radiotherapy techniques since the 1970s when treatments in this study started, and cautions that the risks of modern radiotherapy should not be generalized from these results (Lancet Neurol. 8 779).
Field fluctuations impact proton therapy dose
A team at the MD Anderson Cancer Center (Houston, TX) has studied the effect that fluctuations in the magnetic field strengths of steering magnets in a proton scanning beam nozzle have on the dose delivered during scanned-beam proton therapy. The researchers developed a general analytical relationship linking magnetic field uncertainty and final dose-spot position that can be applied to any nozzle design (Med. Phys. 36 3693).
For the nozzle examined in this study, displacements of four adjacent spots towards or away from each other by 0.5 mm produced a noticeable dose impact (5% hot spot) in the treatment volume, as did random displacements of up to 1.0 mm. Random displacements of up to 1.5 mm caused a 3% decrease in treatment volume coverage. For this nozzle, these displacements correlate with an uncertainty of 2.04% in the steering magnets' field values. The authors conclude that magnetic field fluctuations could have clinically significant effects, noting that differences between scanning nozzles imply that such fluctuations should be evaluated when commissioning each individual nozzle.
Interventional radiology: dose assessment required
Interventional radiology procedures are on the rise in developing countries, both for adults and paediatric patients. But according to a recent study from the International Atomic Energy Agency in Austria, many facilities in these countries lack awareness of patient dose estimation and dose management. The study examined information provided by 55 hospitals in 20 countries (nine in Europe, five in Africa, six in Asia) on radiation protection tools, peak skin dose and kerma-area product (KAP). The study concluded that staff protection was generally acceptable, but patient protection was not, with many exceeding the dose threshold for erythema (AJR 193 559).
"We found that a substantial number of coronary angioplasty procedures performed in the developing countries in this study are above the currently known dose reference level," said study coordinator Madan M Rehani. "We also found that KAP, a method to determine dose estimations, was available in almost half of the facilities, but none had experience in its use. Most training centres need to establish a culture of dose assessment and dose management - including programs for residents with radiation protection as an essential component - to improve patient safety. Dose monitoring devices for angiography equipment should also be considered."
Biomaterial lights up tumour hypoxia
A luminescent biomaterial developed at the University of Virginia (Charlottesville, VA) eases the imaging of tumour hypoxia. The material combines a biocompatible polymer with a fluorescent dye that's also phosphorescent under low-oxygen or oxygen-free conditions. By adjusting the relative intensities of the short-lived blue fluorescence and the long-lived yellow phosphorescence, the researchers created a calibrated coloured glow that allows visualization of minute levels of oxygen. The biomaterial displays this oxygen-sensitive phosphorescence at room or body temperature, making it ideal for use in tissues (Nature Mater. 8 747).
The new material could prove of particular benefit for real-time and extended-time spatial mapping of oxygen levels in tumours. "This technology will enable us to better characterize the influence of tumour hypoxia on tumour growth and treatment response," said co-author Greg Palmer, assistant professor of radiation oncology at Duke University Medical Center (Durham, NC). "It allows imaging of tumour hypoxia on the scale of tumour cells and small blood vessels." The material is currently being used in preclinical studies to gain insight into cancer biology and treatment response. Ultimately, it could be employed as an injectable nanosensor, potentially providing continual data on oxygen levels, biological processes and therapy response.
Iterative reconstruction reduces CT dose
A study at the Mayo Clinic Arizona (Scottsdale, AZ) has revealed that a low-dose technique called adaptive statistical iterative reconstruction (ASIR) can reduce patient radiation dose from CT scans by up to 65%. The researchers performed CT scans using the low-dose ASIR method and standard CT on a phantom and on 12 patients. They found nearly identical image quality with both methods. Patient radiation doses were reduced by 32-65% using the iterative reconstruction method, with an average radiation dose delivered during low-dose CT of 470 mGy, compared with 894 mGy delivered using routine CT imaging (AJR 193 764).