Plasma-based biomaterials for the treatment of cutaneous radiation injury.

Cutaneous wounds caused by an exposure to high doses of ionizing radiation remain a therapeutic challenge. While new experimental strategies for treatment are being developed, there are currently no off-the-shelf therapies for the treatment of cutaneous radiation injury that have been proven to promote repair of the damaged tissues. Plasma-based biomaterials are biologically active biomaterials made from platelet enriched plasma, which can be made into both solid and semi-solid forms, are inexpensive, and are available as off-the-shelf, nonrefrigerated products. In this study, the use of plasma-based biomaterials for the mitigation of acute and late toxicity for cutaneous radiation injury was investigated using a mouse model. A 2-cm diameter circle of the dorsal skin was irradiated with a single dose of 35 Gy followed by topical treatment with plasma-based biomaterial or vehicle once daily for 5 weeks postirradiation. Weekly imaging demonstrated more complete wound resolution in the plasma-based biomaterial vs. vehicle group which became statistically significant (p < 0.05) at weeks 12, 13, and 14 postmaximum wound area. Despite more complete wound healing, at 9 and 17 weeks postirradiation, there was no statistically significant difference in collagen deposition or skin thickness between the plasma-based biomaterial and vehicle groups based on Masson trichrome staining nor was there a statistically significant difference in inflammatory or fibrosis-related gene expression between the groups. Although significant improvement was not observed for late toxicity, plasma-based biomaterials were effective at promoting wound closure, thus helping to mitigate acute toxicity.

Analytic Derivation and Monte Carlo Validation of a Sensitivity Formula for Slit-Slit Collimation With Penetration.

A slit-slit collimator consists of two orthogonal slits and can be conceptualized as a generalized pinhole. Since the two slits are independent of each other, there can be independent axial and transaxial acceptance angles. A small axial acceptance angle may help mitigate axial blurring with circular orbits, allowing multiple copies axially. In addition, since the two slit planes can be placed at different distances with respect to the source, a better detector usage can be achieved, especially in the case of detectors and imaged objects with different aspect ratios. In this paper an analytical expression is derived for the sensitivity of slit-slit collimation including effective slit widths for photon penetration. An analytical expression for sensitivity is necessary in order to accurately model the system response. This expression could also be useful for comparing the slit-slit's sensitivity performance with others. When the effective slit width is used instead of the geometric slit width, the derived analytical expression accurately accounts for photon penetration of the aperture. The derived expression for the sensitivity was validated by Monte Carlo simulation for both geometric and penetrative cases.

On-axis sensitivity and resolution of a slit-slat collimator.

UNLABELLED: A slit-slat collimator combines a slit along the axis of rotation with a set of axial septa, offering both magnification in the transaxial direction and complete sampling with just a circular orbit. This collimator has a sensitivity that increases for points near the aperture slit. The literature treats this collimator as having the same sensitivity as a single-pinhole collimator, ignoring the effect of the axial septa. Herein, the sensitivity and resolution of this collimator are reevaluated. METHODS: Experimental and Monte Carlo methods are used to determine the sensitivity and resolution in both the transaxial and axial directions as a function of distance from the slit (h). Eight configurations are tested, varying the slit width, septal spacing, and septal height. RESULTS: Both the experimental and the Monte Carlo sensitivities agree reasonably with an analytic form that is the geometric mean of the pinhole and parallel-beam formulas, disagreeing with previous literature. Transaxial resolution is consistent with the pinhole-resolution formula. Axial resolution is consistent with the parallel-beam resolution formula. CONCLUSION: The sensitivity of this collimator is proportional to h(-1) and has resolution in the transaxial direction that is consistent with pinhole resolution and in the axial direction that is consistent with parallel-beam resolution.