Keratins are major components of the epithelial cytoskeleton and are believed to play a vital role for mechanical integrity at the cellular and tissue level. Keratinocytes as the main cell type of the epidermis express a differentiation-specific set of type I and type II keratins forming a stable network and are major contributors of keratinocyte mechanical properties. However, owing to compensatory keratin expression, the overall contribution of keratins to cell mechanics was difficult to examine in vivo on deletion of single keratin genes. To overcome this problem, we used keratinocytes lacking all keratins. The mechanical properties of these cells were analyzed by atomic force microscopy (AFM) and magnetic tweezers experiments. We found a strong and highly significant softening of keratin-deficient keratinocytes when analyzed by AFM on the cell body and above the nucleus. Magnetic tweezers experiments fully confirmed these results showing, in addition, high viscous contributions to magnetic bead displacement in keratin-lacking cells. Keratin loss neither affected actin or microtubule networks nor their overall protein concentration. Furthermore, depolymerization of actin preserves cell softening in the absence of keratin. On reexpression of the sole basal epidermal keratin pair K5/14, the keratin filament network was reestablished, and mechanical properties were restored almost to WT levels in both experimental setups. The data presented here demonstrate the importance of keratin filaments for mechanical resilience of keratinocytes and indicate that expression of a single keratin pair is sufficient for almost complete reconstitution of their mechanical properties.
BANG polymer gel dosimetry using magnetic resonance imaging (MRI) was applied to an ophthalmologic 68 MeV proton beam. The object was to examine the use of BANG gel for the verification of proton fields in eye tumor therapy and to explore the applicability of polymer gel dosimetry in proton therapy under practical aspects. The gel phantoms were irradiated with monoenergetic and modulated proton beams. MRI analysis was carried out at clinical 1.5 and 3 T MR scanners. At constant LET, results show a linear relationship between spin-spin relaxation rates and dose. However, depth dose curves in BANG gel reveal a quenching of the Bragg maximum due to LET effects. The dose response of the gel for monoenergetic protons and spread-out depth dose distributions can be calculated based on ionization chamber measurements. Experiment and calculations show good agreement and indicate that BANG polymer gels might become a valuable tool in proton therapy quality assurance.
Data from the literature on normal-tissue complication probability (rectal bleeding) refer to different rectal contours. When applying dose restrictions to the rectum, contouring becomes a significant factor that determines the risk of rectal toxicity. The results of this study show that different ways of rectal contouring significantly influence doses to the rectum. The influence of organ at risk contouring should be considered thoroughly in conformal radiotherapy of prostate cancer patients, especially in dose escalation studies. It is recommended to calculate the doses for absolute rectal volumes and correlate these data with toxicity in order to be able to achieve comparable results among different institutions.
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