A validation of carbon fiber imaging couch top modeling in two radiation therapy treatment planning systems: Philips Pinnacle³ and BrainLAB iPlan RT Dose

<p>Abstract</p> <p>Background</p> <p>Carbon fiber (CF) is now the material of choice for radiation therapy couch tops. Initial designs included side metal bars for rigidity; however, with the advent of IGRT, involving on board imaging, new thicker CF couch tops without metal bars have been developed. The new design allows for excellent imaging at the expense of potentially unacceptable dose attenuation and perturbation.</p> <p>Objectives</p> <p>We set out to model the BrainLAB imaging couch top (ICT) in Philips Pinnacle³ treatment planning system (TPS), to validate the already modeled ICT in BrainLAB iPlan RT Dose treatment planning system and to compute the magnitude of the loss in skin sparing.</p> <p>Results</p> <p>Using CF density of 0.55 g/cm³ and foam density of 0.03 g/cm³, we demonstrated an excellent agreement between measured dose and Pinnacle³ TPS computed dose using 6 MV beam. The agreement was within 1% for all gantry angle measured except for 120^o, which was 1.8%. The measured and iPlan RT Dose TPS computed dose agreed to within 1% for all gantry angles and field sizes measured except for 100^o where the agreement was 1.4% for 10 cm × 10 cm field size. Predicted attenuation through the couch by iPlan RT Dose TPS (3.4% - 9.5%) and Pinnacle³ TPS (2% - 6.6%) were within the same magnitude and similar to previously reported in the literature. Pinnacle³ TPS estimated an 8% to 20% increase in skin dose with increase in field size. With the introduction of the CF couch top, it estimated an increase in skin dose by approximately 46 - 90%. The clinical impact of omitting the couch in treatment planning will be dependent on the beam arrangement, the percentage of the beams intersecting the couch and their angles of incidence.</p> <p>Conclusion</p> <p>We have successfully modeled the ICT in Pinnacle³ TPS and validated the modeled ICT in iPlan RT Dose. It is recommended that the ICT be included in treatment planning for all treatments that involve posteriors beams. There is a significant increase in skin dose that is dependent on the percentage of the beam passing through the couch and the angle of incidence.</p

Does physical activity reduce risk for Alzheimer’s disease through interaction with the stress neuroendocrine system?

Lack of physical activity (PA) is a risk factor for Alzheimer's disease (AD) and PA interventions are believed to provide an effective non-pharmacological approach for attenuating the symptoms of this disease. However, the mechanism of action of these positive effects is currently unknown. It is possible that the benefits may be at least partially mediated by effects on the neuroendocrine stress system. Chronic stress can lead to dysfunction of the hypothalamic pituitary adrenal (HPA) axis, leading to aberrant basal and circadian patterns of cortisol secretion and a cascade of negative downstream events. These factors have been linked not only to reduced cognitive function in the non-demented but also increased levels of Amyloid β plaques and protein Tau "tangles" (the neuropathological hallmarks of AD) in mouse models of this disease. However, there is evidence that PA can have restorative effects on the stress neuroendocrine system and related risk factors relevant to AD. We explore the possibility that PA can positively impact upon AD by restoring normative HPA axis function, with consequent downstream effects upon underlying neuropathology and associated cognitive function. We conclude with suggestions for future research to test this hypothesis in patients with AD