Development of an x-ray-opaque-marker system for quantitative phantom positioning in patient-specific quality assurance.

PURPOSE: We developed an x-ray-opaque-marker (XOM) system with inserted fiducial markers for patient-specific quality assurance (QA) in CyberKnife (Accuray) and a general-purpose linear accelerator (linac). The XOM system can be easily inserted or removed from the existing patient-specific QA phantom. Our study aimed to assess the utility of the XOM system by evaluating the recognition accuracy of the phantom position error and estimating the dose perturbation around a marker. METHODS: The recognition accuracy of the phantom position error was evaluated by comparing the known error values of the phantom position with the values measured by matching the images with target locating system (TLS; Accuray) and on-board imager (OBI; Varian). The dose perturbation was evaluated for 6 and 10 MV single-photon beams through experimental measurements and Monte Carlo simulations. RESULTS: The root mean squares (RMSs) of the residual position errors for the recognition accuracy evaluation in translations were 0.07 mm with TLS and 0.30 mm with OBI, and those in rotations were 0.13° with TLS and 0.15° with OBI. The dose perturbation was observed within 1.5 mm for 6 MV and 2.0 mm for 10 MV from the marker. CONCLUSIONS: Sufficient recognition accuracy of the phantom position error was achieved using our system. It is unnecessary to consider the dose perturbation in actual patient-specific QA. We concluded that the XOM system can be utilized to ensure quantitative and accurate phantom positioning in patient-specific QA with CyberKnife and a general-purpose linac.

Feasibility of using tungsten functional paper as a thin bolus for electron beam radiotherapy.

Containing 80% tungsten by weight, tungsten functional paper (TFP) is a radiation-shielding material that is lightweight, flexible, disposable, and easy to cut. Through experimental measurements and Monte Carlo simulations, we investigated the feasibility of using TFP as a bolus in electron beam radiotherapy. Commercial boluses of thickness 5 and 10 mm and from one to nine layers of TFPs (0.3-2.7 mm) were positioned on the surface of water-equivalent phantoms. The percentage depth dose curves and transverse dose profiles were measured using a 9-MeV electron beam from a clinical linear accelerator. Normalized to the value at the depth of maximum dose without bolus, the relative doses at the phantom surface for no bolus, 5-mm bolus, 10-mm bolus, 1 TFP, 3 TFPs, 6 TFPs, and 9 TFPs were 78%, 88%, 92%, 84%, 92%, 102%, and 112%, respectively; the therapeutic depths corresponding to a 90% dose level were 29.1 mm, 22.7 mm, 17.7 mm, 26.6 mm, 23.2 mm, 19.3 mm, and 15.8 mm, respectively. The TFP contributed to increased skin dose and provided dose uniformity within the target volume. However, it also resulted in increased lateral constriction and penumbra width. The results of Monte Carlo simulation produced similar trends as the experimental measurements. Our findings suggest that using TFP as a novel thin and flexible skin bolus for electron beam radiotherapy is feasible.

PROPOSAL FOR LOCAL DIAGNOSTIC REFERENCE LEVELS IN GENERAL RADIOGRAPHY IN JAPAN.

The present study aimed to propose local diagnostic reference levels (DRLs) formulated by calculating entrance surface doses for general radiography at 20 facilities of Aichi prefecture in Japan, by comparing these values with DRLs established in Japan in 2015 (DRLs 2015) and assessing radiation dose differences among facilities. X-ray outputs (half-value layer and air kerma) of each facility were measured with a non-invasive type of detector. The results were employed to formulate local DRLs based on the 75th percentiles of dose distributions. These local DRLs were lower than the DRLs 2015 for all examinations. If proposed local DRLs from other 46 prefectures can be collected, this paper can be used to benefit the next effort to draft better DRL for Japan.

A mathematical model of type 1 diabetes involving leptin effects on glucose metabolism.

Leptin, a hormone released from fat cells in adipose tissues, was recently found to be capable of normalizing glucose metabolism in animals. Clinical data on patients with lipodystrophy indicates that leptin may have a positive effect on glucose metabolism in individuals with diabetes. There are growing expectations that leptin can improve the current insulin treatment for patients with type 1 diabetes. We investigated this possibility through in silico experiments based on a mathematical model of diabetes, which is currently the only mode of research that eliminates human risk. A model of the brain-centered glucoregulatory system, in which leptin plays a central role, was constructed and integrated within a conventional model of insulin/glucose dynamics. The model has been validated using experimental data from animal studies. The in silico combination experiments showed excellent therapeutic performance over insulin monotherapy.

High performance optical resolution with liposome immobilized hydrogel.

We prepared liposome immobilized hydrogels (LI-gels) for analysis and separation of chiral molecules, to overcome the drawbacks of liposomes such as low stability, and difficulties with handling and isolation from sample solutions. The amounts of liposomes in the hydrogels were larger than those in other solid matrices reported previously. The liposome morphology was intact, and its original properties, such as fluidity and phase transition behaviors, were preserved. We investigated the chiral recognition performance of the LI-gel, as described in our previous paper. Our results indicate that the enantioselectivity of the LI-gel was higher than those of conventional methods and of the liposomes alone. Our prepared LI-gel therefore overcomes the drawbacks of liposomes, and has potential applications in analysis and separation, including chiral separation.