Design and construction of an accelerator-based boron neutron capture therapy (AB-BNCT) facility with multiple treatment rooms at the Southern Tohoku BNCT Research Center

Installation of an accelerator-based boron neutron capture therapy (AB-BNCT) system was started in April 2014 at the Southern Tohoku BNCT Research Center (STBRC), and clinical trials began in January 2016. There are two treatment rooms, which have same specifications, and the beam quality equivalency was confirmed both rooms. Here, we describe the design and construction of the first hospital-based AB-BNCT facility in the world with multiple treatment rooms.

P304Prognostic significance of transvalvular flow rate during exercise in asymptomatic patients with aortic stenosis

Background

The optimal management of asymptomatic aortic stenosis (AS) remains controversial. The aim of this study is to investigate the prognostic value of exercise stress echocardiography (ESE) in asymptomatic patients with AS.

Purpose

To investigate the additive value of ESE in asymptomatic patients with AS.

Methods and results

We retrospectively enrolled 109 consecutive patients (mean age 73±13 years, 55 men) with AS (aortic valve area ≤1.5cm2) who underwent ESE. Of these, 10 patients referred for aortic valve replacement without symptoms were excluded; finally, 99 conservatively managed patients were enrolled. During the mean follow-up period of 14±11 months, 23 patients (23%) suffered from AS related events. Although no differences in mean pressure gradient at rest and during exercise were found between the patients with and without adverse events, transvalvular flow rate during exercise (Ex-FR) was lower in patients with adverse events than those without adverse events (236±55 ml/sec vs 274±64 ml/sec, P=0.01). Using multivariate Cox regression analysis, low Ex-FR (<270 ml/sec) was an independent predictor for adverse events in patients with asymptomatic AS (hazard ratio: 3.53, P<0.01). The Kaplan–Meier analysis showed that Ex-FR was clearly stratified the event-free survival (Figure, log-rank P<0.01).

K-M curve according to Ex-FR

Conclusion

These results suggested that Ex-FR measured by ESE should play crucial roles in risk stratification in asymptomatic patients with AS.

P1493Prognostic significance of right ventricular function during exercise in patients with non-obstructive hypertrophic cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is a heterogeneous condition that may present crucial complication including life-threatening arrhythmia and sudden cardiac death. However, the risk stratification of HCM without left ventricular outflow tract (LVOT) obstruction had not been fully elucidated. Moreover, although recent studies have revealed the right ventricle (RV) involvement of HCM, the prognostic importance of RV function during exercise is unclear.

Purpose

To investigate the prognostic significance of RV function in patients with non-obstructive HCM using exercise stress echocardiography (ESE).

Methods and results

This study conducted on 100 HCM patients (age 62.9±13.6 years, 63% men) with preserved left ventricular ejection fraction who underwent ESE using semi-supine bicycle ergometer. Ten patients with significant LVOT obstruction (≥30mmHg) were excluded and 9 were also excluded because of the inadequate imaging quality or insufficiency of data. Among remaining 81 non-obstructive HCM patients, 9 patients suffered from HCM related cardiac events including cardiac death, unexpected hospitalization, life-threatening arrhythmias, and new-onset of syncope during the mean follow up period of 2.6±1.6 years. A multivariate Cox Hazard analysis revealed that low tricuspid annular plane systolic excursion during exercise (Ex-TAPSE, cut-off: 24mm) was an independent predictor of cardiac events. (hazard ratio: 18.66, 95% confidence interval: 3.66–338.46, P<0.001) The estimated cumulative cardiac event free survival using the Kaplan-Meier method was significantly lower in patients with reduced Ex-TAPSE (<24mm) than those with preserved Ex-TAPSE (Log-rank, P<0.01).

K-M curve according to Ex-TAPSE

Conclusion

Ex-TAPSE had a strong predictive value of clinical outcomes in non-obstructive HCM patients. Right ventricular function during exercise may have crucial role in the risk stratification of non-obstructive HCM.

Electric dipole effect in PdCoO2/β-Ga2O3 Schottky diodes for high-temperature operation

High-temperature operation of semiconductor devices is widely demanded for switching/sensing purposes in automobiles, plants, and aerospace applications. As alternatives to conventional Si-based Schottky diodes usable only at 200°C or less, Schottky interfaces based on wide-bandgap semiconductors have been extensively studied to realize a large Schottky barrier height that makes high-temperature operation possible. Here, we report a unique crystalline Schottky interface composed of a wide-gap semiconductor β-Ga₂O₃ and a layered metal PdCoO₂. At the thermally stable all-oxide interface, the polar layered structure of PdCoO₂ generates electric dipoles, realizing a large Schottky barrier height of ~1.8 eV, well beyond the 0.7 eV expected from the basal Schottky-Mott relation. Because of the naturally formed homogeneous electric dipoles, this junction achieved current rectification with a large on/off ratio approaching 10⁸ even at a high temperature of 350°C. The exceptional performance of the PdCoO₂/β-Ga₂O₃ Schottky diodes makes power/sensing devices possible for extreme environments.

OPTIMIZATION OF AN ADDITIONAL COLLIMATOR IN A BEAM DELIVERY SYSTEM FOR REDUCTION OF THE SECONDARY NEUTRON EXPOSURE IN PASSIVE CARBON-ION THERAPY

The aim of this work is to optimize an additional collimator in a beam delivery system to reduce neutron exposure to patients in passive carbon-ion therapy. All studies were performed by Monte Carlo simulation assuming the beam delivery system at Heavy-Ion Medical Accelerator in Chiba. We calculated the neutron ambient dose equivalent at patient positions with an additional collimator, and optimized the position, aperture size and material of the collimator to reduce the neutron ambient dose equivalent. The collimator located 125 and 470 cm upstream from the isocenter could reduce the dose equivalent near the isocenter by 35%, while the collimator located 813 cm upstream from the isocenter was ineffective. As for the material of the collimator, iron and nickel could conduct reduction slightly better than aluminum and polymethyl methacrylate. The additional collimator is an effective method for the reduction of the neutron ambient dose equivalent near the isocenter.

Effect of anatomical change on dose distribution during radiotherapy for maxillary sinus carcinoma: passive scattering proton therapy versus volumetric-modulated arc therapy

OBJECTIVE

Maxillary sinus carcinomas are anatomically situated next to many organs at risk (OARs), and anatomical change is often observed during radiotherapy. We analyzed the effect of anatomical change on dose distribution of passive scattering proton therapy (PSPT) and volumetric-modulated arc therapy (VMAT) for 20 patients.

METHODS

The first plans were generated based on the first CT images. The second CT images were acquired after 3 weeks, and the second plans were generated by copying the first plans to the second CT images. The effect of anatomical change was estimated by comparing both plans.

RESULTS

Target volume change was observed in all cases, however, the influence on dose coverage of clinical target volume tended to be small. Alternatively, the doses to almost all OARs were increased. In particular, the increase in the dose to brainstem (p < 0.001) and optic chiasm (p < 0.001) was significantly higher in the second PSPT plan than in the first PSPT plan. Although PSPT is sensitive to anatomical change, the dose to OARs remained significantly lower in PSPT plans than that in VMAT plans.

CONCLUSION

PSPT was confirmed to be more effective than VMAT even the effect of anatomical change was taken into account. Therefore, it is expected that the contralateral vision can be preserved reliably while optimal target coverage is provided.

ADVANCES IN KNOWLEDGE

PSPT allowed significant sparing of OARs even in the result of the second plans affected by the anatomical change. PSPT offers benefits over VMAT in reducing dose to several OARs.

Characterizing Adversity of Lysosomal Accumulation in Nonclinical Toxicity Studies: Results from the 5th ESTP International Expert Workshop

Lysosomes have a central role in cellular catabolism, trafficking, and processing of foreign particles. Accumulation of endogenous and exogenous materials in lysosomes represents a common finding in nonclinical toxicity studies. Histologically, these accumulations often lack distinctive features indicative of lysosomal or cellular dysfunction, making it difficult to consistently interpret and assign adverse dose levels. To help address this issue, the European Society of Toxicologic Pathology organized a workshop where representative types of lysosomal accumulation induced by pharmaceuticals and environmental chemicals were presented and discussed. The expert working group agreed that the diversity of lysosomal accumulations requires a case-by-case weight-of-evidence approach and outlined several factors to consider in the adversity assessment, including location and type of cell affected, lysosomal contents, severity of the accumulation, and related pathological effects as evidence of cellular or organ dysfunction. Lysosomal accumulations associated with cytotoxicity, inflammation, or fibrosis were generally considered to be adverse, while those found in isolation (without morphologic or functional consequences) were not. Workshop examples highlighted the importance of thoroughly characterizing the biological context of lysosomal effects, including mechanistic data and functional in vitro readouts if available. The information provided here should facilitate greater consistency and transparency in the interpretation of lysosomal effects.