Monte Carlo study of dosimetric impact of gadolinium contrast medium in transverse field MR-Linac system.

The aim of this study is to evaluate the dosimetric impact of gadolinium contrast medium (Gadovist) in a transverse MR-Linac system using Monte Carlo methods. The dose distributions were calculated using two heterogeneous multi-layer phantoms consisting of Gadovist, water, bone, and lung. The photon beam was irradiated with a filed size of 5 × 5 cm2, and a transverse magnetic field of 0-3.0 T was applied perpendicular to the incident photon beam. Next, dose distributions for brain, head and neck (H&N), and lung cancer patients were calculated using a patient voxel-based phantom with and without replacing the patient's GTV with Gadovist. The dose at the water-Gadovist interface increased by 8% without a magnetic field. A similar dose increment was observed at 0.35 T. In contrast, the dose increment at the water-Gadovist interface was small at 1.5 T and a dose decrement of 5% was observed at 3.0 T. The dose variation at the lung-Gadovist interface was larger than that at the water-Gadovist interface. The mass collision stopping power ratio for Gadovist was 7% lower than that for water, whereas, the electron fluence spectra at the water-Gadovist interface increased by 17.5%. In a patient study, Gadovist increased the Dmean for brain, H&N, and lung cancer patients by 0.65-8.9%. The dose variation due to Gadovist grew large in the low-dose region in H&N and lung cancer. The GTV dose variation due to Gadovist in all treatment site was below 2% at 0-3 T if the Gadovist concentration was lower than 0.2 mmol/ml-1.

Impact of lung density on isolated lung tumor dose in VMAT using inline MR-Linac.

PURPOSE: This study investigated the impact of lung density on the isolated lung tumor dose for volumetric modulated arc therapy (VMAT) in an inline magnetic resonance linear accelerator (MR-Linac) using the Monte Carlo (MC) simulation. METHODS: CT images of the thorax phantoms with lung tumors of 1, 2, and 3 cm diameters were converted into voxel-base phantoms with lung densities of 0.1, 0.2, and 0.3 g/cm3, respectively. The dose distributions were calculated for partial-arc VMAT. The dose distributions were compared using dose differences, dose volume histograms, and dose volume indices. RESULTS: In all cases, the inline magnetic field significantly enhanced the lung tumor dose compared to that at 0 T. For the 1 cm lung tumor, the inline magnetic field of 1 T increased the minimum dose of 95% of the Planning target volume (PTV D95) by 14.0% in 0.1 g/cm3 lung density as compared to that in 0.3 g/cm3 at 0 T. In contrast, at 0 and 0.5 T, the PTV D95 in 0.3 g/cm3 lung density was larger than that in lung density of 0.1 g/cm3. For the 2 cm lung tumor, a similar tendency to 1 cm was observed, whereas the dose impact of lung density was smaller than that for 1 cm. For the 3 cm lung tumor, the lung tumor dose was independent of lung density at 0.5 T and 1.0 T. CONCLUSION: The inline MR-Linac with the magnetic field over 1 T can enhance the PTV D95 for VMAT regardless of the lung density.

Geant4 Monte Carlo investigation of the magnetic field effect on dose distributions in low-density regions in magnetic resonance image-guided radiation therapy.

It is necessary to evaluate the effect of the presence of a magnetic field when treating lung tumors with MRIgRT. In this study, the effect of transverse and longitudinal magnetic fields on dose distributions in low-density regions was quantitatively investigated. The dose distributions in a virtual lung phantom under the influence of magnetic fields were calculated using the Geant4 Monte Carlo code. The phantom size was 30 × 20 × 30 cm3, and it was composed of three layers: water (3 cm thickness), lung (12 cm thickness), and water (5 cm thickness). The density of the lung layer was set to 0.1, 0.3 and 0.6 g/cm3. The uniform magnetic flux densities of 0.35 T and 1.5 T were used for 2 × 2, 5 × 5, and 10 × 10 cm2 fields at a source-to-surface distance of 100 cm, using a 6 MV photon spectrum. The dose at the water-lung interface in a lung phantom increased by 58%, 51%, and 22% for the lung densities of 0.1, 0.3, and 0.6 g/cm3, respectively. In the 1.5 T longitudinal magnetic field, the penumbra at the lung center (at the depth of 9 cm) decreased by 5.14, 1.50 and 0.35 mm for a 5 × 5 cm2 field, respectively. The dose distributions in lowdensity regions are more affected by the magnetic field. In conclusion, the doses at the water-lung interface increased in the transverse magnetic field. The depth dose increased, and the penumbra decreased in the longitudinal magnetic field.

Japanese consensus guidelines for pediatric nuclear medicine. Part 1: Pediatric radiopharmaceutical administered doses (JSNM pediatric dosage card). Part 2: Technical considerations for pediatric nuclear medicine imaging procedures.

The Japanese Society of Nuclear Medicine has recently published the consensus guidelines for pediatric nuclear medicine. This article is the English version of the guidelines. Part 1 proposes the dose optimization in pediatric nuclear medicine studies. Part 2 comprehensively discusses imaging techniques for the appropriate conduct of pediatric nuclear medicine procedures, considering the characteristics of imaging in children.

[Studies on bone mineral status with bone quantitative ultrasonography in severely handicapped school children--correlations with gross motor function and dietary status].

OBJECTIVE: Severely handicapped children and adolescents have reduced bone mineral density and high prevalence of pathological fractures. Bone quantitative ultrasonography (QUS) is a radiation-free method for assessing bone density. It is portable and easy to use in subjects with severe bodily deformities. METHODS: We evaluated 166 students (age 6-20 years) at a school for disabled children for bone mineral density using the osteo-sono-assessment index (OSI) calculated by measuring the velocity of ultrasound waves, the speed of sound (SOS) and the transmission index (TI), at the calcaneus. All examinations were performed using an AOS-100 analyzer (ALOKA Ltd., Tokyo, Japan). The Gross Motor Function Classification System (GMFCS) for cerebral palsy was also applied. We assessed OSI for dietary texture modifications and methods of feeding. RESULTS: Those with pathological fractures tended to have lower OSI than other students. Such fractures were individually unrelated to age, sex and GMFCS. OSI was significantly higher at GMFCS level I than level II. OSI in levels I to III was equally significantly higher than that in levels IV and V. As to feeding methods, the tube feeding group tended to have lower OSI than the oral ingestion group. In the oral ingestion group, those receiving a regular diet had significantly higher OSI than the mixed-minced diet group. However, students with a gastrostomy tended to have higher OSI than those receiving gastro-nasal tube feeding. CONCLUSIONS: Gross motor function (applied GMFCS) is a major factor affecting bone mineral density. Tube feeding reduces bone mineral density. However, forced oral intake may also reduce it. In the tube feeding group, a modified diet of appropriate texture delivered via gastrostomy may be the key to improving bone mineral density.

[Incorrect descriptions about Seicho Kamata in "Seishu Hanaoka and his surgery"].

"Seishu Hanaoka and his surgery" by Shuzo Kure is one of the most important books for the study of Seishu Hanaoka. However, several incorrect descriptions have been pointed out in the book. Therefore, we checked the content about Seicho Kamata, a distinguished disciple of Seishu Hanaoka (p.154-163) in the book, and found three incorrect descriptions. The figure being described as that of Seicho Kamata is his father's. His graveyard being described as "Nyohoji" is truly "Daizenji". Seicho Kamata is also described as the second distinguished disciple of Seishu Hanaoka ; however, authors think that he was the first distinguished disciple from his career. Further investigation into the content of the book is necessary.

Contribution of subtraction ictal SPECT coregistered to MRI to epilepsy surgery: a multicenter study.

OBJECTIVE: A multicenter prospective study was performed to assess the additional value of a subtraction ictal SPECT coregistered to MRI (SISCOM) technique to traditional side-by-side comparison of ictal- and interictal SPECT images in epilepsy surgery. METHODS: One hundred and twenty-three patients with temporal and extratemporal lobe epilepsy who had undergone epilepsy surgery after evaluation of scalp ictal and interictal electroencephalogram (EEG), MRI, and ictal and interictal SPECT scans were followed up in terms of postsurgical outcome for a period of at least 1 year. Three reviewers localized the epileptogenic focus using ictal and interictal SPECT images first by side-by-side comparison and subsequently by SISCOM. Concordance of the localization of the epileptogenic focus by SPECT diagnosis with the surgical site and inter-observer agreement between reviewers was compared between side-by-side comparison and SISCOM. Logistic regression analysis was performed in predicting the surgical outcome with the dependent variable being the achievement of a good postsurgical outcome and the independent variables using the SISCOM, side-by-side comparison of ictal and interictal SPECT images, MRI, and scalp ictal EEG. RESULTS: The SISCOM presented better concordance in extratemporal lobe epilepsy and less concordance in temporal lobe epilepsy than side-by-side comparison. Inter-observer concordance was higher in SISCOM than in side-by-side comparison. Much higher concordance of the epileptogenic focus by SPECT diagnosis with the surgical site was obtained in patients with good surgical outcome than in those with poor surgical outcome. These differences in concordance between good and poor surgical outcomes were greater in SISCOM than in side-by-side comparison. Logistic regression analysis showed the highest odds ratio of 12.391 (95% confidence interval; 3.319, 46.254) by SISCOM evaluation for concordance of the epileptogenic focus with the surgical site in predicting good surgical outcome. CONCLUSIONS: A SISCOM technique of ictal and interictal SPECT images provides higher predictive value of good surgical outcome and more reliability on the diagnosis of the epileptogenic focus than side-by-side comparison in medically intractable partial epilepsy.

[Effect of tacrolimus in a case of autoimmune encephalitis].

We report a 17-year-old boy who was diagnosed as autoimmune encephalitis with various neurological complications such as hemiplegia, aphasia and seizures. An autoimmune process was considered to be responsible for the repeated episodes of encephalitis because the symptoms were highly responsive to steroids and anti-glutamate receptor antibodies were detected in the CSF. After administration of the immunosuppressant tacrolimus, we could taper the steroid dosage. He has had no relapse for three years to date. We demonstrated the possibility of steroid-sparing treatment with tacrolimus for a patient with steroid-responsive encephalitis. There were few reports describing tacrolimus therapy for encephalitis. Tacrolimus may be effective for selected patients with recurrent encephalitis in which an autoimmune mechanism is considered as the pathogenesis.

Flumazenil-induced improvement of the central dopaminergic system in rats with acute hepatic failure.

Several reports have demonstrated the alleviation of hepatic encephalopathy by flumazenil, an antagonist of benzodiazepine receptors. As changes in central monoaminergic activity are involved in the mechanisms for hepatic encephalopathy, the effects of flumazenil on central monoaminergic activity were evaluated in acute hepatic failure produced by ischemia-reperfusion injury in rats. Eighteen male Wistar rats were evenly assigned to three groups: sham-operated group given saline, liver-ischemic group given saline, and liver-ischemic group given flumazenil. Flumazenil (1 mg/kg) or saline (10 mL/kg) was intraperitoneally administered three times, at 1, 6, and 24 hours after 90 minutes of liver ischemia produced by occlusion of the left portal vein. The extracellular concentrations of neurotransmitter amino acids, monoamines, and their metabolites were determined in the striatum using a microdialysis procedure. Another set of 12 rats was subjected to liver ischemia, and the effect of flumazenil on spontaneous motor activity was examined after 24 hours. The extracellular concentration of 3,4-dihydroxyphenylacetic acid, a metabolite of dopamine, decreased to 39% of that in sham-operated animals 24 hours after surgery (P < 0.05), although the dopamine level did not change. The treatment with flumazenil completely abolished the decrease in the metabolite (P < 0.05). Although the glutamate level in the injured animals decreased to 42% of that in sham-operated animals (P < 0.05), no remarkable increase in the glutamate level was observed in animals treated with flumazenil. Spontaneous motor activity decreased 24 hours after surgery in animals subjected to liver ischemia. Flumazenil led to improvement of spontaneous motor activity 5 minutes after administration, but this effect was not observed after 30 minutes. The restoration of the central dopaminergic function may be a contributing factor in the improvement of hepatic encephalopathy.