A robust optimization method for weighted-layer-stacking proton beam therapy.

The layer-stacking method can provide three-dimensional conformal dose distributions to the target based on a passive scattering method using mini-spread-out Bragg peak (SOBP). The purpose of this work is to demonstrate the effectiveness of a new weight optimization algorithm that can enhance the robustness of dose distributions against layer depth variation in layer-stacking proton beam therapy. In the robustness algorithm, the upper limit of the layer's weight was adapted to the conventional algorithm and varied for 620 weight set evaluations. The optimal weight set was selected by using an analytical objective function based on Gaussian function with σ = 3 mm for WED variation. Then, we evaluated the stabilities of the one-dimensional depth dose distribution against WED variation generated by Gaussian samples. Three-dimensional dose distributions in the water phantom were also evaluated using the Monte-Carlo dose calculation. The variation of dose as well as dose volume histograms for the spherical target and the organ at risk (OAR) were evaluated. The robustness algorithm reduced the change of the dose distribution due to the WED variation by a factor of almost 3/4 compared to those with the conventional procedure. The rate of 91.8% in total samples was maintained within 5% change of the maximum dose, compared with the rate of 64.9% in the conventional algorithm. In the MC calculation, the high dose-volume in the OAR was reduced around the lateral penumbra and distal falloff region by the robustness algorithm. The stability of depth dose distributions was enhanced under the WED variation, compared to the conventional algorithm. This robust algorithm in layer-stacking proton therapy may be useful for treatment in which the sharpness of the distal falloff along the depth distribution needs to be maintained to spare the organ at risk and keep the dose coverage for the target tumor.

[The characteristics of a comprehensive geriatric assessment in patients with mild cognitive impairment with a cerebral white matter lesion].

AIM: Vascular dementia may be referred to as "treatable dementia" because its development and progress can be inhibited by intervention in the early stage. In particular, cerebral white matter lesions are readily encountered the clinical setting. In this study, we aimed to clarify the phenomenon and symptoms of patients with mild cognitive impairment (MCI) with cerebral white matter lesions prior to the onset of dementia. METHODS: The subjects included 181 cases diagnosed with MCI among 643 consecutive new patients of the Center for Comprehensive Care on Memory Disorder at Kyorin University Hospital from January 1, 2013 to January 31, 2014. Patients with particular diseases were excluded. An interview, physical examination, comprehensive geriatric assessment, brain MRI and SPECT were performed for all subjects. The cerebral white matter lesions were evaluated using the modified Fazekas scale. We defined Grades 0 and 1 as the group without apparent cerebral white matter lesions and Grades 2 and 3 as the group with apparent cerebral white matter lesions. We compared the laboratory findings and outcomes of these two groups. RESULTS: The age of the group with apparent cerebral white matter lesions was significantly higher than the group without apparent cerebral white matter lesions (P<0.05). No significant difference was observed regarding gender, MMSE, or "vegetable" term retrieval. A significant difference was observed in the total score and the subordinate component of the 21-item fall risk index and geriatric depression scale between the groups (P<0.05). Additionally, a significant difference was observed regarding the subordinate component of the instrumental ADL, the Dementia Behavior Disturbance Scale and the Zarit Care Burden Scale between the groups (P<0.05). CONCLUSIONS: Our results suggest that the presence of white matter lesions at the stage of MCI has a significant relationship to care burden due to the deterioration of ADL, risk of falling, and the presence of depression and behavior disorders. We speculate that our results are useful for the explanation of the characteristics of MCI with white matter lesion to the patients and the care givers. Furthermore, these results may lead to improvements in the appropriate approach, intervention and appropriate nursing of such patients.