Recommendation for reducing the crystalline lens exposure dose by reducing imaging field width in cone-beam computed tomography for image-guided radiation therapy: an anthropomorphic phantom study.

In cone-beam computed tomography (CBCT) for image-guided radiation therapy (IGRT) of the head, we evaluated the exposure dose reduction effect to the crystalline lens and position-matching accuracy by narrowing one side (X2) of the X-ray aperture (blade) in the X-direction. We defined the ocular surface dose of the head phantom as the crystalline lens exposure dose and measured using a radiophotoluminescence dosimeter (RPLD, GD-352 M) in the preset field (13.6 cm) and in each of the fields when blade X2 aperture was reduced in 0.5 cm increments from 10.0 to 5.0 cm. Auto-bone matching was performed on CBCT images acquired five times with blade X2 aperture set to 13.6 cm and 5.0 cm at each position when the head phantom was moved from - 5.0 to + 5.0 mm in 1.0 mm increment. The maximum reduction rate in the crystalline lens exposure dose was - 38.7% for the right lens and - 13.2% for the left lens when blade X2 aperture was 5.0 cm. The maximum difference in the amount of position correction between blade X2 aperture of 13.6 cm and 5.0 cm was 1 mm, and the accuracy of auto-bone matching was similar. In CBCT of the head, reduced blade X2 aperture is a useful technique for reducing the crystalline lens exposure dose while ensuring the accuracy of position matching.

[Implementation and Effectiveness of Measures to Prevent Recurrence of Incidents Developed through Root Cause Analysis Using Work Flowchart].

PURPOSE: Incidents are recommended to be analyzed by root cause analysis (RCA). Our institution also conducts RCA for incidents and takes measures to prevent recurrence. The purpose of this study was to evaluate the effectiveness of countermeasures against the root causes analyzed by RCA in order to prevent recurrence of incidents. METHODS: Since the treatment planning CT scanner was replaced, incidents of failure to zero adjustment the coordinates of the bed position occurred four times during a three-month period. The RCA was used to investigate the root causes of these incidents and to formulate measures to prevent recurrence. To evaluate the effectiveness of the recurrence prevention measures, we collected the number of recurrence of incidents during the first year after the effectiveness of the recurrence prevention measures, and used the chi-square test to determine the significant difference in the probability of an incident occurring at a significance level of 5% or less. RESULTS: The measures to prevent the recurrence of incidents were to double-check that the coordinates of the bed position were adjusted to zero and to simulate operations based on a work flow that incorporated this double-check. During the first year period following the implementation of these recurrence prevention measures, the number of recurrence incidents was zero, and the probability of their occurrence decreased statistically significantly (p<0.05). CONCLUSION: Thorough double-checks and work simulation based on the work flow are effective methods for preventing the recurrence of incidents.

Total Synthesis of GKK1032A2 via Direct 13-Membered Macrocyclization Using a Nucleophilic Aromatic Substitution of an (η6 -Arene)Chromium Complex.

The first enantioselective total synthesis of GKK1032A2 has been achieved. The key step is a direct construction of the highly strained 13-membered macrocycle of GKK1032A2 by an intramolecular nucleophilic aromatic substitution (SN Ar) reaction. This is the first successful example of construction of a macrocycle with an aryl ether linkage utilizing an intramolecular SN Ar reaction of an (η6 -arene)chromium complex.