Objective To measure radiation filed distribution in the treatment room of the Varian Halcyon medical linear accelerator, and to provide a basis for shielding design and potential exposure analysis of treatment rooms for this type of accelerator. Methods Under the 6 MV X-ray (FFF) mode at a maximum dose rate of 800 MU/min and a maximum irradiation field of 28.00 cm × 28.00 cm, a total of 540 MU was delivered during gantry rotation. Radiation field distribution was measured using thermoluminescence dosimeters located at multiple points in the room. The measured data were then applied to shielding calculations, and the results were compared with those obtained using empirical formulas. Results The overall radiation levels in the treatment room were in the range of 12.2 µGy/540 MU to 5.520 Gy/540 MU, with the highest dose (5.520 Gy/540 MU) observed at the isocenter, and the lowest dose (12.2 µGy/540 MU) recorded at approximately 6.5 m from the gantry head. The radiation levels at most points were within the range of 100-1000 µGy/540 MU. At heights of 0.5, 1.1, and 1.7 m, the radiation field exhibited a rapid attenuation from the beam center outward, with a faster decay along the treatment couch direction (Y-axis) than along the perpendicular direction (X-axis). Shielding calculations based on the measured radiation field yielded required wall thicknesses of 1219 mm (east wall), 949 mm (south wall), 1235 mm (west wall), and 1252 mm (north wall), all of which were smaller than those calculated using empirical formulas. Conclusion Thermoluminescence dosimeter is suitable for multi-point in situ measurement of radiation field distribution in Halcyon accelerator treatment rooms. The measurement results can be used to optimize the shielding design of Halcyon accelerator treatment rooms.

Objective: To explore the chain mediating effect of cognitive flexibility and depressive cognition between mindfulness and suicide risk in undergraduates. Methods: Suicidal Behaviors Questionnaire-revised (SBQ-R), mindful attention awareness scale (MAAS), cognitive flexibility inventory (CFI) and depressive cognition scale (DCS) were used to investigate 2 627 freshmen from a medical university in Guangdong Province. Results: The scores of suicide risk, mindfulness, cognitive flexibility and depressive cognition were (M(Q_R)): 4.00(2.00), 67.00(15.00), 78.00(13.00), 5.00(7.00), respectively.The results of correlation analysis showed that suicide risk was positively correlated with depressive cognition (r=0.280, P<0.01), and negatively correlated with the level of mindfulness and cognitive flexibility (r=-0.253, r=-0.196, P<0.01). Mindfulness was positively correlated with cognitive flexibility (r=0.539, P<0.01), negatively correlated with depressive cognition (r=-0.518, P<0.01). Cognitive flexibility was negatively correlated with depressive cognition (r=-0.584, P<0.01). Mediation modeling analysis showed that mindfulness had a significant direct effect on suicide risk.The direct effect value was -0.101, accounting for 34.9% of the total effect.The total indirect effect of mindfulness on suicide risk was -0.188, accounting for 65.1% of the total effect.The mediating effect of cognitive flexibility as mediator between mindfulness and suicide risk was -0.063, accounting for 21.8% of the total effect.The mediating effect of depressive cognition as mediator between mindfulness and suicide risk was -0.054, accounting for 18.7% of the total effect.The chain mediating effect of cognitive flexibility and depressive cognition was -0.071, accounting for 24.6% of the total effect. Conclusion Mindfulness can influence suicide risk, not only through the direct path, but also through the indirect path of cognitive flexibility and depressive cognition, as well as the chain mediating path between these two variables.