RESUMO
The vertical component magnetic field signal in the ground-airborne frequency domain electromagnetic (GAFDEM) method is detected by the air coil sensor, which is parallel to the ground. Unfortunately, the air coil sensor has low sensitivity in the low-frequency band, making it challenging to detect effective low-frequency signals and causing low accuracy and large error for interpreted deep apparent resistivity in actual detection. This work develops an optimized weight magnetic core coil sensor for GAFDEM. The cupped flux concentrator is used in the sensor to reduce the weight of the sensor while maintaining the magnetic gathering capacity of the core coil. The winding of the core coil is optimized to resemble the shape of a rugby ball, taking full advantage of the magnetic gathering capacity at the core center. Laboratory and field experiment results show that the developed optimized weight magnetic core coil sensor for the GAFDEM method is highly sensitive in the low-frequency band. Therefore, the detection results at depth are more accurate compared with those obtained using existing air coil sensors.
RESUMO
Objective To investigate the protective effects of reducing average radiation dose and increasing protective weight on the auditory system (tympanic cavity,the bony portion of eustachian tube,vestibule,and cochlea) during intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC).Methods The planning system (ADAC Pinnacle3 8.0m) with direct machine parameter optimization was used to optimize the IMRT planning for 40 patients with NPC (stage Ⅰ + Ⅱ:20 patients ;stage Ⅲ + Ⅳ:20 patients).Without reducing the radiation dose for target volume,the IMRT planning was optimized by limiting the average dose administered to the auditory system or increasing the protective weight for the protected organs in auditory system.The protective effects were assessed by analyzing the average dose received by the auditory system.Results After limiting the average dose administered to the auditory system without reducing the radiation dose for target volume,the average dose received by the auditory system was significantly reduced (3855.5-5391.3 Gy vs 2960.3-4559.6 Gy,P =0.000 for all) ; when the protective weight for the auditory system was increased,the average dose received by the auditory system was even more reduced (3855.5-5391.3 Gy vs 2725.4-4271.4 Gy,P =0.000 for all).For all three regimens,the average dose was significantly higher in stage Ⅲ + Ⅳ patients than in stage Ⅰ + Ⅱ patients (P =0.000 for all).Conclusions For the IMRT planning for NPC,limiting the average dose administered to the auditory system can greatly reduce the average dose received by the auditory system,and increasing the protective weight for the auditory system can further reduce the average dose received by the auditory system.However,the protective effect on the auditory system may be reduced as the stage of NPC increases.
