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Objective:To investigate the radiation protection effect of furosemide intervention on 18F-2-deoxy-D-glucose ( 18F-FDG) positron emission tomography/computed tomography (PET/CT) imaging. Methods:A total of 146 patients were randomly divided into two groups, with test group of 74 patients and control group of 72. The test group was administrated orally with furosemide of 40 mg for each one before injection, while the normal control group did not undergo special treatment. 60 and 120 min after 18F-FDG injection, the horizontal measurement of ambient dose equivalent rates was carried out at 0.5 m from the front of both chest and abdomen respectively. Results:For the test group, the ambient dose equivalent rates were measured to be (30.80±8.61) and (41.38±11.06) μSv/h 60 min after injection of 18F-FDG whereas (18.26±4.85) and (24.66±6.50) μSv/h 120 min after injection, respectively, both lower than in the control group and with statistically significant difference between the both ( t =15.36, 13.13, 18.73, 17.29, P<0.05) . No significant difference was found between mediastinal SUV max and liver SUV max in the experimental group and control group ( P>0.05) . Multivariate ANOVA showed that body surface area was a major factor influencing ambient dose equivalent rate regardless of furosemide injection ( t=-13.52, 2.96, P<0.05) , and no obvious effects of age and sex on ambient dose equivalence rate were found. Conclusions:Furosemide intervention can promote urination, effectively reduce the internal radiation exposure of the examinated patietns in the premise of not affecting the image quality, and therefore provide a better radiation protection effect.
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Objective To determine the peripheral dose ( PD) of a Trilogy accelerator under different conditions and the feasibility of PD measurement using the semiconductor diode ionization chamber. Methods In a solid water phantom, a CC13 air?filled ionization chamber and a semiconductor diode ionization chamber were used for PD measurements with different distances (13 measurement locations within 1?31 cm) , depth ( 3, 5, 15 cm) , field sizes ( 10, 20, 30 cm) , wedge ( W15, W45, VW15, VW45) , and beam energy (6, 18 MV). The relationship of PD with PDleakage and PDscat er was determined by removing the scatter phantom. Simulating the patients with cervical cancer undergoing radiotherapy, a CIRS phantom received volumetric modulated arc therapy ( VMAT) , step?shoot intensity?modulated radiotherapy ( IMRT) , and sliding?window IMRT to measure PDs of the breast, thyroid, and lens. All the data were normalized to the isocenter. Results PD was gradually reduced with the increase in distance ( 13?41% at 1 cm from the edge to 0?25% at 31 cm from the edge) . With a fixed distance from the edge of the radiation field, there was no significant difference in PD between different depths. A radiation field with a size of 30 cm had a PD about two?fold higher than that with a size of 10 cm. PD increased with the increase in the physical wedge angle and increased by 1% compared with the open field;PD decreased with the increase in the virtual wedge angle and decreased by 2?3% compared with the open field. PD decayed from 13?35% at 1 cm to 0?23% at 31 cm under 6 MV X?ray and from 11?06% at 1 cm to 0?20% at 31 cm under 18 MV X?ray. Dscat er was dominant in the regions close to the edge of radiation field and decreased from 62?45% at 1 cm to 5?71% at 25 cm. In all measurements under 6 MV X?ray, the maximum proportion difference between CC13 ionization chamber and diode ionization chamber was less than 1%. PDs of the breast, thyroid, and lens were 6?72, 2?90, and 2?37 mGy in VMAT mode, 7?39, 4?05, and 2?48 mGy in step?shoot IMRT mode, and 9?17, 4?61, and 3?21 mGy in sliding?window IMRT mode, respectively. Conclusions For the measurement of PDs, the CC13 air?filled ionization chamber and semiconductor diode ionization chamber have good consistency and feasibility under 6 MV X?ray. In clinical practice, the understanding of the relationship of PD with different radiation conditions helps to reduce the doses to organs at risk. Shielding and protective techniques can further reduce dose deposition.
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Objective To evaluate the peripheral dose (PD) from megavoltage cone-beam CT (MVCBCT) imaging for head-and-neck region image-guided radiation therapy,to determine the correlation of PD with monitor unit (MU),and to investigate the impact of imaging field size on the PD.Methods Measurements of PD from MVCBCT were made with a 0.65 cm3 ionization chamber placed in a specially designed phantom at various depths and distances from the field edges.The PD at reference point inside the phantom was measured with the same ionization chamber to investigate the linearity between MU used for MVCBCT and the PD.The homogeneity of PD in the axial plane of the phantom were measured.Results PD from MVCBCT increased with increasing number of MU used for imaging and with increasing the field size.The measured PD in the phantom decreased exponentially as distance from the field edges increased.PD also decreased as the depth from the phantom surface increased.There was a strong linear relationship between PD and MUs used for MVCBCT.The PD was heterogeneous,with higher dose at the anterior than the posterior.Conclusions The PD from MVCBCT depend much on the MVCBCT delivery MU and the scan field size.In clinic,using the smallest number of MU allowable and reducing MVCBCT scanning field size without compromising acquired image quality is an effective method of reducing the PD.
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The authors have studied the feasibility of using three new high-sensitivity radiochromic devices in measuring the doses to peripheral points outside the primary megavoltage photon beams. The three devices were GAFCHROMIC® EBT film, prototype Low Dose (LD) Film, and prototype LD Card. The authors performed point dosimetry using these three devices in water-equivalent solid phantoms at x = 3,5,8,10, and 15 cm from the edge of 6 MV and 15 MV photon beams of 10x10 cm2, and at depths of 0, 0.5 cm, and depth of maximum dose. A full sheet of EBT film was exposed with 5000 MU. The prototype LD film pieces were 1.5x2 cm2 in size. Some LD films were provided in the form of a card in 1.8x5 cm2 holding an active film in 1.8x2 cm2. These are referred to as “LD dosimeter cards”. The small LD films and cards were exposed with 500 MU. For each scanned film, a 6 mm circular area centered at the measurement point was sampled and the mean pixel value was obtained. The calibration curves were established from the calibration data for each combination of film/cards and densitometer/scanner. The doses at the peripheral points determined from the films were compared with those obtained using ion chamber at respective locations in a water phantom and general agreements were found. It is feasible to accurately measure peripheral doses of megavoltage photon beams using the new high-sensitivity radiochromic devices. This near real-time and inexpensive method can be applied in a clinical setting for dose measurements to critical organs and sensitive patient implant devices.
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In order to evaluate the radio-protective advantage of an enhanced dynamic wedge (EDW) over a physical wedge (PW), we measured peripheral doses scattered from both types of wedges using a 2D array of ion-chambers. A 2D array of ion-chambers was used for this purpose. In order to confirm the accuracy of the device, we first compared measured profiles of open fields with the profiles calculated by our commissioned treatment planning system. Then, we measured peripheral doses for the wedge angles of 15 degrees, 30 degrees, 45 degrees, and 60 degrees at source to surface distances (SSD) of 80 cm and 90 cm. The measured points were located at 0.5 cm depth from 1 cm to 5 cm outside of the field edge. In addition, the measurements were repeated by using thermoluminescence dosimeters (TLD). The peripheral doses of EDW were (1.4% to 11.9%) lower than those of PW (2.5% to 12.4%). At 15 MV energy, the average peripheral doses of both wedges were 2.9% higher than those at 6MV energy. At a small SSD (80 cm vs. 90 cm), peripheral dose differences were more recognizable. The average peripheral doses to the heel direction were 0.9% lower than those to the toe direction. The results from the TLD measurements confirmed these findings with similar tendency. Dynamic wedges can reduce unnecessary scattered doses to normal tissues outside of the field edge in many clinical situations. Such an advantage is more profound in the treatment of steeper wedge angles, and shorter SSD.
Subject(s)
Heel , Silver Sulfadiazine , ToesABSTRACT
The peripheral dose distributions of wedge fields of Co-0 gamma-ay and 10MV x-ay were measured by the solid state detector controlled by means of semiautomatic water phentom system. The measurements were made on the principal plane parallel to the cross section of wedge filter (blade and ridge direction). For parallel motion of the detector to the beam axis the distance from the margin of radiation field at surface were 3, 5 and 10cm. For tranverse motion the depth of measurement were dm, 5, 10 and 15cm. The followings were drawn from the measurement. 1. The peripheral dose of the blade side of wedges was generally higher than that of the ridge side at symmetric point about beam axis. 2. In the superficial region phenomena of dose build-p appeared. 3. For Co-0 gamma-ay field, the peripheral dose did not monotonously decrease with the distance from the field margin but increase in some range, consequently showing a peak dose. 4. The peripheral dose did not only depend on radiation quality and field size, but also on wedge angle and wedge direction.