Purpose: Monte Carlo (MC) simulation studies, aimed at evaluating the magnitude of tissue heterogeneity in 125 I prostate permanent seed implant brachytherapy (BT),customarily use clinical post-implant CT images to generate a virtual representation of a realistic patient model (virtual patient model).Metallic artifact reduction (MAR) techniques and tissue assignment schemes (TAS) are implemented on the post-implant CT images to mollify metallic artifacts due to BT seeds and to assign tissue types to the voxels corresponding to the bright seed spots and streaking artifacts, respectively. The objective of this study is to assess the combined influence of MAR and TAS on MC absorbed dose calculations in post-implant CT-based phantoms. The virtual patient models used for 125 I prostate implant MC absorbed dose calculations in this study are derived from the CT images of an external radiotherapy prostate patient without BT seeds and prostatic calcifications, thus averting the need to implement MAR and TAS. Methods: The geometry of the IsoSeed I25.S17plus source is validated by comparing the MC calculated results of the TG-43 parameters for the line source approximation with the TG-43U1S2 consensus data. Four MC absorbed dose calculations are performed in two virtual patient models using the egs_brachy MC code: (1) TG-43-based D w,w-TG43 , (2) D w,w-MBDC that accounts for interseed scattering and attenuation (ISA), (3) D m,m that examines ISA and tissue heterogeneity by scoring absorbed dose in tissue, and (4) D w,m that unlike D m,m scores absorbed dose in water. The MC absorbed doses (1) and ( 2) are simulated in a TG-43 patient phantom derived by assigning the densities of every voxel to 1.00 g cm −3 (water), whereas MC absorbed doses (3) and ( 4) are scored in the TG-186 patient phantom generated by mapping the mass density of each voxel to tissue according to a CT calibration curve. The MC absorbed doses calculated in this study are compared with VariSeed v8.0 calculated absorbed doses. To evaluate the dosimetric effect of MAR and TAS, the MC absorbed doses of this work (independent of MAR and TAS) are compared to the MC absorbed doses of different 125 I source models from previous studies that were calculated with different MC codes using post-implant CT-based phantoms generated by implementing MAR and TAS on post-implant CT images.
Introduction: Performing lymphoscintigraphy in a separate room, frees up the conventional gamma camera, coupled with the desire to directly localize sentinel lymph nodes (SLN) in the operating theatre has led to the development of high-resolution semiconductor-detector based handheld gamma-cameras, CrystalCam. Methods: This work consists of phantom and clinical studies. For the first part, a Jaszczak phantom with hollow spheres of various volumes were filled with the 99m Tc and the camera's sensitivity was measured at various distances to assess the possibilities and limitations of the device.The clinical study evaluates the effectiveness of CrystalCam in localizing SLN in 40 consecutive malignant melanoma patients compared to both conventional planar lymphoscintigraphy and hybrid SPECT/CT. SLNs detected by planar lymphoscintigraphy were marked on the patients' skin using a UV-marker. CrystalCam images were acquired in another room by another examiner and the SLNs were marked with a felt pen. The detected nodes by both camera systems were evaluated using UV-lamp and normal light to visualize the UV-and felt pen marks respectively. The concordance rate of the SLNs and higher-echelon nodes localized by both planar scintigraphy and CrystalCam imaging with respect to the total SLNs and higher-echelon nodes detected by SPECT/CT imaging are compared and statistically analyzed. Results:The results of the phantom study show a good correlation between activity and count-rates for all distancesSPECT/CT, CrystalCamm, and planar lymphoscintigraphy detected 69,58,and 61 SLNs respectively.The concordance rate of 95.65% by the CrystalCam and planar scintigraphy implies both cameras are statistically coequal in preoperative SLN detection of malignant melanoma. For the higher-echelon nodes, SPECT/CT, planar and CrystalCam imaging systems identified 82, 48, and 13 respectively; thus, CrystalCam was statistically inferior to planar imaging. Conclusion:The handheld CrystalCam is a reliable instrument for localizing SLNs in surgical centers without an on-site nuclear medicine department.
Radiation Protection in Radiology, Nuclear Medicine and Radio Oncology is of the utmost importance. Radioiodine therapy is a frequently used and effective method for the treatment of thyroid disease. Prior to each therapy the radioactivity of the false[ 131Ifalse]‐capsule must be determined to prevent misadministration. This leads to a significant radiation exposure to the staff. We describe an alternative method, allowing a considerable reduction of the radiation exposure. Two false[ 131Ifalse]‐capsules false(normalA01=2818.5; normalA02=73.55.0 MBqfalse) were measured multiple times in their own delivery lead containers — that is to say, false[ 131Ifalse]‐capsules remain inside the containers during the measurements (shielded measurement) using a dose calibrator and a well‐type and a thyroid uptake probe. The results of the shielded measurements were correlated linearly with the false[ 131Ifalse]‐capsules radioactivity to create calibration curves for the used devices. Additional radioactivity measurements of 50 false[ 131Ifalse]‐capsules of different radioactivities were done to validate the shielded measuring method. The personal skin dose rate false(normalHPfalse(0.07false)false) was determined using calibrated thermo luminescent dosimeters. The determination coefficients for the calibration curves were normalR2>0.9980 for all devices. The relative uncertainty of the shielded measurement was <6.8%. At a distance of 10 cm from the unshielded capsule the normalHPfalse(0.07false) was 46.18 μSv/false(GBq⋅sfalse), and on the surface of the lead container containing the false[ 131Ifalse]‐capsule the normalHPfalse(0.07false) was 2.99 and 0.27 μSv/false(GBq⋅sfalse) for the two used container sizes. The calculated reduction of the effective dose by using the shielded measuring method was, depending on the used container size, 74.0% and 97.4%, compared to the measurement of the unshielded false[ 131Ifalse]‐capsule using a dose calibrator. The measured reduction of the effective radiation dose in the practice was 56.6% and 94.9 for size I and size II containers. The shielded false[ 131Ifalse]‐capsule measurement reduces the radiation exposure to the staff significantly and offers the same accuracy of the unshielded measurement in the same amount of time. In order to maintain the consistency of the measuring method, monthly tests have to be done by measuring a false[ 131Ifalse]‐capsule with known radioactivity.PACS number(s): 93.85.Np, 92.20.Td, 87.50.yk, 87.53.Bn
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