Rationale and objectives This study aimed to compare the volume computed tomography dose index (CTDIvol), dose length product (DLP), and size-specific dose estimate (SSDE), with the China and updated 2017 American College of Radiology (ACR) diagnostic reference levels (DRLs) in chest CT examinations of adults based on the water-equivalent diameter (Dw). Materials and methods All chest CT examinations conducted without contrast administration from January 2020 to July 2020 were retrospectively included in this study. The Dw and SSDE of all examinations were calculated automatically by “teamplay”. The CTDIvol and DLP were displayed on the DICOM-structured dose report in the console based on a 32cm phantom.The differences in patient CTDIvol, DLP, and SSDE values between groups were examined by the one-way ANOVA. The differences in patient CTDIvol, DLP, and SSDE values between the updated 2017 ACR and the China DRLs were examined with one sample t-tests. Results In total 14666 chest examinations were conducted in our study. Patients were divided into four groups based on Dw:270 (1.84%) in 15–20 cm group, 10287 (70.14%) in the 21–25 cm group, 4097 (27.94%) in the 26–30 cm group, and 12 (0.08%) patients had sizes larger than 30 cm. CTDIvol, DLP, and SSDE increased as a function of Dw (p<0.05). CTDIvol was smaller than SSDE among groups (p<0.05). The mean CTDIvol and DLP values were lower than the 25th, 50th, and 75th percentile of the China DRLs (p <0.05). The CTDIvol, DLP, and SSDE were lower than the 50th and 75th percentiles of the updated 2017 ACR DRLs (p <0.05) among groups. Conclusions SSDE takes into account the influence of the scanning parameters, patient size, and X-ray attenuation on the radiation dose, which can give a more realistic estimate of radiation exposure dose for patients undergoing CT examinations. Establishing hospital’s own DRL according to CTDIvol and SSDE is very important even though the radiation dose is lower than the national DRLs.
The purpose of this study is to compare the response of PET-defined tumor to PLDR radiotherapy to patients treated with conventional delivery through evaluation of pre (scan-1) and posttreatment (scan-2) PET-CT scans of patients not previously irradiated. Materials/Methods: Data for 9 patients treated for esophageal cancer on an IRB-approved Phase I study of neoadjuvant PLDR RT with concurrent chemotherapy for treatment of NSCLC or esophageal cancer were evaluated. The patients were treated to 50.4 Gy in 28 fractions via IMRT or VMAT, prior to surgery. All scan-1 and scan-2 data sets were fused based on boney anatomy with RT planning software. PET volumes were delineated by an experienced Nuclear Medicine physician and a standardized uptake value (SUV) threshold of 3.0 was used to designate tumor. Both scan-1 and 2 PET-defined volumes were delineated within the PTV assuring they received the prescribed dose and all volumes superimposed onto each CT data set through the fusion process and corrected for low density inclusions (air). The average volumes and mean HU values on each CT scan were obtained. The post-treatment mean HU values were corrected for difference in scanner performance. A CT-normalized mean SUV was determined for the volumes on both scan sets according to aveSUV CT-norm Z aveSUV/aveHU. This value reflects active tumor regardless of density or thickness differences that may not be observed from CT alone. Data were compared with those from 18 sequentially selected, esophageal cancer patients conventionally treated to the same dose with concurrent chemotherapy using Fisher's exact and Wilcoxon rank sum tests. Volume reduction and complete response (CR) (no voxels with SUV >3.0) were evaluated using Tweedie generalized linear models and logistic regression, respectively. Results: Under direct comparison, no significant difference was found between demographic and tumor characteristics and the two groups are well balanced. The mean pre to post-treatment percent volume reduction was 90.3% for PLDR and 74.7% for conventional delivery (pZ0.022). Volume reduction was also greater in node negative (pZ0.037) and younger patients (pZ0.065). The CR rate of PLDR was 33.3% vs. 16.7% for conventional delivery (pZ0.203). The mean HU value decrease was not significant. The average normalized mean SUV decrease from scan-1 to 2 for pre-treatment volumes was greater for PLDR delivery by approximately 22.8% (ns). This parameter for the post-treatment volume was greater for PLDR delivery by 6.8% (ns). Conclusion: The decreases in PET-defined volumes and the trends in improved normalized mean SUV and CR rate for PLDR are indications suggestive of treatment effectiveness. Given these results and the small sample size, PLDR delivery may even prove superior to conventional delivery for these patients.
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