Interimager variability in ADC measurement of the human brain.

PURPOSE: Routine clinical practice involves the application of diverse scanning parameters that can affect apparent diffusion coefficient (ADC) values. We evaluated interimager variability in ADC values with respect to their potential effect in clinical applications. METHODS: In 7 healthy volunteers, we obtained diffusion-weighted (DW) images using routine clinical parameters and 1.5- (n = 9) and 3-tesla (n = 3) magnetic resonance (MR) imagers from 5 different vendors, performing 84 MR imaging studies. To evaluate the differences in ADC values among the imagers, vendors, and magnetic field strengths, we measured the mean pixel values of the frontal white matter and thalamus (gray matter) in both cerebral hemispheres of the 7 volunteers and used repeated-measures analysis of variance for multiple comparisons. RESULTS: The laterality of ADC values in the bilateral structures ranged from one to 3% for the 12 imagers. Although the relative difference in ADC values of white matter was 7% for scanners yielding the highest and lowest mean ADC values (P < 0.01), it was within 2 to 4% for instruments from the same vendors. For gray matter, the interimager difference was 4 to 12%, even among the same vendors (P < 0.05). Among the 3T imagers, the difference for white and gray matter was approximately 3%. CONCLUSIONS: There were significant interimager differences in ADC values, especially with respect to gray matter. Taking into consideration the existing laterality, however, the differences among our 3T imagers may be acceptable despite the use of diverse scanning parameters. In routine clinical practice, the existing variability must be considered imager by imager.

[Cone-beam computed tomography-derived adaptive radiotherapy].

The purpose of this study was to evaluate the reliability of cone-beam computed tomography (CBCT)-derived adaptive radiotherapy. We evaluate planning computed tomography (pCT) and CBCT in 50 patients who had undergone image guided radiotherapy (IGRT) with CBCT. Irradiated sites included head, neck, chest, abdomen, and pelvis; there were 10 patients in each group. Treatment plans including 153 beam data were recalculated based on CBCT. To compare between pCT and CBCT, we estimated CT values of normal tissues, body contour, effective depth, and monitor units (MU) calculation. The maximum difference in CT values was observed in lung estimation. The 5 mm or more differences in depth were observed in 2 beams of 2 pelvic cases, but CBCT also demonstrated a shift of abdominal wall due to intestinal motility. There were downward trends for the effective depth and MU based on CBCT, especially in lung cases. However, the differences in prescribed dose due to MU calculation were less than 5% because all patients were treated with a multifield irradiation plan. CBCT provides not only precise daily setup but also accurate anatomical information on body contour. In addition, CBCT may be considered as a useful tool for dose calculation.

Histopathological changes in parotid and submandibular glands of patients treated with preoperative chemoradiation therapy for oral cancer.

We retrospectively evaluated the relationship between computed tomography (CT)- and histopathological findings of parotid and submandibular glands in six patients treated for advanced oral cancer. Eligibility criteria were a pathologic diagnosis of oral squamous cell carcinoma, preoperative chemoradiation therapy (CRT) with a total dose of 30 Gy and oral S-1 (80 mg/m²/day), the availability of morphological assessments by CT and of functional assessments with the Saxon test before- and 2 weeks after CRT, and the availability of histopathological slides of irradiated parotid and submandibular glands. In the histopathological interpretation, gland structures were divided into acinar-, duct-, and adipose cells and other tissues. The Mann-Whitney test and the Spearman rank correlation test were used to determine histopathological changes. After 30-Gy irradiation, saliva production and parotid and submandibular volumes were significantly decreased (P < 0.05 each). Histopathological analysis demonstrated that 30-Gy irradiation resulted in a loss of acinar cells although acinar cells in the submandibular gland were relatively retained; the median acinar rate in the parotid and submandibular glands was 1.1% and 19.0%, respectively. The CT values after CRT were inversely correlated with adipose ratios (r = -0.98, P < 0.01) and there was a strong correlation between CT values before and after CRT (r = 0.97, P < 0.01). Our results suggested that acinar cell loss is a main contributor to changes in the volume and function of irradiated human parotid and submandibular glands. The CT value may reflect the adipose ratio rather than salivary function.

FDG-PET/CT-based gross tumor volume contouring for radiation therapy planning: an experimental phantom study.

As there is continuing controversy over the role of F-18-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT-fused imaging in radiation therapy (RT) planning, we performed a phantom study to assess the feasibility of FDG-PET/CT-based gross tumor volume (GTV) contouring. The phantom set, consisting of an elliptical bowl and 6 spheres measuring from 10-37 mm in diameter, were filled with FDG to obtain 3 source-to-background ratios (SBRs) of 4, 8, and 16. The ratio to maximum intensity at 5% intervals was applied as the threshold for contouring. The ratio between contoured- and actual volumes (volume ratio) was calculated, and the threshold ratio was selected to provide a volume ratio close to 100%. To consider the clinical application, we applied the threshold value (maximum intensity × threshold ratio) for the largest 37-mm sphere to the 6 spheres. The threshold ratio and the volume ratio in 6 spheres with 3 SBRs were compared using the Friedman test. Threshold ratios ranged from 25-80%; they were higher for smaller spheres (p = 0.003) and lower SBRs (p < 0.001). The volume ratios with the threshold value for the largest 37-mm sphere were lower in smaller spheres (p = 0.010). These results suggest that smaller lesions and higher background activities require a higher threshold ratio and smaller lesions a lower threshold value. FDG-PET/CT-fused imaging should not be used as a single modality but rather to obtain supplemental information in RT planning. The contoured GTV should be adjusted based on clinical data including conventional images.

[Computerized estimation of a percent glandular tissue composition in computed radiography mammography].

Measurement of a percent glandular tissue composition (%GTC) is important in terms of the estimation of individual patient exposure dose and the prediction of malignancy, and thus a number of reports for estimating %GTC by use of a mammogram have been published. In this study, we propose a method for estimating individual %GTC by use of computed radiography (CR) mammograms. By employing breast-equivalent phantoms that are able to create breast phantom images with various combinations of fat and glandular tissue, as well as the thickness of whole breast, we determined a reference table for converting an each pixel value on CR mammography to the glandular tissue ratio. Therefore, the %GTC for individual breast was estimated by averaging glandular tissue ratio for a whole region. The clinical image data set that consisted of 49 CR mammograms were used for estimating %GTC. A paired comparison method for determining subjective ranking of the degree of breast density was employed in order to demonstrate the validity of our method. The results indicate that the average estimated %GTC was 35.0% (ranged from 12.0% to 67.0%) and they had a increased correlation with the ranking of those obtained by observer test. Therefore, it was suggested that our proposed method would be utilized for estimating the %GTC in objective manner.

[Impact of setup error and anatomical change on dose distribution during conventional radiation therapy].

The purpose of this study was to evaluate the impact of setup error and anatomical change on dose distribution during conventional radiation therapy. We performed regional irradiation (Plan1) using opposing pair fields, and then we planned local irradiation (Plan2) with a computed tomography (CT) acquired at that time in 10 patients with advanced oral cancer. To consider the setup error, a minimum dose of gross tumor volume (GTV) and a maximum dose for the spinal cord were re-calculated with isocenter shifts of ±5 mm. We also evaluated an alteration of reference dose due to anatomical changes during radiation therapy. A minimum dose of GTV was decreased with isocenter shifts; the trend was stronger in Plan2 than Plan1 (-5.7% vs. -1.2%, p=0.02). Similarly, a maximum dose of spinal cord was increased with isocenter shifts, especially in Plan2 (12.2% vs. 0.5%, p<0.01). Anatomical changes during radiation therapy were observed in all patients, and the mean difference for depth was -4 mm in Plan1; the reference dose was increased in Plan1 and Plan2. Precise setup is necessary, especially for local irradiation in spite of anatomical changes during radiation therapy. Reimaging and replanning are recommended for patients with marked anatomical changes.