Objectives: We developed a prototype CdTe SPECT system with 4-Pixel Matched Collimator for brain study. This system provides high energy resolution (6.6%), high sensitivity (220 cps/MBq/head) and ...high spatial resolution images. The aim of this study is to evaluate dual isotope study of CBF and central benzodiazepine receptor (BZR) images using Tc-99m ECD and I-123 IMZ with the new SPECT system in patients with epilepsy comparing with single isotope study using the conventional scintillation gamma camera. Methods: This study included 13 patients with partial epilepsy. BZR images were acquired at 3 hours after I-123 IMZ injection for 20 minutes. The images of IMZ were acquired with a conventional 3 head scintillation gamma camera. After BZR image acquisition with the conventional camera, Tc-99m ECD was injected and CBF and BZR images were acquired simultaneously 5 minutes after ECD injection with the new SPECT system. CBF images were also acquired with the conventional camera on separate days. The findings were visually and semi-quantitatively analyzed. In semi-quantitative analysis, the maximum Z scores of concordant lesions were compared between the two studies using the Pearson correlation coefficient.The 9mm circular ROI was used and two lesions in each patient were analyzed. A p value < 0.05 was considered as significant. Results: There were 47 abnormal lesions on BZR images and 60 abnormal lesions on CBF images in the single isotope study with the conventional camera. Dual isotope study with the new system showed concordant abnormal findings of 46/47 lesions on BZR and 54/60 lesions on CBF images with the single isotope study with the conventional camera. There was high agreement between the two studies in both BZR and CBF findings (Cohen's kappa values; 0.96 for BZR, 0.78 for CBF). In semi-quantitative analysis, maximum Z scores of dual isotope study with the new system strongly correlated with those of single isotope study with the conventional camera (BZR: r=0.82, p < 0.05, CBF: r=0.87, p < 0.05). Conclusion: Our new SPECT system permits dual-isotope study for pixel-by-pixel analysis of CBF and benzodiazepine receptor information with the same pathophysiological condition in patients with epilepsy.
For high-sensitivity brain imaging, we have developed a two-head single-photon emission computed tomography (SPECT) system using a CdTe semiconductor detector and 4-pixel matched collimator (4-PMC). ...The term, '4-PMC' indicates that the collimator hole size is matched to a 2 × 2 array of detector pixels. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. The performance of the higher-sensitivity 4-PMC was experimentally compared with that of the 1-PMC. The sensitivities of the 1-PMC and 4-PMC were 70 cps/MBq/head and 220 cps/MBq/head, respectively. The SPECT system using the 4-PMC provides superior image resolution in cold and hot rods phantom with the same activity and scan time to that of the 1-PMC. In addition, with half the usual scan time the 4-PMC provides comparable image quality to that of the 1-PMC. Furthermore, (99m)Tc-ECD brain perfusion images of healthy volunteers obtained using the 4-PMC demonstrated acceptable image quality for clinical diagnosis. In conclusion, our CdTe SPECT system equipped with the higher-sensitivity 4-PMC can provide better spatial resolution than the 1-PMC either in half the imaging time with the same administered activity, or alternatively, in the same imaging time with half the activity.
To investigate the clinical significance of adaptive radiotherapy (ART) in locally advanced nasopharyngeal carcinoma treated with intensity-modulated radiotherapy (IMRT).
Eligible patients were ...treated with concurrent chemoradiotherapy using IMRT. Planning computed tomography in ART was performed during radiotherapy, and replanning was performed. Since ART was started in May 2011 (ART group), patients who were treated without ART up to April 2011 (non-ART group) were used as the historical control. The Kaplan-Meier method was used to calculate overall survival (OS), locoregional recurrence-free survival (LRFS), progression-free survival (PFS), and distant metastasis-free survival (DMFS). LRFS for the primary tumor (LRFS_P) and regional lymph node (LRFS_LN) were also studied for more detailed analysis. Statistical significance was evaluated using the log-rank test for survival.
The ART group tended to have higher radiation doses. The median follow-up period was 127 months (range, 10 to 211 months) in the non-ART group and 61.5 months (range, 5 to 129 months) in the ART group. Compared to the non-ART group, the ART group showed significantly higher 5-year PFS (53.8% vs. 81.3%, p = 0.015) and LRFS (61.2% vs. 85.3%, p = 0.024), but not OS (80.7% vs. 80.8%, p = 0.941) and DMFS (84.6% vs. 92.7%, p = 0.255). Five-year LRFS_P was higher in the ART group (61.3% vs. 90.6%, p = 0.005), but LRFS_LN did not show a significant difference (91.9% vs. 96.2%, p = 0.541).
Although there were differences in the patient backgrounds between the two groups, this study suggests the potential effectiveness of ART in improving locoregional control, especially in the primary tumor.
Objectives:
We aimed to investigate whether daily computed tomography (CT) images could predict the daily gastroduodenal, small intestine, and large intestine doses of stereotactic body radiation ...therapy (SBRT) for pancreatic cancer based on the shortest distance between the gross tumor volume (GTV) and gastrointestinal (GI) tract.
Methods:
Twelve patients with pancreatic cancer received SBRT of 40 Gy in five fractions. We recalculated the reference clinical SBRT plan (PLAN
ref
) using daily CT images and calculated the shortest distance from the GTV to each GI tract. The maximum dose delivered to 0.5 cc (D
0.5cc
) was evaluated for each planning at-risk volume of the GI tract. Spearman’s correlation test was used to determine the association between the daily change in the shortest distance (Δshortest distance) and the ratio of ΔD
0.5cc
dose to D
0.5cc
dose in PLAN
ref
(ΔD
0.5cc
/PLAN
ref
) for quantitative analysis.
Results:
The median shortest distance in PLAN
ref
was 0 mm in the gastroduodenum (interquartile range, 0–2.7), 16.7 mm in the small intestine (10.0–23.7), and 16.7 mm in the large intestine (8.3–28.1 mm). The D
0.5cc
of PLAN
ref
in the gastroduodenum was >30 Gy in all patients, with 10 (83.3%) having the highest dose. A significant association was found between the Δshortest distance and ΔD
0.5cc
/ PLAN
ref
in the small or large intestine (p < 0.001) but not in the gastroduodenum (p = 0.404).
Conclusions:
The gastroduodenum had a higher D
0.5cc
and predicting the daily dose was difficult. Daily dose calculations of the GI tract are recommended for safe SBRT.
Advances in knowledge:
This study aimed to predict the daily doses in SBRT for pancreatic cancer from the shortest distance between the GTV and the gastrointestinal tract. Daily changes in the shortest distance can predict the daily dose to the small or large intestines, but not to the gastroduodenum.
We propose a wide aperture parallel-hole collimator that we call a 4-pixel matched collimator (4-PMC) for high-sensitivity SPECT imaging. The hole size of the 4-PMC is matched to four detector ...pixels; that is, there are four (2 × 2) pixels per collimator hole. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. We evaluated four types of collimator (high-resolution collimator versions and high-sensitivity collimator versions of both 4-PMC and 1-PMC) by simulation. SPECT images of a cylindrical phantom with cold spots in the noise-free condition demonstrated that the 4-PMC provided a higher-contrast image than the 1-PMC for the same collimator version. In addition, SPECT images at the noise level corresponding to a human cerebral blood flow study suggested that the high-sensitivity version of the 4-PMC provided the highest contrast image among the four collimator types. In conclusion, the high-sensitivity SPECT system using the 4-PMC can improve the trade-off between spatial resolution and sensitivity and will consequently provide improved image contrast for clinical studies of the human brain compared with the SPECT system using the 1-PMC.
A new design of collimator is proposed that has variable sensitivity and spatial resolution, eliminating the need for exchanging collimators in a gamma camera. Using Monte Carlo simulations, the ...present article evaluates the shielding of undesirable gamma rays in a parallel-hole collimator. It consists of a number of layers of rectangular holes. These layers consist of alternately stacked fixed and movable collimators. In high-resolution mode, the movable collimators are shifted by half the aperture pitch along the diagonal direction. The first collimator (type A) has 50 layers with fixed thicknesses of 1.2 mm. The second collimator (type B) has 25 layers with a thickness of 1.0 mm on the object side and 25 layers with a thickness of 1.4 mm on the opposite side. The third collimator (type C) has 20 layers with non-uniform thicknesses. The ratios of the maximum artificial peak to the main-peak are calculated for point-source responses. The ratios for types A, B, and C collimators are 0.78, 0.08, and 0.03, respectively. The same performance for shielding undesirable gamma rays is achieved in the type C collimator as for a conventional collimator.
Abstract
Modern radiotherapy technologies such as proton beam therapy (PBT) permit dose escalation to the tumour and minimize unnecessary doses to normal tissues. To achieve appropriate patient ...selection for PBT, a normal tissue complication probability (NTCP) model can be applied to estimate the risk of treatment-related toxicity relative to X-ray therapy (XRT). A methodology for estimating the difference in NTCP (∆NTCP), including its uncertainty as a function of dose to normal tissue, is described in this study using the Delta method, a statistical method for evaluating the variance of functions, considering the variance–covariance matrix. We used a virtual individual patient dataset of radiation-induced liver disease (RILD) in liver tumour patients who were treated with XRT as a study model. As an alternative option for individual patient data, dose-bin data, which consists of the number of patients who developed toxicity in each dose level/bin and the total number of patients in that dose level/bin, are useful for multi-institutional data sharing. It provides comparable accuracy with individual patient data when using the Delta method. With reliable NTCP models, the ∆NTCP with uncertainty might potentially guide the use of PBT; however, clinical validation and a cost-effectiveness study are needed to determine the appropriate ∆NTCP threshold.
A pulsed bias voltage shutdown circuit to suppress the polarization effect in a CdTe radiation detector equipped with a matrix readout system was investigated. The matrix readout system is suitable ...for radiation detection systems that have many pixels and that are used at a relatively low counting rate, such as single photon emission computed tomography (SPECT). CdTe detectors have a time-dependent polarization effect that must be suppressed. One method to suppress this effect is pulsed bias voltage shutdown. However, on the bias voltage supply side of the matrix readout system, the speed of the voltage change depends on a time constant consisting of a bias resistor and a coupling capacitor. Therefore, the voltage cannot be changed within the time constant for the matrix readout system. To overcome this limitation, three circuits have been added: a clamp circuit to the noise filter resistor of the bias voltage supply, a clamp circuit to the bias resistor, and protection circuits at the charge amplifier inputs. These circuits make it possible to change the bias voltage faster than the time constant of the bias resistor and the coupling capacitor. Although a noise signal is observed after the bias voltage has recovered, the noise decays below 20 keV about 30 ms after the bias voltage recovery. Our results demonstrated that the proposed pulsed bias voltage shutdown method is very efficient to suppress the polarization effect within 100 ms for the CdTe detector with the matrix readout system.
PURPOSEWe developed a prototype CdTe SPECT system with 4-pixel matched collimator for brain study. This system provides high-energy-resolution (6.6%), high-sensitivity (220 cps/MBq/head), and ...high-spatial-resolution images. The aim of this study was to evaluate dual-isotope study of CBF and central benzodiazepine receptor (BZR) images using Tc-ECD and I-IMZ with the new SPECT system in patients with epilepsy comparing with single-isotope study using the conventional scintillation gamma camera.
METHODSThis study included 13 patients with partial epilepsy. The BZR images were acquired at 3 hours after I-IMZ injection for 20 minutes. The images of IMZ were acquired with a conventional 3-head scintillation gamma camera. After BZR image acquisition with the conventional camera, Tc-ECD was injected, and CBF and BZR images were acquired simultaneously 5 minutes after ECD injection with the new SPECT system. The CBF images were also acquired with the conventional camera on separate days. The findings were visually analyzed, and 3D-SSP maximum Z scores of lesions were compared between the 2 studies.
RESULTSThere were 47 abnormal lesions on BZR images and 60 abnormal lesions on CBF images in the single-isotope study with the conventional camera. Dual-isotope study with the new system showed concordant abnormal findings of 46 of 47 lesions on BZR and 54 of 60 lesions on CBF images with the single-isotope study with the conventional camera. There was high agreement between the 2 studies in both BZR and CBF findings (Cohen κ values = 0.96 for BZR and 0.78 for CBF). In semiquantitative analysis, maximum Z scores of dual-isotope study with the new system strongly correlated with those of single-isotope study with the conventional camera (BZRr = 0.82, P < 0.05, CBFr = 0.87, P < 0.05).
CONCLUSIONSOur new SPECT system permits dual-isotope study for pixel-by-pixel analysis of CBF and BZR information with the same pathophysiological condition in patients with epilepsy.
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