Does ultra-low-dose CT with a radiation dose equivalent to that of KUB suffice to detect renal and ureteral calculi?

The objective of this study was to evaluate the diagnostic yield of multislice CT using a radiation dose equivalent to that of conventional abdominal x-ray (KUB). One hundred forty-two patients were prospectively examined with ultrasound and a radically dose-reduced CT protocol (120 kV, 6.9 eff. mAs). Number and size of calculi, presence of urinary obstruction, and alternative diagnoses were recorded and confirmed by stone removal/discharge or by clinical and imaging follow-up. The mean effective whole-body dose was 0.5 mSv in men and 0.7 mSv in women. The sensitivity and specificity in detecting patients with calculi was 97% and 95% for CT and 67% and 90% for ultrasound. Urinary obstruction was similarly assessed, whereas CT identified significantly more alternative diagnoses than ultrasound (P<0.001). With regard to published data for standard-dose CT, the present CT protocol seems to be comparable in its diagnostic yield in assessing patients with calculi, and its radiation dose is equivalent to that of KUB.     

Accumulated dose to the rectum,measured using dose–volume histograms and dose-surface maps,is different from planned dose in all patients treated with radiotherapy for prostate cancer

Objective:

We sought to calculate accumulated dose (D_A) to the rectum in patients treated with radiotherapy for prostate cancer. We were particularly interested in whether dose–surface maps (DSMs) provide additional information to dose–volume histograms (DVHs).

Methods:

Manual rectal contours were obtained for kilovoltage and daily megavoltage CT scans for 10 participants from the VoxTox study (380 scans). Daily delivered dose recalculation was performed using a ray-tracing algorithm. Delivered DVHs were summated to create accumulated DVHs. The rectum was considered as a cylinder, cut and unfolded to produce daily delivered DSMs; these were summated to produce accumulated DSMs.

Results:

Accumulated dose-volumes were different from planned in all participants. For one participant, all D_A levels were higher and all volumes were larger than planned. For four participants, all D_A levels were lower and all volumes were smaller than planned. For each of these four participants, ≥1% of pixels on the accumulated DSM received ≥5 Gy more than had been planned.

Conclusion:

Differences between accumulated and planned dose-volumes were seen in all participants. DSMs were able to identify differences between D_A and planned dose that could not be appreciated from the DVHs. Further work is needed to extract the dose data embedded in the DSMs. These will be correlated with toxicity as part of the VoxTox Programme.

Advances in knowledge:

DSMs are able to identify differences between D_A and planned dose that cannot be appreciated from DVHs alone and should be incorporated into future studies investigating links between D_A and toxicity.     

Quantifying dose to the reconstructed breast: Can we adequately treat?

To evaluate how immediate reconstruction (IR) impacts postmastectomy radiotherapy (PMRT) dose distributions to the reconstructed breast (RB), internal mammary nodes (IMN), heart, and lungs using quantifiable dosimetric end points. 3D conformal plans were developed for 20 IR patients, 10 autologous reconstruction (AR), and 10 expander-implant (EI) reconstruction. For each reconstruction type, 5 right- and 5 left-sided reconstructions were selected. Two plans were created for each patient, 1 with RB coverage alone and 1 with RB + IMN coverage. Left-sided EI plans without IMN coverage had higher heart Dmean than left-sided AR plans (2.97 and 0.84 Gy, p = 0.03). Otherwise, results did not vary by reconstruction type and all remaining metrics were evaluated using a combined AR and EI dataset. RB coverage was adequate regardless of laterality or IMN coverage (Dmean 50.61 Gy, D95 45.76 Gy). When included, IMN Dmean and D95 were 49.57 and 40.96 Gy, respectively. Mean heart doses increased with left-sided treatment plans and IMN inclusion. Right-sided treatment plans and IMN inclusion increased mean lung V₂₀. Using standard field arrangements and 3D planning, we observed excellent coverage of the RB and IMN, regardless of laterality or reconstruction type. Our results demonstrate that adequate doses can be delivered to the RB with or without IMN coverage.     

Time‐ and dose‐dependent changes of intracellular cytokine and cytokine receptor profile of Ewing tumour subpopulations under the influence of ionizing radiation

Purpose: Cytokines and their corresponding cell surface receptors are involved in intercellular signalling pathways and in the radioresistance of normal and malignant cells. The aim was the characterization of the expression of intracellular cytokines, their receptors and apoptosis‐associated markers under the influence of radiation.

Materials and methods: Two Ewing tumours were characterized in vitro before and 4, 24 and 72?h after radiation with 5 and 10?Gy, and in vivo 4, 6 and 15 days after radiation with 5 and 30?Gy by five parameter flow cytometry. Direct fluorescence‐conjugated antibodies directed against intracellular cytokines (interferon‐gamma, tumour necrosis factor [TNF]‐alpha, interleukin 1) and their receptors (CD119, CD120a, CD121a) were used. Annexin V and 7‐amino‐actinomycin D were used to identify radiation‐induced apoptosis.

Results: Inter‐ and intra‐individual heterogeneities were identified by the expression of cytokine receptors and the intracellular cytokine profile before radiation. Time‐ and dose‐dependent up‐regulation of the cytokines TNF‐alpha and interleukin 1 were found in vitro. In vivo, an up‐regulation of CD120a and CD121a was detectable on tumour cell subpopulations. For interferon‐gamma and CD119, no changes were seen.

Conclusions: The observed radiation‐induced changes of cytokine and receptor profile are an indication for complex intercellular interactions in view of radioresistance‐associated mechanisms between cell populations within one individual tumour. The observed heterogeneous response on radiation might have therapeutic implications for an individualized therapy based on combined radiation and cytokine modulation, defined by flow cytometric characterization of markers potentially informative for radioresistance.     

Influence of magnesium chloride on the dose–response of polyacrylamide-type gel dosimeters

We investigated the effect of magnesium chloride (MgCl₂) on the nuclear magnetic resonance dose–response of polyacrylamide-type (PAGAT, NIPAM, and VIPET) gel dosimeters containing acrylamide, N-isopropylacrylamide, and N-vinylpyrrolidone as a monomer, respectively. The dose-transverse relaxation rates (1/T₂?=?R₂) obtained from magnetic resonance imaging data revealed that a substantial increase in the dose–R₂ response occurred as the concentration of MgCl₂ in the gel dosimeters increased. The sensitivity of the PAGAT gel with 1.0 M MgCl₂ was found to be approximately one order higher than that of the same gel without MgCl₂. In addition, the water equivalences of the gels with MgCl₂ were evaluated over a wide range of photon energies. The results indicated that MgCl₂ acts as a powerful sensitizer to radiation-induced free-radical polymerization in polyacrylamide-type gel dosimeters, but does not interfere with the desirable properties of basic polyacrylamide-type gel dosimeters (i.e., the dose rate and dose integration).     

Carcinogenicity of radon/radon decay product inhalation in rats – effect of dose,dose rate and unattached fraction

Purpose: The effects of inhalation of radon/radon decay products at different total doses, dose rates and ‘unattached’ fractions were investigated in a life span study in rats.

Materials and methods: 1574 rats inhaled radon/radon decay products in a purpose-built recirculating exposure system that provided stable/reproducible exposure conditions. 501 were maintained as controls.

Results: Lung tumour incidences were significantly elevated in most exposed groups. The study power was insufficient to resolve the shape of the dose and dose rate response curves, but combination of this data with that from other studies demonstrated that for high cumulative exposures, the lifetime excess absolute risk increases with increasing exposure durations and for low cumulative exposures the opposite trend occurs. Exposure did not increase leukaemia incidences. A small number of non-lung tumour types including mammary fibroadenoma showed elevated incidences in some exposed groups, however not consistently across all exposure groups and showed no dose or dose rate relationship.

Conclusions: Radon/radon decay product exposure caused excess lung tumours in rats along with limited non-lung effects. The results are consistent with the findings that at low cumulative exposures decreasing exposure concentrations or protracting the time over which the dose is delivered, reduces lung tumour risk. At higher levels, decreasing exposure concentrations or protracting exposure time increases lung tumour risk.     

Comparison between the four-field box and field-in-field techniques for conformal radiotherapy of the esophagus using dose–volume histograms and normal tissue complication probabilities

Purpose

We evaluated and compared the performance of the field-in-field (FIF) to that of the four-field box (4FB) technique regarding dosimetric and radiobiological parameters for radiotherapy of esophageal carcinoma.

Materials and methods

Twenty patients with esophageal cancer were selected. For each patient, two treatment plans were created: 4FB and FIF. The parameters compared included the conformity index (CI), homogeneity index (HI), D _mean, D _max, tumor control probability (TCP), V _20Gy and V _30Gy of the heart and lungs, normal tissue complication probability (NTCP), and monitor units per fraction (MU/fr).

Results

A paired t-test analysis did not show any significant differences (p > 0.05) between the two techniques in terms of the CI and TCP. However, the HI significantly improved when the FIF was applied. D _max of the PTV, lung, and spinal cord were also significantly better with the FIF. Moreover, the lung V _20Gy as well as the NTCPs of the lung and spinal cord significantly reduced when the FIF was used, and the MU/fr was significantly decreased.

Conclusions

The FIF showed evident advantages over 4FB: a more homogeneous dose distribution, lower D _max values, and fewer required MUs, while it also retained PTV dose conformality. FIF should be considered as a simple technique to use clinically in cases with esophageal malignancies, especially in clinics with no IMRT.

     

Radiation dose of cardiac computed tomography �C what has been achieved and what needs to be done

This review highlights the recently introduced techniques by manufacturers and various research workers to reduce radiation dose in coronary CT. It discusses in detail the development of ECG-based tube current modulation, the application of low tube voltage protocols and prospective ECG-gating. It also briefly discusses two further methods of dose reduction, namely minimisation of the x-y anatomical coverage and adaptive statistical iterative reconstruction.     

Can the anode heel effect be used to optimise radiation dose and image quality for AP pelvis radiography?

IntroductionA study was conducted to determine whether the anode heel effect can be used to influence optimisation of radiation dose and image quality (IQ) for AP pelvis radiography.MethodsATOM dosimetry phantom and an anthropomorphic phantom were positioned for AP pelvis. Using a CR system, images were acquired and doses were measured with phantom feet toward anode and then feet toward cathode. Exposure factors (kVp, mAs and SID) were systematically generated using a factorial design. Images were scored visually for quality using relative visual grading together with a 3 point Likert scale. Signal to noise ratio was also calculated as a physical measure of image quality. Dosimetry data were collected for the ovaries and testes.ResultsThe optimum technique for male, which resulted in lower dose and suitable image quality, was with feet positioned toward the anode (0.80 ± 0.03 mGy; SNR of 38 ± 2.9; visual IQ score 3.13 ± 0.35). The optimum technique for female was with feet toward anode (0.23 ± 0.02 mGy; SNR of 34.7 ± 2.6; visual IQ score 3.15 ± 0.26). kVp had the biggest effect on both visual and physical image quality metrics (p < 0.001) for both tube orientations, whereas SID had the lowest effect on both visual and physical image quality metrics compared with mAs and kVp (p < 0.001). The effect of SID on the SNR was not significant (p > 0.05) with feet toward anode.ConclusionPositioning the patient with feet toward the anode, as opposed to the cathode, has no adverse effect on visual image quality assessment but it does have an effect on physical image quality.Implications for practiceThis study would add a new clinical concept in positioning of AP pelvis radiography especially for male positioning.     

Can low-dose CT with iterative reconstruction reduce both the radiation dose and the amount of iodine contrast medium in a dynamic CT study of the liver?

Purpose

To investigate whether low-dose dynamic CT of the liver with iterative reconstruction can reduce both the radiation dose and the amount of contrast medium.

Materials and methods

This study was approved by our institutional review board. 113 patients were randomly assigned to one of two groups. Group A/group B (fifty-eight/fifty-five patients) underwent liver dynamic CT at 120/100 kV, with 0/40% adaptive statistical iterative reconstruction (ASIR), with a contrast dose of 600/480 mg I/kg, respectively. Radiation exposure was estimated based on the manufacturer's phantom data. The enhancement value of the hepatic parenchyma, vessels and the tumor-to-liver contrast of hepatocellular carcinomas (HCCs) were compared between two groups. Two readers independently assessed the CT images of the hepatic parenchyma and HCCs.

Results

The mean CT dose indices: 6.38/4.04 mGy, the dose-length products: 194.54/124.57 mGy cm, for group A/group B. The mean enhancement value of the hepatic parenchyma and the tumor-to-liver contrast of HCCs with diameters greater than 1 cm in the post-contrast all phases did not differ significantly between two groups (P > 0.05). The enhancement values of vessels in group B were significantly higher than that in group A in the delayed phases (P < 0.05). Two reader's confidence levels for the hepatic parenchyma in the delayed phases and HCCs did not differ significantly between the groups (P > 0.05).

Conclusions

Low-dose dynamic CT with ASIR can reduce both the radiation dose and the amount of contrast medium without image quality degradation, compared to conventional dynamic CT without ASIR.     

Should the dose of contrast medium be determined solely on the basis of body weight regardless of the patient’s sex?

Purpose  

The aim of this study was to evaluate prospectively the difference in contrast enhancement of liver parenchyma between male and female subjects when the total amount of contrast material is determined by the total body weight (TBW).     

Detection and appearance of intraparenchymal haematomas of the brain at 1.5 T with spin-echo, FLAIR and GE sequences: poor relationship to the age of the haematoma

The specific appearance of blood related to time at T1- and T2-weighted spin-echo (SE) sequences is generally accepted; thus, these sequences are classically used for estimating the age of haematomas. Magnetic resonance imaging at 1.5 T, including T1- and T2-weighted SE fluid-attenuated inversion recovery (FLAIR) and T2*-weighted gradient-echo (GE) sequences, was performed on 82 intraparenchymal haematomas (IPHs) and 15 haemorrhagic infarcts (HIs) in order to analyse the appearance at different stages and with different sequences, and to investigate how reliably the age of hematomas can be estimated. The IPHs had been previously detected by CT, were spontaneous (n=72) or traumatic (n=10) in origin and were of different sizes (2 mm to 7 cm) and ages (from 7.5 h to 4 years after acute haemorrhagic event). The age of the lesion was calculated from the moment when clinical symptoms started or the traumatic event occurred. The 15 patients with HIs were patients with ischaemic stroke in whom there was either a suspicion of haemorrhagic transformation on CT, or haemorrhage was detected as an additional finding on MR performed for other indications. Patients with conditions that could affect the SI of blood, such as anticoagulant therapy or severe anaemia, were excluded. The signal intensity pattern of the lesions was analysed and related to their ages without prior knowledge of the clinical data. All lesions were detected with T2*-weighted GE. T1-weighted SE missed 13 haematomas and T2-weighted SE and FLAIR sequences missed five. Haemorrhagic transformation was missed in three infarcts by T1-, T2-weighted SE and FLAIR. The signal pattern on FLAIR was identical to that on T2-weighted SE. For all sequences, a wide variety of signal patterns, without a clear relationship to the age of the haematomas, was observed. There was a poor relationship between the real MR appearance of IPHs and the theoretical appearance on SE sequences. T2*-weighted GE was effective for detecting small bleedings but was not useful for estimating the age of a lesion. The FLAIR does not provide any more information than T2-weighted SE.This work was presented at the XXVIII ESNR congress, in Istanbul, Turkey, September 2003