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CT Urography: Efforts to Reduce the Radiation Dose
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Radiology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Computed tomography urography (CTU) is today the imaging method used to investigate patients with suspected urinary tract malignancy, replacing the old imaging method intravenous pyelography (IVP) about a decade ago. The downside of this shift was that the effective radiation dose to the examined patient was eight times higher for CTU compared to IVP. Based on four different studies, the present thesis focused on efforts to reduce the CTU radiation dose.

 

In study I, the number of cysts and solid lesions in the separate scan phases was evaluated in 57 patients undergoing four-phase CTU 1997-98. The number of scans was reduced from four to three when the nephrographic scan was abolished following study I.

Study II registered the diameter of renal cell carcinoma (RCC) and the presenting symptoms in the total number of patients (n=232) diagnosed with RCC between 1997 and 2003. The results from study II showed that the critical size for RCCs to cause macroscopic hematuria was ≥ 4 cm. Study III was a dose-escalation study aimed to decide the minimal possible tube load in the unenhanced and excretory phase scans if the low dose images are reviewed together with normal dose corticomedullary phase images. Study III showed that it is possible to reduce the mean effective dose in three phase CTU from 16.2 mSv to 9.4 mSv with a combined low and normal dose CTU protocol. Study IV investigated the changes in the CTU protocol between 1997 and 2008, and the development of the effective radiation dose. Study IV clarified how the CTU protocol has changed between 1997 and 2008 and as a result the mean effective radiation dose to patients undergoing CTU in 2008 is only 39% of the effective dose in 1997.

 

In conclusion, the findings from the studies included in this thesis have contributed to a reduced radiation dose to patients undergoing CTU. The mean effective dose from CTU is at present only three times higher compared to that from the IVP.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 646
Keyword [en]
Urinary tract malignancy, renal cell carcinoma, urography, x-ray computed tomography, radiation dosage, dose escalation, hematuria/diagnosis
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
URN: urn:nbn:se:uu:diva-146332ISBN: 978-91-554-8009-7OAI: oai:DiVA.org:uu-146332DiVA: diva2:398278
Public defence
2011-04-01, Enghoffsalen, Ing 50, Akademiska Sjukhuset, Uppsala, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2011-03-11 Created: 2011-02-16 Last updated: 2011-05-04Bibliographically approved
List of papers
1. Detection and characterisation of renal lesions by multiphasic helical CT.
Open this publication in new window or tab >>Detection and characterisation of renal lesions by multiphasic helical CT.
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2000 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Acta Radiol., Vol. 41, no 4, 361-366 p.Article in journal (Refereed) Published
Abstract [en]

PURPOSE: The fast helical CT technique allows examination of the kidneys during different phases of contrast medium enhancement. However, every additional phase increases the radiation dosage to the patients. We investigated the detection rate and characterisation of renal lesions during different phases and evaluated them separately, and considered the possibility of excluding phases without loss of important information.

MATERIAL AND METHODS: Sixty patients who underwent contrast-enhanced multiphasic renal helical CT examination were included. Every CT phase was evaluated separately. The number of lesions and the characteristics of the lesions were noted and all lesions were viewed together.

RESULTS: A total of 153 cysts and 17 solid lesions were detected. The largest and an equal number of cysts (142/143) was detected in the nephrographic and excretory phases. However, the nephrographic phase detected more cortical cysts and the excretory phase detected more sinus cysts. All solid lesions were detected in all phases. Renal parenchymal tumours were best characterised in the cortical phase and angiomyolipomas in the native phase.

CONCLUSION: The cortical phase was best for characterisation of renal parenchymal tumours. The nephrographic and excretory phases were best in detecting and characterising renal cysts. The nephrographic phase was the phase giving the least diagnostic information.

Keyword
Kidney Mass, Characterisation, Helical Ct
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-57114 (URN)10.1080/028418500127345479 (DOI)
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2012-03-06Bibliographically approved
2. CT of the kidneys: what size are renal cell carcinomas when they cause symptoms or signs?
Open this publication in new window or tab >>CT of the kidneys: what size are renal cell carcinomas when they cause symptoms or signs?
2007 (English)In: Scandinavian Journal of Urology and Nephrology, ISSN 0036-5599, E-ISSN 1651-2065, Vol. 41, no 6, 490-495 p.Article in journal (Refereed) Published
Abstract [en]

Objective. To investigate the size of renal cell carcinomas (RCCs) when they cause macroscopic hematuria or other symptoms and/or signs. Material and methods. A retrospective review of 232 patients (136 males, 96 females; mean age 68±11 years; age range 40–90 years) with a diagnosis of RCC was undertaken. Patients were grouped according to the presenting symptoms and/or signs caused by the RCCs. Tumor size was measured on CT images. Results. Of the RCCs, 29% were found incidentally and 71% caused symptoms and/or signs. The incidentally found RCCs measured 4.9±2.6 cm (range 2–12 cm) and RCCs causing symptoms and signs measured 8.9±3.2 cm (range 3–18 cm); this size difference was significant (p<0.001). None of the RCCs causing macroscopic hematuria were <4 cm in size and only 3/165 (2%) of the symptomatic RCCs were <4 cm in size. Discussion. If small (<4 cm) RCCs do not cause symptoms, patients with them will not be referred for CT or any other imaging modality. Therefore, if a 2-cm RCC is found in a patient presenting with macroscopic hematuria, it is unlikely that this small RCC caused the hematuria and another cause of the hematuria must be ruled out.

Keyword
CT, Hematuria, Incidental discovery, Renal cell carcinoma, Symptoms and signs
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-17184 (URN)10.1080/00365590701428210 (DOI)000251281000004 ()17853020 (PubMedID)
Available from: 2008-06-17 Created: 2008-06-17 Last updated: 2012-03-06Bibliographically approved
3. How much dose can be saved in three-phase CT Urography ?: A combination of normal dose corticomedullary phase with low-dose unenhanced and excretory phases.
Open this publication in new window or tab >>How much dose can be saved in three-phase CT Urography ?: A combination of normal dose corticomedullary phase with low-dose unenhanced and excretory phases.
(English)Manuscript (preprint) (Other academic)
Keyword
Urography, Tomography X-ray computed, Radiation dosage, Hematuria/diagnosis, Dose escalation
National Category
Radiology, Nuclear Medicine and Medical Imaging
Research subject
Radiology
Identifiers
urn:nbn:se:uu:diva-146395 (URN)
Available from: 2011-02-16 Created: 2011-02-16 Last updated: 2011-05-04
4. Optimization of computed tomography urography protocol, 1997 to 2008: effects on radiation dose
Open this publication in new window or tab >>Optimization of computed tomography urography protocol, 1997 to 2008: effects on radiation dose
2009 (English)In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 50, no 4, 446-454 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Since computed tomography (CT) urography began to replace excretory urography as the primary imaging technique in uroradiology, the collective radiation dose to the patients has increased. PURPOSE: To examine the changes in the CT urography protocol for investigating suspected urinary tract malignancy between the years 1997 and 2008, and how these changes have influenced the mean effective dose. MATERIAL AND METHODS: The study was based on 102 patients (mean age 66.1+/-14.8 years, range 31-89 years; 30 female, 72 male) divided into five groups (groups A-E) corresponding to the time points at which changes were made to the CT urography protocol. The mean effective doses were estimated using the ImPACT CT Patient Dosimetry Calculator. RESULTS: The number of scan phases at CT urography was reduced from four to three in 1999, resulting in a reduction of the mean effective dose from 29.9/22.5 (female [F]/male [M]) mSv (group A) to 26.1/18.9 (F/M) mSv (group B). In 2001, mAs settings were adapted to patient size, and the mean effective dose was reduced to 16.8/12.0 (F/M) mSv (group C). In 2005, scans were performed with a multidetector-row CT equipped with automatic tube current modulation in the x- and y-axis (CARE Dose). The effective mAs was also lowered in the unenhanced and excretory phase, yet the mean effective dose increased to 18.2/13.1 (F/M) mSv (group D), since the effective mAs had to be increased in the corticomedullary phase to maintain image quality. In 2008, as tube current modulation in the x-, y-, and z-axis was introduced (CARE Dose4D), the mean effective dose was reduced to 11.7/8.8 (F/M) mSv (group E). CONCLUSION: This study shows that the individual mean effective dose to patients undergoing CT urography has decreased by 60%, from 29.9/22.5 (F/M) mSv in 1997 to 11.7/8.8 (F/M) mSv in 2008.

Keyword
CT, effective dose, optimization, radiation dose, urinary, urography
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-118808 (URN)10.1080/02841850902821757 (DOI)000265273400015 ()19308762 (PubMedID)
Available from: 2010-02-23 Created: 2010-02-23 Last updated: 2012-03-06Bibliographically approved

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