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Computed tomography dose measurements with radiochromic films and a flatbed scanner
O Rampado1, E Garelli, R Ropolo
1Struttura Complessa Fisica Sanitaria, Azienda Ospedaliera, San Giovanni Battista, Corso Bramante 88, 10126 Torino, Italy. orampado@molinette.piemonte.it
Medical Physics
|February 24, 2010
Summary
Gafchromic XR-QA films offer a viable method for measuring computed tomography dose index (CTDI) using flatbed scanners. This technique provides accurate dosimetry comparable to ionization chambers, with quantifiable uncertainty for patient safety in diagnostic radiology.
Area of Science:
- Medical Physics
- Radiological Imaging
- Radiation Dosimetry
Background:
- Gafchromic XR-QA films are designed for patient dosimetry in diagnostic radiology.
- Computed tomography (CT) dosimetry requires accurate methods for patient dose assessment.
- Evaluating CTDI is crucial for optimizing CT protocols and ensuring patient safety.
Purpose of the Study:
- To develop and validate a method for measuring CTDI using Gafchromic XR-QA films and a flatbed scanner.
- To assess the accuracy and uncertainty of this film-based dosimetry method compared to traditional ionization chambers.
- To investigate the angular dependence of Gafchromic XR-QA film response in a CT environment.
Main Methods:
- Gafchromic XR-QA film strips were cut to specific dimensions for dose integration.
- Angular dependence of film response was analyzed under static X-ray beams.
- Films were exposed to CT beams in air and phantoms using axial and helical scan modes.
- Dose measurements were performed using two different flatbed scanners (Epson Expression 10000 XL, Microtek ScanMaker 9800XL).
- Results were compared against measurements obtained with a standard ionization chamber.
Main Results:
- Angular dependence of film response was significant (49%) under static conditions but negligible (<2%) when integrated over a 360-degree CT exposure.
- For beam collimations >10 mm, the Epson scanner showed CTDI differences <9% (5% uncertainty) compared to ionization chambers.
- The Microtek scanner yielded differences <11% (8% uncertainty) for the same conditions.
- The developed method provided 1-sigma uncertainty for each CTDI measurement.
- Approximately 95% of film-based CTDI measurements fell within the estimated 2-sigma uncertainty range compared to ionization chamber results.
Conclusions:
- Gafchromic XR-QA films, when accurately calibrated, can be reliably used for CTDI evaluation.
- The film-based method offers a practical alternative for CT dosimetry, especially when ionization chambers are not feasible.
- The accuracy is comparable to ionization chambers, with quantifiable uncertainties suitable for clinical applications.
- Flatbed scanner choice impacts measurement accuracy and uncertainty.
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