Radiotherapy film densitometry using a slow-scan, cooled, digital CCD imaging system
A method of performing high-resolution two-dimensional film densitometry for full size radiographic film (35 [times] 43 cm) using a cooled CCD camera was proposed. Studies were performed to evaluate the physical characteristics of the camera system and recommendations were made to assure maximum accuracy of density measurement. Test films of various sizes and densities, as well as clinical dosimetry films, were measured with the CCD densitometer and the reference transmission densitometer. The measured densities agreed within the stated accuracy of the transmission densitometer for all films with maximum density less than or equal to 1.5 optical density units. The 0.2 mm spatial resolution with 4096 shades of gray made it possible to study dose distributions even for films containing areas of high dose gradients. Patient verification radiographs were used to study exit beam dose distributions to detect errors in beam placement, patient position, and proper placement of beam modifying devices such as wedges and compensators. For studying photon beam dose distributions within phantoms, a method was developed using lead foils placed lateral to the film plane to filter very low energy scattered photons. The error in measurement of central axis percentage depth dose from film for 4 MV x-rays, 25 [times] 25 cm field was decreased from 65% to 4%. The method requires only two calibration films for density to dose conversion and represents an important advance in the field of film densitometry for radiotherapy. The technique was applied to the study of dynamic wedge dose distribution from a 6 MV linear accelerator. The phantom modification decreased the error in percentage depth dose from 21% to 1% for the 15 [times] 15 cm beam with 60 degree wedge angle. Profile off-axis errors for the same beam were decreased from 8% to 3%. The film dosimetry system provides fast, high resolution film density data for use in radiotherapy imaging and quality assurance.
- Research Organization:
- Georgia Inst. of Tech., Atlanta, GA (United States)
- OSTI ID:
- 6552314
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
DENSITOMETERS
PERFORMANCE TESTING
RADIOTHERAPY
FILM DOSIMETRY
ACCURACY
CALIBRATION
FILMS
FOILS
PHANTOMS
SPATIAL DOSE DISTRIBUTIONS
SPATIAL RESOLUTION
DOSIMETRY
MEASURING INSTRUMENTS
MEDICINE
MOCKUP
NUCLEAR MEDICINE
PHOTOMETERS
RADIATION DOSE DISTRIBUTIONS
RADIOLOGY
RESOLUTION
STRUCTURAL MODELS
TESTING
THERAPY
560101* - Biomedical Sciences
Applied Studies- Radiation Effects- Dosimetry & Monitoring- (1992-)