Study On Dose Verification Of IMRT With Film Dosimetry

Due to the application of intensity modulated radiation therapy (IMRT) to clinic, dose verifications become important to ensure dose distribution gradient of IMRT to be delivered to patients. Radiographic films are widely used for relative dosimetry in IMRT. Film dosimetry shows a high spatial resolution image and high cost- performance ratio. Film dosimetry offers a convenient and quick method to obtain a two-dimensional dose distribution and store for a long term.Radiographic films of silver halide emulsions will be affected by many factors. In the procedure a little error will reduce the accuracy and even causes a large failure with dose evaluation. The object of this thesis is to explore the different effects in film dosimetry procedure and to set up an IMRT dose verification system on base of film dosimetry.In this thesis, method to definite and to calculate the optical density (OD) value by film dosimetry was explored. Three methods of calibration film of dose&OD responding curve were also explored. The optimization method was confirmed. In film flushing process, the different temperature setting to affect OD, difference between different batches of film, the effect of different batch's developer and fixer solution, the change of dosage and responding curve of the same batch film under the same batch solution were analyzed. As a result, the best process temperature 29-31℃was determined . Different batches of film couldn't be confounded. A new calibration film must be obtained when the film dosimetry to evaluate dose distribution was used. During analysis of influence of the scanning condition, the effect of light uniform, the stabilize work time and the noise of different scanning resolution were discussed. A 10-miniters -delay for stabilize work and the best setting resolution/depth lever were 72dpi/16bit for scanning films were determined .In order to analyze the clinical significance of this study, the passing ratio ofγindex and the NAT index were compared before and after the quality control .The result of dose evaluation showed our research had a strong clinical significance.In addition, the advantages and limits between the film dosimetry and a two-dimensional ion chambers matrix in IMRT dose verification were compared. Because the ion chambers matrix has a lot of interval for 0.76mm of small size ion chambers, it don't suit for some IMRT cases, And the film dosimetry has an excellent resolution for best use in IMRT dose verification. So we can reference the film dosimetry characteristics better to use of the two-dimension ion chambers matrix.