Managing patient dose with daily image guided radiotherapy
| dc.contributor.author | Siew Ping, Heng | |
| dc.date.accessioned | 2015-05-20T09:40:05Z | |
| dc.date.available | 2015-05-20T09:40:05Z | |
| dc.date.issued | 2014 | |
| dc.description.abstract | Kilovoltage cone beam CT (kV-CBCT) based on flat panel technology is a new image guided radiotherapy technique for patient positioning in radiotherapy. It can also be used for dosimetric verification in adaptive radiotherapy by validating the accuracy of CBCT image based treatment planning. This study evaluates the accuracy of dose calculation based on the patients’ CBCT images. The Hounsfield unit to electron density (HU-ED) calibration curves for head and pelvis region were obtained using region of interest (ROI) mapping method and these were compared with the planning HU-ED calibration curve. The isodose distributions of intensity modulated radiotherapy (IMRT)fields were compared between the CT and CBCT image based dose calculation. Simulated identical organs at risks were delineated in the CT and CBCT images for IMRT plans comparisons. The percentage dose differences and dose volume histograms (DVHs) were compared between CT and CBCT based plans. It is found that the CBCT values were highly influenced by the CBCT image acquisition parameters tube voltage, filtering and collimation and patient geometry. This suggests that a single HU-ED table will not be applicable to different imaging presets and different patient geometry. The isodose distributions and DVH computed based on CBCT and CT for IMRT organ and risk doses, the dose difference was as high as ± 3%. From this study, it can be thus concluded that the CBCT images can be used for the dose calculation to study the continuous volume and geometric changes, and resulting dosimetric variations of organ at risks for patients undergoing IMRT. Significant dosimetric variations were observed for spinal cord and parotid glands when there are great changes in lateral neck dimension for head and neck cancer patients; while for the pelvis region, this study shows that rectum and bladder preparation protocol can improve DVHs consistency. For the CBCT imaging dose measurements, a metal oxide semiconductor field effect transistor (MOSFET) and an ion chamber were employed to measure the volume CBCT dose index (CBDIvol) in CT phantom. The CBDIvol of the head scanning protocol were found to be 0.92 mGy and 1.0 mGy for chamber and MOSFET measurements respectively. The CBDIvol of the pelvis scanning protocol were found to be 16 mGy and 20 mGy for chamber and MOSFET measurements respectively. The maximum effective dose (ED) was found to be 1.0 mSv for the head and 6.99 mSV for the pelvis scanning protocols. Hence, when setting up CBCT scanning protocol and should try to reduce the high voltage usage and reduce mAs setting. Reduction in both parameters can reduce radiation dose to the patient, especially for pediatric patients. Care should be given to the long-term follow up of patients under image guided radiation therapy, while the indications for its use in certain cases should be reconsidered. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/651 | |
| dc.language.iso | en | en_US |
| dc.title | Managing patient dose with daily image guided radiotherapy | en_US |
| dc.type | Thesis | en_US |
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