Adaptive Radiotherapy - CBCT Based Dose Calculation | Stine Camilla Claessen
| | Abstract | Background: The aim of this report is to evaluate, if CBCT can be used for dose calculation. The advantage in using CBCT for dose calculation, is to be able to predict and assess the dose delivered to the patient on a daily basis.
Materials & Methods: The study was subdivided into three parts. Part A: Various scan parameters and phantom con gurations were investigated for their impact on the Houns eld units (HUs) for Computed tomography (CT) and CBCT. For this investigation a CIRS water equivalent electron density phantom (DP) was used. The di fferent confi gurations of the DP were used to obtain HUrelative electron density calibration curves. The CT curve from the CT scan obtained with clinic standard parameters (CTS) was used as reference. Part B: The default and the obtained calibration curves from the different CBCT protocols were selected for the dose calculation on the CBCT images. Using the Alderson phantom it was investigated which protocol and calibration curve was the most appropriate for the CBCT based dose calculation. Part C: The results from the Alderson (ARP) study were evaluated in a clinical perspective on an head and neck patient (H&N) treated with intensity-modulated radiotherapy. In order to investigate if a site-specifi c calibration curve for di fferent patient groups was needed di fferent calibration curves were used for the head and neck patient. The calibration curves obtained from the pelvis con figuration on DP were used to calculate the dose distribution on the pelvis patient treated with rapid arc. The intention was to investigate if CBCT can be used for dose calculation for this patient group.
Results: Part A: Compared to CT it was found, that the HUs from CBCT were more easily a ffected when changing the scan parameters. Voltage, DP size and insert arrangements aff ect the HUs the most. Part B: The ARP study showed a maximum dose di fference of 0.6% when comparing the use of the CTS and the default calibration curve. The most appropriate CBCT based dose calculation was achieved with the standard dose head protocol. A 0.3% maximum dose di fference between CBCT and CT was found. It was found that further investigation is needed in order to evaluate whether the CBCT or the CT calibration curve achieves the most accurate CBCT based dose calculation. Part C: For the H&N patient a 1.7% maximum dose di fference between using the CTS and the default calibration curve was detected. A maximum dose di fference between CT and CBCT was found to be 0.3%. As for the ARP study, a further investigation is needed in order to evaluate whether the CBCT or the CT calibration curve achieves the most accurate CBCT based dose calculation. The results for cervix showed that further investigation was needed to conclude whether CBCT can be used for dose calculation on cervix patients. Further it was found that using a site-specifi c calibration curve for di fferent patient groups achieved a CBCT based dose distribution most similar to the CT based dose distribution.
Conclusion: It is concluded that CBCT can be used for dose calculation on H&N patients, but that further investigation is needed for the cervix patient. The standard protocol for CBCT is shown the to achieve a dose calculation similar to that of CT for the H&N patient. Also, it is concluded that the use of site-specifi c calibration curve is needed in order to calculate an accurate dose distribution on CBCT. | | Type | Master's thesis [Academic thesis] | | Year | 2012 | | Publisher | Technical University of Denmark, DTU Informatics, E-mail: reception@imm.dtu.dk | | Address | Asmussens Alle, Building 305, DK-2800 Kgs. Lyngby, Denmark | | Series | IMM-M.Sc.-2012-99 | | Note | | | Electronic version(s) | [pdf] | | Publication link | http://www.imm.dtu.dk/English.aspx | | BibTeX data | [bibtex] | | IMM Group(s) | Image Analysis & Computer Graphics |
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