@MASTERSTHESIS\{IMM2012-06278,
    author       = "R. B. Eiland",
    title        = "Adaptive radiation therapy for head and neck cancer",
    year         = "2012",
    school       = "Technical University of Denmark, {DTU} Informatics, {E-}mail: reception@imm.dtu.dk",
    address      = "Asmussens Alle, Building 305, {DK-}2800 Kgs. Lyngby, Denmark",
    type         = "",
    note         = "Supervised by Associate Professor Rasmus Reinhold Paulsen, rrp@imm.dtu.dk, {DTU} Informatics, and Eva Sams{\o} and David Sj{\"{o}}str{\"{o}}m",
    url          = "http://www.imm.dtu.dk/English.aspx",
    abstract     = "Purpose:
Anatomical changes can occur during radiation therapy of head and neck cancer patients. This can lead to discrepancies between planned and delivered dose. Adaptive radiation therapy has the potential to overcome this using deformable image registration (DIR). The purpose of this study was to evaluate the performance of a {DIR} algorithm using geometric and dosimetric measures.
Materials and Methods: 
Seven patients treated with {IMRT} were included in this study, each with a planning- and midterm {CT} (pCT, ReCT) as well as a {CBCT} acquired at the same time as the ReCT. ReCT served as ground truth for evaluation of the {DIR}. A deformed {CT} (dCT) with structures was created by deforming the pCT and associating manually delineated structures to the {CBCT}. A commercial software package using a Demons type of {DIR} algorithm (SmartAdapt, Varian medical Systems v.11.0) was used. The geometrical comparisons were based on structures of the dCT, and manually delineated structures on the ReCT. In the treatment planning system (Eclipse, Varian Medical Systems, v. 10.0) the initial treatment plan was transferred to the dCT and the ReCT and the dose recalculated.
Results:
Geometrical similarity between target structures of dCT and ReCT was found, especially with respect to {PTV} and {CTV}. Small variation was observed for the Parotid glands. The spinal cord obtained poor geometrical similarity. Non-significant difference between the dosimetric outcome of dCT- and ReCTbased dose calculation was observed. Investigating the possibility for CBCTbased dose calculation revealed no significant difference when comparing to dose based on ReCT.
Conclusion:
Similarity was found between deformed and manually delineated structures of dCT and ReCT. An exception was the spinal cord, indicating that the {DIR} is not usable for this organ. Large similarity in dose provided for the target structures was found for dCT- and ReCT-based dose calculation. Generally, the {DIR} between pCT and {CBCT} represent a feasible tool for adaptive radiation therapy, with regard to target structures and the parotid glands."
}