title: A deformable head and neck phantom with in-vivo dosimetry for adaptive radiotherapy quality assurance.
abstract: OBJECTIVE
  Patients' interfractional anatomic changes can compromise the initial treatment plan quality. To overcome this issue, adaptive radiotherapy (ART) has been introduced. Deformable image registration (DIR) is an important tool for ART and several deformable phantoms have been built to evaluate the algorithms' accuracy. However, there is a lack of deformable phantoms that can also provide dosimetric information to verify the accuracy of the whole ART process. The goal of this work is to design and construct a deformable head and neck (HN) ART quality assurance (QA) phantom with in vivo dosimetry.
  
  
  METHODS
  An axial slice of a HN patient is taken as a model for the phantom construction. Six anatomic materials are considered, with HU numbers similar to a real patient. A filled balloon inside the phantom tissue is inserted to simulate tumor. Deflation of the balloon simulates tumor shrinkage. Nonradiopaque surface markers, which do not influence DIR algorithms, provide the deformation ground truth. Fixed and movable holders are built in the phantom to hold a diode for dosimetric measurements.
  
  
  RESULTS
  The measured deformations at the surface marker positions can be compared with deformations calculated by a DIR algorithm to evaluate its accuracy. In this study, the authors selected a Demons algorithm as a DIR algorithm example for demonstration purposes. The average error magnitude is 2.1 mm. The point dose measurements from the in vivo diode dosimeters show a good agreement with the calculated doses from the treatment planning system with a maximum difference of 3.1% of prescription dose, when the treatment plans are delivered to the phantom with original or deformed geometry.
  
  
  CONCLUSIONS
  In this study, the authors have presented the functionality of this deformable HN phantom for testing the accuracy of DIR algorithms and verifying the ART dosimetric accuracy. The authors' experiments demonstrate the feasibility of this phantom serving as an end-to-end ART QA phantom.
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843 and Department of Physics, University of California San Diego, La Jolla, California 92093.
authors.forename: Yan Jiang
authors.initials: YJ
authors.lastname: Graves
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093.
authors.forename: Arthur-Allen
authors.initials: AA
authors.lastname: Smith
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093.
authors.forename: David
authors.initials: D
authors.lastname: Mcilvena
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093.
authors.forename: Zherrina
authors.initials: Z
authors.lastname: Manilay
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, California 92093.
authors.forename: Yuet Kong
authors.initials: YK
authors.lastname: Lai
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843.
authors.forename: Roger
authors.initials: R
authors.lastname: Rice
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843.
authors.forename: Loren
authors.initials: L
authors.lastname: Mell
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843 and Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas 75235.
authors.forename: Xun
authors.initials: X
authors.lastname: Jia
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843 and Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas 75235.
authors.forename: Steve B
authors.initials: SB
authors.lastname: Jiang
authors.affiliation: Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92037-0843.
authors.forename: Laura
authors.initials: L
authors.lastname: Cerviño
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D005240:Feasibility Studies; D006257:Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006801:Humans; D008954:Models, Biological; D009333:Neck / Q000000981:diagnostic imaging / Q000528:radiation effects; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000379:methods*; D011874:Radiometry; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*; D014057:Tomography, X-Ray Computed