title: Evaluation of on-board kV cone beam computed tomography-based dose calculation with deformable image registration using Hounsfield unit modifications.
abstract: OBJECTIVE
  The purpose of this study was to estimate the accuracy of the dose calculation of On-Board Imager (Varian, Palo Alto, CA) cone beam computed tomography (CBCT) with deformable image registration (DIR), using the multilevel-threshold (MLT) algorithm and histogram matching (HM) algorithm in pelvic radiation therapy.
  
  
  METHODS
  One pelvis phantom and 10 patients with prostate cancer treated with intensity modulated radiation therapy were studied. To minimize the effect of organ deformation and different Hounsfield unit values between planning CT (PCT) and CBCT, we modified CBCT (mCBCT) with DIR by using the MLT (mCBCT(MLT)) and HM (mCBCT(HM)) algorithms. To evaluate the accuracy of the dose calculation, we compared dose differences in dosimetric parameters (mean dose [D(mean)], minimum dose [D(min)], and maximum dose [D(max)]) for planning target volume, rectum, and bladder between PCT (reference) and CBCTs or mCBCTs. Furthermore, we investigated the effect of organ deformation compared with DIR and rigid registration (RR). We determined whether dose differences between PCT and mCBCTs were significantly lower than in CBCT by using Student t test.
  
  
  RESULTS
  For patients, the average dose differences in all dosimetric parameters of CBCT with DIR were smaller than those of CBCT with RR (eg, rectum; 0.54% for DIR vs 1.24% for RR). For the mCBCTs with DIR, the average dose differences in all dosimetric parameters were less than 1.0%.
  
  
  CONCLUSIONS
  We evaluated the accuracy of the dose calculation in CBCT, mCBCT(MLT), and mCBCT(HM) with DIR for 10 patients. The results showed that dose differences in D(mean), D(min), and D(max) in mCBCTs were within 1%, which were significantly better than those in CBCT, especially for the rectum (P<.05). Our results indicate that the mCBCT(MLT) and mCBCT(HM) can be useful for improving the dose calculation for adaptive radiation therapy.
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Onozato
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan. Electronic address: kadoya.n@rad.med.tohoku.ac.jp.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kadoya
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Fujita
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Arai
authors.affiliation: Department of Radiological Technology, School of Health Sciences, Faculty of Medicine, Tohoku University, Sendai, Japan.
authors.forename: Suguru
authors.initials: S
authors.lastname: Dobashi
authors.affiliation: Department of Radiological Technology, School of Health Sciences, Faculty of Medicine, Tohoku University, Sendai, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Takeda
authors.affiliation: Radiation Technology, Tohoku University Hospital, Sendai, Japan.
authors.forename: Kazuma
authors.initials: K
authors.lastname: Kishi
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Rei
authors.initials: R
authors.lastname: Umezawa
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Matsushita
authors.affiliation: Department of Radiation Oncology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Jingu
mesh_terms: D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D006801:Humans; D008297:Male; D009929:Organ Size; D010388:Pelvis; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D047368:Tumor Burden; D001743:Urinary Bladder / Q000000981:diagnostic imaging