title: Assessing cumulative dose distributions in combined radiotherapy for cervical cancer using deformable image registration with pre-imaging preparations.
abstract: BACKGROUND
  The purpose of the study was to evaluate the feasibility of deformable image registration (DIR) in assessing cumulative dose distributions of the combination of external beam radiotherapy (EBRT) and fractionated intracavitary brachytherapy (ICBT) for cervical cancer.
  
  
  METHODS
  Three-dimensional image data sets of five consecutive patients were used. The treatment plan consisted of whole pelvic EBRT (total dose: 45 Gy in 25 fractions) combined with computed tomography (CT)-based high-dose rate ICBT (≥24 Gy in 4 fractions to the high risk clinical target volume (HR-CTV)). Organs at risk and HR-CTV were contoured on each CT images and dose-volume parameters were acquired. Pre-imaging preparations were performed prior to each ICBT to minimize the uncertainty of the organ position. Physical doses of each treatment were converted to biologically equivalent doses in 2 Gy daily fractions by the linear quadratic model. Three-dimensional dose distributions of each treatment were accumulated on CT images of the first ICBT using DIR with commercially available image registration software (MIM Maestro®). To compare with DIR, 3D dose distributions were fused by rigid registration based on bony structure matching. To evaluate the accuracy of DIR, the Dice similarity coefficient (DSC) was measured between deformed contours and initial contours.
  
  
  RESULTS
  The cumulative dose distributions were successfully illustrated on the CT images using DIR. Mean DSCs of the HR-CTV, rectum, and bladder were 0.46, 0.62 and 0.69, respectively, with rigid registration; and 0.78, 0.76, and 0.87, respectively, with DIR (p <0.05). The mean DSCs derived from our DIR procedure were comparable to those of previous reports describing the quality of DIR algorithms in the pelvic region. DVH parameters derived from the 2 methods showed no significant difference.
  
  
  CONCLUSIONS
  Our results suggest that DIR-based dose accumulation may be acceptable for assessing cumulative dose distributions to assess doses to the tumor and organs at risk in combined radiotherapy for cervical cancer under pre-imaging preparations.
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. mrtaka100@yahoo.co.jp.
authors.forename: Takanori
authors.initials: T
authors.lastname: Abe
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. tamakit@saitama-med.ac.jp.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Tamaki
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. smakino@saitama-med.ac.jp.
authors.forename: Souichi
authors.initials: S
authors.lastname: Makino
authors.affiliation: Gunma Prefectural Cancer Center, 617-1 Takabayashinishi-machi, Ohta-shi, Gunma, 373-8550, Japan. tebara@gunma-cc.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ebara
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. rhirai@saitama-med.ac.jp.
authors.forename: Ryuuta
authors.initials: R
authors.lastname: Hirai
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. kmiyaura@saitama-med.ac.jp.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Miyaura
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. kumazaki@saitama-med.ac.jp.
authors.forename: Yu
authors.initials: Y
authors.lastname: Kumazaki
authors.affiliation: Gunma University Heavy Ion Medical Center, 3-39-22 Showa-machi, Maebashi-shi, Gunma, 371-8511, Japan. tohno@gunma-u.ac.jp.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ohno
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. nshikama@saitama-med.ac.jp.
authors.forename: Naoto
authors.initials: N
authors.lastname: Shikama
authors.affiliation: Department of Radiation Oncology, Gunma University, 3-39-22 Showa-machi, Maebashi-shi, Gunma, 371-8511, Japan. tnakano@gunma-u.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
authors.affiliation: Department of Radiation Oncology, Saitama Medical University, International Medical Center, 1397-1 Yamane, Hidaka-shi, 350-1298, Japan. s_kato@saitama-med.ac.jp.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kato
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D005260:Female; D006801:Humans; D058958:Organs at Risk; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*