title: Temporal Evolution of Parotid Volume and Parotid Apparent Diffusion Coefficient in Nasopharyngeal Carcinoma Patients Treated by Intensity-Modulated Radiotherapy Investigated by Magnetic Resonance Imaging: A Pilot Study.
abstract: OBJECTIVE
  To concurrently quantify the radiation-induced changes and temporal evolutions of parotid volume and parotid apparent diffusion coefficient (ADC) in nasopharyngeal carcinoma (NPC) patients treated by intensity-modulated radiotherapy by using magnetic resonance imaging (MRI).
  
  
  METHODS
  A total of 11 NPC patients (9 men and 2 women; 48.7 ± 11.7 years, 22 parotid glands) were enrolled. Radiation dose, parotid sparing volume, severity of xerostomia, and radiation-to-MR interval (RMI) was recorded. MRI studies were acquired four times, including one before and three after radiotherapy. The parotid volume and the parotid ADC were measured. Statistical analysis was performed using SPSS and MedCalc. Bonferroni correction was applied for multiple comparisons. A P value less than 0.05 was considered as statistically significant.
  
  
  RESULTS
  The parotid volume was 26.2 ± 8.0 cm(3) before radiotherapy. The parotid ADC was 0.8 ± 0.15 × 10(-3) mm(2)/sec before radiotherapy. The parotid glands received a radiation dose of 28.7 ± 4.1 Gy and a PSV of 44.1 ± 12.6%. The parotid volume was significantly smaller at MR stage 1 and stage 2 as compared to pre-RT stage (P < .005). The volume reduction ratio was 31.2 ± 13.0%, 26.1 ± 13.5%, and 17.1 ± 16.6% at stage 1, 2, and 3, respectively. The parotid ADC was significantly higher at all post-RT stages as compared to pre-RT stage reciprocally (P < .005 at stage 1 and 2, P < .05 at stage 3). The ADC increase ratio was 35.7 ± 17.4%, 27.0 ± 12.8%, and 20.2 ± 16.6% at stage 1, 2, and 3, respectively. The parotid ADC was negatively correlated to the parotid volume (R = -0.509; P < .001). The parotid ADC was positively associated with the radiation dose significantly (R(2) = 0.212; P = .0001) and was negatively associated with RMI significantly (R(2) = 0.203; P = .00096) significantly. Multiple regression analysis further showed that the post-RT parotid ADC was related to the radiation dose and RMI significantly (R(2) = 0.3580; P < .0001). At MR stage 3, the parotid volume was negatively associated with the dry mouth grade significantly (R(2) = 0.473; P < .0001), while the parotid ADC was positively associated with the dry mouth grade significantly (R(2) = 0.288; P = .015).
  
  
  CONCLUSIONS
  Our pilot study successfully demonstrates the concurrent changes and temporal evolution of parotid volume and parotid ADC quantitatively in NPC patients treated by IMRT. Our results suggest that the reduction of parotid volume and increase of parotid ADC are dominated by the effect of acinar loss rather than edema at early to intermediate phases and the following recovery of parotid volume and ADC toward the baseline values might reflect the acinar regeneration of parotid glands.
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Chun-Jung
authors: CJ
authors: Juan
authors: Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China; Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, Republic of China.
authors: Cheng-Chieh
authors: CC
authors: Cheng
authors: Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China; Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, Republic of China.
authors: Su-Chin
authors: SC
authors: Chiu
authors: Department of Radiation Oncology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiation Oncology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Yee-Min
authors: YM
authors: Jen
authors: Department of Automatic Control Engineering, Feng-Chia University, Taichung, Taiwan, Republic of China.
authors: Yi-Jui
authors: YJ
authors: Liu
authors: Ph.D. program of Technology Management, Chung Hua University, Hsinchu, Taiwan, Republic of China.
authors: Hui-Chu
authors: HC
authors: Chiu
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Hung-Wen
authors: HW
authors: Kao
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Chih-Wei
authors: CW
authors: Wang
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China; Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, Republic of China.
authors: Hsiao-Wen
authors: HW
authors: Chung
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Guo-Shu
authors: GS
authors: Huang
authors: Department of Radiology, National Defense Medical Center, Taipei, Taiwan, Republic of China; Department of Radiology, Tri-Service General Hospital, Taipei, Taiwan, Republic of China.
authors: Hsian-He
authors: HH
authors: Hsu
mesh_terms: D002277:Carcinoma; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D010306:Parotid Gland / Q000473:pathology* / Q000528:radiation effects*; D010865:Pilot Projects; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D014987:Xerostomia / Q000473:pathology / Q000532:radiotherapy