title: Bone mineral density loss in thoracic and lumbar vertebrae following radiation for abdominal cancers.
abstract: OBJECTIVE
  To investigate the relationship between abdominal chemoradiation (CRT) for locally advanced cancers and bone mineral density (BMD) reduction in the vertebral spine.
  
  
  METHODS
  Data from 272 patients who underwent abdominal radiation therapy from January 1997 to May 2015 were retrospectively reviewed. Forty-two patients received computed tomography (CT) scans of the abdomen prior to initiation and at least twice after radiation therapy. Bone attenuation (in Hounsfield unit) (HU) measurements were collected for each vertebral level from T7 to L5 using sagittal CT images. Radiation point dose was obtained at each mid-vertebral body from the radiation treatment plan. Percent change in bone attenuation (Δ%HU) between baseline and post-radiation therapy were computed for each vertebral body. The Δ%HU was compared against radiation dose using Pearson's linear correlation.
  
  
  RESULTS
  Abdominal radiotherapy caused significant reduction in vertebral BMD as measured by HU. Patients who received only chemotherapy did not show changes in their BMD in this study. The Δ%HU was significantly correlated with the radiation point dose to the vertebral body (R=-0.472, P<0.001) within 4-8 months following RT. The same relationship persisted in subsequent follow up scans 9 months following RT (R=-0.578, P<0.001). Based on the result of linear regression, 5 Gy, 15 Gy, 25 Gy, 35 Gy, and 45 Gy caused 21.7%, 31.1%, 40.5%, 49.9%, and 59.3% decrease in HU following RT, respectively. Our generalized linear model showed that pre-RT HU had a positive effect (β=0.830) on determining post-RT HU, while number of months post RT (β=-0.213) and radiation point dose (β=-1.475) had a negative effect. A comparison of the predicted versus actual HU showed significant correlation (R=0.883, P<0.001) with the slope of the best linear fit=0.81. Our model's predicted HU were within ±20 HU of the actual value in 53% of cases, 70% of the predictions were within ±30 HU, 81% were within ±40 HU, and 90% were within ±50 HU of the actual post-RT HU. Four of 42 patients were found to have vertebral body compression fractures in the field of radiation.
  
  
  CONCLUSIONS
  Patients who receive abdominal chemoradiation develop significant BMD loss in the thoracic and lumbar vertebrae. Treatment-related BMD loss may contribute to the development of vertebral compression fractures. A predictive model for post-CRT BMD changes may inform bone protective strategies in patients planned for abdominal CRT.
authors.affiliation: Department of Radiation Oncology, University of California Irvine, Orange, USA.
authors.forename: Randy L
authors.initials: RL
authors.lastname: Wei
authors.affiliation: Department of Radiation Oncology, University of California Irvine, Orange, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Jung
authors.affiliation: Department of Radiation Oncology, University of California Irvine, Orange, USA.
authors.forename: Wilfred
authors.initials: W
authors.lastname: Manzano
authors.affiliation: Department of Radiation Oncology, University of California Irvine, Orange, USA.
authors.forename: Varun
authors.initials: V
authors.lastname: Sehgal
authors.affiliation: Department of Medicine, Division of Hematology-Oncology, University of California Irvine, Orange, USA.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Klempner
authors.affiliation: Department of Radiation Oncology, David Geffen School of Medicine, University of California Los Angeles, USA.
authors.forename: Steve P
authors.initials: SP
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, University of California Irvine, Orange, USA.
authors.forename: Nilam S
authors.initials: NS
authors.lastname: Ramsinghani
authors.affiliation: Department of Radiology, University of California Irvine, Orange, USA. Electronic address: clall@uci.edu.
authors.forename: Chandana
authors.initials: C
authors.lastname: Lall
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use; D018488:Bone Demineralization, Pathologic / Q000209:etiology*; D015519:Bone Density / Q000528:radiation effects*; D059248:Chemoradiotherapy / Q000009:adverse effects; D004067:Digestive System Neoplasms / Q000532:radiotherapy*; D005260:Female; D050815:Fractures, Compression / Q000209:etiology; D005598:Fractures, Spontaneous / Q000209:etiology; D006801:Humans; D008159:Lumbar Vertebrae / Q000293:injuries / Q000528:radiation effects*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011832:Radiation Injuries / Q000209:etiology*; D012189:Retrospective Studies; D016103:Spinal Fractures / Q000209:etiology; D013904:Thoracic Vertebrae / Q000293:injuries / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D000970:Antineoplastic Agents