title: Early dose-dependent cortical thinning of the femoral neck in anal cancer patients treated with pelvic radiation therapy.
abstract: Anal cancer patients treated with radiation therapy (RT) have an increased risk of hip fractures after treatment. The mechanism of these fractures is unknown; however, femoral fractures have been correlated with cortical bone thinning. The objective of this study was to assess early changes in cortical bone thickness at common sites of femoral fracture in anal cancer patients treated with intensity modulated radiation therapy (IMRT).
  
  
  
  RT treatment plans and computed tomography (CT) scans from 23 anal cancer patients who underwent IMRT between November 2012 and December 2014 were retrospectively reviewed. Cortical thickness (Ct.Th) was mapped at homologous vertices within the proximal femur using pre-RT and post-RT (≤4months) CT scans. The bone attenuation measurements were collected at homologous locations within the trabecular bone of the right femoral neck (FN). The percent change in Ct.Th and trabecular bone mineral density (trBMD) were assessed. FN cortical thinning was correlated to RT dose using linear regression. A logistic model for dose dependent cortical thinning was constructed.
  
  
  
  Twenty-two patients were analyzed. Significant post-treatment cortical thinning was observed in the intertrochanteric crest, subcapital and inferior FN (p<0.05). FN volume receiving ≥40Gy (V40Gy) was a significant predictor of focal cortical thinning ≥30% (p=0.03). A significant decrease in FN trBMD was observed (-6.4% [range -34.4 to 3.3%]; p=0.01).
  
  
  
  Significant early decrease in Ct.Th and trBMD occurs at the FN in patients treated with RT for anal cancer. FN V40Gy was predictive of clinically significant focal FN cortical thinning.
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, NC, USA.
authors: Catherine
authors: C
authors: Okoukoni
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC, USA.
authors: David M
authors: DM
authors: Randolph
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC, USA.
authors: Emory R
authors: ER
authors: McTyre
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA.
authors: Andy
authors: A
authors: Kwok
authors: Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, NC, USA; Virginia Tech-Wake Forest University Center for Injury Biomechanics, Winston-Salem, NC, USA.
authors: Ashley A
authors: AA
authors: Weaver
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC, USA.
authors: A William
authors: AW
authors: Blackstock
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Department of Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, NC, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC, USA.
authors: Michael T
authors: MT
authors: Munley
authors: Department of Radiation Oncology, Wake Forest School of Medicine, Winston-Salem, NC, USA; Comprehensive Cancer Center of Wake Forest University, Winston-Salem, NC, USA. Electronic address: jwilley@wakehealth.edu.
authors: Jeffrey S
authors: JS
authors: Willey
mesh_terms: D000328:Adult; D001005:Anus Neoplasms / Q000532:radiotherapy*; D015519:Bone Density; D000071538:Cortical Bone / Q000473:pathology* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005272:Femur Neck / Q000473:pathology* / Q000528:radiation effects; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000528:radiation effects*; D011336:Probability
keywords: Anal cancer; Cortical bone; Femoral neck; Hip fractures; Intensity modulated radiation therapy (IMRT)