Abstract
<h3>Introduction/Background*</h3> Pelvic radiation therapy (RT) is associated with high doses to the lumbo-pelvic girdle. However, the impact of RT dose on bone density (BD) is not known. Present study was designed to understand the impact of RT dose on BD loss. <h3>Methodology</h3> Patients recruited into a phase III trial of adjuvant radiation with at least 2 CT imaging data sets at baseline and follow up were eligible. The primary endpoint was to report correlation if any between RT dose and BD loss. Across the lumbopelvic region (L1-L5 vertebra, pubic symphysis, femur, acetabulum, greater trochanter, and anterior-superior iliac spine) points were predefined to estimate the RT dose received and Hounsfield (HU) units at pre RT and follow up time points on Eclipse version 13.5. Bone health was categorized as Normal >130HU, Osteopenic= 110-130 HU or Osteoporotic <110HU based on CT HU values. Univariate and multivariate analysis was performed. Additionally, linear mixed model was used to report interaction of follow up duration and RT dose. <h3>Result(s)*</h3> Overall 132 patients were included. The median RT doses was as follows: L1-L2: 1.2-2.1 Gy (1.1-2.4Gy), L4:11 Gy (7.5-17.8 Gy), L5: 47 Gy (42.6-49.3 Gy), Femur: 44-48 Gy (41-50 Gy), Acetabulum: 48 Gy (42-49 Gy), Greater Trochanter 26-30 Gy (17-35 Gy). The median HU loss was 33 HU for doses between 1-11 Gy, 45 HU for12-25 Gy and 60 HU for 26-50 Gy. Before RT, 96% patients had normal bone health. At 24 months only 3% had normal bone health whereas 85% were osteoporotic (p<0.001). Both RT dose (p<0.02) and time (p<0.001) predicted for BD loss whereas interaction of dose x time was not significant (p=0.56). No other patient and treatment related factors predicted for BD changes on univariate analysis. Multivariate analysis was not performed. <h3>Conclusion*</h3> RT doses correlated with BD loss in cohort of patients undergoing postoperative pelvic RT. The results highlight the need for structured evaluation of bone density after pelvic RT.
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