title: Influence of body mass index and periprostatic fat on rectal dosimetry in permanent seed prostate brachytherapy.
abstract: OBJECTIVE
  We examined the influence of body mass index (BMI) and body fat distribution on rectal dose in patients treated with permanent seed brachytherapy for localized prostate cancer.
  
  
  METHODS
  We analyzed 213 patients treated with I125 seed brachytherapy for localized prostate cancer. BMI and rectal dosimetry data for all patients were available. Data on visceral and subcutaneous fat distribution at the level of the iliac crest (n = 140) as well as the distribution of periprostatic and subcutaneous fat at the symphysis pubis level were obtained (n = 117). Fat distribution was manually contoured on CT on day 30 after brachytherapy. The correlation between BMI, fat distribution and rectal dose (R100 (in cc), R150 (cc), D2 (Gy)) was analyzed using the Spearman correlation coefficient. Differences in rectal dose between tertiles of body fat distribution were calculated using nonparametric tests.
  
  
  RESULTS
  Periprostatic adipose was only weakly correlated with BMI (r = 0.0.245, p = 0.008) and only weakly correlated with the other fat measurements (r = 0.31-0.37, p < 0.001). On the other hand, BMI was correlated with all other fat measurements (≥0.58, p < 0.001). All the other fat measurements were strongly correlated with each other (r = 0.5-0.87, p < 0.001). Patients with an R100 of >1.3 cc (23% of patients) had less visceral fat (p = 0.004), less subcutaneous fat at the level of the iliac crest (p = 0.046) and a lower BMI (26.8 kg/m2 vs. 28.5 kg/m2, p = 0.02) than patients with an R100 of <1.3 cc. Results were very similar when comparing an R100 of >1.0 cc (34% of patients) across the tertiles. None of the tested linear regression models were predictive (max 12%) of dose to the rectum.
  
  
  CONCLUSIONS
  Dose to the rectum is dependent on BMI and body fat distribution. Periprostatic fat does not influence rectal dose. Dose to the rectum remains difficult to predict and depends on many factors, one of which is body fat distribution.
authors.forename: David
authors.initials: D
authors.lastname: Tiberi
authors.forename: Nelson
authors.initials: N
authors.lastname: Gruszczynski
authors.forename: Aliza
authors.initials: A
authors.lastname: Meissner
authors.forename: Guila
authors.initials: G
authors.lastname: Delouya
authors.affiliation: Département de Radio-Oncologie, Centre Hospitalier de l'Université de Montréal (CHUM) - Hôpital Notre-Dame, Montréal, Québec, Canada. daniel.taussky.chum@ssss.gouv.qc.ca.
authors.forename: Daniel
authors.initials: D
authors.lastname: Taussky
mesh_terms: D000273:Adipose Tissue; D000368:Aged; D015992:Body Mass Index; D001918:Brachytherapy / Q000379:methods*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011874:Radiometry; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*; D012044:Regression Analysis
chemical_list: D007457:Iodine Radioisotopes
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