title: Rectal dose constraints for salvage iodine-125 prostate brachytherapy.
abstract: OBJECTIVE
  Organ-confined prostate cancer recurrences after primary radiotherapy can be treated with salvage iodine-125 brachytherapy. Options include total salvage (TS) or focal salvage (FS). TS often leads to severe late gastrointestinal (GI) toxicity. Differences in rectal dosimetry between TS and FS are presented and dose constraints proposed to reduce late severe GI toxicity (>90 days).
  
  
  METHODS
  Intraoperative dosimetry and 30-day CT-dosimetry of 20 FS and 28 TS patients were evaluated. GI toxicity was evaluated using the common terminology criteria for adverse events-4. With receiver operating characteristic analysis, dosimetry cutoff values to prevent severe late GI toxicity were assessed.
  
  
  RESULTS
  FS reduces rectal dose significantly. Median D(0.1cc), D(1cc), D(2cc), and V100 reductions were 38 Gy (p = 0.002), 46 Gy (p < 0.0001), 46 Gy (p < 0.0001), and 0.41 cc (p = 0.0001), respectively, compared with TS. FS patients had no late severe GI toxicity. TS patients with severe GI toxicity (41%, n = 11) showed significantly higher rectal doses than TS patients without GI toxicity (59%, n = 16). Median D(0.1cc), D(1cc), D(2cc), and V100 differences were 29 Gy (p < 0.001), 17 Gy (p = 0.001), 28 Gy (p < 0.001), and 0.45 cc (p = 0.001). With receiver operating characteristic analysis, restrictions for the D(0.1cc), D(1cc), D(2cc), and V100 are <160 Gy (area under the curve [AUC], 0.88; 95% confidence interval [CI] 0.76-1.00), <119 Gy (AUC, 0.87; 95% CI, 0.74-1.00), <102 Gy (AUC, 0.89; 95% CI, 0.77-1.00), and <0.38 cc (AUC, 0.88; 95% CI, 0.75-1.00), respectively. Thirty-day CT dosimetry showed minor overestimation of intraoperative D(2cc) (median, 10 Gy [p = 0.02]).
  
  
  CONCLUSIONS
  FS reduces rectal dose compared with TS. D(0.1cc), D(1cc), D(2cc), and V100 restrictions were 160 Gy, 120 Gy, 100 Gy, and 0.35 cc. Taking correlation into account, the D2cc <100 Gy might be sufficient for clinical practice. Larger series and multivariable models are necessary to further assess the found restrictions.
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: M.Peters-10@umcutrecht.nl.
authors.forename: Max
authors.initials: M
authors.lastname: Peters
authors.affiliation: Department of Radiotherapy, Radiotherapeutic Institute RISO, Deventer, The Netherlands.
authors.forename: Carel J
authors.initials: CJ
authors.lastname: Hoekstra
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Jochem R N
authors.initials: JR
authors.lastname: van der Voort van Zyp
authors.affiliation: Department of Radiotherapy, Radiotherapeutic Institute RISO, Deventer, The Netherlands.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Westendorp
authors.affiliation: Department of Radiotherapy, Radiotherapeutic Institute RISO, Deventer, The Netherlands.
authors.forename: Sandrine M G
authors.initials: SM
authors.lastname: van de Pol
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Marinus A
authors.initials: MA
authors.lastname: Moerland
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Metha
authors.initials: M
authors.lastname: Maenhout
authors.affiliation: Department of Radiotherapy, Radiotherapeutic Institute RISO, Deventer, The Netherlands.
authors.forename: Rob
authors.initials: R
authors.lastname: Kattevilder
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Marco
authors.initials: M
authors.lastname: van Vulpen
mesh_terms: D000368:Aged; D019540:Area Under Curve; D001918:Brachytherapy / Q000009:adverse effects / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000473:pathology / Q000532:radiotherapy*; D058958:Organs at Risk; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D012372:ROC Curve; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology*; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*; D016879:Salvage Therapy / Q000009:adverse effects / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes
keywords: Dose constraints; Focal salvage; I-125 brachytherapy; Prostate cancer; Rectum; Total salvage; Toxicity