title: Late rectal toxicity after image-based high-dose-rate interstitial brachytherapy for postoperative recurrent and/or residual cervical cancers: EQD2 predictors for Grade ≥II toxicity.
abstract: OBJECTIVE
  To investigate the correlation of rectal dose volume metrics with late rectal toxicity after high-dose-rate pelvic interstitial brachytherapy.
  
  
  METHODS
  From October 2009 to November 2012, 50 patients with residual or recurrent cervical cancer were included. Patients received external radiation 50 Gy in 25 fractions over 5 weeks with weekly cisplatin. Rectum and rectal mucosal (RM) contours were delineated retrospectively. RM was defined as the outer surface of the flatus tube inserted at brachytherapy. The dose received by 0.1, 1, 2, 5 cc of rectum, RM, and sigmoid was recorded. Cumulative equivalent dose in 2 Gy (EQD2) for organs at risk was calculated assuming α/β of 3. Univariate analysis was performed to identify predictors of rectal toxicity.
  
  
  RESULTS
  At a median follow-up of 34 months (12-51 months), Grade II and III late rectal toxicity was observed in 9 (18%) and 2 (4%) patients, respectively. On univariate analysis, rectal doses were not significant predictors; however, D 0.1-cc RM dose >72 Gy (p = 0.04), D 1-cc RM dose >65 Gy (p = 0.004), D 2-cc RM dose >62.3 Gy (p = 0.004), and D 5-cc RM dose >60 Gy (p = 0.007) correlated with Grade ≥II toxicity. On probit analysis, the estimated dose in EQD2 for a 10% and 20% risk of rectal toxicity was D 2-cc rectum of 55 and 66 Gy, and RM <55 and 63 Gy, respectively.
  
  
  CONCLUSIONS
  Limiting 2-cc RM and rectal doses within the proposed thresholds can minimize Grade ≥II toxicity for gynecologic high-dose-rate interstitial brachytherapy.
authors.affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India. Electronic address: schopra@actrec.gov.in.
authors.forename: Supriya
authors.initials: S
authors.lastname: Chopra
authors.affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India.
authors.forename: Tapas
authors.initials: T
authors.lastname: Dora
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India.
authors.forename: Reena
authors.initials: R
authors.lastname: Engineer
authors.affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India.
authors.forename: Siji
authors.initials: S
authors.lastname: Mechanery
authors.affiliation: Department of Radiation Oncology, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Agarwal
authors.affiliation: Epidemiology and Clinical Trials Unit, Advanced Centre for Treatment Research and Education in Cancer, Tata Memorial Centre, Navi Mumbai, Maharashtra, India.
authors.forename: Sadhna
authors.initials: S
authors.lastname: Kannan
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India.
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Ghadi
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India.
authors.forename: Jamema
authors.initials: J
authors.lastname: Swamidas
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India.
authors.forename: Umesh
authors.initials: U
authors.lastname: Mahantshetty
authors.affiliation: Department of Radiation Oncology, Tata Memorial Hospital, Tata Memorial Centre, Mumbai, Maharashtra, India.
authors.forename: Shyam Kishore
authors.initials: SK
authors.lastname: Shrivastava
mesh_terms: D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001918:Brachytherapy / Q000009:adverse effects* / Q000379:methods; D059186:Chemoradiotherapy, Adjuvant; D002945:Cisplatin / Q000627:therapeutic use; D012809:Colon, Sigmoid / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007413:Intestinal Mucosa / Q000528:radiation effects; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000532:radiotherapy* / Q000628:therapy; D018365:Neoplasm, Residual; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000209:etiology*; D012007:Rectum / Q000528:radiation effects*; D012189:Retrospective Studies; D013997:Time Factors; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy* / Q000628:therapy
chemical_list: D000970:Antineoplastic Agents; D002945:Cisplatin
keywords: Cervix cancer; Interstitial brachytherapy; MUPIT; Proctitis