title: Relationship between pelvic organ-at-risk dose and clinical target volume in postprostatectomy patients receiving intensity-modulated radiotherapy.
abstract: OBJECTIVE
  To investigate dose-volume consequences of inclusion of the seminal vesicle (SV) bed in the clinical target volume (CTV) for the rectum and bladder using biological response indices in postprostatectomy patients receiving intensity-modulated radiotherapy (IMRT).
  
  
  METHODS
  We studied 10 consecutive patients who underwent prostatectomy for prostate cancer and subsequently received adjuvant or salvage RT to the prostate fossa. The CTV to planning target volume (PTV) expansion was 7 mm, except posterior expansion, which was 5 mm. Two IMRT plans were generated for each patient, including either the prostate fossa alone or the prostate fossa with the SV bed, but identical in all other aspects. Prescription dose was 68.4 Gy in 1.8-Gy fractions prescribed to ≥95% PTV.
  
  
  RESULTS
  With inclusion of the SV bed in the treatment volume, PTV increased and correlated with PTV-bladder and PTV-rectum volume overlap (Spearman ρ 0.91 and 0.86, respectively; p < 0.05). As a result, the dose delivered to the bladder and rectum was higher (p < 0.05): mean bladder dose increased from 11.3 ± 3.5 Gy to 21.2 ± 6.6 Gy, whereas mean rectal dose increased from 25.8 ± 5.5 Gy to 32.3 ± 5.5 Gy. Bladder and rectal equivalent uniform dose correlated with mean bladder and rectal dose. Inclusion of the SV bed in the treatment volume increased rectal normal tissue complication probability from 2.4% to 4.8% (p < 0.01).
  
  
  CONCLUSIONS
  Inclusion of the SV bed in the CTV in postprostatectomy patients receiving IMRT increases bladder and rectal dose, as well as rectal normal tissue complication probability. The magnitude of PTV-bladder and PTV-rectal volume overlap and subsequent bladder and rectum dose increase will be higher if larger PTV expansion margins are used.
authors.affiliation: Department of Radiation Oncology, University of California, Davis, Sacramento, CA, USA.
authors.forename: Sinisa
authors.initials: S
authors.lastname: Stanic
authors.forename: Mathew
authors.initials: M
authors.lastname: Mathai
authors.forename: Jing
authors.initials: J
authors.lastname: Cui
authors.forename: James A
authors.initials: JA
authors.lastname: Purdy
authors.forename: Richard K
authors.initials: RK
authors.lastname: Valicenti
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects; D010388:Pelvis; D011182:Postoperative Care / Q000379:methods; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D018714:Radiotherapy, Adjuvant / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D012062:Relative Biological Effectiveness; D016879:Salvage Therapy / Q000379:methods; D012669:Seminal Vesicles / Q000000981:diagnostic imaging / Q000528:radiation effects; D047368:Tumor Burden; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects