title: Continuous, pulsed or single acute irradiation of a transplanted rodent tumour model.
abstract: BACKGROUND
  Recent advances in remote afterloading pulsed mode brachytherapy have provided a much needed tool for the radiation oncologist. It has the versatility of optimised physical dose distribution along with improved staff radiation protection and patient nursing.
  
  
  OBJECTIVE
  This preliminary study was designed to explore the radiobiological equivalence between conventional continuous low dose rate tumour irradiation (CLDR) and the new technique of pulsed dose irradiation (PDR).
  
  
  METHODS
  Subcutaneous isogenic sarcomas transplanted in female John's Strain Wistar rats were irradiated locally with acute, pulsed or continuous interstitial low dose-rate exposures at 9-11 mm mean diameter.
  
  
  RESULTS
  As expected, single acute doses (5-40 Gy) were more effective (P < 0.01) in achieving tumour growth delay (1.4 days/Gy) than CLDR exposure (4-51 Gy) over 24-48 h (0.93 days/Gy). However, PDR treatment (8 hourly fractions/day) at high dose-rate (8-48Gy) over 8-72 h was significantly (P = 0.01) more effective (1.66 days/Gy) than CLDR but not acute exposures.
  
  
  CONCLUSIONS
  These data suggest that, clinically a significantly improved therapeutic ratio may also be achievable with pulsed high dose rate brachytherapy, and that further radiobiological studies with in-vivo tumour models are needed.
authors.affiliation: Department of Clinical Oncology, The University of Leeds, UK.
authors.forename: T
authors.initials: T
authors.lastname: Sethi
authors.forename: B
authors.initials: B
authors.lastname: Dixon
authors.forename: A
authors.initials: A
authors.lastname: Flynn
authors.forename: D V
authors.initials: DV
authors.lastname: Ash
mesh_terms: D000818:Animals; D001918:Brachytherapy / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D009368:Neoplasm Transplantation; D011879:Radiotherapy Dosage; D051381:Rats; D017208:Rats, Wistar; D012513:Sarcoma, Experimental / Q000532:radiotherapy*