title: Requirements regarding dose rate and exposure time for killing of tumour cells in beta particle radionuclide therapy.
abstract: OBJECTIVE
  The purpose of this study was to identify combinations of dose rate and exposure time that have the potential to provide curative treatment with targeted radionuclide therapy applying low dose rate beta irradiation.
  
  
  METHODS
  Five tumour cell lines, U-373MG and U-118MG gliomas, HT-29 colon carcinoma, A-431 cervical squamous carcinoma and SKBR-3 breast cancer, were used. An experimental model with 10(5) tumour cells in each sample was irradiated with low dose rate beta particles. The criterion for successful treatment was absence of recovery of cells during a follow-up period of 3 months. The initial dose rates were in the range 0.1-0.8 Gy/h, and the cells were continuously exposed for 1, 3 or 7 days. These combinations covered dose rates and doses achievable in targeted radionuclide therapy.
  
  
  RESULTS
  Continuous irradiation with dose rates of 0.2-0.3 and 0.4-0.6 Gy/h for 7 and 3 days, respectively, could kill all cells in each tumour cell sample. These treatments gave total radiation doses of 30-40 Gy. However, when exposed for just 24 h with about 0.8 Gy/h, only the SKBR-3 cells were successfully treated; all the other cell types recovered. There were large cell type-dependent variations in the growth delay patterns for the cultures that recovered. The U-118MG cells were most resistant and the U-373MG and SKBR-3 cells most sensitive to the treatments. The HT-29 and A-431 cells were intermediate.
  
  
  CONCLUSIONS
  The results serve as a guideline for the combinations of dose rate and exposure time necessary to kill tumour cells when applying low dose rate beta irradiation. The shift from recovery to "cure" fell within a narrow range of dose rate and exposure time combinations.
authors.affiliation: Division of Biomedical Radiation Sciences, Department of Oncology, Radiology and Clinical Immunology, Rudbeck Laboratory, Uppsala University, SE-751 85, Uppsala, Sweden. Jorgen.Carlsson@bms.uu.se
authors.forename: Jörgen
authors.initials: J
authors.lastname: Carlsson
authors.forename: Veronika
authors.initials: V
authors.lastname: Eriksson
authors.forename: Bo
authors.initials: B
authors.lastname: Stenerlöw
authors.forename: Hans
authors.initials: H
authors.lastname: Lundqvist
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D001610:Beta Particles / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009369:Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D011829:Radiation Dosage; D011868:Radioisotopes / Q000627:therapeutic use*; D019275:Radiopharmaceuticals / Q000627:therapeutic use; D011878:Radiotherapy / Q000379:methods*
chemical_list: D011868:Radioisotopes; D019275:Radiopharmaceuticals