[The dosage-performance effects on Ca-Ski and HPK cells in relation to the dose and fractionation].
BACKGROUND
The steep decrease of dose and dose-rate in brachytherapy implies very different radiobiological considerations of the biological effectivity.


METHODS
Therefore, in imitation of the clinical procedure, we compared the LDR-, MDR- and HDR-brachytherapy. We carried out experiments on epidermoid cervix carcinoma cells (Ca-Ski cells) and human primary keratinocytes (HPK cells) obtained after transfection with human papillomavirus type 16 DNA varying the dose-rate (28 cGy/h to 8000 cGy/h), the dose (1 Gy to 100 Gy) and fractionating (protracted, 3, 6 and 12 fractions).


RESULTS
1. At dose-rates of 75 cGy/h (Ca-Ski cells) and 110 cGy/h (HPK cells) respectively we found that the cells "fall asleep" at doses up to 100 Gy; the rate of cell mortality is insignificantly higher than the proliferation rate. 2. A first-time proof of an accumulation of repopulation effects (recovery from the sublethal radiation damage, progression of the cells during the partial cycle/proliferation and the acts of redistribution), if the radiation exposure reaches the median time of the cell cycle (HPK cells, dose-rate: 110 cGy/h, doses: 1 Gy to 100 Gy). 3. Each increase in the dose-rate requires higher fractionating. At dose-rates higher than 300 cGy/h (range of a percutaneous radiotherapy), we found that the survival rates of the cells could only be increased insignificantly in spite of a fractionated therapy (3, 6 or 12 fractions; doses: 1 Gy to 100 Gy); the repopulation effects almost vanished.


CONCLUSIONS
Changing a LDR- into an HDR-brachytherapy the equivalent factors close to the source have to be selected low and with increasing distances from the source high respectively higher-the major problem for a mathematical formula. The reduction of the dose in HDR-radiation therapy is a compromise in order to limit side effects caused by a radiation. The trade-off is a small therapeutic range and reduced therapeutic effectivity at the tumor. The percutaneous dose at the pelvis wall has to be reduced if at the same time an HDR-brachytherapy will be carried out-to avoid side effects.
Schulz-Wendtland
R
R
Abteilung Gynäkologische Radiologie, Universitäts-Frauenklinik Erlangen.
Krämer
S
S
Keilholz
L
L
Pflüger
S
S
Lang
N
N
D001918:Brachytherapy; D002294:Carcinoma, Squamous Cell / Q000473:pathology / Q000532:radiotherapy*; D002455:Cell Division / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D002478:Cells, Cultured; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000528:radiation effects*; D027383:Papillomaviridae / Q000235:genetics; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*
Dosisleistungseffekte an Ca-Ski- und HPK-Zellen in Abhängigkeit von Dosis und Fraktionierung.