title: The influence of once or twice daily irradiation regimens on growth of squamous cell carcinoma spheroids of different diameters.
abstract: Large tumours are in general more difficult to cure by radiation treatment than small tumours. Several factors may be responsible for this phenomenon which evolves during tumour growth. In an earlier study using squamous cell carcinoma cell line HN-1, we have shown in split-dose recovery experiments that the amount of sublethal damage repair is equal in spheroids of different diameters. To elucidate this repair capacity further, we have employed other radiation regimens, calculated with the LQ-equation to be iso-effective, in spheroids of different sessions. Using specific growth delay to quantify radiation response after two to five fractions, it was shown that repair capacity was equal in spheroids of different sizes. For small spheroids the specific growth delay was smaller in once daily fractionation regimens than when radiation was administered in twice daily sessions. In large spheroids this advantage of accelerated fractionation was not observed. If spheroids from this squamous cell carcinoma cell line may be regarded as a relevant model system for their in vivo counterparts, then the results from the present study may indicate that accelerated fractionation of treatment is advantageous for small lesions, but not for larger tumours.
authors.affiliation: Department of Radiotherapy, University Hospital, Nijmegen, The Netherlands.
authors.forename: J H
authors.initials: JH
authors.lastname: Schwachöfer
authors.forename: R P
authors.initials: RP
authors.lastname: Crooijmans
authors.forename: J
authors.initials: J
authors.lastname: Hoogenhout
authors.forename: H B
authors.initials: HB
authors.lastname: Kal
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D002455:Cell Division / Q000528:radiation effects*; D006801:Humans; D011878:Radiotherapy / Q000379:methods; D014407:Tumor Cells, Cultured