Radiobiological hypoxia, histological parameters of tumour microenvironment and local tumour control after fractionated irradiation.
OBJECTIVE
To investigate the relationships between radiobiological hypoxic fraction (rHF), pimonidazole hypoxic fraction (pHF) as well as other histological parameters of the tumour microenvironment, and local tumour control after fractionated irradiation in human squamous cell carcinomas (hSCCs).


METHODS
Ten different hSCC cell lines were transplanted into nude mice and rHF was calculated from local tumour control rates after single dose irradiation under normal or clamped blood flow conditions. In parallel, tumours were irradiated with 30 fractions within 6 weeks. Radiation response was quantified as dose required to cure 50% of tumours (TCD(50)). Unirradiated tumours were excised for histological evaluation including relative hypoxic area (pHF), relative vascular area (RVA), and fraction of perfused vessels (PF).


RESULTS
A weak but significant positive correlation between rHF (R(2)=0.6, p=0.014) and TCD(50) after fractionated irradiation was found. The pHF did not correlate with rHF but was significantly associated with the TCD(50) after single dose clamp (R(2)=0.8, p=0.003) and showed a trend for an association with TCD(50) after fractionated irradiation (R(2)=0.4, p=0.067). Relative vascular area and fraction of perfused vessels did not show an association with rHF or TCD(50) after fractionated irradiation.


CONCLUSIONS
Our data suggest that radiobiological hypoxia contributes to the response after fractionated irradiation but that also other radiobiological mechanisms are involved. In the present study, pimonidazole labelling does not reflect rHF and has a limited value to predict local tumour control after fractionated irradiation. The association between pHF and TCD(50) after single dose clamp warrants further investigation.
Yaromina
Ala
A
OncoRay-Centre for Radiation Research in Oncology, Medical Faculty Carl Gustav Carus, Technische Universität Dresden, Germany.
Thames
Howard
H
Zhou
Xuanjing
X
Hering
Sandra
S
Eicheler
Wolfgang
W
Dörfler
Annegret
A
Leichtner
Thomas
T
Zips
Daniel
D
Baumann
Michael
M
D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000473:pathology* / Q000532:radiotherapy*; D002455:Cell Division / Q000528:radiation effects; D015687:Cell Hypoxia / Q000528:radiation effects; D016001:Confidence Intervals; D004195:Disease Models, Animal; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009389:Neovascularization, Pathologic / Q000473:pathology; D009593:Nitroimidazoles / Q000494:pharmacology; D011836:Radiation Tolerance; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D011853:Radiobiology; D014183:Transplantation, Heterologous; D059016:Tumor Microenvironment / Q000528:radiation effects*
D009593:Nitroimidazoles; D011838:Radiation-Sensitizing Agents; C033815:pimonidazole