Low-dose hyperradiosensitivity of human glioblastoma cell lines in vitro does not translate into improved outcome of ultrafractionated radiotherapy in vivo.
OBJECTIVE
Low dose hyperradiosensitivity (HRS) has been observed in HGL21- and T98G human glioblastoma cells in vitro. The present study investigates whether these effects translate into improved outcome of ultrafractionated irradiation (UF) in vivo.


METHODS
T98G or HGL21 were transplanted on the hind leg of nude mice. Tumours were irradiated with UF (3 fractions of 0.4 Gy per day, interval 4 h, 7 days per week) or with conventional fractionation (CF; 1 fraction of 1.68 Gy per day, 5 days per week) over 2 or 4 weeks in HGL21 and 2,4 or 6 weeks in T98G. In HGL21, graded top-up doses under clamped hypoxia were applied after 4 weeks of fractionated irradiation. Additional groups of animals were irradiated with single doses under clamp hypoxic conditions with or without whole body irradiation (WBI) before tumour transplantation. Experimental endpoints were growth delay (time to 5-fold starting volume, GD(V5)) and local tumour control.


RESULTS
In T98G tumours median relative GD(V5) was 1.2 [95% C.I. 0.96; 8] in the CF and 0.8 [0.7; 1.02] in the UF arm (p = 0.009) indicating that ultrafractionation is less efficient than conventional fractionation. The TCD50 value of 33.5 Gy [22; 45] after UF was higher than TCD50 of 23.6 Gy [16; 31] after CF (p = 0.15). In HGL21 the median relative GD(V5) was not significantly different between CF and UF. The top-up TCD50 value of 16.1 Gy [95% C.I. 9; 23 Gy] after CF was significantly lower than the corresponding value of 33.2 Gy [23; 44] after UF irradiation (p = 0.007), indicating a higher efficacy of CF compared to UF.


CONCLUSIONS
The results on human T98G and HGL21 glioblastoma do not support the hypothesis that HRS in vitro translates into improved outcome of ultrafractionated irradiation in vivo.
Krause
Mechthild
M
Clinic for Radiotherapy and Radiation Oncology, Medical Faculty Carl Gustav Carus, University of Technology, Dresden, Germany.
Wohlfarth
Jana
J
Georgi
Benjamin
B
Pimentel
Nuno
N
Dorner
Daniela
D
Zips
Daniel
D
Eicheler
Wolfgang
W
Hessel
Franziska
F
Short
Susan C
SC
Joiner
Michael C
MC
Baumann
Michael
M
D000818:Animals; D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005909:Glioblastoma / Q000473:pathology / Q000532:radiotherapy*; D006614:Hindlimb; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D011237:Predictive Value of Tests; D011836:Radiation Tolerance; D014183:Transplantation, Heterologous; D016896:Treatment Outcome