Effects of hyperbaric oxygen and normobaric carbogen on the radiation response of the rat rhabdomyosarcoma R1H.
OBJECTIVE
Hypoxic tumor cells are an important factor of radioresistance. Hyperbaric oxygen (HBO) and normobaric carbogen (95% oxygen, 5% carbon dioxide) increase the oxygen delivery to tumors. This study was performed to explore changes of tumor oxygenation during a course of fractionated irradiation and to determine the effectiveness of normobaric carbogen and HBO during the final phase of the radiation treatment.


METHODS
Experiments were performed on the rhabdomyosarcoma R1H growing on WAG/Rij rats. After 20 X-ray fractions of 2 Gy within 4 weeks, oxygen partial pressure (pO2) was measured using the Eppendorf oxygen electrode under ambient conditions, with normobaric carbogen or HBO at a pressure of 240 kPa. Following the 4-week radiation course, a top-up dose of 10-50 Gy was applied in 2-10 fractions of 5 Gy with or without hyperoxygenation.


RESULTS
HBO but not carbogen significantly increased the median pO2 in irradiated tumors. The radiation doses to control 50% of tumors were 38.0 Gy, 29.5 Gy, and 25.0 Gy for air, carbogen, and HBO, respectively. Both high oxygen content gas inspirations led to significantly improved tumor responses with oxygen enhancement ratios (OERs) of 1.3 for normobaric carbogen and 1.5 for HBO (air vs. carbogen: p = 0.044; air vs. HBO: p = 0.02; carbogen vs. HBO: p = 0.048).


CONCLUSIONS
Both normobaric carbogen and HBO significantly improved the radiation response of R1H tumors. HBO appeared to be more effective than normobaric carbogen, both with regard to tumor oxygenation and response to irradiation.
Hartmann
K A
KA
Department of Radiation Oncology, University Duesseldorf, Duesseldorf, Germany. hartmana@uni-duesseldorf.de
van der Kleij
A J
AJ
Carl
U M
UM
Hulshof
M C
MC
Willers
R
R
Sminia
P
P
D000818:Animals; D002245:Carbon Dioxide / Q000627:therapeutic use*; D019583:Dose Fractionation, Radiation; D006931:Hyperbaric Oxygenation; D010100:Oxygen / Q000378:metabolism / Q000627:therapeutic use*; D010313:Partial Pressure; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use*; D011853:Radiobiology; D011879:Radiotherapy Dosage; D051381:Rats; D012208:Rhabdomyosarcoma / Q000098:blood supply / Q000532:radiotherapy*
D011838:Radiation-Sensitizing Agents; D002245:Carbon Dioxide; C011700:carbogen; D010100:Oxygen