The relative significance of repopulation and hypoxic clonogens in the fractionated radiotherapy of a mouse tumor

Journal Article · Mon May 01 04:00:00 EDT 1995 · Radiation Research

DOI:https://doi.org/10.2307/3579030· OSTI ID:81184

Urano, M; Nishimura, Y; Yaes, R ^[1]

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1. Univ. of Kentucky Medical Center, Lexington, KY (United States)

The aim of this study was to analyze the significance of the repopulation of tumor cell clonogens, reoxygenation and hypoxic cells for the outcome of fractionated radiotherapy. Our previous fractionation study using a murine tumor was used for the analysis. In the previous study, single cell suspensions were prepared from the early-generation isotransplants of a spontaneous fibrosarcoma, FSa-II, in a C3Hf/Sed mouse and transplanted into the foot of C3Hf/Sed mice. Fractionation scheduled consisted of equal graded daily doses (1-20 fractions) given in air or under hypoxic conditions with {sup 137}Cs. Treatment was initiated when tumors reached an averaged diameter of 4 mm. A twice-a-day (b.i.d.) irradiation was tested for 20 doses. Tumor control was the end point, and the TCD{sub 50} (50% tumor control dose) was obtained. The surviving fractions resulting from these TCD{sub 50} doses were calculated using the {alpha} and {beta} values for the Fsa-II cells, assuming that these values were constant throughout the fractionation period. These surviving fractions were used to calculate the clonogen repopulation and the reoxygeneration of the hypoxic cells. Tumor clonogens repopulated rapidly and the hypoxic cells appeared to reoxygenate substantially during 10-20 doses. In the fractionation regimens consisting of more than 5 doses, the repopulation was reflected as a small {alpha}/{beta} ratio on the F{sub e} plot. During 20 daily doses given under hypoxic conditions, clonogens repopulated by a factor of 1.9 x 10{sup 6}. The hypoxic clonogens repopulated to a much lesser extent than did the total clonogens. Reoxygenation was not substantial up to 5 daily doses but appeared to become significant during 10 to 20 doses. The magnitude of reoxygenation appeared to be substantially greater during 20 daily doses than during 20 b.i.d. doses. 48 refs., 6 figs., 2 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 81184
• Journal Information: Radiation Research, Journal Name: Radiation Research Journal Issue: 2 Vol. 142; ISSN 0033-7587; ISSN RAREAE
• Country of Publication: United States
• Language: English

Related Subjects

56 BIOLOGY AND MEDICINE
APPLIED STUDIES
ANOXIA
BETA RATIO
FRACTIONATED IRRADIATION
INHIBITION
MICE
OXIDATION
RADIOTHERAPY
RESPONSE MODIFYING FACTORS
TUMOR CELLS