PARENT SESSION
1:30 PM to 3:30 PM
Sunday, April 21, 2002
Poster Session 5 Oxygenation of Tumors and Modification
Room: Nevada Exhibition Center
(P10-83) Improved oxygenation occurs in subcutaneous tumors during fractionated radiotherapy.
O'Hara, Julia*,1, Demidenko, Eugene2, Wilmot, Carmen1, Swartz, Harold1, 1 EPR Center for Study of Viable Systems, Hanover, NH2 Section of Biostatistics and Epidemiology, Hanover, NH
ABSTRACT-
Radiation therapy may be more effective if serial monitoring of tumor PtO2 were used to determine the extent and timing of changes in oxygenation after irradiation in individual tumors. Treatment planning could then be modified to exploit improved oxygenation or to direct patients to therapy appropriate for hypoxic tumors. In this study, we studied two experimental tumor models before and during a course of radiation therapy (2Gy/day x 10days) and report on oxygenation and tumor growth delay. Models were subcutaneous RIF-1 fibrosarcomas (C3H/HeJ mice) or 9L gliosarcomas (athymic nude mice). Oxygen measurements were made by in vivo EPR oximetry with paramagnetic oxygen sensitive material, (dry lithium phthalocyanine, LiPc) implanted directly into the tumor via a 23 ga needle. Tumor PtO2 was assessed in each tumor twice before treatment and then every other day. Mean (±SE) pretreatment PtO2 was 6.8 ± 0.85 mm Hg (n=22mice) for RIF-1 and 5.1± 0.0.7 mmHg (n=20mice) for 9L. During irradiation and EPR assessments, mice were anesthetized with 1.5% isoflurane with spontaneous breathing. The effect of irradiation on tumor growth was to increase the time to reach 3x the volume at treatment by 4 days for RIF-1 and 1 day for 9L. There was heterogeneity of response to radiation in terms of tumor PtO2 for both tumor models with little response in the 9L tumors. For RIF-1, no reoxygenation was noted until several 2 Gy doses had been delivered. The degree and timing of reoxygenation depended on 1) tumor type 2) time after first dose 3) time after previous dose and 4) the individual tumor. These results indicate that reoxygenation does occur during fractionated radiation but investigations into the time course between doses will need to be carried out to determine the pattern of oxygen changes between doses and the relationship between reoxygenation and response. Further studies are needed to investigate the mechanisms of the cumulative effect of the fractionated radiation treatments on oxygenation.
KEYWORDS: fractionated radiotherapy, tumor, oxygen, EPR oximetry