PRETREATMENT OXYGENATION PREDICTS RADIATION RESPONSE IN ADVANCED SQUAMOUS-CELL CARCINOMA OF THE HEAD AND NECK

Background and purpose: Hypoxic tumor cells are known to be relatively radioresistant. The aim of the study was to correlate oxygenation sta tus and radiation response in advanced squamous cell carcinomas of hea d and neck. Methods and patients: Pretreatment oxygenation status was measured in 34 lymph nodes and one primary tumor neck using oxygen ele ctrodes. The primary oxygenation endpoint was the fraction of pO(2) va lues less than 2.5 mmHg. Patients received standardized, conventional, external radiotherapy 66-68 Gy in 33-34 fractions. Results: Sixteen p atients had loco-regional failure. Among these 16 patients the median of the fraction of pO(2) values less than 2.5 mmHg was 22% (range 0-95 %) as compared to 6% (range 0-51%) among patients with loco-regional t umor control. When separating all 35 patients by the median of the fra ction of pO(2) values less than 2.5 mmHg and comparing the 2 years act uarial tumor control probability using Kaplan-Meier estimates. the mos t hypoxic subgroup had significantly lower loco-regional tumor control (P=0.013, Logrank rest). By univariate regression analysis the fractio n of pO(2) values less than 2.5 mmHg was found to be significant as co ntinuous variable (P=0.010). Finally, by Cox multiple regression analy sis the fraction of pO(2) values less than 2.5 mmHg was found to be th e strongest independent variable in predicting radiation response when using tumor control in the site of pO(2) assessment as treatment endp oint (P=0.018). Conclusion: These results suggest that pretreatment tu mor oxygenation status is predictive of radiation response, when using the fraction of pO(2) values less than 2.5 mmHg as endpoint.