Phosphorus NMR study of the response of a murine tumour to hyperthermia as a function of treatment time and temperature

Evaluating the response of tumours to therapy promises to become one of the major applications of in vivo phosphorus (31P) nuclear magnetic resonance spectroscopy. Decreases in the levels of organic phosphates in favour of inorganic phosphate (Pi) as occur in murine tumours after hyperthermia treatment, can be quantified by the ratio ATP/Pi. In this study the relationship between the time of heating (15, 30 and 60 min) and the temperature (43 and 44 degrees C) was investigated in mice with NU-82 tumours by considering the changes in ATP/Pi ratio as a function of both variables. After 30 min treatment at 43 degrees C the percentage decrease in ATP/Pi ratio was similar to that observed after 15 min at 44 degrees C (42 +/- 9 vs. 48 +/- 9); after 60 min at 43 degrees C the decrease was similar to that after 30 min at 44 degrees C (75 +/- 7 vs. 74 +/- 4). These results give further evidence for the validity of a current working definition of thermal dose: thermal dose = t integral of 0 2T-43 dt. In addition this study shows that in vivo 31P NMR spectroscopy can be a useful means for assessment of thermal dose.