CONTINUOUS, PULSED OR SINGLE ACUTE IRRADIATION OF A TRANSPLANTED RODENT TUMOR-MODEL

Background: Recent advances in remote afterloading pulsed mode brachyt herapy have provided a much needed tool for the radiation oncologist. It has the versatility of optimised physical dose distribution along w ith improved staff radiation protection and patient nursing. Purpose: This preliminary study was designed to explore the radiobiological equ ivalence between conventional continuous low dose rate tumour irradiat ion (CLDR) and the new technique of pulsed dose irradiation (PDR). Mat erials and methods: Subcutaneous isogenic sarcomas transplanted in fem ale John's Strain Wistar rats were irradiated locally with acute, puls ed or continuous interstitial low dose-rate exposures at 9-11 mm mean diameter. Results: As expected, single acute doses (5-40 Gy) were more effective (P < 0.01) in achieving tumour growth delay (1.4 days/Gy) t han CLDR exposure (4-51 Gy) over 24-48 h (0.93 days/Gy). However, PDR treatment (8 hourly fractions/day) at high dose-rate (8-48 Gy) over 8- 72 h was significantly (P = 0.01) more effective (1.66 days/Gy) than C LDR but not acute exposures. Conclusions: These data suggest that, cli nically a significantly improved therapeutic ratio may also be achieva ble with pulsed high dose rate brachytherapy, and that further radiobi ological studies with in-vivo tumour models are needed. (C) 1997 Elsev ier Science Ireland Ltd.