Continuous, pulsed or single acute irradiation of a transplanted rodent tumour model

Abstract

Background: Recent advances in remote afterloading pulsed mode brachytherapy have provided a much needed tool for the radiation oncologist. It has the versatility of optimised physical dose distribution along with improved staff radiation protection and patient nursing. Purpose: This preliminary study was designed to explore the radiobiological equivalence between conventional continuous low dose rate tumour irradiation (CLDR) and the new technique of pulsed dose irradiation (PDR). Materials and methods: Subcutaneous isogenic sarcomas transplanted in female John's Strain Wistar rats were irradiated locally with acute, pulsed 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) than CLDR exposure (4–51 Gy) over 24–48 h (0.93 days/Gy). However, PDR treatment (8 hourly fractions/day) at high dose-rate (8–48Gy) over 8–72 h was significantly ( P = 0.01) more effective (1.66 days/Gy) than CLDR but not acute exposures. Conclusions: These data suggest that, clinically a significantly improved therapeutic ratio may also be achievable with pulsed high dose rate brachytherapy, and that further radiobiological studies with in-vivo tumour models are needed.