High dose rate radiation treatment of experimental intramuscular prostate carcinoma.

PURPOSE The Dunning R3327-MLL is a well established transplanted tumour line, and as such it makes a desirable model for evaluative studies of therapy. In the current study, the interstitial growth characteristics as well as the response of this tumour to a single fraction of high dose rate radiation is investigated. MATERIALS AND METHODS The in vitro response to radiation of the Dunning R3327-MLL was studied via a colony forming assay using a Cs-137 irradiator. In vitro radiosensitivity was determined on tumours implanted intramuscularly in the left gastrocnemius muscle of the rat and irradiated using an Ir-192 afterloader. RESULTS The results demonstrate a faster growth rate when compared to the reported subcutaneous growth rates. The Dunning R3327-MLL's radiosensitivity is comparable to that of late response tissues. The dose required to achieve a specific radiobiological response (the alpha:beta ratio) of the in vitro cell line is 2.4 Gy, whereas the ratio for the intramuscularly growing tumour was 0.99 Gy. CONCLUSIONS These findings signify the intramuscularly implanted Dunning R3327-MLL tumour model as a desirable model for the study of single fraction high dose rate radiation treatments.