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 α:β 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.