Quantitative evaluation of abscopal effect based on biological effective dose in breast cancer tumors in mice

Background: due to abscopal effect, cell damage may occur outside of theradiation field and the quantification of this effect is one of the mostchallenging debates in radiation therapy. the aim of this study was toesmate the abscopal effect induced in non-irradiated tumors quantitativelyby means of biological effective dose (bed). materials and methods: breasttumors using 4t1 and mc4-l2 cells, were induced into the flank region of balb/cmice. when palpable, the tumor on one side of the body was irradiated with doseof 28gy in 14 fractions and 2 gy per fraction, 5 fracons per week. the tumor onthe other side of the body was shielded with a lead plate. bed was estimated basedon tumor volume. h&e staining and tunel assay were performed to assesshistological changes and apoptosis in irradiated and non-irradiated tumors. results:the effect of radiation on non-irradiated tumors was more than that onirradiated ones. the bed was 4.49 and 6.74 in 4t1 and mc4-l2 tumors,respectively. the ratio of the tumor volume in the last fracrtion to that in thefirst fraction for irradiated 4t1 tumors was 2.32 and in non-irradiated was1.50. this ratio in irradiated and non- irradiated mc4-l2 tumors was 2.64 and1.98, respectively. the number of apoptotic cells was higher in non-irradiatedtissues. conclusion: results indicate that the occurrence of abscopal effect ishighly depends on the type of tumor. by means of the abscopal effect, moreradiation dose can be delivered to the tumor and metastatic sites.