Two parallel phase-1 studies will assess the safety of preoperative SCRT ( 5 fractions each of 5Gy , on days 1 to 5 ) combined with ( a ) capecitabine alone ( increasing dose levels : 500-825mg / m2/bid ) , on days 1-21 , or ( b ) capecitabine as above plus VPA ( oral daily day -14 to 21 , with an intra-patient titration for a target serum level of 50-100 microg/ml ) followed by surgery 8weeks after the end of SCRT , in low-moderate risk RC patients .