Figure 2.
Relationship between S ratio and degree of normal sparing (PH) achieved by carbon ions for variation in error of relative biological effectiveness (RBE) used. PL is assumed to be 0.8. The “ERROR FACTOR” key describes the assumed error in RBE where 0.2, for example, indicates a 20% error set in the worst-case direction. (a) Only 1 high linear energy transfer (LET) fraction, (b) 4 high-LET fractions or (c) 15 high-LET fractions were used to give an iso-effective tumour dose equivalent to that given by 30 fractions of 2 Gy of low-LET X-rays.