Corrected relationship between % dd ( 10 ) x and stopping‐power ratios

Kosunen and Rogers [Med. Phys. 20 , 1181–1188 (1993)] presented a linear equation relating the Spencer–Attix water/air stopping power ratio to% dd ( 10 ) x , the photon component of the percentage depth‐dose at 10 cm depth for a 10 × 10   cm 2field on the surface of a phantom at SSD = 100   cm . This relationship has been used to calculate extensive tables of k Qfactors for use with dosimetry protocols based on absorbed‐dose calibration factors. Unfortunately, the original paper contained an error which has recently been assessed (Yang et al.). The present paper presents a corrected form of this relationship, viz.:( L ̄ / ρ ) air water= 1.275 − 0.00231 [ % dd ( 10 ) x ] which is based on corrected values of% dd ( 10 ) x . It is shown that despite changes of up to 2% in calculated values of% dd ( 10 ) x , the net effect on calculated values of k Qis less than 0.2%.