Po‐Poster ‐ 31: An improved derivation of the Joiner expressions for determining a simple independent method to derive fully isoeffective schedules following a change in dose per fraction

In the paper written by Joiner (IJROBP 2004; 58(3): 871–875), entitled A simple α/β‐independent method to derive fully isoeffective effective schedules following a change in dose per fraction, the author derived two mathematical expressions by which dosimetric errors in delivering the prescribed dose per fraction in a treatment can be corrected for. In doing so, the author made an invalid assumption in which he assumed α/β is zero for both early and late effects. Even though this assumption is wrong, the author arrived “mistakenly” at the right solution. In this presentation, we use first principles to derive these two expressions and the limits at which they cannot be applied, both from radiobiological and mathematical point of views. We also explain the inherent α/β‐independence of the expressions. Acknowledgment: The authors would like to acknowledge the financial support of CancerCare Manitoba Foundation.