%0 Journal Article
%T Novel approach for the evaluation of dose conformity in radiotherapy.
%A Kuperman VY
%A Altundal Y
%J Med Phys
%V 50
%N 2
%D Feb 2023
%M 36272439
%F 4.506
%R 10.1002/mp.15998
%X <B>OBJECTIVE: </B>We describe a new approach to evaluate conformity of dose distributions in radiotherapy.<BR><B>METHODS: </B>The suggested conformity factor λ is defined by using existing conformity indices and expansion of the planning target volume (PTV). If the average distance (  d ¯ $\bar d$  ) between the PTV and reference isodose surface and an arbitrarily selected PTV expansion margin (  d e x p  ${d_{exp}}$  ) are both much smaller than the size of the PTV, then λ approximately equals the ratio   d ¯ d e x p   $\frac{{\bar d}}{{{d_{exp}}}}$  . We use λ to analyze several cases of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT).<BR><B>RESULTS: </B>In the case of SRS with a single target or multiple targets, treatment plans produced with the help of volumetric modulated arc therapy (VMAT) have smaller λ than plans produced by using dynamic conformal arcs (DCA). Likewise, it is demonstrated that in the case of SBRT, λ is reduced by employing VMAT instead of DCA. It is also shown that if the distance between the reference isodose surface and surface of the PTV is fixed, λ varies less with variations in PTV volume compared to frequently used conformity indices.<BR><B>CONCLUSIONS: </B>The described conformity factor λ can be applied clinically to compare and rank treatment plans for lesions of different sizes. It is suggested that conditions  λ < 1 $\lambda &lt; 1$  and λ > 1 can be employed as "pass" and "fail" criteria, respectively, for dose conformity assessment with appropriate choice of  d e x p  ${d_{exp}}$  .