A new set of conformity indices for evaluating intensity-modulated radiotherapy or three-dimensional conformal radiotherapy plans / 中华放射肿瘤学杂志

ABSTRACT

Objective To propose a new set of conformity indices ( CIs ) that may be useful for evaluating whether the prescribed doses to target volume and organs at risk ( OAR) in intensity-modulated radiotherapy ( IMRT ) or three-dimensional conformal radiotherapy ( 3DCRT ) plans meet clinical requirements. Methods A total of 30 patients' plans were randomly selected from the IMRT or 3DCRT plans for non-small cell lung cancer and analyzed with the newly defined CIs described in this article. The plans to be improved were selected according to the evaluating results, and two schemes were developed to improve these plans. Then, the differences in CI, Dmax , Dmin , and Dmean of the planning target volume ( PTV) , V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were investigated with the paired t-test. Results Among the 30 plans, the average volume covered by the prescribed isodose line ( VRI ) was 25% larger than the PTV, so the normal lung tissue with a volume approximately 25% of PTV was given the same dose as the target volume, and the volume covered by the prescribed isodose line in the target V ( C) R was only 75% of the volume VR. Ninety-five percent of the target volume received a full prescribed dose;only 5% of the target volume received less than the prescribed dose, but which was still within 90% of the prescribed dose. In the comparison between the original plans and the plans improved using the first scheme, CI2 , CI4 , CI5 , CI6 , and homogeneity index ( HI) were not significantly different ( P=0240-0780) , and CI1 and CI3 showed significant differences ( P=0002 and 0);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, V30 and V40 of the heart, and Dmax of the spinal cord were not significantly different ( P=0211-0964) . In the comparison between the original plans and the plans improved using the second scheme, CI2 , CI4 , and CI5 were not significantly different ( P=0308, 0308, and 0106 ) , CI1 , CI3 , CI6 , and HI showed significant differences ( P= 0001-0014);Dmax , Dmin , and Dmean of the PTV, V5 and V20 of the normal lung, and Dmax of the spinal cord showed significant differences ( P=0008-0036 ) , and V30 and V40 of the heart were not significantly different ( P=0083 and 0080) . Conclusions The new set of CIs proposed in this paper may be a good tool for evaluating the conformity of the target and the prescribed dose to OAR and thus developing better individualized treatment plans.