Abstract
Dear editor,
We read with keen interest the recently published article by Patro et al. and appreciate the efforts taken by authors to describe the plan evaluation process in Stereotactic Radiosurgery (SRS) & Stereotactic Body Radiotherapy (SBRT) using Acronym “COSID Index.” 1 To evaluate plan quality, the authors indeed suggested a comprehensive approach. We take this opportunity to highlight our viewpoint of Radiation Therapy Oncology Group (RTOG) and Paddick Conformity index.
The author has described an ideal value of the Paddick Conformity index as 1, and
Paddick conformity index can predict that the quality of a plan decreases with a decrease in the index value. Still, it has limitation in describing that the whether the lack of conformity is due to over or under-treatment. Although CIPaddick has an ideal value of 1 for a perfectly conformal plan, CIPaddick value independently cannot predict undertreatment or overtreatment, as explained in Table 1 below. Two ratios, i.e., under treatment ratio and over treatment ratio can be used to determine under or overtreatment, respectively. 3 Whereas CIRTOG can give a false perfect score, as seen in example 3 (Table 1), CIPaddick can never give a false perfect score in a non-conformal plan.
CIRTOG, UTR, OTR and CIPaddick Index Values for Various Treatment Plans.
CI-Conformity Index, UTR-Under Treatment Ratio, OTR-Over Treatment Ratio, VRI-Prescription Isodose Volume (Blue Color), TV-Target Volume (Red Color), TVPIV-Target volume covered by Prescription Isodose (Purple Color), FPS-False perfect score, TPS-True Perfect Scores