Assessing the quality of conformal treatment planning: a new tool for quantitative comparison

Abstract

We develop a novel radiotherapy plan comparison index, critical organ scoring index (COSI), which is a measure of both target coverage and critical organ overdose. COSI is defined as COSI=1-(V(OAR)>tol/TC), where V(OAR)>tol is the fraction of volume of organ at risk receiving more than tolerance dose, and TC is the target coverage, VT,PI/VT, where VT,PI is the target volume receiving at a least prescription dose and VT is the total target volume. COSI approaches unity when the critical structure is completely spared and the target coverage is unity. We propose a two-dimensional, graphical representation of COSI versus conformity index (CI), where CI is a measure of a normal tissue overdose. We show that this 2D representation is a reliable, visual quantitative tool for evaluating competing plans. We generate COSI-CI plots for three sites: head and neck, cavernous sinus, and pancreas, and evaluate competing non-coplanar 3D and IMRT treatment plans. For all three sites this novel 2D representation assisted the physician in choosing the optimal plan, both in terms of target coverage and in terms of critical organ sparing. We verified each choice by analysing individual DVHs and isodose lines. Comparing our results to the widely used conformation number, we found that in all cases where there were discrepancies in the choice of the best treatment plan, the COSI-CI choice was considered the correct one, in several cases indicating that a non-coplanar 3D plan was superior to the IMRT plans. The choice of plan was quick, simple and accurate using the new graphical representation.

Dosimetric Evaluation of Advanced Radiotherapy Techniques in Treating Patients with Prostatic Cancer

“…The COSI tool was found to be objective, quick and accurate tool in choosing the best plan. Similar to our results, Menhel et al found that a non-coplanar 3D plan was superior to the IMRT plan 25 . Levin et al in their retrospective study on ten patients with maxillary sinus tumors compared treatment plans of 9-field IMRT, directionally optimized IMRT, and 3D noncoplanar planning in terms of critical organ sparing and TC 27 .…”

“…In addition to that, two more indexes were calculated to account for the irradiation of all OARs regarding their tolerance. One of these indexes is the Critical Organ Scoring Index (COSI) which takes into account both the target coverage and the critical organ irradiation 25,26 . The main advantage of this index is its ability to account of the irradiation of all OARs simultaneously in one index.…”

“…Typically; the coverage index should be at least 95%. TC is expressed as: TC = VT,PI / VT 25 . COSI may also be expressed as:…”

“…The COSI was described by Menhel et al in 2006 as a new index to compare between radiotherapy plans 25 . They tested the new index on the planning of the following sites: head and neck, cavernous sinus and pancreas.…”

New conformity indices based on the calculation of distances between the target volume and the volume of reference isodose

“…This index could not provide dissociable information either, and there were no considerations for the tolerance levels of individual OARs. To overcome this drawback, Menhel et al 21 proposed the critical organ scoring index to compare individual involvement of the OARs specifically at various dose levels. Wagner et al 22 proposed the conformity/gradient index (CGI), which is an average of the conformity score (CGI c ) and gradient score (CGI g ).…”