Chapter 2: Role of Plan Evaluation Indices, Chronological Development and Dosimetrical Comparison

This chapter concentrated on the significance of plan evaluation, discusses the role of various plan evaluation indices and chronological development of various indices. Plan evaluation is a key component in treatment planning and radiation treatment process. Most of the time, we rely on the conventional method of plan evaluation such as slice by slice visual verification of prescription isodose line conforming to planning target volume (PTV) and dose volume histogram (DVH). Routinely, for each patient a number of treatment plans can be generated which differs from each other in terms of dose distribution. A best plan is selected and approved for treatment on the basis of merits of the plan. In earlier days this plan selection process was on the basis of subjective evaluation, which was purely dependent on evaluator skill and knowledge. But with the introduction of newer sophisticated treatment techniques (such as Intensity modulated Radiotherapy (IMRT), Image Guided Radiotherapy (IGRT), Stereotactic Surgery / Radiotherapy etc.), the plan evaluation process is become more complex and needs special care to get better clinical treatment outcome. To resolve the evaluator variability and increase the objectivity of plan evaluation process, RTOG in 1993 introduce Conformity index (CI) and Homogeneity Index (HI) to analyses DVH.