Program Information
Dose Conformity Index for the Target in a Multitarget Environment
Sudahar Harikrishnaperumal1*, (1) Apollo Speciality Hospital, Chennai, Tamilnadu
Presentations
SU-E-T-278 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:The existing conformity index formulations are failing when multiple targets present outside the target of interest with same or different dose prescriptions. In the present study a novel methodology is introduced to solve this issue.
Methods:The conformity index used by Nakamura et al (Int J Radiat Oncol Biol Phys 2001; 51(5):1313–1319) is taken as the base for this methodology. In this proposal, the prescription isodose volume (PIV) which normally includes the normal tissue and other target regions is restricted as PIV in annular regions of different thickness around the target of interest. The graphical line plotted between the thickness of annular region and the corresponding conformity index, will increase in the beginning and will reach a flat region, then it will increase again. The second increase in the conformity index depends basically on the distance between the targets, dose prescriptions, and size of the targets. The conformity index in the flat region should be the conformity index of the target of interest. This methodology was validated on dual target environment on a skull phantom in Multiplan planning system (Accuray Inc. Sunnyvale, USA)
Results:When the surrounding target’s (sphere) size is changed from 1.5cm to 6cm diameter, the conformity index of the target of interest (3cm diameter) changed from 1.09 to 1.25. When the distance between the targets changed from 7.5cm to 2.5cm, the conformity index changed from 1.10 to 1.17. Similarly, when the prescribed dose changed from 25Gy to 50Gy the conformity index changed from 1.09 to 1.42. These values were above 2.0 when Nakamura et al formula was used.
Conclusion:The proposed conformity index methodology eliminates the influence of surrounding targets to a greater extend. However, the limitations of this method should be studied further. Application of this method in clinical situations is the future scope.
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