Po-Thur Eve General-09: Dynamic evaluation for the treatment outcome incorporating prostate organ motion

Abstract

This paper is to calculate the cumulative dose considering internal organ motion and patient repositioning of prostate patient using the one fractional treatment plan method for a specific phantom and patients. In the multi‐fractional radiation treatment, it is desirable to consider the internal organ motion from fraction to fraction. The PTV positional variations can be measured and expressed as the fractional equivalent uniform dose (FEUD) deviation by randomly picking up the FEUD using Monte Carlo method in every fraction. The average EUD deviations for PTV with hundreds of simulations are 3.3% for phantom and 1.8% for 5 prostate patients. The changes of rectal volume and position are also simulated by shifting the geometric center of the rectum and changing the rectal radius to model the rectal deformation using Pinnacle3 planning system and FEUD for rectum are estimated. The prostate margin, together with the inter‐fraction variations in rectal position and shape, affects the delivered dose to the rectum. The effect of the dose fluctuations is larger for the normal tissues than the target, and the change of rectal position would cause more complication compared to the rectal volume change. The method provides a simple way to estimate the tumor control probability and normal tissue complication probability dynamically with considering internal organ motion and repositioning errors throughout the whole treatment course. It is possible to test a treatment plan against a range of possible patterns of organ motion with this dynamic evaluation for the treatment outcome.