The dosimetric consequences of inter-fractional patient movement on conventional and intensity-modulated breast radiotherapy treatments.

Abstract

A method has been developed to enable a comparison to be made between the effects of movement on conventional tangential breast treatments and intensity-modulated treatments delivered using compensators. The effects of set-up error and organ motion were studied for a set of six patients. Images were taken of these patients over the course of their treatment and conventional wedged and compensated treatment plans were designed for each. Dose-volume statistics were used to evaluate each of the treatment plans by examining the volume outside the dose range 95-105%. To assess the effects of movement alone, the volume change from day 1 was also calculated. Thirty-six estimated CT-sets were available for evaluation. Measurements of breast volume showed the volume to increase to a peak between fraction 4 and 8 and then decrease back below the initial volume. The standard treatment was found to yield 29/36 plans (81%) with greater than 5% volume outside the dose range 95-105%. For the compensated plans this dropped to 11/36 plans (31%). The analysis of the volume changes from day 1 showed that for both standard and compensated treatments 7/30 plans (23%) had an increase in volume outside the dose range 95-105% of greater than 5% of the total planning target volume. The compensated treatment is more susceptible to patient movement. However, the actual volume of tissue outside 95-105% dose is less when compared to standard treatment implying the compensated treatment is still superior.