The study of target delineation and target movement of whole breast assisted by active breathing control in intensity modulated radiotherapy after breast conservative surgery

Abstract

Objective To explore the influence of different delineators and different delineating time on target determination of the whole breast and to explore intrafraction and interaction target displacements of the breast on moderate deep inspiration breathing hold (mDIBH) assisted by active breathing control (ABC) after breast conservative surgery. Methods Twenty patients received primary CT-simulation assisted by ABC to get five sets of CT image on the three breathing condition which included one set from free breath ( FB), two sets from mDIBH and two sets from deep expiration breathing control (DEBH). After radiotherapy with ten to fifteen fractions, the repeat CT-simulation was carried out to get the same five sets of CT image as the primary CT-simulation. The whole breast target were delineated at different time by the same delineator and delineated respectively by five delineators on the first set of CT images got with mDIBH from the primary CT-simulation,and to compare the influence of delineator and delineating time on the whole breast target. The total silver clips in the cavity were marked respectively on the two sets of CT images got with mDIBH from the primary CT-simulation, and to compare the intrafraction displacement of geometric body structured by the total of silver clips. The two ribs near the isocentric plane of the breast target were delineated respectively on two sets of the mDIBH CT image from the primary CT-simulation and on one set of the mDIBH CT image from the repeat CT-simulation, and comparing the movement of the point of interest (POI) of the ribs delineated to get the value of intrafraction and interfraction thoracic expansion. Results There was not statistically significant between the four volumes of whole breast targets delineated by the same delineator at different time, but with statistics significant between the volumes of whole breast target delineated by the different delineators(F = 19.681, P = 0.000). There was not statistically significant between the intrafraction displacements of the POI of the geometric body at each direction, and with no statistically significant between intrafraction displacements of the POI of the ribs delineated on the same mDIBH condition. There was not statistically significant between the interfraction displacements of the POI of the ribs delineated. Conclusions The influence of different delineators on the whole breast target is statistically significant. The difference of displacement of the breast target with the same mDIBH eondition assisted by ABC at the different direction is not statistically significant. Key words: Active breathing control; Breast; Intensity-modulated radiotherapy; Target delineation; Target displacement