The Influence of Active Breathing Control on the Dose Distribution in the Target of Forward Whole-breast Intensity Modulated Radiotherapy after Breast-conservative Surgery

Abstract

To explore the influence of intrafraction and interfraction target displacement on the dose distribution in the target of forward whole-breast intensity-modulated radiotherapy (IMRT) assisted by active breathing control. Each of the selected patient who received breast-conservative surgery was immobilized and received the primary CT simulation assisted by active breathing control (ABC) device to get five sets of CT images in the three breathing status which included free breath (FB) (one set), moderate deep inspiration breathing hold (mDIBH) (two sets) and deep expiration breathing hold (DEBH) (2 sets), repeat CT simulation was completed and the same five sets of CT images respectively get at FB, mDIBH, and DEBH. In the Pinnacle3 treatment planning system, the forward IMRT planning was completed on the first set of mDIBH CT images from the primary CT simulation and the planning was copied by the special system order to the second set of CT images from the primary CT simulation and first set of CT images from the repeat CT simulation with the primary of angle, direction, size and shape of the MLC field and prescribed dose, the volume covered by selected high dose area in the selected segment were compared. In the planning based on the first set of mDIBH CT images from the primary CT simulation, the volume irradiated by equal and more than 103% of prescribed dose in the segment was 1.155 ± 0.392 cm3, and the volume were 3.877 ± 1.066 cm3 and 51.659 ± 8.676 cm3 in the plannings copied from the first set of mDIBH CT images from the primary CT simulation respectively to the second set of CT images from the primary CT simulation and first set of CT images from the repeat CT simulation, the difference of the volume in the two plannings based the two set mDIBH CT image from the primary CT simulation was not statistically significant (t = -1.672,p = 0.103)and the difference of the volume respectively in the first sets of mDIBH CT images respectively from the primary and repeat CT simulations (t = -5.728, p < 0.01). If the same threshold of mDIBH is remained during IMRT after breast-conservative surgery, the influence of the intrafraction target displacement on the dose distribution is not significant; if set-up error is not corrected, the interfraction change of position of the segment given to cove the high dose area in the IMRT planning will be significant to result in significant change of dose distribution in the breast.