The dosimetric study of the targets and organs at risk in whole breast forward intensity-modulated radiotherapy during free breathing based on 4DCT

Abstract

Objective To explore the correlation between the respiration-induced clinical target volume (CTV) motion and volume variation and the dosimetric variation of planning target volume (PTV) and organs at risk (OAR) during free-breathing (FB) with whole breast intensity-modulated radiotherapy (IMRT).Methods Seventeen patients with breast conserving surgery underwent respiration-synchronized four-dimentional computed tomography (4DCT) simulation scans on the state of FB.The treatment plan was constructed using the end-inspiration phase scan,then copied and applied to the other respiratory phases.The dose distribution was calculated separately to evaluate the dose-volume histograms parameters for the PTV,ipsilateral lung and heart.Results During FB,the CTV motion vector was (2.09 ±0.74) mm,and the volume variation was (3.05 ± 0.94) ％.There was no correlation between the volume variation of CTV and dosimetric variation of PTV/OAR ( r =-0.390 -0.480,P =0.182 -0.775 ).In anteroposterior (AP),superoinferior (SI) and vector directions,the CTV movement correlated well with the PTV mean dose,conformal index,and the lung volume receiving high dose (V20,V30,V40,and V50;r=-0.975-0.791,P =0.000 -0.041 ).In SI and vector directions,the CTV displacement only correlated with the heart volume receiving ＞ 5 Gy ( V5 ) ( r =-0.795,0.687,P =0.006,0.028 ).The lung volume variation and the lung volume receiving high dose correlated reasonably well (r=0.655 -0.882,P=0.001-0.04 0).The heart volume variation only correlated with the V5 of heart (r =-0.701,P =0.024).Conclusions During free-breathing,the effect of breast volume variation can be ignored for whole breast IMRT,and whole breast IMRT assisted with breath-hold may improve the accuracy of dose delivery during radiotherapy. Key words: Radiotherapy,whole breast; Radiotherapy,intensity-modulated; Dosimetry