RESUMO
ObjectiveTo 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).MethodsSeventeen 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.ResultsDuring 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).ConclusionsDuring 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.
RESUMO
Objective To estimate the appropriate margins for the clinical target volume (CTV) with or without online correction using cone-beam CT(CBCT) during the processs of radiation for non-small cell lung cancer(NSCLC) patients. Methods Eight patients with NSCLC treated with three-dimensional conformal ra-diotherapy(3D-CRT) were investigated, kV CBCT scans were performed before and immediately after radio-therapy. Then analysis of these images was performed using automatic and manual registration of the CBCT and planning computed tomography images. The patient positioning and organ motion were corrected by moving the couch in the left- right (X), cranio- caudal (Y), and anterior- posterior (Z) directions accordingly, and CBCTonline-guided correction data were recorded. The clinical study performed 2-3 times per week. CBCT data ac-quired before treatment delivery were used to evaluate the positioning error and organ motion, and that acquired after treatment were used to assess intrafraction tumor displacement and organ motion. These data were used in a standard formula to calculate CTV-to-PTV(planning target volume) margin of online-guided correction and non-online-guided correction. Results Total of 143 sets of CBCT images were analyzed. On the condition of non- correction, the margins required to account for total errors were 8 mm, 9 nun, 11 mm in X, Y and Z direc-tions respectively. When the tumor was corrected every fraction, margins required to account for intrafraction errors were 2 mm in each directions. Conclusion There are some extent of errors from positioning and organ motion in 3D-CRT for NSCLC. Online correction approach based on CBCT images analysis can be used to re-duce the impact obviously and to estimate the appropriate margins for the CTV.