The radiation physics advantages of 4DCT on intensity-modulated radiotherapy of chest wall after radical mastectomy

Objective: To investigate the influence of breathing motion on intensity-modulated radiotherapy (IMRT) of chest wall after radical mastectomy,and explore clinical value of accurately determined target volume. Methods: A total of 17 radical mastectomy patients underwent 3DCT simulation scans sequentially followed by 4DCT simulation scans during free breathing. The targets and normal organs was determined based on CT images respectively. Three sets of radiotherapy plan were designed for each patient: plan 3D, plan 4D and plan 3D-A. The Plan 3D and plan 4D was designed based on 3D and 4D targets respectively. Plan 3D was copied to 4D target with the same isocenter coordinates. The dose distribution was calculated separately to evaluate the dose-volume histograms parameters for PTV, ipsilateral lung and heart, respectively. Two planning parameters was compared with paired t-test or Wilcoxon sign-rank test. Results: The average volume of PTV_4D was (10.35 ± 4.80)% larger than PTV_3D (P=0.000). Compared with plan 3D, the V₁₀₀, V₉₅, V₉₀, D₉₅, D₉₀, D_min of plan 3D-A were reduced, that were (0.78-18.0)% (P=0.000), (0.01-3.90)% (P=0.000), (0-2.12)% (P=0.000), (13-222) cGy (P=0.000), (1-118) cGy (P=0.000), (6-1 910) cGy (P=0.000). However, the V₂₀, V₁₀, V₅, D_mean of the ipsilateral lung and V₃₀ of heart were same between 3D plan and 4D plan (P=0.288, 0.407, 0.435, 0.758, 0.575). Conclusions: The respiratory motion may reduce the target dose and its coverage in chest wall treatments, so 4DCT plan could accurately define target volume without increasing the exposure dose of normal tissues. (authors)