Sparing Lung Tissue with Virtual Block Method in VMAT Planning for Locally Advanced Non-Small Cell Lung Cancer
J Chen*, J Dai, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, CHINA,
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PO-GePV-T-204 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: Despite that VMAT technique has been widely used in the radiotherapy of non-small cell lung cancer, it may increase the low irradiation dose volume to lungs. This study aims to develop a new virtual block method for sparing the normal lung tissue in VMAT planning.
Methods: A retrospectively VMAT planning study was performed and compared without and with virtual block method for 17 patients, named as non-block plan and block plan respectively. The identical initial optimization parameter for the non-block plans were designed by the mdaccAutoPlan system. The block plan adopted all optimization parameters in non-block plan for each patient, in addition of the maximum dose constraint for the virtual block. The two types of plans were compared with dosimetric indexes of targets and normal structures, and the results were statistically analyzed with Wilcoxon signed rank test.
Results: Both block and non-block plans achieved sufficient dose coverage in target volume and similar conformity of target volume. For the structures, block plans have advantages in the following dosimetric metrics: 1) for total lungs, lower V5, V10 and mean dose, NTCP were observed (p < 0.01, respectively); 2) for the contralateral lung, significant reductions in V5 and V10 (P< 0.001, respectively); 3) decrease in the mean dose and V40 of heart; 4) decrease in esophagus V40; 4) significant reductions in mean dose, V5 and V10 of normal tissue. The quality scores of block plans were significantly higher than that of non-block plans (Mean: 82.51±7.07 vs. 80.74±7.22, P＜0.001).
Conclusion: The VMAT plans with the virtual block can significantly reduce the low irradiation dose volume of the lungs and the doses to other normal structures whereas keep similar conformity and homogeneity of targets. The block method might reduce the risk of radiation-related toxicity for patients.
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