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Non-Coplanar VMAT Improves Plan Quality for Locoregional Radiotherapy of Left-Sided Breast Cancer with Internal Mammary Nodes

Y Xu*, Y Xu, Z Hu, Y Tian, P Ma, K Men, S Wang, J Dai, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences, Beijing, BeijingCN,

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: planning study was performed to evaluate the feasibility of non-coplanar volume modulated arc therapy (ncVMAT) for locoregional radiotherapy of left-sided breast cancer with internal mammary nodes.

Methods: patients with left-sided breast cancer after breast conserving surgery were retrospectively studied. The planning target volumes (PTV) were contoured encompassing the whole breast, internal mammary nodes (IMN) and supraclavicular nodal (SCN) region. For each patient, ncVMAT plan with 4 partial arcs composing of two coplanar arcs and two non-coplanar arcs with couch rotating to 90° was generated. The prescription dose was 50 Gy delivering in 25 fractions. For each ncVMAT plan, dosimetric parameters were compared with coplanar VMAT (coVMAT) plans optimizing with identical coplanar beam angle arrangement.

Results: ncVMAT, the mean conformity index of the whole PTV increased from 0.82±0.02 to 0.86±0.01 (p=0.005), and the homogeneity index decreased slightly (p=0.009). The mean coverage of internal mammary target volume (PTVimn) with ncVMAT increased from 88.77±3.07% to 96.53±1.38% comparing with coVMAT (p=0.005). Meanwhile, the V55 in PTVbreast, PTVscn and PTVimn decreased significantly from 13.28±8.95%, 5.76±6.03%, 13.73±7.77% to 9.28±7.82%, 4.27±7.05%, 3.26±4.05%, separately (p<0.05). For organs at risk, the average V20, V10, V5 and Dmean of heart decreased from 12.18±7.29%, 33.98±15.73%, 72.03±16.79% and 10.47±2.97 Gy to 8.76±5.33%, 22.19±10.88%, 58.23±13.77% and 8.60±2.37 Gy, separately (p<0.01). Furthermore, ncVMAT significantly reduced the mean V20, V10, V5, Dmean of left lung, and V10, V5, Dmean of contralateral lung (p<0.01). A better sparing of LAD descending coronary artery and right breast were also shown with ncVMAT (p<0.01).

Conclusion: to coVMAT, ncVMAT provides better conformity, improved homogeneity and lower V55 in PTV, better coverage of PTVimn, better dose sparing in heart, bilateral lung, LAD and right breast for locoregional radiotherapy of left-sided breast cancer, which potentially increase the local control in IMN and reduce the risk of deleterious effects.

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Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China, Grant/Award Number: 11875320; National Key Projects of Research and Development of China, Grant/Award Number: 2017YFC0107501

Keywords

Breast, Radiation Therapy, Treatment Planning

Taxonomy

TH- External Beam- Photons: treatment planning/virtual clinical studies

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