pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2019.30.1.7 pmp-30-7 Original Article Comparison of Dosimetrical and Radiobiological Parameters on Three VMAT Techniques for Left-Sided Breast Cancer KangSeong-Hee 1 ChungJin-Beom 1 KimKyung-Hyeon 2 KangSang-Won 2 EomKeun-Yong 1 SongChanghoon 1 KimIn-Ah 1 KimJae-Sung 1 Department of Radiation Oncology, Seoul National University Bungdang Hospital, Seongnam Department of Biomedicine and Health Sciences, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Korea Corresponding author Jin-Beom Chung (jbchung1213@gmail.com) Tel: 82-31-787-7654 Fax: 82-31-787-4019 032019 19032019 3017 13 12122018 27122018 17012019 Copyright © 2019 Korean Society of Medical Physics 2019 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Purpose:

To compare the dosimetrical and radiobiological parameters among various volumetric modulated arc therapy (VMAT) techniques using restricted and continuous arc beams for left-sided breast cancer.

 Materials and Methods:

Ten patients with left-sided breast cancer without regional nodes were retrospectively selected and prescribed the dose of 42.6 Gy in 16 fractions on the planning target volume (PTV). For each patient, three plans were generated using the EclipseTM system (Varian Medical System, Palo Alto, CA) with one partial arc 1pVMAT, two partial arcs 2pVMAT, and two tangential arcs 2tVMAT. All plans were calculated through anisotropic analytic algorithm and photon optimizer with 6 MV photon beam of VitalBEAMTM. The same dose objectives for each plan were used to achieve a fair comparison during optimization.

 Results:

For PTV, dosimetrical parameters such as Homogeneity index, conformity index, and conformal number were superior in 2pVMAT than those in both techniques. V95%, which indicates PTV coverage, was 91.86%, 96.60%, and 96.65% for 1pVMAT, 2pVMAT, and 2tVMAT, respectively. In most organs at risk (OARs), 2pVMAT significantly reduced the delivered doses compared with the other techniques, excluding the doses to contralateral lung. For the analysis of radiobiological parameters, a significant difference in normal tissue complication probability was observed in ipsilateral lung while no difference was observed in the other OARs.

 Conclusions:

Our study showed that 2pVMAT had better plan quality and normal tissue sparing than 1pVMAT and 2tVMAT but not for all parameters. Therefore, 2pVMAT could be considered the priority choice for the treatment planning for left breast cancer.

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Example of dose distribution in transverse plane for (a) 1pVMAT, (b) 2pVMAT, and (c) 2tVMAT.

The optimization objectives used for inverse IMRT VMAT planning.

Structure Objectives
PTV V44.6Gy<1%, V42.5Gy>95%, V40.4Gy>100%
Heart V10Gy<20% and V20Gy<10%, Dmean<5 Gy
Left lung V10Gy<40%, V20Gy<30% and V30Gy<20%
Contralateral lung V10Gy<10%

Dosimetrical parameters to PTV obtained by three VMAT techniques (mean±standard deviation).

Metric 1pVMAT 2pVMAT 2tVMAT P-value
1pVMAT vs. 2pVMAT 2pVMAT vs. 2tVMAT
Dmax (%) 118.38±1.72 114.93±1.83 115.10±2.25 0.009 0.553
Dmean (%) 102.51±1.86 103.06±1.65 102.84±1.70 0.008 0.007
V95% (%) 91.86±3.58 97.60±1.25 96.65±1.86 0.005 0.009
HI 0.21±0.04 0.12±0.02 0.14±0.03 0.005 0.007
CI 1.12±0.13 1.08±0.11 1.12±0.11 0.017 0.004
CN 0.76±0.05 0.88±0.06 0.83±0.05 0.005 0.005

Dosimetrical and statistical analysis for the organs at risk according to three VMAT techniques (mean±standard deviation).

Organ Metric 1pVMAT 2pVMAT 2tVMAT P-value
1pVMAT vs. 2pVMAT 2pVMAT vs. 2tVMAT
Ipsilateral lung Dmax (%) 115.58±3.81 105.88±1.96 109.57±4.08 0.005 0.007
Dmean (%) 32.60±3.21 28.67±1.71 30.27±2.84 0.005 0.011
V20Gy (%) 26.11±3.34 21.43±1.11 22.76±2.33 0.005 0.022
V10Gy (%) 43.13±6.59 37.49±3.76 39.75±4.95 0.005 0.017
NTCP 0.04±0.03 0.01±0.01 0.02±0.01 0.011 0.038
Contralateral lung Dmax (%) 53.02±8.56 62.51±11.39 47.49±10.66 0.114 0.028
Dmean (%) 6.81±1.65 10.29±6.94 6.94±1.13 0.005 0.007
V20Gy (%) 0.04±0.02 0.41±0.48 0.12±0.06 0.080 0.655
V10Gy (%) 1.70±1.29 4.91±3.23 1.38±1.23 0.009 0.022
V5Gy (%) 16.30±8.17 30.48±11.89 13.61±5.48 0.005 0.013
NTCP <0.001 <0.001 <0.001 - -
Heart Dmax (%) 112.23±9.35 89.24±7.43 97.64±9.03 0.005 0.007
Dmean (%) 17.79±4.03 14.66±1.82 15.98±3.83 0.012 0.185
V20Gy (%) 7.95±6.05 3.07±1.12 6.05±2.93 0.005 0.007
V10Gy (%) 19.77±7.02 15.21±4.05 16.60±8.51 0.012 0.445
NTCP <0.001 <0.001 <0.001 - -