Abstract
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.
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Table 1.
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% |
Table 2.
Dosimetrical parameters to PTV obtained by three VMAT techniques (mean±standard deviation).
Table 3.
Dosimetrical and statistical analysis for the organs at risk according to three VMAT techniques (mean±standard deviation).