Abstract
PurposeThis study evaluates the benefit of a virtual bolus method for volumetric modulated arc therapy (VMAT) plan optimization to compensate breast modifications that may occur during breast treatment.MethodsTen files were replanned with VMAT giving 50 Gy to the breast and 47 Gy to the nodes within 25 fractions. The planning process used a virtual bolus for the first optimization, then the monitors units were reoptimized without bolus, after fixing the segments shapes. Structures and treatment planning were exported on a second scanner (CT) performed during treatment as a consequence to modifications in patient's anatomy. The comparative end‐point was clinical target volume's coverage. The first analysis compared the VMAT plans made using the virtual bolus method (VB‐VMAT) to the plans without using it (NoVB‐VMAT) on the first simulation CT. Then, the same analysis was performed on the second CT. Finally, the level of degradation of target volume coverage between the two CT using VB‐VMAT was compared to results using a standard technique of forward‐planned multisegment technique (Tan‐IMRT).ResultsUsing a virtual bolus for VMAT does not degrade dosimetric results on the first CT. No significant result in favor of the NoVB‐VMAT plans was noted. The VB‐VMAT method led to significant better dose distribution on a second CT with modified anatomies compared to NoVB‐VMAT. The clinical target volume's coverage by 95% (V95%) of the prescribed dose was 98.9% [96.1–99.6] on the second CT for VB‐VMAT compared to 92.6% [85.2–97.7] for NoVB‐VMAT (P = 0.0002). The degradation of the target volume coverage for VB‐VMAT is not worse than for Tan‐IMRT: the median differential of V95% between the two CT was 0.9% for VMAT and 0.7% for Tan‐IMRT (P = 1).ConclusionThis study confirms the safety and benefit of using a virtual bolus during the VMAT planning process to compensate potential breast shape modifications.
Highlights
Adjuvant radiotherapy (RT) for breast cancer is a standard treatment used to improve local tumor control and overall survival.[1–4] Volumetric modulated arc therapy (VMAT) has been evaluated for breast treatment in several publications as attested in a recent review.[5]
A significant better coverage for clinical target volumes (CTV)‐Tevaluation was found for the VB‐VMAT plans compared to the NoVB‐VMAT plans: V95%‐ CTV‐Tevaluation was 99.4% [98.5–99.8] for VB‐VMAT compared to 98.4% [96.9–99.6] for NoVB‐VMAT (P = 0.037)
The Dmean to the contralateral lung was found lower for the VB‐VMAT plans (2.5 Gy [2.1–3]) compared to NoVB‐VMAT (2.7 Gy [2.3–3.1]) (P = 0.024)
Summary
Adjuvant radiotherapy (RT) for breast cancer is a standard treatment used to improve local tumor control and overall survival.[1–4] Volumetric modulated arc therapy (VMAT) has been evaluated for breast treatment in several publications as attested in a recent review.[5]. Volumetric modulated arc therapy (VMAT) has been evaluated for breast treatment in several publications as attested in a recent review.[5]. The location of the mammary gland leads to clinical target volumes (CTV) adjoined to the skin. This particularity of breast's target volume would generate a planning target volume (PTV) located partially outside the external body contour if isotropic margins were applied. It may lead to target volume's lack of coverage in case of inter‐ and/or intrafraction movements. This issue can be taken into account using a skin flash method for fixed fields. For arc therapy techniques, other solutions should be found
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