Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy

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.

Evaluation of organ motion-based robust optimisation for VMAT planning for breast and internal mammary chain radiotherapy

“…The most common approach is to add virtual bolus (VB) in the region of the PTV outside of, or close to, the external contour during optimisation [15] with final dose calculation performed with the VB removed [14] . This approach has been shown to generate VMAT plans with skin flash adequate to achieve acceptable superficial dose coverage [14] with dosimetric advantages over VMAT plans generated without VB in terms of estimated delivered dose to the target [16] . However, plan degradation is inevitable upon removal of the VB for final dose calculation.…”

In regards to Bogue J, Wan J, Lavey RS, Parsai EI. Dosimetric comparison of VMAT with integrated skin flash to 3D field‐in‐field tangents for left breast irradiation. Journal of applied clinical medical physics. 2019 Feb;20(2):24‐9

“…These articles are related to the use of volumetric modulated arc therapy (VMAT) technique for breast and chest wall radiotherapy. We hereby raise two concerns regarding the technique by Bogue J et al, and other authors [2][3][4][5][6] which have more to do with the planning systems and their optimization processes rather than about the authors or their methodologies.…”

“…We have read the article published by Bogue J et al 1 and in conjunction the few other articles [2][3][4] published in your esteemed journal in recent times. These articles are related to the use of volumetric modulated arc therapy (VMAT) technique for breast and chest wall radiotherapy.…”

“…However not all planning systems are capable of producing clinically acceptable dose distributions with shorter arcs. [1][2][3][4][5][6][7][8] Use of large arcs will make dose statistics for planning target volume better (dose coverage, heterogeneity index, hot spot) but will completely change the low dose characteristics of the treatment plan. Changes in low dose characteristics of the treatment plan is highly undesirable since it would make the clinicians uncomfortable with difficult choices for dose limits of critical organs (lung, heart) 9 and have its own demerits and implications.…”

“…10,11 The other point is the generation of the skin flash margin using a virtual bolus for Eclipse planning system. [1][2][3][4][6][7][8]…”