Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy

Abstract

AimTraditional radiotherapy treatment techniques of the breast are insensitive for deformations and swelling of the soft tissue. The purpose of this study was to evaluate the dose changes seen with tissue deformations using different image matching methods when VMAT technique was used, and compare these with tangential technique.MethodsThe study included 24 patients with breast or chest wall irradiations, nine of whom were bilateral. In addition to planar kV setup imaging, patients underwent weekly cone‐beam computed tomography (CBCT) imaging to evaluate soft tissue deformations. The effect of the deformations was evaluated on VMAT plans optimized with 5‐mm virtual bolus to create skin flash, and compared to standard tangential plans with 2.5 cm skin flash. Isocenter positioning using 2D imaging and CBCT were compared.ResultsWith postural changes and soft tissue deformations, the target coverage decreased more in the VMAT plans than in the tangential plans. The planned V90% coverage was 98.3% and 99.0% in the tangential and VMAT plans, respectively. When tattoo‐based setup and online 2D match were used, the coverage decreased to 97.9% in tangential and 96.5% in VMAT plans (P < 0.001). With automatic CBCT‐based image match the respective coverages were 98.3% and 98.8%. In the cases of large soft tissue deformations, the replanning was needed for the VMAT plan, whereas the tangential plan still covered the whole target volume.ConclusionsThe skin flash created using an optimization bolus for VMAT plans was in most cases enough to take into account the soft tissue deformations seen in breast VMAT treatments. However, in some cases larger skin flash or replanning were needed. The use of 2D match decreased the target coverage for VMAT plans but not for FinF plans when compared to 3D match. The use of CBCT match is recommended when treating breast/chest wall patients with VMAT technique.

Evaluation of setup and intrafraction motion for surface guided whole‐breast cancer radiotherapy

“…2 Furthermore, for setup of partial breast treatments it may be crucial to have a high reproducibility of the breast position and deformation. The importance of reproducing the breast deformation is relevant for complex IMRT plans.…”

“…Second SGRT also enables correction of any deformations of the breast tissue resulting in a more accurate dose deposition. 2 Third, SGRT allows avoiding dose from imaging, particular important for this patient group with a relatively young age profile and good prognosis. Lastly, the possibility to avoid tattoos on the patient for setup also count as an advantage.…”

“…The importance of reproducing the breast deformation is relevant for complex IMRT plans. 2 Furthermore, for setup of partial breast treatments it may be crucial to have a high reproducibility of the breast position and deformation.…”

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.…”