Claire Dempsey
Department of Radiation Oncology, University of Washington, Seattle WA, USA
Assistant Professor

Landon Wootton
Medical physics resident
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Hannah Richardson
Dosimetrist
Department of Radiation Oncology, Seattle Cancer Care Alliance, Seattle WA USA

Myra Lavilla
Dosimetrist
Department of Radiation Oncology, Seattle Cancer Care Alliance, Seattle WA USA

Lori Young
Assistant Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Juergen Meyer
Associate Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Ning Cao
Assistant Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Alan Kalet
Assistant Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Li-Ming Fang
Assistant Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Janice Kim
Associate Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Claire Dempsey
Assistant Professor
Department of Radiation Oncology, University of Washington, Seattle WA, USA

Background and Purpose: The Contura applicator is a multi-lumen balloon used to deliver accelerated partial breast irradiation in patients with early-stage breast cancer. It contains 5 treatment channels inside a balloon that is filled with contrast solution to compensate for tissue removed during a lumpectomy procedure. This study focused on creating optimal inverse planning parameters and assessing the dosimetric impact of rotational or treatment length changes for the resulting non-uniform dwell loadings.

Methods: Using Varian’s BrachyVision planning system, ten patients previously treated with Contura were identified. Three test plans using varying plan optimization parameters based on surface constraints were generated for each patient. Each plan underwent one round of optimization with no further modifications. Plan quality was assessed using homogeneity, conformality, planning target volume (PTV) coverage, hots spot size and maximum dose to both ribs and skin. The optimized plan was also compared to the clinical plan, which was optimized using volume constraints.

Once optimal parameters were chosen, simulated applicator rotations up to 45 degrees and treatment length variations up to 2mm were introduced into both the clinically treated plan and the newly optimised plan. Each altered plan was then assessed for plan quality to determine dosimetric effects.

Results: All 3 optimization parameter variations resulted in improvements to the PTV coverage, skin dose and hot spot size whilst maintaining dose homogeneity and conformity. Rotation of the treatment applicator inside the patient caused less than 0.5% change in PTV coverage over a 15 degree rotation with minimal difference between the clinical and more modulated optimised plan. At angles greater than 15 degrees the optimised plan produced greater changes in PTV coverage, skin and rib dose. Introducing 2mm systematic shifts in treatment length (across all channels) caused marked deviations in the dose distribution, significantly in the optimised plan. However 2mm shifts in individual channels and 1 mm systematic shifts had minimal impact on dosimetric criteria for both the clinical and optimised plans.

Conclusions: It has been shown that using surface-based optimisation criteria can improve dose distributions for single entry, multi-channel breast brachytherapy treatments. Increasing the dwell time modulation to improve dosimetry generated concern that these treatments may be more sensitive to positioning errors such as balloon rotation or discrepancies in the treatment channel lengths. Simulation of these errors indicated minimal dosimetric changes for applicator rotations of less than 15 degrees, individual treatment length changes of 2mm and systematic treatment length changes of 1mm.


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