M Prusator*, J Rolfingsmeier, T Kim, N Knutson, N Maughan, M Thomas, I Zoberi, F Reynoso, Washington University in St. Louis, St. Louis, MO

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  M Prusator

PO-BPC-Virtual-12 (Saturday, 4/17/2021)   [Eastern Time (GMT-4)]

Purpose: Deep inspiration breath-hold (DIBH) for left-sided breast/chest-wall irradiation results in significant heart and lung sparing. A bilateral comprehensive irradiation of the chest-wall and locoregional nodes presents a much more challenging case where DIBH is also of benefit. We have developed a robust dual-isocenter DIBH VMAT technique with visual guidance for maximum sparing of the heart and lungs.

Methods: A comprehensive chest-wall plan to irradiate the bilateral chest-wall and locoregional nodes was created using a hypofractionated approach to 4256 cGy in 16 fractions. A total of eight partial arcs in two groups of four were optimized simultaneously using automatic feathering to avoid hot/cold spots in the overlap region. The isocenter for each group of partial arcs was placed just posterior to each side of the chest-wall target to accomplish a tangential irradiation. A 1 cm virtual skin flash bolus (HU=-500) was used for optimization to take into account setup uncertainties and ensure appropriate coverage at the skin. A 5 mm isocenter symmetric shift was used to evaluate robustness. Alliance A221505 trial constraints were used to evaluate the plan.

Results: Total PTV coverage achieved was V95%=98.8%, while mean heart dose was kept at 408 cGy, total lung V18Gy=17.7% and V4.8Gy were 63.0%. All Alliance A221505 hypofractionated dose constraints were met at the preferred or acceptable level while highly exceeding all coverage constraints. Robustness analysis showed a worst case scenario of PTV coverage of V95%=94.0%. Minimal breath-hold coaching was needed from the therapy team with the use of patient visual feedback. Each arc was completed in nearly a single breath-hold and treatment was completed in 30 minutes.

Conclusion: A dual isocenter DIBH VMAT technique was developed using visual-guidance for comprehensive chest-wall and locoregional node irradiation. The technique was able to meet relevant OAR constraints and an efficient and robust treatment delivery.

Keywords

Breast, Dosimetry, Image-guided Therapy

Taxonomy

TH- External Beam- Photons: General (most aspects)

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