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Respiratory-Correlated Dose Rate Modulated Therapy as An Alternative to Gated Radiotherapy

J Fontenot

J Fontenot1,2, (1) Mary Bird Perkins Cancer Center, Baton Rouge, LA, (2) Louisiana State University

TU-E-141-11 Tuesday 2:00PM - 3:50PM Room: 141

Purpose: To investigate the potential of respiratory-correlated dose rate modulation (DRM) as a motion management strategy.

Methods: Like to conventional gating, a DRM plan targets a specific phase of the respiratory cycle. Unlike conventional gating, the binary modes of a DRM plan are high dose and low dose rate. The low dose rate mode facilitates cine-EPID imaging of the irradiated volume. When the target moves within the beam's eye view (BEV), high dose rate mode is enabled to delver the therapeutic dose. This approach is only possible with the ability of the linear accelerator to precisely changes dose rates that has accompanied commercial rotational IMRT deliveries. The dosimetric performance of DRM was investigated using a four-dimensional simulation of dynamic respiratory phantom. Conventional and gated plans were constructed to target all phases and exhale phase of motion, respectively. The DRM plan was constructed as the sum of 2 plans: 1 targeting the exhale phase and 1 targeting all phases of motion, with the weighting determined by the minimum and maximum dose rate values.

Results: Dose coverage and homogeneity in the target was similar over all plans. In the lung, V40Gy, V20Gy, and V10Gy were nearly identical for the gated and DRM plans, and 40% lower than the conventional plan. The value of V5Gy in the gated plan was 30% lower than the conventional plan and 15% lower than the DRM plan (500 MU/min maximum dose rate). If the maximum dose rate was increased (1500 MU/min), the advantage in V5Gy in the gated plan over the DRM plan was reduced to 2%.

Conclusion: DRM plans produce dose distributions comparable to conventional gating, with the advantage of being able to localize the tumor within the BEV of the treatment fields.

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