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Improving Permanent LDR Partial Breast Brachytherapy with CBCT and Surface-Map Guidance

S Richardson

S Richardson1*, (1) Swedish Medical Center, Seattle, WA


SU-I-GPD-T-24 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To describe CBCT and surface-map guided LDR partial breast brachytherapy treatments to achieve millimeter precision.

Methods: An LDR brachytherapy technique for early stage breast cancer patients that is used successfully in Canada has been piloted at our institution for several patients. Historically, ultrasound imaging is used to localize the target on treatment day. We have modified this protocol to use CBCT to localize the target based on post-surgical clips. Patient positioning is aided through the use of a surface mapping technique to help position the arms and head of the patient. Finally, the MLCs of the linac are used to project the TPS outline of the target volume on the patient’s surface. The target volume is then accurately drawn on the patient’s skin before transferring the patient to the OR for interstitial implant.

Results: While LDR brachytherapy has been used for decades for a variety of applications, its use in breast brachytherapy has been relatively limited. This is both due to the complex and deformable nature of the post-lumpectomy breast and also the skill and technique needed for accurate and stable needle/seed placement. Using on-board imaging for localization and skin surface mapping, we have incorporated routine external beam imaging techniques and set-up modalities for target localization for brachytherapy. The patients can be aligned within a millimeter of planned isocenter for target drawing. The drawback of this technique is that it requires linear accelerator room time of approximately half an hour. Compared to the historical method of drawing the target on the skin based on ultrasound imaging, this method positions the patient within a millimeter and uses localization techniques that staff are more familiar with.

Conclusion: CBCT and surface mapping equipment are useful for improving localization and target delineation for LDR partial breast brachytherapy.

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