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Dosimetric Assessment of a New Multi-Center Protocol for Radiotherapy of Multiple Ipsilateral Breast Cancers

G Chen

G Chen*, A Currey, T Yen, X Li, Medical College of Wisconsin, Milwaukee, WI

SU-E-T-464 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To assess dosimetric planning feasibility for enrolling patients into a new prospective multi-center protocol (ACOSOG Protocol Z11102) of breast conservation surgery with radiotherapy (RT) of multiple ipsilateral breast cancers (MIBC) including multicentric and/or multifocal breast cancers.

Methods: CT data for 9 representative breast patients with two lumpectomy cavities in a breast treated in prone position were retrospectively analyzed. The boost PTV for lumpectomy cavity was delineated based on the seroma and/or surgical clips with 1 to 2 cm non-uniform 3D expansion, not including chestwall, skin, and bone. A whole breast irradiation (WBI) of 50 Gy in 25 fractions was planned using 3D tangential beams of 6 or 15 MV photons with necessary wedges and/or field-in-field techniques to provide uniform dose coverage. No nodal irradiation was planned. The dose was calculated with heterogeneity correction using a treatment planning system (Xio v4.80, Elekta). For each boost PTV, additional 10 Gy in 5 fractions was planned by using one single photon beam, either 6 or 15 MV depending on the depth of the PTV, oriented in the direction with shortest depth to the PTV. All plans were evaluated to check whether all the dose-volume criteria required by the protocol can be met.

Results: All plans generated for patients in our study meet the dose-volume criteria required by the protocol. For all dose-volume parameters, the discrepancies between the patient averages and dose-volume goals were separated by at least 1.4 sigmas (standard deviation). The average for the percentage breast volume receiving 60 Gy, a major concern because of the large boost PTVs, was (29.7±7.3)%, well below the required value of 40%.

Conclusion: The dose-volume criteria required for the new multi-center protocol of radiotherapy for multiple ipsilateral breast cancers can be met with no major difficulties with the standard planning techniques.

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