(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Tangential whole breast irradiation is the standard radiotherapy technique for post-lumpectomy breast cancer patients, and is until recently, primarily planned with the Field-in-Field (FiF) technique. For patients with large breast separations, higher energy beams are usually used or mixed with low energy to achieve required target dose uniformity. The Electronic Tissue Compensation (ECOMP) planning technique has recently allowed improved treatment planning efficiency and dose homogeneity. Therefore, this study aims at assessing whether ECOMP planning will allow for elimination of higher energy beam use compared to FiF while creating a dosimetrically equivalent plan.
Methods: 10 post-lumpectomy breast cancer patients (Rx=266cGyx16fx) who were clinically planned with FiF using high energy beam only (10X or 15X) or mixed energies were retrospectively re-planned using ECOMP with low energy only (6X). To evaluate plan quality equivalency, a dosimetric comparison was made between the two plans for each patient with the following target and OAR endpoints: breast PTV_eval: V95%, V105%, Dmax; lumpectomy coverage: PTVe V95%, GTV Dmin; ipsilateral lung: V16Gy; heart: mean, V25Gy, Dmax; contralateral breast: Dmax. Mann-Whitney-Wilcoxon test was used for comparison with p<0.05 as significant.
Results: The studied patients had a median breast volume of 785.4cc and separation of 24.1 cm. ECOMP 6X plans achieved dosimetrically equivalent plans as the corresponding FiF clinical plans with high or mixed energies. No statistical difference was observed for the investigated endpoints between the two plans, except for lumpectomy PTVe where the ECOMP plans achieved a slightly better coverage by 0.4% (p=0.005).
Conclusion: This study suggests that ECOMP planning method allows the planner to eliminate high energy beams for tangential whole breast irradiation compared with FiF. This could lead to increased delivery efficiency (eliminating mixed-energy beams) and reduced OAR dose to heart, lung, and contralateral breast (especially neutron dose).
Keywords
Taxonomy
TH- External Beam- Photons: treatment planning/virtual clinical studies
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