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Using Flattening Filter Free (FFF) Beams in Electronic Tissue Compensation (ECOMP) Whole Breast Irradiation with Deep Inspiration Breath Hold (DIBH) for Left Sided Breast Cancer

S Wisnoskie1*, D Zheng1, A Wahl1, N Bennion1, A Granatowicz1, X Liang2, S Zhou1, (1) University of Nebraska Medical Center, Omaha, NE, (2) University of Florida, Jacksonville, FL

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: DIBH is commonly used for left-sided breast radiotherapy to reduce heart dose. The ECOMP planning technique has been shown to improve planning efficiency and dose homogeneity. We hereby investigate the dosimetric and delivery feasibility of FFF ECOMP plans to reduce required breath-hold lengths and increase patient compatibility.


Methods: 15 left-sided, post-lumpectomy patients previously receiving DIBH whole-breast radiotherapy (266cGyx16) were retrospectively planned using ECOMP for both 6X and 6FFF. A dosimetric comparison was made between the two plans for each patient on the following target and OAR constraints: breast PTV_eval: V95%, V105%, Dmax; lumpectomy coverage: PTVe V95%, GTV Dmin; ipsilateral lung: V16Gy; heart: mean, V25Gy, Dmax; contralateral breast: Dmax; skin: mean, Dmax, Dmin. To evaluate the delivery accuracy, the original 6MV plan was also recalculated using 6FFF without replanning, and both plans were delivered side-by-side to assess Gamma passing rates with beam on time recorded. Mann-Whitney-Wilcoxon test was used for comparison with p<0.05 as significant.


Results: No statistical difference was observed between 6X and 6FFF plans for most dosimetric endpoints except for contralateral breast Dmax (p=0.0008) and skin Dmax (p=0.03) and Dmin (p=0.01). For contralateral breast, 6FFF achieved an average Dmax reduction of 79cGy(26%). For skin, 6FFF showed lower Dmax values and higher Dmin values indicating higher dose homogeneity for skin but the differences were small. 6FFF significantly decreased beam-on time for all patients by 22%-42% but slightly decreased QA Gamma passing rates on 7 patients by 0.1-2.9%, although Gamma(3%,3mm) was >95% for all plans.


Conclusion: ECOMP planning with FFF was found feasible for left-sided breast patients with DIBH. Plan quality is comparable, if not better, as plans using flattened beams. FFF ECOMP plans could significantly reduce the beam-on time and hence required breath-hold lengths, increasing patient compatibility for this treatment. Contralateral breast dose could also be reduced.

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Keywords

Breast, Treatment Planning

Taxonomy

TH- External Beam- Photons: treatment planning/virtual clinical studies

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