Abstract
BackgroundAlthough 3D-conformal accelerated partial breast irradiation (APBI) is widely used, several questions still remain such as what are the optimal treatment planning modalities. Indeed, some patients may have an unfavorable anatomy and/or inadequate dosimetric constraints could be fulfilled ("complex cases"). In such cases, we wondered which treatment planning modality could be applied to achieve 3D-conformal APBI (2 mini-tangents and an "en face" electron field or non-coplanar photon multiple fields; or a mixed technique combining non-coplanar photon multiple fields with an "en face" electron beam).MethodsFrom October 2007 to March 2010, 55 patients with pT1N0 breast cancer were enrolled in a phase II APBI trial. Among them, 7 patients were excluded as they were considered as "complex cases". A dosimetric comparison was performed according to the 3 APBI modalities mentioned above and assessed: planning treatment volume (PTV) coverage, PTV/whole breast ratio, lung and heart distance within irradiated field and exposure of organs at risk (OAR).ResultsAdequate PTV coverage was obtained with the 3 different treatment planning. Regarding OAR exposure, the "mixed technique" seemed to reduce the volume of non-target breast tissue in 4 cases compared to the other techniques (in only 1 case), with the mean V50% at 44.9% (range, 13.4 - 56.9%) for the mixed modality compared to 51.1% (range, 22.4 - 63.4%) and 51.8% (range, 23.1 - 59.5%) for the reference and non-coplanar techniques, respectively. The same trend was observed for heart exposure.ConclusionsThe mixed technique showed a promising trend of reducing the volume of non-target breast tissue and heart exposure doses in APBI "complex cases".
Highlights
While whole breast irradiation (50 Gy/25 fractions) followed by a boost to the tumor bed (16 Gy/8 fractions) is the standard of locoregional care for early breast cancer, the current trend is to shorten overall treatment time by delivering either hypofractionated whole breast irradiation (WBI) or accelerated partial breast irradiation (APBI)
A dosimetric comparison was performed according to the 3 APBI modalities mentioned above and assessed: planning treatment volume (PTV) coverage, PTV/whole breast ratio, lung and heart distance within irradiated field and exposure of organs at risk (OAR)
Regarding OAR exposure, the “mixed technique” seemed to reduce the volume of non-target breast tissue in 4 cases compared to the other techniques, with the mean V50% at 44.9% for the mixed modality compared to 51.1% and 51.8% for the reference and non-coplanar techniques, respectively
Summary
While whole breast irradiation (50 Gy/25 fractions) followed by a boost to the tumor bed (16 Gy/8 fractions) is the standard of locoregional care for early breast cancer, the current trend is to shorten overall treatment time by delivering either hypofractionated whole breast irradiation (WBI) or accelerated partial breast irradiation (APBI). At the Institut Gustave Roussy, we recently reported the early results of a 3D-conformal APBI trial [5] in which treatment planning was performed according to the technique designed by Taghian and colleagues, consisting of 2 mini-tangents and an “en face” electron field contributing around 20% of the total dose (8 Gy) [4,6]. Some patients may have an unfavorable anatomy and/or inadequate dosimetric constraints could be fulfilled ("complex cases”) In such cases, we wondered which treatment planning modality could be applied to achieve 3D-conformal APBI (2 mini-tangents and an “en face” electron field or non-coplanar photon multiple fields; or a mixed technique combining noncoplanar photon multiple fields with an “en face” electron beam)
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