Experimental Determination of Breast Skin Dose On Anthropomorphic Phantom Using VMAT and Field-In-Field Treatment Techniques
A Cardona1*, JA Rojas-Lopez2, P Murina1, A Germanier3, C Venencia1, (1) Instituto Zunino, Cordoba, X, AR (2) Universidad Nacional de Cordoba, Cordoba, ,AR, (3) Unidad Estudios Fisicos, Ceprocor, Ministerio De Ciencia Y Tecnologia
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PO-GePV-T-295 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: The use of volumetric modulated arc therapy (VMAT) on the breast has several dosimetric advantages but its impact on skin dose should be evaluated and compared to well-established treatment techniques using tangential fields. The aim of this work is to contrast the skin dose for VMAT and Field-in-Field (FIF) and to estimate the magnitude of the skin dose involved.
Methods: The skin dose was measured, without build-up, using thermoluminescent dosimeter (TLD) and optically stimulated luminescent dosimeter (OSLD) in breast radiotherapy by an in-house anthropomorphic phantom. Two different treatment techniques were used: FIF and VMAT, based on the planning strategy proposed by Nicolini et al. The dose levels were 4300 cGy, 4600 cGy, and 5600 cGy in 20 fractions. In vivo dosimetry with TLD for VMAT was performed for different breast sizes in the same locations as phantom measurements.
Results: The homolateral phantom breast skin dose using both treatment techniques were equivalent. TLD measured doses by the VMAT technique were up to 5% higher than OSLD, although they agree if we consider the geometry uncertainty of the TLD. In accordance with in vivo dosimetry, the mean dose of the homolateral breast skin was 62 ± 6% [51%, 75%] relative to the prescribed dose, regardless of the breast size for the volumes considered with this small population (n=9) as shown by U-Mann Whitney test (Z=1.9, 95% confidence). The uncertainty expected in this region due to geometry (volume) changes is up to 9% higher for volumes from 225.9 cc to 968.8 cc. According to the treatment techniques and in vivo dosimetry, the contralateral breast skin dose was 1.0% in FIF and 2.5% in VMAT concerning the prescribed dose.
Conclusion: The homolateral breast skin dose measured in an anthropomorphic phantom by the use of luminescent dosimeters using VMAT and FIF is equivalent.
Keywords
TLDs, Optical Dosimetry, In Vivo Dosimetry
Taxonomy
TH- External Beam- Photons: portal dosimetry, in-vivo dosimetry and dose reconstruction
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