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Effect of irradiation time on biological effectiveness and tumor control probability in proton therapy.
Int J Radiat Oncol Biol Phys. 2019 May 11;:
Authors: Takei H, Inaniwa T
Abstract
PURPOSE: The biological effectiveness of proton beams may decrease with the irradiation time due to sublethal damage repair. The purpose of this study is to systematically evaluate this effect in hypofractionated proton therapy for various target sizes, depths and prescribed doses per fraction.
METHODS AND MATERIALS: Plans with single spread-out Bragg peak (SOBP) beam were created using a constant relative biological effectiveness (RBE) of 1.1 to cover the targets of six different sizes located at three different depths in water. Biological doses of 2, 3, 5, 10 and 20 Gy (RBE) were prescribed to the targets. First, to investigate the depth-variation of the biological effectiveness, the biological dose in instantaneous irradiation was recalculated based on the microdosimetric kinetic model (MKM). The sublethal damage repair (SLDR) was then taken into account in the MKM during treatments to obtain the irradiation-time-dependent biological effectiveness for the irradiation time T of 5-60 min and the beam interruption time τ of 0-60 min. The tumor control probabilities (TCPs) were calculated for single-fraction proton therapy fields of different Ts and τs, and the curative doses were evaluated at a TCP of 90%.
RESULTS: The biological effectiveness decreased with longer T and τ, and higher prescribed dose. The maximum decrease in the biological effectiveness was 21% with a 20 Gy (RBE) prescribed dose. In single-fraction proton therapy, the curative dose increased approximately by 33%-35% linearly with the increase of T from 0 to 60 min.
CONCLUSIONS: The biological effectiveness varies largely with T and τ due to SLDR during treatments. This effect was pronounced for high prescribed doses per fraction. Thus, the effect of SLDR needs to be considered in hypofractionated and single-fraction proton therapies in relation to any sizes and depths of the target.
PURPOSE: The biological effectiveness of proton beams may decrease with the irradiation time due to sublethal damage repair. The purpose of this study is to systematically evaluate this effect in hypofractionated proton therapy for various target sizes, depths and prescribed doses per fraction.
METHODS AND MATERIALS: Plans with single spread-out Bragg peak (SOBP) beam were created using a constant relative biological effectiveness (RBE) of 1.1 to cover the targets of six different sizes located at three different depths in water. Biological doses of 2, 3, 5, 10 and 20 Gy (RBE) were prescribed to the targets. First, to investigate the depth-variation of the biological effectiveness, the biological dose in instantaneous irradiation was recalculated based on the microdosimetric kinetic model (MKM). The sublethal damage repair (SLDR) was then taken into account in the MKM during treatments to obtain the irradiation-time-dependent biological effectiveness for the irradiation time T of 5-60 min and the beam interruption time τ of 0-60 min. The tumor control probabilities (TCPs) were calculated for single-fraction proton therapy fields of different Ts and τs, and the curative doses were evaluated at a TCP of 90%.
RESULTS: The biological effectiveness decreased with longer T and τ, and higher prescribed dose. The maximum decrease in the biological effectiveness was 21% with a 20 Gy (RBE) prescribed dose. In single-fraction proton therapy, the curative dose increased approximately by 33%-35% linearly with the increase of T from 0 to 60 min.
CONCLUSIONS: The biological effectiveness varies largely with T and τ due to SLDR during treatments. This effect was pronounced for high prescribed doses per fraction. Thus, the effect of SLDR needs to be considered in hypofractionated and single-fraction proton therapies in relation to any sizes and depths of the target.
PMID: 31085286 [PubMed - as supplied by publisher]
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