ESTRO 37 Abstract book

S1117

ESTRO 37

Management™, Varian) and visual coaching. A DIBH gating window of 0.5 cm is used. The treatment fractionation is about 25-33 fractions and 4-8 treatment fields are used in each fraction. 728 breathing patterns (57 patients) from May 2016 were recorded. Each DIBH in these fractions were automatically analysed by an in-house routine (R DevelopmentCoreTeam) to study stability (S) and reproducibility (R) both intra and inter fraction in each patient treatment. We used the following definitions: 1)Cerviño et al.[1] R=max{d i }-min{d i }, where d i is the average amplitude of and are, respectively, the slope of the linear fit (amplitude respiratory signal vs time) and the duration of each DIBH. 2)Stock et al.[2] R=mean{abs(d i -d ref )}, where d ref is the reference amplitude from the planning CT. S=mean{sd(d i }. Differences between inter and intra-fraction in reproducibility and stability were analysed (paired t- test). CWE was calculated as a)the reference amplitude in the planning CT, and b)the mean DIBH amplitude with respect to the free-breathing baseline immediately before the DIBH(upper Fig.2). Correlation tests were made between CWEs and reproducibility and stability. We also studied the correlation between CWE (definition a , CWE a ) and OAR doses (heart, lung, liver and contralateral breast,CB) obtained from dose-volume histograms of the treatment plan. Results Fig.1 shows the intra and inter-fractions results with both definitions. There are significant differences between both definitions, and between intra and inter fraction in Cerviño’s definition. CWE has significant different values between a and b definitions (Fig.2). CWE doesn’t show significant correlation with reproducibility and stability, nor CWE a with OAR doses. each DIBH. S=max{|m i |Δt i }, where m i

LUNG

LIVER

CB

HEART

p- value V25(%) D mean CWE 0,138 0,160

(Gy) V5(%) D mean

(Gy) D mean

(Gy) V5(%)

0,618 0,533

0,650

0,921

Conclusion Intra-fraction R and S are less than 3 mm and 4 mm, respectively, in 75% of the treatments with both definitions. Thus a smaller DIBH window could be used. The R and S intra-fraction results obtained by our centre are according to literature. Inter-fractions R and S are greater than intra-fraction results. Cerviño’s definition is more sensitive to differences. CWE is not correlated to reproducibility, stability nor OAR doses. [1] Cerviño et al.Using surface imaging and visual coaching to improve the reproducibility and stability of deep-inspiration breath hold for left-breast-cancer radiotherapy.Phys Med Biol2009;54 [2] Stock et al.Development and application of a real- time monitoring and feedback system for deep inspiration breath hold based on external marker tracking.Med Phys2006;33(8)