Advanced Physics for Brachytherapy 2018

Example: systematic uncertainties for target

effect of systematic underestimation of target D 90

on observed dose-response

100%

Systematic 1.5 mm applicator reconstruction uncertainty for MRI- based cervix BT (Tanderup et al., R&O 2008): e.g. D D90 ≤ +3%/fx => „observed“ local control @85 Gy <1% higher than model prediction

98%

96%

high dose, high rate of local control

94%

small targets, good coverage

92%

90%

TCP

Systematically larger contours on CT vs. MRI => underestimation of D90 by CT contours (e.g. Viswanathan et al. 2007, IJROBP 68):

88%

mean +3%

86%

mean +5%

local control probability

e.g. i)

D D =+10%/fx => 2% overestimation of local control @ 85 Gy 90 =+20%/fx => 3.5% overestimation of local control @ 85 Gy 90 D D

84%

mean +10%

mean +20%

82%

ii)

model

80%

65

75

85

95

105

115

total treatment D 90

CTV HR

(EQD2

)

a/b =10Gy

(model based on preliminary retroEMBRACE data: Tanderup et al, GEC-ESTRO workshop, Brussels, 2013 )