الفهرس 
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Abstract
Background: Radiotherapy following Breast-conservative surgery is a standard treatment
for breast cancer, Techniques developed to obtain better target definition, dose homogeneity
and coverage, accurate tumor bed localization and delineation is considered the current
golden standard.
Objectives: The aim of this work is to evaluate interobserver variability (I.O.V) in tumor
bed delineation (evaluated by conformity index) and its effect on planning outcome (e.g
homogenicity, coverage and dose distribution).We tried also to define any subgroup with
marked I.O.V.
Methods: A total number of fifty female patients included in this study with breast
cancer after breast conservative surgery presented for post operative adjuvant radiotherapy.
Target volume delineation by observer (1) on the planning system ,the boost was delineated
by observer (1) and then observer (2) delineated the boost separately using the same plan put
for observer (1)delineation.
Results: Conformity index ranged from0.50 to 0.83 with mean value ± SD (0.66 ± 0.09)
Percentage of volume receiving 90% of prescribed dose(V90) boost mean value for observer
(1) was = 98.6 % ± 2.3 % ,while for observer (2) = 95.5 ± 6.8 ( P value < 0.001). Dose
received by 90% of Planning Target Volume (PTV) (D90) boost for observer (1) = 63.9 Gy
± 2.1 GY while for observer (2) = 62 Gy ± 2.9 GY ( P value < 0.001). .Minimal dose
received by 2% of PTV(D min)for observer (1) = 60.5 Gy ± 4 Gy while for observer (2) = 57
Gy ± 4.6 Gy ( P value < 0.001). and maximal dose received by 2% of PTV(D max)for
observer (1) = 67.5 Gy ± 1.6 Gy while for observer (2)= 67.4 Gy ± 1.7 Gy(p-value =0.095).
We failed to define any specific subgroup with marked I.O.V
Conclusion: There was an Interobserver variability in tumor bed delineation between observer
(1) and observer (2) , and it has a significant effect on treatment plan outcome i.e (coverage,
homogenicity) for tumor bed ,with no subgroup with significant difference.
Keywords : Breast cancer, Radiotherapy, Interobserver variation