Introduction: Verification of absorbed dose in target volume is a key factor for quality assurance in radiotherapy. In vivo measurements allow evaluation of the variations in dose with time and variations between measured doses and calculated doses by TPS. The aim of this work were to evaluate reproducibility of patient positioning and to compare calculated doses by 2 different TPS.
Patients and methods: Twenty patients were divided in 2 groups according to the thickness of their breast (mean SSD = 92.9 cm). In vivo measurement was performed within the first two sessions.
Results: Reproducibility of SSD evaluation was made on 12 beams between 2 fractions. With a tolerance margin of 0.5 cm, positioning errors were present in 33% (4/12). The 2 TPS were in agreement in 75% (30/40).
Conclusion: In vivo dosimetry can be a very interesting tool to assess patients positioning variations and TPS dose calculation.