Background & objective: In order to improve quality assurance (QA) and quality control (QC) of radiotherapy, individualized vacuum bag is used in the localization of radiation treatment, gradually becoming one of the important steps for the QA and QC in the many departments of radiation oncology. It is controversial whether localization with vacuum bags under the simulator influences the precision of direct measurement for tumor depth in the isocentric posterior oblique field in the patients with thoracic and abdominal tumors. This study was designed to explore the influence of vacuum bag on the direct measurement
Methods: Twenty-nine patients with thoracic and abdominal carcinoma who had to need isocentric irradiation in the supine position were immobilized using vacuum bag. The irradiation depths of 45 posterior oblique fields were determined by CT-simulator and conventional simulator, respectively; then the absolute value for the difference of both depths was regarded as error value.
Results: There were 37 fields (82.2%) with error value of smaller than 5 mm; 8 fields (17.8%), more than 5 mm. In the latter, 5 field were belonged to be repositioned in the phase II of radiotherapy because of light leaking air into the vacuum bag in the phase I of radiotherapy.
Conclusion: Vacuum bag has a slight influence on direct measurement for depths of isocentric posterior oblique field.