An Investigation for the Use of OSLDs for in Vivo Patient-Specific Quality Assurance for Patients Requiring Bolus
M Savacool*, R Yaparpalvi, D Mynampati, Y Chen, W Tome, Montefiore Medical Center, Bronx, New YorkSU-E-T-210 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: For treatments that require addition of bolus, dose to the skin and superficial regions must be known for adequate plan evaluation. Dose calculation inaccuracies in these regions may occur because they are in the build-up region, as well as a result of the IMRT/VMAT optimization algorithm ignoring the bolus during optimization. In this study, we evaluated the routine use of optically-stimulated luminescent dosimeters (OSLDs) as a means of in vivo quality assurance for superficial dosimetry in patients requiring bolus during treatment.
Methods: Landauer nanoDot OSLDs were used to perform measurements on 11 patients (total 13 sites) including head and neck, anal, groin, and breast. Treatment techniques included RapidArc, IMRT, and 3D-CRT. All patients were treated with nominal energy 6MV. One OSLD was placed on the patient's skin, under the prescribed bolus, for one fraction. Bolus thickness was 0.5 cm. Each OSLD was read using the Landauer MicroStar reader, which operates in cw mode with a 1-s read period, and corrected for sensitivity. Three readings were taken and the average calculated. Readings that were out of tolerance (15 percent) were repeated. OSLD readings were compared with TPS(Eclipse) calculations at a depth of 4mm (corresponding to the inherent OSLD build-up).
Results: 10 sites passed with less than 10 percent deviation (measurement accuracy of standard nanoDot). 6 Sites showed less than 3 percent deviation, 8 sites showed less than 5 percent deviation. 1 Site showed greater than 13 percent deviation. 2 sites showed greater than 25 percent deviation, and upon repetition, yielded similar results. Large deviations correlated to treatment sites with irregular surfaces (tracheotomy, skin creases).
Conclusion: OSLDs are a quick and efficient way to perform in vivo quality assurance of doses in the superficial regions in patients requiring bolus for treatments. For simple geometries studied, TPS calculations show sufficient accuracy.