SU‐E‐T‐222: Performance Comparison of In‐Vivo Dosimeters, including TLDs, MOSFETs, and OSLDs for Patients Receiving Total Body Irradiation

Purpose: To compare accuracy of in vivo dosimeters such as TLDs, MOSFETs & OSLDs for patients receiving Total Body Irradiation. Methods: Three types of dosimeters were considered for this study, LiF Thermoluminescent Dosimeters, Modified Field Effect Transistors(MOSFET ‐Thomson&Nielsen TN‐502RD) and Optically Stimulated Luminescence Dosimeters(OSLD ‐ Landuer's 2% screened nanoDOTs). All three dosimeters were calibrated under full bulildup conditions at 100cm SSD, dmax = 3.4cm for 18MV photon energy and appropriate correction factors were applied for TBI treatment condition. This study is performed on a 30×30×22cm solid water phantom and a rando phantom at the TBI treatment distance. The separations at different locations for phantom were measured and MUs were calculated to deliver 100cGy at the midplane. Dosimeters were placed on the entrance side of the phantoms to measure dmax dose. Each type of dosimeters were irradiated at five locations in the rando phantom under the same treatment setup. The reproducibility of the dosimeters was verified by solidwater phantom measurements. Ten TBI cases, which were monitored using each dosimeter type were selected and tabulated the percentage difference of measured to expected dose for 5 different patient locations. Results: The reproducibility for TLDs, MOSFETs and OSLDs were 118.3cGy +/− 2.7%(1SD), 118.3cGy +/−2.1%(1SD) and 118.3cGy +/− 1.8%(1SD) resp after 10 consecutive measurements in solidwater phantom (Table 1). From rando phantom measurements, maximum percentage variation of the measured to expected dose with 1SD values are TLDs (1.4 +/− 1.4), MOSFETs (3.9+/− 2.2) and OSLDs (1.6 +/− 1.8) (Table 2). Percentage difference of the measured dose to expected dose for 10 clinical cases were TLDs (2.3+/− 2.9), MOSFETs (3.7+/− 4.9) and OSLDs (1.8+/− 2.9%) (Table 3). Conclusions: Measured values were within +/−5% tolerance level for all dosimeters. OSLDs can give more accurate and reproducible results with an added advantage of ease of use and shorter readout period.