(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose:
Validation studies comparing OSLDs to diodes have often been performed at standard treatment distances. However, detector response can vary due to changes in energy, source-to-surface distance (SSD), or field size. The purpose of this study was to validate OSLD in vivo dosimetry for total body irradiation (TBI) based on a currently used diode system.
Methods:
Diodes were calibrated at 600 cm SSD without bolus. OSLD and diode readings were compared for 6 MV photons at 100 cm, 200 cm, 400 cm, and 600 cm SSD. Field size ranged from 10×10 cm² for 100 cm SSD to 39.5×39.5 cm² for all other SSDs to replicate TBI treatment conditions. Comparisons were made using 1.5 cm bolus for OSLDs and either 1.5 cm of bolus or no bolus on diodes. Measurements were also carried out at an off-axis distance of 60 cm at 600 cm SSD to validate off-axis dose.
Results:
OSLD readings matched the bolus diode readings at 100 and 200 cm SSD within 1.5%. The non-bolus diode readings were ~2% higher than the OSLD readings. Beyond 200 cm SSD, OSLD readings were within 2.3% and 1.2% of bolus and non-bolus diode readings, respectively. Off-axis, OSLD readings were within 3.3% of the non-bolus diode readings.
Conclusion:
OSLDs tend to report lower doses along the central axis at shorter SSD compared to diodes, and higher doses at extended distance. Central-axis values from both systems are still within 1.5%. Off-axis at 600 cm SSD, OSLDs tend to report higher doses (~4%) compared to diodes. These differences are most likely due to the energy, SSD, and field size dependence of diodes. OSLDs and non-bolus diodes, which are used clinically for in vivo dosimetry, are still within 1.2% under TBI conditions, indicating that it is acceptable to use OSLDs for in vivo dosimetry for TBI.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External Beam- Photons: portal dosimetry, in-vivo dosimetry and dose reconstruction
Contact Email
