Evaluation of Total Body Irradiation Technique Using 20 Diodes In-Vivo Dosimetry System
P Zhou*, D Kiszka, H Zhang, Y Jia, C Desrosiers, Indiana University- School of Medicine, Indianapolis, INSU-E-T-322 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To evaluate a new Total Body Irradiation (TBI) technique using CT planning by 20 diodes real time in-vivo dosimetry system.
Material and methods: TBI treatment is typically performed at extended SSD ( 3 to 4 meters) under high energy x-rays (6 MV). Lateral treatment results in a more convenient setup but less dose uniformity as compared with AP/PA treatment. This study evaluated a new TBI treatment which is performed at 2 meter distance, AP/PA. Matched oblique field plan was created by Eclipse TPS with CT simulated data from PIXY phantom; using MLC for lung blocking. Field in Field technique was applied to improve dose uniformity. A steel attenuator with transmission factor 0.55 for 6MV photon field is used to reduce dose rate to 5-20 cGy/min while a 5mm thick Lexan sheet is placed about 20 cm above patient to increase skin dose. Patients will lay supine and prone on a movable bed. Three AP and PA fields were used to deliver prescribed dose. A 20-diodes SunNuclear in-vivo dosimetry system was used for monitoring dose at different sites. Diodes were calibrated with attenuator to accommodate energy spectrum change. SSD, dose rate, angular dependence of diodes were measured. RadCalc MU verification software was also tested for agreement with TPS and measured data.
Results: Attenuator could reduce the dose rate to about 13 cGy/min. By averaging the entrance and exit reading, the doses at patients anatomical mid-line were measured and found to have good agreement with TPS (within 7% difference). Two dry-runs have demonstrated that the TBI plan can achieve and intended dose uniformity better than 10%. The RadCalc verification program agreed with TPS on average within 3%.
Conclusion: CT-image based and TPS generated TBI plan is feasible. Diodes are suitable for both the TBI technique testing and dose monitoring.