In Vivo Dosimetry with GAFCHROMIC EBT3 Film in Twice-A-Day Total-Body Irradiation Radiotherapy
X Zhang*, Y Zhang, R Alibazi Behbahani, J Kilian-Meneghin, X Wang, E Simiele, Y Zhang, K Nie, N Yue, Rutgers Cancer Institute of New Jersey, New Brunswick, NJ
Presentations
PO-GePV-T-250 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
ePoster Forums
Purpose: To investigate the feasibility of in vivo dose measurement using Gafchromic EBT3 film in twice-a-day (BID) total-body irradiation (TBI) radiotherapy.
Methods: The Gafchromic EBT3 films were irradiated with different dose ranging from 100cGy to 200cGy, and the absolute dose response at different reading time was investigated by scanning the films with a 30-minutes post-irradiation interval for a 24-hours continuous scanning. The absolute dose was calculated using a dose response calibration curve which was established with a 24-hours post-irradiation time. Film samples were placed on the surface of the solid-water phantoms of different separations under a clinical TBI setup and the results were compared to the dose measured with silicon diodes. Bolus of 1.5 cm thickness was placed on top of the films to evaluate the dose difference from the bare film measurements. In addition, a cylindrical chamber was used to measure the midline dose as a reference. In vivo measurements using both bare films and diodes were also obtained in three fractions for one BID TBI patient.
Results: The absolute dose of the films read at a 4-hour post-irradiation time was underestimated by roughly 4%. With acknowledging such discrepancy, the absolute dose uncertainty associated with 4 ± 1 hour scanning time window was about 3%. No significant absolute dose difference was observed between the bare films and the films with a 1.5 cm bolus. The film-to-diode conversion factor was 0.95 ± 3% with the phantom set-up, and 0.98 ± 7% with the in vivo measurement of the patient. For different phantom separations, a strong agreement of the surface-to-midline correction factors was observed between the film-to-chamber and diode-to-chamber measurements.
Conclusion: Gafchromic EBT3 film can be a useful tool for in vivo dosimetry in BID TBI treatment, however, uncertainties associated with the absolute dose should be carefully considered.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External Beam- Photons: portal dosimetry, in-vivo dosimetry and dose reconstruction
Contact Email