Room: AAPM ePoster Library
Purpose: Accurate dosimetry in brachytherapy is not an easy task, as most detectors exhibit volume averaging or energy dependance reducing their usability. Free from these limitations are plastic scintillation detectors (PSDs), which makes them well suited for brachytherapy applications, either for in vivo dosimetry or commissioning. This work aims to determine if the HYPERSCINT scintillation dosimetry research platform (Medscint inc., Quebec city, Canada) can be used for brachytherapy dose measurement in the context of commissioning a new brachytherapy technique.
Methods: A custom made, 3D-printed phantom was designed to house vaginal CT/MR applicators (Elekta, Stockholm, Sweden) of multiple diameters, as well as a HYPERSCINT PSD probe and an EBT3 gafchromic film (Ashland, Bridgewater, NJ)l. A total of 30 cylinder plans for varying cylinder diameter and treatment length were planned in Oncentra brachy (Elekta, TG-43 formalism), delivered using a Flexitron source projector (Elekta) and measured on the PSD. 5 of those plans were also simultaneously measured on an EBT3 film. Differences between planned and measured dose were computed for both detectors and the results were compared between them for consistency.
Results: Dose difference between the measured and planned dose for the HYPERSCINT was (0.3±0.7)% (average ±1 standard deviation), for which 24 of the 30 cases were inside 1% of the TG-43 dose. For the EBT3 films these differences stand as (-3.2±1.6)%. When comparing pairs of measurements (PSD vs film), it was found that the film underestimated the PSD dose by (3.8±1.4)%.
Conclusion: Results show the HYPERSCINT scintillation dosimetry platform can be used for accurate brachytherapy dose measurement in the context of technique commissioning (i.e. in phantom). Deviations for the EBT3 films are suspected to originate from an error in film handling (storage conditions, residual film calibration error at high dose, or intra batch variation).