Room: AAPM ePoster Library
Purpose: develop a new method to measure Venezia lunar ovoid offset (the distance from center of the most distal source dwell position to lumen tip end).
Methods: autoradiographs were acquired for offset measurement. EBT3 film was taped to Venezia lunar ovoid applicator (30 mm diameter) which was attached to a Flexitron brachytherapy remote afterloader through a transfer tube. The ovoid was oriented similar to clinical setup of an HDR treatment for gynecologic cancers. An Ir-192 HDR source was sent to dwell at the most distal position for 25 s, leaving a visible mark on the film that defines the 1?? dwell position. With the ovoid still taped to the film, it was exposed to 600 MU from a 12 MeV electron beam from a TrueBeam linac. The tip end of the lumen was visible on the exposed film, which was marked and digitized using a flatbed scanner. Distance from source dwell center to the marked lumen end was measured using ImageJ software. This process was repeated for 22 and 26 mm diameter lunar ovoids.
Results: autoradiograph showed intricate details of the ovoid’s lunar shape, the lumen tip end, and the source dwell position on the EBT3 film. Measured offset for right/left ovoid was 5.21/5.92 mm for a 22mm diameter ovoid, 5.18/5.56 mm for a 26mm diameter ovoid, and 5.14/6.53 mm for a 30mm diameter ovoid.
Conclusion: presented a robust new method for acquiring the Venezia lunar ovoid offset values, which are crucial to safe applicator commissioning. Compared to the more common photon beam approach, the electron beam provided more details of lunar ovoid inner design, which can potentially improve offset measurement accuracy. As there are no vendor-reported values, our measured offsets can be used as comparison data by other clinics when commissioning the Venezia lunar ovoid applicators.
Brachytherapy, Commissioning, HDR