title: An investigation of a PRESAGE® in vivo dosimeter for brachytherapy.
abstract: Determining accurate in vivo dosimetry in brachytherapy treatment with high dose gradients is challenging. Here we introduce, investigate, and characterize a novel in vivo dosimeter and readout technique with the potential to address this problem. A cylindrical (4 mm × 20 mm) tissue equivalent radiochromic dosimeter PRESAGE® in vivo (PRESAGE®-IV) is investigated. Two readout methods of the radiation induced change in optical density (OD) were investigated: (i) volume-averaged readout by spectrophotometer, and (ii) a line profile readout by 2D projection imaging utilizing a high-resolution (50 micron) telecentric optical system. Method (i) is considered the gold standard when applied to PRESAGE® in optical cuvettes. The feasibility of both methods was evaluated by comparison to standard measurements on PRESAGE® in optical cuvettes via spectrophotometer. An end-to-end feasibility study was performed by a side-by-side comparison with TLDs in an (192)Ir HDR delivery. 7 and 8 Gy was delivered to PRESAGE®-IV and TLDs attached to the surface of a vaginal cylinder. Known geometry enabled direct comparison of measured dose with a commissioned treatment planning system. A high-resolution readout study under a steep dose gradient region showed 98.9% (5%/1 mm) agreement between PRESAGE®-IV and Gafchromic® EBT2 Film. Spectrometer measurements exhibited a linear dose response between 0-15 Gy with sensitivity of 0.0133 ± 0.0007 ΔOD/(Gy ⋅ cm) at the 95% confidence interval. Method (ii) yielded a linear response with sensitivity of 0.0132 ± 0.0006 (ΔOD/Gy), within 2% of method (i). Method (i) has poor spatial resolution due to volume averaging. Method (ii) has higher resolution (∼1 mm) without loss of sensitivity or increased noise. Both readout methods are shown to be feasible. The end-to-end comparison revealed a 2.5% agreement between PRESAGE®-IV and treatment plan in regions of uniform high dose. PRESAGE®-IV shows promise for in vivo dose verification, although improved sensitivity would be desirable. Advantages include high-resolution, convenience and fast, low-cost readout.
authors: Medical Physics Graduate Program, Duke University, Durham, NC, USA.
authors: A K
authors: AK
authors: Vidovic
authors: T
authors: T
authors: Juang
authors: S
authors: S
authors: Meltsner
authors: J
authors: J
authors: Adamovics
authors: J
authors: J
authors: Chino
authors: B
authors: B
authors: Steffey
authors: O
authors: O
authors: Craciunescu
authors: M
authors: M
authors: Oldham
mesh_terms: D001918:Brachytherapy; D005240:Feasibility Studies; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D011874:Radiometry / Q000379:methods*; D014057:Tomography, X-Ray Computed
chemical_list: D007496:Iridium Radioisotopes