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Quantification of UVA Emission From Megavoltage Irradiated Tissue-Simulating Phantoms

S Jain1*, S Yoon1, X Zhang2 , J Adamson3 , M Oldham3 (1) Duke University, Durham, NC, (2) ,Seattlle, WA, (3) Duke University Medical Center, Durham, NC


(Wednesday, 7/17/2019) 7:30 AM - 9:30 AM

Room: 303

Purpose: Radiotherapy Enhanced with Cherenkov photo-Activation (RECA) is a novel treatment regimen where the potentially immunogenic drug psoralen is photo-activated in-situ by UVA Cherenkov-Light (CL) produced directly by the treatment beam. This work presents methods and results that quantify RT-induced UVA CL from a range of tissue and phantom materials.

Methods: UVA CL emission (320-400nm) was quantified in tissue samples of porcine and poultry, two kinds of solid waters (SW): brown and white, and in 1% agarose gels variously doped with absorbing dye. Quantification was achieved through cumulative imaging of the samples placed in a light-tight chamber and during irradiation on a Varian 21 EX accelerator. Imaging required a specialised high-sensitivity cooled camera with UVA lenses and filters and careful geometric placement to minimise radiation noise.

Results: A 25% reduction in background noise was achieved by selective shielding of the camera. At 15MV, SW emitted 66 ± 5%, 64 ± 5% and 76 ± 3% less UVA than chicken, pork loin and pork belly respectively. Similar under-response was observed at 6MV. Brown SW had 21 ± 8% less UVA emission than white SW at 15MV, and no significant emission at 6MV. Agarose samples (1%) doped with 250ppm India Ink exhibited equivalent UVA CL emission to chicken breast (within 5%).

Conclusion: The results confirm that for the same absorbed dose, SW emits less UVA light than the tissue samples, indicating that prior in-vitro studies (utilizing SW as the CL-generating source) may have underestimated the RECA therapeutic effect. Agarose doped with 250ppm India Ink is a convenient tissue equivalent phantom for further work.


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