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Optical Characterization of Megavoltage-Radiation Responding Micro-Particles for X-Ray Psoralen Activated Cancer Therapy

S Yoon1*, Z Fathi2 , X Zhang3 , W Beyer2 , H Walder2, J Adamson4 , S Jain1 , M Oldham4 , (1) Duke University Medical Physics Program, Durham, NC, (2) Immunolight LLC, Detroit, Michigan, (3) Duke University Department of Radiology, Durham, North Carolina, (4) Duke University Medical Center, Durham, NC


(Sunday, 7/29/2018) 4:00 PM - 4:55 PM

Room: Davidson Ballroom A

Purpose: X-PACT is a paradigm-shifting treatment where an UV-sensitive anti-cancer drug, psoralen, is photo-activated from within tumors using x-ray-responding micro-particles emitting UVA light. X-PACT is currently limited to diagnostic kilovoltage (kV) x-ray energies, as these particles have not been observed to fluoresce under therapeutic megavoltage (MV) beams. To extend X-PACT utility to MV regime, several novel MV-responding, bio-compatible micro-particles were developed and tested for UVA emission.

Methods: Eight materials and a high-Zeff NaI scintillating control were plated onto two 6-well plates and placed on top of black aluminum foil. UVA emission of the particles and the control was characterized under (1) diagnostic (kV) energies and (2) therapeutic (MV) energies on Varian LINAC. Images were acquired with a high-sensitivity CCD camera equipped with a UVA bandpass filter (315-390nm). UVA emission per delivered patient dose (CCD counts per Gy), a key parameter in determining in-vivo effectiveness of the particles, was calculated under both kV and MV photons.

Results: UVA emission per patient dose was significantly reduced at MV versus kV x-ray energies (1.3 vs. 5.7%, at 6MV and 80kVp, respectively). At kV energies, tube voltage (60-150kVp) significantly affected UVA emission output per dose, varying from -20% to +70% at 150kVp versus 60kVp. Zeff of material may explain this phenomenon, as evidenced by high-Zeff control NaI (+130%) and copper-doped particles (+66%, +50%). At MV energies, most materials decreased in output at 15MV versus at 6MV, though addition of copper seemed to reverse this trend.

Conclusion: Micro-particles scintillated under MV, although emission per dose was lower than at kV. Despite this, MV-responding particles show potential for clinical use, as excessive skin dose at kV energies limit radiation dose that can be safely delivered per fraction compared to MV radiation. Future experiments will be conducted to test in-vivo efficacy of these micro-particles under MV energies.

Funding Support, Disclosures, and Conflict of Interest: Dr. Adamson reports ownership in Clearsight RT LLC, which is not related to this study. Dr. Beyer and Dr. Fathi reports ownership in Immunolight LLC, which provided materials studied in the abstract but was not involved in analysis.


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