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  5. Nanoparticle-Enhanced Focused KV X-Ray Radiotherapy for Ocular Tumor Treatment: A Proof-Of-Concept Study

Nanoparticle-Enhanced Focused KV X-Ray Radiotherapy for Ocular Tumor Treatment: A Proof-Of-Concept Study

H Yan1, 2 , X Ma1 , W Sun3 , S Mendez4 , S Stryker5 , Z Chen2 , R Nath2 , C MacDonald3 , W Liu2* , (1) Capital Medical University, Beijing, China, (2) Yale university School of Medicine, New Haven, CT,(3) University at Albany, State University of New York, Albany, NY, (4) Fairfield University, Fairfield, CT, (5) Duke University, Durham, NC

Presentations

(Tuesday, 7/31/2018) 4:30 PM - 6:00 PM

Room: Davidson Ballroom A

Purpose: To develop and evaluate a novel nanoparticle (NP)-enhanced focused kV X-ray technique in treating small tumors near critical structures, such as intraocular melanomas.

Methods: A polycapillary X-ray lens was used to focus 45-kVp X-ray beams to achieve pinpoint accuracy of dose delivery to shallow tumors. The use of kV energy facilitates more efficient metallic NP radiosensitization due to the photoelectric effect. Comprehensive phantom measurements were carried out to verify our developed Geant4-based Monte Carlo dose calculation program. Treatments of choroidal and iris melanomas were simulated with and without Gold NP radiosensitization. To reduce cornea/lens dose, a novel strategy of replacing the vitreous humor with gas was also simulated for the treatment of posterior intraocular tumors.

Results: The simulated FWHM and central-axis depth dose of the focused kV X-ray beam match the measurements within ~10% around the depth of focus of the beam. The depth dose, with a peak at depth in tissue, is very different from conventional MV/kV beam depth dose. The simulated ocular tumor treatments show that scanning focused X-ray beams can concentrate high dose to the tumor while keeping low dose to the critical organs. Compared to the standard eye plaque brachytherapy, for the simulated posterior choroidal tumor treatment with sufficient tumor coverage, the doses to the optic disc and fovea are significantly lower even without NP sensitization (3.9 vs 39.8 Gy and 19.2 vs 53.8 Gy, respectively). For the energy spectrum used in this study, the average dose enhancement ratios (DERs) are 2.08 and 1.12 for 1.0% and 0.1% Gold NP mass concentration in tumor, respectively. Replacing the vitreous humor with air reduced the average doses to the cornea/lens from 41.1/45.3 Gy to 23.3/24.3 Gy.

Conclusion: The proposed non-invasive focused kV X-ray technique shows significant advantage in sparing healthy critical organs without sacrificing the tumor control.

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