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    University - Student Department: Rad/Radiological Sciences Laboratory Position: Graduate

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  • Mail Code: 5488

All Publications

  • Emerging FLASH therapy platforms for stereotactic radiosurgery and body radiotherapy. Journal of radiosurgery and SBRT Chen, D., Schulz, J. B., Melemenidis, S., Skinner, L., Xing, L., Loo, B. W., Ashraf, M. R. 2026; 10 (1-2): 101-121

    Abstract

    The integration of FLASH radiotherapy with stereotactic techniques presents a promising avenue for improving therapeutic outcomes through normal tissue sparing while maintaining tumor control. However, significant technical challenges must be addressed for successful clinical implementation. This review evaluates emerging platforms and technical requirements for combining FLASH delivery with stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). While electrons have enabled extensive preclinical FLASH research, their limited penetration depth makes them unsuitable for most stereotactic applications. Photon-based systems face significant engineering challenges in achieving both FLASH dose rates (>40 Gy/s) and the beam characteristics necessary for stereotactic delivery, particularly regarding heat management and multi-angle treatment capabilities. Proton and heavy ion systems offer advantages through the Bragg peak but require substantial development to overcome technical limitations in beam delivery and scanning speeds. We evaluate emerging platforms including novel accelerator designs, beam monitoring systems, and delivery techniques aimed at clinical translation. Critical technical requirements are discussed, including specialized dosimetry systems capable of ultra-high dose rate measurements, quality assurance protocols, treatment planning systems that optimize both spatial and temporal aspects of delivery, and novel image guidance strategies.

    View details for DOI 10.1177/0146645319893605

    View details for PubMedID 42004842

    View details for PubMedCentralID PMC13007232

  • FLASH reduces radiation-induced oral mucositis in a mouse model of Fanconi anemia Loo, P., Pan, M., Zhao, M., Melemenidis, S., Chen, D., Casey, K. M., Epperly, M., Greenberger, J. S., Loo, B. W., Rankin, E. AMER ASSOC CANCER RESEARCH. 2026

    View details for DOI 10.1158/1538-7445.AM2026-7192

    View details for Web of Science ID 001734467000021

  • Multi -Institutional Standardized Dosimetry Protocol for Preclinical Radiobiological Experiments Melemenidis, S., Ashraf, R. M., Chen, D., Liu, K., Velasquez, B. D., Connell, L., Schulz, J. B., Duff, S., Katila, N., Flores, K. Z., Schueler, E., Loo, B. W. ELSEVIER SCIENCE INC. 2024: S21-S22

    View details for Web of Science ID 001325892302481

  • Secondary neutron dosimetry for conformal FLASH proton therapy MEDICAL PHYSICS Chen, D., Motlagh, S., Stappen, F., Labarbe, R., Bell, B., Kim, M., Teo, B., Dong, L., Zou, W., Diffenderfer, E. 2024

    Abstract

    Cyclotron-based proton therapy systems utilize the highest proton energies to achieve an ultra-high dose rate (UHDR) for FLASH radiotherapy. The deep-penetrating range associated with this high energy can be modulated by inserting a uniform plate of proton-stopping material, known as a range shifter, in the beam path at the nozzle to bring the Bragg peak within the target while ensuring high proton transport efficiency for UHDR. Aluminum has been recently proposed as a range shifter material mainly due to its high compactness and its mechanical properties. A possible drawback lies in the fact that aluminum has a larger cross-section of producing secondary neutrons compared to conventional plastic range shifters. Accordingly, an increase in secondary neutron contamination was expected during the delivery of range-modulated FLASH proton therapy, potentially heightening neutron-induced carcinogenic risks to the patient.We conducted neutron dosimetry using simulations and measurements to evaluate excess dose due to neutron exposure during UHDR proton irradiation with aluminum range shifters compared to plastic range shifters.Monte Carlo simulations in TOPAS were performed to investigate the secondary neutron production characteristics with aluminum range shifter during 225 MeV single-spot proton irradiation. The computational results were validated against measurements with a pair of ionization chambers in an out-of-field region ( ≤ $\le$ 30 cm) and with a Proton Recoil Scintillator-Los Alamos rem meter in a far-out-of-field region (0.5-2.5 m). The assessments were repeated with solid water slabs as a surrogate for the conventional range shifter material to evaluate the impact of aluminum on neutron yield. The results were compared with the International Electrotechnical Commission (IEC) standards to evaluate the clinical acceptance of the secondary neutron yield.For a range modulation up to 26 cm in water, the maximum simulated and measured values of out-of-field secondary neutron dose equivalent per therapeutic dose with aluminum range shifter were found to be ( 0.57 ± 0.02 ) mSv/Gy $(0.57\pm 0.02)\ \text{mSv/Gy}$ and ( 0.46 ± 0.04 ) mSv/Gy $(0.46\pm 0.04)\ \text{mSv/Gy}$ , respectively, overall higher than the solid water cases (simulation: ( 0.332 ± 0.003 ) mSv/Gy $(0.332\pm 0.003)\ \text{mSv/Gy}$ ; measurement: ( 0.33 ± 0.03 ) mSv/Gy $(0.33\pm 0.03)\ \text{mSv/Gy}$ ). The maximum far out-of-field secondary neutron dose equivalent was found to be ( 8.8 ± 0.5 $8.8 \pm 0.5$ )  μ Sv / Gy $\umu {\rm Sv/Gy}$ and ( 1.62 ± 0.02 $1.62 \pm 0.02$ )  μ Sv / Gy $\umu {\rm Sv/Gy}$ for the simulations and rem meter measurements, respectively, also higher than the solid water counterparts (simulation: ( 3.3 ± 0.3 $3.3 \pm 0.3$ )  μ Sv / Gy $\umu {\rm Sv/Gy}$ ; measurement: ( 0.63 ± 0.03 $0.63 \pm 0.03$ )  μ Sv / Gy $\umu {\rm Sv/Gy}$ ).We conducted simulations and measurements of secondary neutron production under proton irradiation at FLASH energy with range shifters. We found that the secondary neutron yield increased when using aluminum range shifters compared to conventional materials while remaining well below the non-primary radiation limit constrained by the IEC regulations.

    View details for DOI 10.1002/mp.17050

    View details for Web of Science ID 001199495500001

    View details for PubMedID 38597815

  • Characterization of a Spatially resolved multi-element laser ablation ion source INTERNATIONAL JOURNAL OF MASS SPECTROMETRY Murray, K., Chambers, C., Chen, D., Feng, Z., Fraser, J., Ito, Y., Lan, Y., Mendez, S., Rasiwala, H., Richez, L., Roy, N., Simpson, R., Dilling, J., Kwiatkowski, A. A., Brunner, T., Peregrina, M., Fairbank, W. 2022; 472

    View details for DOI 10.1016/j.ijms.2021.116763

    View details for Web of Science ID 000788826700008