Table 3.
Some relevant advantages and disadvantages of current and prospective FLASH radiotherapy sources (color coded by radiation modality).
| Radiation source | Modality of radiation | Advantages (+) | Disadvantages (–) | Currently available for FLASH-RT clinical studies, with which main limitations? |
|---|---|---|---|---|
| Conventional electron linear accelerator (10, 14, 66, 67) | 1–25 MeV Electrons | Inexpensive. Minor beam size limitation. |
Poor depth penetration. Wide penumbra. |
Yes, Limited to treating superficial tumors. |
| Very High Energy Electron linear accelerator (68, 69) or Laser plasma accelerators (70, 71) | 100–250 MeV Electrons | Good depth penetration. Electromagnetic steering and focusing. Not sensitive to tissue heterogeneity. |
Low pulse rate (1–10 Hz) for Laser plasma accelerators. Limited beam size. |
No |
| Laser plasma accelerators (75) | 1–45 MeV Protons | Compact design possible. Electromagnetic steering possible. |
Poor depth penetration. Low pulse rate (1–10 Hz). Very sensitive to tissue. heterogeneity. Higher LET in Bragg peak. Beam contamination. Stability issues. Limited beam size. |
No |
| Cyclotrons, synchrotrons or Synchrocyclotron (11, 76) | 100–250 MeV Protons | Good depth penetration. Electromagnetic steering possible. Limited dose-bath. Electromagnetic steering. |
Large expensive sources. Sensitive to tissue heterogeneity. Higher LET in Bragg peak. Beam scanning or scattering required to cover target volumes |
Yes, FLASH effect might be lost with beam scanning and/or higher LET. |
| X-ray tube (72) | 50–250 keV X-rays | Inexpensive. Compact design. |
Very limited depth penetration. Limited beam size. High entrance dose. |
Yes, Limited to treating small and very superficial tumors. |
| Synchrotron (24, 32) | 50–600 keV X-rays | Microbeam Radiation Therapy possible. | Very large. Very expensive. Limited depth penetration. Very limited availability. Limited beam size requires scanning of sample/target. |
Yes, Very limited availability. |
| Electron linear accelerator with high density target (20) | 6–10 MV X-rays | Good depth penetration. Narrow penumbra. Minor beam size limitation. |
Multiple beam angles required. | No |