Preclinical studies with the photon radiosurgery system (PRS).

Area of Science:

• Medical physics
• Radiation oncology
• Radiobiology

Background:

• The Photon Radiosurgery System (PRS) utilizes low-energy X-rays (average 23 KeV).
• Radiobiological effectiveness (RBE) is crucial for optimizing radiation therapy efficacy.
• Understanding RBE variations with different X-ray energies and depths is essential for treatment planning.

Purpose of the Study:

• To determine the radiobiological effectiveness (RBE) of low-energy X-rays generated by the Photon Radiosurgery System (PRS).
• To compare the RBE of PRS-generated X-rays with conventional X-ray and high-energy photon sources.
• To investigate the influence of cell survival and depth on the RBE of PRS X-rays.

Main Methods:

• Cell survival data from Chinese hamster ovary (CHO), human U373, and T98 glioblastoma cells were used.
• Cells were irradiated with PRS low-energy X-rays, GE Maxitron 100 low-energy X-rays, and Varian 6 MV LINAC high-energy photons.
• Ionization chambers calibrated with 50 kVp X-rays were used to determine and cross-check radiation output and dose rates.

Main Results:

• The RBE for PRS low-energy X-rays was consistently higher than for GE or Varian sources across different cell types and survival levels.
• For CHO cells, PRS RBE was 1.25-3.3 times greater than 90 kVp X-rays and 1.2-1.9 times greater than 6 MeV photons at varying survival rates.
• RBE values increased with depth for the PRS source, with higher RBE observed at 4-mm compared to 1-mm depth.

Conclusions:

• The biological and physical characteristics of PRS low-energy X-rays demonstrate a significant therapeutic potential.
• Under specific conditions, PRS offers an advantage over conventional external beam, stereotactic, or brachytherapy treatments.
• Further research into PRS applications may lead to improved patient outcomes in radiation oncology.