Radiobiological effects of altering dose rate in filter-free photon beams

Area of Science:

• Radiation Oncology
• Cell Biology
• Medical Physics

Background:

• Radiotherapy treatment time can be reduced by increasing the dose rate.
• The effect of altered dose rates on cell survival requires further investigation.

Purpose of the Study:

• To validate if changing radiotherapy dose rate affects cell survival.
• To compare filtered and filter-free beam delivery modes.
• To assess the impact of dose protraction on cell survival.

Main Methods:

• Irradiation of human carcinoma and hamster lung cell lines using a Varian TrueBeam linac in flattening filter-free mode.
• Experiments involved varying pulse repetition frequency and instantaneous dose rate.
• Analysis of DNA double-strand breaks using the γH2AX assay.

Main Results:

• Altering dose rate by changing pulse repetition frequency or instantaneous dose rate had no effect on cell survival.
• No difference in cell survival was observed between filtered and filter-free beam delivery during protracted dose delivery.
• Protracted dose delivery (15, 30, or 60 min) increased cell survival compared to acute delivery in both filtered and filter-free modes.
• The γH2AX assay showed no difference in DNA double-strand breaks between filtered and unfiltered beams.

Conclusions:

• Increasing radiotherapy dose rate is an acceptable method to decrease treatment time.
• Altering dose rate does not detrimentally affect in vitro cell eradication.
• Filtered and filter-free beam delivery show comparable results in protracted dose schemes.