  Background and Objective: Recent experimental studies using ultra-high dose
rate radiation therapy (FLASH-RT) have shown improved normal tissue sparing and
comparable tumor control compared to conventional dose rate RT. Pencil beam
scanning (PBS) proton therapy with superior dosimetry characteristics has begun
to draw attention to the delivery of conformal FLASH-RT for preclinical
studies. This review aims to provide recent updates on the development of PBS
FLASH-RT. Methods: The information summarized in this review article is based
on search results in databases such as PubMed and search engines like Google
Scholar, with keywords including pencil beam scanning, proton therapy, proton
FLASH, Bragg peak FLASH, etc., with English articles from the year of
2014-2022. Content and Findings: This review summarizes of recent developments
in PBS FLASH proton therapy (FLASH-PT), including PBS dose rate
characterization, current delivery limitations, treatment planning, and
biological investigations. Conclusions: As PBS FLASH delivery has enabled
successful biological studies using transmission beams, the further improvement
in PBS Bragg peak FLASH technologies will result in more advanced treatment
plans associated with potentially improved outcomes.
