Recent Progress in Pencil Beam Scanning FLASH Proton Therapy: A Narrative Review

Abstract: 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.