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LET Painting Through Proton Mono-Energetic Arc Therapy (PMAT) to Enhance Radiobiological Effectiveness

A Bertolet*, A Carabe, Hospital of the University of Pennsylvania, Philadelphia, PA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: A new treatment planning technique in proton therapy, called Proton Monoenergetic Arc Therapy (PMAT), is proposed as a method to enhance the biological effectiveness of proton therapy and potentially the indications for proton therapy.

Methods: A PMAT complete arc is composed of monoenergetic sub-arcs, whose length, position and energy are selected by an algorithm that computes the water-equivalent depths (WED) of the target from each angular control point, separated by 1 deg in this work. This algorithm recursively selects the longest consecutive sub-arc with target points within the interval from 50% to 60% of the difference between minimum and maximum WED from each control point. An in-house inverse optimization is used together with dose constraints for target and organs at risk (OARs) to produce clinically acceptable plans. We show here the dosimetric performance of PMAT applied to various sites, such as prostate, brain or H&N.

Results: PMAT produces comparable dose distributions to the CTV to IMPT plans for the three considered cases/sites. As expected, the resulting distributions for LETd contain higher values in the CTVs than in the rest of considered structures. RBE calculations according to different models show a clear enhance of biological effectiveness for PMAT plans with respect to IMPT.

Conclusion: PMAT naturally increases LETd within the target, leading to a potential enhancement of the biological dose and, subsequently, of the tumor control probability (TCP). This opens the door to possible dose de-escalation towards a lower NTCP while maintaining the same biological effectiveness of the plan due to a redistribution of higher LET to the high-dose volume of the plan. The simultaneous decrease of LETd in OARs may also enable dose escalation to increase TCP while controlling NTCP.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by Varian Medical Systems, Palo Alto, California, USA


Protons, LET, RBE


TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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