EDU 39 - Linear Energy Transfer (LET) and Relative Biological Effectiveness (RBE) in Proton Therapy - Controversies and Gaps in Knowledge

Moderator(s)

• 

  Charles Simone, MD, FASTRO

  New York Proton Center and Memorial Sloan Kettering Cancer Center
  New York, NY, United States
• YX

  Ying Xiao, PhD, FASTRO, DABR

  University of Pennsylvania
  Philadelphia, PA

Despite dosimetric benefits, pencil beam scanning (PBS) proton therapy poses many challenges. Among them, relative biological effectiveness (RBE) is a major one. The biological dose of proton therapy is not only related to its physical dose, but also highly dependent on average energy loss per unit distance travelled by protons, i.e., linear-energy transfer (LET). Recently, the TG-256 report suggested assessing potential clinical consequences based on LET in proton therapy.

Despite numerous in vitro and in vivo studies that have been performed, it is unclear whether the derived RBE models are applicable to clinical patient outcomes. Clinical investigations have so far shown noninformative results regarding the impact of LET on patient outcomes. As the number of cancer patients treated with PBS grows worldwide, and as dosimetric evaluation of LET/RBE is implemented in proton centers, more LET/RBE-related patient outcome studies are being reported. It is, therefore, important for us to learn from these reported results to help guide and improve clinical PBS proton therapy practice. In this session, we will first review recent studies that correlate clinical outcomes as the endpoints with dosimetric parameters. We will then discuss the limitations of the reported results and the consequences of such limitations followed by a discussion on what needs to be done further to advance the state of the art. Finally, we will discuss how this new knowledge and the derived models can be translated into clinics. We will use this opportunity to raise awareness of the importance of LET/RBE in the proton community.

Presentations:

• 12:45 PM – 12:47 PM ET

  Introductions
  

  Speaker: Ying Xiao, PhD, FASTRO, DABR – University of Pennsylvania
• 12:47 PM – 1:07 PM ET

  Clinical Evidence for Higher RBEs and Opportunities for Improving Proton Therapy Treatments
  

  Speaker: Charles Simone, MD, FASTRO – New York Proton Center and Memorial Sloan Kettering Cancer Center
• 1:07 PM – 1:27 PM ET

  Laboratory RBE versus Clinical RBE in Proton Therapy
  

  Speaker: Harald Paganetti, PhD – Massachusetts General Hospital
• 1:27 PM – 1:47 PM ET

  Dose Linear-Energy-Transfer Volume Histogram and Dosimetric Seed Spot Analysis in Spot-Scanning Proton Therapy
  

  Speaker: Wei Liu, PhD, MS, BS, FAAPM – Mayo Clinic
• 1:47 PM – 2:00 PM ET

  Questions and Answers
  

  Speaker: Charles Simone, MD, FASTRO – New York Proton Center and Memorial Sloan Kettering Cancer Center