Roundtable Discussion on 15^th November 2000

Risk Assessment Conference (12 – 15 November), Houston, Texas:

 

Moderator:  Dr. Walter Schimmerling

Round Table Participants:  Dr. Fornace, Dr. Dudley, Dr. Groer, and Dr. Cucinotta

Attendance:  About 50 invited guests and participants at the conference

 

Selected comments (paraphrased):

Dr. Fornace:

 

• Sensitivity – it is dependant on several individual variations
  • At NCIH there exists about 60 med cell lines with biomarkers being developed
• Gene – cancer causation
  • Linear dose response and almost no threshold
  • Chip survey mostly monitored in serum (may not be DNA)
• High LET response is roughly proportional to RBE
• Phenomenological intervention is not clear at this time

 

Dr. Dudley:

 

• We do have very large uncertainties for low level effects
• There exists evidences that even one single electron can cause DNA break or damage to DNA
• Perhaps we may not have cancer risk for low energy particles
• High LET:
  • Evidences of its effects are much stronger
  • Effect of carcinogenesis is much stronger
  • No level can be safe
• Uncertainties are not due to the process we adopted
  • One level could be zero (no risk)
  • Other level is the natural cancer mortality
• High LET we do not have such possibilities
  • Q (quality factors) are not certain
  • RBE values have large variations between tumor types (this is expected)
  • Any study that employs the quality factor (Q) increases risk
• Very few studies can get expected high LET tracks
• Large uncertainties are the concerns to be dealt with

 

 

Dr. Groer:

 

“I prepared my sermon a while ago and now the parish changed”

• Part-1:  How to interpolate and extrapolate when human data is available
• Part-2:  How to interpret when no human data is available
• Part-1:  When human data is available
  • Not to try models at cellular level. Reasons – Atomic Bomb data simply turns out to be percentages and estimations
  • There exists an Italian saying that can help us “probability to be used for uncertainties”
  • Artificial Intelligence (AI) switched to probability and probability distributions
  • “May be we are suffering from the sins of the past”
  • Do not extract data from one to other (threshold / non-threshold)
  • Ex. Leukemia / Lung Cancer:  Leukemia is interlinked with other processes in the body.  How can we deal with it independently
  • “Statistical assessment is based on independent nature, in reality, which is not”
  • Sanity check = always to check with fundamental biology
  • “Modeling is the art of knowing what to neglect”

 

·        Part – 2: When no human data is available

o       A “pivotal” data set is needed

o       A “target data” set is needed

o       A “target population” is needed

o       How best we can address the Ra to Pu extrapolation

o       From animal studies, the time-scale is totally different how can we extrapolate or interpret from this.

 

Dr. Cucinotta:

 

• Astronaut Training:
  • To inform and to educate all the crew members
  • It may not be possible to get every crewmember trained and informed as desired due to schedule conflicts and other constraints.
• ALARA:
  • Specifications of the needed radiation limits with the ALARA principle
  • Cost benefit evaluation for mission scenario and success
• Role of Individuals in Radiation Protection:
  • Risks are mostly for late effects and there can exist a temptation to underplay importance in short-term because of limitations on funds, time, resources, etc.
  • Mechanism exist for external review and prioritization, however individuals often play crucial role
  • Effectiveness of Program Managers to Argue for Research Dollars within Agencies, etc. is often crucial
  • Committee Members, for e.g. on ICRP and NCRP make critical argument to other members, boards etc. to make changes.

 

 

 

= Prem Saganti

With Dr. Frank Cucinotta

Space Radiation Health Project at NASA-JSC