Application of the UF Computational Phantoms for Operational Health Physics Dosimetry for NASA

Size: px

Start display at page:

Download "Application of the UF Computational Phantoms for Operational Health Physics Dosimetry for NASA"

Elijah Wilkins
5 years ago
Views:

1 Application of the UF Computational Phantoms for Operational Health Physics Dosimetry for NASA FCHPS & FLAAPM 2015 Fall Meeting November 13 th, 2015 Michelle Sands, M.S. University of Florida

Projection of astronaut risk due to radiation must be evaluated for each proposed mission.

2 Introduction One of the hazards faced by crews of spacecraft in low-earth orbit or in deep space is exposure to ionizing radiation. Projection of astronaut risk due to radiation must be evaluated for each proposed mission. Work done at UF by Dr. Amir Bahadori showed: Differences in whole body risk estimates due to body size variation are small for GCR Large differences for solar particle events

3 Introduction Desirable to use accurate computational phantoms representing each astronaut Increase in accuracy for risk estimates The UF Hybrid Adult Phantoms are wellsuited for manual adjustments NASA Space Radiation Analysis group (SRAG) desired an automated alteration program to morph the body of a UF phantom to that of an astronaut UF Reference Male

4 Goals Develop an auto-scaling algorithm Morph a UF/NCI hybrid computational reference phantom to the outer body contour of an astronaut. Test the auto-scaling algorithm using a cohort of 14 patient CT image sets (7 male/7 female) Perform dosimetry studies for different historical solar particle events.

5 Benefits of Auto-Scaling Provides a more individualized phantom without segmenting Auto-scaling is a quick process Organ dose estimates were expected to increase in accuracy for an auto-scaled phantom when compared to a height and weight matched library phantom.

6 Auto-Scaling Process Uses RhinoPython scripting language Requirements: A polygon mesh surface i.e. a laser measured mesh of astronauts outer body contour UF/NCI adult reference computational phantom

7 Auto-Scaling Process User is instructed to provide anatomical measurements to be used at datum points for the following anatomy: Bicep Forearm Upper Chest (bust) Lower Chest Wait Hip Thigh Calf

8 Patient Specific Fused Phantoms Using a cohort of 14 patient CT image sets Segment organs of interest Organs which are major contributors to risk Organs that have deterministic limits CT exams lack head, arms, and legs of patient A height and weight matched phantom will provide missing anatomy to create a fused phantom

9 Patient Specific Fused Phantoms + =

10 Auto-Scaled Phantom Auto-Scaled phantom created with outer body contour of fused phantom Same polygon mesh surface as NASA laser scanned astronaut outer body contour

11 Auto-Scaling Code Example

12 Auto-Scaling Code Example - Male

13 Auto-Scaling Code Example - Female

14 Dosimetry Monte Carlo radiation transport using PHITS 2.64 Dosimetry goals: Compare the auto-scaled phantom and the patient specific fused phantom organ doses Compare the height and weight matched phantom and the patient specific fused phantom organ doses Compare the dosimetric accuracy that the autoscaled phantom provides over matched phantom

15 Dosimetry Geometry Phantom placed in an aluminum shell Isotropic proton source Monoenergetic 7MeV to 2500 MeV 72 energies Aluminum vehicle shielding 5 g/cm 2 10 g/cm 2 20g/cm 2

16 Dose Calculations Obtain Integral fluence spectrum for a solar particle event (provided by NASA) Differentiate the spectrum Differential Flux Spectrum for August 1972 SPE

17 Dose Calculations Run transport with PHITS for each energy on chosen grid Integrate (differentiated integral spectrum * dose) over all monoenergetic energies. Note: 10g/cm 2 aluminum shielding thickness.

18 Results Organ doses (in Gy) were calculated for 14 patients: Autoscaled Fused Matched Organ dose comparison metric: P1= percent difference between matched and fused phantom organ dose P2= percent difference between autoscaled and fused phantom organ dose P1 - P2 Positive value indicated autoscaled phantom was more accurate Negative value indicates matched phantom was more accurate

19 Dosimetry Results - Males

20 Results - Males

21 Results - Females

22 Conclusions The autoscaled phantoms did not show significant increase in patient organ dose accuracy when compared to a height and weight matched phantom. Increasing patient population would be needed for more conclusive results. It can be concluded, however, that the autoscale program performed just as well as a height and weight matched phantom therefore being a viable replacement if the UF/NCI phantom library is not available. May also have applications in other fields such as medicine

23 Acknowledgments University of Florida ALRADS Dr. Matthew Maynard David Borrego, MS Elliott Stepusin, MS Dr. Wesley Bolch Space Radiation Analysis Group NASA Johnson Space Center Dr. Amir Bahadori Funding Source NASA Bioastronautics Contract NAS

Space Radiation Risks for Long. Duration Missions Edward Semones

Space Radiation Risks for Long Duration Missions Edward Semones Radiation Health Officer Space Life Sciences Directorate Johnson Space Center Presented to the American Astronautical Society November 16,