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Did Proton High Linear-Energy Transfer (LET) Cause the Strange Smell During Cranial-Spinal Irradiation?

Z Su*, W Hsi, M Artz, D Indelicato, Radiation Oncology, University of Florida, Gainesville, FL and University Florida Health Proton Radiotherapy Institute, Jacksonville, FL,

Presentations

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

Room: AAPM ePoster Library

Purpose:
To investigate the LET distribution differences of pediatric proton cranial irradiation plans using either posterior-anterior (PA) beam or two lateral beams. To evaluate the LET distribution inside the olfactory bulbs and nerves of patient with different ages for smell correlation.


Methods:
As a pediatric patient growing up, their olfactory nerves grow further away from their brain volumes. A 6 years old and a 10 years old patients were selected retrospectively for proton IMPT planning with both PA and lateral beam techniques in cranial-spinal treatment of medulloblastoma. High LET to the olfactory nerves may correlate to a strange smell sensation. Large proton spot (5-12mm sigma) nozzle were used for the plan generation. Optimization objectives were kept the same for both plans with a prescription of 23.4 Cobalt-Gray-Equivalent (CGE). Energy layer spacing, spot spacing and target margins were kept the same for all plans. Range shifter (7.4cm water-equivalent thickness) were used with 4cm beam air gaps. Monte-Carlo dose engine was used for optimizations and dose calculations. All plans were re-scaled to the prescribe dose covering 95% of the PTV brain. LET volume histogram for olfactory bulb and nerves were calculated and compared between the two planning techniques.

Results:
For the 6 year old patient, olfactory bulb LET volume was higher in lateral beam plan than that of PA beam plan for a given level of LET; olfactory nerve volume at 3.4keV/micrometer or greater was higher in the PA plan. For the 10 year old patient, olfactory bulb and nerves LET volumes were higher in PA beam plan than that of lateral beam plan.

Conclusion:
LET to the olfactory nerves were higher in the PA beam plan than that of lateral beams, especially for the older child. This potentially support the correlation of high LET to strange smell sensation in pediatric patients.

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Keywords

LET, Protons, Dose Volume Histograms

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – computational dosimetry-Monte Carlo

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