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Practicality of Pyroelectric X-Ray Sources for Grenz and Conventional Radiotherapy

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M Klopfer

M Klopfer*, V Satchouk, Y Alivov, S Molloi, University of California, Irvine, CA

SU-E-T-344 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Pyroelectric crystals can be used as a compact and low cost source for electrons and high energy photons. Only periodic heating cycles are required for energy input. In this study we examine the performance of a simulated pyroelectric x-ray source in delivering a single 2Gy dose fraction for soft x-ray (Grenz) and dermatological conventional x-ray radiotherapy. Grenz radiotherapy applications include the treatment of persistent dermatitis and psoriasis.

Methods: Dose delivery was calculated as the energy deposited per photon in soft tissue for a monoenergetic x-ray source with a beam area of 1.0cm². Monoenergetic x-ray photon energies between 1 and 30keV were plotted for delivered tissue dose between 1 and 3mm tissue depth in 100 micron volume recording elements. From prior experimentation 5x10^13 electrons emitted are assumed to be converted to 5.84x10^10 photons per pyroelectric crystal heating cycle. Absorbed photons are assumed to deliver full energy dose upon absorption. Delivered volume element dose, average dose, heating cycles per fractional dose, and energy absorption efficiency are used as metrics for application performance.

Results: Delivered photons between 8-15KeV produced the lowest number of cycles for delivered doses to 2 and 3mm tissue depth. At 10keV a 2Gy fractional dose can be delivered at 2mm depth in 11 heating cycles. At energies below 6keV, nearly 100% energy deposition occurs within 1mm, and the dose is delivered to shallow to cover treatment volume depth. Above 15keV, dose delivery efficiency decreases, requiring 106 cycles at 80keV to deliver 2Gy at 3mm.

Conclusions: Further study in device design will seek to maximize pyroelectric output x-ray flux, decrease cycle time, and increase treatment coverage area using tiled sources. With decreased cycle times and increased flux, pyroelectric sources can be practical for photon radiotherapy applications.

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