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Monte Carlo Study of a Novel Compensator for IMRT in Low and Middle Income Countries

D Toomeh1*, S Gadoue2 , N Fong1 , G Subrahmanyam3 , M Tamilarasan3 , K Govindarajan4 , E Ford1 , (1) University of Washington, Seattle, WA, (2) Loma Linda University Medical Center, Loma Linda, CA, (3) Panacea Medical Technologies, Bangalore, India, (4) PSG Hospital, Coimbatore, India


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: A novel cost-effective compensator is being developed to provide Intensity- Modulated Radiation Therapy (IMRT) in low and middle income countries. The compensator has advantages of cost-effectiveness, less downtime and repairs, increased reliability and less impact of patient motion during treatment. The system can be used with either a linear accelerator or Cobalt beam. Here we present a Monte Carlo study of the compensator design.

Methods: Simulations were performed with Geant4 10.4 software package for a Cobalt teletherapy machine 2x2cm source with field size 35 cm × 35 cm at 80 cm SAD. The compensator is a PMMA shell whose shape is designed to provide patient-specific fluence modulation. The shell is filled with attenuating material, nominally tungsten beads (diameter 0.5 cm), before each treatment and then emptied afterward so the beads can be re-used from patient to patient. We simulated three cases: a compensator filled with 0.5 cm beads, a compensator made of solid material and open- air (no compensator). The dose was scored in a plane 2.8 cm deep in water phantom under the compensator.

Results: Beam profiles show that the beads have a decreased attenuation compared to solid compensators as expected (factor of 1.55 in tungsten). Additionally there was no obvious signature of the beads in the beam profiles (relative to a solid compensator) even for the relatively large bead diameter of 0.5 cm. Simulations are ongoing to explore the impact of compensator material and formulation on IMRT modulation.

Conclusion: A reusable bead compensator appears to be feasible and provides a dose distribution that is similar to solid compensator material. This motivates further simulation and development of the reusable bead compensator. This will provide a cost-effective IMRT solution for low- and middle-income countries and will allow IMRT with standard Cobalt teletherapy machines for the first time.


Compensators, Monte Carlo, Intensity Modulation


TH- External beam- photons: dose computation engines- Monte Carlo

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