Click here to

Session: Therapy External Beam Radiotherapy - Guidance and Delivery Techniques [Return to Session]

Dosimetric Delivery Validation of Dynamically Collimated Pencil Beam Scanning Proton Therapy

N Nelson1*, W Culberson1, D Hyer2, T Geoghegan2, K Patwardhan2, B Smith2, R Flynn2, J Yu3, A Gutierrez3, P Hill4, (1) University of Wisconsin - Madison, School of Medicine and Public Health, Department of Medical Physics, Madison, WI, USA, (2) University of Iowa, Department of Radiation Oncology, Iowa City, IA, USA, (3) Miami Cancer Institute, Department of Radiation Oncology, Miami, FL, USA, (4) University of Wisconsin - Madison, School of Medicine and Public Health, Department of Human Oncology, Madison, WI, USA


WE-C1000-IePD-F3-5 (Wednesday, 7/13/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To experimentally validate the penumbra sharpening associated with the Dynamic Collimation System (DCS) mounted to the IBA PBS-dedicated nozzle (DN) system through radiochromic film and ionization chamber array measurements.

Methods: A set of uncollimated and DCS-collimated treatments were planned and optimized using a TOPAS Monte Carlo model of the DCS and IBA DN system for 3x3x3 cm3 cubic targets centered at depths of 5, 6, 10, and 15 cm. A special case was studied where the 5 cm target depth was delivered using an external range shifter. Two-dimensional planar dose measurements were performed in water using a DigiPhant PT equipped with either a MatriXX ionization chamber array or a custom-built EBT3 film holder at the center of the spread-out Bragg peak (SOBP). Additional measurements were performed proximal to the SOBP for the deepest target depth to benchmark the expected increase in surface dose resulting from collimation.

Results: For the non-range shifted plans, penumbra reductions (measured as the distance between the 80% and 20% isodose lines) with the DCS ranged from 33% to 64% as the depth of the target decreases. For the range shifted plan, the penumbra was reduced by nearly 50%. MatriXX and film-measured penumbra widths agreed with Monte Carlo to within 0.6 mm for an uncollimated delivery. These differences increased to 0.8 mm and 1.1 mm for film and the MatriXX, respectively, when collimated by the DCS. The high intrinsic resolution of film allowed for the most accurate characterization of penumbral width for the collimated cases.

Conclusion: A combination of Monte Carlo simulations, radiochromic film and ionization chamber measurements were used to benchmark the expected penumbra sharpening associated with the DCS. Overall, excellent agreement was observed between Monte Carlo simulations and measurements.

Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R37CA226518. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.


Dosimetry, Collimation, Protons


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

Contact Email