R Kueng*¹, S Mueller¹, H A Loebner¹, D Frei¹, W Volken¹, D M Aebersold¹, M F M Stampanoni², M K Fix¹, P Manser¹, (1) Inselspital, Bern University Hospital, and University of Bern, Bern, CH, (2) ETH Zurich and PSI, Villigen, CH

• 
  R Kueng

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

Room: AAPM ePoster Library

Purpose:
To develop Triple Beam radiotherapy (TriB-RT) with a new Monte Carlo (MC) based treatment planning process (TPP) enabling the simultaneous optimization of modulated photon, electron and proton beams for improved treatment plan quality in radiotherapy.

Methods:
A framework for simultaneous optimization of MC calculated beamlet dose distributions is developed to generate treatment plans consisting of modulated photon, electron and spot scanning proton fields. Fluence map optimization using a quasi-Newton L-BFGS algorithm is used to optimize the respective beamlet weights. A TriB-RT plan is generated for an exemplary academic case and the dose contributions of the three particle types are investigated. In order to assess the dosimetric potential, a clinically motivated head and neck case is investigated by comparing a TriB-RT plan to an intensity modulated proton therapy (IMPT) plan, both generated using the same TPP. Five photon beam directions, three electron beam directions (with energies of 6, 9, 12, 15, 18 and 22 MeV) and three proton beam directions are set up in a coplanar manner. An additional plan comparison is performed allowing only a single proton field from horizontal direction.

Results:
For the academic case, the resulting TriB-RT plan shows substantial contributions of all particle types. For the clinically motivated case, improved sparing of organs at risk close to the target volume is achieved compared to IMPT (e.g. inner ear and lacrimal gland mean dose -17.6% and -16.4%, respectively) at cost of an increased low dose bath (normal tissue V(10%) +22%) while maintaining equivalent target homogeneity. In the scenario of a single horizontal proton field, the TriB-RT plan (with one proton field) dosimetrically outperforms the single field proton plan.

Conclusion:
TriB-RT, a novel TPP which simultaneously optimizes photon, electron and proton beams was successfully developed and shows the potential for improved treatment plan quality in radiotherapy.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Varian Medical Systems.

Keywords

Treatment Techniques, Protons, Monte Carlo

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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