gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

Realization of dose modulated proton plans with the 3 D Scanning system at the RPTC

Meeting Abstract

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  • M. Mayr - Medizinische Physik, Rinecker proton therapy center, München

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog133

DOI: 10.3205/09ptcog133, URN: urn:nbn:de:0183-09ptcog1338

Published: September 24, 2009

© 2009 Mayr.
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Outline

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Background: With the active 2 dimensional scanning at the RPTC comprising 2 magnetic scan dimensions it is possible to create modulated dose distributions in 3 dimensions. The fluence of the beam is created by raster scanning of a small pencil beam where the neccessary dose is accumulated at every beam position before the beam is steered to the next raster point. It is possible toreach dynamics of 1 to 100 within a single energy layer. To cover the arbitrarily shaped target volume in depth the energy of the beam is reduced in steps of about 3-5 MeV to add the Bragg peaks of the pencil beam in the third dimension and to create an individual "SOBP" for every beamlet position. The flexibility in beam delivery can fully be exploited by defining appropriate constraints in the treatment planning process.

Material and methods: There are 4 different types of dose optimization which are used at the RPTC.

1.
A single field uniform dose SFUD application, where a homogenous dose distribution is prescribed to the PTV. With this technique conformal dose distributions which avoid the inevitable horns known from broad beam therapy can be achieved. This method creates modulated beam fluence which could lead already to dose distributions superior to IMRT by adding multiple SFUD fields
2.
There could be constraints within oder outside the target volume to create a single field with a modulated dose distribution. This could be important if OARs are close or even inside the target. Just by setting the rank and power in the optimizer it is possible to create modulated dose distributions which could also be used for a simultaneously integrated boost concept even with a single beam. We would call this SFMD (Single Field Modulated Dose)
3.
For more than one field which where already optimized with method 1 or 2 these fields can be added and a final fine tuning of dose distribution can be performed with the optimizer which still keeps a rather homogenous dose distribution for every beam but also accounts for OAR constraints. We would call this "IMPT light".
4.
The full IMPT with more than one beam, where all beams are optimized simultaneously to meet the constraints for target volume and organs at risk at the same time. This technique leads to very highly modulated beams.

Results: Examples for the planned and realized dose plans will be shown.

Conclusion: The 3D scanning with protons is the most advanced technique in radiotherapy. Because of the physical properties of protons superior dose distribution and tissue sparing for organs at risc can be achieved. As an important side effect the neutron dose is minimized to the amount that is inevitably created in the patient itself, because the beam does not interact with material in the vicinity of the patient.