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

Proposal for a specific proton therapy facility for the treatment of ocular tumors

Meeting Abstract

  • A. Weber - BerlinProtonen am Helmholtz Zentrum Berlin, Charité – Universitätsmedizin Berlin, Berlin
  • J. Heufelder - BerlinProtonen am Helmholtz Zentrum Berlin, Charité – Universitätsmedizin Berlin, Berlin
  • A. Denker - Protonen in der Therapie (PT), Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin
  • L. Moser - Klinik für Radioonkologie und Strahlentherapie, Campus Benjamin Franklin, Charité – Universitätsmedizin Berlin, Berlin
  • M. H. Foerster - Augenklinik, Campus Benjamin Franklin, Charité – Universitätsmedizin Berlin, Berlin

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog221

DOI: 10.3205/09ptcog221, URN: urn:nbn:de:0183-09ptcog2212

Veröffentlicht: 24. September 2009

© 2009 Weber et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielfältigt, verbreitet und öffentlich zugänglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Background: Proton therapy is a powerful tool in cancer treatment. Technology has developed in a way that commercial clinical proton therapy units are available. Some clinical centers e.g. in Boston, Villigen, Houston, Loma Linda, and others are already working for years. Many more facilities are under construction. They use proton beams of 200 MeV and more for the treatment of deep-seated tumors.

Up to now the biggest cohort of entities treated with protons are uveal melanomas. The tumor control after 5 years is 95% or better. Most of these patients were treated at low energy machines like OPTIS at the Paul-Scherrer-Institute in Switzerland, the Douglas Cyclotron Unit in Clatterbridge (UK), Nice (France) or the Charité at the Helmholtz-Zentrum Berlin (former Hahn Meitner-Institut, Berlin, Germany). They have nearly ideal parameters for the treatment of ocular lesions namely sharp penumbra, sharp distal fall off, and a high dose-rate. All newer clinical units using a high-energy proton beam of 200 MeV or more must reduce their proton energy to about 70 MeV for eye treatments. The physics in doing so implies a lot of compromises, resulting in worse beam parameters compared to a 70 MeV proton accelerator. Our aim is to present a layout and to argue for a low energy facility.

Materials and methods: From our experience in Berlin of operating a cyclotron for more than 30 years and treating more than 1300 patients since 1998, an appropriate facility should have the following treatment parameters: Effective field size of 40 mm in diameter, penumbra (80% to 20%) of 2.0 mm or better, distal fall off of about 1.0 mm, dose rate of at least 20 Gy/min, field symmetry and flatness better than 3%, and a simple and robust scattering system.

We chose a 70 MeV accelerator with two beam lines: one horizontal beam line with a single scattering system for standard eye treatments and one vertical beam line, also equipped with a single scattering system for the treatment of special cases like retinoblastoma or for radiobiological experiments. The software package PBO-Lab was used for the calculation of the beam line optics, the Monte Carlo code MCNPX was used for the simulation of the amount of concrete needed to operate in both rooms simultaneously.

Results: With a 70 MeV proton accelerator it is possible to meet the demands for the above mentioned treatment parameters. In contrast an eye beam line at a high energy turn-key facility cannot fulfill all of them at the same time. There are compromises necessary: e.g. a trade-off between distal fall off and dose rate, or between effective field size and flatness. For example: low energy systems will offer steeper dose gradients than the high energy systems. This might result in a better clinical outcome for patients with tumors at the posterior pole, where the tumor is located near the macula or the papilla: Tumor control should be the same for both systems, but visual acuity should be better after a treatment in a low energy facility.

Conclusions: In spite of all new clinical high-energy proton facilities operating or being under construction we see a need for low energy facilities. Patients will profit from the perfect beam parameters and the sophisticated treatment routines of eye tumors within such a facility. Treating all eye patients of a single country in one specific facility will reduce the costs in the national health-care system. This leads to benefits for the patients and the community.