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

Intensity Modulated Spread Out Bragg Peak in a Uniform Scanning Proton Nozzle Using Novel Applications of Forward Planning

Meeting Abstract

  • K. Shahnazi - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • Chr. Allgower - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • V. Anferov - Indiana University Cyclotron Facility, Bloomington, USA
  • M. Wolanski - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • A. Thornton - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • M. Fitzek - Midwest Proton Radiotherapy Institute, Bloomington, USA
  • A. Chang - Midwest Proton Radiotherapy Institute, Bloomington, USA

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog182

DOI: 10.3205/09ptcog182, URN: urn:nbn:de:0183-09ptcog1828

Published: September 24, 2009

© 2009 Shahnazi et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.en). You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.


Outline

Text

Purpose: The high dose region of a pristine proton beam Bragg peak is only 4-5 mm in width. To be clinically useful, this peak must be modulated into a "Spread Out Bragg Peak" (SOBP). This range modulation can be achieved in a number of ways. At the Midwest Proton Radiotherapy Institute – Indiana University Cyclotron Facility, this is accomplished by sequentially introducing extra energy-absorbing layers before the beam enters the target. The weighting of each layer can be adjusted to shape the SOBP along the beam path.

Method: A SOBP file was modified for specific layer weighting. The file was subsequently manipulated to achieve valleys and peaks within the SOBP by selective layer weighting. The file was put back into the layer files objects and quality assurance performed. This file was then inserted in the treatment planning file and compared to a non-modified SOBP. Treatment planning commissioning was done based on these results.

Results: We tested a proton beam of 16 cm range with a 10 cm SOBP and a rectangular 10 cm by 10 cm aperture. We then modified a few layers by setting them to the lowest possible relative weight within the SOBP. We simulated this SOBP for the treatment planning of a lesion in a thoracic vertebral body of a child with the premise to spare the spinal cord in the middle of the target. It was found that appropriate layer weighting allows a 35-40% lower dose at a critical location of interest along the SOBP and that the dose distribution remains uniform distal and proximal to this critical organ.

Conclusion: With our system of uniform scanning and layer stacking, it is possible to generate an SOBP which selectively spares critical structure within a target volume, while delivering a high dose to the surrounding target volume (Figure 1 [Fig. 1]).