Stereotactical fields applied in proton spot scanning mode with range shifter and collimating aperture
Open Access
- 19 June 2019
- journal article
- research article
- Published by IOP Publishing in Physics in Medicine & Biology
- Vol. 64 (15), 155003
- https://doi.org/10.1088/1361-6560/ab2ae7
Abstract
Some clinical indications require small fields with sharp lateral dose gradients, which is technically challenging in proton beam therapy. This holds especially true for low-range fields applied with the spot scanning technique, where large beam profiles entering from the beam-line or the insertion of range shifting blocks lead to large lateral gradients. We regard the latter case and solve it by shifting the range shifting block far upstream in conjunction with a collimating aperture close to the patient. The experiments of the current work are based on a commercial proton therapy treatment head designed for several delivery modes. In a research environment of the spot-scanning delivery mode a range shifter is inserted downstream of the scanning magnets in a slot which is usually employed only in a scattering delivery mode. This configuration is motivated by equations assuming a simple model of proton transport. In the experiments lateral dose planes are acquired with a scintillation screen and radiochromic films. Dose distributions are calculated with the Monte-Carlo dose engine of the RayStation treatment planning system. We demonstrate that proton fields with 80%-20% lateral dose fall-off values between 1.4 mm and 4.0 mm can be achieved for water equivalent depths between 0 cm and 10 cm. The simulated lateral dose profiles agree with the experimental dose profiles. The sharpening of the field edges is set off by a broadening of the proton spots towards the center of the fields. This limits the clinical application mainly to small fields for which the distal and proximal conformality is of minor importance.This publication has 31 references indexed in Scilit:
- Measurements of lateral penumbra for uniform scanning proton beams under various beam delivery conditions and comparison to the XiO treatment planning systemMedical Physics, 2013
- Radiochromic film dosimetry: Past, present, and futurePhysica Medica, 2011
- On the scattering power of radiotherapy protonsMedical Physics, 2009
- Parametrization and application of scatter kernels for modelling scanned proton beam collimator scatter dosePhysics in Medicine & Biology, 2008
- Computational modeling of beam-customization devices for heavy-charged-particle radiotherapyPhysics in Medicine & Biology, 2008
- Comparison between the lateral penumbra of a collimated double-scattered beam and uncollimated scanning beam in proton radiotherapyPhysics in Medicine & Biology, 2008
- THE INTERNATIONAL COMMISSION ON RADIATION UNITS AND MEASUREMENTSJournal of the ICRU, 2007
- A pencil beam algorithm for proton dose calculationsPhysics in Medicine & Biology, 1996
- Multiple Coulomb scattering of 160 MeV protonsNuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993
- Collimated electron beams and their associated penumbra widthsMedical Physics, 1987