Stereotactical fields applied in proton spot scanning mode with range shifter and collimating aperture.

Stereotactical fields applied in proton spot scanning mode with range shifter and collimating aperture. Phys Med Biol. 2019 Jun 19;: Authors: Bäumer C, Fuentes C, Janson M, Matic A, Timmermann B, Wulff J 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 m...
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research