Dose-response of deformable radiochromic dosimeters for spot scanning proton therapy

Abstract

Intrafractional motion and deformation influence proton therapy delivery for tumours in the thorax, abdomen and pelvis. This study aimed to test the dose-response of a compressively strained three-dimensional silicone-based radiochromic dosimeter during proton beam delivery. The dosimeter was read-out in its relaxed state using optical computed tomography and calibrated for the linear energy transfer, based on Monte Carlo simulations. A three-dimensional gamma analysis showed a 99.3% pass rate for 3%/3 mm and 93.9% for 2%/2 mm, for five superimposed measurements using deformation-including Monte Carlo dose calculations as reference. We conclude that the dosimeter's dose-response is unaffected by deformations.

Keywords: 3D dosimetry; Deformation; Monte Carlo; Proton therapy.

Fig. 1

The dose deposition in a section through the five dosimeters at the different strains indicated by the strained length above each image. The top row shows the MC calculations while the bottom row shows the LET-calibrated dose distributions in the dosimeter. An isocurve of 10% of the maximum dose is indicated by a white line. The 3%/3 mm 3D gamma analysis passed 96.1%, 94.3%, 93.7%, 98.5% and 90.3% of the voxels (left to right), while the 2%/2 mm passed 90.2%, 87.1%, 88.3%, 95.2% and 83.3%.

Fig. 2

The dose deposition in a section through the dosimeter from five superimposed proton spots delivered at deformations of 50 mm to 30 mm in steps of 5 mm. (A) Dose from MC calculation and (B) LET-calibrated dose distribution in the dosimeter. An isocurve of 10% of the maximum dose is indicated by a white line.