Quality assurance for dynamic tumor tracking using the Vero4DRT system

Abstract

Purpose: We perform quality assurance (QA) for indirect dynamic tumor tracking (DTT) using four-dimensional radiation therapy (the Vero4DRT™ system).

Methods: A single photon beam was set with a 40 × 40 mm² field size at a gantry angle of zero degrees and a low monitor unit setting of 200. Doses were measured using a 0.016 cm³ ionization chamber inserted in a phantom under stationary, DTT, and non-DTT conditions for sinusoidal (peak-to-peak) amplitude [A] and breathing period [T] (20 mm, 2 s; 20 mm, 4 s; and 40 mm, 4 s). The stationary condition was measured for comparison. Dose profiles were measured using Gafchromic EBT3 films in the phantom under the same conditions.

Results: For chamber measurement, the relative doses were as follows: 0.99 with non-DTT and 1.00 with DTT at A = 20 mm and T = 2 s; 0.99 with non-DTT and 1.00 with DTT at A = 20 mm and T = 4 s; and 0.84 with non-DTT and 1.00 with DTT at A = 40 mm and T = 4 s. For film measurement, the spatial distances between the 90% dose of the dose profiles were as follows: 6.53 mm for non-DTT and 0.40 mm for DTT at A = 20 mm and T = 2 s; 6.33 mm for non-DTT and 0.15 mm for DTT at A = 20 mm and T = 4 s; and 10.61 mm for non-DTT and 0.17 mm with DTT at A = 40 mm and T = 4 s.

Conclusion: Our results showed high dosimetric and geometric accuracy for DTT using four-dimensional modeling and marked reduction of the blurring effects on dose distribution. We recommend the use of a QA procedure for DTT performed using the Vero4DRT™ system.