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 mm 2 field size at a gantry angle of zero degrees and a low monitor unit setting of 200. Doses were measured using a 0.016 cm 3 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.
Highlights
Through breathing management, stereotactic body radiation therapy (SBRT) can deliver increased doses of radiation to tumors while decreasing the dose delivered to normal tissue.[1,2,3] Several methods for controlling respiratory motion have been reported, including breath holding[4], respiratory gating[5], and dynamic tumor tracking (DTT).[6,7,8] Breath holding is more difficult for patients who cannot repeatedly hold their breath over the delivery time
An IR phantom was positioned on the vertical direction motion table as a surrogate signal. 4D modeling with the Vero4DRTTM system is described elsewhere.[11,12]
The largest deviation occurred when the larger peak-to-peak amplitude was delivered with non-DTT
Summary
Stereotactic body radiation therapy (SBRT) can deliver increased doses of radiation to tumors while decreasing the dose delivered to normal tissue.[1,2,3] Several methods for controlling respiratory motion have been reported, including breath holding[4], respiratory gating[5], and dynamic tumor tracking (DTT).[6,7,8] Breath holding is more difficult for patients who cannot repeatedly hold their breath over the delivery time. Respiratory gating needs a longer treatment time to deliver the dose within a particular portion of the patient’s breathing cycle. DTT is an innovative technique that does not require either a longer treatment time or the burden of breath holding.[6,7,8] DTT can be categorized into direct and indirect methods.
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