Comparison of phase-gated and amplitude-gated dose delivery to a moving target using gafchromic EBT3 film

Abstract

IntroductIonLung stereotactic body radiation therapy (SBRT) is used for the treatment of early-stage nonsmall cell lung cancer and metastatic lung tumors. [1,2] SBRT treatments are delivered in a hypofractionation mode, with high doses in a few fractions (from 3 to 8 fractions), depending on tumor localization (central or peripheral tumors). [3] The treatment of lung cancer with high doses can be impacted by tumor motion and proximity to the organ at risk. [4][5][6][7] Various techniques were developed to take into consideration tumor motion during treatment delivery to accurately target the moving tumor and to spare healthy tissues. [8][9][10] The abdominal compression technique is used to reduce the breathing amplitude, reducing the amplitude of the tumor motion throughout the respiratory cycle. [8] Radiation during a certain phase of the respiratory cycle can be performed using respiratory gating radiation therapy (RGRT). [9] Real-time tumor tracking allows for tumor irradiation throughout the respiratory cycle. [10] RGRT does not require controlled breathing or breath hold during simulation and dose delivery. There are three types of gating: phase gating, amplitude gating, and breath-hold gating techniques. With phase gating, the treatment is delivered during a certain phase of the respiratory cycle. With amplitude gating, the treatment is delivered when a chosen threshold of the breathing amplitude is reached, which is generally during the Introduction: This study compared phase-gated and amplitude-gated dose deliveries to the moving gross tumor volume (GTV) in lung stereotactic body radiation therapy (SBRT) using Gafchromic External Beam Therapy (EBT3) dosimetry film. Materials and Methods: Eighty treatment plans using two techniques (40 phase gated and 40 amplitude gated) were delivered using dynamic conformal arc therapy (DCAT). The GTV motion, breathing amplitude, and period were taken from 40 lung SBRT patients who performed regular breathing. These parameters were re-simulated using a modified Varian breathing mini phantom. The dosimetric accuracy of the phase-and amplitude-gated treatment plans was analyzed using Gafchromic EBT3 dosimetry film. The treatment delivery efficacy was analyzed for gantry rotation, number of monitor unit (MU), and target position per triggering window. The time required to deliver the phase-and amplitude-gated treatment techniques was also evaluated. Results: The mean dose (range) per fraction was 16.11 ± 0.91 Gy (13.04-17.50 Gy) versus 16.26 ± 0.83 Gy (13.82-17.99 Gy) (P < 0.0001) for phase-and amplitude-gated delivery. The greater difference in the gamma passing rate was 1.2% ±0.4% in the amplitude-gated compared to the phase gated. The gantry rotation per triggering time (tt) was 2° ±1° (1.2°-3°) versus 5° ±1° (3°-6°) (P < 0.0001) and MU per tt was 10 ± 3 MU (6-13 MU) versus 24 ± 7 MU (12-32 MU) (P < 0.0001), for phase-versus amplitude-gated techniques. A 90 beam interruption in the phase-gated technique impacted the treatment delivery efficacy, increasing the treatmen...

A 3D-printed phantom for stereotactic body radiation therapy simulation

“…The prosthetic tumor is 3D printed using PLA material. Its outer section is a spherical object with a diameter of 3 cm, whereas its internal section is semihollow with a diameter of 2 cm to facilitate the placement of a Gafchromic film (EBT3), which is to inspect radiation doses and accuracy (Savanović et al 2021), as shown in figure 3(a). The example of beam delivery is in figure figure 3(b).…”