Room: Exhibit Hall
Purpose: To evaluate the dosimetric performance and delivery efficiency for IMRT and VMAT with multicriteria optimization (MCO) for lung SBRT, using a flattening filter-free (FFF) 6 MV photon beam on a Varian TrueBeam linear accelerator (linac). To compare Varian-FFF to the original treatments on an Elekta Infinity linac with Agility multileaf collimator using a 6 MV photon beam with flattening filter (Elekta-FF).
Methods: 13 Elekta-FF lung SBRT patients (four 3D, three IMRT, and six VMAT) were selected. Each patient was re-planned with Varian-FFF-IMRT and Varian-FFF-VMAT in RayStation v5.0. The patient collection represents all tumor locations, prescriptions, and ITV sizes (1.2 to 48.1 cc) seen in our clinic. All investigational plans were approved by a radiation oncologist. The maximum dose rate for Varian-FFF and Elekta-FF is 1200 and 500 MU/min, respectively. ITV coverage, conformity index (CI), lung dose, and beam-on time were compared among Varian-FFF and Elekta-FF treatments. Patient specific QA using ArcCheck with an embedded micro ionization chamber was performed for all Varian-FFF plans. All Varian-FFF plans passed point dose and ArcCheck QA.
Results: On average, the ITV V100 was comparable for Varian-FFF-VMAT (99.64%), Varian-FFF-IMRT (99.53%) and Elekta-FF (99.68%). The CI for Varian-FFF-IMRT, Varian-FFF-VMAT and Elekta-FF was 4.16, 4.66, and 4.48, respectively, all in compliance with the RTOG-0813 criteria for no deviation (<5.163). The combined lungs V20 was approximately 2.7â€“2.8 Gy for all three modalities. For ipsilateral lung V20, the results were also very similar, except for the patient with the largest ITV (48.1 cc), where V20 was highest with the original Elekta-FF-IMRT. Varian-FFF-IMRT reduced the treatment time by 140 seconds compared with Elekta-FF-IMRT, and Varian-FFF-VMAT reduced treated time by 154 seconds compared with Elekta-FF-VMAT.
Conclusion: In RayStation, MCO-based FFF-IMRT and FFF-VMAT provides similar plan quality to their FF counterparts, but offers significant improvement in delivery efficiency.