Planning of lung SBRTA comparative planning study for lung SABR between tri-Co-60 magnetic resonance image guided radiation therapy system and volumetric modulated arc therapy

Background and purposeTo compare the plan quality of tri-60Co magnetic-resonance image-guided radiation therapy (IGRT) to that of volumetric modulated arc therapy (VMAT) for lung stereotactic ablative radiotherapy (SABR).Materials and methodsA total of 22 patients with lung tumors located in the lower lobe were selected retrospectively. For each patient, VMAT plans with linac and intensity-modulated radiation therapy (IMRT) plans with the tri-60Co system were generated with prescription doses of 60 Gy (daily dose = 15 Gy). For both plan types, identical CT image sets and structures were used, with the exception of planning target volumes (PTV). The PTV for VMAT was generated from the internal target volume (ITV) while the PTV for the tri-60Co system was generated from the gross tumor volume (GTV). Clinically relevant dose-volumetric parameters were calculated and analyzed.ResultsThe average PTV volumes of tri-60Co plans and VMAT plans were 10.5 ± 12.3 cc vs. 27.2 ± 23.5 cc, respectively (p < 0.001). The maximum and mean doses to PTVs were 64.0 ± 2.6 Gy vs. 62.5 ± 0.9 Gy (p = 0.005) and 61.4 ± 1.7 Gy vs. 60.0 ± 0.5 Gy (p < 0.001), respectively. The conformity and homogeneity indices were 1.89 ± 0.38 vs. 1.01 ± 0.40 (p < 0.001) and 0.06 ± 0.02 vs. 0.04 ± 0.00 (p < 0.001), respectively. No considerable differences for organs at risk (OARs) were observed between tri-60Co plans and VMAT plans. In terms of target conformity, integral dose and lung mean dose, the plan quality of tri-60Co plans was inferior to that of VMAT plans when the PTV volumes of tri-60Co plans were less than 10 cc. However, all treatment plans of tri-60Co system were clinically acceptable.ConclusionFor lung SABR, the quality of ITV-based VMAT plans was better than that of GTV-based tri-60Co plans especially when the PTV volumes of the tri-60Co plans were less than 10 cc. If the breathing pattern of a patient is reproducible, VMAT is considered the optimal option for lung SABR, otherwise the tri-60Co IGRT should be considered due to the ability to monitor tumor motion during treatment.