Dosimetric Comparison of Stereotactic Body Radiation Therapy Plans With Volumetric Arc Therapy, Helical Tomotherapy, and Raystation for Liver Metastasis

Abstract

To compare dosimetric data of stereotactic body radiotherapy (SBRT) plans with volumetric-arc therapy (VMAT), helical tomotherapy (HT) and RayStation (RS) for liver metastasis. The dosimetric data of 19 patients with liver metastasis treated with liver SBRT were analyzed. Three different plans were generated with same computed tomography (CT) images. The prescribed dose was 54 Gy delivered in 3 fractions and the dose was prescribed to 90% isodose line. For all patients, cumulative dose–volume histograms and dosimetric parameters were calculated and compared for the planning target volume (PTV) and organs at risk (OAR). D2 and D98 were used as a surrogate for maximum and minimum dose, respectively. D2 and D98 are the minimal doses to 2 % and 98 % of target volume, respectively. The target homogeneity and conformal index values (HI and CI, respectively) are compared. OARs doses, including kidneys, liver, bowel, and spinal cord, were also assessed. All plans meet the criteria for PTV coverage. The average maximum doses for PTV (D2) were significantly higher in VMAT plans compared to HT and RS plans (Table 1). The CI and HI indices were significantly lower in RS plans compared to HT plans and VMAT plans. Similarly CI and HI indices were significantly lower in HT plans compared to VMAT plans. Liver Dmean was significantly higher in RS plan (10.9±4.8 Gy) compared to VMAT plan (9.6±3.8 Gy; p=0.001) and HT plan (10.1±4.4 Gy; p=0.006). However there was no significant difference for Liver Dmean between VMAT and HT plans (p=0.08). The liver V5 to V45 were significantly higher in RS plan compared to VMAT and HT plans (Figure 1). There were no significant difference in liver doses between VMAT plans and HT plans except for V5 (p=0.001) and V10 (p=0.005) values. The Dmean of both kidneys were significantly higher in HT plans (2.4±1.8 Gy) compared to VMAT plans (1.9±1.6 Gy; p=0.005) and RS plans (1.4±0.8 Gy; p=0.004). However there were no significant difference in Dmeanof both kidneys between VMAT and RS plans. For the spinal cord and bowel, maximum doses did not differ significantly between each techniques. The monitor unit for RS plan was significantly less in RS plan compared to VMAT plan (2774±271 vs. 4052±1591; p=0.003). The RS plans reduced the maximum dose applied to the target area, with improved the conformality and homogeneity of radiation. However, the liver does were significantly higher in RS plan compared to HT and VMAT plans.Tabled 1Abstract 2428; Table 1ParametersVMAT(Mean±SD)HT(Mean±SD)RayStation(Mean±SD)p(VMAT vs. HT)p(VMAT vs. RS)p(HT vs. RS)D2% (Gy)57.0±1.055.4±0.354.4±0.3<0.001<0.001<0.001D100% (Gy)52.0±2.352.5±1.052.5±0.80.330.190.73D98% (Gy)54.2±0.753.9±0.253.7±0.20.140.003<0.001D95% (Gy)54.5±0.654.2±0.253.8±0.20.02<0.001<0.001D90% (Gy)54.8±0.654.3±0.253.9±0.20.001<0.001<0.001D50% (Gy)55.8±0.654.8±0.354.1±0.2<0.001<0.001<0.001CI1.53±0.101.52±0.101.51±0.100.020.0030.001HI1.05±0.021.03±0.011.01±0.01<0.001<0.001<0.001 Open table in a new tab