Dosimetric Comparison Between Multiple-Arc Rapidarc, Static Beam Intensity Modulated Radiation Therapy, And Helical Tomotherapy For Brain Tumor Treatment

Purpose/Objective(s)Intensity-modulated radiation therapy (IMRT) with multiple non-coplanar static beams delivers conformal dose distribution to planned target volume (PTV) and minimizes dose to organs at risk (OAR), but may have long treatment time with a large number of beams. RapidArc (RA) technology based on volumetric modulated arc therapy (VMAT) may offer considerably shorter treatment time and highly conformal dose distributions delivered with a dynamic rotation of the gantry with beam intensity modulation every 2o throughout the gantry rotation. Non-coplanar partial arcs (NCPA) may deliver beams to the target through the cephalic portion of the brain and avoid OAR. Ring gantry-based Helical TomoTherapy (HT) delivers conformal and highly homogeneous dose distribution inside the tumor volume, while sparing the OAR. In this study, we evaluate RA capabilities using coplanar and non-coplanar arcs and do a dosimetric comparison with IMRT and HT.Materials/MethodsThree brain tumor patients with target volumes of 26.7, 193.4, and 425.2 cc who had completed IMRT were replanned for HT using 0.287 pitch and RA using single 360o arc (SA), double 720o arc (DA), and combinations of SA with 1 and 3 NCPA. Couch rotations were 90o for 1NCPA and 90o, 30o, and 330o for 3NCPA. Partial arcs ranged from 0o-30o to 150o-179.9o. At least 95% of the PTV was required to receive the prescribed dose. IMRT plans used 6-8 non-coplanar beams. Similar dose constrains and PTV coverage criteria were used in all plans.ResultsFor the smallest tumor, PTV coverage D99% was the highest for RA plans (96.4%), followed by HT (94.2%) and IMRT (93.8%). Multiple-arc RA plans were more homogeneous ((D5%-D95%)/D95% ˜3.5%) compared to IMRT (5.9%), RA-SA (6.2%), and HT (7.2%). Conformity was the same for 95% isodose, but higher for RA-NCPA plans at 50% isodose. Average and max dose to most OAR like brainstem, optic chiasm, pituitary and optic nerves were lower with RA. For the larger tumors, HT had the highest PTV dose homogeneity (˜2%) and coverage (99.3%), followed by RA-NCPA (98.6%), RA-DA and SA (97.9%) and IMRT (96.6%). Conformity was similar at 95% and higher with RA-NCPA and IMRT at 50% isodose. Most OAR sparing was similar for HT, RA and IMRT. For all three tumors, average dose to brain was the highest with HT, and dose to lenses and retina was higher but well below the allowed limits with RA.ConclusionsWe compared RapidArc VMAT using multiple coplanar and non-coplanar arcs with static beam IMRT and Helical TomoTherapy for brain tumor treatment. For the smallest tumor (26.7 cc), multiple-arc RA showed advantages over IMRT and HT in PTV coverage, dose homogeneity, and OAR sparing. For the larger brain tumors both HT and RA-NCPA offered high quality of PTV coverage and dose homogeneity. Purpose/Objective(s)Intensity-modulated radiation therapy (IMRT) with multiple non-coplanar static beams delivers conformal dose distribution to planned target volume (PTV) and minimizes dose to organs at risk (OAR), but may have long treatment time with a large number of beams. RapidArc (RA) technology based on volumetric modulated arc therapy (VMAT) may offer considerably shorter treatment time and highly conformal dose distributions delivered with a dynamic rotation of the gantry with beam intensity modulation every 2o throughout the gantry rotation. Non-coplanar partial arcs (NCPA) may deliver beams to the target through the cephalic portion of the brain and avoid OAR. Ring gantry-based Helical TomoTherapy (HT) delivers conformal and highly homogeneous dose distribution inside the tumor volume, while sparing the OAR. In this study, we evaluate RA capabilities using coplanar and non-coplanar arcs and do a dosimetric comparison with IMRT and HT. Intensity-modulated radiation therapy (IMRT) with multiple non-coplanar static beams delivers conformal dose distribution to planned target volume (PTV) and minimizes dose to organs at risk (OAR), but may have long treatment time with a large number of beams. RapidArc (RA) technology based on volumetric modulated arc therapy (VMAT) may offer considerably shorter treatment time and highly conformal dose distributions delivered with a dynamic rotation of the gantry with beam intensity modulation every 2o throughout the gantry rotation. Non-coplanar partial arcs (NCPA) may deliver beams to the target through the cephalic portion of the brain and avoid OAR. Ring gantry-based Helical TomoTherapy (HT) delivers conformal and highly homogeneous dose distribution inside the tumor volume, while sparing the OAR. In this study, we evaluate RA capabilities using coplanar and non-coplanar arcs and do a dosimetric comparison with IMRT and HT. Materials/MethodsThree brain tumor patients with target volumes of 26.7, 193.4, and 425.2 cc who had completed IMRT were replanned for HT using 0.287 pitch and RA using single 360o arc (SA), double 720o arc (DA), and combinations of SA with 1 and 3 NCPA. Couch rotations were 90o for 1NCPA and 90o, 30o, and 330o for 3NCPA. Partial arcs ranged from 0o-30o to 150o-179.9o. At least 95% of the PTV was required to receive the prescribed dose. IMRT plans used 6-8 non-coplanar beams. Similar dose constrains and PTV coverage criteria were used in all plans. Three brain tumor patients with target volumes of 26.7, 193.4, and 425.2 cc who had completed IMRT were replanned for HT using 0.287 pitch and RA using single 360o arc (SA), double 720o arc (DA), and combinations of SA with 1 and 3 NCPA. Couch rotations were 90o for 1NCPA and 90o, 30o, and 330o for 3NCPA. Partial arcs ranged from 0o-30o to 150o-179.9o. At least 95% of the PTV was required to receive the prescribed dose. IMRT plans used 6-8 non-coplanar beams. Similar dose constrains and PTV coverage criteria were used in all plans. ResultsFor the smallest tumor, PTV coverage D99% was the highest for RA plans (96.4%), followed by HT (94.2%) and IMRT (93.8%). Multiple-arc RA plans were more homogeneous ((D5%-D95%)/D95% ˜3.5%) compared to IMRT (5.9%), RA-SA (6.2%), and HT (7.2%). Conformity was the same for 95% isodose, but higher for RA-NCPA plans at 50% isodose. Average and max dose to most OAR like brainstem, optic chiasm, pituitary and optic nerves were lower with RA. For the larger tumors, HT had the highest PTV dose homogeneity (˜2%) and coverage (99.3%), followed by RA-NCPA (98.6%), RA-DA and SA (97.9%) and IMRT (96.6%). Conformity was similar at 95% and higher with RA-NCPA and IMRT at 50% isodose. Most OAR sparing was similar for HT, RA and IMRT. For all three tumors, average dose to brain was the highest with HT, and dose to lenses and retina was higher but well below the allowed limits with RA. For the smallest tumor, PTV coverage D99% was the highest for RA plans (96.4%), followed by HT (94.2%) and IMRT (93.8%). Multiple-arc RA plans were more homogeneous ((D5%-D95%)/D95% ˜3.5%) compared to IMRT (5.9%), RA-SA (6.2%), and HT (7.2%). Conformity was the same for 95% isodose, but higher for RA-NCPA plans at 50% isodose. Average and max dose to most OAR like brainstem, optic chiasm, pituitary and optic nerves were lower with RA. For the larger tumors, HT had the highest PTV dose homogeneity (˜2%) and coverage (99.3%), followed by RA-NCPA (98.6%), RA-DA and SA (97.9%) and IMRT (96.6%). Conformity was similar at 95% and higher with RA-NCPA and IMRT at 50% isodose. Most OAR sparing was similar for HT, RA and IMRT. For all three tumors, average dose to brain was the highest with HT, and dose to lenses and retina was higher but well below the allowed limits with RA. ConclusionsWe compared RapidArc VMAT using multiple coplanar and non-coplanar arcs with static beam IMRT and Helical TomoTherapy for brain tumor treatment. For the smallest tumor (26.7 cc), multiple-arc RA showed advantages over IMRT and HT in PTV coverage, dose homogeneity, and OAR sparing. For the larger brain tumors both HT and RA-NCPA offered high quality of PTV coverage and dose homogeneity. We compared RapidArc VMAT using multiple coplanar and non-coplanar arcs with static beam IMRT and Helical TomoTherapy for brain tumor treatment. For the smallest tumor (26.7 cc), multiple-arc RA showed advantages over IMRT and HT in PTV coverage, dose homogeneity, and OAR sparing. For the larger brain tumors both HT and RA-NCPA offered high quality of PTV coverage and dose homogeneity.