Vmat Planning For Large Volume Stage Iii Lung Cancer

Purpose/Objective(s)Our standard planning technique for locally advanced non-small cell lung cancer patients is a hybrid-IMRT (h-IMRT) technique with most of the dose delivered in an AP-PA direction, and 10-15% of the dose/fraction delivered with IMRT. Compared to 3-dimensional conformal radiation therapy, h-IMRT allows for improved planning target volume (PTV) coverage and better lung sparing. However, delivering 60-66 Gy to large PTVs can be challenging, and due to the relatively small IMRT contribution, h-IMRT offers limited possibilities for dose shaping and additional organ at risk (OAR) sparing. We therefore investigated the possible advantages of full volumetric modulated arc therapy (VMAT) planning.Materials/MethodsWe selected 14 patients with PTVs>750 cm3 (mean ± SD = 1096 ± 188 cm3) previously treated with concurrent chemoradiation therapy. H-IMRT plans delivering 33x2 Gy were compared with 2 coplanar VMAT approaches using either 2 or 4 arcs with avoidance sector to prevent beams entering through the contralateral lung. For treatment planning, a high priority was placed on sparing lung volume receiving ≥20 Gy (V20), V5 and contralateral lung V5 (CL-V5); spinal cord dose to be <50 Gy. In a sub-group of 4 patients further OAR sparing was evaluated with an additional 2 arcs plan that also aimed to reduce dose to skin, esophagus and heart.ResultsCompared to h-IMRT, VMAT significantly reduced V20 and mean lung dose (MLD), but significantly increased V5 and CL-V5. These improvements were at the expense of greater heterogeneity in PTV coverage (see Table). Use of 4 arcs only resulted in a higher PTV dose homogeneity compared to 2 arcs. Even without specific constraints, doses to skin and heart were lower in VMAT plans. In the sub-group of 4 patients planned with 2 arcs, further reductions in esophagus V60 (from 41 to 26%), mean esophagus dose (from 37 to 33 Gy) and skin V50 (from 23 to 14 cm3) were possible while maintaining heart and total lung doses. The trade-off was an increase in PTV heterogeneity (V95% from 95.6 to 94.2%).ConclusionsScientific Abstract 3114; Tableh-IMRTmean ± SD2 arcsmean ± SD4 arcsmean ± SDPTVV95% (%)97.8 ± 1.195.3 ± 1.495.7 ± 1.5V107% (cm3)23 ± 3797 ± 6550 ± 42Lungs-PTVV20 (%)28.9 ± 6.527.2 ± 6.227.1 ± 6.2V5 (%)51.0 ± 9.956.4 ± 11.155.8 ± 10.8Dmean (Gy)18.0 ± 3.616.1 ± 3.316.0 ± 3.3Contralateral lungV5 (%)31 ± 1340 ± 1340 ± 12HeartV60 (%)26 ± 2015 ± 1216 ± 12EsophagusDmean (Gy)36 ± 1035 ± 1035 ± 10SkinV50 (cm3)39 ± 2423 ± 1821 ± 18 Open table in a new tab Purpose/Objective(s)Our standard planning technique for locally advanced non-small cell lung cancer patients is a hybrid-IMRT (h-IMRT) technique with most of the dose delivered in an AP-PA direction, and 10-15% of the dose/fraction delivered with IMRT. Compared to 3-dimensional conformal radiation therapy, h-IMRT allows for improved planning target volume (PTV) coverage and better lung sparing. However, delivering 60-66 Gy to large PTVs can be challenging, and due to the relatively small IMRT contribution, h-IMRT offers limited possibilities for dose shaping and additional organ at risk (OAR) sparing. We therefore investigated the possible advantages of full volumetric modulated arc therapy (VMAT) planning. Our standard planning technique for locally advanced non-small cell lung cancer patients is a hybrid-IMRT (h-IMRT) technique with most of the dose delivered in an AP-PA direction, and 10-15% of the dose/fraction delivered with IMRT. Compared to 3-dimensional conformal radiation therapy, h-IMRT allows for improved planning target volume (PTV) coverage and better lung sparing. However, delivering 60-66 Gy to large PTVs can be challenging, and due to the relatively small IMRT contribution, h-IMRT offers limited possibilities for dose shaping and additional organ at risk (OAR) sparing. We therefore investigated the possible advantages of full volumetric modulated arc therapy (VMAT) planning. Materials/MethodsWe selected 14 patients with PTVs>750 cm3 (mean ± SD = 1096 ± 188 cm3) previously treated with concurrent chemoradiation therapy. H-IMRT plans delivering 33x2 Gy were compared with 2 coplanar VMAT approaches using either 2 or 4 arcs with avoidance sector to prevent beams entering through the contralateral lung. For treatment planning, a high priority was placed on sparing lung volume receiving ≥20 Gy (V20), V5 and contralateral lung V5 (CL-V5); spinal cord dose to be <50 Gy. In a sub-group of 4 patients further OAR sparing was evaluated with an additional 2 arcs plan that also aimed to reduce dose to skin, esophagus and heart. We selected 14 patients with PTVs>750 cm3 (mean ± SD = 1096 ± 188 cm3) previously treated with concurrent chemoradiation therapy. H-IMRT plans delivering 33x2 Gy were compared with 2 coplanar VMAT approaches using either 2 or 4 arcs with avoidance sector to prevent beams entering through the contralateral lung. For treatment planning, a high priority was placed on sparing lung volume receiving ≥20 Gy (V20), V5 and contralateral lung V5 (CL-V5); spinal cord dose to be <50 Gy. In a sub-group of 4 patients further OAR sparing was evaluated with an additional 2 arcs plan that also aimed to reduce dose to skin, esophagus and heart. ResultsCompared to h-IMRT, VMAT significantly reduced V20 and mean lung dose (MLD), but significantly increased V5 and CL-V5. These improvements were at the expense of greater heterogeneity in PTV coverage (see Table). Use of 4 arcs only resulted in a higher PTV dose homogeneity compared to 2 arcs. Even without specific constraints, doses to skin and heart were lower in VMAT plans. In the sub-group of 4 patients planned with 2 arcs, further reductions in esophagus V60 (from 41 to 26%), mean esophagus dose (from 37 to 33 Gy) and skin V50 (from 23 to 14 cm3) were possible while maintaining heart and total lung doses. The trade-off was an increase in PTV heterogeneity (V95% from 95.6 to 94.2%). Compared to h-IMRT, VMAT significantly reduced V20 and mean lung dose (MLD), but significantly increased V5 and CL-V5. These improvements were at the expense of greater heterogeneity in PTV coverage (see Table). Use of 4 arcs only resulted in a higher PTV dose homogeneity compared to 2 arcs. Even without specific constraints, doses to skin and heart were lower in VMAT plans. In the sub-group of 4 patients planned with 2 arcs, further reductions in esophagus V60 (from 41 to 26%), mean esophagus dose (from 37 to 33 Gy) and skin V50 (from 23 to 14 cm3) were possible while maintaining heart and total lung doses. The trade-off was an increase in PTV heterogeneity (V95% from 95.6 to 94.2%). ConclusionsScientific Abstract 3114; Tableh-IMRTmean ± SD2 arcsmean ± SD4 arcsmean ± SDPTVV95% (%)97.8 ± 1.195.3 ± 1.495.7 ± 1.5V107% (cm3)23 ± 3797 ± 6550 ± 42Lungs-PTVV20 (%)28.9 ± 6.527.2 ± 6.227.1 ± 6.2V5 (%)51.0 ± 9.956.4 ± 11.155.8 ± 10.8Dmean (Gy)18.0 ± 3.616.1 ± 3.316.0 ± 3.3Contralateral lungV5 (%)31 ± 1340 ± 1340 ± 12HeartV60 (%)26 ± 2015 ± 1216 ± 12EsophagusDmean (Gy)36 ± 1035 ± 1035 ± 10SkinV50 (cm3)39 ± 2423 ± 1821 ± 18 Open table in a new tab