A Dosimetric Analysis Of Arc Radiotherapy For Stage Iii Non-Small Cell Lung Cancer

Purpose/Objective(s)Arc radiotherapy (ART) potentially provides rapid treatment to complex planning tumor volumes (PTV). We analyzed the dosimetric consequences of single ART (SART), double ART (DART), 3-D conformal radiation therapy (3DCRT), and intensity modulated radiation therapy (IMRT) techniques for the treatment of stage III non-small cell lung cancer (NSCLC).Materials/MethodsEight patients with pathologic or radiographic evidence of mediastinal lymph node involvement were selected. A single radiation oncologist contoured PTV and normal structures. Using guidelines from RTOG 0617, a PTV was prescribed 60Gy. Each patient had SART, DART, fixed-beam IMRT, and 3DCRT plans generated. Conformality index (CI) was the ratio of the volume of the 60Gy isodose surface to the volume of the PTV. Heterogeneity index (HI) was the ratio of the dose delivered to 5% of the PTV to the dose delivered to 95% of the PTV. The 4 techniques were compared in terms of PTV coverage, dose-volume histograms, and sparing of normal tissue using t-test analyses.ResultsThe median PTV for the 8 patients was 419cc (range 237-662). When compared to 3DCRT, IMRT resulted in significantly lower pulmonary V5 (40% vs. 50%, p < 0.001), V10 (34% vs. 40%, p < 0.001), V20 (27% vs. 28.6%, p = 0.05), and mean lung dose (14Gy vs. 16Gy, p < 0.001). 3DCRT achieved lower pulmonary V5, V10, and V20 values compared to SART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.03; V20: 29% vs. 32%, p = 0.02) and DART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.02; V20: 29% vs. 32%, p = 0.02), but mean lung dose was similar between 3DCRT, SART, and DART. When compared to SART, IMRT plans resulted in significantly lower pulmonary V5 (40% vs. 59%, p < 0.001), V10 (34% vs. 48%, p < 0.001), V20 (27% vs. 32%, p = 0.001), and mean lung dose (14Gy vs. 17Gy, p < 0.001). The same held true when IMRT was compared to DART. There was no significant difference in pulmonary DVH between SART and DART. Heart V60 was similar for all planning techniques, but heart V40 was significantly higher with 3DCRT. Mean esophageal dose was lowest with IMRT with no difference between any of the techniques in terms of the esophageal V60. The CI for 3DCRT was significantly inferior compared to the other 3 techniques. The CI for IMRT, SART, and DART were equivalent. There was no difference in HI between the 4 planning techniques. The mean total monitor units for SART was significantly less compared to IMRT (293 vs. 654, p < 0.001) and DART (293 vs. 314, p = 0.02), but similar to 3DCRT.ConclusionsThough ART may provide more rapid treatment delivery for stage III NSCLC compared to IMRT, it is associated with significantly larger volumes of low dose pulmonary irradiation. This increased volume of low dose pulmonary irradiation may increase the risk of clinically significant radiation pneumonitis. Therefore, ART should be used with caution for stage III NSCLC. Purpose/Objective(s)Arc radiotherapy (ART) potentially provides rapid treatment to complex planning tumor volumes (PTV). We analyzed the dosimetric consequences of single ART (SART), double ART (DART), 3-D conformal radiation therapy (3DCRT), and intensity modulated radiation therapy (IMRT) techniques for the treatment of stage III non-small cell lung cancer (NSCLC). Arc radiotherapy (ART) potentially provides rapid treatment to complex planning tumor volumes (PTV). We analyzed the dosimetric consequences of single ART (SART), double ART (DART), 3-D conformal radiation therapy (3DCRT), and intensity modulated radiation therapy (IMRT) techniques for the treatment of stage III non-small cell lung cancer (NSCLC). Materials/MethodsEight patients with pathologic or radiographic evidence of mediastinal lymph node involvement were selected. A single radiation oncologist contoured PTV and normal structures. Using guidelines from RTOG 0617, a PTV was prescribed 60Gy. Each patient had SART, DART, fixed-beam IMRT, and 3DCRT plans generated. Conformality index (CI) was the ratio of the volume of the 60Gy isodose surface to the volume of the PTV. Heterogeneity index (HI) was the ratio of the dose delivered to 5% of the PTV to the dose delivered to 95% of the PTV. The 4 techniques were compared in terms of PTV coverage, dose-volume histograms, and sparing of normal tissue using t-test analyses. Eight patients with pathologic or radiographic evidence of mediastinal lymph node involvement were selected. A single radiation oncologist contoured PTV and normal structures. Using guidelines from RTOG 0617, a PTV was prescribed 60Gy. Each patient had SART, DART, fixed-beam IMRT, and 3DCRT plans generated. Conformality index (CI) was the ratio of the volume of the 60Gy isodose surface to the volume of the PTV. Heterogeneity index (HI) was the ratio of the dose delivered to 5% of the PTV to the dose delivered to 95% of the PTV. The 4 techniques were compared in terms of PTV coverage, dose-volume histograms, and sparing of normal tissue using t-test analyses. ResultsThe median PTV for the 8 patients was 419cc (range 237-662). When compared to 3DCRT, IMRT resulted in significantly lower pulmonary V5 (40% vs. 50%, p < 0.001), V10 (34% vs. 40%, p < 0.001), V20 (27% vs. 28.6%, p = 0.05), and mean lung dose (14Gy vs. 16Gy, p < 0.001). 3DCRT achieved lower pulmonary V5, V10, and V20 values compared to SART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.03; V20: 29% vs. 32%, p = 0.02) and DART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.02; V20: 29% vs. 32%, p = 0.02), but mean lung dose was similar between 3DCRT, SART, and DART. When compared to SART, IMRT plans resulted in significantly lower pulmonary V5 (40% vs. 59%, p < 0.001), V10 (34% vs. 48%, p < 0.001), V20 (27% vs. 32%, p = 0.001), and mean lung dose (14Gy vs. 17Gy, p < 0.001). The same held true when IMRT was compared to DART. There was no significant difference in pulmonary DVH between SART and DART. Heart V60 was similar for all planning techniques, but heart V40 was significantly higher with 3DCRT. Mean esophageal dose was lowest with IMRT with no difference between any of the techniques in terms of the esophageal V60. The CI for 3DCRT was significantly inferior compared to the other 3 techniques. The CI for IMRT, SART, and DART were equivalent. There was no difference in HI between the 4 planning techniques. The mean total monitor units for SART was significantly less compared to IMRT (293 vs. 654, p < 0.001) and DART (293 vs. 314, p = 0.02), but similar to 3DCRT. The median PTV for the 8 patients was 419cc (range 237-662). When compared to 3DCRT, IMRT resulted in significantly lower pulmonary V5 (40% vs. 50%, p < 0.001), V10 (34% vs. 40%, p < 0.001), V20 (27% vs. 28.6%, p = 0.05), and mean lung dose (14Gy vs. 16Gy, p < 0.001). 3DCRT achieved lower pulmonary V5, V10, and V20 values compared to SART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.03; V20: 29% vs. 32%, p = 0.02) and DART (V5: 50% vs. 59%, p = 0.03; V10: 40% vs. 48%, p = 0.02; V20: 29% vs. 32%, p = 0.02), but mean lung dose was similar between 3DCRT, SART, and DART. When compared to SART, IMRT plans resulted in significantly lower pulmonary V5 (40% vs. 59%, p < 0.001), V10 (34% vs. 48%, p < 0.001), V20 (27% vs. 32%, p = 0.001), and mean lung dose (14Gy vs. 17Gy, p < 0.001). The same held true when IMRT was compared to DART. There was no significant difference in pulmonary DVH between SART and DART. Heart V60 was similar for all planning techniques, but heart V40 was significantly higher with 3DCRT. Mean esophageal dose was lowest with IMRT with no difference between any of the techniques in terms of the esophageal V60. The CI for 3DCRT was significantly inferior compared to the other 3 techniques. The CI for IMRT, SART, and DART were equivalent. There was no difference in HI between the 4 planning techniques. The mean total monitor units for SART was significantly less compared to IMRT (293 vs. 654, p < 0.001) and DART (293 vs. 314, p = 0.02), but similar to 3DCRT. ConclusionsThough ART may provide more rapid treatment delivery for stage III NSCLC compared to IMRT, it is associated with significantly larger volumes of low dose pulmonary irradiation. This increased volume of low dose pulmonary irradiation may increase the risk of clinically significant radiation pneumonitis. Therefore, ART should be used with caution for stage III NSCLC. Though ART may provide more rapid treatment delivery for stage III NSCLC compared to IMRT, it is associated with significantly larger volumes of low dose pulmonary irradiation. This increased volume of low dose pulmonary irradiation may increase the risk of clinically significant radiation pneumonitis. Therefore, ART should be used with caution for stage III NSCLC.