Conformal Anal Cancer Pelvis Radiotherapy Treatment with VMAT

Abstract

Purpose/Objective(s)Radiotherapy (RT)-Volumes for anal cancer are large and complex when organs at risk (OAR) like testis/small bowel/bladder are at least partially to be shielded. Step-and-shoot intensity modulated radiotherapy (IMRT) may improve the dose distribution but is still time consuming. Volumetric intensity modulated arc therapy (VMAT) might have the potential to produce comparable results with better treatment efficiency. We compared dose distributions generated with VMAT, conformal 3D-RT and step-and-shoot IMRT for typical anal cancer planning target volumes (PTV).Materials/Methods8 typical patients with anal cancer treated previously at our department were chosen. A typical PTV including the primary tumor, pelvic and inguinal lymph nodes was planned to receive a mean dose of 36 Gy. VMAT plans were generated with ERGO++ 1.7 (Elekta) version based on a recently implemented modified Bortfeld-algorithm. This technique with 2 rotations was compared to a 9 beam step-and-shoot IMRT (Corvus 6.3, Nomos) and the routinely applied refined 3D-RT (Masterplan, Theranostic). All three planning systems used the same structure set for OAR and PTV on identical CT datasets. These 3 treatment techniques were compared using dose-volume histograms (DVH) of the OARs and PTV. In addition, the conformality index (CI) and the homogeneity index (HI) as described in the RTOG guidelines and the total treatment time (TTT) were analyzed. All data are presented as mean values ± standard deviation (SD).ResultsIn the high dose region the VMAT showed the best coverage of the PTV described by the following values (isodose as percentage of prescription dose [PD] encompassing 95% of the PTV / percentage of tissue outside the PTV encompassed by 95% of PD). For VMAT the values are (92 ± 1% / 2.2 ± 0.9%), for IMRT (89.8 ± 1% / 0.7 ± 2.6%) and for 3D-RT (94.7 ± 0.7% / 5.4 ± 1.5%). With values of 1.33 ± 0.21 and 1.39 ± 0.08, the CI's for IMRT and VMAT are better than for 3D-RT with 1.71 ± 0.11. The HIs for the prescribed dose (HI36) for 3D-RT and VMAT with values of 1.06 ± 0.01 and 1.11 ± 0.02, respectively, are slightly better than for IMRT with 1.15 ± 0.02. Dose to OAR for 3D-RT and VMAT were similar with the exception of the bladder (minimal dose [99.0% of PD] to bladder: VMAT 21 Gy ± 9.3; 3D-RT 30 Gy ± 4.8). The TTT considers the beam-on-time (BOT) and the gantry movements. The mean TTT for 3D-RT is 220 seconds and for IMRT 557 seconds. The TTT for VMAT for one single arc is estimated with 90 seconds.ConclusionsVMAT produces high quality treatment plans with excellent conformality and homogeneity. The main advantages of this new approach are the shorter treatment delivery time and a lower number of monitor units. Purpose/Objective(s)Radiotherapy (RT)-Volumes for anal cancer are large and complex when organs at risk (OAR) like testis/small bowel/bladder are at least partially to be shielded. Step-and-shoot intensity modulated radiotherapy (IMRT) may improve the dose distribution but is still time consuming. Volumetric intensity modulated arc therapy (VMAT) might have the potential to produce comparable results with better treatment efficiency. We compared dose distributions generated with VMAT, conformal 3D-RT and step-and-shoot IMRT for typical anal cancer planning target volumes (PTV). Radiotherapy (RT)-Volumes for anal cancer are large and complex when organs at risk (OAR) like testis/small bowel/bladder are at least partially to be shielded. Step-and-shoot intensity modulated radiotherapy (IMRT) may improve the dose distribution but is still time consuming. Volumetric intensity modulated arc therapy (VMAT) might have the potential to produce comparable results with better treatment efficiency. We compared dose distributions generated with VMAT, conformal 3D-RT and step-and-shoot IMRT for typical anal cancer planning target volumes (PTV). Materials/Methods8 typical patients with anal cancer treated previously at our department were chosen. A typical PTV including the primary tumor, pelvic and inguinal lymph nodes was planned to receive a mean dose of 36 Gy. VMAT plans were generated with ERGO++ 1.7 (Elekta) version based on a recently implemented modified Bortfeld-algorithm. This technique with 2 rotations was compared to a 9 beam step-and-shoot IMRT (Corvus 6.3, Nomos) and the routinely applied refined 3D-RT (Masterplan, Theranostic). All three planning systems used the same structure set for OAR and PTV on identical CT datasets. These 3 treatment techniques were compared using dose-volume histograms (DVH) of the OARs and PTV. In addition, the conformality index (CI) and the homogeneity index (HI) as described in the RTOG guidelines and the total treatment time (TTT) were analyzed. All data are presented as mean values ± standard deviation (SD). 8 typical patients with anal cancer treated previously at our department were chosen. A typical PTV including the primary tumor, pelvic and inguinal lymph nodes was planned to receive a mean dose of 36 Gy. VMAT plans were generated with ERGO++ 1.7 (Elekta) version based on a recently implemented modified Bortfeld-algorithm. This technique with 2 rotations was compared to a 9 beam step-and-shoot IMRT (Corvus 6.3, Nomos) and the routinely applied refined 3D-RT (Masterplan, Theranostic). All three planning systems used the same structure set for OAR and PTV on identical CT datasets. These 3 treatment techniques were compared using dose-volume histograms (DVH) of the OARs and PTV. In addition, the conformality index (CI) and the homogeneity index (HI) as described in the RTOG guidelines and the total treatment time (TTT) were analyzed. All data are presented as mean values ± standard deviation (SD). ResultsIn the high dose region the VMAT showed the best coverage of the PTV described by the following values (isodose as percentage of prescription dose [PD] encompassing 95% of the PTV / percentage of tissue outside the PTV encompassed by 95% of PD). For VMAT the values are (92 ± 1% / 2.2 ± 0.9%), for IMRT (89.8 ± 1% / 0.7 ± 2.6%) and for 3D-RT (94.7 ± 0.7% / 5.4 ± 1.5%). With values of 1.33 ± 0.21 and 1.39 ± 0.08, the CI's for IMRT and VMAT are better than for 3D-RT with 1.71 ± 0.11. The HIs for the prescribed dose (HI36) for 3D-RT and VMAT with values of 1.06 ± 0.01 and 1.11 ± 0.02, respectively, are slightly better than for IMRT with 1.15 ± 0.02. Dose to OAR for 3D-RT and VMAT were similar with the exception of the bladder (minimal dose [99.0% of PD] to bladder: VMAT 21 Gy ± 9.3; 3D-RT 30 Gy ± 4.8). The TTT considers the beam-on-time (BOT) and the gantry movements. The mean TTT for 3D-RT is 220 seconds and for IMRT 557 seconds. The TTT for VMAT for one single arc is estimated with 90 seconds. In the high dose region the VMAT showed the best coverage of the PTV described by the following values (isodose as percentage of prescription dose [PD] encompassing 95% of the PTV / percentage of tissue outside the PTV encompassed by 95% of PD). For VMAT the values are (92 ± 1% / 2.2 ± 0.9%), for IMRT (89.8 ± 1% / 0.7 ± 2.6%) and for 3D-RT (94.7 ± 0.7% / 5.4 ± 1.5%). With values of 1.33 ± 0.21 and 1.39 ± 0.08, the CI's for IMRT and VMAT are better than for 3D-RT with 1.71 ± 0.11. The HIs for the prescribed dose (HI36) for 3D-RT and VMAT with values of 1.06 ± 0.01 and 1.11 ± 0.02, respectively, are slightly better than for IMRT with 1.15 ± 0.02. Dose to OAR for 3D-RT and VMAT were similar with the exception of the bladder (minimal dose [99.0% of PD] to bladder: VMAT 21 Gy ± 9.3; 3D-RT 30 Gy ± 4.8). The TTT considers the beam-on-time (BOT) and the gantry movements. The mean TTT for 3D-RT is 220 seconds and for IMRT 557 seconds. The TTT for VMAT for one single arc is estimated with 90 seconds. ConclusionsVMAT produces high quality treatment plans with excellent conformality and homogeneity. The main advantages of this new approach are the shorter treatment delivery time and a lower number of monitor units. VMAT produces high quality treatment plans with excellent conformality and homogeneity. The main advantages of this new approach are the shorter treatment delivery time and a lower number of monitor units.