The application of multi-arc volumetric modulated arc therapy and fixed-field intensity modulated radiotherapy in the treatment of gynecologic cancer with large planning target volume.

To investigate the dosimetry and delivery efficiency differences between multi-arc volumetric modulated arc therapy (VMAT) and fixed-field intensity modulated radiotherapy (IMRT) in the treatment of gynecological cancer with large planning target volume (PTV). Thirteen patients with gynecological cancer (9 cervical and 4 vulvar) with a PTV greater than 1600 cm³ were retrospectively selected. Three-arc VMAT (3ARC) and seven-field IMRT plans were generated using identical objective functions from clinical two-arc VMAT (2ARC) plans to allow a rigorous comparison for each patient. Target coverage, OARs sparing, integral dose and delivery efficiency were compared through dose-volume histogram (DVH) analysis. Compared with 2ARC plans, IMRT exhibited a slightly superior target coverage with higher D_98%, CI and lower D_2%, D_50%, V_110% and HI (P < 0.01). For OARs, IMRT produced lower V_40Gy and D_mean to the bladder and rectum (P < 0.01) and lower V_40Gy to bone marrow than 2ARC (P < 0.05). No significant differences were observed for the colon, small bowel and femoral heads, while 2ARC performed worse at the low dose and integral dose to normal tissue (V_5Gy, V_10Gy and NTID, P < 0.01). Nevertheless, IMRT increased MUs by 1.65% and EDT by 107 s compared to 2ARC. Compared with 2ARC, 3ARC showed no improvement in target dose coverage, including D_98%, D_2%, D_50%, V_110%, CI and HI to PTV, but increased the doses to OARs (D_mean to the bladder, rectum and bone marrow, V_40Gy to the bone marrow and D_5% to both the left and right femoral heads, P < 0.05), low dose and integral dose to normal tissue (V_10Gy,V_15Gy,V_20Gy and NTID, P < 0.01) and simultaneously prolonged the EDT (P < 0.001). In the treatment of gynecological cancer with a large planning target volume, the IMRT technique can be delivered superior conformal dose to the target with somewhat better OARs sparing but increasing the estimated delivery time.