Treatment plan comparison between Tri-Co-60 magnetic-resonance image-guided radiation therapy and volumetric modulated arc therapy for prostate cancer

Abstract

To investigate the plan quality of tri-Co-60 intensity-modulated radiation therapy (IMRT) with magnetic-resonance image-guided radiation therapy compared with volumetric-modulated arc therapy (VMAT) for prostate cancer. Twenty patients with intermediate-risk prostate cancer, who received radical VMAT were selected. Additional tri-Co-60 IMRT plans were generated for each patient. Both primary and boost plans were generated with tri-Co-60 IMRT and VMAT techniques. The prescription doses of the primary and boost plans were 50.4 Gy and 30.6 Gy, respectively. The primary and boost planning target volumes (PTVs) of the tri-Co-60 IMRT were generated with 3 mm margins from the primary clinical target volume (CTV, prostate + seminal vesicle) and a boost CTV (prostate), respectively. VMAT had a primary planning target volume (primary CTV + 1 cm or 2 cm margins) and a boost PTV (boost CTV + 0.7 cm margins), respectively. For both tri-Co-60 IMRT and VMAT, all the primary and boost plans were generated that 95% of the target volumes would be covered by the 100% of the prescription doses. Sum plans were generated by summation of primary and boost plans. In sum plans, the average values of V70 Gy of the bladder of tri-Co-60 IMRT vs. VMAT were 4.0% ± 3.1% vs. 10.9% ± 6.7%, (p < 0.001). Average values of V70 Gy of the rectum of tri-Co-60 IMRT vs. VMAT were 5.2% ± 1.8% vs. 19.1% ± 4.0% (p < 0.001). The doses of tri-Co-60 IMRT delivered to the bladder and rectum were smaller than those of VMAT while maintaining identical target coverage in both plans.

Keywords: magnetic-resonance image-guided radiation therapy; prostate cancer; volumetric modulated arc therapy.

Figure 1. Average dose volume histograms (DVHs) and DVHs of a representative patient (patient 18) are shown for the target volume, bladder, rectum, and femoral heads

The average DVHs from a primary plan (A), boost plan (C), and sum plan (E) are shown. The DVHs of a representative patient, from a primary plan (B), boost plan (D), and sum plan (F) are also shown. The DVHs of the volumetric modulated arc therapy (VMAT) plans are shown with solid lines while those of the tri-Co-60 intensity modulated radiation therapy (IMRT) plans are shown with dashed lines. TV(P), TV(B), FH, and VR are abbreviations of primary target volume, boost target volume, femoral heads and the ViewRay system, respectively.

Figure 2. Dose distributions of a representative patient (patient 18) are shown in axial, coronal and sagittal views

Dose distributions of a primary plan (A), boost plan (C), and sum plan (E) of the volumetric modulated arc therapy (VMAT) are shown. Those of a primary plan (B), boost plan (D), and sum plan (F) of the tri-Co-60 intensity-modulated radiation therapy (IMRT) are shown. The primary target volumes and the boost target volumes are delineated with cyan and green colors, respectively.