A comparison of treatment plan quality between Tri-Co-60 intensity modulated radiation therapy and volumetric modulated arc therapy for cervical cancer

Purpose: To investigate the plan quality of tri-Co-60 intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for cervical cancer. Methods: A total of 20 patients who received postoperative radiotherapy for cervical cancer were selected. For each patient, a tri-Co-60 IMRT plan for which the target volume was the planning target volume (PTV) generated by adding 1 mm isotropic margins from the clinical target volume (CTV) and a VMAT plan for which the target volume was the PTV generated by adding 7 mm and 10 mm margins from the CTV were generated. The tri-Co-60 IMRT plans were generated with the ViewRay (TM) system while the VMAT plans were generated with 15-MV photon beams from a linear accelerator (prescription dose = 50.4 Gy in 28 fractions). Results: The average volumes of the PTVs and CTVs were 704.9 cc +/- 87.8 cc and 271.6 cc +/- 51.6 cc, respectively. No noticeable differences in the dose-volumetric parameters for the target volumes were observed between the tri-Co-60 IMRT and VMAT plans. The values of V-40Gy for the small bowel and rectal wall, V-45Gy of the bladder, and V-35Gy of the femoral heads for the VMAT plans were 14.6% +/- 7.8%, 54.4% +/- 4.2%, 30.0% +/- 4.7%, and 8.9% +/- 3.3%, respectively. Those of the tri-Co-60 IMRT plans were 2.8% +/- 2.1%, 23.0% +/- 8.9%, 17.1% +/- 6.1%, and 0.3% +/- 0.4%, respectively. Conclusions: Owing to the target margin reduction capability, the tri-Co-60 IMRT plans were more favorable than the VMAT plans for cervical cancer. (C) 2017 Published by Elsevier Ltd on behalf of Associazione Italiana di Fisica Medica.