Optimized hybrid arc for improved sparing of organs at risk: balanced combination of IMRT and VMAT in prostate cancer

Abstract

Objective: In order to seek a lower toxicity risk prediction in patients with prostate cancer, we have evaluated whether prescribing a potential hybrid radiotherapy of intensity-modulated radiotherapy (IMRT) & volumetric modulated arc therapy (VMAT) optimization might increase sparing of organs at risk (OAR) and target dose conformity. Methods: The cohort for this dosimetric planning study included ten consecutive prostate cancer patients previously treated with double arc VMAT to 78 Gy. New optimized hybrid arc plans for a combination of IMRT (8 step-and-shoot fix fields: 225°, 260°, 295°, 330°, 30°, 65°, 90°, 135°) and VMAT (182°-178° clockwise) besides new IMRT (8 step-and-shoot fix fields: 225°, 260°, 295°, 330°, 30°, 65°, 90°, 135°) plans were generated per patient. Dose volume histogram parameters were compared between treated VMAT, new IMRT and new optimized hybrid arc plans for OAR doses. Results: The optimized hybrid arc technique revealed significantly lower rectum (p=0.005) and bladder (p= 0.005) doses compared to stand alone VMAT and IMRT. Conclusion: The optimized hybrid arc technique appears to combine the advantages of IMRT and VMAT to provide a more conformal and homogeneous plan with better OAR sparing in comparison to standalone VMAT or IMRT plans.