Dosimetric comparison of Volumetric Modulated Arc Therapy and intensity-modulated radiotherapy for bilateral hip prostheses prostate cancer patient

Abstract

Introduction Volumetric Modulated Arc Therapy (VMAT) is a common technique for prostate cancer patients, due to the conformation of the dose distribution. The high atomic number of the hip prostheses, avoiding beam entry through the prostheses, makes this treatment complicated. Purpose Compare the dosimetric quality of intensity-modulated radiotherapy (IMRT) with VMAT for the treatment of prostate cancer in patients with bilateral hip prostheses. Materials and methods Plans for IMRT and VMAT were optimized, prescribing 78 Gy/39 fractions. First a soft-tissue density was overridden to the artifact CT areas, and both prostheses were contoured to avoid them during the treatment. Three IMRT treatment plans were proposed, 7-field, 9-field and 11-field, all optimized with constrained beam inverse planning, fixing jaws during the optimization. Two VMAT treatment plans were optimized with avoiding sectors (AS), one with large AS, and one with small AS, both VMAT plans were optimized with two arcs. Results IMRT technique has better dose distribution than VMAT technique. 11-field IMRT showed the best dose conformation, and in VMAT technique, small AS was the best solution. 11-field IMRT Homogeneity Index was 0.046 against 0.077 of the VMAT small AS. 11-field IMRT Rectum V50 was 28.50% versus 40.90% for VMAT small AS. UM and treatment had better results in VMAT technique. UM were significantly larger for IMRT, a 60.36% for 11-field IMRT compared with VMAT small AS. Conclusion 11-Field IMRT showed better conformation across PTV and lower rectal and bladder dose comparing to the other plans analyzed, despite of its larger treatment time and number of UM.