Dosimetric impact of collimator angles on VMAT planning for upper thoracic esophageal carcinoma

Objective: To evaluate the dosimetric impact from collimator angles during the VMAT planning for upper thoracic esophageal carcinoma. Methods: VMAT plans for 8 cases of upper thoracic esophageal were studied. Ten different plans with respective collimator angles (0, 5, 10, 15, 20, 25, 30, 35, 40, 45 degrees) were determined for each case, and the treatment planning parameters were compared. Results: The 20 degree group represented with best performance, and 0 and 45 degree group were most frequently used in clinical practice. Statistical analysis shown that among these groups, V₁₀, V₁₅ and V₃₀ of total lung were significantly different (F = 5.328, 8.033, 28.424, P < 0.05), and differences of maximal dose of spinal cord and total MU were also significant (F = 9.608, 4.464, P < 0.05). Conclusions: A proper collimator angle is important in VMAT planning for upper thoracic esophageal and may lead to optimal results. (authors)