SU-E-T-592: Comparison of Low Dose Volume and Integral Dose in Rotational Arc Radiation Therapy Modalities.

PURPOSE To compare low dose volume and integral dose of various rotational arc radiation therapy modalities, including helical tomotherapy (HT) and other volumetric modulated arc therapies (VMAT). METHODS A digital cylindrical phantom and an anthropomorphic pelvic phantom were used in the study. HT treatment was planned on TomoTherapy Planning Station (Accuray) and VMAT plans were generated on Pinnacle (Philips) and Eclipse (Varian). Same objectives and criteria were used for all the planning tasks. Tomotherapy plans were made with both 1cm jaw and 2.5cm jaw. Pinnacle SmartArc and Eclipse RapidArc plans used 1 arc and 2 arcs. Plan quality was evaluated by dose-volume histograms, conformity index (CI), and heterogeneity index (HI). V10% and V20% of body were used in quantifying low dose volume. Integral doses were computed for each plan and compared. Dose profiles across the target center were retrieved to show the rate of dose falls off. RESULTS All arc TPS generated clinically acceptable plan with comparable target CI and HI. The V20% of body of the cylindrical phantom case were 3551cc, 4054cc, 3375cc, 3438cc, 3714cc and 3679cc for tomotherapy 1 cm and 2 cm jaw, SmartArc 1 arc and 2 arc, and RapidArc 1 arc and 2 arc plans, respectively. The integral doses were 19.67, 22.78, 18.68, 18.50, 19.78 and 19.73 Joule, respectively. For the anthropomorphic phantom, the integral doses were 81.69, 102.77, 84.5 and 82.5 Joule for tomotherapy 1cm, 2cm, SmartArc 1arc and RapidArc 1arc, respectively. Dose profiles showed tomotherapy 1cm plan had similar longitudinal penumbra as SmartArc and RapidArc, while tomotherapy 2.5cm plan produced significant broader penumbra. CONCLUSIONS Similar low dose volume and integral dose are found in SmartArc, Rapid Arc, and as well as helical tomotherapy plan of 1cm jaw. Tomotherapy plans of 2.5cm jaw, however, shows higher low dose volume and integral dose.