SU-E-T-529: Study of Second Cancer Risk in the Treatment of Multiple Lung Lesion by SBRT Using Rapid Arc: Comparison Between Different Treatment Planning Parameters




To compare the secondary cancer risk (SCR) between different plan settings (Collimator angle, number of Arcs and manual jaw opening) for Rapid Arc plan in the treatment of multiple lung lesion.


Patient with multiple lung lesion was planned with single isocenter (i) single arc (CW:200-160deg) and (ii) dual complementary arc. The plans were optimized to yield similar plan evaluation/acceptance criteria. The concept of equivalent OED (linear-exponential, plateau, and the linear dose– response model) was used to evaluate the Second Cancer Risk (SCR). Then, the single arc plan was generated using five different collimator setting (0,30,45,90,120 deg) and the OED was analyzed. Also, plans were generated with automatic jaw setting and compared against the manual jaw setting.


The SCR values were normalized to the single arc plan. For dual complementary arc, the relative SCR for Rt.lung were (linear, plateau, linear-exponential) (1.02,1.05,1.04), (0.99,1.02,1.02) for Lt.lung, (1.01,1.07,1.06) for Spinal cord, (1.18,1.1,1.09) for Esophagus, (1.3,1.19,1.16) for Heart, (1,1.01,1.02) for Lt.Breast and (1.05,1.05,1.05) for Rt.Breast. Since the single arc plan was superior in terms of SCR further analysis was carried out for various collimator angles. The low dose bath volumes 5Gy in cc for single and dual arc plans were 5468 and 5886 cc respectively. The computed OED values (linear-exponential) for Rt.Lung were (1,0.94,0.96,1.06,0.97), (1,0.89,0.97,1.11,0.9) for Lt.Lung, (1,0.86,0.98,1.2,0.92) for Spinal cord, (1,0.87,0.99,1.15,0.91) for esophagus, (1,0.88,1.01,1.11,0.94) for heart, (1,0.83,0.97,1.20,0.86) for lt.breast and (1,0.94,0.95,1.03,1.11) for Rt.breast for collimator setting (0,30,45,90,120 deg) respectively.


The Second cancer risk is considerably high for dual arc plan compared with single arc. In single arc plan the 30 degree collimator angle plan showed the least OED values for all critical structures, with the 90 degree collimator angle being the most. No significant difference between the manual and the automatic jaw setting plans were found.