Study for Optimal Beam Angle Optimization in Planning Technique of Spinal Stereotactic Body Radiation Therapy

Kim, Eunseog

Abstract

OBJECTIVE
It is to find the optimum beam angle by comparing the proper directional beam angle with various methods at time of treatment plan of stereotactic spinal radiation therapy. Also, it is to increase the therapy efficiency of spinal stereotactic body radiation therapy (SBRT) by providing the optimal target coverage through the therapy plan establishing various kinds of direction of beams and by decreasing the integral dose.
METHODS
The object patients of treatment plan in this study have targeted 10 persons of thoracic spine bone metastasis patients. The treatment plan of prescription dose with 3 fraction of each 8 Gy has been established, it has been normalized so that it may be D95=2,400 cGy. Total 4 groups of treatment plan: the physical factor has been compared for the part for the target and the critical organ by establishing the treatment plan respectively in intensity-modulated radiation therapy (IMRT) and RapidArc therapy in (1) 1 group of IMRT (9 pieces of beam at 40 degrees equispaced angle intervals), (2) 2 groups of IMRT (9 pieces of half beam of non-equispaced angle), (3) arc 1 group (full arc), (4) arc 2 groups (half 2 arc) and eclipse planning (ver. 8.9). The physical factor for the target has been analyzed for the target coverage, maximum dose, minimum dose, maximum dose/prescribed dose (MD/PD). The maximum dose, mean dose, dose by each volume, and therapy time have been compared and analyzed for the spinal cord and esophagus adjacent to the target.
RESULTS
The maximum dose of patients group of IMRT 1 group has appeared lower by 15% compared with the full arc and half arc plan as the analysis result of therapy plan for the object patients of thoracic spine. There has been no big difference in maximum dose of IMRT 1 group and 2 group. The full arc plan of conformity index showed the best result with the average 1.06, half arc plan of conformity index showed the highest result value with the average 1.15. Half arc plan of MD/PD showed the best value with the average 1.12. The half IMRT in D1 of planning target volumes showed the lowest value with the average 2,605 cGy; it showed the difference from the average from as small as 1% to as big as 11% as the comparison result with other groups. The plan of IMRT group of non-equispaced angle in D99 (cGy) showed the best value with the average 2,287.56 cGy. The IMRT of non-equispaced angle in Dmax of spinal cord showed the lowest with the average 1,779.9 cGy, D0.1cc and D1cc as well showed the lowest value with the average 1,605.19 cGy and 1,272.63 cGy. The IMRT plan of non-equispaced angle in throat showed the lowest value. The full arc (2 arc) of equispaced angle in therapy time was the shortest with 3.54 minutes, full IMRT of equispaced angle showed the longest time with the average 8.08 minutes.
CONCLUSION
The treatment plan for IMRT of non-equispaced angle showed all good value in the target and critical organ as the analysis result of proper beam angle according to the respective therapy technique at time of treatment plan of spinal SBRT. It could find that the good therapy plan satisfactory to all target and critical organ at time of using the beam between 80 degrees and 280 degrees.