Dosimetric comparisons of helical
plans and step-and-shoot intensity-modulated radiosurgery treatment
plans in intracranial stereotactic radiosurgery
Han C, Liu A, Schultheiss TE, Pezner RD, Chen YJ, Wong JYC
International Journal of Radiation Oncology, Biology, Physics 01 June 2006 (Vol. 65, Issue 2, Pages 608-616)
Purpose: To evaluate dose conformity, dose homogeneity, and dose gradient in helical tomotherapy treatment plans for stereotactic radiosurgery, and compare results with step-and-shoot intensity-modulated radiosurgery (IMRS) treatment plans.
Methods and Materials: Sixteen patients were selected with a mean tumor size of 14.65 ± 11.2 cm3. Original step-and-shoot IMRS treatment plans used coplanar fields because of the constraint of the beam stopper. Retrospective step-and-shoot IMRS plans were generated using noncoplanar fields. Helical tomotherapy treatment plans were generated using the tomotherapy planning station. Dose conformity index, dose gradient score index, and homogeneity index were used in plan intercomparisons.
Results: Noncoplanar IMRS plans increased dose conformity and dose gradient, but not dose homogeneity, compared with coplanar IMRS plans. Tomotherapy plans increased dose conformity and dose gradient, yet increased dose heterogeneity compared with noncoplanar IMRS plans. The average dose conformity index values were 1.53 ± 0.38, 1.35 ± 0.15, and 1.26 ± 0.10 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The average dose homogeneity index values were 1.15 ± 0.05, 1.13 ± 0.04, and 1.18 ± 0.09 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean dose gradient score index values were 1.37 ± 19.08, 22.32 ± 19.20, and 43.28 ± 13.78 in coplanar IMRS, noncoplanar IMRS, and tomotherapy plans, respectively. The mean treatment time in tomotherapy was 42 ± 16 min.
Conclusions: We were able to achieve better dose conformity and dose gradient in tomotherapy plans compared with step-and-shoot IMRS plans for intracranial stereotactic radiosurgery. However, tomotherapy treatment time was significantly larger than that in step-and-shoot IMRS.