(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Complex intracranial SRS can be expedited and optimized by comprehensive planning of all lesions to be treated simultaneously. We evaluated SRS plan quality using VMAT and TomoTherapy based treatment planning for a patient with 19 intracranial lesions.
Methods: A patient received linac-based SRS treatment and this was used retrospectively to inter-compare VMAT and TomoTherapy planning and delivery. Target volumes ranged from 0.01 cc to 11.99 cc. Radiation doses of 20 Gy, 18 Gy and 16 Gy were respectively prescribed to 6, 10 and 3 GTVs. VMAT treatment was delivered using 6MV FFF photon beam with a single isocenter and 4 arc rotations on a linac that offered 0.5 and 1.0 cm MLC. The patient was retrospectively re-planned using TomoTherapy with 6MV FFF photon beam and 1 cm collimation to compare the dosimetric results. Nine GTVs with volumes greater than 1 cc were chosen for analysis. Plans were compared using conformity index (CI), V100, D100 and D90. The dose to the OARs (whole brain, brainstem and optic chiasm) was also evaluated.
Results: VMAT showed superior CI (1.27 ± 0.12) compared to TomoTherapy (1.81 ± 0.59). The average V100 was similar for both VMAT (98.8 ± 1.0%) and TomoTherapy (98.4 ± 1.6%). V95 and V90 were 100% for the 9 targets in both plans. D100 and D90 were comparable for both plans. The mean dose to the whole brain was higher for the TomoTherapy (8.6 Gy, range: 1.5 – 23.4 Gy) compared to VMAT (2.6 Gy, range: 0.1 – 29.1 Gy). Brainstem and optic chiasm also received higher maximum dose with TomoTherapy (18.8 and 8.3 Gy) compared to VMAT (1.0 and 0.2 Gy).
Conclusion: Our results demonstrate that for this complex SRS case, VMAT plan was superior with better CI and less dose to the OARs while providing similar dose coverage.
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