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Sci-Thur AM: Planning - 03: Extensive patient specific QA for field junction regions for craniospinal irradiation
1Fraser Valley Centre, Department of Medical Physics, BC Cancer Agency, Surrey, British Columbia, Canada.
Purpose:
Jagged-Junction IMRT was developed for craniospinal irradiation. An extensive QA was performed for the field junction regions.
Methods And Materials:
The Jagged-Junction IMRT plan employed three field sets, each with unique isocentres (Iso1,2,3). Fields from adjacent sets were overlapped and the dose was smoothly integrated inside the overlapped junction. The delivered dose in the junction regions were verified with film and ion chamber measurements on phantoms. An anthropomorphic-wax phantom was created for verifying the cranio-spinal junction. For measuring at the spinal-spinal junction, a solid water phantom was used. The influence of beam mismatching due to setup and mechanical inaccuracy was investigated by shifting all the fields from Iso1 and Iso3 superiorly and inferiorly by 3 mm and at the same time keeping all the fields from Iso2 without any shift.
Results:
The patient-averaged difference between the measured dose with ion chamber and planned dose in the cranio-spinal junction is 0.34 % ± 0.40% and in the spinal-spinal junction this difference is 0.03% ± 0.71%. The dose profile comparison shows that measured and planned dose profiles match well to each other over a junction region. The patient-averaged dose difference discrepancy between the film measurement and the planned is 1.1% ± 1.3% at the cranio-spinal junction and -0.14% ± 1.8% at the spinal junction.
Conclusions:
Jagged-Junction IMRT planning provided smooth dose coverage to the target in the field junction region. The junction dose for the Jagged-Junction IMRT plan is not sensitive to the setup error during the treatment.
