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Feasibility of segmental total body irradiation (SegTBI) using a 1.5T MR-linac
Matthew Manhin Cheung1, Ashley Chi Kin Cheng2,3,4, Louis Lee1,3
1Medical Physics Division, Department of Medical Innovation & Technology, CUHK Medical Centre, Hong Kong SAR, China.
Objective:
To evaluate the technical feasibility of using the elekta unity magnetic resonance linac (MRL) as a backup for tomotherapy in total body irradiation (TBI) treatment.
Methods:
A single pediatric patient's TBI treatment with a prescription of 12 Gy in six fractions was retrospectively re-planned using a multiple-isocentre approach with dose feathering on the MRL system. An additional plan was created and delivered to an anthropomorphic phantom containing OSLDs. The study investigated the MRL system's limitations and capabilities.
Results:
The plan sum of the nine segments not only met the dosimetric criteria of planning targets but also demonstrated the MRL system's capabilities by keeping the mean lung dose below 8 Gy and the mean kidney dose below 10 Gy. The electron streaming effect was observed. Treatment plan verification using ArcCHECK measurements with a global 3%/2 mm gamma analysis had a pass rate greater than 95% for all segments. In 28 out of the 30 OSLDs in brain, bone, and soft tissues, the deviation of the measurement from the reported TPS dose is within ±5%. A much larger deviation was observed in the lung tissues. Segmental TBI using the MRL was a viable option for TBI treatment.
Significance:
This study demonstrates the technical feasibility of MRL for TBI by offering dose modulation and imaging capabilities. The MRL can serve as a backup despite longer planning and treatment times. The potential for future workflow optimizations could enhance its practicality. This research improves flexibility in treatment planning and delivery for TBI patients.
