(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: may arise when treating multiple brain metastases (MBM) with a range of volumes, such that a subset of lesions require multi-fraction treatment. We demonstrate a new planning technique using Brainlab Elements combining single fraction and fractionated radiosurgery plans, to deliver the intended dose while minimizing undesirable dose contributions.
Methods: tumors were identified on MRI with volumes as follows: Tumor1 (7.261cc), Tumor2 (0.284cc), Tumor3 (0.348cc), and Tumor4 (1.227cc). Tumor1 was prescribed a five-fraction treatment (Plan1). The remaining lesions were prescribed a single-fraction treatment (Plan2). Both plans were generated with Brainlab Elements MBM (v2.0) for treatment on a Varian Truebeam STX Linear Accelerator. The summation plan was evaluated in Dose Review mode. The final dose to Tumor1 and Tumor3 exceeded the intended prescription dose, due to the close proximity of these lesions to one another. To mitigate this, Tumor3 was designated an organ at risk (OAR) in Plan1, and Tumor1 was designated an OAR in Plan2. The summation plan was again reviewed, and if needed, provided the basis for further changes to achieve the desired prescription.
Results: creating the OARs, Maximum dose contribution (MDC) from Plan1 to Tumor3 was reduced from 8.87CGy to 1.93Gy. MDC from Plan2 to Tumor1 was reduced from 3.55Gy to 1.51Gy. Tumor1 received 25Gy in 5 fractions to 95% of the target volume, and Tumor2, Tumor3, and Tumor4 received 20.25Gy, 15Gy, and 20.25Gy in a single fraction to 95% the target volume, respectively.
Conclusion: of the summation plan dose distribution using Dose Review mode revealed unintended dose contributions from adjacent lesions. This was mitigated by designating tumors as OARs and implementing dose constraints to reduce dose contributions. Combining SRS and FSRS is a feasible technique to achieve the prescription dose with the increased efficiency of MBM planning and delivery.
Keywords
Taxonomy
TH- External Beam- Photons: treatment planning/virtual clinical studies
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