eContour

69 year old male with primary CNS lymphoma of the right temporal lobe s/p 5 cycles of IV methotrexate based chemotherapy with re-staging MRI showing 1 cm of residual tumor.

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Technique: He was treated with a combination of 2D RT (whole-brain radiation therapy volume) and VMAT (boost volume).

Dose: He received whole-brain radiation therapy followed by a sequential boost to the residual and at-risk areas of disease, as described below:

  • Initial volume: 23.4 Gy in 13 fractions to the whole brain (2D RT).
  • Boost volume: 22 Gy in 10 fractions to the gross residual disease, 18 Gy in 10 fractions to the residual edema, 15 Gy in 10 fractions to the edema present on initial pre-chemotherapy imaging (all boost volumes using VMAT).

Simulation: He was simulated supine with a thermoplastic mask and his arms at his sides. The following scans should be fused with the simulation images:

  • Initial MRI (T1, T1+contrast, T2, T2+FLAIR).
  • Interim MRI (T1, T1+contrast, T2, T2+FLAIR) if available.
  • Post-chemotherapy MRI (T1, T1+contrast, T2, T2+FLAIR).

 

Case contributed by MD Anderson Cancer Center

Contours/dosing per Morris JCO 2013 and Dabaja IJORBP 2020.

  • Whole-brain radiation therapy (WBRT): 23.4 Gy/13 fractions (no contours needed besides organs-at-risk).
  • Special considerations for WBRT:
    • Ensure dose coverage of the anterior temporal lobe, cribriform plate, and posterior aspect of the eyes.
    • Include the entire globes if slit-lamp exam indicates ocular involvement.
      • ~20% of patients will have ocular involvement at diagnosis 
    • Inferior field border to the lower border of the C2 vertebrae

  • Boost: 22 Gy/10 fractions to the post-chemotherapy GTV, 18 Gy/10 fractions to the post-chemotherapy CTV, 15 Gy/10 fractions to the pre-chemotherapy CTV.
    • Post-chemotherapy GTV = residual gross disease after chemotherapy completion, use fusion with post-chemotherapy MRI T1+contrast.
    • Post-chemotherapy CTV = residual edema/T2 FLAIR signal after chemotherapy completion, use fusion with post-chemotherapy MRI.
    • Pre-chemotherapy CTV = initial edema/T2 FLAIR signal present before chemotherapy initiation, use fusion with pre-chemotherapy MRI.

  • It is important to fuse different MRI sequences with the simulation images to identify gross disease, microscopic disease, and edema at the following timepoints: before treatment, at interim chemotherapy stages, and post-chemotherapy.
    • Using the fused images, it is essential to contour the initial tumor and extent of edema as well as the residual tumor and extent of edema on interim and post-chemotherapy MRIs as this represents different volumes that are at-risk for lymphoma involvement and will determine the differential radiation boost doses.

  • It is necessary to use a combination of radiation modalities (2D RT and IMRT/VMAT) to effectively target the whole-brain and boost volumes while decreasing the risk of significant toxicities that has been historically reported for high doses of whole-brain radiation therapy (per RTOG 9310/DeAngelis JCO 2002).