65 year old male with stage IVA NSCLC (large cell carcinoma) with single right 3.5cm symptomatic occipital metastasis status post subtotal resection for linac based FSRT to post-op cavity.


Rx: The patient received LINAC-based, fractionated stereotactic radiotherapy to a single post-operative brain metastasis cavity.


  • The patient was CT-simulated using 1mm image slices with immobilization using a thermoplastic mask in supine position.
  • Volumetric MRIs with 1-2 mm slice thickness were fused with the planning image set using rigid registration, utilizing the T1 weighted post gadolinium and T2 weighted sequences.
  • Treatment was delivered by two co-planar arcs and one non-planar arc at a single isocentre with a 6MV FFF photon beam using VMAT technique on a hexapod couch with a 1mm tolerance for positional error.
  • Daily CBCT was used for treatment setup verification.


Case contributed by Queen's University



  • Gross residual disease if present.
  • Hypoxic tumor volume (HTV) if present. 
  • The enhancing cavity was delineated using the T1 post gadolinium sequence as the GTV.
  • Finally, a 2mm isotropic expansion was applied to the GTV or CTV for intact and cavities, respectively, to generate a planning target volume (PTV).


CTV (per Soliman IJROBP 2018, Mahajan Lancet Oncol 2017, Minniti Radiation Oncology 2021)

  • Entire contrast-enhancing surgical cavity on T1-weighted post-gad MRI.
  • A subsequent 2-3mm expansion is added to the GTV to incorporate any microscopic disease as a clinical target volume.
  • Do not include edema or bone.
  • Include entire surgical tract.
  • Bone flap coverage:
    • If tumor was in contact with dura, include 5-10 mm along bone flap beyond the initial contact.
    • If not in contact with dura, include 1-5 mm along the bone flap.
    • If tumor contacted venous sinus preoperatively, include 1-5 mm along the sinus
  • PTV: 2 mm* uniform expansion on CTV
    • *Dependent on institution, technology, and setup

Post-op FSRT Prescription Alliance A071801 trial

PTV Volume

Dose / Fractionation


27 Gy / 3 fractions

≥ 30 cc to <5cm

30 Gy / 5 fractions

Plan Specification: The dose should be prescribed to the highest isodose line encompassing the PTV (surgical cavity plus 2mm), which can range from 45-95% of the maximum dose

Dose Uniformity, Conformity, and Dose Spillage:

Conformity Index CI = V100%/PTV should be between 1-2, for lesions less than 5mm up to 3.0 is acceptable



3 fractions

5 fractions


V18 Gy ≤ 0.5cc;

Maximum point dose  ≤ 23.1 Gy

V23Gy ≤

 0.5 cc;

Maximum point dose < 28 Gy

Optic Pathway

V13.8 Gy < 0.2cc;

Maximum point dose < 17.4 Gy

V20 Gy < 0.2cc;

Maximum point dose < 23 Gy