eContour

58 y/o F with borderline resectable pancreatic adenocarcinoma cT4N0M0, s/p neoadjuvant FOLFIRINOX x4C with local progression, gem/nab-paclitaxel x3C, now on single-agent gem. Referred for consideration of pre-operative radiotherapy.

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Technique: She was treated with SBRT 40 Gy in 5 fractions daily.

  • She was treated with expiratory gating using her biliary stent as a fiducial.
  • For IGRT, we used daily CBCT (alignment to fiducial), and fluoroscopy with continuous imaging during treatment (to ensure fiducial remains in target contour).

Dose: 40 Gy to the tumor, 25 Gy to elective nodal regions, performed as simultaneous integrated boost.

Simulation:

  • NPO ~3 hours, supine, arms up, vac bag/alpha cradle, wingboard.
  • Biphasic CT (arterial and venous), 4D CT, fuse PET and/or MRI if available.
    • Arterial CT provides peak lesion to parenchymal contrast as the lesion remains hypodense while normal pancreas enhances.
  • Motion management/IGRT: Respiratory gating with fiducials (ie, biliary stent, gold seeds) versus breath hold, respiratory tracking (with CyberKnife); CBCT daily, fluoroscopy.
  • Delivery QD or QOD (extrapolating from studies in prostate and HCC).

Contours per RTOG-0848 atlas and 2012 RTOG Consensus Guidelines.

GTV: Visible tumor on CT/PET/MR.

CTV: None

ITV: Use 4DCT. We prefer expiratory gating with fiducials (breath hold if does not have/cannot get fiducials).

  • Also contour fiducial+1mm isotropic expansion for tracking on fluoroscopy.

PTV40: ITV + 3mm (given immobilization, fiducials, and CBCT daily).

CTV25: Elective nodal regions (peripancreatic, celiac, superior mesenteric artery, porta hepatic, para-aortic nodes). 

PTV25: CTV25 + 5mm (no ITV, and slightly bigger PTV since IGRT is aligned to tumor)

Optional: PTV50 simultaneous integrated boost to tumor/vascular interface (if can still safely meet duodenum/bowel constraints).

OARs: Duodenum given proximity (granted irradiated duodenum will be removed if patient goes to surgery, but can be hard to predict so we prioritize duodenal constraints over tumor coverage).

  • Dmax<40Gy (strict), V33<1cc (strict), and V30<5cc (softer constraint).
  • Requires very careful contouring of pancreas versus duodenum.
  • We do not use a duodenum PRV.

Higher BED improves local control:

  • 40 Gy in 5 fractions has BED ~70 with local control ~80%.
  • Recent interest in escalating 50 Gy in 5 fractions (BED ~100), but requires MRI Linac for accurate delivery.
  • Reference Koay PRO 2020 for dose escalation techniques and OAR constraints.

Pros of SBRT:

  • Dose-escalation and shortened treatment time to prioritize intensive chemotherapy (ie, FOLFIRINOX).
  • Caution adjacent duodenum (requires motion management and stringent IGRT to minimize risk duodenal toxicity).

Elective nodal irradiation (ENI) is controversial:

  • While nodal recurrences are not common, ENI may reduce marginal misses (Kharofa AJCO 2019, Miller IJROBP 2022).
  • SBRT delivery is targeted/precise with steep dose gradient, but tumor delineation can be difficult given infiltrative nature of pancreatic cancer.
  • ENI is also tolerable and does not increase late or serious acute toxicity (Miller IJROBP 2022).