Proton Beam Therapy

Overview

Proton beam therapy uses accelerated protons rather than photons to deliver radiation, exploiting the Bragg peak to deposit the maximum dose at a precisely defined depth and reduce exit dose beyond the target. This physical property can potentially reduce doses to organs at risk (duodenum, liver, kidneys, bowel) in gastrointestinal tumours. In pancreatic cancer, proton SBRT has been evaluated in the neoadjuvant setting.

Used by

  • Harvard proton beam Phase I/II programme (50 patients across studies, 25 Gy in 5 fractions with concurrent capecitabine) evaluated for neoadjuvant locally advanced and borderline-resectable pancreatic cancer; achieved 84% R0 resection in 39 resected patients, 4.1% grade 3 acute toxicity, 27-month median survival, and 16% locoregional recurrence. PMID:27826200

Notes

  • Dose regimen in pancreatic neoadjuvant series: 25 Gy in 5 fractions with concurrent capecitabine.
  • R0 resection rate 84% among patients who proceeded to surgery — comparable to or exceeding linac-based SBRT series.
  • Low acute toxicity (4.1% grade 3) due to reduced doses to adjacent OARs from Bragg peak dosimetry.
  • No prospective head-to-head comparison vs photon SBRT in pancreatic cancer.
  • As of 2016, proton beam therapy for pancreatic SBRT was limited to a small number of specialised centres.

Sources

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