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preliminary Protons toxicity dosimetry

Brain radiotherapy alone did not deplete circulating lymphocytes in a prospective cohort

Circulating lymphocyte counts remained stable during brain radiotherapy without concurrent chemotherapy, consistent with low estimated blood and cervical lymph-node dose

RadOncToday · ·1 min read

KEY POINTS

  • This prospective exploratory study enrolled 35 adults with primary brain tumors receiving radiotherapy without concurrent chemotherapy; 27 had benign tumors, predominantly meningiomas, and 8 had malignant tumors, predominantly gliomas.
  • Patients received proton therapy (n=26) or photon volumetric modulated arc therapy (n=9), with blood sampling before, during, at completion of, and after radiotherapy.
  • Absolute lymphocyte counts and evaluated lymphocyte subpopulations, including natural killer cells and CD4-positive and CD8-positive T cells, showed no significant population-level depletion during the observation period.
  • Estimated mean blood doses were approximately 0.1–0.2 Gy, while most superior cervical lymph nodes received minimal exposure.
  • Proton therapy produced approximately 25% lower blood dose and greater cervical lymph-node sparing than photon therapy, but neither modality was associated with significant lymphopenia.

CLINICAL TAKEAWAY

For patients receiving conformal radiotherapy to limited intracranial volumes without concurrent systemic therapy, brain irradiation alone may have little measurable effect on circulating lymphocyte populations. These findings suggest that lymphopenia observed during glioma chemoradiotherapy is unlikely to be explained solely by direct irradiation of circulating blood, but the small cohort and sparse subgroup sampling make the results hypothesis-generating rather than practice-changing.

SOURCE

International Journal of Radiation Oncology, Biology, Physics