Kaplan lecture 2023: lymphopenia in particle therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Immunology

Background:

• Lymphopenia, a decrease in lymphocytes, is a recognized negative prognostic factor in radiotherapy.
• Previous research indicated that high-energy carbon ions cause less lymphocyte damage than X-rays, despite higher efficacy in inducing chromosomal aberrations ex-vivo.
• The 'volume effect' in Bragg peak therapy, sparing larger normal tissue volumes, explains this difference.

Purpose of the Study:

• To review current knowledge on the differential impact of particle versus photon therapy on lymphopenia.
• To discuss the clinical consequences of radiotherapy-induced lymphopenia.

Main Methods:

• Review of existing scientific literature and clinical evidence comparing particle therapy (e.g., carbon ions) and photon therapy (X-rays).
• Analysis of the radiobiological mechanisms underlying lymphocyte sparing.
• Evaluation of the clinical implications of lymphopenia in the context of different radiation modalities.

Main Results:

• Particle therapy significantly reduces radiotherapy-induced lymphopenia across various tumor sites.
• This reduction is attributed to the physical properties of particle beams, such as the Bragg peak, which allow for better sparing of surrounding healthy tissues.
• X-ray therapy, conversely, is associated with more pronounced lymphopenia.

Conclusions:

• Particle therapy offers a significant advantage in mitigating radiation-induced lymphopenia.
• Reduced lymphopenia may enhance immune responses to checkpoint inhibitors, suggesting particle therapy as an ideal partner for combined radiation and immunotherapy.
• Particle therapy should be considered for patients at risk of severe lymphopenia with conventional X-ray treatment.