Discussing the discrepancy between analytical calculations and the observed biological effectiveness in proton boron capture therapy (pbct)

TL;DR

This paper investigates the discrepancy between experimental evidence of enhanced biological effectiveness in proton boron capture therapy and traditional analytical calculations, highlighting the need for micro- and nano-dosimetric considerations.

Contribution

It demonstrates experimentally the biological enhancement in proton therapy with boron and discusses the limitations of classical dose calculations, emphasizing the importance of micro- and nano-dosimetry.

Findings

Experimental evidence of increased efficacy with boron in proton therapy

Classical dose calculations cannot explain the observed effects

Micro- and nano-dosimetry are crucial for understanding the phenomena

Abstract

A work recently published experimentally demonstrates an increase in the radiobiological efficacy of clinical proton beams when a tumour is treated in the presence of a concentration of 11B. The paper, for the first time, demonstrates the potential role of the p+11B to 3{\alpha} (for brevity, p-B) reaction in the biological enhancement of proton therapy effectiveness. The work reports robust experimental data in terms of clonogenic cell survival and chromosomal aberrations and unambiguously shows the presence of an enhancement when cells were exposed to a clinical proton beam subject to treatment with sodium boroncaptate (BSH). Moreover, the greater occurrence of complex-type chromosomal exchanges points to the effect as due radiation of a LET (Linear Energy Transfer) greater than that of protons alone, possibly the alpha particles generated by the reaction. At the same time, we emphasized that analytical calculations, performed on the basis of the well-known total production cross section data, are not able to explain the effect in a macroscopic way, i.e. solely in terms of a trivial increase in the total dose released in the cells by the alpha-particles. In this paper, thanks to simulations and analytical calculations, we will discuss the theoretically expected alpha particle yield and the corresponding LET and RBE (Relative Biological Effectiveness) increase related to the 11B presence. We conclude that a mere calculation based on the classical concepts of integral Dose, and average LET and RBE cannot be used to justify the observed radiobiological phenomena. We, therefore, suggest that micro- and nano-dosimetric aspects must be taken into account.