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Particle therapy such as PT has significant advantages over photon RT
The advancements and advantages of proton-based technology PT utilises charged particles to deliver radiation to tumours , depositing the dose at a narrow depth . This is advantageous for RT for two reasons : the tissue penetration of protons is deeper than photons , and the density of ionisation is narrower meaning less radiation dose is exposed to surrounding tissues . The depth-dose curve of photons can be represented by a Bragg peak , exemplifying the superiority of dose confinement compared to photons , meaning PT has a superior relative biological effectiveness (“ RBE ”) compared to photons ( Figure 25 ). Although to date most PT has been delivered via passively scattered PT (“ PSPT ”) – effectively single beam treatment – there is potential to optimise the dose delivery using intensity-modulated PT (“ IMPT ”) further still – employing beamlets of protons in layers via pencil beam scanning (“ PBS ”) which utilises a magnet to optimise delivery . These methods further limit the dose of protons to the target area of cancer cells to minimise tissue damage . There is also evidence to suggest that PT is less toxic to radiosensitive circulating lymphocytes , thus reducing the depletion of these cells and radiation-induced lymphopenia seen in response to standard RT , however this does still occur to an extent . This therefore spares the patient ’ s immune cell population following rounds of PT and could also indicate a superior synergy with immunotherapy than standard RT .
Figure 25 : Bragg peak and energy distribution
Source : goetzpartners Research
Figure 26 : Comparative dosimetry for protons therapy vs . photon radiotherapy
Source : goetzpartners Research
Challenges to address for radiotherapy
Clear challenges remain to be solved for PT to be adopted as the SoC
The limitations of PT systems Despite clear advantages of PT , there are drawbacks and difficulties implementing it as the SoC . It is difficult to compare the direct advantages of proton and photon therapy , as most head-to-head studies employ IMRT for photons and PSPT for protons , thus major differences are likely masked by the superiority of multi-beam construction and TPS . It is clear PT offers improved side effects , there is
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