Radiation Without Tears – Particle Therapy
Radiation therapy is a key treatment modality for non-invasive and targeted cancer therapy Radiation delivery technology has now advanced to offering radiotherapy with high-energy charged particles as an attractive therapeutic option for patients with several tumour types because this approach better spares healthy tissue from radiation than conventional photon therapy.
The aim of radiation oncologists and medical physicists has been to maximize the radiation dose to the cancer and minimize the dose to healthy tissues. This has led to research with improvement of dose deposition and relatively equi-effective biological outcomes. Heavy charge particles like protons, neutrons, pions, and charged-nuclei (with argon, carbon, helium [alpha particles], neon, nitrogen, and silicon) have been assessed for their physical, biological, and clinical effects.
Charged particles have improved dose delivery accurately to the tumor with reduced exposure to nearby healthy tissue minimizing healthy tissue damage or ‘tears’. Charged particle radiotherapy uses beams of protons or other charged particles such as helium, carbon or other heavy ions.
Charged particles deposit most of their energy at the end of their path in a dose deposition pattern, termed the Bragg peak. The initial energy of the charged particles determines how deep in the body the Bragg peak will form. The intensity of the beam determines the dose that will be deposited to the tissues.
By adjusting the energy of the charged particles and by adjusting the intensity of the beam one can deliver prespecified doses anywhere in the patient’s body with high precision. To irradiate a whole tumor area, multiple Bragg peaks of different energies and intensities are combined.
These charged particles do not have an exit dose and actually lower dose deposition along the path of the beam. This makes charged particles have the potential to spare healthy tissue and to allow a more accurate targeting of energy deposition within tumor cells, potentially providing opportunities for focused dose escalation. Thus, particle therapy can reduce toxicities and risk for secondary tumors as a result of radiation exposure of healthy tissues.
The use of charged particle therapy to control tumours non-invasively offers advantages over conventional photon-(X-Ray) based radiotherapy. Charged particles are also useful for treating tumours located in areas that surround tissues that are radiosensitive and in anatomical sites in critical locations, e.g. at the skull base, where surgical access is limited.
In liver cancers and recurrent rectal cancers, Protons have shown that with one or two beams of energy the whole of cancer can be covered minimizing the time on table for the patient. For cancers in children, charged particles can eliminate cancers without giving a risk of second primary cancers or growth disturbances like limb shortening.
The treatment with Protons and charged particles is available in relatively few centers around the world and needs special teams including anesthesiologists for young children to keep them from moving during treatment.
Clinical outcomes indicate that accelerated ions may potentially replace surgery for radical cancer treatments.