Proton therapy employs proton beams to treat cancer. These beams penetrate tumors directly, doing most of their damage within them before dissipating into healthy tissues with little radiation left over in surrounding areas.
Protons offer another effective tool in cancer therapy compared to photons: precise targeting.
Accelerators
Accelerators used in proton therapy focus beams of protons using magnetic fields and radiofrequency energy, often including both. Common types of proton accelerators used are cyclotrons and synchrotrons.
A cyclotron employs a large single magnet to accelerate protons around a fixed radius vacuum tube where they are held. Once released from this accelerator at high energy levels, they are fed into another set of magnets known as degrader or energy selector system to reduce both their speed and energy level to meet patient treatment goals.
Protons in clinical settings are then focused using an array of quadrupole lenses that can be customized to the dimensions and shape of the patient. This produces a tight packed beam with high spatial resolution; quality of focus is verified using a detector such as PIXE (Particle Induced X-ray Emission), to produce grid images at various focal points in the beam; then its quality evaluated against an intensity distribution generated using Monte Carlo simulations using Los Alamos’ MCNPX code.
Proton therapy offers numerous advantages over photon radiation, as its much narrower range means protons deposit dose only where needed, leaving healthy tissues relatively undamaged. Furthermore, energy modifications to spread out their Bragg peak in patients allow more of their total beam’s radiation dose to reach its intended site of delivery.
Due to these reasons, precise positioning of patients is critical and should be guided by imaging methods such as X-ray and CT (in future also MRI). Any inaccuracy in positioning could result in errors of up to several millimeters between target and exit point of beam which result in errors in dose distribution.
To prevent this from occurring, ridge filters or range modulators are used to alter the beam path and stopping aperture of the proton beam, enabling therapists to select an ideal patient positioning in relation to shaping Bragg peaks more precisely. Furthermore, such devices also help ensure uniform proton dose distribution around targets.
Dose Delivery
Proton beam therapy uses protons rather than photons as its radiation source, and to determine an appropriate dose, radiation oncologists use CT scanner images of your tumor and surrounding area to develop a treatment plan that details how much radiation should be delivered in order to both destroy it and preserve healthy tissues.
Dosimetrists use computer programs to determine exactly how many protons and at what depth into the body should be delivered using computer simulation, as well as how best to position and move the beam around during treatment – this process is known as beam simulation. After creating this plan using real proton beams created from physical simulations by physicists based on this plan; delivered via large machines called gantries that rotate during treatment so that their protons reach you at precisely the right spot over your tumors.
Treatment typically comprises daily sessions over six weeks, each lasting less than an hour and conducted by an radiation oncologist. At each session, they ensure the proton beam covers the IGTV; due to tumor movement or changes in anatomy during treatment this may prove challenging; 4D-CT scans help identify such changes so that you can compensate for them accordingly.
Radiation from protons damages DNA within tumor cells, leading to their death and thus decreasing or eliminating tumor growth. Cellular damage also kills treatment-resistant cancer stem cells; perhaps explaining why proton beam therapy may be more successful in treating certain forms of cancers than photon radiation treatments.
Numerous studies have investigated proton beam therapy versus photon radiation in treating different tumors. One such research project with 55 medically inoperable patients with stage I non-small cell lung cancer found both treatments provided effective local control, while proton therapy improved lung function while decreasing risk of toxicity for this group of patients.
Safety
Proton beam therapy offers an alternative form of radiotherapy which may reduce side effects like dry cough, esophageal damage or liver and heart complications that are commonly experienced with traditional photon radiotherapy treatments. Your radiation oncologist can assess both its risks and benefits to tailor proton therapy specifically to your case.
Your health care team will use additional imaging scans, such as X-rays or CT scans, to plan proton therapy treatment. The images will allow them to mark where on your body the proton beam should be delivered and also create immobilization devices so you are in the optimal position throughout each treatment session.
The shape of a proton beam significantly impacts dose distribution at tumour sites. A uniform first scatterer produces a Gaussian beam profile at patient sites, with more energy reaching its center than its edges. Therefore, our aim should be to design a second scatterer which contours this profile and results in flat dose distribution at patient sites.
Since proton beams are more flexible than photon beams, they can be used to reach hard-to-reach spots such as brain and spine tumours more easily. Their flexibility also helps minimize radiation exposure to nearby healthy organs – an especially crucial aspect in pediatric cancer treatments where keeping doses as small as possible is paramount.
Proton beam therapy can be used to treat head and neck tumors as well as many other solid tumors, sparing delicate structures like the optic nerve while protecting surrounding healthy tissues. They have even proven successful against eye tumours – with protons penetrating deep enough to reach and treat eye tumours without harming nearby healthy tissue structures like retina.
Studies comparing proton beam therapy to standard photon radiotherapy for various cancer types, such as Glioblastoma (GBM). One such trial, known as Phase II Randomized Controlled Trial of photons and protons versus GBM, revealed that patients who received proton therapy had lower rates of recurrence and less severe long-term side effects; the difference was especially evident among those suffering from GBM – an aggressive form of brain tumour.
Side Effects
Traditional X-ray radiation goes beyond just targeting tumors, also damaging surrounding healthy tissue and vital organs with radiation exposure. While adults can typically tolerate some collateral damage caused by traditional X-ray treatment, children’s growing tissues may be severely damaged as a result. Proton beam therapy instead targets higher doses directly onto tumor sites and significantly less dose to surrounding tissues – providing faster healing with reduced side effects and side effects.
Proton therapy machines use a device known as a gantry to move around you during treatments, keeping you still. A mask (or shell) is placed over your head or body to ensure that each time you attend therapy you remain in the same position and protons hit only your tumor rather than healthy tissues nearby. Before your first treatment session begins, team members use x-rays or CT scan pictures as a baseline and laser mark the treatment area on your body using laser. Afterward, once in the treatment room they use their gantry to direct protons onto your tumor.
Proton beams’ high energy allows them to penetrate deeper than X-rays into the body, enabling them to treat more difficult-to-reach tumors like those near organs such as the brain or heart more effectively and reduce side effects associated with traditional X-ray radiation which may be more severe for pediatric patients and those suffering from head/neck cancer, lung cancer in chest areas or breast cancers close to nerves and glands.
Protons may also be used to specifically target cancer stem cells (CSC), which have proven resistant to treatment and could be responsible for treatment resistance. While photons can potentially aggravate treatment resistance by targeting CSCs through different mechanisms, protons directly damage DNA in cells to kill them and research has indicated they might even be more effective at alleviating irradiation-induced toxicity, particularly gastrointestine toxicity in patients with NSCLC.
