Lasers produce biological effects at both the molecular and cellular levels, such as increasing mitochondrial ATP energy stores, speeding wound healing processes, and decreasing inflammation.
Electrons and photons deposit radiation differently, leading to differences in relative biological effectiveness (RBE). RBE increases with higher energy output; for clinical proton beams this translates to flat central regions and rapid drops in penumbra width.
High Energy Photons
Xia’s research employs silicon nanoparticles coated with organic molecules to capture and combine electrons. This creates triplets which can then be separated out and used to produce high energy photons that researchers can control the direction and magnitude of in order to provide more targeted radiation delivery to hard-to-reach locations.
This work builds upon previous studies, which demonstrated the effectiveness of low energy photons to enhance patient outcomes in some cases. Our team examined how beam energy affects dose distribution and characterization across several treatment scenarios such as lung cancer and pediatric head and neck cancer treatment scenarios.
Our team has measured the LET of various photon energies using both PTW 30013 and IBA FC65-G Farmer-type chambers, using values traceable back to Lillicrap et al 1990’s primary standard of absorbed dose in water (Lillicrap). From these measurements we determined correlation coefficients (CCs) between the chambers for each photon energy in order to create an energy look-up table enabling selection of optimal photon energies for every case.
For comparative purposes, CCs from this study were also utilized to simulate 3D percentile depth dose curves and dose profiles in a rectilinear water phantom using Monte Carlo simulations. PDDs and dose profiles generated for 6MV photon beams displayed good agreement with actual measurements within the phantom.
The findings from this study support the use of lower energy photons for lung cancer EMXRT planning. Their rapid dose fall-off with shorter penumbrae at field edges allows significant reduction in normal tissue and organ exposure, especially beneficial in cases such as cranial radiotherapy where high OAR doses have a strong and well-documented link with cognitive morbidity over time. For other instances, using lower energy photons allows more customized and personalized treatments by expanding treatment options available to physicians.
Low Energy Photons
Photon beams of lower energies have the capability of providing tightly focused dose distributions within their fields of influence, making them particularly suited to treating small target volumes such as those seen in gynecologic malignancies. Unfortunately, however, their application may be restricted due to insufficient radiation sources. A recent study demonstrated that low energy photons could be effective for treating IORT of gynecological cancer when combined with multi-leaf collimators technology for optimizing collimation geometry.
Photon beam effectiveness depends on its interaction with tissue it traverses and this interaction is determined by comparing its energy per unit of time against attenuation rates in medium it is traversing. Higher photon energy leads to stronger interactions with medium, and consequently reduced attenuation rates.
Modern linac-generated photon beams usually consist of a spectrum of energies up to their maximum permitted limit, with attenuation being determined by adding up all irradiation times across this range; this process is known as “beam hardening.”
Photons that enter homogeneous media like water are predominantly affected by Compton scattering and their interactions with the ions present; when entering heterogeneous environments such as dust, their interactions with pairs of electrons also play a large role; therefore it is necessary to measure accurately ionization density of such environments in order to ascertain attenuation rates and attenuation factors.
Inhomogeneities are regions of non-uniform electron density within a medium that disrupt the dose distribution. Their impact is most prominent at higher energy beams due to increased interactions with charged particles present within it; however, they remain significant even at lower energies.
This article presents an easy-to-use energy selector tool for EMXRT planning that incorporates attenuation effects as low energy photons travel through patients. This energy selector tool has been shown to significantly decrease dose to adjacent critical structures in lung cancer plans as well as help avoid overdosing of targets, while BEAMnrc/EGSnrc’s Monte Carlo simulation allows researchers to investigate how low-energy photons affect spectra within and outside radiation fields.
High Energy Photon Damage
Photons, the high-energy X-rays commonly used in diagnostic imaging, can also be directed at cancerous tissue to kill it. Like X-rays, photons break DNA inside cancer cells to stop them making copies or repairing themselves – effectively stopping cancer growth while the body can naturally dispose of the damaged cells. Proton therapy works similarly, except it uses charged particles called protons instead of photons as targeting agents; their lower energy output means less collateral damage to healthy tissues, so doctors can provide higher doses over shorter treatments with less side effects for more effective cancer care.
Proton beams may provide more precise coverage of smaller areas than photon beams by covering specific tumor sites more precisely and shaping it to your tumor’s shape while decreasing dose to nearby healthy tissues – this form of radiotherapy, known as stereotactic body radiation therapy (SBRT), has proven its worth treating head and neck cancer, lymphoma, prostate, pancreatic, gastrointestinal liver tumors as well as brain tumors.
Under SBRT, doctors create a three-dimensional image of your entire body to pinpoint where and how your tumor should be treated. They may mark where the radiation should go on your skin to guide its beam; additionally, immobilization devices may also be utilized during each treatment session to keep you in place during each session.
Proton beams can be targeted at your tumor from different angles and moved up to 300 mm from their point of origin in the treatment room, providing greater flexibility and precision for physicians. Furthermore, protons can be directed more precisely than photons using an approach known as intensity modulated radiation therapy (IMRT), which divides one radiation beam into multiple focused beams of different intensities for pinpoint targeting more areas of your tumor with minimal side effects.
VHEE radiation may present one major hurdle to its clinical implementation due to thermal neutrons that emit thermal neutrons that may damage cardiac implantable electronic devices (CIEDs). To combat this potential hazard, physicists have conducted characterization experiments on CIEDs as well as simulations to understand radiation response more thoroughly, then compare to well-established radiotherapy modalities using Relative Biological Effectiveness (RBE).
Low Energy Photon Damage
Photons are electromagnetic waves of light with enormous levels of kinetic energy, capable of inflicting irreparable harm or death when they interact with living tissue atoms and molecules. Their interactions depend on their wavelength; photons with matter change according to visible (red to violet), infrared and ultraviolet wavelengths whose energies increase accordingly – as such their likelihood of absorption by molecules or atoms also increases accordingly.
Photons can release large amounts of energy when they encounter an atom or molecule through photoionization and Auger decay processes, liberating electrons with various energies which then damage or disrupt biological function of that atom or molecule.
As electrons decay, they release photons that can cause secondary radiation damage – often as severe as primary damage- to nearby cells. This phenomenon, known as secondary radiation damage, often manifests with symptoms including nausea, vomiting, fatigue, hair loss or skin problems that are manifest as clinical manifestations.
Low power laser rays have been tested in research studies to treat pain, but the results have been inconclusive. Some have shown that laser light accelerates wound healing while others show no significant change; it remains unknown what factors lead to such effects.
Regular radiation therapies like Gamma Knife and Brachytherapy involve targeting tumors with high-energy X-rays or gamma particles that damage DNA. Due to ionization process causing DNA fragmentation, radiation therapy may also damage healthy cells nearby; estimates indicate that 30%-40% of dose from conventional treatment passes through and damages tissue beyond tumor, known as exit dose. Proton beam treatments such as SBRT or IMRT reduce exit dose significantly for some patients making treatment safer than ever.
Model-based treatment planning software like matRad allows clinicians to precisely calculate the dose to organs at risk in three dimensions across various photon beam energies and shapes, including calculations for both Compton and photoelectric effects of photons at treatment energies between 6-18 MV. Importantly, Compton effects depend on electron density within tissue while photoelectric effects depend more heavily on Z; conventional CT-based TPSs use dose matrices which incorporate both effects but fail to address differences between them.
