Search

With the advent of computers and especially with 3D conformal radiotherapy, the use of Patient Archiving and Communication System and common Digital Imaging and Communications in Medicine files has become increasingly important. Also of importance is the understanding of the various three-dimensional treatment planning systems including measurement-based systems, Monte Carlo, pencil beam, convolution/superposition, and collapsed cone algorithms. It is also important to understand the concept of simulated annealing for the purpose of intensity-modulated radiotherapy planning.

Electromagnetic radiation is used in radiation therapy for its unique properties and relative ease of production compared to other forms of particle radiation. Particles are directly ionizing while electromagnetic radiation is indirectly ionizing because it sets other particles in motion to deposit the dose. The majority of innovation in radiation therapy has focused on electromagnetic radiation, beginning with x-ray tubes and γ-rays emitted from man-made radioisotopes. Later on, with the development of the waveguide and accelerator tube came the linear accelerator and the microtron which offered the ability to deliver photons and electrons in the megavoltage energy range. More recently, electromagnets were developed to be powerful enough to accelerate heavier particles to extremely high energies in a cyclotron or a synchrotron for particle beam therapy.

The Nuclear Regulatory Commission (NRC) is responsible for regulating nuclear material, including any nuclides used in brachytherapy. All medical sources are classified as nuclear byproduct material. Use of byproduct material requires an authorized user and a radiation safety officer, as well as a written directive and a quality management program (QMP). Deviations from the written directive may be classified as medical events (misadministrations) depending on their severity.

Most radiation therapy is delivered by linear accelerators capable of photon and electron irradiation. However, alternative modalities may have advantages in some clinical situations. Brachytherapy is radiation delivered by a radioactive source placed within or in close contact to the target, causing a rapid dose falloff with distance. Brachytherapy is classified as low dose rate (LDR) or high dose rate (HDR), and sealed or unsealed sources. Unsealed sources are free-floating radionuclides that can be injected into an anatomical space or administered systemically. Heavy charged particles include protons and heavy ions. These charged particles exhibit a high-dose Bragg peak, with little to no exit dose beyond the intended depth of treatment. Protons have an RBE approximating photons, however heavy ions have a much higher RBE. Neutron beam therapy has a very high RBE, allowing for a greater effect on radioresistant tumors but also greater normal tissue toxicity. Boron-containing drugs may react with neutrons to further increase radiation dose to tumor.

There are many types of lesions that may be induced in DNA by ionizing radiation. Radiation creates ion pairs in water. If clusters of ionization are formed near DNA, they can potentially damage the DNA. Normal well-oxygenated cells may utilize various pathways to repair different types of DNA damage. Single strand breaks are usually easy for a cell to repair while double strand breaks, which may be repaired by NHEJ or HRR repair pathways, are more difficult. Unrepaired or misrepaired double strand breaks can result in unstable chromosomal aberrations that can, in turn, lead to either death or senescence of the cell. The mechanisms of DNA repair are important to understand, not only in regard to radiation damage repair, but also because their absence or inhibition may play a role in the genetic predisposition to cancer or the response of tissues to DNA-damaging chemotherapy agents.

Post-irradiation cell survival as a function of radiation dose can be biophysically modeled in several different ways, using Poisson statistics as the basis for survival equations. The single-hit, multitarget model has parameters D0, the dose correlating with one hit per cell, and Dq, which is the width of the “shoulder,” and correlates with repair capacity. The linear-quadratic (LQ) model utilizes terms α (single-hit kill) and β (two-hit kill) which correlate with low-dose killing and high-dose killing, respectively. The LQ model can be used to determine biologically equivalent doses between various dose fractionation schemes. The various survival curve parameters can be altered if irradiated cells undergo either sublethal damage repair (which is modeled with split dose experiments), potentially lethal damage repair (which is modeled with plating delay experiments), or if cells are irradiated at low or ultrahigh dose rates. In addition to these two commonly used models, there are multiple other models that have their own strengths and weaknesses.

Oxygen is one of the most effective dose-modifying agents. Oxygen causes “fixation” of radiation-induced DNA damage. The oxygen enhancement ratio (OER) is equal to the ratio of doses of radiation (hypoxic over oxic) required to achieve the same biological effect. Similarly, effectiveness of different types of radiation can be assessed by determining the ratio of doses required to achieve the same effect. This number is called relative biological effectiveness (RBE). Linear energy transfer (LET) is the density of ionizations deposited by each radiation type along its track. As LET increases, OER decreases until it becomes 1 (e.g., there is no oxygen effect). As LET increases, RBE increases up to a point (100 KeV/μm), and then declines due to the “overkill effect.”

Radiation dosimetry is based on exposure defined as C/kg (Roentgen). The energy transferred by photons to a medium is called KERMA, and the subsequent absorption of energy in a medium is quantified as dose, measured in Gray. Due to the different effects of radiation in different tissues as well as the need for radiation safety and protection standards, dose is further described in Sieverts for equivalent radiation dose and effective radiation dose. Radiation measurements are performed by various types of detectors.

Photons are a type of boson that carries electromagnetic energy. They have no charge and are therefore an indirectly ionizing particle. At lower energies, they predominantly interact with matter through coherent scatter and the photoelectric effect. For the photoelectric effect, a photon goes in and an electron comes out. At energies in the range of radiotherapy treatment, the predominant interaction is Compton scatter, where photons bounce off of electrons and transfer some of their energy to the electrons in the process. At higher energies, pair production becomes possible such that a photon will cause the production of an electron and a positron that can cause annihilation. Also at higher energies, photons may interact with the nucleus and cause it to release nucleons. Pair production and photonuclear disintegration are generally undesirable for the purposes of radiation therapy.

MRI-Linac is a new device that combines an MRI unit and a 6 MV linear accelerator (on a single circular gantry) very similar to a tomotherapy unit for image-guided and adaptive therapy. It uses MRI for planning and image guidance. This device is most useful for treating soft tissue tumors such as liver, pancreas, kidney, and so on. The MRI signal is converted to a pseudo-CT called synthetic CT for planning and dose calculation. Using a fast MLC on a linac, this device provides on-line image verification and IMRT/VMAT treatment.

The linear-quadratic (LQ) model utilizes the terms α (single-hit kill) and β (two-hit kill) which correlate with low-dose killing and high-dose killing, respectively. Fractionation experiments with normal tissues (Chap. 23) for survival and functional tissue endpoints and tumor survival have allowed calculation of α/β ratios. These α/β ratios along with dose per fraction and total dose can be used to calculate biologically equivalent doses (BEDs) based on fraction size and total dose for various tissues and tumors compared to standard single fractions of no more than 2 Gy once a day, 5 days per week.

Simple dose calculations are based on photon dose to water. When treating patients, dose corrections must be introduced to account for anatomic variations in shape and density. These dose correction techniques range from very simple rules to complex computer algorithms. Wedges and compensators may be used to correct for patient surface shape. Bolus may be used to increase the surface dose. Field matching techniques may be used for treatments with closely abutting fields. Finally, ICRU specifications for target volumes and dose prescription are described.

Electrons are a charged particle with a finite range directly proportional to energy. They are limited to more superficial depths than photons. Surface dose increases with energy, unlike photons. Simple dose calculations are based on electron dose to water, using SSD setup geometry. Density inhomogeneities greatly alter electron dose distributions. Electrons take the path of least resistance, increasing the dose to low-density structures that abut high-density structures. Matching Bolus and spoilers can increase superficial dose and decrease range. Obliquity can greatly increase superficial dose and decrease range.

Radiation carcinogenesis is considered a stochastic effect, and is modeled by the linear no-threshold (LNT) model. The excess risk of dying from a radiation-related cancer (above the natural baseline) is based on age at exposure, gender, total dose, and dose rate. Secondary leukemias may show up after just a few years with a decrease in incidence after about a decade, while secondary solid tumors typically occur after a decade or more. Cataractogenesis was long-regarded as a deterministic late effect (since deterministic effects are usually associated with a dose threshold), but there has been much debate about this in recent years. Genetic risk is associated with increased rate of mutations in the offspring of irradiated animals. It is generally recommended that humans avoid planned conception for at least 6 months after receiving radiation to the gonads. For radiation protection purposes, recommended dose limits for stochastic, deterministic, and heritable effects are often expressed in Sv, taking into account dose, type of radiation, and the specific tissue. Equivalent dose is defined as physical dose multiplied by a weighting factor, correcting for the type of radiation. Effective dose is defined as equivalent dose multiplied by tissue weighting factor, correcting for the volume of tissue irradiated.

Radiation therapy can be modified by increasing the effectiveness of radiation on tumors (radiosensitizers), protecting normal tissues (radioprotectors), increasing oxygen concentration, or by using systemic therapy drugs. Radioprotectors are described by their dose reduction factor (DRF) while radiosensitizers are described by their enhancement ratio (ER). Both numbers are a ratio of radiation doses required to achieve a biological effect. Systemic agents can be classified as hypoxic radiosensitizers, hypoxic cytotoxins, classic alkylators, platinum agents, antibiotics, antimetabolites, vinca alkaloids, taxanes, topoisomerase inhibitors, hormonal agents, monoclonal antibodies, small molecule inhibitors (usually tyrosine kinase inhibitors), and immunomodulators. Progress is also being made in the field of gene therapy, although this is not yet mainstream.

Male fertility in farm animals is considered as an important economic trait. The phenomenon of spermatogenesis plays a dynamic functional role in determining the viability of sperm and thereby can impact on fertility-driven complications. The process of spermatogenesis is controlled by numerous molecular factors and requires a precisely regulated pattern of gene expression. The role of small noncoding RNAs in altering gene expression has been extensively studied. However, limited information is available apropos their role in yak spermatogenesis. The present study aimed to evaluate the assessment of some significant microRNAs and their expression pattern in the body tissues and sperm of fertile and subfertile yak from Arunachal Pradesh besides identified a novel class of sperm enriched small RNA 'mature-sperm-enriched small RNA' (mse-tsRNA) in Yak spermatozoa. The RNAwas extracted from tissue and sperm using 27 gauge needles and subsequently reverse transcribed into small RNA cDNAs. The PCR positive sperm-predominant miRNAs were validated by quantitative reverse transcriptase PCR (qRT-PCR) for their expression in fertile and subfertile yak. Of the 22 microRNAs, the miRNA19a, miRNA142 and miRNA143 showed higher expression in the subfertile yak, whereas expression of miRNA7d, miRNA23a and miRNA23b were found elevated in the fertile animal. The presence of these small noncoding RNAs in yak sperm and testis indicated the legitimate involvement of their role in yak bull fertility.

Background: In the present study, a set of non-linear prediction equation was developed using records of body measurement traits, namely heart girth, punch girth, height at shoulder, height at back, height at fore leg, height at back leg and body length of pigs. Repeated measurement of traits at birth, 15 d, 30 d and weaning (42 d) of 394 piglets were used. Methods: The regression of body weight on body measurement traits showed non-linear relationship based on equation, Y = aXb. Correlation of heart girth with body weight (r2 = 0.968 for male and 0.969 for females; P less than 0.01) was highest among the traits studied. Result: Heart girth was found to be most suited among the traits to predict body weight in an exponential equation, Y = 0.00058 H2.49 and Y = 0.00061 H2.47 for male and females, respectively, explaining 96 percent of variation.

The use of radiochromic film (RCF) dosimetry in radiation therapy is extensive due to its high level of achievable accuracy for a wide range of dose values and its suitability under a variety of measurement conditions. However, since the publication of the 1998 AAPM Task Group 55, Report No. 63 on RCF dosimetry, the chemistry, composition, and readout systems for RCFs have evolved steadily. There are several challenges in using the new RCFs, readout systems and validation of the results depending on their applications. Accurate RCF dosimetry requires understanding of RCF selection, handling and calibration methods, calibration curves, dose conversion methods, correction methodologies as well as selection, operation and quality assurance (QA) programs of the readout systems. Acquiring this level of knowledge is not straight forward, even for some experienced users. This Task Group report addresses these issues and provides a basic understanding of available RCF models, dosimetric characteristics and properties, advantages and limitations, configurations, and overall elemental compositions of the RCFs that have changed over the past 20 yr. In addition, this report provides specific guidelines for data processing and analysis schemes and correction methodologies for clinical applications in radiation therapy.

To assess cosmesis [Breast Cancer Conservation Treatment. Cosmetic Results (BCCT.CORE) software]QOL [EORTC QLQ (Quality of Life Questionnaire)-C30, BR23 questionnaires] using objective methodsto correlate effect of cosmesis on QOL (Quality of life) in breast cancer patients post BCT (Breast conservation therapy) using a cross-sectional observational study from a tertiary hospital.CosmesisQOL had been assessed in all biopsy-proven adult patients of unilateral breast cancer, who had undergone BCT with minimum three months post-BCTthree months post last adjuvant chemotherapy cycle, whichever is delivered last (with just hormonal therapy or followup remaining based on hormone receptor status). Pearson chi-squareKendall correlation Tau-b tests had been used for testing association between CosmesisQOL. Variation of QOL scores between Cosmetic groups had been assessed using Mann-Whitney U-test.Cosmesis was Excellent/Good in 60.4 % of patients. 58.4 % of patients had Excellent/Good Quality of Life. CosmesisQOL had a positive correlation (intermediate strength) [Kendall correlation factor-0.484]. QOL-Global scale had better median scores in Excellent/ Good cosmetic group when compared to Fair/Poor group, while for functionalsymptomatic scales, contrary had been true. Difference of median-scores between the two groups hadn't been statistically significant in five aspects - being upset over hair loss (p-0.09), sexual-enjoyment (p-0.33), nausea-vomiting (p-0.29), constipation (p0.32)diarrhea (p-0.72).About 2/3rds of patients post-BCT had Excellent/Good CosmesisExcellent/Good QOL. Every measure taken before, duringpost-BCT to improve Cosmesis might result in better QOL. Future studies must use more accurate three-dimensional methods to assess Cosmesisits effect on QOL.

PURPOSE This study investigated the characteristics of a new shielded diode detector, microSilicon X (model 60022: MSX), for small-field and large-field dosimetry. METHODS The percent depth dose (PDD), beam profiles, detector output factor (OFdet ), temperature dependence, dose rate dependence, dose-per-pulse (DPP) dependence, and dose-response linearity of MSX were evaluated in Cyberknife and TrueBeam photon beams and compared with various detectors including microDiamond (PTW model 60019: MD), Sun Nuclear EDGE detector, Photon diode (PTW model 60016: PD), and semiflex ionization chamber (PTW model 31010: IC). RESULTS For field sizes ranging from 50 × 50 mm2 to 400 × 400 mm2 , MSX-measured OFdet values were within 1% of the IC-measured values. For the CyberKnife small fields, the maximum difference between the MSX-measured OFdet and the MD-measured field output factor (Ω) was 4.0%, while the maximum differences were 8.8% and 10.9% for PD and EDGE, respectively. MSX showed a stable response within 0.7% for water temperatures of 5°C to 34°C, while PD and EDGE showed a linear correlation between the water temperature and the response. MSX showed small variations within 0.2% for the dose rate, and PD and EDGE showed logarithmic increases in the response with the dose rate. MSX and MD had smaller DPP dependences than PD and EDGE. CONCLUSIONS The characteristics of MSX for measurements of small- and large-field photon beams are favorable. Compared to PD, MSX exhibited significant improvement in the over-response for small fields. The OFdet values measured by MSX were approximately in-between those measured by MD and PD. MSX showed stable responses against water temperature, dose rate, and DPP variations and provided suitable data for a wide range of field sizes. However, careful attention is required for measurements of OFdet for field sizes of

Interval Management (IM) is an FAA Next-Gen Automatic Dependent Surveillance – Broadcast (ADS-B) In application designed to decrease the variability in spacing between aircraft, thereby increasing the efficiency of the National Airspace System (NAS). One application within IM is Paired Approach (PA). In a PA operation, the lead aircraft and trail aircraft are both established on final approach to dependent parallel runways with runway centerline spacing less than 2500 feet. The trail aircraft follows speed guidance from the IM Avionics to achieve and maintain a desired spacing behind the lead aircraft. PA operations are expected to require a new separation standard that allows the aircraft to be spaced more closely than current dependent parallel separation standards. The behavior of an airborne collision avoidance system, such as TCAS II or ACAS Xa, must be considered during a new operation such as PA, because the aircraft are so closely spaced. This analysis quantified TAs and RAs using TCAS II Change 7.1 and ACAS Xa software with simulated IM PA operations. The results show no RAs using either TCAS II Change 7.1 or ACAS Xa, negligible TAs using TCAS II Change 7.1, and acceptable numbers of TAs using ACAS Xa software during simulated PA operations.

Invasive pathogens and bark beetles have caused precipitous declines of various tree species around the globe. Here, we characterized long‐term patterns of mountain pine beetle (Dendroctonus ponderosae; MPB) attacks and white pine blister rust, an infectious tree disease caused by the pathogen, Cronartium ribicola. We focused on four dominant white pine host species in Sequoia and Kings Canyon National Parks (SEKI), including sugar pine (Pinus lambertiana), western white pine (P. monticola), whitebark pine (P. albicaulis), and foxtail pine (P. balfouriana). Between 2013 and 2017, we resurveyed 152 long‐term monitoring plots that were first surveyed and established between 1995 and 1999. Overall extent (plots with at least one infected tree) of white pine blister rust (blister rust) increased from 20% to 33%. However, the infection rate across all species decreased from 5.3% to 4.2%. Blister rust dynamics varied greatly by species, as infection rate decreased from 19.1% to 6.4% in sugar pine, but increased in western white pine from 3.0% to 8.7%. For the first time, blister rust was recorded in whitebark pine, but not foxtail pine plots. MPB attacks were highest in sugar pines and decreased in the higher elevation white pine species, whitebark and foxtail pine. Both blister rust and MPB were important factors associated with elevated mortality in sugar pines. We did not, however, find a relationship between previous fires and blister rust occurrence. In addition, multiple mortality agents, including blister rust, fire, and MPB, contributed to major declines in sugar pine and western white pine; recruitment rates were much lower than mortality rates for both species. Our results highlighted that sugar pine has been declining much faster in SEKI than previously documented. If blister rust and MPB trends persist, western white pine may follow similar patterns of decline in the future. Given current spread patterns, blister rust will likely continue to increase in higher elevations, threatening subalpine white pines in the southern Sierra Nevada. More frequent long‐term monitoring efforts could inform ongoing restoration and policy focused on threats to these highly valuable and diverse white pines.

Covid-19 is a morbid respiratory disease that has caused desperate times on a global scale due to the lack of any effective medical treatment. Some in the radiation community are actively proposing low-dose radiation therapy (LDRT) for managing the viral pneumonia associated with Covid-19. This commentary provides a rationale for exercising caution against such a decision as the efficacy of LDRT for viral diseases is unknown, while its long-term adverse risks are well known.