Imaging dose from cone beam computed tomography in radiation therapy

Imaging dose in radiation therapy has traditionally been ignored due to its low magnitude and frequency in comparison to therapeutic dose used to treat patients. The advent of modern, volumetric, imaging modalities, often as an integral part of linear accelerators, has facilitated the implementation of image-guided radiation therapy (IGRT), which is often accomplished by daily imaging of patients. Daily imaging results in additional dose delivered to patient that warrants new attention be given to imaging dose. This review summarizes the imaging dose delivered to patients as the result of cone beam computed tomography (CBCT) imaging performed in radiation therapy using current methods and equipment. This review also summarizes methods to calculate the imaging dose, including the use of Monte Carlo (MC) and treatment planning systems (TPS). Peripheral dose from CBCT imaging, dose reduction methods, the use of effective dose in describing imaging dose, and the measurement of CT dose index (CTDI) in CBCT systems are also reviewed.     

Treatment of Cushing's disease with low dose radiation therapy.

Nineteen patients with Cushing''s disease were treated with low dose external pituitary irradiation (20 Gy (2000 rad) in eight fractions over 10 days). While awaiting the effects of pituitary irradiation all patients were treated with metyrapone. Seven patients had a complete remission of their disease within six to 12 months of irradiation. They did not require any further treatment and were followed up for a mean of three and a half (range one to eight) years. Another patient had a complete remission after a second course of pituitary irradiation. A further two patients showed a significant biochemical improvement after irradiation, although they were not rendered eucorticoid. There were no complications after this dose of irradiation. These results compare favourably with those reported after pituitary irradiation at conventional doses (40-50 Gy (4000-5000 rad) over four or five weeks) but were not associated with any complications. It is therefore recommended that low dose external pituitary irradiation be used as definitive first line treatment for Cushing''s disease.     

The importance of patient-specific radiation dose calculations for the administration of radionuclides in therapy.

This paper advocates patient-specific approaches to radiation dose calculations for radionuclides used in therapy and outlines strategies for implementing such approaches. The use of a simple approaches to radionuclide therapy, e.g. a single amount of activity for all patients or the same amount of activity administered per unit body weight do not permit the optimization of individual patient therapy. While limitations in current models and logistic problems prevent dose calculations of the quality currently enjoyed with external radiation therapy approaches, improvements can be made, and models are constantly evolving. Specific suggestions regarding the extension of current models, and of the use of new models which use image data from individual patients, are discussed in the context of allowing radiotherapy with internal emitters to employ the kind of patient-specific approaches that are used in other therapeutic modalities, which are clearly in the patients' best interests.     

Functional imaging in radiation therapy planning for head and neck cancer

Functional imaging and its application to radiotherapy (RT) is a rapidly expanding field with new modalities and techniques constantly developing and evolving. As technologies improve, it will be important to pay attention to their implementation. This review describes the main achievements in the field of head and neck cancer (HNC) with particular remarks on the unsolved problems.     

Radiation dose and cancer risks from radiation exposure during abdominopelvic computed tomography (CT) scans: comparison of diagnostic and radiotherapy treatment planning CT scans

In the present study, radiation doses and cancer risks resulting from abdominopelvic radiotherapy planning computed tomography (RP-CT) and abdominopelvic diagnostic CT (DG-CT) examinations are compared. Two groups of patients who underwent abdominopelvic CT scans with RP-CT (n = 50) and DG-CT (n = 50) voluntarily participated in this study. The two groups of patients had approximately similar demographic features including mass, height, body mass index, sex, and age. Radiation dose parameters included CTDI_vol, dose–length product, scan length, effective tube current, and pitch factor, all taken from the CT scanner console. The ImPACT software was used to calculate the patient-specific radiation doses. The risks of cancer incidence and mortality were estimated based on the BEIR VII report of the US National Research Council. In the RP-CT group, the mean ± standard deviation of cancer incidence risk for all cancers, leukemia, and all solid cancers was 621.58 ± 214.76, 101.59 ± 27.15, and 516.60 ± 189.01 cancers per 100,000 individuals, respectively, for male patients. For female patients, the corresponding risks were 742.71 ± 292.35, 74.26 ± 20.26, and 667.03 ± 275.67 cancers per 100,000 individuals, respectively. In contrast, for DG-CT cancer incidence risks were 470.22 ± 170.07, 78.23 ± 18.22, and 390.25 ± 152.82 cancers per 100,000 individuals for male patients, while they were 638.65 ± 232.93, 62.14 ± 13.74, and 575.73 ± 221.21 cancers per 100,000 individuals for female patients. Cancer incidence and mortality risks were greater for RP-CT than for DG-CT scans. It is concluded that the various protocols of abdominopelvic CT scans, especially the RP-CT scans, should be optimized with respect to the radiation doses associated with these scans.

     

Effect of low dose rate radiation on cell growth kinetics.

Experimental determinations were made of cell number as a function of time for two strains of L5178Y mammalian cells maintained continuously in various environments of radiation. One strain possessed a shoulder in its dose response curve whereas the other did not. Neither strain showed any significant difference in growth rate for interdivision doses on the order of the median lethal dose or less delivered continuously at a low dose rate or pulsed every 4 h at a high instantaneous dose rate. It was also shown that large numbers of dead cells have little effect on growth rate and that these dead cells last as discrete entities for many days. A simple theory of growth rate in the presence of radiation is presented, and the agreement with the observations implies that there is no effect of any sublethal low dose rate radiation received in one generation on the growth rate or radiation sensitivity of the succeeding generation. Further analysis of the data also showed that for the no-shoulder cells at 37 degrees C, tritiated water had a relative biological effect close to unity for cell sterilization.     

Presentation of antigen by B cells: functional dependence on radiation dose, interleukins, cellular activation, and differential glycosylation

Whether resting B cells can present antigen to T cells is controversial. Several factors can influence the outcome of an assessment of the presenting function of resting B cells: the method of purifying resting B cells and maintaining them in culture without altering their resting state, the sensitivity of resting B cells to gamma-irradiation, the activation state of the T cells used to assess presenting function, and the requirement for exogenous interleukin 1. We have examined all of these variables and find that one adherent antigen-presenting cell is functionally equivalent to four LPS-activated B cells and to 1000 resting B cells. In addition, we have examined the potential functional relevance of the differential glycosylation of Ia molecules on resting B cells compared with adherent antigen-presenting cells. Altering the surface glycosylation of resting B cells by neuraminidase treatment results in a 25-fold increase in B cell antigen presentation without altering their resting state. More important, among antigen-presenting cells the effect of neuraminidase is limited to resting B cells. It also appears to involve a restricting element such as the Ia molecule rather than total cell surface charge, because neuraminidase treatment has no effect on the capacity of resting B cells to serve as accessory cells in the Con A response.     

Gene dose effects in Ir gene-controlled systems.

(B10.A x B10.S)F1 hybrid mice produce lower levels of anti-GL phi antibody than B10.S(9R) and B10.HTT mice. To determine whether this difference is due to a gene dose or a cis-trans effect, [B10.S(9R) x B10.S(8R)]F1 mice were immunized with GL phi. These mice carry one dose of the responder Ir gene alleles in the cis position whereas the recombinant B10.S(9R) and B10.HTT mice carry two doses of the relevant genes. Both (B10.A x B10.S) and [B10.S(9R) x B10.S(8R)] F1 mice produced comparably lower amounts of antibodies as compared to the recombinant strains. The data therefore demonstrate that gene dose and not cis-trans effect accounts for the differences between F1 and recombinant strains in their antibody response to GL phi controlled by complementary Ir genes.     

Daily nurse requirements planning based on simulation of patient flows

Nurses account for approximately 50 % of total hospital budgets and their allocation to medical units and shifts can significantly affect the quality of care provided to patients. The adoption of flexible shift schedules and the assessment of actual nursing time can enable sensible resource planning, balancing the quality of care with efficiency in resource use. Starting from the concept that nurse requirements are triggered by patient needs, which are stochastic in nature both for clinical activities and their duration, this paper proposes an innovative Nurse Requirement Planning model grounded on the concept of the clinical pathway (the “standard” sequence of diagnostic, therapeutic and care activities a patient with certain pathology should undertake over time) with its inner routing probability and patient dependence on nurses, which can be correlated to the time needed to perform nursing tasks. In merging and modelling these two aspects, the method summarizes the best features of acuity-quality and timed-task/activity techniques, well known although not usually applied for reasons of demands on clinicians’ time. Instead, in this paper, for each shift of the day, hospital management is enabled to choose the optimal number of nurses to meet actual requirements according to a desired service level and personnel saturation by means of a tool that simulates the patient flow in a medical unit based on automatic data retrieval from hospital databases. The validation and verification of the proposal were undertaken in a stroke unit.     

Space radiation absorbed dose distribution in a human phantom.

The radiation risk to astronauts has always been based on measurements using passive thermoluminescent dosimeters (TLDs). The skin dose is converted to dose equivalent using an average radiation quality factor based on model calculations. The radiological risk estimates, however, are based on organ and tissue doses. This paper describes results from the first space flight (STS-91, 51.65 degrees inclination and approximately 380 km altitude) of a fully instrumented Alderson Rando phantom torso (with head) to relate the skin dose to organ doses. Spatial distributions of absorbed dose in 34 1-inch-thick sections measured using TLDs are described. There is about a 30% change in dose as one moves from the front to the back of the phantom body. Small active dosimeters were developed specifically to provide time-resolved measurements of absorbed dose rates and quality factors at five organ locations (brain, thyroid, heart/lung, stomach and colon) inside the phantom. Using these dosimeters, it was possible to separate the trapped-proton and the galactic cosmic radiation components of the doses. A tissue-equivalent proportional counter (TEPC) and a charged-particle directional spectrometer (CPDS) were flown next to the phantom torso to provide data on the incident internal radiation environment. Accurate models of the shielding distributions at the site of the TEPC, the CPDS and a scalable Computerized Anatomical Male (CAM) model of the phantom torso were developed. These measurements provided a comprehensive data set to map the dose distribution inside a human phantom, and to assess the accuracy and validity of radiation transport models throughout the human body. The results show that for the conditions in the International Space Station (ISS) orbit during periods near the solar minimum, the ratio of the blood-forming organ dose rate to the skin absorbed dose rate is about 80%, and the ratio of the dose equivalents is almost one. The results show that the GCR model dose-rate predictions are 20% lower than the observations. Assuming that the trapped-belt models lead to a correct orbit-averaged energy spectrum, the measurements of dose rates inside the phantom cannot be fully understood. Passive measurements using 6Li- and 7Li-based detectors on the astronauts and inside the brain and thyroid of the phantom show the presence of a significant contribution due to thermal neutrons, an area requiring additional study.     

Use of three-dimensional computed tomography overlay for real-time cryoballoon ablation in atrial fibrillation reduces radiation dose and contrast dye

Aims

Cryoballoon pulmonary vein (PV) isolation in patients with atrial fibrillation has proven to be effective in short-term and long-term follow-up. To visualise the PV anatomy, pre-ablation contrast pulmonary venography is commonly performed. Three-dimensional (3D) computed tomography (CT) overlay is a new technique creating a live 3D image of the left atrium by integrating a previously obtained CT scan during fluoroscopy. To evaluate the benefits of 3D CT overlay during cryoballoon ablation, we studied the use of 3D CT overlay versus contrast pulmonary venography in a randomised fashion in patients with paroxysmal atrial fibrillation undergoing cryoballoon PV isolation.

Methods and results

Between October 2012 and June 2013, 30 patients accepted for PV isolation were randomised to cryoballoon PV isolation using either 3D CT overlay or contrast pulmonary venography. All patients underwent a pre-procedural cardiac CT for evaluation of the anatomy of the left atrium (LA) and the PVs. In the 3D CT overlay group, a 3D reconstruction of the LA and PVs was made. An overlay of the CT reconstruction was then projected over live fluoroscopy. Patients in the contrast pulmonary venography group received significantly more contrast agent (77.1 ± 21.2 cc vs 40.1 ± 17.6 cc, p < 0.001) and radiation (43.0 ± 21.9?Gy.cm2 vs 28.41 ± 11.7?Gy.cm2, p = 0.04) than subjects in the 3D CT overlay group. There was no difference in total procedure time, fluoroscopy time and the amount of cryoapplications between the two groups.

Conclusion

The use of 3D CT overlay decreases radiation and contrast dye exposure and can assist in guiding cryoballoon-based PV isolation.

     

Correlation of intensity-modulated radiation therapy at a specific radiation dose with the prognosis of nasal mucous damage after radiotherapy

Radiation and Environmental Biophysics - Objective of the present study was to investigate the tolerant radiation dose of nasal mucosa by observing and analyzing patients who received...     

Optical and NMR dose response of N-isopropylacrylamide normoxic polymer gel for radiation therapy dosimetry

Background

Application of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.

Aim

In the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.

Materials and methods

NIPAM normoxic polymer gel was prepared and irradiated by 9 MV photon beam of a medical linac. The optical absorbance was measured using a conventional laboratory spectrophotometer in different wavelengths ranging from 390 to 860 nm. R₂ measurements of NIPAM gels were performed using a 1.5 T scanner and R₂–dose curve was obtained.

Results

Our results showed R₂ dose sensitivity of 0.193 ± 0.01 s⁻¹ Gy⁻¹ for NIPAM gel. Both R₂ and optical absorbance showed a linear relationship with dose from 1.5 to 11 Gy for NIPAM gel dosimeter. Moreover, absorbance–dose response varied considerably with light wavelength and highest sensitivity was seen for the blue part of the spectrum.

Conclusion

Our results showed that both optical and NMR approaches have acceptable sensitivity and accuracy for dose determination with NIPAM gel. However, for optical reading of the gel, utilization of an optimum optical wavelength is recommended.