Absolute dose calculations for Monte Carlo simulations of radiotherapy beams

Monte Carlo (MC) simulations have traditionally been used for single field relative comparisons with experimental data or commercial treatment planning systems (TPS). However, clinical treatment plans commonly involve more than one field. Since the contribution of each field must be accurately quantified, multiple field MC simulations are only possible by employing absolute dosimetry. Therefore, we have developed a rigorous calibration method that allows the incorporation of monitor units (MU) in MC simulations. This absolute dosimetry formalism can be easily implemented by any BEAMnrc/DOSXYZnrc user, and applies to any configuration of open and blocked fields, including intensity-modulated radiation therapy (IMRT) plans. Our approach involves the relationship between the dose scored in the monitor ionization chamber of a radiotherapy linear accelerator (linac), the number of initial particles incident on the target, and the field size. We found that for a 10 x 10 cm2 field of a 6 MV photon beam, 1 MU corresponds, in our model, to 8.129 x 10(13) +/- 1.0% electrons incident on the target and a total dose of 20.87 cGy +/- 1.0% in the monitor chambers of the virtual linac. We present an extensive experimental verification of our MC results for open and intensity-modulated fields, including a dynamic 7-field IMRT plan simulated on the CT data sets of a cylindrical phantom and of a Rando anthropomorphic phantom, which were validated by measurements using ionization chambers and thermoluminescent dosimeters (TLD). Our simulation results are in excellent agreement with experiment, with percentage differences of less than 2%, in general, demonstrating the accuracy of our Monte Carlo absolute dose calculations.

Modelling an extreme water–lung interface using a single pencil beam algorithm and the Monte Carlo method

The goal of this study was to quantify, in a heterogeneous phantom, the difference between experimentally measured beam profiles and those calculated using both a commercial convolution algorithm and the Monte Carlo (MC) method. This was done by arranging a phantom geometry that incorporated a vertical solid water-lung material interface parallel to the beam axis. At nominal x-ray energies of 6 and 18 MV, dose distributions were modelled for field sizes of 10 x 10 cm(2) and 4 x 4 cm(2) using the CadPlan 6.0 commercial treatment planning system (TPS) and the BEAMnrc-DOSXYZnrc Monte Carlo package. Beam profiles were found experimentally at various depths using film dosimetry. The results showed that within the lung region the TPS had a substantial problem modelling the dose distribution. The (film-TPS) profile difference was found to increase, in the lung region, as the field size decreased and the beam energy increased; in the worst case the difference was more than 15%. In contrast, (film-MC) profile differences were not found to be affected by the material density difference. BEAMnrc-DOSXYZnrc successfully modelled the material interface and dose profiles to within 2%.

Pemphigus vulgaris - approach and management

The place of pemphigus vulgaris (PV) among autoimmune bullous dermatoses is well known. In pemphigus, IgG autoantibodies are directed against desmogleins 1 and 3, which are part of the cadherin family of cell-cell adhesion molecules. These structures are responsible for maintaining the intercellular adherence in stratified squamous epithelia, such as the skin and oral mucosa. The incidence of autoimmune bullous dermatoses is steadily increasing, being associated with a high degree of morbidity. The pathophysiology of these dermatoses is very well understood, complemented by recent genetic studies. The gold standard for the diagnosis of pemphigus vulgaris is the detection of autoantibodies or complement component 3 by direct immunofluorescence microscopy of a perilesional biopsy. Early diagnosis and initiation of treatment are necessary in order to achieve a favorable prognosis. Although the first line of treatment is corticotherapy, there are no clear guidelines on dosing regimens, and long-term adverse effects are important. Corticosteroid-sparing adjuvant therapies have been employed in the treatment of PV, aiming to reduce the necessary cumulative dose of corticosteroids. In addition, therapies with anti-CD20 antibodies are used, but antigen-specific immune suppression-based treatments represent the future.

Implementation of random set-up errors in Monte Carlo calculated dynamic IMRT treatment plans

The fluence-convolution method for incorporating random set-up errors (RSE) into the Monte Carlo treatment planning dose calculations was previously proposed by Beckham et al, and it was validated for open field radiotherapy treatments. This study confirms the applicability of the fluence-convolution method for dynamic intensity modulated radiotherapy (IMRT) dose calculations and evaluates the impact of set-up uncertainties on a clinical IMRT dose distribution. BEAMnrc and DOSXYZnrc codes were used for Monte Carlo calculations. A sliding window IMRT delivery was simulated using a dynamic multi-leaf collimator (DMLC) transport model developed by Keall et al. The dose distributions were benchmarked for dynamic IMRT fields using extended dose range (EDR) film, accumulating the dose from 16 subsequent fractions shifted randomly. Agreement of calculated and measured relative dose values was well within statistical uncertainty. A clinical seven field sliding window IMRT head and neck treatment was then simulated and the effects of random set-up errors (standard deviation of 2 mm) were evaluated. The dose-volume histograms calculated in the PTV with and without corrections for RSE showed only small differences indicating a reduction of the volume of high dose region due to set-up errors. As well, it showed that adequate coverage of the PTV was maintained when RSE was incorporated. Slice-by-slice comparison of the dose distributions revealed differences of up to 5.6%. The incorporation of set-up errors altered the position of the hot spot in the plan. This work demonstrated validity of implementation of the fluence-convolution method to dynamic IMRT Monte Carlo dose calculations. It also showed that accounting for the set-up errors could be essential for correct identification of the value and position of the hot spot.

Monte Carlo calculation of dose distribution in early stage NSCLC patients planned for accelerated hypofractionated radiation therapy in the NCIC-BR25 protocol

The dosimetric consequences of plans optimized using a commercial treatment planning system (TPS) for hypofractionated radiation therapy are evaluated by re-calculating with Monte Carlo (MC). Planning guidelines were in strict accordance with the Canadian BR25 protocol which is similar to the RTOG 0236 and 0618 protocols in patient eligibility and total dose, but has a different hypofractionation schedule (60 Gy in 15 fractions versus 60 Gy in 3 fractions). A common requirement of the BR25 and RTOG protocols is that the dose must be calculated by the TPS without tissue heterogeneity (TH) corrections. Our results show that optimizing plans using the pencil beam algorithm with no TH corrections does not ensure that the BR25 planning constraint of 99% of the PTV receiving at least 95% of the prescription dose would be achieved as revealed by MC simulations. This is due to poor modelling of backscatter and lateral electronic equilibrium by the TPS. MC simulations showed that as little as 75% of the PTV was actually covered by the 95% isodose line. The under-dosage of the PTV was even more pronounced if plans were optimized with the TH correction applied. In the most extreme case, only 23% of the PTV was covered by the 95% isodose.

Use of imaging techniques for melanocytic naevi and basal cell carcinoma in integrative analysis (Review)

Early detection of skin cancer is essential in order to obtain an improved prognosis. Clinicians need more objective and non-invasive examination methods to support their decision whether to biopsy or not tumoral lesions. These may include several imaging techniques such as dermoscopy, videodermoscopy, also known as sequential digital dermoscopy (SDD), computer-aided diagnosis (CAD), total body photography, imaging and high-frequency ultrasonography (HFUS), reflectance confocal microscopy, multiphoton tomography, electrical impedance spectroscopy, Raman spectroscopy, stepwise two-photon-laser spectroscopy and quantitative dynamic infrared. This review summarizes the current developments in the field of melanocytic lesions, such as naevi and basal cell carcinoma (BCC) imaging techniques. The aim was to collect and analyze data concerning types, indications, advantages and disadvantages of modern imaging techniques for in vivo skin tumor diagnosis. Two main methods were focused on, namely videodermoscopy and HFUS, which can be included in daily dermatologists' practice. In skin tumors HFUS allows the assessment of tumoral lesions with depth smaller than 1.5 cm, being described a correlation between ultrasonographic depth and the histologic index.

Predictive value of immunological markers in systemic sclerosis

Systemic sclerosis (SSc) is a collagenosis characterized by excessive deposition of collagen in the skin and viscera, in a background of immune disorder. The immunological profile of SSc often shows elevated levels of antinuclear antibodies (ANAs). However, many authors have identified cases of SSc having normal ANA levels, framed as paraneoplastic SSc. Among patients with negative ANAs in our group, we did not identify any neoplastic process that could support this hypothesis. The extended detection of autoantibodies is extremely useful in establishing the subset of SSc. Thus, anti-Scl70 antibodies are specific for the diffuse subset of SSc, while anticentromere antibodies (ACAs) have specificity for a limited subset. However, studies have shown the existence of cases of diffuse SSc having high titers of ACAs and cases of limited SSc with high titers of anti-Scl70 antibodies. This indicates an inconsistent association between the disease subset and the autoantibodies specific to each subset. Our study found a more balanced consistency between disease subsets and autoantibodies specific for each subset. Therefore, the percentages of patients having an immunological profile inconsistent with the subset of SSc, are lower than those found by other authors. This observation opens the perspective of larger studies on the immunological profile in SSc.

Imaging techniques in the diagnosis and monitoring of psoriasis

Plaque psoriasis is a chronic, immune-mediated disease, which has a multifactorial etiopathogenesis. Practical non-invasive techniques to monitor plaque psoriasis progression and treatment are necessary. Imaging techniques available for psoriasis assessment may vary in terms of resolution, depth of penetration and visual representation. This review summarizes the current developments in the field of psoriasis non-invasive imaging techniques, such as dermoscopy, conventional ultrasound and high frequency ultrasonography (HFUS), videocapillaroscopy (VC), reflectance confocal microscopy (RCM), optical microangiography (OMAG), laser Doppler imaging (LDI), multiphoton tomography (MPT) and optical coherence tomography (OCT). The aim was to collect and analyze data concerning types, indications, advantages and disadvantages of modern imaging techniques for in vivo psoriasis assessment. We focused on two main methods, videodermoscopy and HFUS, which can be included in daily dermatologists' practice and which may assist in establishing diagnosis, as well as monitoring response to topical and/or systemic therapy of psoriasis. Dermoscopy may be useful for a first evaluation and may offer an understanding of the type and distribution of blood vessels, as well as the color of the scale and the background of the lesion. Videodermoscopy allows magnification and offers a detailed evaluation of the vessel type. The utility of HFUS consists mainly in monitoring therapy response. These methods may be comparable with virtual histopathology.

Association between personality type, affective distress profile and quality of life in patients with psoriasis vs. patients with cardiovascular disease

Common chronic conditions, such as cardiovascular diseases and psoriasis, are associated with increased psychological distress. Health-related quality of life and personality type in patients with these two diseases were evaluated, including the patient's ability to respond truthfully or his/her tendency to be introverted or extroverted. The subjects (n=63) responded to questionnaires including: SF-36 questionnaire, Eysenck test and the questionnaire of the affective distress profile designed to assess the subjective dimension of functional negative emotions, dysfunctional negative emotions and positive emotions. Psoriasis patients had significantly higher average scores of physical functions and limitations brought on by emotional problems. Emotional instability was common for both types of patients and anxiety was associated with a low level of education. Overall, we believe that it is necessary to include items evaluating the patients' affective profile and personality in the assessment protocols of these diseases. These items could help the clinician in identifying possible factors that signal worsening of the disease or of non-response to treatment.

Mega-voltage versus kilo-voltage cone beam CT used in image guided radiation therapy: comparative study of microdosimetric properties

Mega-voltage computed tomography (MVCT) and kilo-voltage cone beam CT (CBCT) are routinely used in image-guided radiation therapy. In current practice, doses from MVCT and CBCT are reported with no correction for radiation quality. In this study, we compared microdosimetric properties as well as doses for MVCT and CBCT. Monte Carlo simulation codes BEAMnrc and DOSXYZnrc were used to simulate a Varian CBCT 125 kVp photon beam and primary electron spectra for CT sets of two patients. The revised Oak Ridge Electron transport Code (NOREC) was used to simulate electron tracks in liquid water. C++ code was developed to compute lineal energy in a sphere of 1 μm diameter. Dose-mean lineal energy-based quality factors were calculated for critical organs in-field. The estimated quality factor for CBCT is up to a factor of 1.3 times that of MV beams.

Etiological factors of systemic sclerosis in the southeast region of Romania

Systemic sclerosis (SSc) is a relatively rare autoimmune disease with skin and visceral involvement, having a yet unknown etiopathogenesis. Research has shown that professional exposure to various polluting chemicals such as dyes, aliphatic and aromatic organic solvents, inhalable silica dust or certain heavy metals, can be triggering factors for this disease when they overlap a predisposing genetic profile. Smoking is still a debated factor involved in the etiology of SSc, as authors have divergent opinions on this matter. The present study was designed to analyze the etiological factors identified in the group of 37 patients with diffuse and limited SSc from the southeast region of Romania and the results were compared to the literature data. In the group of patients included in this study, occupational exposure and smoking history were not present in all patients, and a hereditary factor was identified only in an isolated case. The majority of patients suffered from a major negative psychological event or from long-term stressful situations and these factors were associated with smoking history or occupational exposure; this suggests that SSc is initiated in a set of cumulative triggering factors.

A new DOSXYZnrc method for Monte Carlo simulations of 4D dose distributions

The purpose of this study is to present a novel method for generating Monte Carlo 4D dose distributions in a single DOSXYZnrc simulation. During a standard simulation, individual energy deposition events are summed up to generate a 3D dose distribution and their associated temporal information is discarded. This means that in order to determine dose distributions as a function of time, separate simulations would have to be run for each interval of interest. Consequently, it has not been clinically feasible until now to routinely perform Monte Carlo simulations of dose rate, time-resolved dose accumulation, or electronic portal imaging devices (EPID) cine-mode images for volumetric modulated arc therapy (VMAT) plans. To overcome this limitation, we modified DOSXYZnrc and defined new input and output variables that allow a time-like parameter associated with each particle history to be binned in a user-defined manner. Under the new code version, computation times are the same as for a standard simulation, and the time-integrated 4D dose is identical to the standard 3D dose. We present a comparison of scintillator measurements and Monte Carlo simulations for dose rate during a VMAT beam delivery, a study of dose rate in a VMAT total body irradiation plan, and simulations of transit (through-patient) EPID cine-mode images.

RENEB - THE ROMANIAN PERSPECTIVE

The European Commission supports the development of an European network in biodosimetry (RENEB), in which a large number of experienced laboratories from 16 European countries are involved. The final goal will be the significant improvement of the biodosimetry capacity for response to accidents and radiological emergencies, based on a well-organized cooperative action with a rapid and rigorous dose assessment. The project is aimed at consolidating the network with its operational platform, inter-comparison exercises, training activities, proceedings in quality assurance and implementation and integration of new network partners and new methods. In the project context, the Romanian perspective on the participation benefits for the Romanian biodosimetry is described.

Contribution of Imaging Techniques in the Management of Cutaneous Pathology

The management of skin pathology of tumors and inflammatory disorders is difficult due to the existence of constantly changing diagnostic and treatment algorithms. The incidence of cutaneous melanoma and other melanocytic or non-melanoma tumors is currently increasing. Melanoma is difficult to treat in advanced stages due to its aggressiveness, and early diagnosis is required to improve the prognosis of these patients. Imaging techniques, such as classical and digital dermatoscopy can provide information on structure, vascular pattern, prognostic factors and detailed morphological analysis that can lead to improved individual management. This article presents a retrospective study that aims to analyze the contribution of imaging techniques to clinical and histological data.

Catching Cancer Early: The Importance of Dermato-Oncology Screening

The European Society for Medical Oncology experts have identified the main components of the long-term management of oncological patients. These include early diagnosis through population screening and periodic control of already diagnosed patients to identify relapses, recurrences, and other associated neoplasms. There are no generally accepted international guidelines for the long-term monitoring of patients with skin neoplasms (nonmelanoma skin cancer, malignant melanoma, precancerous-high-risk skin lesions). Still, depending on the experience of the attending physician and based on the data from the literature, one can establish monitoring intervals to supervise these high-risk population groups, educate the patient and monitor the general population.

Epidemiological Study of Autoimmune Bullous Dermatoses in Northeastern Romania

BACKGROUND

Autoimmune bullous diseases (ABDs) are a rare but significant group of dermatoses that pose great challenges to the treating dermatologist. ABDs are characterized by the presence of tissue-bound and circulating autoantibodies directed against disease-specific target antigens of the skin. Most epidemiological studies have focused on a single ABD. More than that, there are few data about the incidence and prevalence of autoimmune blistering diseases in Romania.

METHODS

In this study, between 2015 and 2019, we retrospectively investigated a total of 225 patients with autoimmune bullous diseases from the northeastern region of Romania. The diagnosis was based on the clinical and histo- and immunohistological findings.

RESULTS

Pemphigus was the most frequently encountered ABD, with an incidence of 8.16/1,000,000 inhabitants, representing 58.7% (132 cases), followed by 24% cases of bullous pemphigoid (54 cases), 15.4% of patients were diagnosed with dermatitis herpetiformis (37 cases), and 0.9% other subepidermal autoimmune bullous dermatoses. The average age of onset of pemphigus vulgaris was 59.4 years, the majority of patients being male, while the average age of patients diagnosed with bullous pemphigoid was 73.8 years, the majority being female.

CONCLUSIONS

Pemphigus vulgaris is the most frequently encountered ABDs in the northeast of Romania, with a higher incidence than in Western European countries, and this may be due to specific peculiarities of the geographical area, as well as to a genetic susceptibility of the population in this region.