Understanding the Role of Radio-Sensitizing Nanoparticles in Enhancing Pathologic Response in Soft Tissue Sarcomas.

High-atomic-number (Z) nanoparticles produce a cascade of low-energy secondary electrons and characteristic X-rays when ionized by X-ray irradiation. These secondary particles deposit their energy in the vicinity of the nanoparticles and, provided that the latter are selectively accumulated within tumor cells, this results in increased DNA damage and tumor cell deaths. This study reviews the utilization of high-Z nanoparticles in the treatment of soft tissue sarcomas (STS). Both in vitro and in vivo experiments demonstrated that the dose is enhanced by approximately 1.2 when polyethelyne glycol (PEG)-modified gold nanoparticles, and from 1.4 to 1.8 when hafnium oxide nanoparticles (NBTXR3, Nanobiotix SA, France) are introduced into tumor cells and activated by X-ray beams. In a phase 2/3 clinical trial investigating the therapeutic benefit of using nanoparticles in preoperative external beam radiotherapy for locally advanced STS, the proportion of patients with a pathological complete response in their resected tumor was doubled when NBTXR3 nanoparticles were used. Additionally, a higher percentage of patients with complete tumor resection was observed in the NBTXR3 plus radiotherapy group. Similar toxicity profiles were found for both the NBTXR3 plus radiotherapy and the radiotherapy alone patient groups. The incorporation of radio-sensitizing nanoparticles in the preoperative radiotherapy of STS could enhance treatment outcomes.

Multimodality treatment of primary cardiac angiosarcoma: A systematic literature review.

BACKGROUND: Primary cardiac angiosarcoma (PCA) is the most prevalent histological type of cardiac sarcoma but its rarity poses a challenge for standardizing treatment protocols. Moreover, published studies are limited by small patient numbers and lack of randomization, making it challenging to establish evidence-based treatment strategies. This systematic review aims to consolidate the heterogeneous published data and identify factors related to the treatment outcome of PCA patients. METHODS: The PubMed and Scopus bibliographic databases were systematically searched for original articles reporting clinical, treatment and outcome data for PCA patients. Kaplan-Meier analysis was used to calculate the time to progression and survival. The Log-Rank test was used to compare progression-free and overall survival data. The Cox proportional hazards regression model was used for univariate and multivariate analysis of survival data. RESULTS: A total of 127 studies containing data for 162 patients were analyzed. The median age of the patient cohort was 45 years, with males being 1.5 times more frequently affected than females. Tumors were primarily located on the right side of the heart, with a median size of 6 cm. Median progression-free and overall survival of 5 months and 12 months, respectively, were calculated. Age, sex, and resection margins did not have a significant impact on PCA survival, as determined by both univariate and multivariate analyses. The presence of metastases at diagnosis was associated with lower overall survival in univariate analysis, although this effect was not significant in multivariate analysis. Multimodality treatment that incorporated surgery and adjuvant chemo-radiotherapy was associated with a statistically significant survival benefit. Median overall survival increased from 6 months with surgery alone to 13 months and 27 months with adjuvant chemotherapy and chemo-radiotherapy, respectively. CONCLUSION: Multimodality treatment including surgery and chemo-radiotherapy was found to offer the greatest survival benefit for PCA patients.

Treatment of an unresectable cardiac angiosarcoma using paclitaxel and image guided radiotherapy: Case report and literature review.

Primary cardiac angiosarcomas (PCAs) are rare tumors that are typically found in the right atrium between the third and the fifth decade of life. While surgical removal of the tumor combined with adjuvant chemotherapy and/or radiotherapy is the treatment of choice, most of the patients present with unresectable tumors and metastatic disease carrying a dismal prognosis with a median survival of less than 1 year. Doxorubicin and ifosfamide based chemotherapy combined with radiotherapy is currently employed in these patients, but no standardized treatment algorithms exist. In this report, we present the management of a patient with an unresectable PCA treated using weekly paclitaxel (120 mg) combined with radiotherapy (60 Gy in 30 fractions) delivered by a helical TomoTherapy system. Follow-up imaging studies showed a remarkable tumor regression which allowed for surgical excision of the tumor 10 months post treatment. Histopathological examination of the resected mass showed no viable tumor cell. On the latest follow-up study, 12 months post treatment, no sign of disease progression (local or distant) was found, and the patient is in good clinical condition.

Case report: skeletal muscle metastasis from follicular thyroid carcinoma presenting as synovial sarcoma.

Differentiated thyroid carcinomas tend to remain localized and usually are of slow progression with excellent long-term survival. The major sites of distant metastases are cervical lymph nodes, lungs and bones and the minor sites include the brain, liver, pericardium, skin, kidney, pleura and muscle. Skeletal muscle metastases from differentiated thyroid carcinoma, are exceedingly rare. In this report, a 42-year-old woman with follicular thyroid cancer that had had a total thyroidectomy and radioiodine ablation nine years ago was presented with a painful right thigh mass and negative PET/CT scan. The patient had also lung metastases during the follow-up period which were treated with surgery, chemotherapy and radiation therapy. An MRI scan of the right thigh showed a deep-seated lobulated mass with cystic regions, bleeding elements and strong heterogeneous post contrast administration enhancement. Due to the similarities in clinical manifestations and imaging features between soft tissue tumors and skeletal muscle metastases, the case was initially misdiagnosed in favor of synovial sarcoma. Histopathological, immunohistochemistry and molecular analysis of the soft tissue mass confirmed to be a thyroid metastasis and, as a result, a final diagnosis of skeletal muscle metastasis was provided. Even though the probability of a skeletal muscle metastasis from thyroid cancer approaches zero, this study aims to raise the awareness to the medical community that these events do in fact occur in the clinical setting and should be considered in the differential diagnosis of patients with thyroid carcinomas.

Dosimetric accuracy of the Convolution algorithm for Leksell Gamma Plan radiosurgery treatment planning: Evaluation in the presence of clinically relevant inhomogeneities.

PURPOSE: The Leksell Gamma Plan Convolution algorithm (LGP-Convolution) has not been widely adopted. This mainly stems from the higher calculated beam-on times relative to the standard ray tracing-based LGP-TMR10 dose calculation algorithm. This study aims to evaluate the accuracy of the LGP-Convolution in scenarios where the treated lesions are in the vicinity of or encompassed by bone and/or air inhomogeneities. METHODS: The solid water dosimetry phantom provided by the vendor was modified to include bone and air inhomogeneities. Two treatment planning scenarios were investigated involving a single shot and multiple shots, respectively. Treatment planning and dose prescription were performed using the LGP-Convolution algorithm. Triple channel film dosimetry was performed using GafChromic EBT3 films calibrated in terms of absorbed dose to water in a 60 Co beam. Monte Carlo (MC) simulation dosimetry was also performed in the inhomogeneous experimental geometry using the EGSnrc MC platform and a previously validated sector-based phase-space source model. MC simulations were also employed to determine correction factors required for converting EBT3 measurements at points within the bone and air inhomogeneities from dose-to-water values to the corresponding dose to medium values. RESULTS AND CONCLUSIONS: EBT3 dose to medium correction factors ranged with field size (4, 8, or 16 mm) within 0.941-0.946 for bone and 0.745-0.749 for air inhomogeneities. An excellent agreement was found between the LGP-Convolution calculations with corresponding EBT3 and MC dose to medium results at all measurement points, except those located inside the air inhomogeneity. The latter is of no clinical importance and excluding them yielded gamma index passing rates of nearly 100% for 3% local dose difference and 1 mm distance-to-agreement criteria. The excellent agreement observed between LGP-Convolution calculations and film as well as MC results of dose to medium indicates that the latter is the quantity reported by the LGP-Convolution.

Dosimetry in 1.5 T MR-Linacs: Monte Carlo determination of magnetic field correction factors and investigation of the air gap effect.

BACKGROUND: In Magnetic Resonance-Linac (MR-Linac) dosimetry formalisms, a new correction factor, kB,Q , has been introduced to account for corresponding changes to detector readings under the beam quality, Q, and the presence of magnetic field, B. PURPOSE: This study aims to develop and implement a Monte Carlo (MC)-based framework for the determination of kB,Q correction factors for a series of ionization chambers utilized for dosimetry protocols and dosimetric quality assurance checks in clinical 1.5 T MR-Linacs. Their dependencies on irradiation setup conditions are also investigated. Moreover, to evaluate the suitability of solid phantoms for dosimetry checks and end-to-end tests, changes to the detector readings due to the presence of small asymmetrical air gaps around the detector's tip are quantified. METHODS: Phase space files for three irradiation fields of the ELEKTA Unity 1.5 T/7 MV flattening-filter-free MR-Linac were provided by the manufacturer and used as source models throughout this study. Twelve ionization chambers (three farmer-type and nine small-cavity detectors, from three manufacturers) were modeled (including their dead volume) using the EGSnrc MC code package. kB,Q values were calculated for the 10 × 10 cm2 irradiation field and for four cardinal orientations of the detectors' axes with respect to the 1.5 T magnetic field. Potential dependencies of kB,Q values with respect to field size, depth, and phantom material were investigated by performing additional simulations. Changes to the detectors' readings due to the presence of small asymmetrical air gaps (0.1 up to 1 mm) around the chambers' sensitive volume in an RW3 solid phantom were quantified for three small-cavity chambers and two orientations. RESULTS: For both parallel (to the magnetic field) orientations, kB,Q values were found close to unity. The maximum correction needed was 1.1%. For each detector studied, the kB,Q values calculated for the two parallel orientations agreed within uncertainties. Larger corrections (up to 5%) were calculated when the detectors were oriented perpendicularly to the magnetic field. Results were compared with corresponding ones found in the literature, wherever available. No considerable dependence of kB,Q with respect to field size (down to 3 × 3 cm2 ), depth, or phantom material was noticed, for the detectors investigated. As compared to the perpendicular one, in the parallel to the magnetic field orientation, the air gap effect is minimized but is still considerable even for the smallest air gap considered (0.1 mm). CONCLUSION: For the 10 × 10 cm2 field, magnetic field correction factors for 12 ionization chambers and four orientations were determined. For each detector, the kB,Q value may be also applied for dosimetry procedures under different irradiation parameters provided that the orientation is taken into account. Moreover, if solid phantoms are used, even the smallest asymmetrical air gap may still bias small-cavity chamber response. This work substantially expands the availability and applicability of kB,Q correction factors that are detector- and orientation-specific, enabling more options in MR-Linac dosimetry checks, end-to-end tests, and quality assurance protocols.

Spatial distribution of the imaging dose and characterization of the scatter radiation contribution in CyberKnife radiosurgery.

PURPOSE: The imaging dose for intra- and extra-cranial CyberKnife radiosurgery applications was calculated and the scattered radiation reaching the digital detectors was quantified and analyzed with regard to its origin. METHODS: The image guidance subsystem of the CyberKnife was modeled based on vendor-provided information. The emitted X-ray energy spectrum for 120 kV was estimated using the SpekPy software tool. Monte Carlo (MC) image acquisition simulations were performed to calculate the total, primary and scattered photon fluences reaching each detector as a function of the imaged object dimensions. MC calculations of the imaging dose were performed for intra- and extra-cranial applications assuming 120 kV and 10 mAs acquisition settings. RESULTS: The amount of scattered radiation reaching each detector was found to depend on the dimensions of the imaged anatomical region, contributing more than 40 % to the total photon fluence for regions more than 20 cm thick. More than 20 % of this scattered radiation originates from the contralateral imaging field. A maximum organ dose of 1.5 mGy at the nasal bones and an average dose of 0.37 mGy to the eye lenses per image pair acquisition was calculated for head applications. An entrance imaging dose of 0.4 mGy was calculated for extracranial applications. CONCLUSIONS: Scattered radiation reaching each detector in the skull and spine tracking applications can be reduced by acquiring the pair of radiographs sequentially instead of simultaneously. A dose of 3.7 cGy to the eye lenses is estimated assuming 100 image pair exposures required for treatment completion.

Impact of systematic MLC positional uncertainties on the quality of single-isocenter multi-target VMAT-SRS treatment plans.

PURPOSE: To study the impact of systematic MLC leaf positional uncertainties (stemming from mechanical inaccuracies or sub-optimal MLC modeling) on the quality of intracranial single-isocenter multi-target VMAT-SRS treatment plans. An estimation of appropriate tolerance levels is attempted. METHODS: Five patients, with three to four metastases and at least one target lying in close proximity to organs-at-risk (OARs) were included in this study. A single-isocenter multi-arc VMAT plan per patient was prepared, which served as the reference for dosimetric impact evaluation. A range of leaf offsets was introduced (±0.03 mm up to ±0.30 mm defined at the MLC plane) to both leaf banks, by varying the leaf offset MLC modeling parameter in Monaco for all the prepared plans, in order to simulate projected leaf offsets of ±0.09 mm up to ±0.94 mm at the isocenter plane, respectively. For all offsets simulated and cases studied, dose distributions were re-calculated and compared with the corresponding reference ones. An experimental dosimetric procedure using the SRS mapCHECK diode array was also performed to support the simulation study results and investigate its suitability to detect small systematic leaf positional errors. RESULTS: Projected leaf offsets of ±0.09 mm were well-tolerated with respect to both target dosimetry and OAR-sparing. A linear relationship was found between D95% percentage change and projected leaf offset (slope: 12%/mm). Impact of projected offset on target dosimetry was strongly associated with target volume. In two cases, plans that could be considered potentially clinically unacceptable (i.e., clinical dose constraint violation) were obtained even for projected offsets as small as 0.19 mm. The performed experimental dosimetry check can detect potential small systematic leaf errors. CONCLUSIONS: Plan quality indices and dose-volume metrics are very sensitive to systematic sub-millimeter leaf positional inaccuracies, projected at the isocenter plane. Acceptable and tolerance levels in systematic MLC uncertainties need to be tailored to VMAT-SRS spatial and dosimetric accuracy requirements.

Quantification of Nanoscale Dose Enhancement in Gold Nanoparticle-Aided External Photon Beam Radiotherapy.

The recent progress in Nanotechnology has introduced Gold Nanoparticles (AuNPs) as promising radiosensitizing agents in radiation oncology. This work aims to estimate dose enhancement due to the presence of AuNPs inside an irradiated water region through Monte Carlo calculations. The GATE platform was used to simulate 6 MV photon histories generated from a TrueBeam® linear accelerator with and without a Flattening Filter (FF) and model AuNPs clusters. The AuNPs size, concentration and distribution pattern were examined. To investigate different clinical irradiation conditions, the effect of field size, presence of FF and placement of AuNPs in water were evaluated. The range of Dose Enhancement Factors (DEF = DoseAu/DoseWater) calculated in this study is 0.99 ± 0.01-1.26 ± 0.02 depending on photon beam quality, distance from AuNPs surface, AuNPs size and concentration and pattern of distribution. The highest DEF is reported for irradiation using un-flattened photon beams and at close distances from AuNPs. The obtained findings suggest that dose deposition could be increased in regions that represent whole cells or subcellular targets (mitochondria, cell nucleus, etc.). Nevertheless, further and consistent research is needed in order to make a step toward AuNP-aided radiotherapy in clinical practice.

Monte Carlo simulation to assess free space and end-weld thickness variation effects on dose rate for a new Ir-192 brachytherapy source.

A new Iridium-192 seed for brachytherapy is under development. Specific dose rate contribution by two different factors were evaluated: the effect from movement of the core in the free space within the seed and the effect of the end-weld thickness variation. Both were investigated through use of the Monte Carlo radiation transport code MCNP6 and an in-house routine programmed with MATLAB. Differences greater than 15% compared to results from the nominal seed were found near the source, indicating a significant dose variation.

Dosimetric impact of rotational errors on the quality of VMAT-SRS for multiple brain metastases: Comparison between single- and two-isocenter treatment planning techniques.

PURPOSE: In the absence of a 6D couch and/or assuming considerable intrafractional patient motion, rotational errors could affect target coverage and OAR-sparing especially in multiple metastases VMAT-SRS cranial cases, which often involve the concurrent irradiation of off-axis targets. This work aims to study the dosimetric impact of rotational errors in such applications, under a comparative perspective between the single- and two-isocenter treatment techniques. METHODS: Ten patients (36 metastases) were included in this study. Challenging cases were only considered, with several targets lying in close proximity to OARs. Two multiarc VMAT plans per patient were prepared, involving one and two isocenters, serving as the reference plans. Different degrees of angular offsets at various orientations were introduced, simulating rotational errors. Resulting dose distributions were evaluated and compared using commonly employed dose-volume and plan quality indices. RESULTS: For single-isocenter plans and 1° rotations, plan quality indices, such as coverage, conformity index and D95% , deteriorated significantly (>5%) for distant targets from the isocenter (at> 4-6 cm). Contrarily, for two-isocenter plans, target distances to nearest isocenter were always shorter (≤4 cm), and, consequently, 1° errors were well-tolerated. In the most extreme case considered (2° around all axes) conformity index deteriorated by on-average 7.2%/cm of distance to isocenter, if one isocenter is used, and 2.6%/cm, for plans involving two isocenters. The effect is, however, strongly associated with target volume. Regarding OARs, for single-isocenter plans, significant increase (up to 63%) in Dmax and D0.02cc values was observed for any angle of rotation. Plans that could be considered clinically unacceptable were obtained even for the smallest angle considered, although rarer for the two-isocenter planning approach. CONCLUSION: Limiting the lesion-to-isocenter distance to ≤4 cm by introducing additional isocenter(s) appears to partly mitigate severe target underdosage, especially for smaller target sizes. If OAR-sparing is also a concern, more stringent rotational error tolerances apply.

Staged Image-guided Robotic Radiosurgery and Deferred Chemotherapy to Treat a Malignant Glioma During and After Pregnancy.

A 26-year-old pregnant woman with a fast-growing malignant deep-seated brain glioma was offered a therapeutic abortion to allow subsequent surgical resection. This option was refused by the mother, but the fast tumor growth placed the life of both mother and child at risk. A staged CyberKnife radiosurgery treatment was then planned, aiming to provide at least temporary tumor growth control and allow a safe delivery while keeping the doses received by the fetus well below the allowed doses. Growth control and the safe delivery of a healthy child were achieved after this first treatment. An intensive chemotherapy program based on the combination of Avastin, irinotecan, and Temodal was then started. Recurring tumor growth was treated with a second CyberKnife procedure while continuing the above chemotherapy protocol. At 43 months after the second CyberKnife procedure, the tumor had disappeared on magnetic resonance imaging. Neither mother nor child showed the neurological sequelae. Staged radiosurgery and deferred chemotherapy proved to be a safe and effective treatment to allow the delivery of a healthy child and the long-term control of an aggressive brain glioma.

A comparative assessment of inhomogeneity and finite patient dimension effects in 60Co and 192Ir high-dose-rate brachytherapy.

PURPOSE: To perform a comparative study of heterogeneities and finite patient dimension effects in 60Co and 192Ir high-dose-rate (HDR) brachytherapy. MATERIAL AND METHODS: Clinically equivalent plans were prepared for 19 cases (8 breast, 5 esophagus, 6 gynecologic) using the Ir2.A85-2 and the Co0.A86 HDR sources, with a TG-43 based treatment planning system (TPS). Phase space files were obtained for the two source designs using MCNP6, and validated through comparison to a single source dosimetry results in the literature. Dose to water, taking into account the patient specific anatomy and materials (Dw,m), was calculated for all plans using MCNP6, with input files prepared using the BrachyGuide software tool to analyze information from DICOM RT plan exports. RESULTS: A general TG-43 dose overestimation was observed, except for the lungs, with a greater magnitude for 192Ir. The distribution of percentage differences between TG-43 and Monte Carlo (MC) in dose volume histogram (DVH) indices for the planning target volume (PTV) presented small median values (about 2%) for both 60Co and 192Ir, with a greater dispersion for 192Ir. Regarding the organs at risk (OARs), median percentage differences for breast V50% were 3% (5%) for 60Co (192Ir). Differences in median skin D2cc were found comparable, with a larger dispersion for 192Ir, and the same applied to the lung D10cc and the aorta D2cc. TG-43 overestimates D2cc for the rectum and the sigmoid, with median differences from MC within 2% and a greater dispersion for 192Ir. For the bladder, the median of the difference is greater for 60Co (~2%) than for 192Ir (~0.75%), demonstrating however a greater dispersion again for 192Ir. CONCLUSIONS: The magnitude of differences observed between TG-43 based and MC dosimetry and their smaller dispersion relative to 192Ir, suggest that 60Co HDR sources are more amenable to the TG-43 assumptions in clinical treatment planning dosimetry.

On source models for (192)Ir HDR brachytherapy dosimetry using model based algorithms.

A source model is a prerequisite of all model based dose calculation algorithms. Besides direct simulation, the use of pre-calculated phase space files (phsp source models) and parameterized phsp source models has been proposed for Monte Carlo (MC) to promote efficiency and ease of implementation in obtaining photon energy, position and direction. In this work, a phsp file for a generic (192)Ir source design (Ballester et al 2015) is obtained from MC simulation. This is used to configure a parameterized phsp source model comprising appropriate probability density functions (PDFs) and a sampling procedure. According to phsp data analysis 15.6% of the generated photons are absorbed within the source, and 90.4% of the emergent photons are primary. The PDFs for sampling photon energy and direction relative to the source long axis, depend on the position of photon emergence. Photons emerge mainly from the cylindrical source surface with a constant probability over ±0.1 cm from the center of the 0.35 cm long source core, and only 1.7% and 0.2% emerge from the source tip and drive wire, respectively. Based on these findings, an analytical parameterized source model is prepared for the calculation of the PDFs from data of source geometry and materials, without the need for a phsp file. The PDFs from the analytical parameterized source model are in close agreement with those employed in the parameterized phsp source model. This agreement prompted the proposal of a purely analytical source model based on isotropic emission of photons generated homogeneously within the source core with energy sampled from the (192)Ir spectrum, and the assignment of a weight according to attenuation within the source. Comparison of single source dosimetry data obtained from detailed MC simulation and the proposed analytical source model show agreement better than 2% except for points lying close to the source longitudinal axis.

On the impact of improved dosimetric accuracy on head and neck high dose rate brachytherapy.

PURPOSE: To study the effect of finite patient dimensions and tissue heterogeneities in head and neck high dose rate brachytherapy. METHODS AND MATERIALS: The current practice of TG-43 dosimetry was compared to patient specific dosimetry obtained using Monte Carlo simulation for a sample of 22 patient plans. The dose distributions were compared in terms of percentage dose differences as well as differences in dose volume histogram and radiobiological indices for the target and organs at risk (mandible, parotids, skin, and spinal cord). RESULTS: Noticeable percentage differences exist between TG-43 and patient specific dosimetry, mainly at low dose points. Expressed as fractions of the planning aim dose, percentage differences are within 2% with a general TG-43 overestimation except for the spine. These differences are consistent resulting in statistically significant differences of dose volume histogram and radiobiology indices. Absolute differences of these indices are however small to warrant clinical importance in terms of tumor control or complication probabilities. CONCLUSIONS: The introduction of dosimetry methods characterized by improved accuracy is a valuable advancement. It does not appear however to influence dose prescription or call for amendment of clinical recommendations for the mobile tongue, base of tongue, and floor of mouth patient cohort of this study.

A user-oriented procedure for the commissioning and quality assurance testing of treatment planning system dosimetry in high-dose-rate brachytherapy.

PURPOSE: To develop a user-oriented procedure for testing treatment planning system (TPS) dosimetry in high-dose-rate brachytherapy, with particular focus to TPSs using model-based dose calculation algorithms (MBDCAs). METHODS AND MATERIALS: Identical plans were prepared for three computational models using two commercially available systems and the same (192)Ir source. Reference dose distributions were obtained for each plan using the MCNP v.6.1 Monte Carlo (MC) simulation code with input files prepared via automatic parsing of plan information using a custom software tool. The same tool was used for the comparison of reference dose distributions with corresponding MBDCA exports. RESULTS: The single source test case yielded differences due to the MBDCA spatial discretization settings. These affect points at relatively increased distance from the source, and they are abated in test cases with multiple source dwells. Differences beyond MC Type A uncertainty were also observed very close to the source(s), close to the test geometry boundaries, and within heterogeneities. Both MBDCAs studied were found equivalent to MC within 5 cm from the target volume for a clinical breast brachytherapy test case. These are in agreement with previous findings of MBDCA benchmarking in the literature. CONCLUSIONS: The data and the tools presented in this work, that are freely available via the web, can serve as a benchmark for advanced clinical users developing their own tests, a complete commissioning procedure for new adopters of currently available TPSs using MBDCAs, a quality assurance testing tool for future updates of already installed TPSs, or as an admission prerequisite in multicentric clinical trials.

Radiation dose to the fetus during CyberKnife radiosurgery for a brain tumor in pregnancy.

PURPOSE: Pregnancy during radiosurgery is extremely rare in clinical practice. We report fetal dose results during CyberKnife radiosurgery for a brain tumor in pregnancy. METHODS AND MATERIALS: A 26 year old pregnant woman with a rapidly growing deep-seated grade-III glioma was treated during the third trimester of gestation using CyberKnife. Ultrasound imaging was used to determine the position of the embryo prior to treatment. A dose of 1400 cGy was prescribed aiming to control tumor growth until delivery of the child. Prior to radiosurgery, the treatment was simulated on an anthropomorphic phantom. Radiation dose to the embryo was measured using a Farmer chamber and EBT3 films. RESULTS: Fetal doses of 4.4 cGy and 4.1 cGy were measured for the embryo's head and legs, lying at 56 cm and 72 cm from the isocenter, respectively, using the Farmer chamber situated at 8.5 cm depth beneath the phantom surface. Dose results of 4.4 cGy, 3.5 cGy and 2.0 cGy were measured with the films situated at depths of 6.5 cm, 9.5 cm and 14.5 cm, respectively. An average dose of 4.2 cGy to the fetus was derived from the above values. A corresponding dose of 3.2 cGy was also calculated based on results obtained using EBT3 films situated upon the patient skin. CONCLUSIONS: The measured fetal doses are below the threshold of 10 cGy for congenital malformations, mental and growth retardation effects. The radiogenic cancer risk to the live-born embryo was estimated less than 0.3% over the normal incidence. The treatment was administered successfully, allowing the patient to deliver a healthy child.

BrachyGuide: a brachytherapy-dedicated DICOM RT viewer and interface to Monte Carlo simulation software.

This work presents BrachyGuide, a brachytherapy-dedicated software tool for the automatic preparation of input files for Monte Carlo simulation from treatment plans exported in DICOM RT format, and results of calculations performed for its benchmarking. Three plans were prepared using two computational models, the image series of a water sphere and a multicatheter breast brachytherapy patient, for each of two commercially available treatment planning systems: BrachyVision and Oncentra Brachy. One plan involved a single source dwell position of an 192Ir HDR source (VS2000 or mHDR-v2) at the center of the water sphere using the TG43 algorithm, and the other two corresponded to the TG43 and advanced dose calculation algorithm for the multicatheter breast brachytherapy patient. Monte Carlo input files were prepared using BrachyGuide and simulations were performed with MCNP v.6.1. For the TG43 patient plans, the Monte Carlo computational model was manually edited in the prepared input files to resemble TG43 dosimetry assumptions. Hence all DICOM RT dose exports were equivalent to corresponding simulation results and their comparison was used for benchmarking the use of BrachyGuide. Monte Carlo simulation results and corresponding DICOM RT dose exports agree within type A uncertainties in the majority of points in the computational models. Treatment planning system, algorithm, and source specific differences greater than type A uncertainties were also observed, but these were explained by treatment planning system-related issues and other sources of type B uncertainty. These differences have to be taken into account in commissioning procedures of brachytherapy dosimetry algorithms. BrachyGuide is accurate and effective for use in the preparation of commissioning tests for new brachytherapy dosimetry algorithms as a user-oriented commissioning tool and the expedition of retrospective patient cohort studies of dosimetry planning.

A Web simulation of medical image reconstruction and processing as an educational tool.

Web educational resources integrating interactive simulation tools provide students with an in-depth understanding of the medical imaging process. The aim of this work was the development of a purely Web-based, open access, interactive application, as an ancillary learning tool in graduate and postgraduate medical imaging education, including a systematic evaluation of learning effectiveness. The pedagogic content of the educational Web portal was designed to cover the basic concepts of medical imaging reconstruction and processing, through the use of active learning and motivation, including learning simulations that closely resemble actual tomographic imaging systems. The user can implement image reconstruction and processing algorithms under a single user interface and manipulate various factors to understand the impact on image appearance. A questionnaire for pre- and post-training self-assessment was developed and integrated in the online application. The developed Web-based educational application introduces the trainee in the basic concepts of imaging through textual and graphical information and proceeds with a learning-by-doing approach. Trainees are encouraged to participate in a pre- and post-training questionnaire to assess their knowledge gain. An initial feedback from a group of graduate medical students showed that the developed course was considered as effective and well structured. An e-learning application on medical imaging integrating interactive simulation tools was developed and assessed in our institution.