Maximum Dose Values Research Articles

3-D dose distribution for organ dose measurement in CT thoracic exams using Gafchromic™ XR-QA2 films

The patient dose in radiodiagnostic is currently monitored through an ionizing radiation exposure index named Volume Computed Tomography Dose Index (CTDIvol) and the Dose-Length Product (DLP), displayed by CT scanner and measurable through a 100 mm long pencil ionization chamber, inserted in a homogeneous cylindrical PMMA phantom. The phantom is 14 cm long and has a diameter of 16 (32) cm that represents the adult head (body). One of the main flaws of such a method is that it does not return any information on the dose distribution to organs, and the average absorbed dose value, due to the material and dimensions of both the phantom and the ionization chamber, might be either underestimated or overestimated depending upon the patient size. With the aim to obtain complementary information, this work presents a method to estimate organ dose in the thoracic area of an anthropomorphic woman phantom in CT, by employing GafchromicTM XR-QA2 and computational 3-D reconstruction methods. Lungs, heart, and spinal cord have been chosen as a dosimetry case study. XR-QA2 films have been placed between the phantom slabs in the thoracic area and scanned with a multi-slice CT scanner. 2-D and 3-D absorbed dose distributions for each organ have been analyzed, by means of a custom code in Matlab®. Critical aspects in the dose distributions have been found for the spinal-cord case (serial organ) where the dose distribution is non normal and the maximum dose value is ∼ 30 mGy while a maximum dose value between 26 and 28 mGy has been measured elsewhere.

Characterizing Wildland Firefighters' Thermal Environment During Live-Fire Suppression.

Wildland firefighters work under adverse environments (e.g., heat and fire exposure), which contribute to increasing the heat strain. Despite this there is a paucity of knowledge about the thermal environment in real wildfire suppression scenarios. Therefore, the main purpose of this study was to characterize the environmental thermal exposure and the risk of heat burn injuries during real wildfire suppression (n = 23). To characterize the wildland firefighter’s (n = 5) local thermal exposure, measurements of air temperature and heat flux were performed. Heat flux measurements were made using four thin-planar heat flux sensors. Two were affixed on the outer surface of the garment on the left chest and thigh. Two other sensors were placed on the inner surface of the fabric in parallel to those placed externally. Four thermal classes were defined based on the heat flux across the inner sensors (≤1000, ≤5000, ≤7000, and >7000 W⋅m–2). The risk of pain and first-degree burns were calculated using the dose of thermal radiation method. The inner sensors mean and maximum heat flux and environment temperature were 286.7 ± 255.0 and 2370.4 ± 3004.5 W⋅m–2 and 32.6 ± 8.9 and 78.0 ± 8.9°C, respectively. Approximately 81, 15, and 3.5% of the exposure time the heat flux was ≤1000, >1000–5000, and >5000 W⋅m–2, respectively. The highest average and maximum thermal dose values were ∼94 and ∼110 (kW⋅m–2)4/3⋅s. In conclusion, the thermal exposure obtained may be considered light. However, high thermal exposure values may be obtained in punctual moments, which can elicit first-degree burns.

Experimental validation of magnetically focused proton beams for radiosurgery

We performed experiments using a triplet of quadrupole permanent magnets to focus protons and compared their dose distributions with unfocused collimated beams using energies and field sizes typically employed in proton radiosurgery. Experiments were performed in a clinical treatment room wherein small-diameter proton beams were focused by a magnet triplet placed immediately upstream of a water tank. The magnets consisted of segments of Sm2Co17 rare-earth permanent magnetic material adhered into Halbach cylinders with nominal field gradients of 100, 150, 200, and 250 T m−1. Unmodulated beams with initial diameters of 3 mm–20 mm were delivered using a single scattering system with nominal energies of 127 and 157 MeV (respective ranges of ~10 cm and 15 cm in water), commonly used for proton radiosurgery at our institution. For comparison, small-diameter unfocused collimated beams were similarly delivered. Transverse and depth dose distributions were measured using radiochromic film and a diode detector, respectively, and compared between the focused and unfocused beams (UNF). The focused beams produced low-eccentricity beam spots (defined by the 80% dose contour) at Bragg depth, with full width at 80% maximum dose values ranging from 3.8 to 7.6 mm. When initial focused beam diameters were larger than matching unfocused diameters (19 of 29 cases), the focused beams peak-to-entrance dose ratios were 13% to 73% larger than UNF. In addition, in 17 of these cases the efficiency of dose delivery to the target was 1.3× to 3.3× larger. Both peak-to-entrance dose ratios and efficiency tended to increase with initial beam diameter, while efficiency also tended to increase with magnet gradient. These experimental results are consistent with our previous Monte Carlo (MC) studies and suggest that a triplet of quadrupole Halbach cylinders could be clinically useful for irradiating small-field radiosurgical targets with fewer beams, lower entrance dose, and shorter treatment times.

A comparative assessment of acute oral toxicity and traditional pharmacological activities between extracts of Fritillaria cirrhosae Bulbus and Fritillaria pallidiflora Bulbus

Ethnopharmacological relevanceFritillariae Bulbus (“Beimu” in Chinese) is a famous traditional Chinese medicine used to treat cough, expectoration and asthma for more than 2000 years, which belongs to the Fritillaria genus in Liliaceae family. Bulbs of Fritillaria cirrhosa D.Don (BFC) and bulbs of Fritillaria pallidiflora Schrenk (BFP) are two important drugs of Beimu. Due to the significant similarities in their outward appearance characters and chemical profiles, BFC has often been adulterated with BFP in Chinese Traditional Medicine markets. Aim of the studyThis study aims to compare the oral acute toxicity and the traditional pharmacological activities including antitussive, expectorant and anti-inflammatory effects between the extract of BFC and BFP, to clear and definite if the BFP can be used as a substitute of the BFC in the application of traditional medicine. Materials and methodsThe extracts were prepared through refluxing with 80% ethanol solvent. For the acute toxicity tests, graded doses of BFP extracts and the maximum dose of BFC extracts were administered orally to mice. The animals were observed for toxic symptoms and mortality daily for 14 days. For the pharmacological activities tests, graded doses of BFP and BFC extracts were administered orally to mice. To observe the effects relieving cough, expelling phlegm and lessening the ear swelling of BFC extracts and BFP extracts through ammonia liquor inducing cough, phenol red apophlegmating in mice and the xylene-induced auricular swelling of mouse, respectively. ResultsIn the acute toxicity study, the LD50 value of BFP in mice was calculated to be 213.57 g/kg body weight, and the maximum feasible dose (MFD) value of BFC in mice was 452.14 g/kg. Histopathological analysis has shown inflammatory cells infiltration and cells edema in liver, multinucleated giant cell proliferation in spleen, perivascular exudate and hemorrhage in lung, glomerulus atrophy in kidney of mice after oral administrations of BFP extracts. But only liver cells edema was observed in BFC group. Both BFC extract and BFP extract significantly increased latent period of cough and inhibited cough frequency in mice induced by ammonia. Besides, the two extracts also obviously enhanced mice's tracheal phenol red output in expectorant assessment and inhibited the development of ear edema in anti-inflammatory evaluation assay. ConclusionTo summarize, the BFP has the significant similarities in morphological characteristics, chemical profiles and traditional pharmacological activities compared with the BFC. The result of this study provide some valid scientific support for using BFP as a plant substitute of the BFC, but considering the toxicity of BFP is much higher than BFC, we don't recommend long-term oral administration of BFP or exceeding recommended dosage of Chinese Pharmacopoeia 2015.

Hydrogel Spacer Reduces Rectal Dose during Proton Therapy for Prostate Cancer: A Dosimetric Analysis.

Proton therapy for prostate cancer may reduce bowel dose and risk of bowel symptoms relative to photon-based methods. Here, we determined the effect of using a biodegradable, injectable hydrogel spacer on rectal dose on plans for treating prostate cancer with intensity-modulated proton therapy (IMPT) or passive scattering proton therapy (PSPT). Pairs of IMPT and PSPT plans for 9 patients were created from fused computed tomography/magnetic resonance imaging scans obtained before and after spacer injection. Calculated values of rectal V40, V60, V70, V80, and maximum dose (Dmax) were compared with Wilcoxon signed rank tests. Displacements at the base (BP), midgland (MP), and apex (AP) of the prostate relative to the anterior rectal wall with the spacer in place were averaged for each patient and correlated with V70 by using linear regression models. The presence of a spacer reduced all dosimetric parameters for both PSPT and IMPT, with the greatest difference in V70, which was 81.1% lower for PSPT-with-spacer than for IMPT-without-spacer. Median displacements at BP, MP, and AP were 12 mm (range 7-19), 2 mm (range 0-4), and 1 mm (range 0-5) without the spacer and 19 mm (range 12-23), 10 mm (range 8-16), and 7 mm (range 2-12) with the spacer. Modest linear trends were noted between rectal V70 and displacement for IMPT-with-spacer and PSPT-with-spacer. When displacement was ≥8 mm, V70 was ≤5.1% for IMPT-with-spacer and PSPT-with-spacer. Use of biodegradable hydrogel spacers for prostate cancer treatment provides a significant reduction of radiation dose to the rectum with proton therapy. Significant reductions in rectal dose occurred in both PSPT and IMPT plans, with the greatest reduction for IMPT-with-spacer relative to PSPT alone. Prospective studies are ongoing to assess the clinical impact of reducing rectal dose with hydrogel spacers.

Dosimetric effectiveness in implants with distinct ho166-seed distributions in a prostate model

Currently, there is a need to produce new therapeutic techniques for the treatment of prostate tumors, considering the high incidence of the disease and significant morbidity rates associated with surgery and radiotherapy. Simulations in brachytherapy produce essential information about the efficiency and dosimetric efficacy compared to other techniques. This study estimated the efficiency of dosimetry by parameters of merit generated from volumetric distributions of absorbed doses simulating two spatial distributions of Ho-166 seeds in a prostate model. A computer voxel model was developed, using the SISCODES (Computational System for Dosimetry by Neutrons and Photons by Stochastic Methods applied to radiology and radiotherapy) code. The virtual model reproduced a cubic box, filled with muscle equivalent tissue (TE), in which a 5-cm diameter sphere with TE-prostate was positioned 2-cm from the air-interface. Two Ho-166 seed distributions were employed with distinct pitches: 9 and 10 mm, with same distance between seed of 8mm in a fillet (needle). The MCNP5 code generated the energy deposited per unit mass in each voxel .The spatial dose distributions were obtained for each of the seed distributions. The following parameters-of-merit were evaluated: maximum dose values and histograms. The parameters were compared between the two simulated groups. It was possible to evaluate the most appropriate distribution to the prostate brachytherapy, which has been shown to be a function of the injected seed activity.

ESTIMATION OF ENTRANCE SURFACE RADIATION DOSE TO THYROID REGION IN COMPUTED TOMOGRAPHY BRAIN EXAMINATION

Objective: The objective of this study was to estimate the entrance surface radiation dose to the thyroid region in a computed tomography (CT) brain scan.Methods: Unfors Multi-O-Meter equipment was used to measure the entrance surface at the thyroid region of adult patients ranging from 18 to 70 years of age. A total of 115 patients were included in the study based on convenience sampling. The Multi-O-Meter was kept at the thyroid region during the scan, and the values for entrance surface dose (ESD) were noted from its monitor after the scan was complete.Results: The obtained data were analyzed and violate normal distribution; therefore, the median and quartiles were computed. The overall median (Q1, Q2), ESD of the patients, was 1.335 (1.213, 1.529) mGy. The minimum and maximum dose values recorded were 1.015 mGy and 1.964 mGy, respectively.Conclusions: The result showed a significant amount of entrance surface radiation dose to the thyroid region while taking a brain scan. This data can be used for optimization of radiation protection while undergoing CT scans of brain to reduce exposure to thyroid region.

ESTIMATION OF ENTRANCE SURFACE RADIATION DOSE TO THYROID REGION IN COMPUTED TOMOGRAPHY BRAIN EXAMINATION

Objective: The objective of this study was to estimate the entrance surface radiation dose to the thyroid region in a computed tomography (CT) brain scan.Methods: Unfors Multi-O-Meter equipment was used to measure the entrance surface at the thyroid region of adult patients ranging from 18 to 70 years of age. A total of 115 patients were included in the study based on convenience sampling. The Multi-O-Meter was kept at the thyroid region during the scan, and the values for entrance surface dose (ESD) were noted from its monitor after the scan was complete.Results: The obtained data were analyzed and violate normal distribution; therefore, the median and quartiles were computed. The overall median (Q1, Q2), ESD of the patients, was 1.335 (1.213, 1.529) mGy. The minimum and maximum dose values recorded were 1.015 mGy and 1.964 mGy, respectively.Conclusions: The result showed a significant amount of entrance surface radiation dose to the thyroid region while taking a brain scan. This data can be used for optimization of radiation protection while undergoing CT scans of brain to reduce exposure to thyroid region.

303: Effect of oxytocin maximum dose and duration of exposure on postpartum hemorrhage following vaginal delivery

Recent data suggest rising rates of postpartum hemorrhage (PPH) secondary to uterine atony in developed countries. Oxytocin (OT) use is associated with increased rates of PPH as a result of uterine atony. We sought to determine the effect of prolonged use or high doses of OT on risk of PPH and transfusion. This was a secondary analysis of a prospective cohort study of all women who had a vaginal delivery of a singleton gestation at ≥37 weeks gestation within a single institution from 2010-2014. Women with a prior cesarean delivery and with multiple gestations were excluded. The cohort was stratified by duration of OT exposure < or ≥15 hours from initiation to delivery (≥15 hours OT duration represented the 90th percentile) and by maximum dose of OT (<20mU/min vs ≥20mU/min). The primary outcomes were rates of PPH (estimated blood loss >500cc), severe PPH (estimated blood loss >1000cc), and need for blood transfusion. Multivariable logistic regression was used to account for confounders, including prolonged labor duration, obesity and nulliparity. Receiver operating characteristic (ROC) curves were used to examine the predictive value of OT duration and maximum dose on PPH. Among 4,202 patients, maximum OT dose ≥20mU/min or OT exposure ≥15hrs was associated with an increased risk of PPH (aOR 2.48, 95%CI 1.72-3.59 and aOR 2.10, 95%CI 1.34-3.29, respectively; Table 1). OT ≥15hrs was also associated with an increased risk of blood transfusion (aOR 2.62, 95%CI 1.08-6.34; Table 1). Although OT duration and maximum dose were modest predictors of PPH at best, OT duration was a better predictor of PPH than maximum OT dose (AUC 0.70 vs 0.66, p = 0.02; Graph 1). In the stratified analysis by low or high dose OT, OT exposure >15 hours was associated with PPH, severe PPH and need for blood transfusion only among women exposed to low dose OT (<20mU/min) but not among women exposed to high dose OT. Prolonged OT exposure during labor is associated with increased rates of PPH and transfusion following a vaginal delivery. This trend remains after controlling for prolonged labor duration and is strongest among women receiving lower doses of OT. This suggests that long exposure to low doses of OT may be an important factor to consider in active labor management as it may predict or contribute to PPH.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Green synthesis of silver nanoparticles from medicinal plants and evaluation of their antiviral potential against chikungunya virus.

The exploration of nanoscale materials for their therapeutic potential against emerging and re-emerging infections has been increased in recent years. Silver nanoparticles (AgNPs) are known to possess antimicrobial activities against different pathogens including viruses and provide an excellent opportunity to develop new antivirals. The present study focused on biological synthesis of AgNPs from Andrographis paniculata, Phyllanthus niruri, and Tinospora cordifolia and evaluation of their antiviral properties against chikungunya virus. Synthesized plants AgNPs were characterized to assess their formation, morphology, and stability. The cytotoxicity assays in Vero cells revealed that A. paniculata AgNPs were most cytotoxic with maximum non-toxic dose (MNTD) value of 31.25μg/mL followed by P. niruri (MNTD, 125μg/mL) and T. cordifolia AgNPs (MNTD, 250μg/mL). In vitro antiviral assay of AgNPs based on degree of inhibition of cytopathic effect (CPE) showed that A. paniculata AgNPs were most effective, followed by T. cordifolia and P. niruri AgNPs. The results of antiviral assay were confirmed by cell viability test using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) dye, which revealed that A. paniculata AgNPs inhibited the virus to a maximum extent. The cell viability of CHIKV-infected cells significantly increased from 25.69% to 80.76 and 66.8%, when treated with A. paniculata AgNPs at MNTD and ½MNTD, respectively. These results indicated that use of plants AgNPs as antiviral agents is feasible and could provide alternative treatment options against viral diseases which have no specific antiviral or vaccines available yet.

Dosimetric Evaluation of The Field-In-Field Technique For Large Breast Cancer Irradiation.

The aim of this work is using multi-segmented conformal radiotherapy, field in field (FIF) for large breast cancer treatment, the dose coverage of the planning target volume (PTV) and evaluation the radiation load on the organs at risk (OARs). Ten patients with large breast of mean PTV was 1489 ± 335 Cm3 were included. Many parameters used in the dose evaluations in the planning target volume (PTV) and the organs at risk (OARs) volume including ipsi lateral lung, heart, and the contralateral breast, Dose homogeneity index (DHI) and conformity index (PITV). The FIF technique for all patients improved the homogeneity and conformity of the PTV, where the mean values of maximum dose of the PTV was 107%, the volumes over the prescription dose in irradiated volumes received very low doses. For each dosimetry of the organs at risk, the FIF technique reduced the dose received to theses organs. In conclude the FIF technique provided better dose distribution in the PTV and reduced the doses in the OARs and improving homogeneity and conformity of the planning volume.

P224] Analytical anisotropic algorithm vs Acuros algorithm comparison

Purpose The aim of this work is to compare Acuros and Analytical Anisotropic Algorithm (AAA), focussing on tissue interfaces. Methods 20 head and neck pathology treatment plans were calculated with both algorithms. Density heterogeneities and air tissue interfaces in the lungs and oral cavity have been analysed. Radiotherapy Treatment Planning System (TPS) Eclipse version 13.7 was used. The grid size set was 0.25 cm. Dose matrix were exported from the RTP and compared with gamma 3D evaluation method with different distance and dose parameters using the software VeriSoft version 5.1. For every treatment plan gamma 3D analysis was performed in two dose planes (head and lung) to check dose differences. Values under 20% of the maximum dose are excluded of the comparison. Γ(3/1) and Γ(1/3) were also performed to evaluate dependence on dose and distance. Results The Γ(2/2) in 80% of cases between both dose distribution was higher than 95%. Γ(3/3) was higher than 100% for all the cases tested in the case of the head. For the case of the lung, 90% of cases Γ(2/2) between both dose distribution was higher than 95%. Γ(3/3) was higher than 100% for all the cases tested. Γ(3/1) vs. Γ(1/3) averages were 91.3% vs. 77% for head and 91.8% vs. 56.4% for lung. Conclusions Dose difference is much more dependent on the distance of the points under the Γ criteria than on the dose. Main differences are obtained at the skin, dose calculated with the Acuros algorithm is higher than the values with AAA algorithm, nevertheless maximum dose values are higher when the AAA algorithm is used. No significant dose difference has been observed in lungs.

P251] Dosimetric impact of intermediate dose calculation on heterogeneous region radiotherapy planning

Purpose In radiotherapy planning of heterogeneous regions, differences which negatively affect the quality of the plan in terms of homogeneity and conformity may occur between the optimal dose volume histogram (DVH) and the final calculated DVH. The intermediate dose calculation (IDC) module, which is included in the Analytical Anisotropic Algorithm (AAA), is used even though the planning period is slightly increased in radiotherapy plans of lung tumors with low tissue density to reduce these differences. The purpose of this study is to examine the impact of IDC on radiotherapy planning for the heterogeneous maxillary sinus region. Methods In this study, the homogeneity index (HI) and the conformity index (CI) of the intensity modulated radiotherapy plans prepared using Eclipse-TPS and AAA v8.9 of 12 patients with maxillary sinus cancer were calculated. The original plans were re-optimized with the same optimization criteria by using AAA v15.1 with and without IDC. HI and CI values of the new plans were calculated after re-optimization. The HI and CI values, maximum doses and the critical organ doses were compared between the original and new plans. Results AAA v15.1 with IDC increased the plan quality in terms of HI, CI and maximum dose values. The HI values (ideal value=0) were found to be 0.093, 0.090 and 0.067; the CI values (ideal value=1) were found to be 1.149, 1.142 and 1.055; the maximum doses were found to be 108.1%, 107.8% and 105.3% for AAA v8.9, AAA v15.1 without IDC and AAA v15.1 with IDC, respectively. The differences between AAA v15.1 with IDC and the others are statistically significant for HI values, CI values and maximum doses but there is no significant difference for the doses received by critical organs. Conclusions The use of the IDC increases the quality of intensity modulated radiotherapy plans in heterogeneous regions such as head and neck. This work was supported by Scientific Research Projects Coordination Unit of Istanbul University (Project Number: I.U.BAP-23057)

OA097] Comparison between skin dose values of a software tool and gafchromic films using test fields and clinical cases

Purpose To validate the tool for calculation of skin dose absorbed by patients during interventional radiology procedures, which is available in the radiation dose tracking software NEXO[DOSE]® provided by Bracco, Italy. Methods In NEXO[DOSE], the distribution of skin dose and the peak skin dose (PSD), that is the maximum cumulative dose value resulting from interventional radiology procedures, are displayed and calculated on the surface of a mathematical torso phantom. To determine these quantities, the software uses exposure parameters from Radiation Dose Structured Report and additional information specific of the angiography (table and mattress attenuation, KAP correction factor and tube position relative to the table). To test the accuracy of the algorithm, we irradiated GAFCHROMIC XR-RV3 films wrapped on a cylindrical PMMA phantom with different square fields using two Philips Integris Allura FD20 angiography and a Siemens Artis Zeego. Absolute dose values and geometric accuracy of the phantom dose map calculated by NEXO[DOSE]® were compared with the film. The tool was also clinically tested during high doses interventional procedures by placing a film on the patient’s back, at the beam entrance side. Results In the tested devices, the spatial distribution of the dose estimated by NEXO[DOSE]® was within 10% of the film one. For the dosimetric values, the cumulative dose was in good agreement for high dose fields ( Conclusion NEXO[DOSE]® provides a good estimate of skin dose distribution and PSD. This tool can be useful for the patient follow-up.

Variations in dosimetric distribution and plan complexity with collimator angles in hypofractionated volumetric arc radiotherapy for treating prostate cancer.

PurposeHypofractionated radiotherapy can reduce treatment durations and produce effects identical to those of conventionally fractionated radiotherapy for treating prostate cancer. Volumetric arc radiotherapy (VMAT) can decrease the treatment machine monitor units (MUs). Previous studies have shown that VMAT with multileaf collimator (MLC) rotation exhibits better target dose distribution. Thus, VMAT with MLC rotation warrants further investigation.Methods and materialsTen patients with prostate cancer were included in this study. The prostate gland and seminal vesicle received 68.75 and 55 Gy, respectively, in 25 fractions. A dual‐arc VMAT plan with a collimator angle of 0° was generated and the same constraints were used to reoptimize VMAT plans with different collimator angles. The conformity index (CI), homogeneity index (HI), gradient index (GI), normalized dose contrast (NDC), MU, and modulation complexity score (MCSV) of the target were analyzed. The dose–volume histogram of the adjacent organs was analyzed. A Wilcoxon signed‐rank test was used to compare different collimator angles.ResultsOptimum values of CI, HI, and MCSV were obtained with a collimator angle of 45°. The optimum values of GI, and NDC were observed with a collimator angle of 0°. In the rectum, the highest values of maximum dose and volume receiving 60 Gy (V60 Gy) were obtained with a collimator angle of 0°, and the lowest value of mean dose (Dmean) was obtained with a collimator angle of 45°. In the bladder, high values of Dmean were obtained with collimator angles of 75° and 90°. In the rectum and bladder, the values of V60 Gy obtained with the other tested angles were not significantly higher than those obtained with an angle of 0°.ConclusionThis study found that MLC rotation affects VMAT plan complexity and dosimetric distribution. A collimator angle of 45° exhibited the optimal values of CI, HI, and MCSv among all the tested collimator angles. Late side effects of the rectum and bladder are associated with high‐dose volumes by previous studies. MLC rotation did not have statistically significantly higher values of V60 Gy in the rectum and bladder than did the 0° angle. We thought a collimator angle of 45° was an optimal angle for the prostate VMAT treatment plan. The findings can serve as a guide for collimator angle selection in prostate hypofractionated VMAT planning.

Comparison of Different Algorithms in the Radiotherapy Plans of Breast Cancer

It is aimed to evaluate portal dosimetry results of planned breast cancer patients with intensity-modulated radiotherapy (YART) of Anisotropic Analytical Algorithm (AAA) and Pencil Beam Convolution (PBC) dose calculation algorithms. The plans of 10 treated patients will receive 6 MV photon energy and a total of 25 fractions of 50 Gray dose using the inverse YART technique, which is reverse planned in the Eclipse (ver.13.6) treatment planning system with Varian Trilogy Linear Accelerator prescribing. For each plan, dose was calculated after optimization using PBC and then AAA algorithms. The quality controls of the plans were made using the Electronic Portal Imaging Device (EPID) by creating individual verification plans for each algorithm. In addition, the maximum and average dose values in the target volume were compared in inverse YART plans calculated using PBC and AAA. When treatment plans generated by AAA and PBC dose calculation algorithms are analyzed using EPID, for the PBC algorithm, the mean values of VArea and VAvg are 98.15 ± 1.07, 0.40 ± 0.048 and 98.72 ± 1.13, 0.37 ± 0.051, respectively, for the AAA algorithm. The PTV Dmax value for the PBC algorithm is 109.3 ± 1.09 and the DAvg value is 101.7 ± 0.51. For the AAA algorithm, the PTV Dmax value is 110.6 ± 1.12 and the DAvg value is 102.9 ± 0.62. When the mean values of portal dosimetry VArea and VAvg evaluated using PBC and AAA algorithms were compared, the differences between the algorithms were not statistically significant (p&gt; 0.05). Differences between the algorithms for PTV Dmax and DAvg values are not statistically significant (p&gt; 0.05).

Fetal dose estimation in a case of unintended pregnancy during brain radiotherapy

Introduction Pregnancy during radiotherapy is not a common clinical situation. We describe a fetal dose estimation necessary before starting a course of radiotherapy for a brain tumor in a patient unexpectedly pregnant at the time scheduled for the beginning of treatment. Purpose To estimated the dose to the fetus during the programmed course of radiotherapy before deciding if the patient should advance with the treatment or not. Materials and methods The initial plan was optimized to avoid fetus exposure to radiation without compromising dose to the target volume. We considered the real patient distances between plan isocenter and 3 critical points: uterus fundus, umbilical and pubis. Using an anthropomorphic phantom and solid water slabs we positioned an ionizing chamber at different depths, corresponding to these points, and determined the estimated doses for the complete course of radiotherapy. Results The maximum dose value measured was 2,5 cGy, well below the 10 cGy reported tolerance value. After explaining the situation to the patient and the risks involved, a decision was taken to go on with the treatment as planned. A set of 3 pairs of TLD dosimeters was used over the patient belly, in these same positions during every treatment fraction. The TLDs readings at the end confirmed the estimated values measured in the phantom. Conclusion The previous evaluation of the estimated dose to the fetus allowed the patient to successfully complete the radiotherapy course. The pregnancy went on normally and the patient delivered a healthy child. Disclosure The authors have nothing to disclose.

SU-F-T-601: Equivalence of CyberKnife and TrueBeam STx for Spine Irradiation

Purpose: To evaluate the equivalence of spine SBRT treatment plans created in Eclipse for the TrueBeam STx (Varian Medical System, Palo Alto, CA) compared to plans using CyberKnife and MultiPlan (Accuray, Sunnyvale, CA). Methods: CT data and contours for 23 spine SBRT patients previously treated using CyberKnife (CK) were exported from MultiPlan treatment planning system into Eclipse where they were planned using static IMRT 6MV coplanar beams. Plans were created according to the original prescription dose and fractionation schedule while limiting spinal dose according to the RTOG 0631 protocol and maintaining target coverage comparable to the original CK plans. Plans were evaluated using new conformity index (nCI), homogeneity index (HI), dose-volume histogram data, number of MU, and estimated treatment time. To ensure all Eclipse plans were deliverable, standard clinical IMRT QA was performed. The plan results were matched with their complimentary CK plans for paired statistical analysis. Results: Plans generated in Eclipse demonstrated statistically significant (p<0.01) improvements compared to complimentary CK plans in median values of maximum spinal cord dose (17.39 vs. 18.12 Gy), RTOG spinal cord constraint dose (14.50 vs. 16.93 Gy), nCI (1.28 vs. 1.54), HI (1.13 vs. 1.27), MU (3918 vs. 36416), and estimated treatment time (8 vs. 48 min). All Eclipse generated plans passed our clinically used protocols for IMRT QA. Conclusion: CK spine SBRT replanned utilizing Eclipse for LINAC delivery demonstrated dosimetric advantages. We propose improvements in plan quality metrics reviewed in this study may be attributed to dynamic MLCs that facilitate treatment of complicated geometries as well as posterior beams ideal for centrally located and/or posterior targets afforded by gantry-based RT delivery.

SU‐G‐TeP3‐08: Pre‐Clinical Radionuclide Therapy Dosimetry in Several Pediatric Cancer Xenografts

Purpose:The focus of this work is to perform Monte Carlo‐based dosimetry for several pediatric cancer xenografts in mice treated with a novel radiopharmaceutical 131I‐CLR1404.Methods:Four mice for each tumor cell line were injected with 8–13 µCi/g of the 124124I‐CLR1404. PET/CT images of each individual mouse were acquired at 5–6 time points over the span of 96–170 hours post‐injection. Following acquisition, the images were co‐registered, resampled, rescaled, corrected for partial volume effects (PVE), and masked. For this work the pre‐treatment PET images of 124I‐CLR1404 were used to predict therapeutic doses from 131I‐CLR1404 at each time point by assuming the same injection activity and accounting for the difference in physical decay rates. Tumors and normal tissues were manually contoured using anatomical and functional images. The CT and the PET images were used in the Geant4 (v9.6) Monte Carlo simulation to define the geometry and source distribution, respectively. The total cumulated absorbed dose was calculated by numerically integrating the dose‐rate at each time point over all time on a voxel‐by‐voxel basis.Results:Spatial distributions of the absorbed dose rates and dose volume histograms as well as mean, minimum, maximum, and total dose values for each ROI were generated for each time point.Conclusion:This work demonstrates how mouse‐specific MC‐based dosimetry could potentially provide more accurate characterization of efficacy of novel radiopharmaceuticals in radionuclide therapy.This work is partially funded by NIH grant CA198392.

SU‐F‐T‐452: Influence of Dose Calculation Algorithm and Heterogeneity Correction On Risk Categorization of Patients with Cardiac Implanted Electronic Devices Undergoing Radiotherapy

Purpose:There is a lack of studies with significant cohort data about patients using pacemaker (PM), implanted cardioverter defibrillator (ICD) or cardiac resynchronization therapy (CRT) device undergoing radiotherapy. There is no literature comparing the cumulative doses delivered to those cardiac implanted electronic devices (CIED) calculated by different algorithms neither studies comparing doses with heterogeneity correction or not. The aim of this study was to evaluate the influence of the algorithms Pencil Beam Convolution (PBC), Analytical Anisotropic Algorithm (AAA) and Acuros XB (AXB) as well as heterogeneity correction on risk categorization of patients.Methods:A retrospective analysis of 19 3DCRT or IMRT plans of 17 patients was conducted, calculating the dose delivered to CIED using three different calculation algorithms. Doses were evaluated with and without heterogeneity correction for comparison. Risk categorization of the patients was based on their CIED dependency and cumulative dose in the devices.Results:Total estimated doses at CIED calculated by AAA or AXB were higher than those calculated by PBC in 56% of the cases. In average, the doses at CIED calculated by AAA and AXB were higher than those calculated by PBC (29% and 4% higher, respectively). The maximum difference of doses calculated by each algorithm was about 1 Gy, either using heterogeneity correction or not. Values of maximum dose calculated with heterogeneity correction showed that dose at CIED was at least equal or higher in 84% of the cases with PBC, 77% with AAA and 67% with AXB than dose obtained with no heterogeneity correction.Conclusion:The dose calculation algorithm and heterogeneity correction did not change the risk categorization. Since higher estimated doses delivered to CIED do not compromise treatment precautions to be taken, it's recommend that the most sophisticated algorithm available should be used to predict dose at the CIED using heterogeneity correction.