Dose Calculation Method Research Articles

Method and software for photon dose calculation in phantoms of human body

The current study is focused on the development of the method of the calculation of the dose quantities required for the assessment or limitation of the ionizing exposure (mean organ doses, effective dose, distribution of the absorbed dose in the critical organ) based on the measured characteristics of the fields of the photon computational (kerma free-in-air, readings of the individual dosimeters) with the energy of 0,02-10 mEv. The dedicated software was developed based on the results of the study, allowing estimating the values of more than 20 mean organ doses, effective dose and the distribution of the absorbed dose in the red bone marrow in 8 computational children and adult models. Additionally, it is possible to calculate the ratios of the effective dose to the readings of the “individual dosimeters”, placed in 48fixed points on the phantom surface. The developed method and software can be used for: (1) calculation of the doses from external exposure and estimation of the level of the radiation injuries in case of the acute radiation exposure of the staff and public; (2) development of the models of the exposure of the staff working in the radiation fields with non-uniform distribution of their characteristics; (3)planning of the countermeasures for the remediation of the consequences of the radioactive contamination (calculation of the routes and working time in contaminated zones); (4) education and training of the staff participating in the investigation and remediation of the consequences of the radioactive contamination.

Use of busulfan in conditioning for allogeneic hematopoietic stem cell transplantation in adults: a survey by the Transplant Complications Working Party of the EBMT.

A survey was carried out among EBMT centers about the use of busulfan for conditioning in allogeneic stem cell transplantation. Of 109 responding centers, 106 used busulfan for conditioning, 102 in conventional myeloablative doses, and 93 in reduced doses (RIC). The route of administration was mostly intravenous, but ~10% of the centers gave the drug orally. The number of doses in i.v. administration varied and was in myeloablative conditioning mostly one (50 centers) or four (43 centers) doses a day. Seventeen of the 106 centers used pharmacokinetics for dose adjustment in myeloablative conditioning, nine in RIC. The details of pharmacokinetic monitoring varied markedly. Three quarters of the centers reported adjusting the dose based on obesity in myeloablative conditioning and about 60% in RIC. The most common method for dose calculation was ideal body weight + 0.25 × (actual body weight - ideal body weight). In conclusion, the present survey showed marked heterogeneity in the current practices of busulfan administration for conditioning. The impact of the heterogeneity is not well known. Due to this and the scarcity of support from controlled clinical studies, no clear guidelines can be presented, but some prevailing policies to be recommended were identified.

Comparison of two dose calculation methods of intra-arterial carboplatin in the treatment of recurrent glioblastoma multiforme.

e13503 Background: Glioblastoma is a deadly brain cancer, and as part of the natural evolution, its relapses will mostly occur 32 to 36 weeks after the initial diagnosis. The standard of care for recurrent glioblastomas is not well defined and multiple options exist. Intra-arterial chemotherapy as one option is currently practiced at the Centre hospitalier universitaire de Sherbrooke, the only center doing this procedure in Canada. The aim of this study is to evaluate the impact of using the area under the curve (AUC) or body surface area (BSA) dosing formula to guide intra-arterial carboplatin administration. It was designed to explore the relation of two dose calculation methods on efficacy and toxicity, determined by progression-free survival (PFS) and hematologic toxicity, respectively. Methods: A retrospective observational study was conducted, which includes adult in-patients who received intra-arterial carboplatin for recurrent glioblastoma from June 1st, 2000 to December 31st, 2017. It examined the associations of the method used to calculate the doses, in mg or mg/mL x min-1, with clinical outcomes. Results: One hundred ninety patients were included in the analysis. For the primary endpoint, an exposure greater than 6 of AUC was found potentially harmful in terms of efficacy compared to AUC under 6 (HR 0.529, p = 0.0044). In terms of toxicity, a higher AUC is highlighted to correlate with a slightly higher incidence of thrombocytopenia and neutropenia (OR 1.051 p = 0.0271; OR 1.072 p = 0.049). No significant association between toxicity and dose calculated with BSA could be established. Conclusions: AUC greater than 6 is detrimental in terms of effectiveness according to progression free survival. Moreover, AUC could be used to predict neutropenia and thrombocytopenia. However no significant predictions were found using BSA method. We recommend the use of AUC method in intra-arterial carboplatin instead of BSA method since the latter was not statistically related to toxicity. A prospective trial comparing the two dosage methods would be needed.

Characterization of Extrafocal Dose Influence on the Out-of-Field Dose Distribution by Monte Carlo Simulations and Dose Measurements.

Out-of-field scattered and transmitted extrafocal radiation may induce secondary cancer in long-term survivors of external radiotherapy. Pediatric patients have higher life expectancy and tend to receive higher secondary radiation damage due to geometric and biological factors. The goal of this study is to characterize the location and the magnitude of extrafocal dose regions in the case of three-dimensional conformal radiotherapy and volumetric arc therapy, to apply this information to clinical treatment cases, and to provide mitigation strategies. Extrafocal dose has been investigated in a Varian TrueBeam linac equipped with a high-definition 120 multileaf collimator using different physical and virtual phantoms, dose calculation (including Monte Carlo techniques), and dose measurement methods. All Monte Carlo calculations showed excellent agreement with measurements. Treatment planning system calculations failed to provide reliable results out of the treatment field. Both Monte Carlo calculations and dose measurements showed regions with higher dose (extrafocal dose areas) when compared to the background. These areas start to be noticeable beyond 11 cm from the isocenter in the direction perpendicular to the multileaf collimator leaves' travel direction. Out-of-field extrafocal doses up to 160% of the mean dose transmitted through the closed multileaf collimator were registered. Two overlapping components were observed in the extrafocal distribution: the first is an almost elliptical blurred dose distribution, and the second is a well-defined rectangular dose distribution. Extra precautions should be taken into consideration when treating pediatric patients with a high-definition 120 multileaf collimator to avoid directing the extrafocal radiation into a radiosensitive organ during external beam therapy.

Photon and electron backscatter dose and energy spectrum analysis around Lipiodol using flattened and unflattened beams.

PurposeThe aim of the current study was to evaluate the backscatter dose and energy spectrum from the Lipiodol with flattening filter (FF) and flattening filter‐free (FFF) beams. Moreover, the backscatter range, that was defined as the backscatter distance (BD) are revealed.Methods6 MVX FF and FFF beams were delivered by TrueBeam. Two dose calculation methods with Monte Carlo calculation were used with a virtual phantom in which the Lipiodol (3 × 3 × 3 cm3) was located at a depth of 5.0 cm in a water‐equivalent phantom (20 × 20 × 20 cm3). The first dose calculation was an analysis of the dose and energy spectrum with the complete scattering of photons and electrons, and the other was a specified dose analysis only with scattering from a specified region. The specified dose analysis was divided into a scattering of primary photons and a scattering of electrons.ResultsThe lower‐energy photons contributed to the backscatter, while the high‐energy photons contributed the difference of the backscatter dose between the FF and FFF beams. Although the difference in the dose from the scattered electrons between the FF and FFF beams was within 1%, the difference of the dose from the scattered photons between the FF and FFF beams was 5.4% at a depth of 4.98 cm.ConclusionsThe backscatter range from the Lipiodol was within 3 mm and depended on the Compton scatter from the primary photons. The backscatter dose from the Lipiodol can be useful in clinical applications in cases where the backscatter region is located within a tumor.

An evaluation of techniques for dose calculation on cone beam computed tomography.

To assess the accuracy and efficiency of four different techniques, thus determining the optimum method for recalculating dose on cone beam CT (CBCT) images acquired during radiotherapy treatments. Four established techniques were investigated and their accuracy assessed via dose calculations: (1) applying a standard planning CT (pCT) calibration curve, (2) applying a CBCT site-specific calibration curve, (3) performing a density override and (4) using deformable registration. Each technique was applied to 15 patients receiving volumetric modulated arc therapy to one of three treatment sites, head and neck, lung and prostate. Differences between pCT and CBCT recalculations were determined with dose volume histogram metrics and 2.0%/0.1 mm gamma analysis using the pCT dose distribution as a reference. Dose volume histogram analysis indicated that all techniques yielded differences from expected results between 0.0 and 2.3% for both target volumes and organs at risk. With volumetric gamma analysis, the dose recalculation on deformed images yielded the highest pass-rates. The median pass-rate ranges at 50% threshold were 99.6-99.9%, 94.6-96.0%, and 94.8.0-96.0% for prostate, head and neck and lung patients, respectively. Deformable registration, HU override and site-specific calibration curves were all identified as dosimetrically accurate and efficient methods for dose calculation on CBCT images. With the increasing adoption of CBCT, this study provides clinical radiotherapy departments with invaluable information regarding the comparison of dose reconstruction methods, enabling a more accurate representation of a patient's treatment. It can also integrate studies in which CBCT is used in image-guided radiation therapy and for adaptive radiotherapy planning processes.

Absorbed Dose Calculation In Irregular Blocked Radiation Fields: Evaluation of Clarkson’s Sector Integration Method for Radiation Fields Commonly Used in Conventional Radiotherapy

Introduction: Irregular/blocked fields are routinely used in radiotherapy. The doses of these fields are usually calculated by means of equivalent square method that is inherently prone to uncertainty. On the other hand, Clarkson’s sector integration method is a dose calculation method which offers far better accuracy in dose calculation of irregular fields. The Scatter Air Ratio (SAR) of an individual sector, in which whole field has been divided, is calculated and averaged over all sectors to find total SAR for the whole field. Percentage depth dose (PDD) and tissue-maximum ratio (TMR) for irregularly shaped beams can be calculated by the SAR values using the standard relationships of these measurement quantities. Material and Methods: The present study was conducted on 40 actual patient treatment fields. The PDD values for depths up to 15 cm were calculated using both Clarkson’s sector integration method and conventional methods, and their results were compared with the measured PDDs for all patients. Results: Maximum deviation for Clarkson’s calculation was under 2.7% for any field size, shape, and depth. However for conventional methods, this value exceeded ±5.5% for some field shapes, specifically at larger depths. Conclusion: Better results of sector integration are more prominent for field shapes with a large field size and a shielded area of regular shape. For the treatment fields with a very large degree of approximation for assessing reduced field size, Clarkson’s method is the most accurate technique for the calculation of absorbed dose.

The comparison between 6 MV Primus LINAC simulation output using EGSnrc and commissioning data

Introduction: Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy. The purpose of this research is comparison between 6 MV Primus LINAC simulation output with commissioning data using EGSnrc and build a Monte Carlo geometry of 6 MV Primus LINAC as realistically as possible. The BEAMnrc and DOSXYZnrc (EGSnrc package) Monte Carlo model of the LINAC head was used as a benchmark. Materials and Methods In the first part, the BEAMnrc was used for the designing of the LINAC treatment head. In the second part, dose calculation and for the design of 3D dose file were produced by DOSXYZnrc. The simulated PDD and beam profile obtained were compared with that calculated using commissioning data. Good agreement was found between calculated PDD (1·1%) and beam profile using Monte Carlo simulation and commissioning data. After validation, TPR20,10, TMR and Sp values were calculated in five different field. Results Good agreement was found between calculated values by using Monte Carlo simulation and commissioning data. Average differences for five field sizes in this approach is about 0·83% for Sp. For TPR20,10 differences for field sizes 10 × 10 cm2 is 0·29% and for TMR in five field sizes, the average value is ~ 1·6%. Conclusion: In conclusion, the BEAMnrc and DOSXYZnrc codes package have very good accuracy in calculating dose distribution for 6 MV photon beam and it can be considered as a promising method for patient dose calculations and also the Monte Carlo model of primus linear accelerator built in this study can be used as method to calculate the dose distribution for cancer patients.

Determination of internal absorbed dose from radiation of111In-Rituximab in body

Introduction: There are many ways to treat cancer and pain relief. One of the methods is radiopharmaceutical therapy. Indium 111-rituximab contains the radioisotope indium-111 and rituximab. The Indium-111, after decay, emits gamma rays with energies of 245 KeV and 171 KeV, and beta-radiation of 26 KeV. In this study, the absorbed dose of 111In-Rituximab in human body was calculated using mice data and MCNPX simulation code for the organs of heart, lung, liver, spleen, kidney, stomach, intestine and pancreas. Materials and Methods: Male phantom was used for this simulation. The source and target organs were defined in code and absorbed dose obtained for per particle with error of 5 percent. The source organs were determined as volume source in SDEF card of MCNP code. Simulations were done in two steps for gamma and beta sources and the final absorbed dose of each organ were multiplied by the amount of cumulated activity of 1MBq. Results: The results showed that the absorbed dose due to injection of 111In-Rituximab for organs of spleen and stomach are 2.2252E-02, 5.5979E-03 respectively. so these organs are at risk in treating cancer with this radionuclide. The errors for were less than 5 percent. Conclusion: Monte Carlo method and MCNPX simulation code are important methods for calculation of the absorbed dose after the distribution of rradionuclides in the body. Also the results show that two organs spleen and stomach are at risk in Indium 111-rituximab therapy.

Surface scanning for 3D dose calculation in intraoperative electron radiation therapy

BackgroundDose calculations in intraoperative electron radiation therapy (IOERT) rely on the conventional assumption of water-equivalent tissues at the applicator end, which defines a flat irradiation surface. However, the shape of the irradiation surface modifies the dose distribution. Our study explores, for the first time, the use of surface scanning methods for three-dimensional dose calculation of IOERT.MethodsTwo different three-dimensional scanning technologies were evaluated in a simulated IOERT scenario: a tracked conoscopic holography sensor (ConoProbe) and a structured-light three-dimensional scanner (Artec). Dose distributions obtained from computed tomography studies of the surgical field (gold standard) were compared with those calculated under the conventional assumption or from pseudo-computed tomography studies based on surfaces.ResultsIn the simulated IOERT scenario, the conventional assumption led to an average gamma pass rate of 39.9% for dose values greater than 10% (two configurations, with and without blood in the surgical field). Results improved when considering surfaces in the dose calculation (88.5% for ConoProbe and 92.9% for Artec).ConclusionsMore accurate three-dimensional dose distributions were obtained when considering surfaces in the dose calculation of the simulated surgical field. The structured-light three-dimensional scanner provided the best results in terms of dose distributions. The findings obtained in this specific experimental setup warrant further research on surface scanning in the IOERT context owing to the clinical interest of improving the documentation of the actual IOERT scenario.

87. Lesion dosimetry in metastatic thyroid cancer treated with 131I: Method and preliminary results

Purpose 131I treatment of metastatic thyroid cancer should take into account doses to metastasis for an optimized approach as highlighted by EU 2013/59 Directive. A SPECT-TC dose calculation method is proposed and verified to standardize the operating protocol; patients’ preliminary results are shown. Methods SPECT-TC was calibrated with a phantom (spheres 11.5, 5.6, 1.1 ml, cylinder 130 ml) filled with liquid 131I (13 MBq/ml). Acquisition (64views, circular-orbit, 256 × 256, Iterative SCAC) on successive days allowed partial volume effects, dead-time and detector radius (25 ÷ 33 cm) corrections to calculate the dose, whose accuracy was verified. For 8 patients after the therapeutic administration and for 2 patients also in pre-therapy phase 4 SPECT-TC (4 ÷ 6, 24, 48, 96 ÷ 144 h) were performed to calculate the dose to 30 lesions (24 bone,7 lymph node,6 pulmonary) with the MIRD spheres model. Results Calibration factors (cylinder 1.4 kcts/MBq) confirmed partial volume effects (130 ml:100%, 11 ml:75%, 5.5 ml:58%, 1.1 ml:6%) and radius dependence ( ∼ 10%). Dead-time strongly influences counts in early acquisition (up to 17 %). Mean accuracy on activity −15% [−9% ÷ −24%] and dose −13 % [−9% ÷ −18%] for volumes larger than 2.5 cc validates the dosimetric method, according to literature (MIRD24). Dose to lesions per activity unit varies among patients (mean ± 1dev.st 26 ± 38, range 0.1 ÷ 189 Gy/GBq) and within the same patient (up to +583 %) and uptake seems to decrease in following treatments: individualized dosimetry is needed. CT-based method is recommended for VOIs segmentation (mean – 4.9% compared to the isocontour threshold one). In-therapy dose values show high differences (up to −126%) compared to pre-therapy results, whose efficacy must be further investigated with more patients also in terms of optimal activity to be administered to simulate the treatment. Conclusions Lesion dosimetry of metastatic thyroid cancer treated with radioiodine is accurate with SPECT-TC and provides to the physician a fundamental tool to optimize the treatment. Download : Download high-res image (119KB) Download : Download full-size image Download : Download high-res image (118KB) Download : Download full-size image

Optimization of Clarkson's Method for Calculating Absorbed Dose under Compensator Filters used in Intensity-modulated Radiation Therapy.

Background: Intensity Modulated Radiation Therapy (IMRT) is extensively used in the treatment of malignancies. Clarkson’s method is one of the leading methods for dose calculation at open points present in irregular fields.Objective: The aim of this study is to generalize the Clarkson’s method for dose calculation at points under compensator filters in IMRT method and its application in IMRT quality control as well.Material and Methods: In this experimental study, compensator filters were designed in two forms: flat filter and block piled-up compensator. The measurements for the compensator filters and open fields in 5 and10 cm depths at energy levels (6, 10 and 18 MV) and in fields with different dimensions were performed using “Mapcheck2” dosimeter. The aim of performing calculations is to derive the theoretical dose by the generalized Clarkson’s equation and comparing it with data resulted from the measurement for confirming the Clarkson’s equation presented. Results: These results demonstrate the data derived from the generalized Clarkson’s method are in good agreement with the data resulted from measurement; the highest error of the proposed equation was 3% for flat filter, and less than 5% for block-piled-up filter. Higher error in the block-piled-up filter compared with the flat filter was due to the presence of leakage between these blocks.Conclusion: The results of this study demonstrated that the presented equation is reliable and valid, and the proposed equation can be applied for dose calculation at all points under the compensator filter or the shielded areas.

Dosage Problems in Children: Well-Known Facts and Unresolved Issues

The problem of dosing drugs at an early age is conditioned by specific metabolism of medicinal products (MP) in the child's body. Currently, there are a few clinical trials on the study of physiological characteristics in different periods of childhood and systematised data. It is still relevant to understand the characteristic differences that affect the bioavailability, distribution and excretion of MP, especially in children over one month of life. The results of such studies are necessary in order to formulate the recommendations for use of MP in children taking into account their age and compensate for the lack of data from direct clinical trials in pediatrics. The possibility of using a dose calculation method regarding the fat content of the body in different periods of childhood and the chemical properties of the substance has been discussed.

Variability of carboplatin dose calculation methods in Spain.

To describe and analyze the variability in carboplatin dosing strategies in Spanish hospitals. We designed a questionnaire consisting of 19 multiple-choice items structured in two sections (hospital characteristics and carboplatin dosing data). The questionnaire was sent by e-mail to all the oncology pharmacists included in the register of the Spanish Oncology Pharmacy Group (GEDEFO), and we analyzed the completed questionnaires. Response rate was 33.5% from a total of 185 pharmacy services invited to take part in the survey. All hospitals used the Calvert formula to calculate carboplatin dose with glomerular filtration rate estimated by a formula, most commonly the Cockcroft-Gault equation (80.7%). Carboplatin doses were capped in most hospitals (91.9%): 54.8% capped creatinine clearance at 125 mL/min, 11.3% capped serum creatinine, and 19.3% capped both creatinine clearance and serum creatinine. Serum creatinine cut-off values ranged from 0.36 mg/dL to 1 mg/dL. The most commonly used body weight was actual body weight for underweight, normal weight, and overweight patients. The use of adjusted ideal body weight increased in obese and especially in morbidly obese patients. The results from this survey show the variability that exists in carboplatin dose calculation methods among Spanish hospitals and the need to continue investigating to find the optimum dose calculation method and unify criteria to avoid differences between sites that can affect effectiveness and toxicity of carboplatin-containing treatments.

Probabilistic roadmap method for path-planning in radioactive environment of nuclear facilities

In order to reduce the radiation exposure of the staff in radioactive environment of nuclear facilities, the probabilistic roadmap method is applied to optimize the walking path, which is on the basis of the map model, collision detection technology and dose calculation method. The proposed method can make a route in a very short time. The advantages of the path-planning method are reflected in two simulation experiments. From the first experiment, you can see the necessity and significance of path-planning in radioactive environment. To be specific, the cumulative dose is reduced greatly. In the other experiment, the computing speed of the proposed method is striking. Compared with the traditional A* algorithm, the reaction of this proposed method is almost instantaneous. Therefore, the proposed method has a good effect on path-planning in the radioactive environment of nuclear facilities.

Radiological habitability evaluation of the control room of the high-temperature reactor pebble-bed module: post-accident dose assessment and sensitivity studies

ABSTRACT The radiological habitability of a control room is important for nuclear emergency response, which is also a licensing prerequisite for nuclear power plants. It is determined by both atmospheric relative concentrations and doses received via different pathways. However, most recent studies have focused only on the former, which may not be adequate. The present study therefore investigates the radiological habitability and its sensitivity to different parameters in the high-temperature gas-cooled reactor pebble-bed module power plant. For three typical accidents, the study estimates the body, thyroid and skin doses received via different pathways using the Nuclear Regulatory Commission recommended ARCON96 and dose calculation method in RG 1.195. To make a realistic evaluation, the latest design and site-specific information, including the unique accidental source term, are collected and used as input parameters. The evaluation results reveal that the total dose of different pathways in the control room is far below the limit, which demonstrates the effectiveness of the current design. The inhalation exposure is the dominant pathway, and iodine and caesium are the primary contributors of the inhalation dose. The particle filter removal fraction is the most influential parameter in an accident which the activities of metal radionuclides are high.

ArcCHECK® with Monaco® – Tricks of the trade

Dynamic deliveries have become increasingly common and these techniques demand great diligence during pre-treatment Quality Assurance (QA). The ArcCHECK® is an efficient QA tool but requires careful commissioning prior to use and have specific issues to be addressed when used in combination with a Monte Carlo based TPS. We determined the best fit for the RED to be used with various methods. The variation of bulk RED was studied as a function of (a) make and model of the ArcCHECK (b) Beam energy (c) Field size and (d) static Vs arc fields. Effects of array calibration and the reference diode calibration dose were determined. The effect of Dose to Medium (Dm) Vs Dose to Water (Dw) was studied and its effect on point dose measurement determined. No significant difference was found in the RED between different ArcCHECKs, field size and type of delivery but beam energy. Gamma results are comparable if the dose calculation method (Dw or Dm) is maintained. Appropriate stopping power ratio correction must be applied for point dose measurement if Dm is used. The ArcCHECK when used with a MC TPS needs special considerations during commissioning compared to non-MC TPS.

Abstract 605: Investigating the potential impact of dose-banding for systemic anticancer therapy (SACT) in the pediatric setting based on pharmacokinetic evidence

Abstract Background: In order to make systemic anticancer therapy (SACT) preparation more practicable, dose-banding approaches are currently being introduced in many clinical centers. This involves the individual dose for a particular patient being calculated according to a single body surface area (BSA) value per band, usually the mid-point of the band in which the actual BSA of the patient lies. Advantages of such an approach include a rationalization of chemotherapy provision, with the preparation of drugs with sufficient long-term stability feasible well in advance of treatment, reduced potential for medication errors and improved capacity planning of pharmacy production. The current study aimed to determine the potential impact of utilizing recently developed National Health Service in England (NHSE) dose-banding tables in a pediatric setting, according to pharmacokinetic criteria determined from previously-published clinical trials for a range of commonly used anticancer drugs. Methods: Using pharmacokinetic parameters obtained from 385 drug administrations in 352 children aged from 1 month to 18 years, treated with 5 drugs (dactinomycin, busulfan, carboplatin, cyclophosphamide, etoposide), individual exposures (area under the curve; AUC) obtained using doses rounded according to the published NHSE tables (or banded using the same method) were calculated and compared to those obtained by standard dose calculation methods. The patients included in the study were treated for a wide range of tumors including neuroblastoma, B cell non-Hodgkin's lymphoma, Wilms tumor, rhabdomyosarcoma and Ewing's sarcoma. Results: For all five drugs, the relative variation between the NHSE dose and the recommended dose (standard individually calculated dose) was between -6% and +5% as expected. Indeed, more marked differences were observed between the actual dose administered and the recommended dose for these retrospective datasets, particularly for carboplatin and dactinomycin. In terms of AUC, there was no statistically significant difference in precision between exposures obtained by the recommended dose and those obtained with dose-banding (absolute value of relative difference 15-34%). Conclusion: Based on pharmacokinetic data from 352 children, the results generated from the current study support the implementation of NHSE dose-banding tables, at least for the five drugs investigated here. Indeed, inter-patient variability in drug clearance and exposure would appear to far outweigh the impact of relatively small drug dose changes associated with dose-banding. Further evaluation of the effect of using dose-banding for other drugs would be needed to confirm these results and extend them to additional anticancer drugs. Citation Format: Melanie White-Koning, Caroline Osborne, Angelo Paci, Alan V. Boddy, Etienne Chatelut, Gareth J. Veal. Investigating the potential impact of dose-banding for systemic anticancer therapy (SACT) in the pediatric setting based on pharmacokinetic evidence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 605.

A simple method to account for skin dose enhancement during treatment planning of VMAT treatments of patients in contact with immobilization equipment.

PurposeThe ability to accurately predict skin doses and thereby design radiotherapy treatments that balance the likelihood of skin reactions against other treatment objectives is especially important when hypofractionated prescription regimes are used. However, calculations of skin dose provided by many commercial radiotherapy treatment planning systems are known to be inaccurate, especially if the presence of immobilization equipment is not accurately taken into account. This study proposes a simple method by which the accuracy of skin dose calculations can be substantially improved, to allow informed evaluation of volumetric modulated arc therapy (VMAT) treatment plans.MethodA simple method was developed whereby dose calculation is split into grid regions, each with a correction factor which determines MU scaling for skin dose calculation. Correction factors were derived from film measurements made using a geometrically simple phantom in partial contact with a vacuum immobilization device. This method was applied to two different test treatments, planned for delivery to a humanoid phantom with a hypofractionated stereotactic body radiotherapy technique, and results were verified using film measurements of surface dose.ResultsCompared to the measured values, calculations of skin dose volumes corresponding to different grade tissue reactions were greatly improved through use of the method employed in this study. In some cases, the accuracy of skin dose evaluation improved by 76% and brought values to within 3% of those measured.ConclusionThe method of skin dose calculation in this study is simple, can be made as accurate as the user requires and is applicable for various immobilization systems. This concept has been verified through use on SBRT lung treatment plans and will aid clinicians in predicting skin response in patients.

Comparison of normal tissue dose calculation methods for epidemiological studies of radiotherapy patients

Radiation dosimetry is an essential input for epidemiological studies of radiotherapy patients aimed at quantifying the dose–response relationship of late-term morbidity and mortality. Individualised organ dose must be estimated for all tissues of interest located in-field, near-field, or out-of-field. Whereas conventional measurement approaches are limited to points in water or anthropomorphic phantoms, computational approaches using patient images or human phantoms offer greater flexibility and can provide more detailed three-dimensional dose information. In the current study, we systematically compared four different dose calculation algorithms so that dosimetrists and epidemiologists can better understand the advantages and limitations of the various approaches at their disposal. The four dose calculations algorithms considered were as follows: the (1) Analytical Anisotropic Algorithm (AAA) and (2) Acuros XB algorithm (Acuros XB), as implemented in the Eclipse treatment planning system (TPS); (3) a Monte Carlo radiation transport code, EGSnrc; and (4) an accelerated Monte Carlo code, the x-ray Voxel Monte Carlo (XVMC). The four algorithms were compared in terms of their accuracy and appropriateness in the context of dose reconstruction for epidemiological investigations. Accuracy in peripheral dose was evaluated first by benchmarking the calculated dose profiles against measurements in a homogeneous water phantom. Additional simulations in a heterogeneous cylinder phantom evaluated the performance of the algorithms in the presence of tissue heterogeneity. In general, we found that the algorithms contained within the commercial TPS (AAA and Acuros XB) were fast and accurate in-field or near-field, but not acceptable out-of-field. Therefore, the TPS is best suited for epidemiological studies involving large cohorts and where the organs of interest are located in-field or partially in-field. The EGSnrc and XVMC codes showed excellent agreement with measurements both in-field and out-of-field. The EGSnrc code was the most accurate dosimetry approach, but was too slow to be used for large-scale epidemiological cohorts. The XVMC code showed similar accuracy to EGSnrc, but was significantly faster, and thus epidemiological applications seem feasible, especially when the organs of interest reside far away from the field edge.