Total Skin Electron Irradiation Research Articles

Life after total skin electron irradiation; A perspective through the eyes of a radiation oncologist.

Mycosis fungoides (MF) remains a challenge as a disease from its diagnosis through treatment and follow-up. The rarity of the disease and uncharacteristic clinical manifestations pose difficulty in diagnosis, and the lack of treatment facilities adds to the management woes. Though the Stanford technique is the most accepted modality of total skin electron beam therapy (TSEBT), the implementation details are still unstandardized. Different centers adopt different methodologies as per their convenience and suitability. We present a patient of MF with many dimensions of prediagnosis clinical features to the diagnosis, treatment, and follow-up with subsequent developments over a period of 24 years that may help to understand the disease and management in a better manner.

Comparison of commercially available detectors used for the dosimetry of the High Energy Electron Beams.

In modern radiotherapy, electron beams are used less and less often. However, there are still techniques where this type of particles is irreplaceable, like intraoperative radiotherapy (IORT) or total skin electron irradiation (TSEI). Due to low range of electrons penetrating the medium, dosimetric measurements and beam characteristics are challenging. One of the most important steps during this process is to select the right detector in order to collect reliable data. The purpose of this work was to perform beam characteristics using six commercially available detectors: Semiflex 3D (Type 31021), Advanced Markus (Type 34045), Markus (Type 23343), Roos (Type 34001), microDiamond (Type 60019), Diode E (Type 60017). Collected data shows various parameters describing electron beams, depending on the used detector. Obtained results showed that the most useful detector for beam characteristics is microDiamond Type 60019. Thanks to the very small effective volume, microDiamond showed a superior spatial resolution, which is especially handful during the measurements of dose profiles, allowing estimating beam parameters very precisely.

Dosimetry, Optimization and FMEA of Total Skin Electron Irradiation (TSEI)

PurposeTotal Skin Electron Irradiation (TSEI) is a method for treating malignant cutaneous T-cell lymphomas. This work aims to implement and optimize the total skin technique established at Strahlenklinik Erlangen, Germany on two new linear accelerators and to quantify the risks using failure mode and effects (FMEA) analysis. Material and methodsTSEI is performed at a VersaHD accelerator (Elekta, Stockholm) with 6MeV in the “high dose rate mode” HDRE and a nominal field size of 40×40cm2. To reach the entire skin surface, the patients perform 6 different body positions at a distance of 330cm behind an acrylic scatter plate, with two overlapping irradiation fields being radiated at 2 gantry angles per position. The irradiation technique was commissioned according to the recommendation of AAPM report 23. With the help of a reference profile at 270°, 2 gantry angles were calculated, which in total resulted in an optimal dose distribution. This was metrologically verified with ion-chamber measurements in the patient's longitudinal axis. The influence of the shape of the acrylic scatter plate and the distance between the acrylic scatter plate and patient was determined by measurements. The dose homogeneity was verified using an anthropomorphic disc phantom equipped with GafChromic films. The workflows and failure modes of the total skin technique were described in a process map and subsequently quantified with a FMEA analysis. ResultsAn optimal dose distribution is achieved at a distance of SSD=330cm, using the gantry angles 289° and 251°. The previously used segmented acrylic scatter plate was replaced by a flat plate (200×120×0.5cm3), which is placed at a distance of 50cm in front of the patient. The densitometric evaluation of the GafChromic films in the anthropomorphic disc phantom revealed an expected dose distribution of 3Gy at a depth of up to 1.5cm below the skin surface, with a homogeneity of ±10% over the phantom's longitudinal axis. By FMEA a maximum risk priority number of 30 was determined. ConclusionBased on the calculations and measurements performed on the new accelerators as well as the risk analysis, we concluded that total skin therapy can be implemented clinically.

Development of an Intensity Modulated Total Skin Electron Irradiation Technique

During total skin electron irradiation (TSEI) of the pot-bellied patients, the anterior skin areas other than the abdominal area move away from the treatment machine and receive a different dose than that of the prescribed. In this study intensity modulated total skin electron irradiation (IM-TSEI) technique is developed to eliminate the dose irregularity in anterior skin areas. Tissue equivalence of a black ABS filament for 3D printer was determined. Abdominal phantoms of different thicknesses (3-6-9-12-15 cm) were created by a 3D printer. Characteristics of IM-TSEI technique were defined by determining the properties of Stanford technique. In this technique a new angle pair, 12FF and treatment time were determined based on the thickness of the abdominal region at the anterior beam positions and SSD was adjusted on the sternum point. Since there were no contour irregularities in the posterior treatment positions SSD was adjusted to the posterior waist point as in the Stanford technique, and the treatment angle pair and treatment time which created a homogeneous profile were used. The parameters affected by abdominal thickness were determined and depth-dependent dose change measurements were performed. IM-TSEI application parameters for different abdominal thicknesses were determined by combined dose measurements and calculation of treatment times. Quality assurance was done by TLD skin dose and intra-phantom film measurements for each abdominal thickness added on an anthropomorphic human phantom. Non-parametric two related Wilcoxon signed rank test was used for statistical analysis, p value <0.05 was considered significant. Average percent doses of IM-TSEI and TSEI profiles were 99.7% and 101.5%(p = 0.006), 100% and 96.5%(p = 0.000), 98.7% and 94.7% (p = 0.000), 99.8% and 94.4% (p = 0.000), 98.9% and 93% (p = 0.000) for 3,6,9,12,15 cm thicknesses respectively in favor of IM-TSEI. More homogeneous doses were obtained with IM-TSEI technique. Average skin doses of IM-TSEI and TSEI were 0.971 and 0.998 Gy for 3 cm (p = 0.088), 1.046 and 1.044 Gy for 6 cm (p = 0.737), 1.019 and 1.075 Gy for 9 cm (p = 0.013) , 1.009 and 1.073 Gy for 12 cm (p = 0.007), 1.023 and 1.081 Gy for 15 cm (p = 0.014) respectively. Absolute dose difference between anterior body regions and the treatment dose for IM-TSEI and TSEI were 2.94% and 4.24%, 11.65% and 11.46%, 9.04% and 17.12%, 9.98% and 19.30%, 7.42% and 16.52% for 3,6,9,12,15 cm thicknesses respectively. In IM-TSEI technique the absolute dose differences between the prescribed dose and anterior body region and the average skin dose were lower at abdominal thicknesses of 9 cm and above. TLD measurements also revealed that IM-TSEI technique corrected the dose irregularity in anterior body surface due to abdominal thickness. Although IM-TSEI technique can be used safely in all abdominal thicknesses, it is more advantageous than Stanford technique in abdominal thicknesses of 9 cm and above, so it can be used in pot-bellied patients.

Six Sigma-driven Automated Plan Check (APC) Tool Enhances Safety and Efficiency in External Beam Radiation Therapy

To evaluate the impact on safety and efficiency of an in-house developed Automated Plan Check (APC) tool. The common treatment planning error pathways reported to our departmental incidence learning system (ILS) were combined with our departmental physics plan check list, as well as AAPM TG-275 identified plan check items to serve as the foundation for the APC check items. This list was further evaluated using Failure Mode and Effects Analysis (FMEA) by a multidisciplinary team of physicians, physicists, dosimetrists and therapists to identify high-severity and high-risk Priority Numbers (RPN) check items and prioritize them for implementation into the APC tool. The tool was built using a treatment planning system, implemented in the clinic in January 2018 and since then is continually updated within a Six Sigma Define-Measure-Analyze-Implement-Control (DMAIC) framework. At 2 years post-APC implementation, the tool encompassed 154 plan check items verifying 3D-Conformal, clinical electron, VMAT, SBRT, Total Skin Electron Irradiation (TSEI) and Total Body Irradiation (TBI) plans. Full plan check automation was achieved for the templated TSEI treatment plans. Population statistics was used to identify outliers for TBI treatment plans. Evaluation of dosimetric indices based on site-specific and physician-specific dosimetric constraints and RTOG/NRG/QUANTEC/TG-101 dosimetric constraints was added to the APC to improve evaluation of plan quality and clinical trial compliance. The APC effectiveness was assessed by comparing FMEA RPN values and rates of reported errors. To test the efficiency gains, physics plan check time and reported error rate were prospectively compared for 20 treatment plans. The APC tool was successfully implemented for external beam plan checking. Since its implementation, the APC tool was used to verify 5946 treatment plans. FMEA RPN ranking re-evaluation at 2 years post-APC showed a statistically significant decrease in average RPN values from 129.2±51.1 to 66.1±57.5 (p < 0.001). After the introduction of APC, the average frequency of reported treatment-planning errors was reduced from 16.1% to 2.3%. For high-severity errors, the reduction was 82.7% for prescription/plan mismatches and 84.4% for incorrect shift note. There were no reported high-severity treatment planning errors that propagated to treatment since the APC introduction. The process shifted from 4σ to 5σ quality for isocenter-shift errors frequent prior to APC implementation. The efficiency study showed a statistically significant gain in plan check time (10.1±7.3 minutes, p = 0.005) and decrease in errors propagating to physics plan check (80%). Incorporation of APC tool has significantly reduced the error rate. The Six Sigma-driven framework can provide an iterative and robust workflow to improve the efficiency and quality of treatment planning procedure enabling a safer radiotherapy process.

Maintenance Therapy for Cutaneous T-cell Lymphoma After Total Skin Electron Irradiation: Evidence for Improved Overall Survival With Ultraviolet Therapy

BackgroundTreatment of cutaneous T-cell lymphoma (CTCL) with total skin electron beam (TSEB) therapy has been associated with deep responses but short progression-free intervals. Maintenance therapy might prolong the response duration; however, limited data assessing the outcomes with maintenance therapy after TSEB are available. We evaluated the effect of maintenance therapy on the outcomes for patients with CTCL receiving TSEB therapy. Materials and MethodsWe conducted a single-center retrospective analysis of 101 patients with CTCL who had received TSEB therapy from 1998 to 2018 at the Winship Cancer Institute of Emory University and compared the overall survival (OS) and progression-free survival (PFS) for patients had received maintenance therapy, including retinoids, interferon, ultraviolet therapy, nitrogen mustard, and extracorporeal photopheresis compared with those who had not. ResultsWe found that pooled maintenance therapies improved PFS (hazard ratio [HR], 0.60; P = .026) but not OS (median HR, 0.73; P = .264). The median PFS and OS was 7.2 months versus 9.6 months and 2.4 years versus 4.2 years for the no maintenance and maintenance groups, respectively. On exploratory analysis of the individual regimens, ultraviolet therapy was associated with improved OS (HR, 0.21; P = .034) and PFS (HR, 0.26; P = .002) compared with no maintenance. ConclusionAmong the patients with CTCL who had received TSEB therapy, maintenance therapy improved PFS for all patients, and ultraviolet-based maintenance improved both PFS and OS in a subset of patients.

Cherenkov imaging of total skin electron irradiation (TSEI)

Total Skin Electron Irradiation (TSEI) utilizes high-energy electrons to treat skin cancers, mostly mycosis fungoides. The otherwise invisible radiation beam can be visualized using the optical Cherenkov light emitted from interaction between incident electron beams and tissue during radiation therapy. Using a gated camera system with built-in intensifier, the Cherenkov emission can be used to evaluate the dose uniformity on the surface of the patient in real-time. Each patient was also monitored on the skin surface using in-vivo diode or OSLD dosimeters.

Total skin electron therapy (TSET): Monte Carlo Simulation and implementation

Introduction: Total skin electron irradiation technique is used in treatment of the mycosis fungoid. The implementation of this technique requires non-standard measurements and complex dosimetry methods. Operating procedures for total skin electron irradiation and its dosimetry vary in different radiation therapy centers in the world. In this article, validation of TSET technique dosimetry data by Monte Carlo simulation is done. Materials and Methods: The electron beam characteristic of RTSEI for the only electron accelerator, located at the radiation center of the Seyed Alshohada Hospital of Isfahan (NEPTUN 10PC) determined by performing Monte Carlo simulations and using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). For the best uniformity of the vertical profile, the optimal angle of gantry was defined at SSD=300 cm. The effect of the degrader plane that is located at a distance of 20 cm from the patient surface, was evaluated on the amount of energy reduction of the beam, the opening of the electron beam field and the homogeneity of the dose distribution. The transversal dose distribution from the whole treatment with Rotational technique was simulated in a CT- based anthropomorphic phantom. Also, the percentage depth dose in the head, neck, thorax, abdomen and legs was obtained for RTSET technique. TSET dosimetry requires measurements in nonreference conditions. Because of the complexity of the required measurements for the commissioning process of this technique, different dosimetric systems were employed such as radiochromic films (EBT3) and an ionization chamber. In particular, for dual-field beams irradiation, the optimal tilt angle was investigated and the dose distribution in the treatment plane was measured by radiochromic films. Dose distributions and percentage depth dose measurements for a total skin electron therapy were measured in an anthropomorphic phantom. Results: The optimal angle of 20o would give the most uniform total profile and the use of a 0.8 cm PMMA degrader in front of the patient leads to a homogeneous distribution of the dose in all directions (the mean relative dose value was 97%±5%, normalizing to 100% at the calibration point level). The percentage depth dose curves in different organs of anthropomorphic phantom for RTSEI indicates that the depth of maximum dose is on the surface of the phantom, Isodose curve of 80% is formed at a depth less than 4 mm and at the depth less than 1.5 mm, the dose decreases to 20% of the maximum dose. Conclusion: The main purpose of this study was to commission and optimize a TSET technique for the treatment of mycosis fungiodes with the NEPTUN 10PC linear accelerator. This was done through an extensive set of measurements and a large number of MC simulations. The results of Monte Carlo calculations were found to be in general agreement with the measurements, providing a promising tool for further studies of dose distribution calculations in TSEI.

Total Skin Electron Irradiation (TSEI) May Induce Systemic Progression of Mycosis Fungoides (MF) - Cutaneous T-Cell Lymphoma (CTCL)

The management of MF-CTCL is based on a 'stage-based' approach and an evaluation by a multidisciplinary team is preferred. Initial treatment in patients with local (patch/plaque) disease includes skin-directed therapies (localized or generalized), with the addition of systemic biologic therapy for refractory, or progressive disease. In patients with unfavorable prognostic features (e.g., folliculotropic or large-cell transformed MF, or B1 involvement) systemic biologic therapies may be introduced earlier in the treatment algorithm.

Total Skin Electron Irradiation and Sequential Malignancies in Mycosis Fungoides Patients: Longitudinal Study

The purpose of this study was to determine the role of total skin electron irradiation (TSEI) as a cause of second malignancies in mycosis fungoides (MF) patients. Mycosis Fungiodes patients referred to Total Skin Electron Irradiation were followed in a longitudinal study. Other diagnosed malignancies were obtained after cross-matching with the Israel National Cancer Registry database. Between 1970 and 2010, 197 patients were treated; 134 (68%) males, 63 (32%) females; mean age 58±17years. Topical/systemic treatment was given to 134 (68%) patients. TSEI was given to 104 (68.9%) patients. Seven (4.6%) received sub-TSEI and 40 (26.5%) received focal electron irradiation fields. Forty-six (23%) patients did not receive radiotherapy. Second primaries rate was 6.7 times higher in male MF patients and 13.1 times higher in female MF patients than in the general Israeli population. Malignant melanoma developed in eight patients after radiotherapy, in one patient without irradiation. Skin-related cancers rate after irradiation versus no irradiation was higher (p=.011). Combination radiotherapy with psoralen+UVA and/or nitrogen mustard yielded 11 cases of skin cancer vs no case without irradiation. MF patients have a high incidence of sequential malignancies. TSEI is associated with higher "skin-related cancers" rates. Close longitudinal follow-up of MF patients is obligatory.

Total Skin Electron Irradiation and Sequential Malignancies in Mycosis Fungoides Patients: Longitudinal Study

AimsTo determine the role of total skin electron irradiation (TSEI) as a cause of second malignancies in mycosis fungoides patients. Materials and methodsMycosis fungoides patients referred to TSEI were followed in a longitudinal study. Other diagnosed malignancies were obtained after cross-matching with the Israel National Cancer Registry database. ResultsBetween 1974 and 2010, 197 patients were treated: 134 (68%) men, 63 (32%) women; mean age 58 ± 17years. Topical/systemic treatment was given to 134 (68%) patients. TSEI was given to 104 (68.9%) patients. Seven (4.6%) received sub-TSEI and 40 (26.5%) received focal electron irradiation fields. Forty-six (23%) patients did not receive radiotherapy. The second primaries rate was 6.7 times higher in male mycosis fungoides patients and 13.1 times higher in female mycosis fungoides patients than in the general Israeli population. Malignant melanoma developed in eight patients after radiotherapy, in one patient without irradiation. The skin-related cancer rate after irradiation versus no irradiation was higher (P = 0.018). Combination radiotherapy with psoralen + ultraviolet A and/or nitrogen mustard yielded 11 cases of skin cancer versus no cases without irradiation. ConclusionsMycosis fungoides patients have a high incidence of sequential malignancies. TSEI is associated with higher ‘skin-related cancer’ rates. Close longitudinal follow-up of mycosis fungoides patients is obligatory.

Monte Carlo study and design of system for implementation of Rotational Total Skin Electron Irradiation technique

Total skin electron irradiation technique is used in treatment of the mycosis fungoid. The implementation of this technique requires non-standard measurements and complex dosimetry methods. Depending on the linear accelerator (Linac) type, bunker size, room dimensions and dosimetry equipment, the design of instruments for appropriate set up and implementation of TSEI in different radiation therapy centers varies. The studies which have been done in this article provide an introduction to the implementing of this method for the first time in Iran and its results can be used for the centers with similar specifications in the world. This article determined the electron beam characteristic of TSEI for the only electron accelerator, located at the radiation center of the Seyed Alshohada Hospital of Isfahan (NEPTUN 10PC), by performing Monte Carlo simulations and using EGSnrc-based codes (BEAMnrc and DOSXYZnrc). For the best uniformity of the vertical profile, the optimal angle of gantry was defined at SSD=350 cm. The effect of the degrader plane that is located at a distance of 20 cm from the patient surface, was evaluated on the amount of energy reduction of the beam, the opening of the electron beam field and the homogeneity of the dose distribution. The transversal dose distribution from the whole treatment with Stanford technique (six dual fields) and Rotational technique was simulated in a CT-based anthropomorphic phantom. Also, the percentage depth dose in the head, neck, thorax, abdomen and legs was obtained for both methods. The simulation results show that the 20̂ angle between the horizontal and the beam central axis is optimal in order to provide the best vertical dose uniformity. The mean energy decreases from 6.1 MeV (the exit window) to 3 MeV (the treatment surface) by placing a degrader with 0.8 cm thickness in front of the treatment plane. FWHM of the angular distribution of the electron beam increased from 15̂ at SSD=100 cm to more than 30̂ on the treatment surface by traversing the PMMA degrader. The MC calculated percentage depth dose curves in different organs of anthropomorphic phantom for RTSEI indicates that the depth of maximum dose is on the surface of the phantom and Isodose curve of 80% is formed at a depth less than 4 mm. the results also show, with the degrader plane in front of the patient, the degree of homogeneity of the dose distribution for both Stanford and rotational techniques is the same.

Dose optimization of total or partial skin electron irradiation by thermoluminescent dosimetry.

Due to the complex surface of the human body, total or partial skin irradiation using large electron fields is challenging. The aim of the present study was to quantify the magnitude of dose optimization required after the application of standard fields. Total skin electron irradiation (TSEI) was applied using the Stanford technique with six dual-fields. Patients presenting with localized lesions were treated with partial skin electron irradiation (PSEI) using large electron fields, which were individually adapted. In order to verify and validate the dose distribution, in vivo dosimetry with thermoluminescent dosimeters (TLD) was performed during the first treatment fraction to detect potential dose heterogeneity and to allow for an individual dose optimization with adjustment of the monitor units (MU). Between 1984 and 2017, a total of 58patients were treated: 31patients received TSEI using 12treatment fields, while 27patients underwent PSEI and were treated with 4-8treatment fields. After evaluation of the dosimetric results, an individual dose optimization was necessary in 21patients. Of these, 7patients received TSEI (7/31). Monitor units (MU) needed to be corrected by amean value of 117 MU (±105, range 18-290) uniformly for all 12 treatment fields, corresponding to amean relative change of 12% of the prescribed MU. In comparison, the other 14patients received PSEI (14/27) and the mean adjustment of monitor units was 282 MU (±144, range 59-500) to single or multiple fields, corresponding to amean relative change of 22% of the prescribed MU. Asecond dose optimization to obtain asatisfying dose at the prescription point was need in 5patients. Thermoluminescent dosimetry allows an individual dose optimization in TSEI and PSEI to enable areliable adjustment of the MUs to obtain the prescription dose. Especially in PSEI in vivo dosimetry is of fundamental importance.

Failure modes and effects analysis of total skin electron irradiation technique.

Total skin electron irradiation (TSEI) is a radiotherapy technique which consists of an homogeneous body surface irradiation by electrons. This treatment requires very strict technical and dosimetric conditions, requiring the implementation of multiple controls. Recently, the Task Group 100 report of the AAPM has recommended adapting the quality assurance program of the facility to the risks of their processes. A multidisciplinary team evaluated the potential failure modes (FMs) of every process step, regardless of the management tools applied in the installation. For every FM, occurrence (O), severity (S) and detectability (D) by consensus was evaluated, which resulted in the risk priority number (RPN), which permitted the ranking of the FMs. Subsequently, all the management tools used, related to the TSEI process, were examined and the FMs were reevaluated, to analyze the effectiveness of these tools and to propose new management tools to cover the greater risk FMs. 361 FMs were identified, 103 of which had RPN ≥80, initially, and 41 had S≥8. Taking this into account the quality management tools FMs were reevaluated and only 30 FMs had RPN≥80. The study of these 30 FMs emphasized that the FMs that involved greater risk were related to the diffuser screen placement and the patient's position during treatment. The quality assurance program of the facility has been adapted to the risk of this treatment process, following the guidelines proposed by the TG-100. However, clinical experience continually reveals new FMs, so the need for periodic risk analysis is required.

EP-1744: Failure modes and effects analysis of Total Skin Electron Irradiation (TSEI) technique

EP-1744: Failure modes and effects analysis of Total Skin Electron Irradiation (TSEI) technique

Room scatter effects in Total Skin Electron Irradiation: Monte Carlo simulation study.

PurposeTotal Skin Electron Irradiation (TSEI) is a complex technique which usually involves the use of large electron fields and the dual‐field approach. In this situation, many electrons scattered from the treatment room floor are produced. However, no investigations of the effect of scattered electrons in TSEI treatments have been reported. The purpose of this work was to study the contribution of floor scattered electrons to skin dose during TSEI treatment using Monte Carlo (MC) simulations.MethodsAll MC simulations were performed with the EGSnrc code. Influence of beam energy, dual‐field angle, and floor material on the contribution of floor scatter was investigated. Spectrum of the scattered electrons was calculated. Measurements of dose profile were performed in order to verify MC calculations.ResultsFloor scatter dependency on the floor material was observed (at 20 cm from the floor, scatter contribution was about 21%, 18%, 15%, and 12% for iron, concrete, PVC, and water, respectively). Although total dose profiles exhibited slight variation as functions of beam energy and dual‐field angle, no dependence of the floor scatter contribution on the beam energy or dual‐field angle was found. The spectrum of the scattered electrons was almost uniform between a few hundred KeV to 4 MeV, and then decreased linearly to 6 MeV.ConclusionsFor the TSEI technique, dose contribution due to the electrons scattered from the room floor may be clinically significant and should be taken into account during design and commissioning phases. MC calculations can be used for this task.

Wearable glass beads for in vivo dosimetry of total skin electron irradiation treatments

Glass beads have recently been proposed for use as radiation therapy dosimeters. Glass beads have a number of characteristics that make them suitable for in vivo skin dose measurements, including an ability to be worn on a string, and therefore avoid possible patient discomfort that may result from the use of adhesives. In this study, their use for in vivo dose measurements in total skin electron irradiation treatments has been tested. First, the dosimetric properties of cylindrical beads with a 3mm diameter were characterised using electron fields produced by a linear accelerator. The mean individual bead reproducibility was demonstrated to be within 3%; and a batch variation of 7% was observed. The beads were shown to have a linear dose response, and both dose rate and beam energy independence, within the measurement uncertainty. Phantom measurements were then performed for a total skin electron irradiation beam arrangement, and results compared against optically stimulated luminescent dosimeters at five anatomical sites. For a majority of measurement locations, agreement within 3% was observed between the two dosimetry techniques, demonstrating the feasibility of glass beads as in vivo dosimeters for total skin electron irradiation; though further investigation may be needed to minimise uncertainty in results.

The dose penumbra of a custom-made shield used in hemibody skin electron irradiation.

We report our technique for hemibody skin electron irradiation with a custom‐made plywood shield. The technique is similar to our clinical total skin electron irradiation (TSEI), performed with a six‐pair dual field (Stanford technique) at an extended source‐to‐skin distance (SSD) of 377 cm, with the addition of a plywood shield placed at 50 cm from the patient. The shield is made of three layers of standard 5/8” thick plywood (total thickness of 4.75 cm) that are clamped securely on an adjustable‐height stand. Gafchromic EBT3 films were used in assessing the shield's transmission factor and the extent of the dose penumbra region for two different shield‐phantom gaps. The shield transmission factor was found to be about 10%. The width of the penumbra (80%‐to‐20% dose falloff) was measured to be 12 cm for a 50 cm shield‐phantom gap, and reduced slightly to 10 cm for a 35 cm shield‐phantom gap. In vivo dosimetry of a real case confirmed the expected shielded area dose.PACS number(s): 87.53.Bn

Validation of total skin electron irradiation (TSEI) technique dosimetry data by Monte Carlo simulation.

Total skin electron irradiation (TSEI) is a complex technique which requires many nonstandard measurements and dosimetric procedures. The purpose of this work was to validate measured dosimetry data by Monte Carlo (MC) simulations using EGSnrc‐based codes (BEAMnrc and DOSXYZnrc). Our MC simulations consisted of two major steps. In the first step, the incident electron beam parameters (energy spectrum, FWHM, mean angular spread) were adjusted to match the measured data (PDD and profile) at SSD=100 cm for an open field. In the second step, these parameters were used to calculate dose distributions at the treatment distance of 400 cm. MC simulations of dose distributions from single and dual fields at the treatment distance were performed in a water phantom. Dose distribution from the full treatment with six dual fields was simulated in a CT‐based anthropomorphic phantom. MC calculations were compared to the available set of measurements used in clinical practice. For one direct field, MC calculated PDDs agreed within 3%/1 mm with the measurements, and lateral profiles agreed within 3% with the measured data. For the OF, the measured and calculated results were within 2% agreement. The optimal angle of 17° was confirmed for the dual field setup. Dose distribution from the full treatment with six dual fields was simulated in a CT‐based anthropomorphic phantom. The MC‐calculated multiplication factor (B12‐factor), which relates the skin dose for the whole treatment to the dose from one calibration field, for setups with and without degrader was 2.9 and 2.8, respectively. The measured B12‐factor was 2.8 for both setups. The difference between calculated and measured values was within 3.5%. It was found that a degrader provides more homogeneous dose distribution. The measured X‐ray contamination for the full treatment was 0.4%; this is compared to the 0.5% X‐ray contamination obtained with the MC calculation. Feasibility of MC simulation in an anthropomorphic phantom for a full TSEI treatment was proved and is reported for the first time in the literature. The results of our MC calculations were found to be in general agreement with the measurements, providing a promising tool for further studies of dose distribution calculations in TSEI.PACS number(s): 87.10. Rt, 87.55.K, 87.55.ne

SU‐F‐T‐248: FMEA Risk Analysis Implementation (AAPM TG‐100) in Total Skin Electron Irradiation Technique

Purpose:Total Skin Electron Irradiation (TSEI) is a radiotherapy treatment which involves irradiating the entire body surface as homogeneously as possible. It is composed of an extensive multi‐step technique in which quality management requires high consumption of resources and a fluid communication between the involved staff, necessary to improve the safety of treatment. The TG‐100 proposes a new perspective of quality management in radiotherapy, presenting a systematic method of risk analysis throughout the global flow of the stages through the patient. The purpose of this work has been to apply TG‐100 approach to the TSEI procedure in our institution.Methods:A multidisciplinary team specifically targeting TSEI procedure was formed, that met regularly and jointly developed the process map (PM), following TG‐100 guidelines of the AAPM. This PM is a visual representation of the temporal flow of steps through the patient since start until the end of his stay in the radiotherapy service.Results:This is the first stage of the full risk analysis, which is being carried out in the center. The PM provides an overview of the process and facilitates the understanding of the team members who will participate in the subsequent analysis. Currently, the team is implementing the analysis of failure modes and effects (FMEA). The failure modes of each of the steps have been identified and assessors are assigning a value of severity (S), frequency of occurrence (O) and lack of detection (D) individually. To our knowledge, this is the first PM made for the TSEI. The developed PM can be useful for those centers that intend to implement the TSEI technique.Conclusion:The PM of TSEI technique has been established, as the first stage of full risk analysis, performed in a reference center in this treatment.