Technical and dosimetric aspects of the total skin electron beam technique implemented at Heidelberg University Hospital

Electron beam detection in radiotherapy using a capacitor dosimeter equipped with a silicon photodiode

In this study, a newly developed capacitor dosimeter was evaluated using electron beams commonly utilized in radiotherapy. The capacitor dosimeter comprised a silicon photodiode, 0.47-μF capacitor, and dedicated terminal (dock). Before electron beam irradiation, the dosimeter was charged using the dock. The doses were measured without using a cable by reducing the charging voltages using the currents from the photodiode during irradiation. A commercially available parallel-plane-type ionization chamber and solid-water phantom were used for dose calibration with an electron energy of 6 MeV. In addition, the depth doses were measured using a solid-water phantom at electron energies of 6, 9, and 12 MeV. The doses were proportional to the discharging voltages, and the maximum dose difference in the calibrated doses measured using a two-point calibration was approximately 5% in the range of 0.25-1.98 Gy. The depth dependencies at energies of 6, 9, and 12 MeV corresponded to those measured using the ionization chamber.

Total Skin Treatment with Helical Arc Radiotherapy

For widespread cutaneous lymphoma, such as mycosis fungoides or leukemia cutis, in patients with acute myeloid leukemia (AML) and for chronic myeloproliferative diseases, total skin irradiation is an efficient treatment modality for disease control. Total skin irradiation aims to homogeneously irradiate the skin of the entire body. However, the natural geometric shape and skin folding of the human body pose challenges to treatment. This article introduces treatment techniques and the evolution of total skin irradiation. Articles on total skin irradiation by helical tomotherapy and the advantages of total skin irradiation by helical tomotherapy are reviewed. Differences among each treatment technique and treatment advantages are compared. Adverse treatment effects and clinical care during irradiation and possible dose regimens are mentioned for future prospects of total skin irradiation.

Computational dose visualization & comparison in total skin electron treatment suggests superior coverage by the rotational versus the Stanford technique

INTRODUCTION/BACKGROUND

The goal of Total Skin Electron Therapy (TSET) is to achieve a uniform surface dose, although assessment of this is never really done and typically limited points are sampled. A computational treatment simulation approach was developed to estimate dose distributions over the body surface, to compare uniformity of (i) the 6 pose Stanford technique and (ii) the rotational technique.

METHODS

The relative angular dose distributions from electron beam irradiation was calculated by Monte Carlo simulation for cylinders with a range of diameters, approximating body part curvatures. These were used to project dose onto a 3D body model of the TSET patient's skin surfaces. Computer animation methods were used to accumulate the dose values, for display and analysis of the homogeneity of coverage.

RESULTS

The rotational technique provided more uniform coverage than the Stanford technique. Anomalies of under dose were observed in lateral abdominal regions, above the shoulders and in the perineum. The Stanford technique had larger areas of low dose laterally. In the rotational technique, 90% of the patient's skin was within ±10% of the prescribed dose, while this percentage decreased to 60% or 85% for the Stanford technique, varying with patient body mass. Interestingly, the highest discrepancy was most apparent in high body mass patients, which can be attributed to the loss of tangent dose at low angles of curvature.

DISCUSSION/CONCLUSION

This simulation and visualization approach is a practical means to analyze TSET dose, requiring only optical surface body topography scans. Under- and over-exposed body regions can be found, and irradiation could be customized to each patient. Dose Area Histogram (DAH) distribution analysis showed the rotational technique to have better uniformity, with most areas within 10% of the umbilicus value. Future use of this approach to analyze dose coverage is possible as a routine planning tool.

Sweeping-beam technique with electrons for large treatment areas as total skin irradiation : Dosimetric and technical aspects of a modified Stanford technique

PURPOSE

Total skin electron beam therapy (TSEBT) is still a technical and therapeutic challenge today. Thus, we developed TSEBT using a sweeping-beam technique.

METHODS

For treatment delivery, a linear accelerator Versa HD (ELEKTA, Stockholm, Sweden) with high-dose-rate electrons (HDRE) was used with a dose rate of 9000 MU/min. Dosimetry quality assurance was performed by multiple measurements with film dosimetry, 2D array, and Roos chamber.

RESULTS

Clinical experience shows that treatment durations of 75 to 90 min are usual for the Stanford technique without using HDRE. With this new sweeping-beam irradiation technique, the total treatment time of a daily fraction could be reduced to 20 min while keeping over- and underdosing low. The treatment area is about 60 cm × 200 cm and the dose distribution is uniform within 2% and 5% in vertical and horizontal directions, respectively. Initially, the electron energy of 6 MeV is reduced to 3.2 MeV by 1‑cm polymethylmethacrylat (PMMA) scatter and the irradiation conditions of a source-surface distance (SSD) of 350 cm. The photon contamination drops to under 1%.

CONCLUSION

These results show that the mean dose to total skin varies between 1.3 and 1.8 Gy. The sweeping-beam technique with electrons has a homogeneous dose distribution in connection with a short treatment time.

Monte Carlo study on dose distributions from total skin electron irradiation therapy (TSET)

Total skin electron therapy (TSET) has been used to treat mycosis fungoides since the 1950s. Practitioners of TSET rely on relatively crude, phantom-based point measurements for commissioning and treatment plan dosimetry. Using Monte Carlo simulation techniques, this study presents whole-body dosimetry for a patient receiving rotational, dual-field TSET. The Monte Carlo codes, BEAMnrc/DOSXYZnrc, were used to simulate 6 MeV electron beams to calculate skin dose from TSET. Simulations were validated with experimental measurements. The rotational dual-field technique uses extended source-to-surface distance with an acrylic beam degrader between the patient and incident beams. Simulations incorporated patient positioning: standing on a platform that rotates during radiation delivery. Resultant patient doses were analyzed as a function of skin depth-dose coverage and evaluated using dose-volume-histograms (DVH). Good agreement was obtained between simulations and measurements. For a cylinder with a 30 cm diameter, the depths that dose fell to 50% of the surface dose was 0.66 cm, 1.15 cm and 1.42 cm for thicknesses of 9 mm, 3 mm and without an acrylic scatter plate, respectively. The results are insensitive to cylinder diameter. Relatively uniform skin surface dose was obtained for skin in the torso area although large dose variations (>25%) were found in other areas resulting from partial beam shielding of the extremities. To achieve 95% mean dose to the first 5 mm of skin depth, the mean dose to skin depth of 5-10 mm and depth of 10-15 mm from the skin surface was 74% (57%) and 50% (25%) of the prescribed dose when using a 3mm (9 mm) thickness scatter plate, respectively. As a result of this investigation on patient skin dose distributions we changed our patient treatments to use a 3 mm instead of a 9 mm thickness Acrylic scatter plate for clinically preferred skin depth dose coverage.

Validation of the dosimetry of total skin irradiation techniques by Monte Carlo simulation

Purpose

To validate the dose measurements for two total skin irradiation techniques with Monte Carlo simulation, providing more information on dose distributions, and guidance on further technique optimization.

Methods

Two total skin irradiation techniques (stand‐up and lay‐down) with different setup were simulated and validated. The Monte Carlo simulation was primarily performed within the EGSnrc environment. Parameters of jaws, MLCs, and a customized copper (Cu) filter were first tuned to match the profiles and output measured at source‐to‐skin distance (SSD) of 100 cm where the secondary source is defined. The secondary source was rotated to simulate gantry rotation. VirtuaLinac, a cloud‐based Monte Carlo package, was used for Linac head simulation as a secondary validation. The following quantities were compared with measurements: for each field/direction at the treatment SSDs, the percent depth dose (PDD), the profiles at the depth of maximum, and the absolute dosimetric output; the composite dose distribution on cylindrical phantoms of 20 to 40 cm diameters.

Results

Cu filter broadened the FWHM of the electron beam by 44% and degraded the mean energy by 0.7 MeV. At SSD = 100 cm, MC calculated PDDs agreed with measured data within 2%/2 mm (except for the surface voxel) and lateral profiles agreed within 3%. At the treatment SSD, profiles and output factors of individual field matched within 4%; d_max and R₈₀ of the simulated PDDs also matched with measurement within 2 mm. When all fields were combined on the cylindrical phantom, the d_max shifted toward the surface. For lay‐down technique, the maximum x‐ray contamination at the central axis was (MC: 2.2; Measurement: 2.1)% and reduced to 0.2% at 40 cm off the central axis.

Conclusions

The Monte Carlo results in general agree well with the measurement, which provides support in our commissioning procedure, as well as the full three‐dimensional dose distribution of the patient phantom.

Ultra-Low-Dose Radiotherapy for Palliation of Mycosis Fungoides

Introduction. Mycosis fungoides (MF) is a form of primary cutaneous T-cell lymphomas, and radiotherapy (RT) has been used to treat localized/limited lesions of MF. In this case report, the results of low-dose RT applied for palliative purpose are shared. Case Report. A 70-year-old male patient was admitted to the outpatient clinic 7 months ago with a generalized itchy rash. The result of the biopsy was reported as mycosis fungoides. Systemic treatment was not performed due to comorbid diseases. The hemibody RT was applied. 2 Gy was given per fraction, with a total dose of 6 Gy. The significant clinical relief was observed with 6 Gy RT. The patient died due to multiorgan failure 2 months later, and no recurrence was observed. Conclusion. The palliation was achieved in the advanced MF patient with fractionated 6 Gy hemibody RT for the remaining 2 months of life.

Electron Scattering in Conventional Cell Flask Experiments and Dose Distribution Dependency

Electron beam therapy (EBT) is commonly used for treating superficial and subdermal tumors. Previous cellular radiosensitivity research using EBT may be underestimating the contribution from flask wall scattering and the corresponding dose distribution. Single cell suspensions of Chinese hamster ovary (CHO) cells were plated on flasks and irradiated with 3, 4, 7, 9, and 18 MeV energy electron beams from two different institutions, and the spatial locations of surviving colonies were recorded. Gafchromic film dosimetry and Monte Carlo simulations were carried out to determine the spatial electron scattering contribution from the flask walls. Low electron irradiation resulted in an uneven surviving colony distribution concentrated near the periphery of the flasks, while spatial colony formation was statistically uniform at energies above 7 MeV. Our data demonstrates that without proper dosimetric corrections, studies using low energy electrons can lead to misinterpretations of energy dependent cellular radiosensitivity in culture vessels, and radiotherapeutic applications.

In vivo monitoring of total skin electron dose using optically stimulated luminescence dosimeters

AIM

This study retrospectively analysed the results of using optically stimulated radiation dosimeters (OSLDs) for in vivo dose measurements during total skin electron therapy (TSET, also known as TSEI, TSEB, TSEBT, TSI or TBE) treatments of patients with mycosis fungoides.

BACKGROUND

TSET treatments are generally delivered to standing patients, using treatment plans that are devised using manual dose calculations that require verification via in vivo dosimetry. Despite the increasing use of OSLDs for radiation dosimetry, there is minimal published guidance on the use of OSLDs for TSET verification.

MATERIALS AND METHODS

This study retrospectively reviewed in vivo dose measurements made during treatments of nine consecutive TSET patients, treated between 2013 and 2018. Landauer nanoDot OSLDs were used to measure the skin dose at reference locations on each patient, as well as at locations of clinical interest such as the head, hands, feet, axilla and groin.

RESULTS

1301 OSLD measurements were aggregated and analysed, producing results that were in broad agreement with previous TLD studies, while providing additional information about the variation of dose across concave surfaces and potentially guiding future refinement of treatment setup. In many cases these in vivo measurements were used to identify deviations from the planned dose in reference locations and to identify anatomical regions where additional shielding or boost treatments were required.

CONCLUSIONS

OSLDs can be used to obtain measurements of TSET dose that can inform monitor unit adjustments and identify regions of under and over dosage, while potentially informing continuous quality improvement in TSET treatment delivery.

Cutaneous Lymphomas

Primary cutaneous lymphomas are the second most common form of extra-nodal lymphomas. They have special characteristics compared with other lymphomas. They are most frequently of T-cell origin and they generally have a much more indolent course than lymphomas of similar histology in other locations. Mycosis fungoides is the most common type of cutaneous lymphoma. Primary cutaneous lymphomas remain confined to the skin for a long time. Skin-directed therapies are the main treatments; systemic treatments are not very effective for the skin lesions. Skin-directed therapies used for the early and thin lesions are topical corticosteroids, phototherapy and topical retinoids and, for the more widespread or thick lesions, topical nitrogen mustard and radiation. Radiation therapy is highly effective and is indicated in virtually all cases of localised disease. Radiation therapy may be given to the whole skin surface, so-called total skin electron beam therapy. However, if the disease spreads to other organs, systemic treatments are indicated, often combined with skin-directed therapies. Conventional cytotoxic therapy is less effective in cutaneous lymphomas. The commonly used therapies, such as interferon, enhanced anti-tumour immunity and the recent advances in immune therapies may improve our treatments for cutaneous lymphomas.

Characterization of a non-contact imaging scintillator-based dosimetry system for total skin electron therapy

Surface dosimetry is required for ensuring effective administration of total skin electron therapy (TSET); however, its use is often reduced due to the time consuming and complex nature of acquisition. A new surface dose imaging technique was characterized in this study and found to provide accurate, rapid and remote measurement of surface doses without the need for post-exposure processing. Disc-shaped plastic scintillators (1 mm thick  ×  15 mm [Formula: see text]) were chosen as optimal-sized samples and designed to attach to a flat-faced phantom for irradiation using electron beams. Scintillator dosimeter response to radiation damage, dose rate, and temperature were studied. The effect of varying scintillator diameter and thickness on light output was evaluated. Furthermore, the scintillator emission spectra and impact of dosimeter thickness on surface dose were also quantified. Since the scintillators were custom-machined, dosimeter-to-dosimeter variation was tested. Scintillator surface dose measurements were compared to those obtained by optically stimulated luminescence dosimeters (OSLD). Light output from scintillator dosimeters evaluated in this study was insensitive to radiation damage, temperature, and dose rate. Maximum wavelength of emission was found to be 422 nm. Dose reported by scintillators was linearly related to that from OSLDs. Build-up from placement of scintillators and OSLDs had a similar effect on surface dose (4.9% increase). Variation among scintillator dosimeters was found to be 0.3  ±  0.2%. Scintillator light output increased linearly with dosimeter thickness (~1.9  ×  /mm). All dosimeter diameters tested were able to accurately measure surface dose. Scintillator dosimeters can potentially improve surface dosimetry-associated workflow for TSET in the radiation oncology clinic. Since scintillator data output can be automatically recorded to a patient medical record, the chances of human error in reading out and recording surface dose are minimized.

Rapid Multisite Remote Surface Dosimetry for Total Skin Electron Therapy: Scintillator Target Imaging

PURPOSE

The goal of this work is to produce a surface-dosimetry method capable of accurately and remotely measuring skin dose for patients undergoing total skin electron therapy (TSET) without the need for postexposure dosimeter processing. A rapid and wireless surface-dosimetry system was developed to improve clinical workflow. Scintillator-surface dosimetry was conducted on patients undergoing TSET by imaging scintillator targets with an intensified camera during TSET delivery.

METHODS AND MATERIALS

Disc-shaped scintillator targets were attached to the skin surface of patients undergoing TSET and imaged with an intensified, time-gated, and linear accelerator-synchronized camera. Optically stimulated luminescence dosimeters (OSLDs) were placed directly adjacent to scintillators at several dosimetry sites to serve as an absolute dose reference. Real-time image-processing methods were used to produce background-subtracted intensity maps of Cherenkov and scintillation emission. Rapid conversion of scintillator-light output to dose was achieved by using a custom fitting algorithm and calibration factor. Surface doses measured by scintillators were compared with those from OSLDs.

RESULTS

Absolute surface-dose measurements for 99 dosimetry sites were evaluated. According to paired OSLD estimates, scintillator dosimeters were able to report dose with <3% difference in 88 of 99 observed dosimetry sites and <5% difference in 98 of 99 observed dosimetry sites. Fitting a linear regression to dose data reported by scintillator versus OSLD, per dosimetry site, yielded an R² = 0.94.

CONCLUSIONS

Scintillators were able to report dose within <3% accuracy of OSLDs. Imaging of calibrated scintillator targets via an intensified, linear accelerator-synchronized camera provides rapid absolute surface-dosimetry measurements for patients treated with TSET. This technique has the potential to reduce the amount of time and effort necessary to conduct full-body dosimetry and can be adopted for use in any surface-dosimetry setting where the region of interest is observable throughout treatment.

Light and shadows of a new technique: is photon total-skin irradiation using helical IMRT feasible, less complex and as toxic as the electrons one?

BACKGROUND

Radiotherapy is one of the standard treatments for cutaneous lymphoma and Total Skin Electrons Beam Irradiation (TSEBI) is generally used to treat diffuse cutaneous lymphoma and some cases of localized disease. Helical IMRT (HI) allows to treat complex target with optimal dose distribution and organ at risk sparing, so helical tomotherapy has been proposed as alternative technique to TSEBI but only one preliminary report has been published.

METHODS

Three patients treated (from May 2013 to December 2014) with Helical IMRT, with a total dose between 24 and 30 Gy, were retrospectively evaluated. Data about dosimetric features, response and acute toxicity were registered and analyzed. Planned target coverage was compared with daily in vivo measures and dose calculation based on volumetric images used for set up evaluation as well.

RESULTS

The patients had a mean measured surface fraction dose ranging from 1.54 Gy up to 2.0 Gy. A planned target dose ranging from 85 to 120% of prescription doses was obtained. All doses to Organs At Risk were within the required constraints. Particular attention was posed on "whole bone marrow" planned V10Gy, V12Gy and V20Gy values, ranging respectively between 23 and 43%, 20.1 and 38% and 9.8 and 24%. A comparison with the theoretical homologous values obtained with TSEBI has shown much lower values with TSEBI. Even if treatment was given in sequence to the skin of the upper and lower hemi-body, all the patients had anaemia, requiring blood transfusions, leukopenia and thrombocytopenia.

CONCLUSION

Based on our limited results TSEBI should still be considered the standard method to treat total skin because of its pattern of acute and late toxicities and the dose distribution. In this particular case the better target coverage obtained with HI can be paid in terms of worse toxicity. Helical IMRT can instead be considered optimal in treating large, convex, cutaneous areas where it is difficult to use multiple electrons fields in relation with the clinical results and the limited and reversible toxicities.

Improving treatment geometries in total skin electron therapy: Experimental investigation of linac angles and floor scatter dose contributions using Cherenkov imaging

PURPOSE

The purpose of this study was to identify the optimal treatment geometry for total skin electron therapy (TSET) using a new optimization metric from Cherenkov image analysis, and to investigate the sensitivity of the Cherenkov imaging method to floor scatter effects in this unique treatment setup.

METHODS

Cherenkov imaging using an intensified charge coupled device (ICCD) was employed to measure the relative surface dose distribution as a 2D image in the total skin electron treatment plane. A 1.2 m × 2.2 m × 1 cm white polyethylene sheet was placed vertically at a source to surface distance (SSD) of 300 cm, and irradiated with 6 MeV high dose rate TSET beams. The linear accelerator coordinate system used stipulates 0° is the bottom of the gantry arc, and progresses counterclockwise so that gantry angle 270° produces a horizontal beam orthogonal to the treatment plane. First, all unique pairs of treatment beams were analyzed to determine the performance of the currently recommended symmetric treatment angles (±20° from the horizontal), compared to treatment geometries unconstrained to upholding gantry angle symmetry. This was performed on two medical linear accelerators (linacs). Second, the extent of the floor scatter contributions to measured surface dose at the extended SSD required for TSET were imaged using three gantry angles of incidence: 270° (horizontal), 253° (-17°), and 240° (-30°). Images of the surface dose profile at each angle were compared to the standard concrete floor when steel plates, polyvinyl chloride (PVC), and solid water were placed on the ground at the base of the treatment plane. Postprocessing of these images allowed for comparison of floor material-based scatter profiles with previously published simulation results.

RESULTS

Analysis of the symmetric treatment geometry (270 ± 20°) and the identified optimal treatment geometry (270 + 23° and 270 - 17°) showed a 16% increase in the 90% isodose area for the latter field pair on the first linac. The optimal asymmetric pair for the second linac (270 + 25° and 270 - 17°) provided a 52% increase in the 90% isodose area when compared to the symmetric geometry. Difference images between Cherenkov images captured with test materials (steel, PVC, and solid water) and the control (concrete floor) demonstrated relative changes in the two-dimensional (2D) dose profile over a 1 × 1.9 m region of interest (ROI) that were consistent with published simulation data. Qualitative observation of the residual images demonstrates localized increases and decreases with respect to the change in floor material and gantry angle. The most significant changes occurred when the beam was most directly impinging the floor (gantry angle 240°, horizontal -30°), where the PVC floor material decreased scatter dose by 1-3% in 7.2% of the total ROI area, and the steel plate increased scatter dose by 1-3% in 7.0% of the total ROI area.

CONCLUSIONS

An updated Cherenkov imaging method identified asymmetric, machine-dependent TSET field angle pairs that provided much larger 90% isodose areas than the commonly adopted symmetric geometry suggested by Task Group 30 Report 23. A novel demonstration of scatter dose Cherenkov imaging in the TSET field was established.

ACPSEM ROSG TBE working group recommendations for quality assurance in total body electron irradiation

The Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) Radiation Oncology Specialty Group (ROSG) formed a series of working groups in 2011 to develop recommendations for guidance of radiation oncology medical physics practice within the Australasian setting. These recommendations are intended to provide guidance for safe work practices and a suitable level of quality control without detailed work instructions. It is the responsibility of the medical physicist to ensure that locally available equipment and procedures are sufficiently sensitive to establish compliance to these recommendations. The recommendations are endorsed by the ROSG, and have been subject to independent expert reviews. For the Australian readers, these recommendations should be read in conjunction with the Tripartite Radiation Oncology Reform Implementation Committee Quality Working Group: Radiation Oncology Practice Standards (2011), and Radiation Oncology Practice Standards Supplementary Guide (2011). This publication presents the recommendations of the ACPSEM ROSG Total Body Electron Irradiation Working Group and has been developed in alignment with other international associations. However, these recommendations should be read in conjunction with relevant national, state or territory legislation and local requirements, which take precedence over the ACPSEM recommendations. It is hoped that the users of this and other ACPSEM recommendations will contribute to the development of future versions through the Radiation Oncology Specialty Group of the ACPSEM. This document serves as a guideline for calibration and quality assurance of equipment used for TBE in Australasia.

Modern radiation therapy for primary cutaneous lymphomas: field and dose guidelines from the International Lymphoma Radiation Oncology Group

Primary cutaneous lymphomas are a heterogeneous group of diseases. They often remain localized, and they generally have a more indolent course and a better prognosis than lymphomas in other locations. They are highly radiosensitive, and radiation therapy is an important part of the treatment, either as the sole treatment or as part of a multimodality approach. Radiation therapy of primary cutaneous lymphomas requires the use of special techniques that form the focus of these guidelines. The International Lymphoma Radiation Oncology Group has developed these guidelines after multinational meetings and analysis of available evidence. The guidelines represent an agreed consensus view of the International Lymphoma Radiation Oncology Group steering committee on the use of radiation therapy in primary cutaneous lymphomas in the modern era.