Total skin electron arc irradiation using a reclined patient position

In-vivo dosimetry in Total Skin Electron Therapy: Literature review

Aim:

Total Skin Electron Therapy (TSET) is a specialised radiotherapy technique to treat cutaneous T-cell lymphomas. The purpose of this article is to review different in-vivo dosimetry techniques and to identify further research direction in TSET

Materials and methods:

Studies focused on in-vivo dosimetry in TSET were included. Studies based on absolute dosimetry in TSET were excluded and no restriction was applied regarding the type of treatment technique and the type of dosimeter.

Result:

From the review of articles, we have found that obesity index and patient position during treatment plays a major role in underdose or overdose in TSET. Many studies favour individualised boost dose to patients. The analysis showed that thermoluminescent dosimeters are the most widely used dosimeters in TSET, and time-consuming is the only drawback in the use of dosimetry.

Conclusion:

Study showed that the practice of using in-vivo dosimetry would be better way to treat TSET by ensuring accuracy of dose delivery to the patients. Further, only limited studies are available for dosimetry with radiochromic films. With this observation, we have started exploring the use of radiochromic film in our TSET dosimetry, and the results can be analysed to standardise the technique in future.

In-vivo dosimetric analysis in total skin electron beam therapy

Background and purpose

Thermoluminescent dosimetry (TLD) is an important element of total skin electron beam therapy (TSEBT). In this study, we compare radiation dose distributions to provide data for dose variation across anatomic sites.

Materials and methods

Retrospectively collected data on 85 patients with cutaneous lymphoma or leukemia underwent TSEBT were reviewed. Patients were irradiated on two linear accelerators, in one of two positions (standing, n = 77; reclined, n = 8) and 1830 in vivo TLD measurements were obtained for various locations on 76 patients.

Results

The TLD results showed that the two TSEBT techniques were dosimetrically heterogeneous. At several sites, the dose administered correlated with height, weight, and gender. After the first TLD measurement, fourteen patients (18%) required MU modification, with a mean 10% reduction (range, −25 to +35). Individual TLD results allowed us to customize the boost treatment for each patient. For patients who were evaluated in the standing position, the most common underdosed sites were the axilla, perineum/perianal folds, and soles (each receiving 69%, 20%, and 34% of the prescribed dose, respectively). For patients evaluated in a reclining position, surface dose distribution was more heterogeneous. The sites underdosed most commonly were the axilla and perineum/perianal folds (receiving less than one third of prescribed dose). Significant variables were detected with model building.

Conclusion

TLD measurements were integral to quality assurance for TSEBT. Dose distribution at several anatomical sites correlated significantly with gender, height, and weight of the treated individual and might be predicted.

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.

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

AIM

To give a technical description and present the dosimetric proporties of the total skin electron beam technique implemented at Heidelberg University Hospital.

BACKGROUND

Techniques used for total skin electron beam irradiation were developed as early as in the 1960s to 1980s and have, since then, hardly changed. However, new measurements of the established methods allow deeper insight into the dose distributions and reasons for possible deviations from uniform dose.

MATERIALS AND METHODS

The TSEI technique applied at Heidelberg University Hospital since 1992 consists of irradiating the patient with a superposition of two beams of low energy electrons at gantry angles of 72° and 108° while he is rotating in a standing position on a turntable at 370 cm distance from the accelerator. The energy of the electron beam is degraded to 3.9 MeV by passing through an attenuator of 6 mm of Perspex. A recent re-measurement of the dose distribution is presented using modern dosimetry tools like a linear array of ionization chambers in combination with established methods like thermoluminescent detectors and film dosimetry.

RESULTS

The measurements show a strong dependence of dose uniformity on details of the setup like gantry angles.

CONCLUSIONS

Dose uniformity of -4/+8% to the majority of the patient's skin can be achieved, however, for the described rotational technique overdoses up to more than 20% in small regions seem unavoidable.

Total skin electron irradiation techniques: a review

Total skin electron irradiation (TSEI) has been employed as one of the methods of mycosis fungoides treatment since the mid-twentieth century. In order to improve the effects and limit the complications following radiotherapy, a number of varieties of the TSEI method, frequently differing in the implementation mode have been developed. The paper provides a systematic review of the different varieties of TSEI. The discussed differences concerned especially: (i) technological requirements and geometric conditions, (ii) the alignment of the patient, (iii) the number of treatment fields, and (iv) dose fractionation scheme.

Matching the dosimetry characteristics of a dual-field Stanford technique to a customized single-field Stanford technique for total skin electron therapy

PURPOSE

To compare the dosimetry characteristics of a customized single-field and a matching dual-field electron beam for total skin electron therapy (TSET) within the framework of the Stanford technique. To examine and quantify its impact on patient dosimetry.

METHODS AND MATERIALS

Two characteristically different electron beams were used for TSET employing the Stanford technique: a single-field beam created from a pencil beam of electrons passing through 7 meters of air and a dual-field beam created from two heavily scattered electron beams directed at oblique angles to patients. The dosimetry characteristics of the two beams were measured by using ionization chambers, radiographic films, and thermal luminescent detectors. The impact of beam characteristic on patient dosimetry was quantified on both anthromorphic phantoms and on patients. Treatment protocols aimed at matching the patient dose between the two systems were established on the basis of these and other measurements.

RESULTS

The dual-field beam was matched to the single-field beam, resulting in approximately the same mean energy (approximately 4.0 MeV) and most probable energy (approximately 4.5 MeV) at their respective treatment source-to-patient-surface distance (SSD). The depth dose curves on the beam axis were nearly identical for both beams. X-ray contamination on the beam axis was 0.43% for the dual-field beam, slightly higher than that (0.4%) of the single-field beam. The beam uniformity, however, was quite different: the dual-field beam was more uniform in the vertical direction but was worse in the lateral direction compared to the single-field beam. For a TSET treatment using the Stanford technique, the composite depth dose curves were nearly identically at the level of beam axis: with an effective depth of maximum buildup (d(max)) at approximately 1 mm below the skin surface and the depth to 80% depth dose at around 6 mm. The overall X-ray contamination was approximately 1.0% and 1.2% for the single-field and dual-field system, respectively. Away from the beam axis level, treatment using either beam was able to deliver over 90% of prescription dose to the main body surfaces. For body surfaces tangential to the beam axis (e.g., top of head and shoulders), the dose was low especially when using the dual-field beam. By adding boost radiation to the tangential surfaces and by adjusting the planned shielding for critical structures, the total dose to the patient over a complete course of TSET treatment could be matched closely for the two systems.

CONCLUSIONS

Although the depth doses can be matched at the level of the beam axis, there exist some characteristic differences in the angular distribution of the electrons between the large SSD single-field beam and the short SSD dual-field beam. These differences resulted in lower dose delivered to "tangential" body surfaces and to body structures that extended farther laterally when using the dual-field beam. However, by adjusting the treatment protocol regarding the boost irradiation and planned shielding, the total dose to patients from a complete course of TSET treatment using the dual-field beam can be matched to that given by the single-field beam. Special attention should be paid to the dosimetry at the "tangential" body surfaces when commissioning a dual-field TSET system.

Mycosis fungoides: radiation therapy

Radiation therapy is the most effective single agent for the treatment of mycosis fungoides. There are well-defined dose-response relationships for achieving a complete response as well as the durability of this response. Techniques of electron beam therapy have been developed that permit treatment of the entire skin. Total-skin electron beam therapy is an important form of management, especially for patients who have thick generalized plaque or tumorous disease. Radiation therapy may also be used selectively for treatment of extracutaneous disease.

Lying-on position of total skin electron therapy

PURPOSE

A technique for whole-body electron therapy with the patient in a lying position has been developed. This technique allows Total Skin Electron Therapy (TSET) for those patients who were previously unable to be treated in a conventional standing position.

METHODS AND MATERIALS

This study was carried out on a Varian 2100C linear accelerator with a 6 MeV high dose rate electron beam. The collimator was open to a width of 36 x 36 cm. There were two main procedures, with six dual-field techniques: 1) two static AP/PA vertical dual fields (VDF): the patient laid on the floor transversely under the collimator when the gantry was in a vertical position. A 0.6 cm acrylic board was placed 15 cm away from the patient, then the gantry was rotated 25 degrees clockwise and counterclockwise to treat the patient in the supine and prone positions, respectively. 2) Four oblique junction fields (OJF): the patient laid on the floor in a prone and supine position parallel to the wave guide at (227 - body thickness x tan 60 degrees) cm away from the vertical axis of the gantry, then the gantry was rotated 60 degrees toward the patient. A 0.6 cm acrylic board was placed 15 cm away from the patient perpendicular to the beam. The patient was move along the field central axis. It allowed the patient's body to be within the 160 cm effective treatment profile. When the patient's body axis move 5 degrees toward the lateral side of the field central axis, we could obtain a better dose distribution in the vertex of the scalp and the soles of the feet. The angle of the VDF was measured by chamber detectors to obtain the effective treatment profile. Likewise, the optimal profile for the OJF was determined by the same procedures. The Rando phantom was used to measure the superficial dose of the body.

RESULTS

The dimension of effective treatment profile for the VDF was 188 x 72 cm at 87% dose level For the OJF, we had to move the patient along the field central axis to obtain the effective treatment profile in a 180 x 85 cm dimension at a 87% dose level. The vertex and sole dose measured in this setup was in the range of 80-88%.

CONCLUSIONS

The empirical data showed that the lying-on position for TSET was technically feasible. The dose distribution in the body surface was also compatible with the Stanford standing technique. The nonambulatory skin malignancy patient can be treated in a comfortable and reproducible position.

Evaluation of dose variation during total skin electron irradiation using thermoluminescent dosimeters

PURPOSE

To determine acceptable dose variation using thermoluminescent dosimeters (TLD) in the treatment of Mycosis Fungoides with total skin electron beam (TSEB) irradiation.

METHODS AND MATERIALS

From 1983 to 1993, 22 patients were treated with total skin electron beam therapy in the standing position. A six-field technique was used to deliver 2 Gy in two days, treating 4 days per week, to a total dose of 35 to 40 Gy using a degraded 9 MeV electron beam. Thermoluminescent dosimeters were placed on several locations of the body and the results recorded. The variations in these readings were analyzed to determine normal dose variation for various body locations during TSEB.

RESULTS

The dose to flat surfaces of the body was essentially the same as the dose to the prescription point. The dose to tangential surfaces was within +/- 10% of the prescription dose, but the readings showed much more variation (up to 24%). Thin areas of the body showed large deviations from the prescription dose along with a large amount of variation in the readings (up to 22%). Special areas of the body, such as the perineum and eyelid, showed large deviations from the prescription dose with very large (up to 40%) variations in the readings.

DISCUSSION

The TLD results of this study will be used as a quality assurance check for all new patients treated with TSEB. The results of the TLDs will be compared with this baseline study to determine if the delivered dose is within acceptable ranges. If the TLD results fall outside the acceptable limits established above, then the patient position can be modified or the technique itself evaluated.

Implementation of total skin electron therapy using an optional high dose rate mode on a conventional linear accelerator

A technique for total skin electron therapy (TSET) has been implemented using a standard accelerator that has been equipped with an optional special procedures mode to permit high dose-rate therapy with a 6-MeV electron beam. Patients are treated in a standing position using dual angled fields at a source to skin distance of 3.6 m. Dosimetric characteristics of the dual field technique were investigated for the 6-MeV beam as well as for a lower energy beam produced by the introduction of an acrylic beam degrader. A treatment stand, which incorporates the degrader in addition to devices used for patient support and shielding, is described. Acceptable beam uniformity and depth dose have been achieved while maintaining a low level of x-ray contamination. Treatment times are reasonably short since the output of the machine in the high-dose-rate mode is 25 Gy/min at the isocenter. Beam uniformity, dose rate, and x-ray contamination are relatively unaffected by the presence of the beam degrader if it is positioned near the treatment plane. The high dose-rate electron option is a useful treatment mode that provides the advantage of reduced treatment times while retaining proper functioning of all accelerator dosimetry systems and interlocks. Use of a dual field technique permits TSET in a treatment room of standard dimensions. The machine is easily set up for treatment, and patient setup is simplified through use of a customized support system.

Cable-induced effects on plane-parallel ionization chamber measurements in large clinical electron beams

The interaction between photon or electron fields and cables of ionization chambers induces the flow of leakage currents affecting the measured signal; this "cable effect" is particularly important when large electron and photon fields are used, i.e., when large portions of cable are irradiated. Therefore it is more interesting to investigate cable-induced effects when ionization chambers are used for clinical situations where large fields are used, for example, total body and total skin electron irradiations (TSEI). In TSEI fields these effects are particularly important. Cable and connector effects using an NE2534 Markus chamber in total skin irradiation conditions with different electron energies (from 1.6 to 4.5 MeV) have been investigated. These effects are significant and show that for TSI dosimetry it is vital to take them into account.

Total scalp treatment of mycosis fungoides: the 4 x 4 technique

PURPOSE

A technique for treating mycosis fungoides confined to the scalp using a method known as the 4 x 4 technique is presented.

METHODS AND MATERIALS

Uniform dose distribution on the scalp and acceptable "hot spots" along five match lines is accomplished by using four sets of four fields (i.e., 4 x 4) on the patient. Precise and reproducible patient and field alignment was accomplished with a solid thermoplastic mask, which is the surface on which match lines are drawn. In-vivo dosimetry (thermoluminescent dosimeters and film) are easily attached to the mask which also provides a portion of the 7 mm bolus used to shift the characteristic 6 MeV electron depth dose toward the skin surface.

RESULTS

In-vivo dosimetry demonstrated that single fraction match line doses are within 25% to 30% of central axis dose. Shifting these match lines to four locations reduces these "hot spots" to satisfactory levels (less than 120%). Three patients have been treated with this technique and each patient continues to have a complete clinical response at 14 to 21 months post treatment. In addition, each patient has excellent cosmetic results with no evidence of acute or chronic side effects at the match lines.

CONCLUSION

The 4 x 4 technique has proven to be useful in the treatment of mycosis fungoides confined to the scalp.

Total skin electron therapy: a technique which can be implemented on a conventional electron linear accelerator

PURPOSE

A technique for treating whole-body skin with an electron linear accelerator with nominal energies in the range 4-8 MeV is presented. Stationary fields at an extended source-skin distance are used with the patient treated in a reclined position.

METHODS AND MATERIALS

The relative beam data, absolute dosimetry measurements and the patient setup parameters are presented. The calculations required to correct for patient size are discussed.

RESULTS

The technique described uses a six field circumferential cycle, with longitudinally matched fields along the length of the patient. Treatment times are reasonable using the standard dose rate of the machine. The uniformity of the skin dose measured on three patients was found to be comparable to that of other total skin treatment techniques.

CONCLUSION

A technique for treating conditions like mycosis fungoides is presented requiring relatively simple supporting dosimetry. No modifications to the unit are required and no sophisticated treatment apparatus is necessary, which makes the technique attractive to smaller Institutions, especially in developing countries, where technical support may be limited.