Guidelines by the AAPM and GEC-ESTRO on the use of innovative brachytherapy devices and applications: Report of Task Group 167

Although a multicenter, Phase III, prospective, randomized trial is the gold standard for evidence-based medicine, it is rarely used in the evaluation of innovative devices because of many practical and ethical reasons. It is usually sufficient to compare the dose distributions and dose rates for determining the equivalence of the innovative treatment modality to an existing one. Thus, quantitative evaluation of the dosimetric characteristics of innovative radiotherapy devices or applications is a critical part in which physicists should be actively involved. The physicist's role, along with physician colleagues, in this process is highlighted for innovative brachytherapy devices and applications and includes evaluation of (1) dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use, (2) risks and benefits from a regulatory and safety perspective, and (3) resource assessment and preparedness. Further, it is suggested that any developed calibration methods be traceable to a primary standards dosimetry laboratory (PSDL) such as the National Institute of Standards and Technology in the U.S. or to other PSDLs located elsewhere such as in Europe. Clinical users should follow standards as approved by their country's regulatory agencies that approved such a brachytherapy device. Integration of this system into the medical source calibration infrastructure of secondary standard dosimetry laboratories such as the Accredited Dosimetry Calibration Laboratories in the U.S. is encouraged before a source is introduced into widespread routine clinical use. The American Association of Physicists in Medicine and the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) have developed guidelines for the safe and consistent application of brachytherapy using innovative devices and applications. The current report covers regulatory approvals, calibration, dose calculations, radiobiological issues, and overall safety concerns that should be addressed during the commissioning stage preceding clinical use. These guidelines are based on review of requirements of the U.S. Nuclear Regulatory Commission, U.S. Department of Transportation, International Electrotechnical Commission Medical Electrical Equipment Standard 60601, U.S. Food and Drug Administration, European Commission for CE Marking (Conformité Européenne), and institutional review boards and radiation safety committees.

Review of clinical brachytherapy uncertainties: analysis guidelines of GEC-ESTRO and the AAPM

Background and purpose

A substantial reduction of uncertainties in clinical brachytherapy should result in improved outcome in terms of increased local control and reduced side effects. Types of uncertainties have to be identified, grouped, and quantified.

Methods

A detailed literature review was performed to identify uncertainty components and their relative importance to the combined overall uncertainty.

Results

Very few components (e.g., source strength and afterloader timer) are independent of clinical disease site and location of administered dose. While the influence of medium on dose calculation can be substantial for low energy sources or non-deeply seated implants, the influence of medium is of minor importance for high-energy sources in the pelvic region. The level of uncertainties due to target, organ, applicator, and/or source movement in relation to the geometry assumed for treatment planning is highly dependent on fractionation and the level of image guided adaptive treatment. Most studies to date report the results in a manner that allows no direct reproduction and further comparison with other studies. Often, no distinction is made between variations, uncertainties, and errors or mistakes. The literature review facilitated the drafting of recommendations for uniform uncertainty reporting in clinical BT, which are also provided. The recommended comprehensive uncertainty investigations are key to obtain a general impression of uncertainties, and may help to identify elements of the brachytherapy treatment process that need improvement in terms of diminishing their dosimetric uncertainties. It is recommended to present data on the analyzed parameters (distance shifts, volume changes, source or applicator position, etc.), and also their influence on absorbed dose for clinically-relevant dose parameters (e.g., target parameters such as D₉₀ or OAR doses). Publications on brachytherapy should include a statement of total dose uncertainty for the entire treatment course, taking into account the fractionation schedule and level of image guidance for adaptation.

Conclusions

This report on brachytherapy clinical uncertainties represents a working project developed by the Brachytherapy Physics Quality Assurances System (BRAPHYQS) subcommittee to the Physics Committee within GEC-ESTRO. Further, this report has been reviewed and approved by the American Association of Physicists in Medicine.

A dosimetric uncertainty analysis for photon-emitting brachytherapy sources: report of AAPM Task Group No. 138 and GEC-ESTRO

This report addresses uncertainties pertaining to brachytherapy single-source dosimetry preceding clinical use. The International Organization for Standardization (ISO) Guide to the Expression of Uncertainty in Measurement (GUM) and the National Institute of Standards and Technology (NIST) Technical Note 1297 are taken as reference standards for uncertainty formalism. Uncertainties in using detectors to measure or utilizing Monte Carlo methods to estimate brachytherapy dose distributions are provided with discussion of the components intrinsic to the overall dosimetric assessment. Uncertainties provided are based on published observations and cited when available. The uncertainty propagation from the primary calibration standard through transfer to the clinic for air-kerma strength is covered first. Uncertainties in each of the brachytherapy dosimetry parameters of the TG-43 formalism are then explored, ending with transfer to the clinic and recommended approaches. Dosimetric uncertainties during treatment delivery are considered briefly but are not included in the detailed analysis. For low- and high-energy brachytherapy sources of low dose rate and high dose rate, a combined dosimetric uncertainty <5% (k=1) is estimated, which is consistent with prior literature estimates. Recommendations are provided for clinical medical physicists, dosimetry investigators, and source and treatment planning system manufacturers. These recommendations include the use of the GUM and NIST reports, a requirement of constancy of manufacturer source design, dosimetry investigator guidelines, provision of the lowest uncertainty for patient treatment dosimetry, and the establishment of an action level based on dosimetric uncertainty. These recommendations reflect the guidance of the American Association of Physicists in Medicine (AAPM) and the Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology (GEC-ESTRO) for their members and may also be used as guidance to manufacturers and regulatory agencies in developing good manufacturing practices for sources used in routine clinical treatments.

Radiation transmission data for radionuclides and materials relevant to brachytherapy facility shielding

To address the limited availability of radiation shielding data for brachytherapy as well as some disparity in existing data, Monte Carlo simulation was used to generate radiation transmission data for 60Co, 137CS, 198Au, 192Ir 169Yb, 170Tm, 131Cs, 125I, and 103pd photons through concrete, stainless steel, lead, as well as lead glass and baryte concrete. Results accounting for the oblique incidence of radiation to the barrier, spectral variation with barrier thickness, and broad beam conditions in a realistic geometry are compared to corresponding data in the literature in terms of the half value layer (HVL) and tenth value layer (TVL) indices. It is also shown that radiation shielding calculations using HVL or TVL values could overestimate or underestimate the barrier thickness required to achieve a certain reduction in radiation transmission. This questions the use of HVL or TVL indices instead of the actual transmission data. Therefore, a three-parameter model is fitted to results of this work to facilitate accurate and simple radiation shielding calculations.

Development of a TLD mailed system for remote dosimetry audit for 192Ir HDR and PDR sources

BACKGROUND AND PURPOSE

In the framework of an ESTRO ESQUIRE project, the BRAPHYQS Physics Network and the EQUAL-ESTRO laboratory have developed a procedure for checking the absorbed dose to water in the vicinity of HDR or PDR sources using a mailed TLD system. The methodology and the materials used in the procedure are based on the existing EQUAL-ESTRO external radiotherapy dose checks.

MATERIALS AND METHODS

A phantom for TLD postal dose assurance service, adapted to accept catheters from different HDR afterloaders, has been developed. The phantom consists of three PMMA tubes supporting catheters placed at 120 degrees around a central TLD holder. A study on the use of LiF powder type DTL 937 (Philitech) has been performed in order to establish the TLD calibration in dose-to-water at a given distance from (192)Ir source, as well as to determine all correction factors to convert the TLD reading into absorbed dose to water. The dosimetric audit is based on the comparison between the dose to water measured with the TL dosimeter and the dose calculated by the clinical TPS. Results of the audits are classified in four different levels depending on the ratio of the measured dose to the stated dose. The total uncertainty budget in the measurement of the absorbed dose to water using TLD near an (192)Ir HDR source, including TLD reading, correction factors and TLD calibration coefficient, is determined as 3.27% (1s).

RESULTS

To validate the procedures, the external audit was first tested among the members of the BRAPHYQS Network. Since November 2004, the test has been made available for use by all European brachytherapy centres. To date, 11 centres have participated in the checks and the results obtained are very encouraging. Nevertheless, one error detected has shown the usefulness of this audit.

CONCLUSION

A method of absorbed dose to water determination in the vicinity of an (192)Ir brachytherapy source was developed for the purpose of a mailed TL dosimetry system. The accuracy of the procedure was determined. This method allows a check of the whole dosimetry chain for this type of brachytherapy afterloading system and can easily be performed by mail to any institution in the European area and elsewhere. Such an external audit can be an efficient QC method complementary to internal quality control as it can reveal some errors which are not observable by other means.

Quality Assurance in the EORTC Randomized Trial 22922/10925 Investigating the Role of Irradiation of the Internal Mammary and Medial Supraclavicular Lymph Node Chain Works

BACKGROUND AND PURPOSE

A quality assurance (QA) program in conjunction with the EORTC trial investigating the role of adjuvant internal mammary and medial supraclavicular irradiation in stage I-III breast cancer is presented. The results of a dummy run procedure and of an individual case review are compared to each other. The effects of recommendations based on QA procedures on the protocol compliance are evaluated.

MATERIAL AND METHODS

Prior to protocol activation all participating institutes were asked to produce treatment plans according to the guidelines of the protocol based on manual outlines of an average patient. Thereafter, they were asked to provide data on each of their first six randomized patients.

RESULTS

The dummy run provided a lot of information on specific treatment techniques. In the individual case review, additional patient- and tumor-related data were collected, showing the use of anatomic information for treatment planning. A comparison between both procedures revealed that the individual case reports concurred more accurately with protocol guidelines than the dummy run.

CONCLUSION

It was observed that the number of systematic protocol deviations was substantially decreased in trial patients compared to the dummy run case. Therefore, it is concluded that this extensive QA program had a positive effect on the consistency of all institutes participating in the trial.

The EQUAL-ESTRO audit on geometric reconstruction techniques in brachytherapy

BACKGROUND AND PURPOSE

A geometric check procedure of the reconstruction techniques used in brachytherapy treatment planning systems was developed by the EQUAL (European Quality Laboratory) Laboratory in the framework of the ESTRO's (European Society for Therapeutic Radiology and Oncology) project 'ESQUIRE' (Education Science and QUality assurance In Radiotherapy in Europe [Baumann M, Brada M. Towards equity in turbulent Europe ESTRO, European cooperation and the European Commission. Radiother Oncol 2005;75:251-2. Heeren G. The bright but ephemeral life of a rainbow. A chronical of seventeen years of intensive ESTRO-EU cooperation. Radiother Oncol 2005;75:253-7]) by the task group Braphyqs (Brachytherapy physics quality system).

PATIENTS AND METHODS

The check is performed by using the so-called 'Baltas' phantom, mailed to the participating centres in order to check the local technique of geometric reconstruction used in dose calculation.

RESULTS

To validate the procedures, the check was first tested among the members of the Braphyqs Network. Since November 2002, the system is open to other centres. Until now 152 reconstructions have been checked. Eighty-six percent of the results were within an acceptance level after the first check. For the remaining 14%, a second check has been proposed. The results of the re-checks are in most cases within an acceptance level, except for 2% of the reconstructions.

CONCLUSIONS

The geometric check is available from the EQUAL Laboratory for all the brachytherapy centres. The decrease of the deviations observed between the two checks demonstrates the importance of this kind of external audit as some errors were revealed, which were not discovered before with techniques used in clinical quality control routines.

Quality control of brachytherapy equipment in the Netherlands and Belgium: current practice and minimum requirements

BACKGROUND AND PURPOSE

Brachytherapy is applied in 39 radiotherapy institutions in The Netherlands and Belgium. Each institution has its own quality control (QC) programme to ensure safe and accurate dose delivery to the patient. The main goal of this work is to gain insight into the current practice of QC of brachytherapy in The Netherlands and Belgium and to reduce possible variations in test frequencies and tolerances by formulating a set of minimum QC-requirements.

MATERIALS AND METHODS

An extensive questionnaire about QC of brachytherapy was distributed to and completed by the 39 radiotherapy institutions. A separate smaller questionnaire was sent to nine institutions performing intracoronary brachytherapy. The questions were related to safety systems, physical irradiation parameters and total time spent on QC. The results of the questionnaires were compared with recommendations given in international brachytherapy QC reports.

RESULTS

The answers to the questionnaires showed large variations in test frequencies and test methods. Furthermore, large variations in time spent on QC exist, which is mainly due to differences in QC-philosophy and differences in the available resources.

CONCLUSIONS

Based on the results of the questionnaires and the comparison with the international recommendations, a set of minimum requirements for QC of brachytherapy has been formulated. These guidelines will be implemented in the radiotherapy institutions in The Netherlands and Belgium.