Recommendations of the American Association of Physicists in Medicine regarding the impact of implementing the 2004 task group 43 report on dose specification for 103Pd and 125I interstitial brachytherapy

Patient-specific dose correction for prostate postimplant evaluation with flexible timing of postimplant imaging

PURPOSE

The dosimetric effect of edema on prostate implants have long been realized, but large uncertainties still exist in the estimation of dose actually received by the prostate. This study attempted to develop a new method to accurately estimate dose delivered to the prostate accounting for the variation of prostate volume and seed distribution, edema half-lives, and times for postimplant evaluation.

METHODS AND MATERIALS

A series of prostate seed implants for Cs-131, Pd-103, and I-125 with various prostate volumes were simulated in a water phantom using the TG-43 algorithm on the Varian Eclipse treatment planning system. Dose analysis was performed to derive a quantitative relationship between the prostate peripheral dose and the prostate radius with the variation of prostate volume and seed distribution. Using this relationship to calculate dynamically, the total dose accumulated in the prostate (D_T ) accounting for the variation of prostate volume and seed distribution and edema half-lives. Moreover, the total dose can be estimated statically based on the prostate volume that can be determined in a computerized tomography (CT) image taken at a time after implantation. The statically estimated total dose (D_CT ) was compared with D_T to determine optimal imaging times as well as dose correction factors for other imaging times.

RESULTS

An inverse power law was established between the prostate peripheral dose and prostate radius. The value of the power was 1.3 for Cs-131 and I-125, and 1.5 for Pd-103, respectively. D_T was derived dynamically using the inverse power law. Given the edema half-lives, T_E , of 4, 9.3, and 25 days and the volume expansion of 1.1 and 2.0 times of the prostate without edema, the optimal times for postimplant imaging were: 7, 9, and 16 days for T_E  = 4 days; 10, 14, and 28 days for T_E  = 9.3 days; and 12, 19, 45 days T_E  = 25 days, for Cs-131, Pd-103, and I-125, respectively. D_CT calculated using the prostate volume determined on the optimal days agreed with D_T to 0.0%-1.8% and within 0.3% for most cases. For various prostate volumes, edema half-lives, and nonoptimal times, D_CT was able to achieve a 1% accuracy.

CONCLUSION

The postimplant dose calculation based on the proposed inverse power law for prostate seed implants with edema has improved the accuracy of postimplant dosimetry with accurate and patient-specific dose corrections accounting for prostate size, edema half-life, and postimplant imaging times. Optimal times for postimplant imaging have been accurately determined, and the high accuracy of postimplant dose calculation can be achieved for both optimal imaging times and nonoptimal imaging times.

Re-Irradiation for Recurrent Cervical Cancer: A State-of-the-Art Review

The recurrence rate of cervical cancer after primary treatment can reach 60%, and a poor prognosis is reported in most cases. Treatment options for the recurrence of cervical cancer mainly depend on the prior treatment regimen and the location of recurrent lesions. Re-irradiation is still considered as a clinical challenge, owing to a high incidence of toxicity, especially in in-field recurrence within a short period of time. Recent advances in radiotherapy have preliminarily revealed encouraging outcomes of re-irradiation. Several centers have concentrasted on stereotactic body radiation therapy (SBRT) for the treatment of well-selected cases. Meanwhile, as the image-guiding techniques become more precise, a better dose profile can also be achieved in brachytherapy, including high-dose-rate interstitial brachytherapy (HDR-ISBT) and permanent radioactive seed implantation (PRSI). These treatment modalities have shown promising efficacy with a tolerable toxicity, providing further treatment options for recurrent cervical cancer. However, it is highly unlikely to draw a definite conclusion from all of those studies due to the large heterogeneity among them and the lack of large-scale prospective studies. This study mainly reviews and summarizes the progress of re-irradiation for recurrent cervical cancer in recent years, in order to provide potential treatment regimens for the management of re-irradiation.

Acute and late side-effects after low dose-rate brachytherapy for prostate cancer; incidence, management and technical considerations

PURPOSE

To review common reported side effects and complications after primary LDR-BT (monotherapy) and discuss some of the technical aspects that could impact the treatment outcomes.

METHODS AND MATERIALS

A literature search was undertaken using medical subject headings (MeSH) complemented by the authors' personal and institutional expertise.

RESULTS

The reported incidence of acute and late grade 2 or above urinary, bowel and sexual side effects is very variable across the literature. The learning curve and the implant quality have a clear impact on the toxicity outcomes. Being aware of some of the technical challenges encountered during the procedure and ways to mitigate them could decrease the incidence of side effects. Careful planning of seed placement and seed deposition allow sparing of the organs at risk and a lower incidence of urinary and gastro-intestinal toxicity.

CONCLUSIONS

Low dose-rate brachytherapy remains a standard monotherapy treatment in the setting of favorable-risk prostate cancer. High disease control and low long-term toxicities are achievable in expert hands with a good technique.

Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry

The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.

Dose perturbation and inhomogeneity of multi-arrays of 125I seed-loaded stent for treatment of portal vein tumor thrombosis

PURPOSE

To investigate the dosimetry of ¹²⁵I seed-loaded stent system currently used for an adjuvant treatment of portal vein tumor thrombosis (PVTT).

METHODS

The stent system consisted of an inner metallic stent and outer seed-loaded capsules. Four arrays of ¹²⁵I seeds were attached longitudinally to the outer surface of the stent at 90° separation. 145 Gy was prescribed at 5 mm from the axes of seed-arrays. For the geometries of the 4-array, and potential 6- and 8-array configurations, treatment planning system (TPS) and Monte Carlo (MC) calculations were performed to evaluate 3D dose distributions and dosimetric impact of the metallic stent.

RESULTS

The MC simulations indicated the metallic stent reduced a dose to the prescription points by over 10%, compared to the water-based TPS results. The total activity calculated by the water-based TPS to deliver the prescription dose should compensate for this amount of reduction. The MC- and TPS-calculated doses normalized to the prescription points for the current configuration were in agreements within 4.3% on a cylindrical surface along 5 mm from the axes of seed-arrays. The longitudinal underdosage worsened as approaching the edge of arrays, and ranged from 2.8% to 25.5%. The angular underdosage between neighboring arrays was 2.1%-8.9%.

CONCLUSIONS

With this compensation and a special care of near-edge underdosage, the current 4-array system can provide adequate dose coverage for treatment of PVTT. Further dosimetric homogeneity can be achieved using 6-or 8-array configurations.

CT-guided 125I brachytherapy for recurrent ovarian cancer

This retrospective study was to evaluate the local control and survival of ¹²⁵I brachytherapy for recurrent ovarian cancer. 52 ¹²⁵I brachytherapy procedures were performed in 47 patients with 51 recurrent ovarian cancer lesions. The follow-up period was 1-55 months (median 12 months). The local control rate (LC) of 3, 6, 12, 24 and 36 months was 93.3%, 77.7%, 58.9%, 38.7% and 19.3%, respectively. Patients with tumor size ≤ 4cm (85.7% vs 40.0%, P = 0.037) and actual D90 between 110 to 130Gy (47.4% vs 66.7% vs 62.5%, P = 0.029) had better LC. The 1, 2 and 3 years of overall survival (OS) was 79.3%, 63.0% and 52.5%, respectively. The poor performance status (HR 3.821, 95% CI 1.383-10.555; P = 0.010), concurrent distant metastasis (HR 9.222, 95% CI 1.710-49.737; P = 0.010) and large postoperative residual tumor size (HR 6.157, 95% CI 1.438-26.367; P = 0.014) were closely correlated with a poor OS. Our data indicate thatCT-guided ¹²⁵I brachytherapy is an effective and safe modality for the local treatment of recurrent ovarian cancer.

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.

An endoscopic ultrasonography-guided interstitial brachytherapy based special treatment-planning system for unresectable pancreatic cancer

EUS-guided interstitial brachytherapy is promising in the treatment of unresectable malignant carcinoma adjacent to the digestive tract. The feasible treatment plan is not established. Thus, our study aimed to develop a novel treatment plan and evaluate the feasibility in patients with unresectable pancreatic cancer. A total of 42 patients with unresectable pancreatic cancer (stage III: n = 18; stage IV: n = 24) were retrospectively included. A special treatment-planning system (TPS) for EUS was designed and evaluated by comparing with the traditional TPS. The patients underwent EUS-guided interstitial brachytherapy based on the new software. In the test model, there was no obvious difference of irradiation doses calculated by the two softwares (EUS TPS vs. traditional TPS) (P > 0.05). Under the support of EUS TPS, a novel treatment plan for EUS-guided interstitial brachytherapy was successfully established, which contained seven principles. All patients tolerated the treatment well without any serious complications. In 15 patients (stage III) whose minimal peripheral dose was larger than 90 Gy, partial remission rate was 80% (12/15). Twelve patients (12/18) in stage III were alive for over 12 months with a median peripheral dose of 107.5 Gy. The expected median survival time of the 42 patients was 9.0 months (95%CI 7.6-10.4 months). The results demonstrated that the new EUS TPS will play an important role in EUS-guided interstitial brachytherapy in patients with unresectable pancreatic malignant cancer.

Development of a brachytherapy audit checklist tool

PURPOSE

To develop a brachytherapy audit checklist that could be used to prepare for Nuclear Regulatory Commission or agreement state inspections, to aid in readiness for a practice accreditation visit, or to be used as an annual internal audit tool.

METHODS AND MATERIALS

Six board-certified medical physicists and one radiation oncologist conducted a thorough review of brachytherapy-related literature and practice guidelines published by professional organizations and federal regulations. The team members worked at two facilities that are part of a large, academic health care center. Checklist items were given a score based on their judged importance. Four clinical sites performed an audit of their program using the checklist. The sites were asked to score each item based on a defined severity scale for their noncompliance, and final audit scores were tallied by summing the products of importance score and severity score for each item.

RESULTS

The final audit checklist, which is available online, contains 83 items. The audit scores from the beta sites ranged from 17 to 71 (out of 690) and identified a total of 7-16 noncompliance items. The total time to conduct the audit ranged from 1.5 to 5 hours.

CONCLUSIONS

A comprehensive audit checklist was developed which can be implemented by any facility that wishes to perform a program audit in support of their own brachytherapy program. The checklist is designed to allow users to identify areas of noncompliance and to prioritize how these items are addressed to minimize deviations from nationally-recognized standards.

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.

Salvage Low-Dose-Rate Brachytherapy for Prostate Cancer Local Recurrence after Radical Prostatectomy: Our First three Patients

Purpose of the Study

To present our initial experience with brachytherapy (BT) as a primary salvage procedure for the treatment of prostate cancer (PCa) local recurrence following radical retropubic prostatectomy (RRP).

Methods

From December 2009 to May 2010, three patients underwent salvage BT due to local recurrences of high risk PCa after extrafascial RRP without additional adjuvant therapies. Local recurrence was confirmed by prostate biopsy and the relapse was well defined by endorectal ultrasonography and magnetic resonance imaging. Metastatic screening was negative. The patients were followed-up according to the American Brachytherapy Society guidelines.

Results

The median dose delivered to 90% of the local relapse (D90) was 115 Gy. The three patients reached a prostate specific antigen (PSA) nadir value within the first year that remained stable at a mean follow-up of 32 months. As regards morbidity, moderate de novo urgency was reported by only one patient.

Conclusions

We think that our data confirms the feasibility and safety of salvage BT as a possible alternative option to external beam radiotherapy (EBRT) for the treatment of locally recurrent PCa in selected patients when performed by experienced centers. However, larger series of patients with longer follow-ups are needed to define the oncologic role of this procedure.

Dosimetry of (125)I and (103)Pd COMS eye plaques for intraocular tumors: report of Task Group 129 by the AAPM and ABS

Dosimetry of eye plaques for ocular tumors presents unique challenges in brachytherapy. The challenges in accurate dosimetry are in part related to the steep dose gradient in the tumor and critical structures that are within millimeters of radioactive sources. In most clinical applications, calculations of dose distributions around eye plaques assume a homogenous water medium and full scatter conditions. Recent Monte Carlo (MC)-based eye-plaque dosimetry simulations have demonstrated that the perturbation effects of heterogeneous materials in eye plaques, including the gold-alloy backing and Silastic insert, can be calculated with reasonable accuracy. Even additional levels of complexity introduced through the use of gold foil "seed-guides" and custom-designed plaques can be calculated accurately using modern MC techniques. Simulations accounting for the aforementioned complexities indicate dose discrepancies exceeding a factor of ten to selected critical structures compared to conventional dose calculations. Task Group 129 was formed to review the literature; re-examine the current dosimetry calculation formalism; and make recommendations for eye-plaque dosimetry, including evaluation of brachytherapy source dosimetry parameters and heterogeneity correction factors. A literature review identified modern assessments of dose calculations for Collaborative Ocular Melanoma Study (COMS) design plaques, including MC analyses and an intercomparison of treatment planning systems (TPS) detailing differences between homogeneous and heterogeneous plaque calculations using the American Association of Physicists in Medicine (AAPM) TG-43U1 brachytherapy dosimetry formalism and MC techniques. This review identified that a commonly used prescription dose of 85 Gy at 5 mm depth in homogeneous medium delivers about 75 Gy and 69 Gy at the same 5 mm depth for specific (125)I and (103)Pd sources, respectively, when accounting for COMS plaque heterogeneities. Thus, the adoption of heterogeneous dose calculation methods in clinical practice would result in dose differences >10% and warrant a careful evaluation of the corresponding changes in prescription doses. Doses to normal ocular structures vary with choice of radionuclide, plaque location, and prescription depth, such that further dosimetric evaluations of the adoption of MC-based dosimetry methods are needed. The AAPM and American Brachytherapy Society (ABS) recommend that clinical medical physicists should make concurrent estimates of heterogeneity-corrected delivered dose using the information in this report's tables to prepare for brachytherapy TPS that can account for material heterogeneities and for a transition to heterogeneity-corrected prescriptive goals. It is recommended that brachytherapy TPS vendors include material heterogeneity corrections in their systems and take steps to integrate planned plaque localization and image guidance. In the interim, before the availability of commercial MC-based brachytherapy TPS, it is recommended that clinical medical physicists use the line-source approximation in homogeneous water medium and the 2D AAPM TG-43U1 dosimetry formalism and brachytherapy source dosimetry parameter datasets for treatment planning calculations. Furthermore, this report includes quality management program recommendations for eye-plaque brachytherapy.

Stereotactic iodine-125 brachytherapy for brain tumors: temporary versus permanent implantation

Stereotactic brachytherapy (SBT) has been described in several publications as an effective, minimal invasive and safe highly focal treatment option in selected patients with well circumscribed brain tumors <4 cm. However, a still ongoing discussion about indications and technique is hindering the definition of a clear legitimation of SBT in modern brain tumor treatment. These controversies encompass the question of how intense the irradiation should be delivered into the target volume (dose rate). For instance, reports about the use of high does rate (HDR) implantation schemes (>40 cGy/h) in combination with adjuvant external beam radiation and/or chemotherapy for the treatment of malignant gliomas and metastases resulted in increased rates of radiation induced adverse tissue changes requiring surgical intervention. Vice versa, such effects have been only minimally observed in numerous studies applying low dose rate (LDR) regiments (3-8 cGy/h) for low grade gliomas, metastases and other rare indications. Besides these observations, there are, however, no data available directly comparing the long term incidences of tissue changes after HDR and LDR and there is, furthermore, no evidence regarding a difference between temporary or permanent LDR implantation schemes. Thus, recommendations for effective and safe implantation schemes have to be investigated and compared in future studies.

The correlation between annular treatment margins and biochemical failure in prostate brachytherapy patients with optimized intraprostatic dosimetry

PURPOSE

To determine whether periprostatic treatment margins correlate with biochemical control in prostate brachytherapy patients with optimized intraprostatic dosimetry.

METHODS AND MATERIALS

Nineteen biochemically failed brachytherapy patients were matched to 74 dosimetric and clinically equivalent nonfailures. The median followup time for the entire study population was 9.4 years. Eligibility requirements included a Day 0 intraprostatic D(90) of 100% or greater and V(100) of 90% or greater, absence of androgen deprivation therapy, and no evidence of distant metastasis in biochemically failed patients. A 5-mm annulus was constructed around the perimeter of each prostate. D(90) and V(100) at the anterior, posterior, superior, inferior, right lateral, and left lateral aspects of the annulus were evaluated for patients with biochemically controlled and failed disease. Biochemical progression-free survival (bPFS) was defined as a prostate-specific antigen level of 0.40ng/mL or less after nadir. D(90) and V(100) parameters were compared between the controlled and failed groups using logistic regression. Predictors of biochemical failure were identified using Cox regression.

RESULTS

No statistically significant differences in prostate-specific antigen level, Gleason score, percent positive biopsies, or intraprostatic dosimetry were observed between the controlled and failed patients. The D(90) and V(100) at the anterior, posterior, superior, inferior, right lateral, and left lateral aspects of the annulus were not statistically different between biochemically controlled and failed groups.

CONCLUSION

In this study, there was no relationship observed between annular dosimetry and biochemical control. It is unlikely that further radial dose intensification would have altered treatment outcome in this population of patients with optimized intraprostatic dosimetry.

A detailed radiobiological and dosimetric analysis of biochemical outcomes in a case-control study of permanent prostate brachytherapy patients

The purpose of this study is to determine dosimetric and radiobiological predictors of biochemical control after recalculation of prostate implant dosimetry using updated AAPM Task Group 43 (TG-43) parameters and the radiobiological parameters recommended by TG-137. All biochemical failures among patients implanted with 125I Or 103Pd sources between 1994 and March 2006 were matched 2:1 with nonfailure controls. The individual matching was by risk group, radionuclide, prescribed dose, and time of implant (one match before and one after the failed patient) resulting in a median follow-up of 10.9 years. Complete dose volume histogram (DVH) data were recalculated for all 55 cases and 110 controls after updating the original source strength by the retrospectively determined ratios of TG-43. Differential DVH data were acquired in 179 increments of prostate volume versus percentage prescribed dose. At each incremental dose level i, the biologically equivalent dose BEDi, equivalent uniform dose EUDi, and tumor control probability TCPi were calculated from the implant dose plus any external beam delivered to the patient. Total BED, EUD, and TCP were then derived from the incremental values for comparison with single point dosimetric quality parameters and DVH-based averages. There was no significant difference between failures and controls in terms of total BED (143 vs 142 Gy), EUD (95 vs 94 Gy), or TCP (0.87 vs 0.89). Conditional logistic regression analysis factored out the matching variables and stratified the cohort into each case and its controls, but no radiobiological parameter was predictive of biochemical failure. However, there was a significant difference between radiobiological parameters of 125I and 103Pd due to less complete coverage of the target volume by the former isotope. The implant BED and TCP were highly correlated with the D90 and natural prescription doses and a series of mean DVH-based doses such as the harmonic mean and expressions of the generalized EUD. In this case-control study of prostate brachytherapy biochemical failures and nonfailures, there were no radiobiological parameters derived from detailed DVH-based analysis that predicted for biochemical control. This may indicate that in our approach, implant dosimetry is at or near the limits of clinically effective dose escalation.

Dosimetry of 125I radioactive seed implantation in therapy for hepatocellular carcinoma

Radioactive seed implantation, especially ¹²⁵I seeds implantation, which has provided an effective method for treatment of hepatocellular carcimoma (HCC), is attracting more and more attention all over the world, but its dosimetry need standardizing. Therefore, it is necessary to perform the prospective study on the dosimetry of ¹²⁵I radioactive seed implantation and seek for the best dosage and seed activity in order to enhance the therapeutic efficacy of ¹²⁵I seeds implantation in HCC treatment and protect the normal tissues surrounding the tumors.

Anniversary paper: fifty years of AAPM involvement in radiation dosimetry

This article reviews the involvement of the AAPM in various aspects of radiation dosimetry over its 50 year history, emphasizing the especially important role that external beam dosimetry played in the early formation of the organization. Topics covered include the AAPM's involvement with external beam and x-ray dosimetry protocols, brachytherapy dosimetry, primary standards laboratories, accredited dosimetry chains, and audits for machine calibrations through the Radiological Physics Center.

Challenges in credentialing institutions and participants in advanced technology multi-institutional clinical trials

The Radiological Physics Center (RPC) has functioned continuously for 38 years to assure the National Cancer Institute and the cooperative groups that institutions participating in multi-institutional trials can be expected to deliver radiation treatments that are clinically comparable to those delivered by other institutions in the cooperative groups. To accomplish this, the RPC monitors the machine output, the dosimetry data used by the institutions, the calculation algorithms used for treatment planning, and the institutions' quality control procedures. The methods of monitoring include on-site dosimetry review by an RPC physicist and a variety of remote audit tools. The introduction of advanced technology clinical trials has prompted several study groups to require participating institutions and personnel to become credentialed, to ensure their familiarity and capability with techniques such as three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic body radiotherapy, and brachytherapy. The RPC conducts a variety of credentialing activities, beginning with questionnaires to evaluate an institution's understanding of the protocol and their capabilities. Treatment-planning benchmarks are used to allow the institution to demonstrate their planning ability and to facilitate a review of the accuracy of treatment-planning systems under relevant conditions. The RPC also provides mailable anthropomorphic phantoms to verify tumor dose delivery for special treatment techniques. While conducting these reviews, the RPC has amassed a large amount of data describing the dosimetry at participating institutions. Representative data from the monitoring programs are discussed, and examples are presented of specific instances in which the RPC contributed to the discovery and resolution of dosimetry errors.

Current brachytherapy quality assurance guidance: does it meet the challenges of emerging image-guided technologies?

In the past decade, brachytherapy has shifted from the traditional surgical paradigm to more modern three-dimensional image-based planning and delivery approaches. The role of intraoperative and multimodality image-based planning is growing. Published American Association of Physicists in Medicine, American College of Radiology, European Society for Therapeutic Radiology and Oncology, and International Atomic Energy Agency quality assurance (QA) guidelines largely emphasize the QA of planning and delivery devices rather than processes. These protocols have been designed to verify compliance with major performance specifications and are not risk based. With some exceptions, complete and clinically practical guidance exists for sources, QA instrumentation, non-image-based planning systems, applicators, remote afterloading systems, dosimetry, and calibration. Updated guidance is needed for intraoperative imaging systems and image-based planning systems. For non-image-based brachytherapy, the American Association of Physicists in Medicine Task Group reports 56 and 59 provide reasonable guidance on procedure-specific process flow and QA. However, improved guidance is needed even for established procedures such as ultrasound-guided prostate implants. Adaptive replanning in brachytherapy faces unsolved problems similar to that of image-guided adaptive external beam radiotherapy.

Quality assurance issues for computed tomography-, ultrasound-, and magnetic resonance imaging-guided brachytherapy

The requirements of quality assurance (QA) for both brachytherapy and imaging devices are well-defined, but image-guided brachytherapy has raised new issues. Image guidance in brachytherapy involves the transition from reference point dosimetry using films to volumetric imaging such as computed tomography, ultrasonography, and magnetic resonance imaging for treatment planning and guidance of applicator, needle, or seed placement. The QA of these devices might not reflect the conditions of use in brachytherapy or the requirements of brachytherapy treatment planning. Image interpretation becomes much more important with image-guided brachytherapy. The success of a procedure could depend on the interpretation of a single image in a calibration phase done under the time pressures of the operative setting. This change has implications at the level of treatment, the process, and the field of brachytherapy as a whole. The QA concerns arising from brachytherapy procedures using ultrasound, computed tomography, and magnetic resonance imaging guidance are discussed, as are the problems associated with using imaging in an interventional setting. This report was intended to indicate the QA concerns arising from the convergence of brachytherapy and imaging-highlighting areas in which technical improvements are needed.

Quality assurance needs for modern image-based radiotherapy: recommendations from 2007 interorganizational symposium on "quality assurance of radiation therapy: challenges of advanced technology"

This report summarizes the consensus findings and recommendations emerging from 2007 Symposium, "Quality Assurance of Radiation Therapy: Challenges of Advanced Technology." The Symposium was held in Dallas February 20-22, 2007. The 3-day program, which was sponsored jointly by the American Society for Therapeutic Radiology and Oncology (ASTRO), American Association of Physicists in Medicine (AAPM), and National Cancer Institute (NCI), included >40 invited speakers from the radiation oncology and industrial engineering/human factor communities and attracted nearly 350 attendees, mostly medical physicists. A summary of the major findings follows. The current process of developing consensus recommendations for prescriptive quality assurance (QA) tests remains valid for many of the devices and software systems used in modern radiotherapy (RT), although for some technologies, QA guidance is incomplete or out of date. The current approach to QA does not seem feasible for image-based planning, image-guided therapies, or computer-controlled therapy. In these areas, additional scientific investigation and innovative approaches are needed to manage risk and mitigate errors, including a better balance between mitigating the risk of catastrophic error and maintaining treatment quality, complimenting the current device-centered QA perspective by a more process-centered approach, and broadening community participation in QA guidance formulation and implementation. Industrial engineers and human factor experts can make significant contributions toward advancing a broader, more process-oriented, risk-based formulation of RT QA. Healthcare administrators need to appropriately increase personnel and ancillary equipment resources, as well as capital resources, when new advanced technology RT modalities are implemented. The pace of formalizing clinical physics training must rapidly increase to provide an adequately trained physics workforce for advanced technology RT. The specific recommendations of the Symposium included the following. First, the AAPM, in cooperation with other advisory bodies, should undertake a systematic program to update conventional QA guidance using available risk-assessment methods. Second, the AAPM advanced technology RT Task Groups should better balance clinical process vs. device operation aspects--encouraging greater levels of multidisciplinary participation such as industrial engineering consultants and use-risk assessment and process-flow techniques. Third, ASTRO should form a multidisciplinary subcommittee, consisting of physician, physicist, vendor, and industrial engineering representatives, to better address modern RT quality management and QA needs. Finally, government and private entities committed to improved healthcare quality and safety should support research directed toward addressing QA problems in image-guided therapies.

Clinical practice and quality assurance challenges in modern brachytherapy sources and dosimetry

Modern brachytherapy has led to effective treatments through the establishment of broadly applicable dosimetric thresholds for maximizing survival with minimal morbidity. Proper implementation of recent dosimetric consensus statements and quality assurance procedures is necessary to maintain the established level of safety and efficacy. This review classifies issues as either "systematic" or "stochastic" in terms of their impact on large groups or individual patients, respectively. Systematic changes affecting large numbers of patients occur infrequently and include changes in source dosimetric parameters, prescribing practice, dose calculation formalism, and improvements in calculation algorithms. The physicist must be aware of how incipient changes accord with previous experience. Stochastic issues involve procedures that are applied to each patient individually. Although ample guidance for quality assurance of brachytherapy sources exists, some ambiguities remain. The latest American Association of Physicists in Medicine guidance clarifies what is meant by independent assay, changes source sampling recommendations, particularly for sources in sterile strands and sterile preassembled needles, and modifies action level thresholds. The changing environment of brachytherapy has not changed the fact that the prime responsibility for quality assurance in brachytherapy lies with the institutional medical physicist.

Supplement to the 2004 update of the AAPM Task Group No. 43 Report

Since publication of the 2004 update to the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report (TG-43U1), several new low-energy photon-emitting brachytherapy sources have become available. Many of these sources have satisfied the AAPM prerequisites for routine clinical use as of January 10, 2005, and are posted on the Joint AAPM/RPC Brachytherapy Seed Registry. Consequently, the AAPM has prepared this supplement to the 2004 AAPM TG-43 update. This paper presents the AAPM-approved consensus datasets for these sources, and includes the following 125I sources: Amersham model 6733, Draximage model LS-1, Implant Sciences model 3500, IBt model 1251L, IsoAid model IAI-125A, Mentor model SL-125/ SH-125, and SourceTech Medical model STM1251. The Best Medical model 2335 103Pd source is also included. While the methodology used to determine these data sets is identical to that published in the AAPM TG-43U1 report, additional information and discussion are presented here on some questions that arose since the publication of the TG-43U1 report. Specifically, details of interpolation and extrapolation methods are described further, new methodologies are recommended, and example calculations are provided. Despite these changes, additions, and clarifications, the overall methodology, the procedures for developing consensus data sets, and the dose calculation formalism largely remain the same as in the TG-43U1 report. Thus, the AAPM recommends that the consensus data sets and resultant source-specific dose-rate distributions included in this supplement be adopted by all end users for clinical treatment planning of low-energy photon-emitting brachytherapy sources. Adoption of these recommendations may result in changes to patient dose calculations, and these changes should be carefully evaluated and reviewed with the radiation oncologist prior to implementation of the current protocol.

Dosimetry of an Extracapsular Anulus Following Permanent Prostate Brachytherapy

PURPOSE

Recent studies have suggested that extracapsular brachytherapy treatment margins correlate with biochemical control. It is likely that volumetric geographic dosimetric parameters will be more robust than selected radial measurements. Accordingly, we evaluated extracapsular volumetric dosimetric parameters in low-risk patients.

MATERIALS AND METHODS

A total of 263 low-risk prostate cancer patients randomized to Pd-103 versus I-125 were implanted with a brachytherapy target volume consisting of the prostate with a 5-mm periprostatic margin. The median follow-up was 4.2 years. All patients were implanted at least 3 years prior to analysis. Within 2 hours of implantation, an axial CT was obtained for postimplant dosimetry. A 5-mm three-dimensional periprostatic anulus was constructed around the prostate and evaluated in its entirety and in 90 degrees segments. Prostate and anular dosimetric parameters consisted of V100/V150/V200 and D90. Biochemical progression-free survival (bPFS) was defined as a PSA < or =0.50 ng/mL after nadir.

RESULTS

The Pd-103 and I-125 arms were well-matched in terms of clinical, biochemical, and pathologic presentation. Six-year bPFS was 96.8% versus 99.2% for I-125 versus Pd-103 (P = 0.149). The most recent median posttreatment PSA was <0.04 ng/mL for both isotopes. No significant differences in postoperative anular doses were discerned between bPFS and failed patients.

CONCLUSIONS

A postimplant 5-mm, three-dimensional periprostatic anulus provides substantial information regarding dosimetric coverage. However, with a median follow-up of 4.2 years, such volumetric and geographic parameters have not proven useful in predicting biochemical outcome in low-risk patients.

American Brachytherapy Society recommends no change for prostate permanent implant dose prescriptions using iodine-125 or palladium-103

PURPOSE

In 2004, the American Association of Physicists in Medicine (AAPM) issued a report outlining recommended 125I and 103Pd datasets for consistency in calculating brachytherapy dose distributions. In 2005, to aid evaluating the clinical impact of implementing these datasets, the AAPM assessed the historical dependence of how prescribed doses differed from administered doses for 125I and 103Pd for permanent implantation of the prostate. Consequently, the American Brachytherapy Society (ABS) considered the nature of these changes towards issuing recommended dose prescriptions for 125I and 103Pd interstitial brachytherapy implants for monotherapy and standard boosts.

METHODS AND MATERIALS

An investigation was performed of the 2005 AAPM analysis to determine changes in administered dose while affixing prescribed dose using 2004 AAPM 125I and 103Pd brachytherapy dosimetry datasets for prostate implants. For 125I and 103Pd, administered dose would change by +1.4% and +4.2%, respectively. The biological and societal impact of changing prescribed dose was considered.

RESULTS

Based on the need for clinical constancy and in recognition of overall uncertainties, the ABS recommends immediate implementation of the 2004 AAPM consensus brachytherapy dosimetry datasets and no changes to 125I and 103Pd dose prescriptions at this time.

CONCLUSIONS

Radiation oncologists should continue to prescribe monotherapy doses of 145 Gy and 125 Gy for 125I and 103Pd, respectively, and standard boost doses of 100-110 Gy and 90-100 Gy for 125I and 103Pd, respectively.

Brachytherapy technology and physics practice since 1950: a half-century of progress

The 50-year tenure of Physics in Medicine and Biology has coincided with some of the most important developments in radiological science, including the introduction of artificial radioactivity, computers and 3D imaging into medicine. These events have profoundly influenced the development of brachytherapy. Although it is not the dominant radiotherapy modality, it continues to play an important role in cancer therapy, more than a century after its introduction. This paper reviews the impact of three broad categories of innovation introduced since 1950 from the North American perspective: the introduction of artificial radioactivity, computer- and image-based treatment planning, and basic single-source dosimetry.

Interstitial brachytherapy dosimetry update

In March 2004, the American Association of Physicists in Medicine (AAPM) published an update to the AAPM Task Group No. 43 Report (TG-43) which was initially published in 1995. This update was pursued primarily due to the marked increase in permanent implantation of low-energy photon-emitting brachytherapy sources in the United States over the past decade, and clinical rationale for the need of accurate dosimetry in the implementation of interstitial brachytherapy. Additionally, there were substantial improvements in the brachytherapy dosimetry formalism, accuracy of related parameters and methods for determining these parameters. With salient background, these improvements are discussed in the context of radiation dosimetry. As an example, the impact of this update on the administered dose is assessed for the model 200 (103)Pd brachytherapy source.