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      Evaluation of the dosimetric impact of loss and displacement of seeds in prostate low-dose-rate brachytherapy

      research-article
      , MSc 1 , , MD, PhD 2 , , PhD 1 , , MBBS, MD, FRCPC 3 , 4 ,
      Journal of Contemporary Brachytherapy
      Termedia Publishing House
      brachytherapy, dosimetry, LDR, prostate cancer, seeds

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          Abstract

          Purpose

          To analyze the seed loss and displacement and their dosimetric impact in prostate low-dose-rate (LDR) brachytherapy while utilizing the combination of loose and stranded seeds.

          Material and methods

          Two hundred and seventeen prostate cancer patients have been treated with LDR brachytherapy. Loose seeds were implanted in the prostate center and stranded seeds in the periphery of the gland. Patients were imaged with transrectal ultrasound before implant and with computerized tomography/magnetic resonance imaging (CT/MR) one month after implant. The seed loss and displacement had been analyzed. Their impact on prostate dosimetry had been examined. The seed distribution beyond the prostate inferior boundary had been studied.

          Results

          The mean number of seeds per patient that were lost to lung, pelvis/abdomen, urine, or unknown destinations was 0.21, 0.13, 0.03, and 0.29, respectively. Overall, 40.1% of patients had seed loss. Seed migration to lung and pelvis/abdomen occurred in 15.5% and 10.5% of the patients, respectively. Documented seed loss to urine was found in 3% of the patients while 20% of patients had seed loss to unknown destinations. Prostate length difference between pre-plan and post-implant images was within 6 mm in more than 98% of cases. The difference in number of seeds inferior to prostate between pre-plan and post-implant dosimetry was within 7 seeds for 93% of patients. At time of implant, 98% of seeds, inferior to prostate, were within 5 mm and 100% within 15 mm, and in one month post-implant 83% within 9 mm and 96.3% within 15 mm. Prostate post-implant V 100, D 90, and rectal wall RV 100 for patients without seed loss were 94.6%, 113.9%, and 0.98 cm 3, respectively, as compared to 95.0%, 114.8%, and 0.95 cm 3 for the group with seed loss.

          Conclusions

          Seed loss and displacement have been observed to be frequent. No correlation between seed loss and displacement and post-plan dosimetry has been reported.

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          Most cited references29

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          American Brachytherapy Society consensus guidelines for transrectal ultrasound-guided permanent prostate brachytherapy.

          To provide updated American Brachytherapy Society (ABS) guidelines for transrectal ultrasound-guided transperineal interstitial permanent prostate brachytherapy (PPB). The ABS formed a committee of brachytherapists and researchers experienced in the clinical practice of PPB to formulate updated guidelines for this technique. Sources of input for these guidelines included prior published guidelines, clinical trials, published literature, and experience of the committee. The recommendations of the committee were reviewed and approved by the Board of Directors of the ABS. Patients with high probability of organ-confined disease or limited extraprostatic extension are considered appropriate candidates for PPB monotherapy. Low-risk patients may be treated with PPB alone without the need for supplemental external beam radiotherapy. High-risk patients should receive supplemental external beam radiotherapy if PPB is used. Intermediate-risk patients should be considered on an individual case basis. Intermediate-risk patients with favorable features may appropriately be treated with PPB monotherapy but results from confirmatory clinical trials are pending. Computed tomography-based postimplant dosimetry performed within 60 days of the implant is considered essential for maintenance of a satisfactory quality assurance program. Postimplant computed tomography-magnetic resonance image fusion is viewed as useful, but not mandatory. Updated guidelines for patient selection, workup, treatment, postimplant dosimetry, and followup are provided. These recommendations are intended to be advisory in nature with the ultimate responsibility for the care of the patients resting with the treating physicians. Copyright © 2012. Published by Elsevier Inc.
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            AAPM recommendations on dose prescription and reporting methods for permanent interstitial brachytherapy for prostate cancer: report of Task Group 137.

            During the past decade, permanent radioactive source implantation of the prostate has become the standard of care for selected prostate cancer patients, and the techniques for implantation have evolved in many different forms. Although most implants use 125I or 103Pd sources, clinical use of 131Cs sources has also recently been introduced. These sources produce different dose distributions and irradiate the tumors at different dose rates. Ultrasound was used originally to guide the planning and implantation of sources in the tumor. More recently, CT and/or MR are used routinely in many clinics for dose evaluation and planning. Several investigators reported that the tumor volumes and target volumes delineated from ultrasound, CT, and MR can vary substantially because of the inherent differences in these imaging modalities. It has also been reported that these volumes depend critically on the time of imaging after the implant. Many clinics, in particular those using intraoperative implantation, perform imaging only on the day of the implant. Because the effects of edema caused by surgical trauma can vary from one patient to another and resolve at different rates, the timing of imaging for dosimetry evaluation can have a profound effect on the dose reported (to have been delivered), i.e., for the same implant (same dose delivered), CT at different timing can yield different doses reported. Also, many different loading patterns and margins around the tumor volumes have been used, and these may lead to variations in the dose delivered. In this report, the current literature on these issues is reviewed, and the impact of these issues on the radiobiological response is estimated. The radiobiological models for the biological equivalent dose (BED) are reviewed. Starting with the BED model for acute single doses, the models for fractionated doses, continuous low-dose-rate irradiation, and both homogeneous and inhomogeneous dose distributions, as well as tumor cure probability models, are reviewed. Based on these developments in literature, the AAPM recommends guidelines for dose prescription from a physics perspective for routine patient treatment, clinical trials, and for treatment planning software developers. The authors continue to follow the current recommendations on using D90 and V100 as the primary quantitles, with more specific guidelines on the use of the imaging modalities and the timing of the imaging. The AAPM recommends that the postimplant evaluation should be performed at the optimum time for specific radionuclides. In addition, they encourage the use of a radiobiological model with a specific set of parameters to facilitate relative comparisons of treatment plans reported by different institutions using different loading patterns or radionuclides.
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              Permanent prostate seed implant brachytherapy: report of the American Association of Physicists in Medicine Task Group No. 64.

              There is now considerable evidence to suggest that technical innovations, 3D image-based planning, template guidance, computerized dosimetry analysis and improved quality assurance practice have converged in synergy in modern prostate brachytherapy, which promise to lead to increased tumor control and decreased toxicity. A substantial part of the medical physicist's contribution to this multi-disciplinary modality has a direct impact on the factors that may singly or jointly determine the treatment outcome. It is therefore of paramount importance for the medical physics community to establish a uniform standard of practice for prostate brachytherapy physics, so that the therapeutic potential of the modality can be maximally and consistently realized in the wider healthcare community. A recent survey in the U.S. for prostate brachytherapy revealed alarming variance in the pattern of practice in physics and dosimetry, particularly in regard to dose calculation, seed assay and time/method of postimplant imaging. Because of the large number of start-up programs at this time, it is essential that the roles and responsibilities of the medical physicist be clearly defined, consistent with the pivotal nature of the clinical physics component in assuring the ultimate success of prostate brachytherapy. It was against this background that the Radiation Therapy Committee of the American Association of Physicists in Medicine formed Task Group No. 64, which was charged (1) to review the current techniques in prostate seed implant brachytherapy, (2) to summarize the present knowledge in treatment planning, dose specification and reporting, (3) to recommend practical guidelines for the clinical medical physicist, and (4) to identify issues for future investigation.
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                Author and article information

                Journal
                J Contemp Brachytherapy
                J Contemp Brachytherapy
                JCB
                Journal of Contemporary Brachytherapy
                Termedia Publishing House
                1689-832X
                2081-2841
                09 June 2015
                June 2015
                : 7
                : 3
                : 203-210
                Affiliations
                [1 ]Department of Radiation Physics, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada
                [2 ]Department of Radiation Oncology, Memorial Sloan- Kettering Cancer Centre, New York, New York, USA
                [3 ]Department of Radiation Oncology, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada
                [4 ]Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
                Author notes
                Address for correspondence: Saibishkumar Elantholi Parameswaran, M.B.B.S, MD, FRCPC, Department of Radiation Oncology, Princess Margaret Cancer Centre, University Health Network, 610 University Ave., Toronto, Ontario, Canada M5G 2M9. phone: +1 416-946-2919, fax: +1 416-946-6561. e-mail: saibish.elantholi@ 123456rmp.uhn.on.ca
                Article
                25222
                10.5114/jcb.2015.52127
                4499516
                26207108
                e9fa4429-48cc-49f8-bec2-2854e1020749
                Copyright © 2015 Termedia

                This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License, permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 10 January 2015
                : 20 March 2015
                : 21 May 2015
                Categories
                Original Paper

                Oncology & Radiotherapy
                brachytherapy,dosimetry,ldr,prostate cancer,seeds
                Oncology & Radiotherapy
                brachytherapy, dosimetry, ldr, prostate cancer, seeds

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