COMP report: CPQR technical quality control guidelines for low‐dose‐rate permanent seed brachytherapy

Abstract The Canadian Organization of Medical Physicists (COMP), in close partnership with the Canadian Partnership for Quality Radiotherapy (CPQR) has developed a series of Technical Quality Control (TQC) guidelines for radiation treatment equipment. These guidelines outline the performance objectives that equipment should meet in order to ensure an acceptable level of radiation treatment quality. The TQC guidelines have been rigorously reviewed and field tested in a variety of Canadian radiation treatment facilities. The development process enables rapid review and update to keep the guidelines current with changes in technology. This article contains detailed performance objectives and safety criteria for low‐dose‐rate (LDR) permanent seed brachytherapy.

the universal availability of high quality and safe radiotherapy for all The development of the individual TQC guidelines, this one included, is spearheaded by expert practitioners and involves broad stakeholder input from the medical physics and radiation oncology community. 3 All information contained in this document is intended to be used at the discretion of each individual center to help guide quality and safety program improvement. There are no legal standards supporting this document; specific federal or provincial regulations and licence conditions take precedence over the content of this document. seed brachytherapy. [4][5][6][7][8][9][10][11] Most of these publications have extensive reference lists. Some have detailed descriptions indicating how to conduct the various quality control tests. The guidelines promoted in this document are based on the experience of the authors and expert practitioners and are broadly consistent with recommendations from other jurisdictions. [6][7][8][9][10][11] Brachytherapy is a procedure in which sealed radionuclide sources are placed in close proximity to, or inside, the tumor. For example, brachytherapy modalities for prostate cancer presently used in Canada include ultrasound guided transperineal interstitial permanent prostate brachytherapy (TIPPB) and high dose rate (HDR) brachytherapy. In prostate brachytherapy, four radionuclides are cur- Transperineal interstitial permanent prostate brachytherapy was first proposed by Holm and colleagues. 13 The procedure consists of using a transrectal ultrasound probe to first define the prostate contours in 1-5 mm-thick transaxial images for dosimetric planning and then, some weeks later, delivering radioactive seeds (sources 0.8 mm in diameter 9 4.5-5 mm in length) into the prostate gland. In both steps, the patient is placed in the lithotomy position. Over the years, other approaches have been introduced such as intra-operative preplanning and interactive planning. 10 In such cases, treatment planning and seeds loading in needles take place during the operative procedure. Needles containing the seeds are inserted through the perineum and into the prostate under the guidance of the transrectal ultrasound probe. The needles are prepared for the procedure in one of three ways: manual loading on site, purchased pre-loaded needles, and seed loading devices. Some customization of the quality control guidelines presented here may be necessary to accommodate the particular method of needle loading in use.
Transperineal interstitial permanent prostate brachytherapy has become a very popular treatment alternative for low risk prostate cancer patients due to the pioneering work of the Seattle group. 14 This treatment option is offered to patients having early localized prostate cancer (Stage < T2c, Gleason score < 7, and PSA < 10).
Biochemical disease-free survival rates have now been reported for this procedure for extended follow-up periods. [14][15][16][17][18][19][20][21] Similar results are also available in a Canadian context. [22][23][24][25] For intermediate and high-risk patients (PSA > 10 and/or Gleason score > 6 and/or stage > T2c), HDR brachytherapy is more commonly used, mainly as a boost strategy, producing excellent PSA control and negative biopsy results in patients with intermediateand high-risk prostate cancer. [26][27][28] However, TIPPB alone is a treatment option for some low-tier intermediate risk prostate cancer patients and can also be used as a boost modality. [23][24][25] Recently, permanent seed implants have been proposed for breast cancer by Dr. Jean-Philippe Pignol from Sunnybrook hospital in Toronto. 29 The general guidelines described in this document and the literature review provided should enable the clinical physicists to adapt the standards set forth to that procedure. ibration. Alternatively, a single seed can be sent to an ADCL for measurement of its air-kerma strength, and this value used to obtain a calibration factor for the well chamber. Compliance with applicable radiation safety codes must be ensured for each radionuclide, source type, and activity range to be used.

| RELATED TECHNICAL QUALITY CONTROL GUIDELINE S
In order to comprehensively assess low-dose-rate brachytherapy system performance, additional guideline tests, as outlined in related CPQR TQC guidelines must also be completed and documented, as applicable. Related TQC guidelines, available at cpqr.ca, include: • Safety Systems. • Major Dosimetry Equipment. Any maintenance on the ultrasound, treatment planning computer, seed loading devices, and so on should be followed by thorough quality assurance testing involving the daily and/or annual quality assurance appropriate to the situation.
For seed implants, some of the daily tests should be performed either before each procedure (before each implant) or once at the start of the day, depending of the nature of the test. Tables 1 and 2 but must be part of a comprehensive quality assurance pro-

gram (see CPQR's companion guidance document Quality Assurance
Guidelines for Canadian Radiation Treatment Programs 38 ). Specific license requirements and applicable safety codes must be followed. Notes on daily tests.

DPB1
Verify that the handheld radiation survey meter (e.g., Geiger counter) is functional.

DPB2
The AAPM Low Energy Brachytherapy Source Calibration Working Group has outlined specific criteria. 39 In general 10% of the seeds or 10 seeds, whichever number is larger, should be tested. For a sterile assembly, such as a sterile seed cartridge or pre-loaded needle, the recommendation is the lowest of 5% of the seeds or 5 seeds. Complete descriptions of the scenarios between these two extremes are given in "table 1" of Butler et al., 2008. 39 Remember that manufacturers usually ship seed strength within a range that can be as large as AE4% of the average strength. 11 In addition to the above, a secondary device can be further used as part of a seed loader (e.g., Isoloader from Mentor or SeedSelectron from Nucletron) for which more than 10% and up to 100% of the seeds can be measured.
Validation studies of the Isoloader 40 and SeedSelectron 41 have been published.

DPB3
In addition, visually inspect images for any artifacts, such as black lines or bands. Ensure they are not due to poor contact between the probe and tissue. If present, such (Continues) bands may indicate non-functioning ultrasound detector elements within the probe. Persistence of these artifacts may warrant image quality tests using a dedicated ultrasound phantom to characterize the location of the signal dropout and identify non-functioning elements within the probe, which may have to be sent for repairs.

DPB4
Could be performed in conjunction with DPB2 above if done on the same day as the procedure. Otherwise, inventory should be validated before moving the sources to the procedure room.

DPB5
Documentation relating to the daily quality control checks, preventive maintenance, service calls, and subsequent checks must be complete and legible. The operator(s) must be identified.

DPB6
The workspace (including the floor), needles, template, probes, etc., must be surveyed using a calibrated survey meter (see DPB1). Reading should be consistent with no radioactive materials outside the seeds implanted in the patient. This task must be performed after each implant.

DPB7-15
The configuration of these tests will depend on the equipment selected and the clinical workflow (preplanning/live planning with or without a seed loading device). Safety is the concern and tests should be designed accordingly. As a minimum, manufacturer's recommendations and applicable regulations must be followed.
DPB16 See DPB2 above regarding detector such as the SeedSelectron.
DPB17 It is crucial that the needle loading sequence of each needle composing a given plan be validated and correspond to the treatment plan. For pre-loaded needles, auto-radiograph or x-ray imaging will confirm the seedspacer sequence (or seed sequence for stranded seeds). For intra-operative loading, a second person could visually confirm the loading as it is being done and most brachytherapy needle have graduation that can confirm the overall sequence length. In any case, this length should be confirmed (pre-loaded or intra-operative loading) before every needle insertion. Some devices, such as the SeedSelectron, have an array of radiation detectors that is used to confirm the seed (radiation present) and spacer (no radiation) sequence before loading. In such a case, the device itself should be regularly tested (see APB9 below).

Notes on annual and bi-annual tests.
APB1-4 AAPM Task Group 128 constitutes the reference document with regard to ultrasound system performance and related quality assurance tasks; a detail description of each test is given. 9 Transverse and longitudinal positional accuracy, as well as volume accuracy, can be measured using specially designed phantoms, (e.g., Computerized Imaging Reference Systems [CIRS] brachytherapy phantom model 45). Information about ultrasound verification (Continues) procedures (e.g., use of ethylene glycol-water mixture and water temperature) for prostate can be found in Goldstein et al., 2002 42 A simple prostate implant template verification setup is also described in Mutic et al., 2000 43 In addition, various manufacturers also have their own recommendations. Please note that the speed of sound of tissue is 1540 m/s and phantom should mimic this property. Room temperature water-like speed of sound is not acceptable (1482 m/s) for these tests.

APB5
Peer reviewed articles giving dosimetric parameters of each approved seed model can be found in the registry (http://rpc.mdanderson.org/rpc). The source data are usually based on Monte Carlo calculations and on experimental measurements, the combination being referred to as a consensus dataset. 7,37 Validation of the parameters in the TPS can be performed in two ways: (1) a simple 1D hand calculation for a single source compared to the TPS or (2) a simple geometry involving a few seeds which can be reproduced in the TPS and in independent software (Excel, Matlab, or another commercial TPS). Tolerance and action levels refer to agreement between the TPS and an independent calculation. If another commercial TPS is used, validation of a reference structure volume can also be performed at the same time (volume handling can be a source of discrepancy between TPSs with regard to dose-volume histograms [DVHs]). Volumes between the two TPSs should agree within 5%.

APB6
The configuration of these tests will depend on the design of the facility and equipment used. Review the emergency procedures for seed/needle loading if a seed loading device is normally used and fails. Emergency procedures (e.g., if a seed should drop on the floor, is stuck in a needle, or is found in the urine bag) should be reviewed.

APB7
To ensure redundancy and adequate monitoring, a second qualified medical physicist must independently verify the implementation, analysis, and interpretation of the quality control tests at least annually.

APB8
It is recommended that a complete system validation be conducted once a year. In the present document this would include all the necessary validation for full system recovery from power outage (planning system recovery, seed delivery system, etc.,), delivery interruption, and other potentially deleterious events, as indicated in DBP6 to DPB13. These tests should be performed away from the daily clinical pressure and busy operating room environment.

BPB1
The well chamber should be sent to an accredited dosimetry calibration laboratory once every 2 years. A calibrated source, of each seed model used, could also be acquired from the manufacturer each year for verification purposes.

ACKNOWLEDG MENTS
We would like to thank the people who participated in the production of this guideline.

CONFLI CT OF INTEREST
The authors declare no conflict of interest.