Nick Chng

Radiation oncology and medical physicists quality assurance in British Columbia Cancer Agency Provincial Prostate Brachytherapy Program

PURPOSE To describe in detail British Columbia (BC) Cancer Agency (BCCA) Provincial Prostate Brachytherapy (PB) Quality Assurance (QA) Program. METHODS AND MATERIALS The BCCA PB Program was established in 1997. It operates as one system, unified and supported by electronic and information systems, making it a single PB treatment provider for province of BC and Yukon. To date, >4000 patients have received PB (450 implants in 2011), making it the largest program in Canada. The Program maintains a large provincial prospective electronic database with records on all patients, including disease characteristics, risk stratification, pathology, preplan and postimplant dosimetric data, follow-up of prostate-specific antigen, and toxicity outcomes. RESULTS QA was an integral part of the program since its inception. A formal QA Program was established in 2002, with key components that include: unified eligibility criteria and planning system, comprehensive database, physics and oncologist training and mentorship programs, peer review process, individual performance outcomes and feedback process, structured continuing education and routine assessment of the programs dosimetry, toxicity and prostate-specific antigen outcomes, administration and program leadership that promotes a strong culture of patient safety. The emphasis on creating a robust, broad-based network of skilled providers has been achieved by the programs requirements for training, education, and the QA process. CONCLUSIONS The formal QA process is considered a key factor for the success of cancer control outcomes achieved at BCCA. Although this QA model may not be wholly transferable to all PB programs, some of its key components may be applicable to other programs to ensure quality in PB and patient safety.

Use of Needle Track Detection to Quantify the Displacement of Stranded Seeds Following Prostate Brachytherapy

We aim to compute the movement of permanent stranded implant brachytherapy radioactive sources (seeds) in the prostate from the planned seed distribution to the intraoperative fluoroscopic distribution, and then to the postimplant computed tomography (CT) distribution. We present a novel approach to matching the seeds in these distributions to the plan by grouping the seeds into needle tracks. First, we identify the implantation axis using a sample consensus algorithm. Then, we use a network flow algorithm to group seeds into their needle tracks. Finally, we match the needles from the three stages using both their transverse plane location and the number of seeds per needle. We validated our approach on eight clinical prostate brachytherapy cases, having a total of 871 brachytherapy seeds distributed in 193 needles. For the intraoperative and postimplant data, 99.31% and 99.41% of the seeds were correctly assigned, respectively. For both the preplan to fluoroscopic and fluoroscopic to CT registrations, 100% of the needles were correctly matched. We show that there is an average intraoperative seed displacement of 4.94 ± 2.42 mm and a further 2.97 ± 1.81 mm of postimplant movement. This information reveals several directional trends and can be used for quality control, treatment planning, and intraoperative dosimetry that fuses ultrasound and fluoroscopy.

Source strength verification and quality assurance of preloaded brachytherapy needles using a CMOS flat panel detector

PURPOSE Current methods of low dose rate brachytherapy source strength verification for sources preloaded into needles consist of either assaying a small number of seeds from a separate sample belonging to the same lot used to load the needles or performing batch assays of a subset of the preloaded seed trains. Both of these methods are cumbersome and have the limitations inherent to sampling. The purpose of this work was to investigate an alternative approach that uses an image-based, autoradiographic system capable of the rapid and complete assay of all sources without compromising sterility. METHODS The system consists of a flat panel image detector, an autoclavable needle holder, and software to analyze the detected signals. The needle holder was designed to maintain a fixed vertical spacing between the needles and the image detector, and to collimate the emissions from each seed. It also provides a sterile barrier between the needles and the imager. The image detector has a sufficiently large image capture area to allow several needles to be analyzed simultaneously.Several tests were performed to assess the accuracy and reproducibility of source strengths obtained using this system. Three different seed models (Oncura 6711 and 9011 (125)I seeds, and IsoAid Advantage (103)Pd seeds) were used in the evaluations. Seeds were loaded into trains with at least 1 cm spacing. RESULTS Using our system, it was possible to obtain linear calibration curves with coverage factor k = 1 prediction intervals of less than ±2% near the centre of their range for the three source models. The uncertainty budget calculated from a combination of type A and type B estimates of potential sources of error was somewhat larger, yielding (k = 1) combined uncertainties for individual seed readings of 6.2% for (125)I 6711 seeds, 4.7% for (125)I 9011 seeds, and 11.0% for Advantage (103)Pd seeds. CONCLUSIONS This study showed that a flat panel detector dosimetry system is a viable option for source strength verification in preloaded needles, as it is capable of measuring all of the sources intended for implantation. Such a system has the potential to directly and efficiently estimate individual source strengths, the overall mean source strength, and the positions within the seed-spacer train.

Quantifying stranded implant displacement following prostate brachytherapy

We aim to compute radioactive stranded-implant displacement during and after prostate brachytherapy. We present the methods used to identify corresponding seeds in planned, intra-operative and postimplant patient data that enable us to compute seed displacements. A minimum cost network flow algorithm is used, on 8 patients, for needle track detection to group seeds into needles that can be matched between datasets. An iterative best line detection algorithm is used both to help with needle detection and to register the different datasets. Our results show that there was an average seed misplacement of 5.08 +/- 2.35 mm during the procedure, which then moved another 3.10 +/- 1.91 mm by the time the quality assurance CT was taken. Several directional trends in different regions of the prostate were noted and commented on.

Population-based phase II trial of stereotactic ablative radiotherapy (SABR) for up to 5 oligometastases: SABR-5

BackgroundOligometastases refer to a state of disease where cancer has spread beyond the primary site, but is not yet widely metastatic, often defined as 1–3 or 1–5 metastases in number. Stereotactic ablative radiotherapy (SABR) is an emerging radiotherapy technique to treat oligometastases that require further prospective population-based toxicity estimates.MethodsThis is a non-randomized phase II trial where all participants will receive experimental SABR treatment to all sites of newly diagnosed or progressing oligometastatic disease. We will accrue 200 patients to assess toxicity associated with this experimental treatment. The study was powered to give a 95% confidence on the risk of late grade 4 toxicity, anticipating a < 5% rate of grade 4 toxicity.DiscussionSABR treatment of oligometastases is occurring off-trial at a high rate, without sufficient evidence of its efficacy or toxicity. This trial will provide necessary toxicity data in a population-based cohort, using standardized doses and organ at risk constraints, while we await data on efficacy from randomized phase III trials.Trial RegistrationRegistered through clinicaltrials.gov NCT02933242 on October 14, 2016 prospectively before patient accrual.

The Dosimetric Impact of Supplementing Pre-Planned Prostate Implants With Discretionary 125I Seeds

Purpose:TheBritishColumbiaCancerAgency (BCCA) Provincial Prostate Brachytherapy program was established in 1998. Over 3000 implants have been done to date. Implants are performed using a pre-planned, real time ultrasound-guided transperineal technique, with stranded seeds and modified peripheral loading to deliver an mPD of 144 Gy to the prostate plus margins. For each implant, 5 extra seeds (2 stranded and 3 loose) are provided to be used at the discretion of the physician. The aim of this research was to investigate the dosimetric impact of these extra seeds, and the circumstances under which they are most commonly used. Materials and Methods: Post-implant questionnaires were completed by 5 experienced physicians to prospectively collect information on 70 consecutive implants performed over a 4 month period. After each implant, the location and rationale for using any extra seeds was recorded by each physician. All study patients underwent day-0 post implant dosimetry. A previously developed plan reconstruction algorithm was used to distinguish the extra seeds from those which were planned. The dose distributions with and without the extra seeds were compared for the whole prostate, anterior-superior (ASQ), anterior-inferior (AIQ), posteriorsuperior (PSQ), and posterior-inferior (PIQ) prostate quadrants, urethra and rectum. The Conformity Index (CI) and External Index (EI) were computed to assess collateral dose outside the target. Results:Extra seeds were used in 83%of the cohort with amedian of 5 extra seeds/implant. The majority of the extra seeds were deposited in the ASQ (64%) and less frequently in other quadrants; PSQ (24%), AIQ (7%) and PIQ (5%). The most commonly reported reasons for the use of extra seeds was to improve coverage of the anterior base (42% of responses), and target regions of biopsy confirmed cancer (26%). The use of extra seeds resulted in a mean increase in whole prostate V100, V150 and V200 of 3.7% (mean V100 90.5% to 93.8%), 13% (mean V150 45% to 50.6%) and 19% (mean V200 13.5% to 16%), respectively. Mean whole prostate D90 increased from 147Gy to 156Gy. The use of extra seeds increased V100 over the 90% threshold in 15 (26%) patients. Five patients (9%) who received dose supplementation would otherwise have been classified as having suboptimal coverage (mean V100 of 83.2% improved to 91.1% after using extra seeds). Quadrant analysis demonstrated that extra seeds had the most impact on ASQ coverage, in line with the stated goals of their use, with a mean V100 increase of 13.6% (mean V100 74% to 83%) and a mean D90 increase of 9.1% (mean D90 123Gy to 134Gy). Extra seeds increased the rectal dose (VR100) by a mean of 5.9% (mean VR100 0.543 cc to 0.579cc). The mean urethral dose increased from 134.8Gy to 140.6Gy with a mean increase of 4.5% (range 1.16Gy to 5.8 Gy). The CI increased from a mean of 1.89 to 1.92 while the mean EI increased from 0.809 to 0.869. Conclusions: Bolstering coverage of the anterior prostate base is the main reason extra seeds were used in this cohort, and this aim was consistently achieved with only minor impact on the urethral, rectal and extraprostatic tissues. However, there was a considerable increase in prostate V150 and V200. The accuracy with which dose was boosted in the biopsy positive regions is under investigation.