Cynthia Araujo

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.

Ultrasound–CT fusion compared with MR–CT fusion for postimplant dosimetry in permanent prostate brachytherapy

PURPOSE Postplan evaluation is essential for quality assurance in prostate brachytherapy. MRI has demonstrated greater interobserver consistency in prostate contouring compared with CT. Although a valuable tool in postimplant assessment, MRI is costly and not always available. Our purpose is to compare dosimetry obtained using fusion of postimplant CT with preimplant transrectal ultrasound (TRUS) vs. CT-MR fusion. METHODS AND MATERIALS Twenty patients receiving permanent (125)I seed prostate brachytherapy underwent preimplant TRUS with urethrography, 1-month CT with a Foley catheter, and 1-month MRI. No patient received androgen deprivation therapy or external beam radiotherapy. The prescription dose of (125)I implant monotherapy was 144Gy. The preimplant TRUS and postimplant CT images were fused based on urethral position, and the CT-TRUS images were subsequently fused to the MRI using a seed-to-seed match. Dosimetric parameters for the ultrasound- and MR-derived prostate were compared. RESULTS The mean absolute difference between dosimetry from MRI or CT-TRUS fusion for D(90) was 3.2% and in V(100) was 1.2%. Only 1 patient had a difference in MR- and ultrasound-derived D(90) of more than 10% (11.4%) and only 1 had a difference in V(100) of more than 5%. CONCLUSIONS Fusion of preimplant TRUS with 1-month postimplant CT appears to lead to acceptable agreement with MR-based dosimetric parameters in postplan evaluation. TRUS-based volumes may be a reasonable alternative to MRI in settings where MRI is not available.

Defining a magnetic resonance scan sequence for permanent seed prostate brachytherapy postimplant assessment

PURPOSE We describe a magnetic resonance (MR) scan sequence for prostate brachytherapy postimplant assessment. METHODS AND MATERIALS One brachytherapy team at the British Columbia Cancer Agency has incorporated MR-CT fusion into their permanent seed prostate brachytherapy quality assurance procedure. Several attempts were required to ensure that the diagnostic MR scanner at the adjoining general hospital performed the desired sequence, providing many examples of suboptimal scans and underlining the pitfalls for a center trying to incorporate the use of MR scanning into their brachytherapy program. RESULTS The recommended sequence (Fast Spin Echo T2-weighted, repetition time [TR]/echo time [TE] 4500/90, echo train length [ETL] 10, 20×20 field of view [FOV], 80 bandwidth [BW]) is associated with superior edge detection when compared with those images in which a typical diagnostic sequence was used. The use of a low bandwidth sequence does not compromise edge detection or seed identification when compared with a higher bandwidth. CONCLUSIONS We have defined a magnetic resonance imaging sequence, which appears to optimize both prostate delineation and identification of seeds, lending itself to straightforward fusion with CT images and allowing for less uncertainty in permanent seed prostate brachytherapy quality assurance.

Implications of CT-imaging for Postplan Quality Assessment in Prostate Brachytherapy

PURPOSE Postplan quality assurance using CT shows considerable interobserver contour variability. We examined CT postplans of four experienced brachytherapists for comparison with MR-determined prostate volumes. METHODS AND MATERIALS Seventy-five patients had CT and MR scans 1 month post-(125)I prostate brachytherapy. CT scans were contoured by the treating physician and dosimetry calculated. The prostate was contoured independently on MR by one observer with extensive MR experience, the scans were fused and dosimetric parameters compared. RESULTS The mean prostate volume on CT was 38.3 cc (17.5-78.6 cc), on MR 33.3 cc (16.3-66.1 cc). On average, the volume on CT was 16.1% larger than on MR (range, 8% smaller to 64% larger). Craniocaudal discordance of the CT vs. MR prostate contours ranged from 4 mm cranial to 10 mm caudal to MR base and from 6 mm cranial to 14 mm caudal to MR apex. The CT prostate volume not only included an average of 90% of the MR prostate (range, 75-99%) but also included normal tissue (mean, 8.3 cc; range, 2.9-17.1 cc). The average difference between the calculated D(90) from CT contours vs. MR contours was 10.0 Gy (standard deviation, 8.8; range, -37.6 to +41.6 Gy). CONCLUSIONS On average, only 90% of the MR-defined prostate is included in CT contours, while a volume of normal tissue is erroneously designated as prostate. Lack of awareness of this deficiency in planning and/or operative technique gives a false sense of appreciation of the true conformality, delays implementation of corrective measures, and risks unnecessary side effects.

An Internet-Based Means of Monitoring Quality of Life in Post-Prostate Radiation Treatment: A Prospective Cohort Study

Background Widespread integration of the Internet has resulted in an increase in the feasibility of using Web-based technologies as a means of communicating with patients. It may be possible to develop secure and standardized systems that facilitate Internet-based patient-reported outcomes which could be used to improve patient care. Objective This study investigates patient interest in participating in an online post-treatment disease outcomes and quality of life monitoring program developed specifically for patients who have received radiation treatment for prostate cancer at a regional oncology center. Methods Patients treated for prostate cancer between 2007 and 2011 (N=1113) at the British Columbia Cancer Agency, Centre for the Southern Interior were invited by mail to participate in a standardized questionnaire related to their post-treatment health. Overall participation rates were calculated. In addition, demographics, access to broadband Internet services, and treatment modalities were compared between participants and nonparticipants. Results Of the 1030 eligible invitees, 358 (358/1030, 34.7%) completed the online questionnaire. Participation rates were higher in individuals younger than age 60 when compared to those age 60 or older (42% vs 31%) and also for those living in urban areas compared with rural (37% vs 29%) and in those who received brachytherapy versus external beam radiotherapy (EBRT) (41% vs 31%). Better participation rates were seen in individuals who had access to Internet connectivity based on the different types of broadband services (DSL 35% for those with DSL connectivity vs 29% for those without DSL connectivity; cable 35% vs 32%; wireless 38% vs 26%). After adjusting for age, the model indicates that lack of access to wireless broadband connectivity, living in a rural area, and receiving EBRT were significant predictors of lower participation. Conclusions This study demonstrates that participation rates vary in patient populations within the interior region of British Columbia, especially with older patients, those in rural areas, and those with limited access to quality Internet services.

Extension of CadPlan algorithm to model the dose distribution under a motorized wedge

The CadPlan treatment planning system models the dose distribution in the non-wedge direction under a wedged field by converting the wedge thickness to an equivalent water thickness. The algorithm estimates the off-axis ratio (OAR) in the non-wedged direction using the open field OAR at a depth deeper by this equivalent water thickness. This model has been shown to work well for a Siemens Mevatron KD-2 Linac. However, the motorized wedge of the Elekta (formerly Philips) accelerators is tapered off-axis to give a flat dose profile in the non-wedged direction. The CadPlan model assumes that the wedge has a uniform thickness in the non-wedged direction and so cannot model the off-axis dose for the motorized wedge. For a 4 MV beam of a SL75/5 accelerator this leads to a 7% overestimate and a 9% underestimate of the OAR under the thin and thick edge of the wedge respectively. For 6 and 18 MV beams of a SL20 accelerator and a 6 MV beam of a SL75/5 accelerator, the model underestimates the OAR in the order of 10% under the thick end of the wedge. We have shown that by appropriate modification of the effective water thickness values at off-axis distances, the algorithm models the OAR in the non-wedged direction to within 2.5% of the measured values for the 4, 6 and 18 MV beams, for the Elekta motorized wedge.

A Phase II trial of 8 weeks of degarelix for prostate volume reduction: Efficacy and hormonal recovery

PURPOSE The purpose of this study was to determine the efficacy of 8 weeks of degarelix for prostate downsizing before interstitial brachytherapy. We also report associated toxicity and the time course of endocrine recovery over the following 12 months. METHODS AND MATERIALS Fifty patients were accrued to an open-label Phase II clinical trial (www.clinicaltrials.gov ID NCT01446991). Baseline prostate transrectal ultrasound (TRUS) was performed on all patients followed by degarelix administration and a repeat TRUS at Week 8. Brachytherapy was performed within 4 weeks of the 8-week TRUS for all patients who achieved suitable downsizing. RESULTS The median prostate volume was reduced from 65.0 cc (interquartile range [IQR]: 55.2-80.0 cc) to 48.2 cc at 8 weeks (IQR: 41.2-59.3 cc), representing a median decrease of 26.2% (IQR: 21-31%). Functional recovery of testosterone within an age-adjusted normal range occurred at a median of 34.1 weeks (IQR: 28.2-44.5 weeks) from the date of the final injection. Despite this recovery, follicle-stimulating hormone and luteinizing hormone levels remained abnormally elevated throughout 12 months. Quality-of-life implications are discussed. CONCLUSIONS Degarelix is effective for prostate downsizing before prostate brachytherapy with a median volume decrease of 26.2% by 8 weeks. Despite the short course of treatment and eventual testosterone recovery, follicle-stimulating hormone and luteinizing hormone remain elevated beyond 12 months. Further investigation with randomized comparisons to other hormonal agents is warranted.

One-step ultrasound-based high dose rate (HDR) prostate brachytherapy with dose escalation to the dominant intra-prostatic lesion.

106 Background: To demonstrate feasibility of using high dose rate (HDR) brachytherapy to deliver 25% higher than prescription dose to the dominant intra-prostatic lesion (DIL) as defined on multi-parametric MRI for intermediate and high risk prostate cancer. Methods: Twenty six patients with predominantly unilateral disease consented to a University Ethics-approved phase II study of selective dose escalation. HDR brachytherapy was performed in weeks 1 and 3 of treatment, each delivering one fraction of 10 Gy to the whole prostate. External beam consisted of 46Gy/23 fractions starting 3 days after the first HDR fraction.T2 FSE images were obtained using 1.5T endorectal MRI in transverse, sagittal and coronal planes followed by Dynamic Contrast Enhancement after injection of gadolinium. Apparent Diffusion Coefficient maps were calculated. The DIL was contoured on the MRI and, following image registration, transposed to the preoperative TRUS performed in the treatment position. Intra-operative TRUS with sou...

Development of a Micro-Simulation Model for Breast Cancer to Evaluate the Impacts of Personalized Early Detection Strategies

Breast cancer screening with mammography has been shown to reduce breast cancer mortality. However the frequency and the age range for screening eligibility has been controversial. Individual risk based screening regimens have recently been proposed to overcome some of the weaknesses of screening mammography. However, it is not possible to evaluate the full impact of such risk based individualized screening strategies in Canadian context. Therefore a mathematical cancer control model for breast cancer using care paths and cancer control data from the province of BC is being developed to model different early detection strategies. The model will incorporate the incidence, detection, diagnosis, progression, and case fatality of breast cancer in BC as baseline to make projections of the population health and economic impacts of different early detection methods for breast cancer. Once the model is validated, it will be possible to test early detection pathways and strategies, frequencies and durations, as well as any health care costs associated with detection, diagnosis, treatment and on-going care of breast cancer patients.

Characterization of Varian on-board imaging systems for use in automatic exposure control software

Modern image guided radiation therapy involves the use of an isocentrically mounted on-board imager (OBI) to take kV images of a patient’s position. Orthogonal OBI images are used with 2D-2D match software to determine the treatment couch shifts required for ideal alignment based on digitally reconstructed radiographs created in treatment planning. The lack of an automatic exposure control (AEC) on Varian OBI systems requires x-ray techniques to be selected manually which may result in over or under exposed images and compromise the accuracy of the image matching. A software based AEC system is being developed in order to predict the optimal, patient specific exposure factors. This software requires that each OBI system be uniquely characterized in terms of both the x-ray tube output and the detector response for a clinical range of energies (kVp). Characteristic curves show that the detector is highly energy dependent at low energies and increasingly energy independent with increasing energy. The detector response (per unit exposure) was determined as a function of the beam quality and the level of detector saturation due to scattered radiation was modeled based on patient thickness, kVp, and field size. Using this model, the optimal exposure can be determined to produce the highest quality image.