B.W. Cox

Continuous Monitoring and Intrafraction Target Position Correction During Treatment Improves Target Coverage for Patients Undergoing SBRT Prostate Therapy

PURPOSE To compare the potential benefits of continuous monitoring of prostate position and intervention (CMI) using 2-mm displacement thresholds during stereotactic body radiation therapy (SBRT) treatment to those of a conventional image-guided procedure involving single localization prior to treatment. METHODS AND MATERIALS Eighty-nine patients accrued to a prostate SBRT dose escalation protocol were implanted with radiofrequency transponder beacons. The planning target volume (PTV) margin was 5 mm in all directions, except for 3 mm in the posterior direction. The prostate was kept within 2 mm of its planned position by the therapists halting dose delivery and, if necessary, correcting the couch position. We computed the number, type, and time required for interventions and where the prostate would have been during dose delivery had there been, instead, a single image-guided setup procedure prior to each treatment. Distributions of prostate displacements were computed as a function of time. RESULTS After the initial setup, 1.7 interventions per fraction were required, with a concomitant increase in time for dose delivery of approximately 65 seconds. Small systematic drifts in prostate position in the posterior and inferior directions were observed in the study patients. Without CMI, intrafractional motion would have resulted in approximately 10% of patients having a delivered dose that did not meet our clinical coverage requirement, that is, a PTV D95 of >90%. The posterior PTV margin required for 95% of the dose to be delivered with the target positioned within the PTV was computed as a function of time. The margin necessary was found to increase by 2 mm every 5 minutes, starting from the time of the imaging procedure. CONCLUSIONS CMI using a tight 2-mm displacement threshold was not only feasible but was found to deliver superior PTV coverage compared with the conventional image-guided procedure in the SBRT setting.

Incident Learning and Failure-Mode-and-Effects-Analysis Guided Safety Initiatives in Radiation Medicine

By combining incident learning and process failure-mode-and-effects-analysis (FMEA) in a structure-process-outcome framework we have created a risk profile for our radiation medicine practice and implemented evidence-based risk-mitigation initiatives focused on patient safety. Based on reactive reviews of incidents reported in our departmental incident-reporting system and proactive FMEA, high safety-risk procedures in our paperless radiation medicine process and latent risk factors were identified. Six initiatives aimed at the mitigation of associated severity, likelihood-of-occurrence, and detectability risks were implemented. These were the standardization of care pathways and toxicity grading, pre-treatment-planning peer review, a policy to thwart delay-rushed processes, an electronic whiteboard to enhance coordination, and the use of six sigma metrics to monitor operational efficiencies. The effectiveness of these initiatives over a 3-years period was assessed using process and outcome specific metrics within the framework of the department structure. There has been a 47% increase in incident-reporting, with no increase in adverse events. Care pathways have been used with greater than 97% clinical compliance rate. The implementation of peer review prior to treatment-planning and use of the whiteboard have provided opportunities for proactive detection and correction of errors. There has been a twofold drop in the occurrence of high-risk procedural delays. Patient treatment start delays are routinely enforced on cases that would have historically been rushed. Z-scores for high-risk procedures have steadily improved from 1.78 to 2.35. The initiatives resulted in sustained reductions of failure-mode risks as measured by a set of evidence-based metrics over a 3-years period. These augment or incorporate many of the published recommendations for patient safety in radiation medicine by translating them to clinical practice.

Prospective contouring rounds: A novel, high-impact tool for optimizing quality assurance

PURPOSE This study was designed to present the results of a novel prospective contouring rounds (CR), in which peer review occurs once the contours and written directive are completed but before initiation of treatment planning. METHODS AND MATERIALS Beginning in 2012, all patients undergoing conventionally fractionated radiation therapy at a high-volume academic center were reviewed in a newly initiated daily, prospective, multidisciplinary CR. Cases were scheduled for presentation 2 days after simulation with the expectation that contours would be complete. The clinical suitability of the clinical plan, prescription, contours, and written directive were evaluated and recorded in a prospective database. Treatment planning did not commence until CR approval. Patient information and the prospective database from the first 6 months since program inception, which represented 581 consecutive treatment plans, were pooled and analyzed retrospectively to determine the impact of the prospective peer review at this stage of care delivery. RESULTS Sixty-four percent of cases were completed on time without correction. The remaining 36% of cases required modification before treatment planning was initiated. Incomplete contours, target-volume modifications, and alterations to the written directive were the most common corrections or reasons for delay. Decreasing rates of incomplete contours, contour modifications, and miscellaneous delays were seen over time as the program became established. The percentage of cases that had no delays or modifications increased continuously as the program matured in the first 6 months, from 59% to 70%. CONCLUSIONS Prospective CR is a meaningful and impactful tool in the quality assurance process. More than one-third of cases required contour, directive, or scheduling modification. The establishment of CR improved quality of care, with the percentage of timely, errorless cases increasing steadily over time. The impact of clinical peer review may be optimized by implementation at this early stage of delivery of care rather than at the time of traditional chart rounds.

Early Results of a Phase I Dose Escalation Study Using Stereotactic Body Radiosurgery for Patients with Clinically Localized Prostate Cancer

Objectives: To report the acute and late toxicity outcomes as well as preliminary PSA relapsefree survival results among patients treated on a prospective dose escalation study using highdose 5 fraction stereotactic body radiosurgery (SBRT) for patients with low and intermediate risk prostate cancer. Methods: 136 patients were accrued to a Phase I dose escalation study to determine the tolerance of escalating radiation dose levels of SBRT in the treatment of localized prostate cancer. The initial dose level was 32.5Gy in 5 fractions delivered every other day. After 30 patients were accrued and at least 50% of these were followed for a minimum of 3 months, the dose level was escalated by 2.5 Gy increments. In this fashion 30 patients received a prescription dose of 32.5 Gy, 35 patients were treated to 35 Gy, 36 patients to 37.5 Gy and 35 patients to 40 Gy. Doses were prescribed to the planning target volume where 5 mm margins were used around the prostate and seminal vesicles except posteriorly where a 3 mm margin was used at the prostate-rectal interface. All patients were monitored with intra-fraction motion fiducial-based targeting (Calypso TM), and target positions were corrected if deviations were noted beyond a 2mm set threshold. Eligibility criteria included only low and intermediate risk patients, and patients treated with neo-adjuvant androgen deprivation were excluded. The CTC-4 clinical toxicity score was used to characterize acute and late toxicity. The median follow up for the 4 dose levels were 60 months, 48 months, 24 months, and 18 months respectively. Results: The incidence of acute grade 2 rectal toxicities for dose levels 1-4 were 0%, 5.7%, 3.2% and 3.2% respectively. No grade 3 or 4 acute rectal toxicities were observed. The incidence of acute grade 2 urinary toxicities for dose levels 1-4 were 13.3%, 8.6%, 13.9% and 6.5% respectively. Only 1 patient at the 40 Gy dose level experienced a grade 3 acute toxicity (urinary retention requiring foley catheter placement). The incidence of late grade 2 rectal toxicities for dose levels 1-4 were 3.3%, 0%, 2.8% and 0% respectively. No grade 3 or 4 late rectal toxicities were observed. The incidence of late grade 2 urinary toxicities for dose levels 1-4 were 13.3%, 14.3%, 8.3% and 9.7% respectively. Only one late grade 3 urinary toxicity (urethral stricture) developed in the 32.5 Gy dose arm after treatment which was corrected with transurethral resection. No grade 4 late urinary toxicities were observed. The median PSA nadir value at 2 1 2 3 4 2 Open Access Abstract

Accuracy evaluation of a six‐degree‐of‐freedom couch using cone beam CT and IsoCal phantom with an in‐house algorithm

Purpose: The accuracy of a six degree of freedom (6DoF) couch was evaluated using a novel method. Methods: Cone beam CT (CBCT) images of a 3D phantom (IsoCal) were acquired with different, known combinations of couch pitch and roll angles. Pitch and roll angles between the maximum allowable values of 357 and 3 degrees were tested in one degree increments. A total of 49 combinations were tested at 0 degrees of yaw (couch rotation angle). The 3D positions of 16 tungsten carbide ball bearings (BBs), each 4 mm in diameter and arranged in a known geometry within the IsoCal phantom, were determined in the 49 image sets with in‐house software. The BB positions at different rotation angles were determined using a rotation matrix from the original BB positions at zero pitch and roll angles. A linear least squares fit method estimated the rotation angles and differences between detected and nominal rotation angles were calculated. This study was conducted for the case with and without extra weight on the couch. Couch walk shifts for the system were investigated using eight combinations of rotation, roll and pitch. Results: A total of 49 CBCT images with voxel sizes 0.5 × 0.5 × 1.0 mm3 were taken for the case without extra weight on the couch. The 16 BBs were determined to evaluate the isocenter translation and rotation differences between the calculated and nominal couch values. Among all 49 calculations, the maximum rotation angle differences were 0.10 degrees for pitch, 0.15 degrees for roll and 0.09 degrees for yaw. The corresponding mean and standard deviation values were 0.028 ± 0.032, −0.043 ± 0.058, and −0.009 ± 0.033 degrees. The maximum translation differences were 0.3 mm in the left–right direction, 0.5 mm in the anterior–posterior direction and 0.4 mm in the superior–inferior direction. The mean values and corresponding standard deviations were 0.07 ± 0.12, −0.05 ± 0.25, and −0.12±0.14 mm for the planes described above. With an 80 kg phantom on the couch, the maximum translation shift was 0.69 mm. The couch walk translation shifts were less than 0.1 mm and rotation shifts were less than 0.1 degree. Conclusions: Errors of a new 6DoF couch were tested using CBCT images of a 3D phantom. The rotation errors were less than 0.3 degree and the translation errors were less than or equal to 0.8 mm in each direction. This level of accuracy is warranted for clinical radiotherapy utilization including stereotactic radiosurgery.

Radiation Therapy: Brachytherapy

Prostate brachytherapy is an interventional procedure that is highly safe and effective for the treatment of localized prostate cancer. Brachytherapy offers equivalent to superior biochemical outcomes when compared to external beam radiation therapy and radical prostatectomy but offers an attractive toxicity prolife, improved quality of life, and preservation of sexual function when compared to these modalities. Modern prostate brachytherapy has benefitted significantly from the integration of advanced radiologic technologies, which have led to significant advances in the diagnosis and staging of prostate cancer, in the intraoperative imaging and placement of radioactive sources, and in the dosimetric assessment and toxicity management of patients undergoing prostate brachytherapy.