C Peng

Optimizing patient positioning for intensity modulated radiation therapy in hippocampal-sparing whole brain radiation therapy

PURPOSE Sparing the hippocampus during whole brain radiation therapy (WBRT) offers potential neurocognitive benefits. However, previously reported intensity modulated radiation therapy (IMRT) plans use multiple noncoplanar beams for treatment delivery. An optimized coplanar IMRT template for hippocampal-sparing WBRT would assist in clinical workflow and minimize resource utilization. In this study, we sought to determine the optimal patient position to facilitate coplanar treatment planning and delivery of hippocampal-sparing WBRT using IMRT. METHODS AND MATERIALS A variable angle, inclined board was utilized for patient positioning. An anthropomorphic phantom underwent computed tomography simulation at various head angles. The IMRT goals were designed to achieve target coverage of the brain while maintaining hippocampal dose-volume constraints designed to conform to the Radiation Therapy Oncology Group 0933 protocol. Optimal head angle was then verified using data from 8 patients comparing coplanar and noncoplanar WBRT IMRT plans. RESULTS Hippocampal, hippocampal avoidance region, and whole brain mean volumes were 1.1 cm(3), 12.5 cm(3), and 1185.1 cm(3), respectively. The hippocampal avoidance region occupied 1.1% of the whole brain planning volume. For the 30-degree head angle, a 7-field coplanar IMRT plan was generated, sparing the hippocampus to a maximum dose of 14.7 Gy; D100% of the hippocampus was 7.4 Gy and mean hippocampal dose was 9.3 Gy. In comparison, for flat head positioning the hippocampal Dmax was 22.9 Gy with a D100% of 9.2 Gy and mean dose of 11.7 Gy. Target coverage and dose homogeneity was comparable with previously published noncoplanar IMRT plans. CONCLUSIONS Compared with conventional supine positioning, an inclined head board at 30 degrees optimizes coplanar whole brain IMRT treatment planning. Clinically acceptable hippocampal-sparing WBRT dosimetry can be obtained using a simplified coplanar plan at a 30-degree head angle, thus obviating the need for complex and time consuming noncoplanar IMRT plans.

Process Mapping and Time Study to Improve Efficiency of New Procedure Implementation for High–Dose Rate Prostate Brachytherapy

New technologies and procedures have the potential to improve outcomes; however, initial implementation is often associated with a steep learning curve, decreased efficiency, and patient safety implications. Implementation of a real-time, ultrasound-based prostate high–dose rate brachytherapy procedure involved a multidisciplinary team composed of approximately 6–8 team members and numerous complex tasks. To characterize time spent on various aspects of the procedure and improve efficiency, the team developed a detailed process map, time study, and team debriefings. A benchmark was created based on an experienced institution which has performed >100 procedures annually. The process map was analyzed based on clinical tasks and treatment planning tasks. Over the course of 17 cases at a single institution, total procedure time ranged from 222 to 107 minutes. Implementation of the process map resulted in a reduction of total time by 52%. The implementation of a new procedure benefits from the integration and utilization of a process map. We were able to reduce procedure time significantly, which resulted in decreased time under general anesthesia, reduced risk of deep vein thrombosis, improved overall patient safety, patient throughput, and decreases in staffing demands.

SU-E-T-116: Analysis of Patient Specific VMAT QA Passing Rates with Delta4 for Matched Machines

Purpose: To test whether unified vendor specified beam conformance for matched machines implies volumetric modulated arc radiotherapy(VMAT) delivery consistency. Methods: Twenty-two identical patient QA plans, eleven 6MV and eleven 15MV, were delivered to the Delta⁴(Scandidos, Uppsala, Sweden) on two Varian TrueBEAM matched machines. Sixteen patient QA plans, nine 6 MV and seven 10 MV, were delivered to Delta⁴ on two Elekta Agility matched machines. The percent dose deviation(%DDev), distance-to-agreement(DTA), and the gamma analysis(γ) were collected for all plans and the differences in measurements were tabulated between matched machines. A paired t-test analysis of the data with an alpha of 0.05 determines statistical significance. Power(P) was calculated to detect a difference of 5%; all data except Elekta %DDev sets were strong with above a 0.85 power. Results: The average differences for Varian machines (%DDev, DTA, and γ) are 6.4%, 1.6% and 2.7% for 6MV, respectively, and 8.0%, 0.6%, and 2.5% for 15MV. The average differences for matched Elekta machines (%DDev, DTA, and γ) are 10.2%, 0.6% and 0.9% for 6 MV, respectively, and 7.0%, 1.9%, and 2.8% for 10MV.A paired t-test shows for Varian the %DDev difference is significant for 6MV and 15MV(p-value6MV=0.019, P6MV=0.96; p-value15MV=0.0003, P15MV=0.86). Differences in DTA are insignificant for both 6MV and 15MV(p-value6MV=0.063, P6MV=1; p-value15MV=0.907, P15MV=1). Varian differences in gamma are significant for both energies(p-value6MV=0.025, P6MV=0.99; p-value15MV=0.013, P15MV=1). A paired t-test shows for Elekta the difference in %DDev is significant for 6MV but not 10MV(p-value6MV=0.00065, P6MV=0.68; p-value10MV=0.262, P10MV=0.39). Differences in DTA are statistically insignificant(p-value6MV=0.803, P6MV = 1; p-value10MV=0.269, P10MV=1). Elekta differences in gamma are significant for 10MV only(p-value6MV=0.094, P6MV=1; p-value10MV=0.011, P10MV=1). Conclusion: These results show vendor specified beam conformance across machines does not ensure equivalent patient specific QA pass rates. Gamma differences are statistically significant in three of the four comparisons for two pairs of vendor matched machines.

SU-E-T-115: Analysis of Patient Specific QA for VMAT by Disease Site and Planning-Delivery System Using the ScandiDos Delta4 Phantom

Purpose: To evaluate patient specific quality assurance (PSQA) for the delivery of volumetric modulated arc therapy (VMAT) by disease site. To compare planning-delivery system (PDS) PSQA pass rates in a dual vendor institution. Methods: PSQA is performed for VMAT plans using a ScandiDos Delta4 phantom. Verification plans are calculated using Varian Eclipse and Elekta Monaco treatment planning systems (TPS) for patients treated using Varian Truebeam and Elekta linear accelerators respectively. Individual arcs are delivered to the Delta4 phantoms and assessed using the gamma index pass criterion(3% Dose Deviation(DD%), 3mm Distance to Agreement(DTA),10% dose threshold and 90% gamma index). Results: A total of 287 VMAT plans and 680 arcs were analyzed. The passing rates for VMAT QA plans were 95% and 98% for head/neck and pelvis/prostate plans respectively, and 100% for chest/abdomen, spine, lung Stereotactic Body Radiotherapy (SBRT) and Stereotactic Radiosurgery(SRS) plans. Average gamma indices were: (99 ± 2) % for pelvis/prostate, chest/abdomen and lung SBRT plans, (97 ± 4) % for head and neck plans and (98 ± 3) % for spine plans. The average DD% and DTA pass rates ranged from 82% to 90% and 98% to 99% respectively for plans in different disease sites. Paired t-test analysis (two tails) indicated no significant differences in the gamma indices between plans delivered using different PDS; the P values were: 0.08, 0.45, and 0.94 for lung SBRT, head/neck and pelvis/prostate plans respectively. The statistical power for comparing PDS in different disease sites with an alpha of 0.05 is 1. Conclusion: The Gamma indices based on 3% DD%, 3 mm DTA and 10% dose threshold for the VMAT QA plans in all disease sites were well above 90%, suggesting the possibility of using a more stringent PSQA criterion. No significant differences were observed in the QA of VMAT plans delivered using different PDS.

SU-E-T-441: Gamma Passing Rates for IMRT QA and VMAT QA.

Purpose: This study compares gamma passing rates for a cohort of similar intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) quality assurance (QA) plans to determine the equivalence of the patient specific QA plan delivery. The passing criterion is 90% gamma index with 3% dose difference (DD), 3mm distance-to-agreement (DTA) and a dose threshold of 10%. Methods: Gamma passing results of previously treated IMRT QA plans, delivered to Sun Nuclear MapCheck phantom, and VMAT QA plans, delivered to ScandiDos Delta4 phantom, are organized by anatomical site and treatment machine. Both Varian and Elekta machines are included. Pairs of IMRT and VMAT plans are matched based on site, machine, and PTV volume to ensure similar plan cohorts. A two-tailed t-test analysis of the data with an alpha of 0.05 determines if there exists a statistically significant difference. Power was calculated to detect a difference of 4%; all data sets were strong with above a 0.8 power. Results: The first data set consisting of 20 matched pairs of prostate plans was statistically insignificant (p-value=0.90, Power=0.99). The 14 matched pairs set of head and neck plans has a statistically significant Result (p-value=0.028, Power=0.88). The head and neck IMRT gamma indexes have a mean of 93.1% and range of 82%-100% while the VMAT gamma indexes have a mean of 96.7% and range of 92%-100%. The two combined data sets of matched plans had a statistically insignificant Result (p-value=0.073, Power=0.99). Conclusion: Overall, IMRT and VMAT have equivalent passing rates when comparing the gamma analysis using a passing criterion of 3% DD and 3mm DTA. When separated by site, prostate IMRT and VMAT plans have equivalent passing rates while head and neck plans have a statistically significant variation of passing rates. The passing rates for the two modalities are independent of delivery machine for matched PTV target volumes.

SU‐E‐T‐408: Evaluation of the Type and Frequency of Variations Discovered During Routine Secondary Patient Chart Review

Purpose: Desire to improve efficiency and throughput inspired a review of our physics chart check procedures. Departmental policy mandates plan checks pre-treatment, after first treatment and weekly every 3–5 days. This study examined the effectiveness of the “after first” check with respect to improving patient safety and clinical efficiency. Type and frequency of variations discovered during this redundant secondary review was examined over seven months. Methods: A community spreadsheet was created to record variations in care discovered during chart review following the first fraction of treatment and before the second fraction (each plan reviewed prior to treatment). Entries were recorded from August 2014 through February 2015, amounting to 43 recorded variations out of 906 reviewed charts. The variations were divided into categories and frequencies were assessed month-to-month. Results: Analysis of recorded variations indicates an overall variation rate of 4.7%. The initial rate was 13.5%; months 2–7 average 3.7%. The majority of variations related to discrepancies in documentation at 46.5%, followed by prescription, plan deficiency, and dose tracking related variations at 25.5%, 12.8%, and 12.8%, respectively. Minor variations (negligible consequence on patient treatment) outweighed major variations 3 to 1. Conclusion: This work indicates that this redundant secondary check is effective. The first month spike in rates could be due to the Hawthorne/observer effect, but the consistent 4% variation rate suggests the need for periodical re-training on variations noted as frequent to improve awareness and quality of the initial chart review process, which may lead to improved treatment quality, patient safety and increased clinical efficiency. Utilizing these results, a continuous quality improvement process following Deming’s Plan-Do-Study-Act (PDSA) methodology was generated. The first iteration of this PDSA was adding a specific dose tracking checklist item in the pre-treatment plan check assessment; the ramification of which will be assessed in future data.

SU‐E‐T‐620: Dosimetric Compliance Study for a New Prostate Protocol of Combined High Dose Rate Brachytherapy and Stereotactic Body Radiotherapy

PURPOSE To investigate the adherence of treatment plans of prostate cancer patients with the dosimetric compliance criteria of the new in house phase I trial of high dose rate (HDR) brachytherapy combined with stereotactic body radiotherapy (SBRT) for intermediate risk prostate cancer patients. METHODS Ten prostate cancer patients were treated using this trial. They received one fraction of HDR to 15Gy, followed by external beam(EB) boost of 3.2Gy(Level 1, five patients) or 3.94Gy(level 2, five patients) per fraction for 10 or 7 fractions, respectively, both equivalent to EB treatments of 113.5Gy in 2Gy fractions. The EB plans were either IMRT or VMAT plans. DVH analysis was performed to verify the adherence of treatment plans to the dosimetric criteria of the trial. RESULTS For Level 1 patients, target coverage were adequate, with CTV V32Gy(%) of 99.0±1.0 (mean ± 1 standard deviation), and PTV V31Gy(%) of 99.6±0.3. PTV V32.9Gy(%) is 1.4±3.1 and PTVmax is 32.9±0.2Gy. Rectum, bladder and femoral heads sparing were well within protocol criteria. For Level 2 patients, CTV V27.6Gy(%) is 98.7±1.8; PTV V26.7Gy(%) is 99.0±1.4. PTV V28.4Gy(%) is 1.3±1.4, with three patients having minor deviation from protocol. Again critical structures were spared compliant to the protocol. The analysis of HDR plans show similar results, with adequate dose coverage to the prostate and sparing of critical structures including urethra and rectum. V100(%) and V90(%) of prostate are 96.0±1.1 and 98.9±0.5. Urethra D10(%) is 113.1±2.9. Rectum V80(cc) is 1.4±0.5. Hotspot in prostate is substantially higher than what the protocol specifies. But the criteria for hotspot are only guidelines, serving to lower the dose to urethra . CONCLUSION This new high biological equivalent dose prostate trial has been carried out successfully for ten patients. Based on dosimetric analysis, all HDR and external plans were compliant to the protocol criteria, with only minor deviations.

Process mapping and time study to improve efficiency of HDR prostate brachytherapy.

103 Background: New technologies and procedures have the potential to improve outcomes; however, initial implementation is often associated with a steep learning curve, decreased efficiency, and patient safety implications. Since process mapping, checklists and external benchmarks have been proven to be useful quality improvement (QI) tools in health care, we sought to use these QI tools in a novel setting to decrease new procedure times without sacrificing the quality of care. METHODS Implementation of a real-time, ultrasound based prostate high-dose-rate brachytherapy procedure involved a multidisciplinary team composed of approximately 6-8 team members and numerous complex tasks. To characterize time spent on various aspects of the procedure and improve efficiency, our team developed a detailed process map including checklists and team debriefings. A benchmark was created based on an experienced institution which has performed >100 procedures annually. Times for key events, such as induction of general anesthesia, acquisition of first image, catheter insertion and completion of planning were recorded during each case. The process map was analyzed based on clinical tasks and treatment planning tasks. RESULTS The expert institution completed a procedure in 65 minutes. Over the course of ten cases at our institution, total procedure time ranged from 222-107 minutes. Implementation of the process map resulted in a reduction of total time by 52% (51% for clinical tasks and 65% for planning). Process improvements included changes to room layout, availability of supplies and identification of parallel processes. Improvement in efficiency was done without compromising quality as defined by dosimetric parameters. CONCLUSIONS The implementation of a new procedure benefits from the integration and utilization of a process map. We were able to reduce procedure time significantly, which resulted in decreased time under general anesthesia, reduced risk of deep vein thrombosis and improved overall patient safety.

SU‐E‐T‐136: Measure the Actual Radiation Dose Delivered for Prostate IMRT Treatment Using An Implantable MOSFET Dosimeter

Purpose: To report the initial clinical experience using an in‐vivo, implantable metal oxide semiconductors field effect transistors(MOSFET)dosimeters for the daily dose verification of prostate IMRTtreatment.Methods: The dose verification system (DVS) from Sicel Technologies was used to measure the actual dose delivered for prostate IMRT patients. Fifteen patients (10 prostate IMRT; 5 Sequential IMRT, pelvis then prostate) were implanted with two DVS dosimeters in the prostate gland: one on the right and the other on the left. The location of the DVS dosimeters were identified on the CTimages and the expected doses were calculated. The measured readings of the dosimeters were compared to the expected dose values. Daily orthogonal portal film or CBCT was used for patient setup.Results: The average difference between predicted and measured doses was 1.1% for all 15 patients (30 dosimeters) over the whole course of treatment. The range of the difference between the measured cumulative doses to the planned doses for the whole treatment course was from −5.3% to 5.1%. For three out of fifteen patients, a new plan was created as the measured doses disagreed with the expected value for the original plans. For those three patients, the difference between measured and the predicted doses was as large as 11.3%. The discrepancies were much smaller after replanning. The average dosimeter measurement for the nine prostate IMRTtreatment (exclude one prostate IMRT patient who had been re‐planned) over the course of treatment was decreasing signifying a possible decrease in the sensitivity of the dosimeters Conclusions: This study demonstrated DVS dosimeters could provide valuable information about actual dose delivered and actual dose fluctuations of the daily treatment. The DVS dosimeters could serve as a patient specific quality assurance and guidance for adaptive radiation therapy.