Luis E. Fong de los Santos

Clinical outcomes and dosimetric considerations using stereotactic body radiotherapy for abdominopelvic tumors.

Purpose/ObjectivesTo present clinical outcomes, early toxicity, and dosimetric constraints for patients undergoing stereotactic body radiation therapy (SBRT) for abdominal or pelvic tumors. Materials and MethodsFrom May 2008 to February 2010, 47 patients with 50 lesions in proximity to hollow viscous organs at risk, including stomach, duodenum, small bowel, and colon, underwent SBRT at Mayo Clinic. Treated sites included liver (21), lymph node (14), adrenal gland (6), intramuscular (4), pancreas (3), and spleen (2). Treatment planning was performed with full body immobilization and 4-dimensional computed tomography (CT)-based planning with daily cone-beam CT or stereoscopic kV imaging for pretreatment image guidance. SBRT was delivered in 1 to 5 consecutive daily fractions in a single week. The most commonly prescribed dose was 50 Gy in 5 fractions (median 45 Gy, range: 20 to 60 Gy). Toxicities were scored by CTCAE v.3. Local failure was defined as per the Response Evaluation Criteria in Solid Tumors. ResultsMedian follow-up was 12 months (range: 2 to 28 mo). Tumor responses of the 48 target lesions evaluable by Response Evaluation Criteria in Solid Tumor were complete response in 18 lesions (36%), partial response in 12 lesions (24%), stable disease in 12 lesions (24%), and progressive disease in 6 lesions (12%). Kaplan-Meier estimates of local control, overall survival, and freedom from metastasis at 6 and 12 months were 98%, 90%, and 63%, and 87%, 62%, 37%, respectively. Treatment was well-tolerated acutely without reported grade ≥3 toxicity. Five grade 3 late toxicities were reported, and 1 patient died of complications from duodenal perforation 11 months after SBRT. No dose correlation with toxicity could be established. ConclusionsSBRT is a practical treatment option for patients with abdominopelvic tumors. Relapse typically occurs outside treatment fields, and most patients achieve a favorable response. The dose constraints used in this cohort of patients was associated with acceptable early treatment-related toxicity.

Analysis of automatic match results for cone-beam computed tomography localization of conventionally fractionated lung tumors.

PURPOSE To evaluate the dependence of an automatic match process on the size of the user-defined region of interest (ROI), the structure volume of interest (VOI), and changes in tumor volume when using cone-beam computed tomography (CBCT) for tumor localization and to compare these results with a gold standard defined by a physicians manual match. METHODS AND MATERIALS Daily CBCT images for 11 patients with lung cancer treated with conventionally fractionated radiation therapy were retrospectively matched to a reference CT image using the Varian On Board Imager software (Varian, Palo Alto, CA) and a 3-step automatic matching protocol. Matches were performed with 3 ROI sizes (small, medium, large), with and without a structure VOI (internal target volume [ITV] or planning target volume [PTV]) used in the last step. Additionally, matches were performed using an intensity range that isolated the bony anatomy of the spinal column. All automatic matches were compared with a manual match made by a physician. RESULTS The CBCT images from 109 fractions were analyzed. Automatic match results depend on ROI size and the structure VOI. Compared with the physicians manual match, automatic matches using the PTV as the structure VOI and a small ROI resulted in differences ≥ 5 mm in 1.8% of comparisons. Automatic matches using no VOI and a large ROI differed by ≥ 5 mm in 30.3% of comparisons. Differences between manual and automatic matches using the ITV as the structure VOI increased as tumor size decreased during the treatment course. CONCLUSIONS Users of automatic matching techniques should carefully consider how user-defined parameters affect tumor localization. Automatic matches using the PTV as the structure VOI and a small ROI were most consistent with a physicians manual match, and were independent of volumetric tumor changes.

Separating the dosimetric consequences of changing tumor anatomy from positional uncertainty for conventionally fractionated lung cancer patients

PURPOSE To separate the dosimetric consequences of changing tumor volume from positional uncertainty for patients undergoing conventionally fractionated lung radiation therapy (RT) and to quantify which factor has a larger impact on dose to target volumes and organs at risk (OAR). METHODS AND MATERIALS Clinical treatment plans from 20 patients who had received conventionally fractionated RT were retrospectively altered by replacing tumor and atelectasis with lung equivalent tissue in the treatment planning system calculations. To simulate positional uncertainty, the isocenter was shifted in both the altered and original plans by 2 and 5 mm in 6 directions. Rotational uncertainty was introduced by rotating each computed tomographic image set by ± 3 degrees about a superior-inferior axis extending through patient center. Additionally, after rotation the isocenter was translated back to its original point within the patient to evaluate whether purely translational corrections could minimize dosimetric consequences due to rotations. RESULTS Dosimetric statistics for each altered plan were compared with the original. Average changes in the planning target volume (PTV) receiving 95% of prescription dose (PTV V95%) resulting from changing tumor anatomy alone were approximately 0.1%. Average changes in PTV V95% resulting from positional uncertainty were greater (0.2%-4.2%) but were largely independent of whether or not the original tumor volume was present. For 3 patients, increases in volumes receiving 110% of the prescription dose were seen but were largely limited to within the PTV. Translational corrections for patient rotations were effective in minimizing differences in target coverage but had less effect on reducing the maximum spinal cord dose. CONCLUSIONS Anatomic changes alone, such as reductions in tumor volume and atelectasis, had minimal effect on the overall dose distribution. Greater dosimetric consequences were seen with positional uncertainty. With accurate patient localization, replanning during the course of treatment for conventionally fractionated lung cancer patients may not be necessary.

Technical Note: Initial characterization of the new EBT-XD Gafchromic film

PURPOSE To assess the dosimetric accuracy and energy dependence of the new EBT-eXtended Dose (XD) Gafchromic film and to compare the lateral response artifact (LRA) between EBT-XD and EBT3 film. METHODS EBT3 and EBT-XD calibration curves were created by exposing films to known doses from 0 to 3000 cGy using a 6 MV beam. To assess the accuracy and dynamic range of EBT-XD, a 60° enhanced dynamic wedge (EDW) was used to deliver a dose range of approximately 200-2900 cGy. Comparison to treatment planning system (TPS) calculation was made using a gamma analysis with 2%/2 mm passing criteria. To assess and compare the LRA between EBT3 and EBT-XD, 21 × 21 cm(2) open fields delivered doses of 1000, 2000, and 3000 cGy to both types of film. Films were placed at the center of the scanner, and ratios of measured to TPS predicted doses were calculated at 50 and 80 mm lateral from the scanner center in order to quantitatively assess the LRA. To evaluate the energy dependence of EBT-XD film, seven known doses ranging from 400 to 3000 cGy were delivered using both 6 and 18 MV beams and the resulting optical densities (ODs) compared. RESULTS The gamma passing rate was 99.1% for the 6 MV EDW delivery. EBT-XD film exhibited minimal LRA (<1%) up to 3000 cGy. In contrast, EBT3 demonstrated an under-response of 11.3% and 22.7% at lateral positions of 50 and 80 mm, respectively, for the 3000 cGy exposure. Differences between ODs of the EBT-XD films exposed to known doses from 6 to 18 MV beams were <0.8% suggesting minimal energy dependence throughout this energy range. CONCLUSIONS The LRA of EBT-XD is greatly reduced when compared to EBT3. This in combination with its accuracy from 0 to 3000 cGy and minimal energy dependence from 6 to 18 MV makes EBT-XD film well suited for dosimetric measurements in high dose SRS/SBRT applications.

Radiation oncology information systems and clinical practice compatibility: Workflow evaluation and comprehensive assessment

PURPOSE To map the level of clinical practice compatibility with a radiation oncology information system (ROIS) through a workflow- and clinical process-based method aimed at optimizing the safety, efficacy, and efficiency of patient care; to improve the understanding of the critical relationship between the clinical practice and ROIS. METHODS AND MATERIALS Clinic-specific workflow and infrastructure were classified into clinical processes, information management, and technological innovation integration. Clinical information systems-information technology infrastructure and process maps were generated by a team of experts, representing clinical constituents. These maps served as the basis for evaluating connectivity and process flow and to guide the development of a quantitative survey where all clinical tasks and subprocesses were ranked according to importance in patient care and scored by the team of experts for performance. Process maps and survey output were used to measure ROIS compatibility with the practice and to guide practice improvement. RESULTS Practice-specific process and infrastructure maps were generated. The developed survey was applied and results indicate a range of ROIS compatibility with clinical workflow and infrastructure. Survey results combined with experiential feedback provided specific prioritized guidance to improve both ROIS performance and clinic-specific processes and infrastructure. CONCLUSIONS This work provides a systematic and customizable tool to understand and evaluate clinical information and workflow and its compatibility with a given ROIS. The analysis provides insight into workflow improvements and information systems and information technology infrastructure limitations. Participating in such a process provides the entire team with a deeper understanding of the critical relationship between the clinical practice and the ROIS.

Cadaveric verification of the Eclipse AAA algorithm for spine SBRT treatments with titanium hardware.

PURPOSE To assess the accuracy of the Eclipse Analytical Anisotropic Algorithm when calculating dose for spine stereotactic body radiation therapy treatments involving surgically implanted titanium hardware. METHODS AND MATERIALS A human spine was removed from a cadaver, cut sagittally along the midline, and then separated into thoracic and lumbar sections. The thoracic section was implanted with titanium stabilization hardware; the lumbar section was not implanted. Spine sections were secured in a water phantom and simulated for treatment planning using both standard and extended computed tomography (CT) scales. Target volumes were created on both spine sections. Dose calculations were performed using (1) the standard CT scale with relative electron density (RED) override of image artifacts and hardware, (2) the extended CT scale with RED override of image artifacts only, and (3) the standard CT scale with no RED overrides for hardware or artifacts. Plans were delivered with volumetric modulated arc therapy using a 6-MV beam with and without a flattening filter. A total of 3 measurements for each plan were made with Gafchromic film placed between the spine sections and compared with Eclipse dose calculations using gamma analysis with a 2%/2 mm passing criteria. A single measurement in a homogeneous phantom was made for each plan before actual delivery. RESULTS Gamma passing rates for measurements in the homogeneous phantom were 99.6% or greater. Passing rates for measurements made in the lumbar spine section without hardware were 99.3% or greater; measurements made in the thoracic spine containing titanium were 98.6 to 99.5%. CONCLUSIONS Eclipse Analytical Anisotropic Algorithm can adequately model the effects of titanium implants for spine stereotactic body radiation therapy treatments using volumetric modulated arc therapy. Calculations with standard or extended CT scales give similarly accurate results.

Phantom Verification of AAA and Acuros Dose Calculations for Lung Cancer: Do Tumor Size and Regression Matter?

PURPOSE This study aimed to evaluate dose calculation accuracy for the Eclipse Analytical Anisotropic Algorithm (AAA) and Acuros XB algorithm for various lung tumor sizes and to investigate dosimetric changes associated with treatment of regressing tumors. METHODS AND MATERIALS A water phantom with cylindrical cork inserts (lung surrogates) was fabricated. Large (202 cm3), medium (54 cm3), and small (3 cm3) solid water tumors were implanted within cork inserts. A plain cork insert was used to simulate a lung without a tumor. The cork inserts and tumors were cut along the long axis, and Gafchromic film was placed between the sections to measure dose distributions. Three-dimensional conformal plans were created using 6 MV and 10 MV beams, and volumetric modulated arc therapy plans were created using 6 MV beams for each tumor size. Doses were calculated using Eclipse AAA and Acuros XB. The measured and calculated dose distributions were compared for each tumor size and treatment algorithm. To simulate a regressing tumor, the original plans created for the large tumor were separately delivered to the phantom that contained a small, medium, or no tumor. The dosimetric effects were evaluated using gamma passing rates with a 2%/2 mm criterion and dose profile comparisons. RESULTS Agreement between the measurements and AAA calculations decreased as tumor size decreased, but Acuros XB showed better agreement for all tumor sizes. The largest difference was observed for a 6 MV volumetric modulated arc therapy plan created to treat the smallest tumor. The gamma passing rate was 89.7% but that of Acuros was 99.5%. For the tumor regression evaluation, the gamma passing rates ranged from 53% to 99% for AAA. For Acuros XB, the gamma passing rates were >98% for all scenarios. CONCLUSION Both AAA and Acuros XB calculated the dose accurately for the largest lung tumor. For the smallest and regressing tumors, Acuros XB more accurately modelled the dose distribution compared with AAA.

Design and clinical use of a rotational phantom for dosimetric verification of IMRT/VMAT treatments

PURPOSE To describe the design and clinical use of a rotational phantom for dosimetric verification of IMRT/VMAT treatment plans using radiochromic film. METHODS A solid water cylindrical phantom was designed with separable upper and lower halves and rests on plastic bearings allowing for 360° rotation about its central axis. The phantom accommodates a half sheet of radiochromic film, and by rotating the cylinder, the film can be placed in any plane between coronal and sagittal. Calculated dose planes coinciding with rotated film measurements are exported by rotating the CT image and dose distribution within the treatment planning system. The process is illustrated with 2 rotated film measurements of an SRS treatment plan involving 4 separate targets. Additionally, 276 patient specific QA measurements were obtained with the phantom and analyzed with a 2%/2 mm gamma criterion. RESULTS The average 2%/2 mm gamma passing rate for all 276 plans was 99.3%. Seventy-two of the 276 plans were measured with the plane of the film rotated between the coronal and sagittal planes and had an average passing rate of 99.4%. CONCLUSIONS The rotational phantom allows for accurate film measurements in any plane. With this technique, regions of a dose distribution which might otherwise require multiple sagittal or coronal measurements can be verified with as few as a single measurement. This increases efficiency and, in combination with the high spatial resolution inherent to film dosimetry, makes the rotational technique an attractive option for patient-specific QA.

Image‐guided radiotherapy quality control: Statistical process control using image similarity metrics

PURPOSE The purpose of this study was to demonstrate an objective quality control framework for the image review process. METHODS AND MATERIALS A total of 927 cone-beam computed tomography (CBCT) registrations were retrospectively analyzed for 33 bilateral head and neck cancer patients who received definitive radiotherapy. Two registration tracking volumes (RTVs) - cervical spine (C-spine) and mandible - were defined, within which a similarity metric was calculated and used as a registration quality tracking metric over the course of treatment. First, sensitivity to large misregistrations was analyzed for normalized cross-correlation (NCC) and mutual information (MI) in the context of statistical analysis. The distribution of metrics was obtained for displacements that varied according to a normal distribution with standard deviation of σ = 2 mm, and the detectability of displacements greater than 5 mm was investigated. Then, similarity metric control charts were created using a statistical process control (SPC) framework to objectively monitor the image registration and review process. Patient-specific control charts were created using NCC values from the first five fractions to set a patient-specific process capability limit. Population control charts were created using the average of the first five NCC values for all patients in the study. For each patient, the similarity metrics were calculated as a function of unidirectional translation, referred to as the effective displacement. Patient-specific action limits corresponding to 5 mm effective displacements were defined. Furthermore, effective displacements of the ten registrations with the lowest similarity metrics were compared with a three dimensional (3DoF) couch displacement required to align the anatomical landmarks. RESULTS Normalized cross-correlation identified suboptimal registrations more effectively than MI within the framework of SPC. Deviations greater than 5 mm were detected at 2.8σ and 2.1σ from the mean for NCC and MI, respectively. Patient-specific control charts using NCC evaluated daily variation and identified statistically significant deviations. This study also showed that subjective evaluations of the images were not always consistent. Population control charts identified a patient whose tracking metrics were significantly lower than those of other patients. The patient-specific action limits identified registrations that warranted immediate evaluation by an expert. When effective displacements in the anterior-posterior direction were compared to 3DoF couch displacements, the agreement was ±1 mm for seven of 10 patients for both C-spine and mandible RTVs. CONCLUSIONS Qualitative review alone of IGRT images can result in inconsistent feedback to the IGRT process. Registration tracking using NCC objectively identifies statistically significant deviations. When used in conjunction with the current image review process, this tool can assist in improving the safety and consistency of the IGRT process.

Patient safety is improved with an incident learning system—Clinical evidence in brachytherapy

BACKGROUND AND PURPOSE Health leaders have advocated for incident learning systems (ILSs) to prevent errors, but there is limited evidence demonstrating that ILSs improve cancer patient safety. Herein, we report a long-term retrospective review of ILS reports for the brachytherapy practice at a large academic institution. MATERIAL AND METHODS Over a nine-year period, the brachytherapy practice was encouraged to report all standard operating procedure deviations, including low risk deviations. A multidisciplinary committee assigned root causes and risk scores to all incidents. Evidence based practice changes were made using ILS data, and relevant incidents were communicated to all staff in order to reduce recurrence rates. RESULTS 5258 brachytherapy procedures were performed and 2238 incidents were reported from 2007 to 2015. A ramp-up period was observed in ILS participation between 2007 (0.12 submissions/procedures) and 2011 (1.55 submissions/procedures). Participation remained stable between 2011 and 2015, and we achieved a 60% (p<0.001) decrease in the risk of dose error or violation of radiation safety policy and a 70% (p<0.001) decrease in frequency of high composite-risk scores. Significant decreases were also observed in incidents with root causes of poor communication (60% decrease, p<0.001) and poor quality of written procedures (59% decrease, p<0.001). CONCLUSIONS Implementation of an ILS in brachytherapy significantly reduced risk during cancer patient care. Safety improvements have been sustained over several years.