T.J. Whitaker

Spot-scanned pancreatic stereotactic body proton therapy: A dosimetric feasibility and robustness study

PURPOSE We explored the dosimetric potential of spot-scanned stereotactic body proton therapy (SBPT) for pancreatic cancer. METHODS We compared SBPT to stereotactic body intensity-modulated radiotherapy (SB-IMRT) in 10 patients. We evaluated 3 variables in SBPT planning: (1) 4 and 6 mm spot size; (2) single vs. multi-field optimization (SFO vs. MFO); and (3) optimization target volume (OTV) expansion. Robustness analysis was performed with unidirectional isocenter shifts of ±3 mm in x, y, and z and ±3% stopping power uncertainties. RESULTS SBPT plans had lower V10Gy for the stomach and small and large bowels. Under static robustness, a 5 mm OTV and SFO-6 mm spot size represented the best compromise between target and normal structure. A 4-mm spot-size and 3 mm OTV resulted in significant target underdosing with deformable dose accumulation analysis. CONCLUSIONS This study provides a critical basis for clinical translation of spot size, optimization technique, and OTV expansion for pancreatic SBPT.

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.

Present developments in reaching an international consensus for a model-based approach to particle beam therapy

Abstract Particle beam therapy (PBT), including proton and carbon ion therapy, is an emerging innovative treatment for cancer patients. Due to the high cost of and limited access to treatment, meticulous selection of patients who would benefit most from PBT, when compared with standard X-ray therapy (XRT), is necessary. Due to the cost and labor involved in randomized controlled trials, the model-based approach (MBA) is used as an alternative means of establishing scientific evidence in medicine, and it can be improved continuously. Good databases and reasonable models are crucial for the reliability of this approach. The tumor control probability and normal tissue complication probability models are good illustrations of the advantages of PBT, but pre-existing NTCP models have been derived from historical patient treatments from the XRT era. This highlights the necessity of prospectively analyzing specific treatment-related toxicities in order to develop PBT-compatible models. An international consensus has been reached at the Global Institution for Collaborative Research and Education (GI-CoRE) joint symposium, concluding that a systematically developed model is required for model accuracy and performance. Six important steps that need to be observed in these considerations include patient selection, treatment planning, beam delivery, dose verification, response assessment, and data analysis. Advanced technologies in radiotherapy and computer science can be integrated to improve the efficacy of a treatment. Model validation and appropriately defined thresholds in a cost-effectiveness centered manner, together with quality assurance in the treatment planning, have to be achieved prior to clinical implementation.

SU-F-T-169: A Periodic Quality Assurance Program for a Spot-Scanning Proton Treatment Facility

PURPOSE To develop daily and monthly quality assurance (QA) programs in support of a new spot-scanning proton treatment facility using a combination of commercial and custom equipment and software. Emphasis was placed on efficiency and evaluation of key quality parameters. METHODS The daily QA program was developed to test output, spot size and position, proton beam energy, and image guidance using the Sun Nuclear Corporation rf-DQA™3 device and Atlas QA software. The program utilizes standard Atlas linear accelerator tests repurposed for proton measurements and a custom jig for indexing the device to the treatment couch. The monthly QA program was designed to test mechanical performance, image quality, radiation quality, isocenter coincidence, and safety features. Many of these tests are similar to linear accelerator QA counterparts, but many require customized test design and equipment. Coincidence of imaging, laser marker, mechanical, and radiation isocenters, for instance, is verified using a custom film-based device devised and manufactured at our facility. Proton spot size and position as a function of energy are verified using a custom spot pattern incident on film and analysis software developed in-house. More details concerning the equipment and software developed for monthly QA are included in the supporting document. Thresholds for daily and monthly tests were established via perturbation analysis, early experience, and/or proton system specifications and associated acceptance test results. RESULTS The periodic QA program described here has been in effect for approximately 9 months and has proven efficient and sensitive to sub-clinical variations in treatment delivery characteristics. CONCLUSION Tools and professional guidelines for periodic proton system QA are not as well developed as their photon and electron counterparts. The program described here efficiently evaluates key quality parameters and, while specific to the needs of our facility, could be readily adapted to other proton centers.

Data collection of patient outcomes: one institution’s experience

Abstract Patient- and provider-reported outcomes are recognized as important in evaluating quality of care, guiding health care policy, comparative effectiveness research, and decision-making in radiation oncology. Combining patient and provider outcome data with a detailed description of disease and therapy is the basis for these analyses. We report on the combination of technical solutions and clinical process changes at our institution that were used in the collection and dissemination of this data. This initiative has resulted in the collection of treatment data for 23 541 patients, 20 465 patients with provider-based adverse event records, and patient-reported outcome surveys submitted by 5622 patients. All of the data is made accessible using a self-service web-based tool.

Initial experience with intensity modulated proton therapy for intact, clinically localized pancreas cancer: Clinical implementation, dosimetric analysis, acute treatment-related adverse events, and patient-reported outcomes

Purpose Pencil-beam scanning intensity modulated proton therapy (IMPT) may allow for an improvement in the therapeutic ratio compared with conventional techniques of radiation therapy delivery for pancreatic cancer. The purpose of this study was to describe the clinical implementation of IMPT for intact and clinically localized pancreatic cancer, perform a matched dosimetric comparison with volumetric modulated arc therapy (VMAT), and report acute adverse event (AE) rates and patient-reported outcomes (PROs) of health-related quality of life. Methods and materials Between July 2016 and March 2017, 13 patients with localized pancreatic cancer underwent concurrent capecitabine or 5-fluorouracil-based chemoradiation therapy (CRT) utilizing IMPT to a dose of 50 Gy (radiobiological effectiveness: 1.1). A VMAT plan was generated for each patient to use for dosimetric comparison. Patients were assessed prospectively for AEs and completed PRO questionnaires utilizing the Functional Assessment of Cancer Therapy-Hepatobiliary at baseline and upon completion of CRT. Results There was no difference in mean target coverage between IMPT and VMAT (P > .05). IMPT offered significant reductions in dose to organs at risk, including the small bowel, duodenum, stomach, large bowel, liver, and kidneys (P < .05). All patients completed treatment without radiation therapy breaks. The median weight loss during treatment was 1.6 kg (range, 0.1-5.7 kg). No patients experienced grade ≥3 treatment-related AEs. The median Functional Assessment of Cancer Therapy-Hepatobiliary scores prior to versus at the end of CRT were 142 (range, 113-163) versus 136 (range, 107-173; P = .18). Conclusions Pencil-beam scanning IMPT was feasible and offered significant reductions in radiation exposure to multiple gastrointestinal organs at risk. IMPT was associated with no grade ≥3 gastrointestinal AEs and no change in baseline PROs, but the conclusions are limited due to the patient sample size. Further clinical studies are warranted to evaluate whether these dosimetric advantages translate into clinically meaningful benefits.

Biological Model for Predicting Toxicity in Head and Neck Cancer Patients Receiving Proton Therapy

Purpose To use a linear energy transfer (LET) dependent formula for relative biological effectiveness (RBE) to generate a biological model that can be used to predict toxicity in patients treated with proton therapy for cancer of the head and neck. Patients and Methods Patients treated with protons to a dose of 60 to 70 Gy (RBE = 1.1) for head and neck cancer were eligible to participate in this study. Treatment plans were developed using graphics processing unit Monte Carlo calculations. The equation, RBE = (1.1)[0.08(LETd)+0.88], was the biological model. The physical model assumes RBE = 1.1. Tumor volumes and organs at risk (OARs) were contoured, and isodose lines were created for 105%-120% of the prescribed dose. Dose to volume of OARs was calculated for both models for comparative purposes. Physician-reported toxicity was graded from 0 to 5 using the Common Terminology Criteria for Adverse Events, version 4.03. Patient-reported outcomes were obtained using the Promis10 and European Organisation for Research and Treatment of Cancers QLQ-H&N35 instruments. Results Eleven patients were included in this study. In each case the biological model revealed an increased dose to several OARs compared with the physical model. For selected OARs, the volume receiving >105% of the target dose was 2-fold to 15-fold greater in the biological model than the volume predicted by the physical model. Patients experienced toxicity that was consistent with the dose to OARs predicted by the biological model. Furthermore, 1 patient developed mucosal ulceration and another developed osteoradionecrosis at the location of a biological hot spot. In each case, the biological hot spot was located 2 mm inside the clinical target volume. Conclusion The results suggest that increases in dose predicted by the biological model are clinically relevant and that LET and RBE corrections and optimization should be a component of the treatment-planning process in proton therapy.

Carbon fiducials for large choroidal melanoma treated with gamma knife radiosurgery

Koyanagi-Harada disease and punctuate inner choroidopathy, choroidal thickness increased and choroidal blood flow velocity decreased in the acute stage (Hirooka et al. 2014, 2015). Thus, our EDI-OCT and LSFG results on MEWDS eyes were comparable to previous observations in choroiditis and may be described as an ‘inflammatory’ pattern in the choroid. Taken together, inflammation-related choroidal circulation disturbance is likely to play a role in the mechanism which causes outer retinal impairment in MEWDS.

SU-E-T-337: Treatment Planning Study of Craniospinal Irradiation with Spot Scanning Proton Therapy

PURPOSE To develop a treatment planning technique that achieves optimal robustness against systematic position and range uncertainties, and interfield position errors for craniospinal irradiation (CSI) using spot scanning proton radiotherapy. METHODS Eighteen CSI patients who had previously been treated using photon radiation were used for this study. Eight patients were less than 10 years old. The prescription dose was 23.4Gy in 1.8Gy fractions. Two different field arrangement types were investigated: 1 posterior field per isocenter and 2 posterior oblique fields per isocenter. For each field type, two delivery configurations were used: 5cm bolus attached to the treatment table and a 4.5cm range shifter located inside the nozzle. The target for each plan was the whole brain and thecal sac. For children under the age of 10, all plan types were repeated with an additional dose of 21Gy prescribed to the vertebral bodies. Treatment fields were matched by stepping down the dose in 10% increments over 9cm. Robustness against 3% and 3mm uncertainties, as well as a 3mm inter-field error was analyzed. Dose coverage of the target and critical structure sparing for each plan type will be considered. Ease of planning and treatment delivery was also considered for each plan type. RESULTS The mean dose volume histograms show that the bolus plan with posterior beams gave the best overall plan, and all proton plans were comparable to or better than the photon plans. The plan type that was the most robust against the imposed uncertainties was also the bolus plan with posterior beams. This is also the plan configuration that is the easiest to deliver and plan. CONCLUSION The bolus plan with posterior beams achieved optimal robustness against systematic position and range uncertainties, as well as inter-field position errors.

SU‐E‐J‐30: Intuitive Display Coordinates for Six‐Degree‐Of‐Freedom Treatment Couches

PURPOSE To define couch display coordinates of six-degree-of-freedom treatment couches in a manner that is more intuitively linked to the position of isocenter in the patient, permits easy identification of irregularities in couch positioning, and permits the tightest possible override tolerances for all couch motions. The display coordinates should be calculated from the IEC table-top coordinate system with no patient-specific information. METHODS Couch display coordinates are proposed as the position of radiation isocenter in IEC table-top coordinates. Coordinate systems are compared across multiple radiation therapy machines and then compared to the proposed display coordinates. Examples are provided showing how the proposed definition can be applied across a variety of different couch designs. RESULTS Consistent with IEC standards, most machines with six-degree-of-freedom couches, and particularly those with robotic couches, measure rotations about a point fixed with respect to the couch and independent of all translational motions. This convention has the undesirable consequence of eliminating the one-to-one relationship between the translational coordinates displayed and the position of the radiation isocenter in the patient. By defining the display coordinates as the position of radiation isocenter in IEC table-top coordinates, the one-to-one relationship is reestablished. Examples provided show that the proposed definition insures that a one-to-one relationship between the position of isocenter in the patient and the three translational display coordinates regardless of the values of the three angular degrees of motion. CONCLUSION The examples illustrate how the proposed couch display coordinates lead to easier identification of irregularities in couch positioning such as identifying laterality of isocenter or shifts in multi-isocenter treatments. The proposed display also allows tighter tolerances for couch overrides. These advantages suggest a revised IEC display standard following these conventions has the potential to reduce setup errors at the treatment machine and enhance the utility of the couch display coordinates.