Accuray (United States)

Abstract The purpose of this document is to provide the qualified medical physicist (QMP) with guidance on the critical evaluation and independent validation of “closed” or “black box” systems in a radiation oncology setting. Radiotherapy delivery systems and their associated subsystems are highly sophisticated and complicated. In recent years, vendors have worked closely with QMPs, information technology (IT) personnel, and clinical engineers to develop and ultimately provide an entire package of resources at the time of purchase of radiotherapy delivery equipment. Commissioning and routine quality assurance (QA) on these new, black‐box systems is not necessarily more difficult or time‐consuming; however, there are different factors to consider with black‐boxes. Independence in the vendor's own validation techniques now becomes critical to establish. For vendor‐provided tools, the user must understand the implications of working with a service tool or a true QA tool. Lastly, the user must determine which components of the system are unknown and differ from a classic white‐box system. Understanding these characteristics of the black‐box will guide the user in determining which quality management (QM) tools are applicable and which verification and validation (V&V) procedures to follow. Black‐box systems are becoming more and more prevalent in the radiation oncology setting. For example, true black‐box systems in the form of machine learning (ML) algorithms are already widely used within common treatment planning systems (TPS). These systems present a unique challenge to the QMP who is responsible for conducting independent V&V performance measurements on such systems. Although these systems require a different approach from classic treatment delivery systems, we present new terms for characterizing black‐box systems and a methodology for using alternative methods of independent validation.

Helical TomoTherapy has unique challenges in handling intrafractional motion compared to a conventional LINAC. In this study, we analyzed the impact of intrafractional motion on cumulative dosimetry using actual patient motion data from clinically treated patients and investigated real time jaw and multileaf collimator (MLC) compensation approaches to minimize the motion-induced dose discrepancy in clinically acceptable TomoTherapy lung SBRT treatments. Intrafractional motion traces from eight fiducial tracking CyberKnife lung tumor treatment cases were used in this study. These cases were re-planned on TomoTherapy for SBRT, with 18 Gy × 3 fractions to a planning target volume (PTV) defined on the breath-hold CT without ITV expansion. Each case was planned with four different jaw settings: 1 cm static, 2.5 cm static, 2.5 cm dynamic and 5 cm dynamic. In-house 4D dose accumulation software was used to compute the dose distributions with tumor motion and then compensate for that motion by modifying the original jaw and MLC positions to track the trajectory of the tumor. The impact of motion and effectiveness of compensation on the PTV coverage depends on the motion type and plan settings. On average, the PTV V100% (the percent volume of the PTV receiving the prescription dose) accumulated from three fractions changed from 96.6% (motion-free) to 83.1% (motion-included), 97.5% to 93.0%, 97.7% to 92.1%, and 98.1% to 93.7% for the 1 cm static jaw, 2.5 cm static jaw, 2.5 cm dynamic jaw and 5 cm dynamic jaw setting, respectively. When the jaw and MLC compensation algorithm was engaged, the PTV V100% was restored back to 92.2%, 95.9%, 96.6% and 96.4%, for the four jaw settings mentioned above respectively. TomoTherapy lung tumor SBRT treatments using a field width of 2.5 cm or larger are less sensitive to motion than treatments using a 1 cm field width. For 1 cm field width plans, PTV coverage can be greatly compromised, even over three fractions. Once the motion pattern is known, the jaw and MLC compensation algorithm can largely minimize the loss of PTV coverage induced by the motion.

Radiotherapy (RT) is a mainstay of oncology treatment in both curative and palliative situations. With respect to palliative and supportive care, RT improves local control of disease and relieves symptoms, particularly pain, compression of surrounding structures, and/or bleeding. The aim here was to evaluate the effects and toxicity of palliative RT in our department from April 2015 to April 2018. During this period, 338 cases received palliative RT, representing approximately one third of indications for this treatment method. We evaluated selected subgroups of patients: those with advanced lung cancer, bone metastases, or soft tissue metastases. Patients were irradiated by the IMRT (intensity modulated radiation therapy) technique using the TomoTherapy HD (Accuray, USA) platform. Palliative RT for primary lung cancer was performed for 29 patients. Of these, symptoms were relieved in 22 patients (76%) and local control (confirmed by imaging) was achieved in 19 patients (66%). Treatment-related toxicity was acceptable. Overall, 104 patients received irradiation for bone metastases; pain relief was achieved in more than 75% of cases. Another 71 patients were irradiated to treat soft tissue metastases; symptoms were relieved in 60% of cases. Treatment-related toxicity in our patients was lower than reported previously, suggesting improved quality of life for patients irradiated using modern RT technologies. Palliative RT provided excellent symptom control in our patients, with minimal toxicity. Thus, RT is an effective and easy-to-use method for many palliative indications. Key words: palliative care - radiotherapy - lung neoplasms - neoplasm metastasis - bone metastases - pain management The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submitted: 28. 8. 2018 Accepted: 29. 10. 2018.

Purpose:Accuray recommends daily evaluation of the treatment localization and delivery systems (TLS/TDS) of the CyberKnife. The vendor‐provided solution is a Winston‐Lutz‐type test that evaluates film shadows from an orthogonal beam pair (known as AQA). Since film‐based techniques are inherently inefficient and potentially inconsistent and uncertain, this study explores a method which provides a comparable test with greater efficiency, consistency, and certainty. This test uses the QAStereoChecker (QASC, Standard Imaging, Inc., Middleton, WI), a high‐resolution flat‐panel detector with coupled fiducial markers for automated alignment. Fiducial tracking is used to achieve high translational and rotational position accuracy.Methods:A plan is generated delivering five circular beams, with varying orientation and angular incidence. Several numeric quantities are calculated for each beam: eccentricity, centroid location, area, major‐axis length, minor‐axis length, and orientation angle. Baseline values were acquired and repeatability of baselines analyzed. Next, errors were induced in the path calibration of the CK, and the test repeated. A correlative study was performed between the induced errors and quantities measured using the QASC. Based on vendor recommendations, this test should be able to detect a TLS/TDS offset of 0.5mm.Results:Centroid shifts correlated well with induced plane‐perpendicular offsets (p < 0.01). Induced vertical shifts correlated best with the absolute average deviation of eccentricities (p < 0.05). The values of these metrics which correlated with the threshold of 0.5mm induced deviation were used as individual pass/fail criteria. These were then used to evaluate induced offsets which shifted the CK in all axes (a clinically‐realistic offset), with a total offset of 0.5mm. This test provided high and specificity and sensitivity.Conclusion:From setup to analysis, this filmless TLS/TDS test requires 4 minutes, as opposed to 15–20 minutes for film‐based methods. The techniques introduced can potentially isolate errors in individual joints of the CK robot.Spectrum Medical Physics, LLC of Greenville, SC has a consulting contract with Standard Imaging of Middleton, WI

Purpose:To validate dose calculations in a rigidly moving object.Methods:An off‐line version of the TomoTherapy™ dose calculation software was extended to allow dose calculation for rigidly moving objects. The interface allows users to extract the necessary data from TomoTherapy patient archives to perform an off‐line dose calculation, and to specify arbitrary translational motion by creating a text file with a column for time, and columns for x, y, and z translations. Film measurements were performed using a phantom that was rigidly moved with the same motion profile as used in the calculation. A variety of motion profiles were studied and the motion profiles were applied to delivery plans with varying field sizes (1, 2.5, and 5 cm) and with dynamic jaws and static jaws.Results:Calculations matched measurements to within 2% or 1 mm for the variety of motion profiles studied. A 4‐mm step motion in the longitudinal (IEC‐Y) direction timed to occur halfway through a 1 cm field‐width delivery resulted in a 29% decrease in both the calculated dose and measured dose in a central region of the dose profile. For a 5 cm field‐width dynamic jaw delivery, the 4 mm step motion resulted in a more broadly distributed reduction in dose of 8%. A 6 mm sinusoidal motion in the longitudinal direction with a 6 second period had a negligible impact on delivered dose for one particular delivery plan. Similarly, a step motion in the transverse direction (IEC‐X) had a negligible impact on delivered dose other than to shift the dose volume.Conclusion:A research version of the TomoTherapy™ dose calculator can accurately calculate dose for a rigidly moving object. Further studies with more clinical motion traces and with clinical treatment delivery plans will yield valuable insight into the impact of motion on the delivered dose.

Purpose: To study the effect of energy variation on standard IMRT plans, MU chamber ratio (MU1/MU2) and cone ratio (CR) for non‐flattened beam e.g., Tomotherapy. Methods: In this controlled experiment, we varied the energy (PDD10) on TomoTherapy Hi‐ARTTM from −1.6 % to +1.6% in six steps while keeping calibrated output unchanged. For achieving this, injector current (Injl) and pulse forming network (pfn) voltage were adjusted. The effect of this variation in energy(δE) on standard IMRT plans and energy indicators were studied. To quantify sensitivity of standard IMRT plans with δE, cheese phantom was used with multiple calibrated ionization chambers. ΔD was calculated as a percent variation of measured vs. expected dose. Ratio of ΔDon‐axis with ΔDoff‐axis for each commissioned field width (FW) was tabulated against δE. The effect of this on other energy indicators was also studied to verify the sensitivity of TMR20 10 MU chamber ratio, and detector data‐based‐CR. Results: Good agreement between PDD10 vs TMR20 10 (R2=0.97, slope=1.01) and PDD10 vs MU chamber ratio(R2=0.99, slope=−0.9) was observed. CR is more sensitive to energy change with slope =−2.5 than PDD10. Ratio of ΔDon‐axis with ΔDoff‐axis for FW 2.5 cm (R2=0.91, slope =0.63) and FW 1 cm (R2=0.94, slope =0.80) of standard IMRT plan also agreed well with PDD10. Conclusion: CR is more sensitive to energy changes compared to PDD10, thus CR with MU1/MU2 can definitely be used as quality measure on a daily/weekly basis. Though the on‐axis vs off‐axis variation is not as sensitive, output across the 6 standard IMRT plans can vary up to 2% for a 1% increase in energy. Hence, it is of utmost important to manage the PDD10 tightly around +/− 0.5%. This study can be easily extended to monitor the calibration and beam quality for other emerging technologies based on flattening‐filter‐free (FFF) delivery mode e.g., TrueBeamTM.

Purpose: To investigate the use of dose‐area product (DAP) as a highresolution tool for QA of small field sizes as an alternative to more complex alternatives such as film or water tank scanning. Method: An 81 mm diameter PTW Bragg Peak parallel plate chamber was used in combination with an Iris variable circular aperture collimator fitted to a CyberKnife System and a vendor‐supplied alignment jig. The Iris collimator is designed to deliver field diameters between 5 mm and 60 mm, with a tolerance of ±0.2 mm. First the sensitivity of the chamber reading to influence parameters (SSD, angle misalignment, lateral displacement, output variation) was investigated. Next the dependency of DAP on field diameter was investigated. Finally the sensitivity of the method to detect small field size changes consistent with the device specification was evaluated. Comparisons were made with film and diode water scans using four CyberKnife systems and three chambers. Results: Expected variations in chamber position/orientation within the jig resulted in measurement changes <0.2%. Measurement variations due to LINAC output changes can be removed by normalising measurements to a fixed collimator reading obtained at the same time. The variation in chamber reading with field size followed a quadratic dependency over the 5mm ‐ 60mm range. The change in chamber reading associated with a 0.2 mm field diameter change ranged from 10% at 5 mm nominal to 0.5% at 60 mm, and was reasonably consistent across tests performed on four units. Measurements were more consistent than routine film tests, and were stable over two years. Conclusion: DAP provides a practical, efficient, robust, and sensitive method for routine QA of field aperture changes as small as ±0.2mm across the field size range 5 mm – 60 mm. The method may also have applications for QA of small fields formed by MLC.