IBA is the only vendor on the market that can offer this type of workflow in one software package.

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1 What is COMPASS? Answer: COMPASS is IBA Dosimetry s innovative 3D dosimetry analysis package. It is comprised of the MatriXX or MatriXX Evolution ion chamber array for measurement procurement and the COMPASS software for patient QA analysis. The COMPASS software contains a full-featured beam modelling suite that allows our users to create independent beam models for almost any linac and energy that they may require. This is in stark contrast to competitive products that provide generic or template beam models. COMPASS allows users to import the same scans that are in their planning system in order to create an equivalent, but independent, beam model. Because the software has its own TPS-class dose engine, users receive multiple and essential QA products in one: i) An independent secondary check software to verify TPS calculations with no measurements required. ii) A patient- specific 3D measurement based QA software suite that allows for the evaluation of dose discrepancies in an anatomical and DVH- based context. iii) A simplified 2D workspace for quick fluence comparisons as well familiar planar and profile analysis tools. IBA is the only vendor on the market that can offer this type of workflow in one software package. What is the difference between standard IMRT/Rotational QA and Patient QA with COMPASS? Answer: Patient-specific IMRT or rotational QA is typically verified via film or an electronic detector that has been placed within a phantom. In both cases, the dose to the patient is not verified directly; rather, a hybrid plan using the original patients fields is applied to the phantom geometry and a transcribed plan is generated. In doing this, the QA validation does not use the original patient anatomy as defined in the planning CT and is instead created in more simple geometry composed of water density material. Dose computation in this configuration does not include the effect of inhomogeneity or complex geometries, nor can it evaluate the effect of delivery discrepancies to the target and organ at risk structures. COMPASS does not suffer from these limitations and can determine the actual 3D dose distribution in the patient anatomy based on the measured beam intensity. Therefore, it directly addresses the expected clinical consequences of delivery discrepancies, which are evaluated as Dose Volume Histograms (DVH s) and many other quantitative statistical metrics on a structure-by-structure basis. Through this methodology, users can judge the quality of their QA plans much like they would evaluate the quality of the initial treatment plan via adherence to department specific clinical goals for each and every plan. COMPASS QA s the actual patient plan to be delivered, not just a simplified phantom approximation. Why do I need COMPASS 3D Dose Reconstruction? My 2D planar QA process works just fine. Answer: Over the last few years, there has been mounting evidence (1) to suggest that 2D planar gamma passing rates have little correlation with predicting clinically relevant patient outcomes. Planar gamma passing rate provide the physicist with a total error count for a 2D patient plane of interest. This type of analysis offers no information regarding the direction or magnitude of these errors. What the gamma passing rate metric does offer is a relative level of confidence that the machine was able to deliver the plan as it was instructed. However, due to the way that planar gamma statistics are generated, false positives and negatives (in terms of planar gamma passing rates) can abound (2). The generalized gamma passing rate metric can mask extremely large discrepancies in absolute dose within individual structures. This is

2 especially concerning when one is evaluating plans with highly dose intolerant critical serial organs, e.g., the spinal cord, where small, but highly sensitive voxels can be overshadowed. It is simply not enough to provide a planar error count. To ensure patient safety, a full understanding of the actual dose deposition in every voxel of the patient needs to be characterized. That is, any discrepancies between measured and calculated dose from the plan needs to be discriminated against with respect to anatomical localization. This is especially true for high-dose SRS and SBRT plans, where the combination of COMPASS s highly accurate collapsed cone convolution/superposition and 3D volumetric information can provide an additional layer of safety that no other patient QA system on the market can provide. So important is calculation accuracy and integrity to the SRS/SBRT process, Task Groups 85 and 101 (3,4) specifically require advanced algorithms, such as COMPASS employs, for targets surrounded by low density tissue, to ensure uncertainties in the planning process are kept to a minimum. Given that this level of accuracy is required during the planning stage, it is clear that there is a need to have both a secondary plan check as well as pre-treatment QA software that is equivalently accurate for these complex and hypo-fractioned treatments. What is verified with COMPASS dose, fluence, or...? Answer: COMPASS determines the fluence for all segments in a beam or arc. As this quantity cannot be directly measured, COMPASS performs a calculation of the expected response (for each ion chamber in the MatriXX detector) for each segment based on the LINAC and detector models prior to the measurement. After the measurement, predicted and delivered responses are compared. The residual response (response difference) is then used for a computation of the fluence that was actually delivered, i.e., entrance fluence to the patient. The dose computation in COMPASS is a second, independent step in which the resulting dose to the patient is forward calculated with the collapsed-cone algorithm using the indirectly measured entrance fluence. For more information regarding the response to fluence convolution please refer to Appendix A. Which measurement devices are used in combination with the COMPASS software? Answer: The MatriXX or MatriXX Evolution detector (1020 pixels) for pre-treatment verification of conventional IMRT plans MatriXX Evolution and the Gantry Angle Sensor for pre-treatment verification of rotational plans Via the MatriXX, fluence is measured from the actual patient plan (not a phantom plan) and then forwardprojected through our independent collapsed cone convolution superposition algorithm. Dose is then reconstructed throughout the 3D patient volume with no angular corrections due to the detector being mounted to the linac head. What algorithm is used to calculate dose in COMPASS? Answer: Compared to more simplistic methods (e.g., ray tracing) of dose calculation in competitive patient QA products, COMPASS leverages the full power of a collapsed cone superposition algorithm for 3D dose calculation. This dose engine is essentially identical to that employed in the commercial TPS RayStation. If my TPS currently calculates with collapsed cone, how is COMPASS an independent verification? Answer: COMPASS uses the collapsed cone convolution/superposition algorithm, but in an implementation which is different from any TPS. The primary quantity determined by COMPASS is the fluence for each segment. Discrepancies in the delivery are visualized as differences in the response pattern. The fluence determined in

3 COMPASS (difference between predicted and measured MatriXX response) is then used (together with the planning CT) as input for the dose computation with the collapsed cone algorithm, whose accuracy can be seen at the same level as state-of-the-art TPS algorithms. As an added benefit, a comparison of COMPASS and TPS algorithms (and commissioning) can be done with a purely computational (virtual) calculation. This dose distribution, as well as the reconstructed dose distribution (via measurements), can be exported as 3D DICOM dose cube for analysis with other tools. What data is required in order to create the beam model? Answer: The beam modelling and COMPASS commissioning process is analogous to that performed on a commercial TPS, albeit a bit reduced in scope. Typically, data from the primary TPS s commissioning are used (i.e., profiles, depth dose curves, output factors, absolute calibration, etc.). There is usually no need for new data to be collected. A list of recommended input data is given in Appendix A. Which file formats will COMPASS accept? Answer: COMPASS accepts the following file formats: For TPS Plan import: DICOM ü RTDose ü RTPlan ü RTStructures ü CTImages For beam modelling: ü.rfb (IBA format) ü.asc (IBA format) ü.csv (general) ü.data (Eclipse) ü.d (Masterplan) How is the MatriXX Evolution detector used in conjunction with the COMPASS software? Answer: There are two versions of the vendor-specific gantry mount. The first has an SDD of 762 mm (ion chamber spacing of 1 cm at isocenter and a 31 x31 cm 2 max field size). The other option has an SDD of 1000 mm (ion chamber spacing of cm at isocenter and 23.6 x 23.6 cm 2 max field size). The 76cm holder allows users to capture larger fields (at lesser resolution) and the 100cm holder allows for better resolution (with a reduced max field size). Both options offer different advantages, and this gives the user flexibility to choose based on their clinical requirements. An additional build-up (30 x 30 cm 2 plates, 20-50cm depth) is placed on top of the array. Backscatter is not required. Prior to a measurement session, the background signal is measured, the device is pre-irradiated with a flood field, and then detector alignment (relative to the central axis of the radiation) is checked via the delivery of a reference

4 field. If the detector is misaligned within certain tolerances, a software shift of the detector is performed. Lastly, the gantry angle sensor is independently calibrated by moving the linac to 0 and 90 degrees. The detector is then ready to begin measurements. All of this can be done in less than five minutes. How is patient and measurement data stored and handled within COMPASS? Answer: The newest version of COMPASS stores model, patient, and measurement data on an SQL database platform. The SQL database can be installed locally, or accessed at many different locations within the same local network. Patient data is imported to the COMPASS application and SQL database via a direct DICOM push or retrieval from the TPS, or can be imported directly from a local or network drive. The patient database within COMPASS includes the ability to query and filter patient data by many different criteria. Can I use COMPASS to verify Rotational Therapy plans? Answer: Yes. COMPASS is the perfect solution for Rotational Plan QA when used in conjunction with the MatriXX Evolution and the Gantry Angle Sensor. Measured frames are tagged with the independently measured angles from the angle sensor. Thus, the 3D dose calculation takes the independently measured gantry angle into account (a 4D measurement) and reconstructs the dose with another layer of independence. Another benefit of the system is that no angular corrections are employed during the measurement process. Since the MatriXX is mounted onto the linac head with the measurement plane always normal to the radiation field, there is no need to add or account for ion chamber anisotropic response. If I already have a MatriXX or MatriXX Evolution, may I purchase just the COMPASS software? Answer: For either detector option (MatriXX or MatriXX Evolution ) when used together with COMPASS, a softwareinterface is required. This interface contains detector modelling and control functionalities. For verification of rotational plans, the MatriXX must be upgraded to a MatriXX Evolution in order to use the Gantry Angle Sensor with this part of the upgrade package. How does COMPASS compare to other 3D Patient Specific QA solutions on the market? Answer: Only COMPASS can: Independently reconstruct measured fluence in each and every voxel of the patient volume (CT image set) with full heterogeneities. Leverage an independent TPS- class Collapsed Cone Convolution Superposition dose engine for unparalleled accuracy when it comes to measurement reconstruction. Offer both independent secondary plan calculations AND measurement- based 3D patient QA software in ONE innovative workflow and package. Allows users the flexibility to perform patient QA analysis on a volumetric (3D), planar (2D), or profile (1D) basis, all within the same platform.

5 References 1 B. E. Nelms, H. Zhen, and W. A. Tomé, Per-beam, planar IMRT QA passing rates do not predict clinically relevant patient dose errors, Med.Phys. 38, (2011). 2 B. E. Nelms, H. Zhen, and W. A. Tomé, Moving from gamma passing rates to patient DVHbased QA metrics in pre-treatment dose QA, Med. Phys. 38, 5477 (2011). 3 N. Papanikolaou, J. Battisata, A. Boyer, et. al., AAPM Report No 85: Tissue inhomogeneity corrections for megavoltage photon beams. The report of Task Group No. 65 of the Radiation Therapy Committee of the American Association of Physicists in Medicine, (2004). 4 S.H. Benedict, K.M. Yenice, D. Followill, et. al., Stereotactic body radiation therapy: The report of Task Group 101, Med. Phys. 37, (2010).