Clinical Experiences with a Patient Skin Dose Monitoring and Tracking Program

Transcription

1 Clinical Experiences with a Patient Skin Dose Monitoring and Tracking Program Allen R. Goode, MS, DABR Chief Diagnostic Medical Physicist Department of Radiology & Medical Imaging University of Virginia Health System Disclosures: - Member, Bayer Healthcare Global Advisory Board - Software shown is in controlled commercial release Dose Level Comparisons CT Dose- Often, race to the bottom: Interventional Dose- on the Rise: Rad Therapy Dose- checked by physicist! IR Doses can be at the Therapeutic Level Tracking of these doses is not only wise but necessary for protection of the patient and the users! AAPM 2018 MO B Ballroom

2 Brief Outline What do you need to track Interventional Doses? What tools are available? Peak Skin Dose (PSD) estimation discussion Examples of the fluoroscope setup in software UVA Health System Experience: Radimetrics Simple validation experiment Case 1 AAPM 2018 MO B Ballroom Before we ask what tools are needed to track interventional dose perhaps we should ask. What is the Goal of Tracking Interventional Dose? Calculation of Peak Skin Dose? Tracking or estimating patient Stochastic Risk? Meeting Regulatory requirements? TJC? Track operator metrics? Most or All of the above?? AAPM 2018 MO B Ballroom What do you need to track Interventional Doses? Radiation Dose Index Monitoring System (RDIM) or Patient Radiation Dose Monitoring and Tracking Program (PRDMT) 4 legged Table Each leg represents a necessary support function System or tracking is incomplete and unstable without one of the legs RDSR Catalog Corrections Peak Skin Dose (PSD) AAPM 2018 MO B Ballroom

3 What do you need to track Interventional Doses? Radiation Dose Structured Report or RDSR Like DICOM file but better Contains more detailed information eg. filtration Entries generated for EACH Event during case As Report or as Table Once data is available, it can be shared or compared in a Registry AAPM 2018 MO B Ballroom What is Peak Skin Dose? The highest dose to a single area of the skin, units of Gy 1. Includes overlap of all beams Useful for prediction of Deterministic Risk Useful for analysis of TJC 15 Gy Sentinel Event Does not need to be displayed but is helpful for localizing dose on the skin 1. Jones et al. Journal of Applied clinical Medical Physics, Vol. 12, no. 4, Fall 2011 Chang, CY, Simeone, FJ, DeLorenzo, MC et al, Skeletal Radiology, Feb. 2018, Volume 47, 2, Dose reduction for fluoroscopically guided injections: phantom simulation and patient procedures AAPM 2018 MO B Ballroom Peak Skin Dose Use in IR Suite Images courtesy of Andrew Kuhls-Gilcrist, Canon Medical Systems, USA At least one vendor is adding Real Time PSD maps to their monitor configuration to assist DURING the case AAPM 2018 MO B Ballroom

4 Tracking Interventional Doses at UVA: IR Structure/Layout 6 IR Rooms, 1 Vendor, 3 models RDSR RDIM: Radimetrics Enterprise Server Queries/Alerts Medical Physics Offices Only DICOM Event Streams and DICOM & RDSR s sent from rooms PSD Module (v2.8 beta) Other RDIM s claiming Interventional dose tracking: AAPM 2018 MO B Ballroom How do we Estimate and Show PSD? Get RDSR Catalog Data Apply Corrections Paint Dose on Model DAP Meter correction Geometric Corrections Table/Pad Attenuation (or not) Back Scatter f factor Difficult with lots of Events AAPM 2018 MO B Ballroom Necessary Corrections What is the Peak Skin Dose here?? Receptor Setup standard PA orientation of a typical IR system viewed from the head of the table To understand corrections a basic understanding of where the beam is on the patient and the path it travels is critical KAP Meter Collimator X ray Tube AAPM 2018 MO B Ballroom X Cushy Table Pad Carbon Fiber Table Reference Point 12 4

5 Necessary Corrections What is the Peak Skin Dose here?? Table Attenuation x Table Pad Attenuation Receptor X Other Needed Corrections: Back Scatter Factor f-factor Beam Quality Distance Corrections KAP meter corrections (+/- 35% allowance!) AAPM 2018 MO B Ballroom Necessary Corrections Pink area no attenuation correction Green area Pad attenuation only Blue area Table and Pad attenuation Partial Table Attenuation x Partial Table Pad Attenuation This orientation presents a significant challenge to correct the beam from partial blockage of the Table and the Pad AAPM 2018 MO B Ballroom Necessary Corrections Receptor NO Table Attenuation x NO Table Pad Attenuation Lateral projections require NO corrections from attenuation of table or pad In this orientation, the skin is experiencing all of the beam and is likely closer to the X-ray tube presenting an orientation than really needs scrutiny if the case dose is high- without the table we do not know where the skin is Geometric corrections are difficult because some of descriptors for the system coordinates/direction were BUILT with respect to the OPERATOR- not the PATIENT AAPM 2018 MO B Ballroom

6 Equipment Setup: Geometry Determination of lateral table offset in the Z directiondifference between center of image and Z-axis or Lateral travel reported in the RDSR Compute the offset between center of the image and the value reported in the RDSR for the AAPM 2018 MO B Ballroom image Equipment Setup: Geometry Determination of table offset in the X directiondifference between center of image and X-axis or Longitudinal travel reported in the RDSR AAPM 2018 MO B Ballroom Equipment Setup: Geometry Determination of table offset in the Y directiondifference between center of image and Y-axis or Height reported in the RDSR AAPM 2018 MO B Ballroom

7 Equipment Setup: Table Parameters Building a table for all of the tables Can be for one single unit or applied to same model units AAPM 2018 MO B Ballroom Equipment Setup: Table Attenuation Table and table pad attenuation based on HVL and kvp values Values for equipment have to be manually entered Interpolation possible between kvp s but not filter thicknessmust have values for all filter possibilities. AAPM 2018 MO B Ballroom Equipment Setup: Back Scatter Factor Current PSD calcs in the software have heavy dependence on HVL for table/pad attenuation Note that HVL s utilized are quite a bit lower than what we typically measure for spectral filtered beams ICRU Report 74, vol 5 (2) 2005 AAPM 2018 MO B Ballroom

8 Calculating Skin Dose in Radimetrics Once skin model selected- skin dose is calculated for all points falling inside of the beam pyramid on that model r is the position of the skin relative to source RP = Reference Point DAP Meter correction CF x Dose RP x rrp 2 r 2 Geometric Corrections Table/Pad Attenuation (or not) Back Scatter f factor Jones et al. Journal of Applied clinical Medical Physics, Vol. 12, no. 4, Fall 2011 Johnson, Borrego, et al, Skin Dose Mapping for Fluoroscopically Guided Interventions, Med Phys. 38 (10), 2011 AAPM 2018 MO B Ballroom Corrections One of the most challenging aspects is we simply do not know WHERE the patient is on the table. Placement of the patient higher, lower or off center will affect where the dose is assumed to be on the patient Until vendors add patient localization on their fluoroscopes, localization of skin dose needs to be confirmed by other means. Receptor AAPM 2018 MO B Ballroom (Head) Example Angulation Map (Right) (Left) Shows C-arm angle vs. dose Primary angles (LAO- RPO) Secondary angles (cranial-caudal) Displays dose in coarse increments from an unwrapped cylinder (Foot) AAPM 2018 MO B Ballroom

9 Example Peak Skin Dose Determination Painting of dose on symbolic manikin phantom or skin model Radimetrics uses 31 patient models, including arms up/down, gender peds/neonate and weight AAPM 2018 MO B Ballroom Example Dose Timeline Dose timeline shows when and what Rate events occurred May be helpful for training Events with high reference point dose are long fluoro events or acquisitions AAPM 2018 MO B Ballroom Example Protocols used during case This tool shows which programs were selected during the case and the dose from each of those programs May be useful for training AAPM 2018 MO B Ballroom

10 Validation Experiment Assess accuracy with torso anthro phantom in IR suite with parameters for table loaded into the software. 0.6 cm 3 RadCal ion chamber placed in the center of the phantom back on table Acquire clinical like imagesmixture of Single Shots and Fluoro AAPM 2018 MO B Ballroom Image seen during fluorocircle outlines chamber IVC Filter 100 SID 22 cm FOV 28 Validation Experiment In this limited case initial results indicate good agreement between measured dose and PSD Experimental limitations- simple case- no angulationno changes to FOV, table, etc. Metric Air Kerma measured, Phantom back Phantom Kerma, corrected for f factor mgy Radimetrics Predicted PSD Radimetrics PSD, DAP Corrected % Difference from measured 2% AAPM 2018 MO B Ballroom Case Alert triggered by thresholds set in Radimetrics Key metrics sent in allow for triage of higher dose cases Already paints a picture of what occurred, where, and what service. 9.2 Gy AAPM 2018 MO B Ballroom

11 Case Catalog of data We know who did the case, where, and we can start to see what programs were used We can also see the contributions from Recorded images vs. Fluoro work AAPM 2018 MO B Ballroom Case Angulation map showing concentration of dose PA, from under table, centrally located. Additional dose to Left lateral area AAPM 2018 MO B Ballroom Case PSD map showing ~5 Gy to lower back Confirm in PACS Discuss with performing MD (post) AAPM 2018 MO B Ballroom (L Lat) 33 11

12 Case Response to Alert Categorize Comments can reflect next steps /issues during the case for documentation. Document conversations with MD for future reference AAPM 2018 MO B Ballroom Alerts: where are you? Alert that needs attention Categories created for Alerts Alerts filtered by service Analysis over time TJC pre pub requirements coming on this AAPM 2018 MO B Ballroom Alerts: what to do/next Steps? With an estimate of PSD work can begin on F/U activities according to dose level Several great resources Balter, Miller, AJR, 2014, W335-W342 AAPM 2018 MO B Ballroom

13 Conclusions: Doses from FGI s are much higher than CT s doses that many institutions are currently tracking There are tools to track interventional dose both in and outside of the lab Peak Skin Dose is the metric we typically watch Corrections to arrive at accurate PSD are difficult and may not fully be ready commercially Patient location on the table is a significant hurdle Alerts for elevated or Substantial Radiation Dose Levels or SRDL s need responding to Tracking these doses is the right thing to do for our patients Registries using tracked data may provide useful insight into better or Best Practices AAPM 2018 MO B Ballroom THANK YOU! Questions? AAPM 2018 MO B Ballroom