Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Brachytherapy wikipedia , lookup
Center for Radiological Research wikipedia , lookup
Positron emission tomography wikipedia , lookup
Radiation therapy wikipedia , lookup
Proton therapy wikipedia , lookup
Industrial radiography wikipedia , lookup
Neutron capture therapy of cancer wikipedia , lookup
Nuclear medicine wikipedia , lookup
Radiosurgery wikipedia , lookup
Backscatter X-ray wikipedia , lookup
Image-guided radiation therapy wikipedia , lookup
4/3/2011 High Profile Over-exposures Lead to Growing Concern Accounting for Imaging Dose FDA issues warning in October 2009 - 209 patients exposed to 8 times typical dose for CT brain perfusion scan (3-4 Gy) - Some patients experienced erythema and hair loss - No hardware malfunction was found NYT Series “The Radiation Boom” Josephine Chen, PhD UCSF Radiation Oncology Update April 1-3, 2011 How Can Large Over-Exposures Happen? CT images are reconstructed from raw data - noise level may change with patient exposure, but reconstructed image will never look over-exposed Operator can manually change scan parameters affecting CT output. Some scanners have automatic controls that adjust output. - highlights over-exposures and errors in diagnostic imaging and radiotherapy CA Legislature Responds with New Regulations CA Senate Bill 1237 passed Sep 2010 Section 1 (effective July 1, 2012) • Record CT dose parameters for each CT scan • Annual verification of the CT dose displayed by scanner Section 2 (effective July 1, 2013) Mandatory CT accreditation Section 3 (effective Jan 1, 2011, SB 38 July 1, 2012) • Report CT over-exposures exceeding certain dose limits • Report CT or RT over-doses to fetus or incorrect site, etc www.legislature.ca.gov 1 4/3/2011 Radiation Oncology Exemption Understanding Patient Dose from CT CA Dept of Public Health Information Notice, Jan 14, 2011 • Factors Determining Patient Dose “By definition, CTs used for radiation therapy planning is defined as radiation therapy simulation systems, and so are not subject to this new reporting requirements.” • Quantities Used to Describe CT Dose Rad Onc depts are not required to report CT doses/incidents. • Recommendations and Sources of Additional Information • Typical and Recommended CT Dose Values www.cdph.ca.gov/programs/pages/radiologichealthbranch.aspx Parameters that Affect Patient Dose CT mAs: xray tube current × time for one rotation Effective mAs: mAs / slice (spiral scans) pitch: table travel (for 1 rotation) / total beam width kVp: tube acceleration potential beam filtration, beam collimation, ring geometry scan length Patient size/weight New CT Technology Also Affects Patient Dose MDCT (multiple-detector-row CT): multiple slices acquired in one rotation AEC (automatic exposure control) or ATCM (automatic tube current modulation): automatic adjustment to output to compensate for variation in patient size/attenuation - small vs. large patient - neck vs. abdomen AEC can both decrease and increase patient dose organ size/location 2 4/3/2011 How Do We Measure CT Dose Standard measures of CT output Finding CTDIvol and DLP CT study protocol page CTDIvol (Volume CT Dose Index) [mGy] Ion chamber measurement in standardized phantoms 32 cm dia cylinder (body), 16 cm diameter cylinder (head) Ave dose to center slice of phantom for 10 cm scan DLP (Dose Length Product) [mGy cm] CTDIvol × (Length of scan) - increases with scan range - Although these parameters refer to “dose”, the dose is for a specific phantom. Dose to the patient depends on patient shape/size, length/range of scan, organ position. - Most CT scanners report CTDIvol and DLP How Does CTDIvol Relate to Organ Doses Dose Quantities Used for Non-therapeutic Exposures Focus is potential stochastic effects (cancer induction) Use Monte Carlo or measurements to find organ doses. Organ Dose Equivalent (Sv): dose multiplied by radiation weighting factor (1 for photons/electrons) Brain Adult Dose/CTDI 0.84a Thyroid 1.84b 2.45b Breast 1.03b 1.98b Effective Dose (Sv): weighted sum of dose equivalent × tissue weighting factors effective uniform whole body dose - sensitivity of each tissue to stochastic effects - averaged over gender and age Lung 1.53b 2.25b Liver 1.14b 1.94b Stomach 1.22b 1.11b Skin 2.18c Absorbed Dose (Gy) aPhys Child (6 yrs) Dose/CTDI Med Biol 53:N9; bBr J Radiol 82:1010; cAJR 190:W100 3 4/3/2011 How Does DLP Relate to Effective Dose Empirical relationship proposed by the NRPB (UK) Typical CT Doses Effective Doses Examination Effective Dose = k × DLP k [mSv mGy-1 cm-1] Region of Body Head Neck Chest Abdomen/Pelvis Adult 0.0021* 0.0059* 0.014 0.015 5-year old 0.004* 0.011* 0.018* 0.020* Head Neck Chest Abdomen Average Effective Dose (mSv) 2* 3* 7* 8* Pelvis 4D CT Lung 6* 15 (annual background dose ~ 3 mSv) * CTDI measured in head phantom Organ Doses: 15-30* mGy ICRP 102 CT Dose Compared to RT Dose Inside treatment volume: ~ 0.1% of RT dose Exit beam: ~ 1% of RT dose In treatment plane, No direct beam: ~ 2% of RT dose Peripheral (10-30 cm outside field): 10-100% of RT dose *Radiology 2008 248:254 Recommended CTDIvol Limits 2008 ACR Guidelines Adult Abdomen < 25 mGy Adult Head < 75 mGy Image Gently Recommendations for Reduction in mAs/slice 5 yr-old Abdomen - 41% reduction 5 yr-old Head – 7% reduction Alliance for Radiation Safety in Pediatric Imaging www.imagegently.org 4 4/3/2011 Recommended Actions Additional Information • CT operator training for specific scanner AAPM Report 96 (TG 23): CTDIvol and DLP • Periodic evaluation of CT protocols remove unused protocols, create new protocols ICRP Pub 102: CT technology and dose • Check for accidental changes in protocol presets Image Wisely and Image Gently Campaigns www.imagewisely.org www.imagegently.org • Record the CTDIvol and DLP for each scan (SB 1237) 2011 AAPM CT Dose Summit, Oct 2011 5