Hybrid Imaging

Shahid YounasM.Sc. Medical Physics (Surrey) UK

M.Sc. Applied Physics (UET) Lahore

Sr. Medical Physicist & RPA

Picture courtesy of:

Shahnawaz Shahid,

Shazanan Shahid,

Shazeen Shahid

Department of Nuclear Medicine SKMCH&RC, LAHORE

SPECT CT: HOW MUCH RADIATION DOSE

Thanks to:

SPECT CT HYBRID

Material and Methodology

Reference 1: The Mnaual of SYMBIA SPECT/CT:SIEMENS, GERMANY.

We analyzed 151 patients from a dual-headed SIEMENS’ SYMBIA

T-16 unit with an integrated 16-slice CT scanner.

This CT portion of this system has,

variable tube current (20– 345 mA),

slice thickness of 0.6–10 mm,

rotational speed of 0.6–1.5 secs.

tube voltage up to 130 kVp.

Effective Dose

Reference 2: E. J. Hall and A. J. Giaccia, Radiolobiology for the Radiologist, Lippincott Williams &

Wilkins, Philadelphia, Pa, USA, 6th edition, 2005.

The quantity Effective Dose can have practical value for comparing

the relative doses related to the stochastic effects and comparing

different technologies [2]

Radiation Dose Conversation Mechanism

Reference 3: The Essential Physics of Medical Imaging, Third Edition Third, North American Edition Edition by Jerrold T. Bushberg (Author),

J. Anthony Seibert , Edwin M. Leidholdt Jr. , John M. Boone

Game of 10-10 sec [3]

Risk Factor

Reference 2: E. J. Hall and A. J. Giaccia, Radiolobiology for the Radiologist, Lippincott Williams &

Wilkins, Philadelphia, Pa, USA, 6th edition, 2005.

According to ICRP, the risk of developing a lethal cancer is

approximately 4% per Sievert. The lifetime risk for cancer has been

shown to be greater in the younger patients.

Dose Conversion

Reference 4: (AAPM, 2008), Report, Shope et al, 1981

CT dose index Volume (CTDIv) and Dose Length Product (DLP) are

two basic quantities used to estimate the average absorbed dose in

the organs and tissues based for the helical (volumetric) CT

scanners.[4]

Dose Length Product & CT Dose Indexvolume

CT Dose Calculations

Reference 5: International Commission on Radiological Protection (ICRP) Publication 53 and 80.

𝐷𝑜𝑠𝑒 𝐿𝑒𝑛𝑔𝑡ℎ 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 = 𝐶𝑇𝐷𝐼𝑣 ∗ 𝑃𝑎𝑡𝑖𝑒𝑛𝑡 𝐿𝑒𝑛𝑔𝑡ℎ

𝐷𝐿𝑃 = 𝐶𝑇𝐷𝐼𝑣 ∗ 𝐿

DLP is measured in mGy*cm

CT Dose Calculations

Reference 5: International Commission on Radiological Protection (ICRP) Publication 53 and 80.

𝐸𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝐷𝑜𝑠𝑒 = 𝐷𝑜𝑠𝑒 𝐿𝑒𝑛𝑔𝑡ℎ 𝑃𝑟𝑜𝑑𝑢𝑐𝑡 . 𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 𝐹𝑎𝑐𝑡𝑜𝑟

Effective dose is measured in mSv

𝐸𝑒𝑓𝑓 = 𝐷𝐿𝑃 . 𝑘

CT Dose Conversion Factors

Reference 5: International Commission on Radiological Protection (ICRP) Publication 53 and 80.

Reference 6: Doses to Computed Tomography Examinations in the UK – 2003 Review (Table 3)

Region of Body Effective Dose per DLP for adult

(mSv per mGy.cm)

Head & Neck 0.0031

Head 0.0021

Neck 0.0059

Chest 0.014

Abdomen & Pelvis 0.015

Trunk 0.015

Nuclear Dose Conversion

Reference 7 : “Radiation dose to patients from radiopharmaceuticals ICRP Publication 53,” Annals of the ICRP, vol. 18, no. 1–4, 1987.

J. Valentin, “Radiation dose to patients from radiopharmaceuticals (Addendum 2 to ICRP publication 53) ICRP publication

80 approved by the commission in September 1997,” Annals of the ICRP, vol. 28, no. 3, pp. 1–126, 1998.

Effective dose per unit administered activity” conversion factors

listed in the International Commission on Radiological Protection

(ICRP) Publication 53 and 80.

Results

Reference 8: F. A. Mettler, W. Huda, T. T. Yoshizumi, and M. Mahesh, “Effective doses in radiology and diagnostic nuclear medicine: a

catalog,” Radiology, vol. 248, no. 1, pp. 254–263, 2008.

Primary Scan99mTc-MDP Bone Mean: 868 MBqAverage DLP: 46.98

% increase in patient dose due to CT Component

CT Dose

from

SPECT

8Diagnostic

CT Dose

NM Dose NM + CT Dose % increase

w.r.t. RP Dose

Chest 0.65 7

4.95

5.6 13.13

Abd & Pelvis 0.87 8-14 5.75 16.17

Trunk 10.45 8-12 15.4 211.11

Neck 0.29 3 5.24 5.85

All doses are in milli-Sievert (mSv)

Results

Primary Scan99mTc-MIBI ParathyroidMean: 842.5 MBqAverage DLP: 135

% increase in patient dose due to CT Component

CT Dose

from

SPECT

8Diagnostic CT

Dose

NM Dose NM + CT

Dose

% increase

w.r.t. RP Dose

Neck 0.8 3 7.58 8.37 10.55

All doses are in milli-Sievert (mSv)

Results

Primary Scan99mTc-ThyroidMean: 165.5 MBqAverage DLP: 63.5

% increase in patient dose due to CT Component

CT Dose

from

SPECT

8Diagnostic

CT Dose

NM Dose SPECT + CT

Dose

% increase w.r.t.

NM Dose

CT Region: Neck 0.01 3 2.15 2.16 0.46

All doses are in milli-Sievert (mSv)

Results

Primary Scan131I-Post-therapyMean: 2790 MBqAverage DLP: 63.5

% increase in patient dose due to CT Component

CT Dose

from

SPECT

8Diagnostic CT

Dose

NM Dose NM + CT

Dose

% increase

w.r.t. RP Dose

Neck 0.43 3 2790 2790.43 0.015

All doses are in milli-Sievert (mSv)

Secret to low dose

As images are not meant to be diagnostic in the SPECT mounted

CT consequently Effective Dose would be expected to be lower

than typical diagnostic values – This is the secret (lower mA).

Cancer Risk from SPECT

In our calculations the increased risk of cancer by additional

exposure of low does CT ranges from 0.01% to 0.04 %.

Cancer Risk from SPECT

Although imparted CT dose is quite lower however this lower dose

can be balanced by decreasing the injected radiotracer dose at the

cost of increased image time.

Thanks