Radiation Protection when using PET/CT for Treatment Planning Sithoeun Sam Liverpool Hospital

Background • Liverpool Hospital has 2 PET/CT scanners – Philips Gemini GXL – GE Discovery 710

• 15 patients routinely scheduled per day (FDG/68Ga-Dotatate) • Uptake 60 mins (± 10%)

• Cancer Therapy Centre is linked with Campbelltown Hospital • Nuclear Medicine staff attend MDT meetings

– LUNG, GIT, Thyroid, H&N, CRC, Lymph, Gynae, NET

Background • PET/CT scanning in radiotherapy planning position can lead to better tumour volume definition • PET/CT scans in RTP position are more accurately reproduced if the radiation therapists (RT) are involved in the scan setup

Background • Internal interest in regards to radiation dose to setup staff during the positioning of patients for PET/CT in treatment position. • Interest in the workflow implications – State-wide service – 3 PET/CT scanners in NSW – Staffing issues

Previous Study • A study was undertaken 1.

2.

To determine if there is a time difference between Nuclear Medicine Technologists (NMT) and Radiation Therapists (RT) in setting up PET/CT scans To determine the difference in radiation dose between the 2 groups

Method • 40 patients were measured

– 20 RT group (10 = H&N, 10 = Lung) – Flatbed + immobilisation equipment

– 20 NMT group (10 = H&N, 10 = Lung) – Routine bed

• Radiation monitor used to measure maximum reading (µSv/hr)

– GM Survey Rate Meter (Inspector+ Model) – Calibrated 2 months prior to study commencement – Precision ± 10%

• Timed the setup duration using a stop watch

Acquisition Parameters • General – Philips Gemini GXL – 5.18 MBq/Kg FDG – 60 minute uptake

• Weight Dependent – – – –

1.5 to 2 min/bed 15 to 30 min scan 120 to 140 kV 30 to 50 mAs

Results

Sam, S., et al., Workflow and Radiation Safety Implications of 18F-FDG PET/CT Scans for Radiotherapy Planning. J Nucl Med Technol, 2012. 11: p. 11.

Other results •

Carson et al looked at setup doses for “hot PET patients” (lung ca) – 5.1 µSv – N=28

Carson, K.J., et al., Personnel radiation dose considerations in the use of an integrated PET-CT scanner for radiotherapy treatment planning. Br J Radiol, 2009. 82(983): p. 946-9.

•

Liverpool Experience – 4.9 µSv – N=10

NMT Average Photon Dose (p.a.) (SSWAHS Radiation Safety Intranet)

RT Average Photon Dose (p.a.) (SSWAHS Radiation Safety Intranet)

RT Average Photon Dose • ARPANSA benchmark is 228 µSv* • RT are well below the stated benchmark • Cancer Therapy Centre rotate 10-12 RT through PET • Average 2 RTP PET/CT scans per week – Extra 40 µSv (estimated)

• Radiation dose not an issue for current demands *ARPANSA Personal Radiation Monitoring Service and Assessment of Doses Received by Radiation Workers (2004)

RT Average Photon Dose (p.a.) (SSWAHS Radiation Safety Intranet)

Radiation Protection Principles • Time – RT will spend double the time in setting up the scan (x2 operators) • Immobilisation devices • Laser alignment • Patient position

– It takes as long as it takes!

Radiation Protection Principles • Distance – Close proximity to the patient - use of immobilisation devices, lasers etc

• Shielding – None (as yet) – Shield to be installed

Future Investigations • Repeat study on the GE Discovery 710 – Improved camera specifications

• Injected dose has been decreased – Discovery 4.18 MBq/Kg – Gemini 5.18 MBq/Kg Mean setup time (min:ss) RT Group (n=4)

4:02

Estimated mean setup dose (µSv) 3.40

Future Investigations • Faster gantry motions • Mark SSN instead of proximal femora • Wall mounted shielding to be installed

Conclusion • RT will spend more time in setting up a patient than NMT staff • As a result there is some increased dose to the RT staff but it’s well below the limit for a radiation worker • RT staff set up all RTP PET/CT scans routinely • Review again once numbers increase

References 1.

2.

3. 4.

Sam, S., et al., Workflow and Radiation Safety Implications of 18F-FDGPET/CT Scans for Radiotherapy Planning. J Nucl Med Technol, 2012. 11: p. 11. Carson, K.J., et al., Personnel radiation dose considerations in the use of an integrated PET-CT scanner for radiotherapy treatment planning. Br J Radiol, 2009. 82(983): p. 946-9. ARPANSA Personal Radiation Monitoring Service and Assessment of Doses Received by Radiation Workers (2004) KEARNS, William T. et al. Radiation safety issues with PET/CT simulation for stereotactic body radiation therapy. Journal of Applied Clinical Medical Physics, [S.l.], v. 9, n. 3, jun. 2008. ISSN 15269914. Available at: . Date accessed: 05 Feb. 2015. doi:10.1120/jacmp.v9i3.2763.