Measurement uncertainty and prostate seed brachytherapy

Presented by Kent GregoryDepartment of Medical Physics

Royal Adelaide Hospital

Kent Gregory, John E. Pattison, Giovanni Bibbo

What is a prostate seed implant?

c/o NY Times website

Post-implant: in OR

melbourneprostate.org

Post-implant: some hours later

melbourneprostate.org

How is implant quality assessed?

One indicator is the value of D90…

How is implant quality assessed?

Interpreting D90 values…•>130 Gray = good treatment•110-130 Gray = closer assessment•<110 Gray = may need top-up

Most implants are assessed using CT images…

CT contouring

However RAH ‘Fuses’ Ultrasound contours onto CT images

Schiffler Cancer Centre (USA)~1500 implants between 1995 and 2006, 55 biochemical failures to 2008

The correlation between D90 value and biochemical failure seems poor.Q1. What factors contribute to D90 uncertainty?Q2. What is the uncertainty of D90?Q3. Can we make better use of clinical resources?

Q1: What factors contribute to D90 uncertainty?

• Seed activity• Hardware cal. • Seed placement• Fusion match• CT contouring

• 30 mins (1 MP)• 15 mins (2 MPs) • 60 mins (3 medical + 5 staff)• 15 min (1 MP)• 20 min (1 medical, 1 MP)

Q2: What is the uncertainty of D90?

• Seed activity• Hardware cal. • Seed placement• Fusion match• CT contouring

• 2%• 2%• 3%• ? %• 10%

Han et al., Med Phys, Vol. 30, No. 6, June 2003

CT contouring results

80

90

100

110

120

130

140

150

160

170

180

0 1 2 3 4 5 6 7 8 9 10

Patient

D90

 (Gray)

CT contouring & KG fusion

80

90

100

110

120

130

140

150

160

170

180

0 1 2 3 4 5 6 7 8 9 10Patient

D90

 (Gray)

CT contouring & all fusion

80

90

100

110

120

130

140

150

160

170

180

0 1 2 3 4 5 6 7 8 9 10

Patient

D90

 (Gray)

Q2: What is the uncertainty of D90?

• Seed activity• Hardware cal. • Seed placement• Fusion match• CT contouring

• 2%• 2%• 3%• 9% + Oedema• 10%

Han et al., Med Phys, Vol. 30, No. 6, June 2003

Conclusions

• Even preliminary analysis of data indicates D90 values have large uncertainties, due mainly to the contouring or fusion step

• Lower D90 uncertainty may be achieved if MR images are used

• D90 uncertainty may be improved if more time is invested getting MR images, and less time with seed placement

Thank you!Acknowledgements•A/Prof Loredana Marcu

(Senior Medical Physicist, Royal Adelaide Hospital)

•Dr Raghu Gowda(Radiation Oncologist , Royal Adelaide Hospital)

•And the rest of the Brachytherapy team at RAH