measurement uncertainty and prostate seed brachytherapy gregory
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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