Effect of a Novel Prostate Implant Technique on Post-Implant Dosimetry and Potency

1
Effect of a Novel Prostate Implant Technique on
Post-Implant Dosimetry and Potency

• Jenny P. Nobes
• St. Lukes Cancer Centre
• The Royal Surrey County Hospital Guildford

2
Overview

• Discussion of potential targets in prostate
  brachytherapy-induced erectile dysfunction (ED)
• Guildford study
• Conclusions

3
Background

• Balance between treatment and toxicity
• Prostate brachytherapy (BXT) alone has been
  reported to result in ED in 6 - 53 of cases

Incrocci et al, Int Rad Oncol Biol Phys 2002
4
Aetiology of ED after BXT

• Neurogenic compromise
• Vascular insufficiency
• Local trauma
• Psychogenic causes

Zelefsky et al, Int Rad Oncol Biol Phys 1998
5
Anatomy
6
Neurovascular Bundle

• 54 patients undergoing BXT alone or boost
• 33 developed ED, median FU 37m
• Potent patients 4 years younger
• Mean NVB dose 217 55 mPD both groups NS

NO RELATIONSHIP between NVB dose and development
of ED
Merrick et al, Int Rad Oncol Biol Phys 1998
7
Proximal Crura
Wallner et al, Int Rad Oncol Biol Phys 2002
8
Proximal Crura

• 30 pt with ED post-BXT and 30 pt maintained
  potency after implant
• Median FU 48m
• Dose to proximal crura statistically greater in
  pt who develop ED in all dosimetric parameters
• To maximise potency, D50 should be kept lt28 mPD

RELATIONSHIP between proximal crura dose and
development of ED
Merrick et al Int Rad Oncol Biol Phys 2002
9
Penile Bulb
Wallner et al Int Rad Oncol Biol Phys 2002
10
Penile Bulb

• 23 pt with ED post-BXT and 23 pt maintained
  potency after implantation
• Median FU 34m
• Dose to penile bulb statistically greater in pt
  who develop ED in all dosimetric parameters
• Radiation dose to 50 of bulb should be lt40
  mPD to minimise development of ED

Merrick et al Int Rad Oncol Biol Phys 2001
11
Summary

• No consistent data on dose to NVB

• Dose to 50 (D50) crura lt28 mPD
• Dose to 25 (D25) crura lt40 mPD

• Dose to 50 (D50) of bulb lt40 mPD
• Dose to 25 (D25) of bulb lt60 mPD

12
Guildford Study

• 94 patients
• Prospective data collection
• Comparison between classical and
  second-generation Guildford implant techniques
• Novel technique implemented Feb 2005
• Aims to
• Minimise penile bulb dose
• Preserve prostate dosimetry
• Improve post-implant potency rate

13
Methods - Patients

• No external beam RT
• No androgen deprivation therapy
• All potent pre-BXT
• Defined by International Index of Erectile
  Function (IIEF) score gt11/25
• IIEF score completed at baseline and 12 months

14
Methods

• TRUS-guided I125 seed implant
• Each patient prescribed minimal peripheral dose
  (mPD) 145Gy
• Day 1 post-implant CT scan
• Penile bulb outlined at 5mm intervals

15
Group 1

• n64
• Classical (Seattle) implant technique
• Stranded seeds
• Modified-uniform distribution

16
Group 1 Classical Technique
Urethra
PTV
Prostate
Modified-uniform seed distribution
17
Group 2

• n30
• From February 2005
• Second-generation Guildford technique
• Stranded seeds peripherally
• Loose seeds implanted centrally using Mick
  applicator
• Visualised in sagittal TRUS plane
• Greater flexibility implanting apex

18
Group 2 - Mick Applicator
19
Group 2 Guildford Technique
RAPID Strand
Central Needles containing loose seeds
Modified-peripheral seed distribution
20
Patient Demographics
Classical n64 Guildford n30
Parameter Mean ? SD Mean ? SD p value
Age 61 ? 6 62 ? 7 0.41
PSA 6.3 ? 2.4 6.7 ? 2.6 0.67
Prostate vol 43.4 ? 9.8 42.7 ? 12.8 0.82
21
ResultsPenile Bulb Dosimetry
Classical n64 Guildford n30
Parameter Minimal Peripheral Dose Mean SD Minimal Peripheral Dose Mean SD p value
D10 78 ? 49 34 ? 17 lt0.0001
D25 60 ? 35 27 ? 12 lt0.0001
D50 45 ? 26 20 ? 8 lt0.0001
D90 29 ? 15 13 ? 6 lt0.0001
22
Mean Dosimetric Coverage Penile Bulb
Prescribed Dose
23
ResultsProstate Dosimetry
Classical n64 Guildford n30
Parameter Mean ? SD Mean ? SD p value
D90 147Gy ? 21 160Gy ? 17 lt0.05
V100 90.7 ? 5.9 93.4 ? 3.9 lt0.05
V150 56.8 ? 10.3 58 ? 11.7 0.99
24
ResultsPost-Implant Potency

• 12 months post-implant
• IIEF score gt11/25
• Group 1 60.9
• Group 2 83.3
• p0.017
• PDE5-inhibitor use similar

25
Conclusions

• Relationship between ED and technique needs
  further investigation given
  multi-factorial aetiology
• Novel implant technique results in
• Improved prostate dosimetry
• Lower penile bulb doses
• Higher potency rate

26
Acknowledgements

• Dr Robert Laing
• Professor Stephen Langley
• Dr Sara Khaksar
• Dr Abdul Ismail
• Dr Maria Hawkins
• Mrs Donna Higgins
• Miss Claire Deering