SIGNIFICANCE OF INTRAFRACTIONAL MOTION IN PELVIC ORGANS A MUTLIPLANAR 3D CINE MRI STUDY

1
SIGNIFICANCE OF INTRAFRACTIONAL MOTION IN PELVIC
ORGANS A MUTLIPLANAR 3D CINE MRI STUDY

• Raj Sripadam1, Phil Sharrock2, Cath McBain3, John
  Logue3, Vincent Khoo1, Chris Moore2, Pat Price1
• 1 Academic Department of Radiation Oncology,
  Christie Hospital, Manchester, UK.
• 2 Developing Technologies Group, North Western
  Medical Physics, Christie Hospital, Manchester,
  UK.
• 3 Department of Clinical Oncology, Christie
  Hospital, Manchester, UK

2
Why is this important?
3
Purpose

• To characterise the intrafractional changes in
  the rectum, bladder and prostate organ
  configuration with the help of Dynamic or Cine
  MRI.
• To study the effect of rectal and bladder filling
  on the position and shape of the prostate.

4
Methods

• 31 bladder cancer patients had pelvic T2 weighted
  MRI scans at median intervals of 33 seconds over
  a 25-30 minute period (typically 48 volume scans
  each).
• Measurements were taken in the sagittal, coronal
  and axial planes. In the axial plane, the
  displacements were noted at two levels at the
  base and apex.
• The scans were analysed spatially and temporally
  in the chosen plane. The maximum displacement of
  the prostate borders, bladder rectal walls was
  noted through time.

5
Axial view
6
Sagittal view showing small bowel displacement
due to bladder filling within ½ hour.
7
Sagittal view showing intrafractional movement
due to rectal peristalsis
8
Results

• Lateral wall displacements of the bladder and
  rectum were lt5mm in 95.
• Deformation of the lateral borders of prostate
  was lt2.5 mm in 100.
• Measurements in millimetres with standard
  deviations

9
Results
10
SUMMARY OF RESULTS

• The rectal wall and prostate move mainly in the
  AP direction but the motion is small (less than
  5mm in gt95) and generally transient. The seminal
  vesicles move more than the body and apex of the
  prostate.
• There is hardly any movement at the level of the
  apex.
• The anterior and posterior borders of the
  prostate move more or less symmetrically (Pearson
  correlation coefficient -0.846 2-tailed
  plt0.001). Prostate deformation effects are small.

11
SUMMARY OF RESULTS

• Rectal filling closely corresponds to the rectal
  wall and ultimately prostate displacement
  (p0.034). Intrafractional prostatic movements
  are greater if the rectum is distended because of
  greater peristaltic activity.
• The anterior rectal wall movement corresponds
  closely to the prostate movement (plt0.001).

12
SUMMARY OF RESULTS

• Bladder filling is generally small (lt8 mm roof
  displacement in 90 of patients) The predominant
  movement is in the superior direction which is
  generally small (lt6 mm) however there can be
  extreme movements up to 24 mm in a few patients.
  This will be of relevance for tumours on the
  roof.
• Bladder filling, however had little effect on the
  prostate shape and position (p0.764).
• Bowel peristalsis transiently deformed the
  bladder.
• Small bowel displacement out of the pelvis was
  mainly due to bladder filling. (see movie)

13
Discussion literature review

• Occurs due to peristalsis and filling of rectum
  with gas / stool mainly.
• Measured by Cine MRI , BAT Ultrasound, gold seeds
  etc

gt95 of treatments displacement lt5mm.
14
Discussion and conclusions

• We studied not only the intrafractional changes
  of the prostate but also other pelvic organs such
  as bladder, rectum and small bowel in all 3
  planes. We studied the interplay of rectal and
  bladder filling on the pelvic organ
  configuration.
• We found that
• Intrafraction motion of the prostate is not a
  significant component of organ motion. Our study
  reinforces results from previous studies
  (ref1-3). Interfraction motion, on the other
  hand can be a significant component of organ
  motion as evidenced from other studies.
• Majority of the displacements are due to rectal
  peristalsis (passage of wind) and are transient.
• Intrafractional bladder motion too is not a major
  problem in the majority. Some form of screening
  (ultrasound) may be appropriate to identify the
  few patients who do show significant filling
  especially for tumours on the roof of the
  bladder.

15
The way forward

• Current margins for prostate radiotherapy (8-10mm
  ) should be adequate to correct for intrafraction
  motion in the majority of patients. However, if
  margins are reduced further to facilitate say,
  dose escalation for prostate or partial bladder
  radiotherapy, intrafraction motion will become
  important.
• Strict adherence to rectal and bladder protocols
  (empty rectum and a comfortably full bladder)
  will help decrease intrafractional as well as
  interfractional movements (as surmised from
  previous studies refs 1,2,3 ).

16
REFERENCES

• 1. Ghilezan MJ, Jaffray DA, Siewerdsen JH, et al.
  Prostate gland motion assessed with cine-magnetic
  resonance imaging (cine-MRI). International
  Journal of Radiation OncologyBiologyPhysics
  200562(2)406.
• 2. Mah D, Freedman G, Milestone B, et al.
  Measurement of intrafractional prostate motion
  using magnetic resonance imaging. International
  Journal of Radiation OncologyBiologyPhysics
  200254(2)568.
• 3. Padhani AR, Khoo VS, Suckling J, Husband JE,
  Leach MO, Dearnaley DP. Evaluating the effect of
  rectal distension and rectal movement on prostate
  gland position using cine MRI. International
  Journal of Radiation OncologyBiologyPhysics
  199944(3)525.

17
ACKNOWLEDGEMENTS

• Mr.Ric Swindell, Principal Medical Statistician,
  Christie Hospital, Manchester.
• Department of Radiology, Christie Hospital,
  Manchester
• Academic Department of Radiation Oncology,
  Christie Hospital, Manchester.
• Developing Technologies Group, North Western
  Medical Physics, Manchester, UK
• The Wade Centre for Radiotherapy Research,
  Christie Hospital, Manchester, UK.