Kesho Conference 2014

1. ELECTRONIC PORTAL IMAGING: Achieving
accuracy and precision for external beam
radiation therapy
Rose Wekesa : Cancer Care Kenya, Nairobi

2. Image Comparison
Digitally Reconstructed Radiograph Portal Image

3. Radiotherapy goal
• The inherent goal of radiation therapy is to eradicate all the
cancer cells or palliate symptoms by delivering enough
doses to the tumour, while minimizing injury to normal
tissues
• This is normally described in terms of tumour control
probability (TCP) and normal tissue complication probability
(NTCP).
• Imaging for treatment planning and for verification of
treatment among other factors makes it possible to achieve
the radiotherapy goal.
• This presentation focuses on treatment verification by portal
imaging.

4. TCP and NTCP Curves
SuntharalingamN, Podgorsak EB & Hendry JH 2005. Basic radiobiology. IAEA. Vienna

5. Introduction
Radiation therapy is one of the safest and most effective ways
to treat cancer.
Errors do occur, but they are extremely rare, with a very small
fraction of treatments involving an incident that puts a patient
at risk of harm.
These errors can be avoided if we put certain measures in our
daily practice.

6. Sequential process of planning and delivering radiotherapy.

7. Purpose
• To evaluate patient set-up variations for oesophageal
cancers treated with External Beam Radiation Therapy
• Six anatomical landmarks were selected for comparison and
recorded; the X (Left-Right, L-R), Y(Superior-Inferior, S-I)
and Z (Anterior-Posterior, A-P) directions
• Data was used to set acceptable tolerance limits for portal
imaging of the oesophagus.

8. Methods and Materials
• Fifty seven patients with locally advanced disease treated
with chemoradiation were randomly selected for this study
over a period of two years.
• Patients were positioned using body tattoos.
• EPI's were performed prior to treatment and registered to
the digitally reconstructed radiographs (DRR).
• DRRs were used to adjust patient setups before treatment
delivery. A total of 163 EPI pairs were analyzed and errors
calculated
• Orthogonal pair images were acquired, which were used to
give displacement
• If a patient had a single field or two opposing fields, the
accuracy of field placement was assessed in two
dimensions only.

9. Treatment verification Process
PRE-TREATMENT: Acquire reference images
TREATMENT
1
Fraction 1 Acquire portal images
2
Fraction 1
3
Fraction 1
Acquire portal images
Acquire portal images
Online review of
images against
reference
Gross error?
Action level?
No Yes
Continue with
current set up
STOP: Revise
set up, re-image
Calculate the mean displacement
(MD) in all 3 axes
No Yes
MD Action level?
Continue with
current set up
Revise set up,
re-image X2 #s
Fraction 4
Fraction 5
No imaging
No imaging
Portal Imaging
Portal Imaging
Calculate the mean displacement
(MD) in all 3 axes
MD No Action level? Yes
Continue with
current set up
STOP: Investigate
further
Weekly Portal Imaging

10. Portal imaging by anatomical matching
• Isocenter variation in X and in Y directions were measured
on anterior (AP) portal images, whereas, in Z and Y direction
were measured on lateral portal images.
• After the anatomical matching was performed on the
treatment fields for an individual patient, variations were
recorded into a Microsoft Excel spreadsheet.
• The reported X, Y and Z displacement of isocenter between
simulation and treatment was applied into the appropriate
shifts along each body axis.

11. Radiotherapy Targeting!
• For treatment,
same position
as of simulation
is set
• Lasers,
immobilization &
tattoo's are used
to verify the
correct position.

12. during Radiation therapy
 Two questions
always emerge.
1. Are they
hitting the
right spot?
2. Am I getting
the right
dose?

13. Anatomical match structures used

14. RESULTS
Displacement No of
Patients
Portal
image pairs
(Total=163)
Total
Mean
(Mpop)
mean (%)
Left-Right (L-R) 57 57 2.05 3.6
Supero- Inferior
(S-I)
57 57 2.79 4.9
Antero-posterior
(A-P)
57 49 3.09 6.3

15. DISCUSSION:
• The systematic and random errors for EPI’s were;
2.05mm in L-R, 2.79mm in S-I and 3.09mm in A-P
directions.
• The population-based mean variation is less than 5 mm, thus the
set-up provides sufficient targeting for all of the patients.
• Consistent with recommendations by the RCR, Institute of
Physics & Engineering in Medicine & Royal college of
radiographers (in line with ICRU Reports 50 & 62)
• Variations were more significant during the first sessions in
treatment than the weekly portals.
• This could be attributed to patient relaxing in the course of the
treatment and getting over the anxiety.

16. CONCLUSION
• Radiotherapy verification is a process that helps us
ascertain that we are treating tumor volume as planned.
• EPI results in different position correction for verification of
radiotherapy in all malignancies.
•When protocols are formulated & used at specified intervals,
patients can benefit in terms of treatment accuracy since
most of the set up errors if not all can be corrected.
• Portal imaging is therefore a must in every radiation
treatment.

17. Thanks for your attention!
www.Cancercare kenya.com