challenges of treatment verification - beacon...
TRANSCRIPT
• Air or metal within the abdominal cavity can cause
artefact on daily CBCTs increasing the challenge of
verification
Image Quality - Artefact
3rd Annual SRS/SBRT Symposium
• Motion occurs within the abdominal cavity independently
of breathing
• Breath hold (BH) delivered kidney treatment
Abdominal Lesions - Motion
3rd Annual SRS/SBRT Symposium
• Fiducial markers:
– Essential for liver SBRT
– Implant 7 days prior to planning CT
• BH is preferable
• Fasting for scan and treatment to reduce variation in
anterior abdominal wall
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
• Fiducial migration can occur, may need to use a surrogate
in conjunction with your fiducial
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
‘Ideal’ patient : 3 fiducials, BH, fasting
Day 1 :
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
‘Ideal’ Patient : 3 fiducials, BH, Fasting
Day 1 : 1 hour break, ate a light snack
Abdominal Lesions- Liver
3rd Annual SRS/SBRT Symposium
• ‘Non-protocol patient’ : free breathing, not fasting, did
have 3 fiducials implanted
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
• Verified patient positioning using CBCT and that
fiducials were along the expected trajectory
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
• Verify gate position by flouroscopy images to check dome
of diaphragm and fiducials
Abdominal Lesions - Liver
3rd Annual SRS/SBRT Symposium
• CT datasets
• CBCT and flouroscopy images
• Changes within the lung
• BH delivered treatments
Lung Lesions
3rd Annual SRS/SBRT Symposium
• Free breathing 3DCT – not used for lung SBRT at Beacon
• BH
• 4DCT
– CT 50 %
– Average Intensity Projection CT (AV-IP)
Lung Lesions - Datasets
3rd Annual SRS/SBRT Symposium
• CT 50 versus average intensity projection (AV - IP)
matching
• Average pixel densities among all the phases
• Best approximates the slow acquisition of the CBCT
Lung Lesions - Datasets
3rd Annual SRS/SBRT Symposium
• Possible AV-IP matching issues
Lung Lesions - Datasets
3rd Annual SRS/SBRT Symposium
AV-IP planning CT vs CBCT acquired on treatment
• Possible AV-IP matching issues- lower lobes
• Match using CBCT but verify using flouro
Lung Lesions - Datasets
3rd Annual SRS/SBRT Symposium
• Some inter-fractionation variation can be observed with BH
• 121 fractions of BH SBRT were retrospectively analysed and it was
found that mean magnitude of tumour displacement of 0.41 cm with
a standard deviation of ± 0.28 cm (in line with published data*)
• This variation was not found to correlate significantly with small
variations of BH amplitude on treatment, overall BH amplitude,
small variations in RPM block positioning or tumour location within
the lung
Lung Lesions - Breath Hold
3rd Annual SRS/SBRT Symposium
*Zhang G et al. J Nucl Med Radiat Ther2012, (Suppl 6): 12.*Kimura T et al. Brit J Radiol 2007, 80: 355–361
• All soft tissue moves required were applied retrospectively to each
fraction, the plan was recalculated using the same MUs and
composite plans for each patient generated.
• The DVH from composite plans were compared to the approved plan
evaluating the max, min, mean dose to each OAR as well as any
relevant dose volume constraints set by the physician
Lung Lesions - Breath Hold
3rd Annual SRS/SBRT Symposium
• Verification on treatment can be difficult and may
require multi-modality imaging
• IGRT protocols may need to be tailored to the needs of
the individual patient
• Further training/education may be required for image
matching – what you see isn’t always what you get!
Conclusions
3rd Annual SRS/SBRT Symposium