challenges of treatment verification - beacon...

Sarah BarrettClinical Specialist Radiation Therapist

Challenges of treatment verification

• Overview

– Image quality

– Abdominal lesions

– Liver lesions

– Lung lesions

Overview

2

• Spine SBRT post stabilisation

Image Quality - Artefact

3rd Annual SRS/SBRT Symposium

• Air or metal within the abdominal cavity can cause

artefact on daily CBCTs increasing the challenge of

verification

Image Quality - Artefact


• Motion occurs within the abdominal cavity independently

of breathing

• Breath hold (BH) delivered kidney treatment

Abdominal Lesions - Motion


• 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


• Fiducial migration can occur, may need to use a surrogate

in conjunction with your fiducial



‘Ideal’ patient : 3 fiducials, BH, fasting

Day 1 :



‘Ideal’ Patient : 3 fiducials, BH, Fasting

Day 1 : 1 hour break, ate a light snack

Abdominal Lesions- Liver


• ‘Non-protocol patient’ : free breathing, not fasting, did

have 3 fiducials implanted



• Verified patient positioning using CBCT and that

fiducials were along the expected trajectory



• Verify gate position by flouroscopy images to check dome

of diaphragm and fiducials



• CT datasets

• CBCT and flouroscopy images

• Changes within the lung

• BH delivered treatments

Lung Lesions


• Free breathing 3DCT – not used for lung SBRT at Beacon

• BH

• 4DCT

– CT 50 %

– Average Intensity Projection CT (AV-IP)

Lung Lesions - Datasets


• CT 50 versus average intensity projection (AV - IP)

matching

• Average pixel densities among all the phases

• Best approximates the slow acquisition of the CBCT



• Possible AV-IP matching issues



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 - changes within the lung


• 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


*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


• 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


• Thanks to all the MDT at Beacon for help with this talk

• Any questions?!

Questions


challenges of treatment verification - beacon...

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