2. Deviation Details
CBCT misaligned to the wrong vert body
Date/Time: 08/16/2013 2:24 pm
Machine: SL2
Treatment Site: Left Lower Lung
◦ Fraction 31
Dose: 200 cGy daily x 37 fx = 7400 cGy
◦ Dose Spec: Volume
Modality: 6x Photons
Technique: IMRT (8 field)
3. Documentation
The error was discovered by the imaging specialist while
reviewing images from the previous day
A deviation report was filled out by the imaging specialist who
discovered it
◦ No med tech note was made since it was discovered at a later time
◦ No further documentation by the therapist(s) is necessary
4. Brief Patient History
71 y/o male with hx of stage IIB Squamous Cell Carcinoma of the Rt.
upper lung treated surgically with Rt. Upper lobectomy in 2006 and
post op chemotherapy
43 yr hx of smoking 1-2 packs/day, quit in 2006 during previous CA
diagnoses
Routine imaging studies were negative until abnormal chest x ray and
f/up CT scan in March 2013 showed a lobulated necrotic mass in the
left lower lobe of the lung
New primary stage IIIA Squamous Cell Carcinoma in left lower lobe
of lung (N2 M0)
Curative treatment with IMRT and concurrent chemotherapy
7. Possible Reasons This Error Occurred
Therapists may have set up to a freckle instead of the tattoo
What was included in the clip box may have thrown off the
automatic registration
◦ If the arm is too high and it is included in the clip box, the software may
try to line up with the bony anatomy of the arm
The problem is that this is a “moveable” structure and should not be
considered when aligning the patient for treatment
Imaging specialist was not consulted
9. Red Flags
You are off by more than a cm
You see lots of purple and green
Moves that have been consistent suddenly change
◦ In this case the patient’s moves were consistently in the negative direction
through out his treatment, but this day, the moves were suddenly in the
positive direction
If you can clinically see that your patient is flat on the table but x-
axis rotation is still off by 10 degrees or more
◦ You are probably off by a vert body
10. Dose Deviation
This was an IMRT case, so dose deviation is measured in terms of volume, not C/A
Basically, you are looking to see if the gross tumor volume is still falling within the
planned treatment volume
In this case, most of the GTV was still contained in the PTV
During this particular fraction, the volume did not get the full dose it was intended to
get
However the deviation in dose was so small that it did not need to be made up for
Even if the entire gross tumor volume had fallen outside of the planned treatment
volume, it would only have missed 2.7% of the total dose planned
200 cGy/7400 cGy= 0.027 x 100 = 2.7%
In this particular case, the patient was getting a very high dose (7400 cGy total),
similar cases might only get 6000 cGy total, so this is another reason why the dose
did not need to be made up for
The greater concern is the treatment of normal tissue/structures
14. Policy Recommendations
If the clip box is throwing off your alignment, adjust its position or size so that it doesn’t
include unnecessary anatomy
If you can see the image is way off (lots of purple and green) click on manual method and
drag the image to superimpose it on the initial scan, click back on bone, and then click
automatic registration and convert to correction
Look for something on each patient’s scan that stands out (usually something unique about one vert body
compared to the rest) once identified, see if it corresponds to the location on the sim day
Don’t just look at one structure, look at all surrounding anatomy to be sure everything is
lined up correctly
If you have a move greater than 0.9 cm in any direction, call the imaging specialist, if the
imaging specialist is out or unavailable, call physics (this is part of the current policy!)
In the words of Shannon: “Don’t just bone and go!”
◦ Review your image carefully in all planes, don’t just click automatic registration, convert, and accept
w/o looking!
