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Jonathan Taylor
Clinical Practicum I
February 29, 2012
Adenocarcinoma of Left Lung Treatment Planning Case Study
History of Present Illness: AS is a 55 year old male with history of heavy smoking diagnosed
with adenocarcinoma of the left lung. AS first presented with persistent cough, dyspnea on
exertion, chest pain, clubbing, and leg swelling. A chest x-ray was performed on 8/12/14
showing subtle left upper lobe central infiltrate. A chest CT was performed on 9/19/14 revealing
a mass in the left upper lobe. On 9/24/14 a bronchoscopy with biopsy of the left upper lung
revealed moderately differentiated adenocarcinoma of lung origin. Adenocarcinoma of the lung
is the most common type of lung cancer, and lung cancer is the second most common type of
cancer in men and women in the USA.1 Sadly, lung cancer is the number one cause of cancer
death in the USA due to difficulty in detection as well as treatment. Patient was referred by
medical oncologist to discuss radiation therapy options, and met with radiation oncologist on
2/4/15. The radiation oncologist reviewed possible treatment options and their risks and benefits,
as well as recommending a PET/CT study. A PET/CT study was performed on 2/5/2015 showing
a left upper lobe nodule of 0.9 cm x 1.0 cm with a peak SUV of 1.8. The patient consented to
proceed with radiation therapy and a planning CT simulation with and without contrast was
performed on 2/12/15.
Past Medical History: The patient has no known drug allergies. In addition to current cancer,
cough, dyspnea on exertion, chest pain, clubbing, and leg swelling, patient also has a past history
of atherosclerosis, COPD, coronary artery disease, gastro esophageal reflux,
hypercholesterolemia, hypertension, myocardial infarction in 2000 and pneumonia in 9/2014.
Patient had angioplasty in 1998.
Diagnostic Imaging Studies: Patient received diagnostic chest x-ray and CT scans in 9/2014, as
well as PET/CT study on 2/5/2015. A planning thin slice CT with and without contrast was
performed prior to the start of treatment planning.
Family History: Patient has no known family history of cancer. The current state of health or
morbidity of parents and grandparents is unknown.
Social History: AS is a married man who recently quit smoking after smoking for over 30 years.
Previously patient was a heavy smoker and smoked one pack per day since age 24. Patient uses
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alcohol occasionally at social occasions and denies the use of recreational drugs. Patient is a
research engineer who is occupationally exposed to metal dust and laser radiation and wears a
protective mask during exposure.
Medications: Patient currently takes Breo Ellipta, Levaquin, Losartan, Metoprolol,
Pantoprazole, and ProAir HFA.
Recommendations: Stereotactic body radiation therapy (SBRT) to the left lung was prescribed
for AS in order to provide high dose to the target while minimizing dose to surrounding critical
structures.
Treatment Plan/Prescription: SBRT of 50 Gy @ 10 Gy x 5 fractions was prescribed. No boost
was prescribed.
Patient Setup/Immobilization: Patient was simulated in supine position with hands and arms
resting above head (Figure 1). A foot strap was used to hold the patient’s feet together, and a
support cushion was used under the patient’s knees. A vacuum lock bag was used to immobilize
the patient’s head and arm positioning (Figure 2). A GE Hispeed Fx/I single slice CT simulator
was used for simulation covering the lower head, neck and thorax inferiorly to the L2 vertebral
body. Images were taken at 0.2 cm slices. Radiopaque markers were used to mark laser position
on the patient’s body.
Anatomic Contouring: Simulation CT studies with and without contrast were imported into
Varian Eclipse 11.0.42 treatment planning system (TPS) for treatment planning. The CT study
without contrast was used for planning, and the CT with contrast was fused with this study to
help identify critical structures as well as target volume. The critical structures included the
lungs, esophagus, spinal cord, and heart which were contoured by the dosimetrist. The physician
contoured the target volume and in doing so accounted for intrafractional organ motion during
treatment by creating an ITV from the CTV. The PTV was created as the final volume by
expansion from the ITV of 4mm.
Beam Isocenter/Arrangement: A Varian Trilogy linear accelerator, equipped with 6 MV and
18 MV capability, as well as onboard kV and MV imaging, was used for treatment delivery. The
treatment plan employed three axial non-coplanar IMRT Rapid Arc beams named RA Lt Lung1,
RA Lt Lung2, and RA Lt Lung3 (Figures 3-11). All beams were at 6 MV energy and used the
same isocenter. RA Lt Lung1 had a couch rotation of 20o, a collimator rotation of 10o and a
counter clockwise (CCW) gantry rotation of 179.9o to 0.1o. RA Lt Lung2 had a couch rotation of
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340o, a collimator rotation of 28o and a clockwise gantry rotation of 10.1o to 179.9o. RA Lt
Lung3 had a couch rotation of 0o, a collimator rotation of 20.0o, and a CCW gantry rotation of
179.9o to 40.1o. The prescription and organ at risk (OR) objectives were entered into the TPS and
optimized to meet target coverage and objectives.
Treatment Planning: Varian Eclipse 11.0.42 TPS was used for creating the treatment plan to be
implemented on a Varian Trilogy linear accelerator. Dose prescription, target volume, and
objectives were set by physician. A homogenous dose was desired across the target volume
while minimizing exposure to spinal cord, esophagus, heart, and lungs. A total of three IMRT
Rapid Arc beams were used in order to provide maximum dose to the target volume while
minimizing dosage to OR. All of the beam arcs were restricted to between 0.1o and 179.9o in
order to minimize exposure to the right side of the patient’s body as well as the more central
heart, spinal cord, and esophagus. Non-coplanar beam arcs were used in order to maximize and
conform high dose to the target. The treatment delivered a total of 50 Gy at 10 Gy/day for 5
fractions with the calculation point set to beam isocenter by the dosimetrist. Appropriate normal
tissue objectives for high dose SBRT were used for OR including the spinal cord point maximum
less than 30 Gy, lung volume of less than 1500 cc receiving a dose of 12.5 Gy, esophagus
volume of less than 5 cc receiving less than 27.5 Gy, and heart maximum point dose of 30 Gy.
The cumulative dose volume histogram (DVH) after optimization yielded OR well within these
objectives, with the left lung receiving the largest dose of the OR with a mean dose of 602.2
cGy, a maximum point dose of 5397.4 cGy, and only 14.8% of the volume (187.6 cc) receiving
12.5 Gy (Figure 12). Normalization was set to 100%. The physician reviewed and approved this
plan for treatment.
Quality Assurance/Physics Check: Monitor units (MU) were double checked using Oncology
Data Systems’ MU Check to compare with the TPS calculated MU (Figure 13). All beams were
within the tolerance limit of 5%, with RA Lung1 at 993 mu for 0.88% difference, RA Lung2 at
1193 mu for 4.09% difference, and RA Lung3 at 767 mu for 4.71% difference. The medical
physicist performed QA testing with Math Resolution’s Dosimetry Check which utilizes the on
board MV imaging to collect QA data. The physicist evaluated the plan and found it to be within
acceptable tolerance limits. Due to the nature of high dose SBRT, additional physics QA was
performed before each treatment. This QA was based on the Winston-Lutz test and tested the
accuracy of the positioning of the beam central axis (CAX) in relation to different couch and
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gantry angles. The gantry and couch are rotated through different angles while shooting the beam
at a phantom target and recording the images on the MV panel. Measurements were made to
verify that at all angles the beam CAX did not vary by an amount greater than 1 mm. As well
prior to beam on, the physician verified the positioning accuracy of the patient using on board
imaging.
Conclusion: Small, spherical shaped lung tumors can be very effectively treated with a large and
highly conformal dose while mimimizing dose to OR using SBRT applied with IMRT
technology such as Varian’s Rapid Arc. I was amazed to see how large of a dose gradient could
be achieved with this technique, and found this case to be my cornerstone for understanding the
application of SBRT technique. The use of multiple non-coplanar arcs combined with VMAT
technology allows for high dose SBRT treatment with remarkably minimal OR exposure that
would not be possible with traditional static field therapy. This high degree of conformality is in
fact what enables the application of SBRT involving doses of 10 Gy or more at a time; without
this conformality the OR exposure would be prohibitively high. For this reason SBRT has now
become the primary treatment modality for non-operable early stage non-small-cell lung cancer,
yielding local control of 80%-90% at 2-3 years and a high overall survival of 50%-60%
compared to traditional radiation therapy.2 Although adenocarcinoma is the most common form
of lung cancer in the USA, it is often excluded from SBRT trial studies due to concerns with
properly defining the target volume. 3 Recent studies such as Badiyan et al and Mak et al2
suggest that SBRT is appropriate for adenocarcinoma of the lung as well with similar outcomes
and survival rates. As our ability to deliver conformal high dose radiation therapy grows, the
benefits of SBRT in lung cancer treatment is a promising avenue of both clinical practice and
research.
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References
1. National Cancer Institute. A snapshot of lung cancer. National Cancer Institute at the
National Institute of Health Web site.
http://www.cancer.gov/researchandfunding/progress/snapshots/lung. November 5, 2014.
Accessed April 18, 2015.
2. Mak RH, Hermann G, Lewis JH et al. Outcomes by tumor histology and KRAS mutation
status after lung stereotactic body radiation therapy for early-stage non-small-cell lung
cancer. Clin Lung Cancer. Jan 2015; 16(1):24-32.
http://dx.doi.org/10.1016/j.cllc.2014.09.005
3. Badiyan SN, Bierhals AJ, Olsen JR et al. Stereotactic body radiation therapy for the
treatment of early-stage minimally invasive adenocarcinoma or adenocarcinoma in situ
(formerly bronchioloalveolar carcinoma): a patterns of failure analysis. Radiat Oncol. 2013;
8(4). http://dx.doi.org/10.1186/1748-717X-8-4
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Figure 1. Patient simulation positioning with positioning mark.
Figure 2. Patient in treatment position with vacuum lock bag.
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Figure 3. AP View.
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Figure 4. Lateral View
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Figure 5. Isocenter in axial plane.
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Figure 6. Isocenter in sagittal plane.
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Figure 7. Isocenter in coronal plane.
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Figure 8. RA Lung1 Field size
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Figure 9. RA Lung2 Field size
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Figure 10. RA Lung3 Field size
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Figure 11. Plan Summary
Figure 12. Dose Distribution (Light Green Isodose Line = 100%, Blue Contour with Interior
Red Shading Is PTV)
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Figure 13. Dose Volume Histogram
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Figure 14. MU Check