Download Case study 1 - Christopher J. Schneider Medical Dosimetrist

Chris Schneider
Case Study 1
March 30, 2015
Adenocarcinoma of the Left Lung Stereotactic Ablative Radiation Therapy (SABR)
History of Present Illness: Patient DS was a 70-year-old white male who was recently
diagnosed with malignant neoplasm of the upper lobe of the left lung. The reason for the consult
was stage IV, T3 N0M018 adenocarcinoma of the lung and he was referred for consideration of
stereotactic ablative radiation therapy (SABR) to 3 small lung nodules. Patient DS underwent a
right lower lobectomy in 2006 for non-small cell lung cancer. In 2009, he underwent left lower
lobectomy and received adjuvant chemotherapy from medical oncologist for a stage III nonsmall cell lung cancer.
Diagnostic Imaging Studies: Routine screening chest computed tomography (CT) scan on
December 15, 2014 showed a 1.4 CM nodule in the posterior aspect of the left upper lobe, a 0.7
cm nodule in the anterior aspect of the left upper lobe and a 6 mm nodule in the right upper lobe.
The patient was referred to a medical oncologist for treatment recommendations on December
16, 2014. Medical oncologist scheduled a Positron emission tomography–computed tomography
(PET/CT) scan on January 5, 2015, which shows the posterior left upper lobe nodule to have
standardized uptake value (SUV) 6.2, the anterior left upper lobe nodule to have SUV 2.7, and
the nodule in the posterior aspect of the right upper lobe to have SUV of 1.7. There were no
other suspicious lesions. The medical oncologist then scheduled a CT guided core biopsy of the
posterior left upper lobe nodule on January 12, 2015, which demonstrated adenocarcinoma of the
lung. The medical oncologist then referred the patient for radiation therapy treatment. The
patient denies cough, hemoptysis, increased dyspnea, weight loss, or pain. His appetite has been
normal. He feels well. The left lung lesion is actually quite small measuring only 1.4 cm at its
widest part. Because of the optimal tumor location (away from the chest walls and mediastinum)
and the correct stage made him a good candidate for SABR. His insurance then preauthorized
SABR treatment.
Past Medical History: DS has a medical history of chronic obstructive pulmonary disease
(COPD), emphysema, high cholesterol, hypertension and pulmonary hemorrhage on 1/12/2015.
Past Surgical History: DS had a pet scan on 1/5/2015 and a colonoscopy with polypectomy on
8/27/2010. The patient also had a left lung biopsy on 1/12/2015; he also had a left lung
lobectomy in 2009 and right lung lobectomy in 2006.
Family History: The patient has no family history of cancer. His paternal uncle died from
prostate cancer. No other cancers were reported by the patient and his wife.
Social History: The patient admits to smoking cigarettes 1 pack per day for 42 years. The
patient still smokes today. The patients’ alcohol consumption was at 4 drinks per day. No other
drug use or exposure to dangerous substances was reported. The patient has a long history of
hypertension. DS is married and one daughter age 20 years old. He worked at General Motors for
30 years and is now retired.
Medications: The patients’ medications include Fenofibrate, Simvastatin, Spiriva, Ventolin
ProAir Inhaler, and Amlodipine. The only medication allergies noted was Keflex.
Diagnostic and Radiation Therapy Image Fusions:
The radiation oncologist (RO) image fusion ordered for the physics and dosimetry staff to fuse
the simulation CT images with diagnostic PET/CT images to better delineate the target and
radiosensitive organs at risk named above. The image fusion is required to determine the correct
target and avoidance volumes, as they cannot be adequately identified using the simulation CT
scan alone. The scan that was to be fused with the Varian Eclipse treatment planning system
was done on 1/5/15. The PET/CT resulted in the radiologist and oncologist agreement that there
was no evidence of lymph node involvement.
Radiation Oncologist Recommendations:
The radiation oncologist ordered (SABR) to be performed. SABR was deemed medically
necessary and preferable to 3-dimensional conformal, conventional radiation therapy, and
intensity-modulated radiation therapy to eradicate the target while sparing the above-named
radiosensitive normal tissues adjacent to the target volume. SABR has been shown to permit
escalation of the radiobiologically effective dose to the target without causing undue toxicity to
the surrounding normal tissues. SABR is required because an escalated radiosurgical dose was
required to effectively obliterate the target and An exceptionally rapid dose falloff outside the
target volume must be achieved in order to protect the above-named radiosensitive organs at risk
that are within or in close proximity to the target volume and keep those risks below their
tolerance limits.
The Plan (7000 cGy): The SBRT radiation therapy planning technique called for a total dose of
6000 cGy. The number of fractions was prescribed at 3 total fractions of 2000 cGy per day. The
fractionation plan was for alternating days, meaning treatments on Monday, Wednesday, and
Friday, and leaving Tuesday and Thursday to recover and heal.
Patient Setup: The RO selected a reference center for the CT scan. Radio-opaque BB markers
were placed on the patient’s skin under laser guidance over the reference center. Radio-opaque
wires were not placed per his specifications. A 4-dimensional radiation treatment planning CT
scan was acquired using 1.0 mm slice thickness of the patient’s chest. The radiation therapists
and dosimetrist then performed per RO’s specifications and under RO supervision with the
patient in treatment position using their immobilization and positioning devices. Intravenous and
Esophageal contrast were used to better delineate the target and normal tissues on the CT scan.
Following the CT scan, the reference center and appropriate positioning points were then marked
on the patient’s skin using a permanent marking pen. Photographs were then taken of the patient
in treatment position with their skin markings. The patient Position is listed below:1. Head First
Supine 2. Head Rest: Clear D 3. Arms: Holding Handles 4. Knees: Knee-fix 5.Feet: Bound with
plastic band 6. Index Bar: Yes (indicated in photo). 7. SABR board 8. Compression belt at
settings I1/J1, Lt side-J3 top strap, Right side-D6 bottom strap, compression (1-1.5lbs) 9. Tattoos
and References marks for tattoos are configured in a 3-pt setup.
Anatomical Contouring The organs at risk (OR) included the lungs, spinal cord, heart,
esophagus, ribs. These contours were all done by a dosimetrist and verified by the physicist and
RO physician. The RO contoured the gross tumor volume (GTV), and after propagating the GTV
with MIM deformable registration the internal target volume (ITV) was created and touched up
by the RO physician. The planning treatment volume (PTV) margin was added by all parties
mentioned above. See table 5 below.
A 4-dimensional CT simulation scan was done to determine patient positioning, establish field
parameters, define the movement of the tumor during the breathing cycle, and acquire CT images
for treatment planning purposes. A 4-dimensional scan was required because the tumor changes
its anatomic position significantly during the respiratory cycle. The 4-dimensional scan permits
the RO to determine the range of movement of the tumor and define and create a treatment plan
that encompasses the internal target volume (ITV) of the tumor. Planning using the ITV assures
that the tumor will be irradiated throughout the respiratory cycle while minimizing the dose and
damage to the surrounding above-named organs at risk.
Beam Isocenter / Arrangement: Volumetric Modulated Arc Therapy (VMAT) beam
optimization was utilized for this SABR treatment on a Varian Truebeam 2.0 linear accelerator.
Isocenter was placed by the dosimetrist at the centroid of the PTV volume. The 2 coplanar half
arc beams were aligned to that Isocenter. The VMAT Rapid Arc technique was planned on
Varian Eclipse treatment planning system (TPS) version 11. The energy of both photons beams
was 6MV flattening filter free (FFF). The dose rate of the 6MV FFF beam was 1200. Two half
arcs on the left side of the body started at 1790 then rotating to 00, and then back down to 1790
again. The patient was positioned head first supine. The clockwise beam collimator rotation was
450 and the counter clockwise beam was 3150. The number monitor units (MU) for each beam
was 2884, and 3078 respectively.
Treatment Planning: The RO’s treatment intent was curative, and ordered the staff to treat the
patient using stereotactic body radiation therapy technique. Varian Eclipse was the radiation
therapy treatment planning system (TPS) used on a Varian Truebeam 2.0 linear accelerator. Two
6MV FFF coplanar half arcs, Source to axis (SAD) was used. The VMAT Rapid Arc technique
was used with two half arcs on the left side of the body starting at 1790 then rotating to 00, and
then back down to 1790 again. Multileaf collimator blocking will be used to shape the radiation
fields. Since this was a SBRT case we delivered 2000 cGy in 3 fractions (Monday, Wednesday,
and Friday) to 6000 cGy. This fractionation scheme was utilized as it offers one day between
each fraction. See Figure 3, Eclipse.
Quality Assurance / Physics Check: This information can be found in the chart and tables
below. Radcalc software was used for the MU second check. The dosimetrist and physicist also
performed a daily Winston-Lutz test with the Winston-Lutz phantom to verify table and
Isocenter shifts. An ArcCheck/MapCheck dose profiler unit with a central ion chamber were
used to independently measure dose and compare that to that of the TPS. See QA figure below.
Conclusion: In results are listed in table 5 for the organs at risk as well as the target volumes.
All three of the target volumes achieved the goals set for each dose prescribed. The gross tumor
volume, GTV, called for a minimum dose of 60 Gray and was achieved at 61.1 Gy to 100% of
the volume. The ITV exceeded its goal dose at 61 Gy at 99% of the volume. And the PTV
achieved all three of its goal doses were 60 Gy covered 97%, 58.5 Gy covered 98%, and 57 Gy
covered 100% of the volume.
The summary of the dose volume sheet shows the exact doses at each volume that the organs
received, and can be found on figure 4 DVH. The most significant organ at risk in this case was
the total lung constraint. Total lung volume combines the volume of both the right and left lung
into one, and is considered critical as it represents how damaging the treatment will be on a
patient’s entire lung volume and ability to breathe. In the table above, the total lung constraint
calls for 500 cGy to cover no more than 30% of the volume. This constraint was more than met
at only 8.33% of the total lung receiving 499.9 cGy.
This was a difficult case for the whole department because it was our first SABR and first time
using the 6MV FFF very high dose rate beams. When a 2000 cGy was delivered in a single
fraction, extra precautions must be taken. The other challenging part was that the field was so
small. The physics and dosimetry staff had to rush to calibrate the Truebeam for that energy for
that small field size. The gold beam data that was provided by Varian for this Truebeam model
does not include reference beam data for fields smaller than 3cm x 3cm. Small field dosimetry is
a controversial topic anyway because of the difficulty and very small ion chambers are needed
because the penumbra region is squeezed almost to the central axis.
Dose Rx
(cGy)
No. of
Fractions
Total
(cGy)
2000
3
6000
Treatment Site
L posterior upper lobe tumor
Pl a nni ng Dos e V ol um e Ob j ect i ves (A l l Dos es i n cGy)
Target V olumes
Objectives
Goal Dose Max Dose
GTV
ITV
6000
6000
PTV
6000
Starting V olume
% V ol
Achieved
Min Dose
% V ol
6000
6000
5700
6000
5700
100
99
100
97
100
5850
98
Goal Dose Max Dose
6000
Margins (cm)
Ant
Post
Sup
Inf
Left
Right
ITV
Organ at Risk
Uniform
0.5
Min Dose
% V ol
6116.5
6116.5
6116.5
6000.13
5700.4
100
100
100
97.59
99.8
5850.23
99.37
Resulting V olume
D
Ineq Sign
% V ol
1800
1100
3000
3500
3000
3200
Table 5, (above)
500
to <
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30
Special Note
PTV
Objectives
Max D
Spinal Cord
Heart
Skin
Esophagus
L Mainstem Bronchus
Total Lung
% V ol
6000
6000
Achieved
Mean D
Abs. V ol.
Max D
<0.25 cc
<1.2 cc
1202.6
1202.6
44.8
< 1800
1476.1
1285.3
Mean D
D
499.9
Ineq Sign
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to <
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% V ol
8.33
Abs. V ol.
Figure 1, patient setup.
Figure 2, MIM (below)
MIM ITV generation
Isocenter placement.
Figure 3, Eclipse.
3D view.
DVH and Dose Statistics:
Figure 4 DVH
Quality Assurance/ Physics: Radcalc Second MU Check and AcrCheck Phantom Report
References:
1. Radiation Oncology UCLA. UCLA.edu. http://radonc.ucla.edu/body.cfm?id=227
Accessed March 4th 2015
2. National Comprehensive Cancer Network (NCCN). Non-Small Cell Lung CancerUnited States, 2015. NCCN Guidelines Version 4. 2015