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Curtis Wilgenbusch
March Case Study
March 10, 2014
Stereotactic Body Radiation Therapy (SBRT) for Lung Cancer
History of Present Illness: Patient AF is an 84 year-old male who presented with dizziness and
an abnormal electrocardiogram (EKG) in May 2013. At that time, he underwent several
diagnostic studies; including chest x-rays and computed tomography (CT) studies of the chest
and abdomen, to determine the cause of his symptoms. The chest CT showed a spiculated
pulmonary nodule in the right upper lobe that measured (1.0 x 0.9) centimeters (cm) that was
suggestive of malignancy. There were also extensive emphysematous changes in the upper lobes
of the lungs. The patient was sent for a positron emission tomography (PET)/CT for further
investigation of the pulmonary nodule. There was an intense focal region of increased
fluorodeoxyglucose (FDG) uptake within the posterior aspect of the right upper lobe (RUL) with
a maximum standard uptake value (SUV) of 3.4. This area corresponded to the spiculated RUL
pulmonary nodule that measured 1.3 cm on an axial slice of the CT study. This was consistent
with an FDG avid malignant process. The patient underwent a lung mass needle biopsy in the
RUL at the end of June 2013, which revealed cellular evidence of squamous cell carcinoma. The
patient was staged with T1N0M0 poorly differentiated squamous cell carcinoma of the RUL of
the lung.
The patient was referred to the radiation oncology department and met with the radiation
oncologist in January 2014 to discuss treatment options. Pending the outcome of a new PET/CT
study to determine if there was evidence of mediastinal adenopathy or distant metastasis, the
patient was told that he was a good candidate for stereotactic body radiation therapy (SBRT).
The radiation oncologist explained that the cure rates were comparable to surgery. The entire
process as well as the risks and benefits, from treatment planning through treatments, were
discussed. The patient expressed understanding and agreed to proceed with radiation therapy.
A new PET/CT study was performed in February 2014, which showed no evidence of
adenopathy or distant metastasis. These results were consistent with the requirements of the
radiation oncologist for SBRT.
Past Medical History: AF has a history of left-sided renal cell carcinoma for which he
underwent a neprectomy 18 years ago. In addition, he was found to have early stage prostate
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cancer in 2006. His maximum pretreatment prostate-specific antigen (PSA) was 3.54. He was
treated with definitive radiation therapy for prostate cancer from November 2006 through
January 2007. He received a total dose of 7740 centigray (cGy) in 43 fractions. The patient also
has a history of chronic obstructive pulmonary disease (COPD), hypertension, benign prostatic
hypertrophy, hyperlipidemia, and cataracts.
Social History: AF is originally from Cuba. The patient was in the airport food service business
and retired at the age of 63. The patient is a widower with two children. AF has a 60 pack-year
history of smoking but quit 40 years ago. He drinks alcoholic beverages socially.
Medications: AF takes the following medications: Advair, Astepro, Hexacetonide
Triamcinolone, Clonazepam, CoQ10, Fenofibrate, Finasteride, Loratadine, Ranitidine, Vitamin
B1, Spiriva, Carvedilol, Crestor, Vitamin C, and Vitamin D.
Diagnostic Imaging: AF had chest x-rays performed in May 2013, which revealed a cardiac
silhouette that was mildly enlarged and hazy opacities in the left lung base suggestive of possible
early developing infiltrate. The right lung was clear and there were no pleural effusions or
pneumothorax seen. In the same month, AF had a CT study of the chest and abdomen
performed. The CT of the chest revealed a spiculated pulmonary nodule in the RUL measuring
(1.0 x 0.9) cm that was suggestive of malignancy. In June 2013, AF had a PET/CT study from
the skull base to the mid-thigh performed. This revealed an intense focal region of increased
FDG uptake in the posterior aspect of the RUL that corresponded to a spiculated RUL
pulmonary nodule measuring 1.3 cm in diameter on an axial slice of the CT study. The patient
underwent an additional PET/CT study for treatment planning purposes in February 2014. This
study revealed an intense FDG uptake corresponding to a 1.5 cm spiculated nodule in the RUL,
which had grown in size since the previous PET/CT that is consistent with a primary lung
cancer. There was no evidence of adenopathy or distant metastasis.
Radiation Oncologist Recommendations: After a review of AF's diagnostic studies, biopsy
report, and pathology, the radiation oncologist recommended that AF receive external beam
radiation to the RUL of the lung. The patient was not a good candidate for surgery because of
his comorbidities and age. The recommendation included SBRT of the RUL of the lung with
intensity modulated radiation therapy (IMRT)/image-guided radiation therapy (IGRT) using a
volumetric modulated arc therapy (VMAT) technique. The VMAT technique has been shown to
be more efficient and have faster delivery times compared to static field IMRT.1
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The Plan (prescription): The treatment plan recommended by the radiation oncologist was
SBRT of the lung with IMRT/IGRT utilizing the VMAT technique. This plan was designed to
deliver a total of 5400 cGy to the planning target volume (PTV) at 1800 cGy per fraction, for a
total of 3 fractions. An internal target volume (ITV), which is the clinical target volume (CTV)
plus an internal margin (IM) as defined by the Internal Commission on Radiation Units (ICRU)
62 report, was created using a 4-dimensional (4D) CT study with respiratory gating. The PTV
included the ITV plus a 0.5 cm uniform margin, which were included to account for uncertainties
such as patient motion and setup errors.
Patient Setup / Immobilization: The Philips Brilliance Big Bore CT/simulator (Sim) was used
for the simulation. The patient was placed in the supine position with his upper body
immobilized in an Elekta BodyFix cradle (Figure 1). The hands were placed above the head
with the right hand over the left hand. Once the patient was immobilized properly, a 4DCT scan
of the thorax using 0.3 cm axial slices was performed to obtain a treatment planning data set.
The volume that contained the pulmonary nodule, plus a margin above and below, was scanned
with 0.15 cm axial slices. The medical physicist was called to the CT/Sim to review the acquired
images. The isocenter was placed near the center of the target volume and reference marks were
put on the patient using the LAP laser system in the CT/Sim room (Figure 2).
Anatomical Contouring: The CT data set was exported to the Varian Eclipse 11.0 treatment
planning system (TPS). The medical dosimetrist contoured the left and right lung, total lung,
skin, right chest wall, heart, spinal cord, and trachea. A structure that included the total lung
minus the PTV plus a 0.2 cm uniform margin was created by the medical dosimetrist for
planning purposes. A planning organ at risk volume (PRV) was created for the spinal cord by
adding a 0.2 cm margin for uncertainties in daily positioning and patient motion. The radiation
oncologist contoured the right bronchus, and the esophagus. The radiation oncologist also
contoured the gross tumor volume (GTV), which was used to create the ITV. All of the contours
were then reviewed and subsequently approved by the radiation oncologist.
Beam Isocenter / Arrangement: A Varian TrueBeam STX was used to plan this patient. The
medical dosimetrist placed the beam isocenter in the geometrical center of the ITV (Figures 3-9).
The VMAT plan consisted of 2 half arcs: the first arc rotated clockwise from 181.0 degrees to
0.0 degrees in the Varian International Electrotechnical (IEC) 61217 scale and the second arc
rotated counter-clockwise from 0.0 degrees to 181.0 degrees. The collimator angle for the first
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arc was set at 30.0 degrees (Figure 8). The collimator angle for the second arc was set at 330.0
degrees (Figure 9). The couch angle was set at 0.0 degrees for both arcs. The energy used for
each arc was 6 megavolts (MV) in the flattening-filter free (FFF) mode. By removing the
flattening-filter from the beam, it is possible to increase the dose rate up to a factor of 2.5 for 6
MV without compromising the quality of the plan.2-4 This FFF mode along with the VMAT
technique will dramatically reduce the total treatment time when compared with coplanar and
noncoplanar static field IMRT, which is paramount with SBRT cases. Once the treatment
objectives were entered into the TPS, the field sizes and multileaf collimator (MLC) positions
were automatically set to deliver the optimal target coverage, while sparing the organs at risk
(OR) and the normal tissue. The monitor units (MU) for the first and second arc fields were
2359 and 2582, respectively.
Treatment Planning: Treatment planning was performed using Eclipse 11.0. The radiation
oncologist outlined the treatment prescription and the dose constraints to the OR. The patient
received a total of 5400 cGy in 3 fractions at 1800 cGy per fraction. The objectives for the target
were a maximum and minimum dose, which corresponded to the treatment prescription. The
goal was to achieve 95% coverage of the target volume with 100% of the prescribed dose. The
objectives for the spinal cord were a maximum volume of 0% to receive 900 cGy and a
maximum volume of 17% to receive 300 cGy. The objectives for the heart were a maximum
volume of 5% to receive 3400 cGy and a mean dose of 100 cGy. The objective for the left lung
was a maximum volume of 0% to receive 650 cGy. The objective for the right lung was a
maximum volume of 10% to receive 2000 cGy. The objectives for the right chest wall were a
maximum volume of 2% to receive 2000 cGy and a maximum volume of 38% to receive 650
cGy. After several iterations, the TPS achieved an acceptable dose distribution, which included
sufficient coverage of the target while maintaining acceptable doses to the OR (Figures 5-7, 10).
The plan was designed for treatment on a Varian TrueBeam STX with 120 leaf high-definition
MLC (HD-MLC). The energy used for both arcs was 6 MV FFF. The maximum dose rate of
1400 MU per minute was chosen. The angular resolution value was set at 5 degrees. The
calculation grid size was set at 0.25 cm and the heterogeneity correction was on. The plan was
normalized to 100% at the primary reference point after being reviewed and approved by the
radiation oncologist.
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Quality Assurance/Physics Check: A quality assurance (QA) plan was delivered to a Sun
Nuclear ArcCHECK phantom as well as a Sun Nuclear MapPhan device and subsequently
evaluated by Sun Nuclear's SNC Patient software. The measured plan was then compared with
the expected plan that was exported by the Eclipse TPS and was within the ±5% tolerance. The
treatment plan and QA measurements were then reviewed by the radiation oncologist and a
medical physicist as a final check before treatment began.
Conclusion: According to the American Cancer Society, there will be an estimated 224,200
new cases of lung and bronchus cancer in 2014.5 They also estimate that there will be 159,260
deaths related lung and bronchus cancer, which is the leading cause of all cancers.5 The use of
SBRT allowed for the delivery of high doses per fraction as well as a high total dose in just 3
fractions, which is necessary for local control and a cure. This case was well suited for SBRT
because of the lack of adenopathy and distant metastasis. This was an excellent option for the
patient because of the reduced time spent in radiation therapy. By using FFF mode along with
VMAT, the total treatment time was dramatically reduced. The ability to deliver several
thousand MUs in a relatively short period of time with FFF mode makes it especially conducive
for SBRT treatments. One of the challenges with this case was keeping the doses to the OR at an
acceptable level. It was difficult to meet the objective for the right chest wall due to its close
proximity to the target. It was necessary to place several optimization objectives on the right
chest wall to overcome this difficulty. The dose to the skin was comparable to what is
achievable using multiple coplanar and noncoplanar beams. The VMAT technique along with
the FFF mode made it relatively easy to achieve excellent coverage of the target while
minimizing the doses to the OR.
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References
1. Bedford JL. Treatment planning for volumetric modulated arc therapy. Med Phys 2009;36:51285138. http://dx.doi.org/10.1118/1.3240488
2. Scorsetti M, Alongi F, Castlioni S, Fogliata A et al. Feasibility and early clinical assessment of
flattening filter free (FFF) based stereotactic body radiotherapy (SBRT) treatments. Radiat Oncol
2011;6:113. http://dx.doi.org/10.1186/1748-717X-6-113
3. Ong C, Verbakel W, Dahele M, Cuijpers J et al. Fast arc delivery for stereotactic body
radiotherapy of vertebral and lung tumors. Int J Radiat Oncol 2012;83(1):137-143.
http://dx.doi.org/10.1016/j.ijrobp.2011.12.014
4. Kim G, Rice R, Lawson J, Murphy K, and Pawlicki T. Stereotactic Radiosurgery with FFF
mode photon beams. Int J Radiat Oncol 2012;84(3):S823. doi:10.1016/j.ijrobp.2012.07.2205
5. American Cancer Society. Cancer Facts and Figures 2014. Atlanta: American Cancer Society;
2014.
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Figures
Figure 1. Image of Elekta BodyFix BlueBAG system used. Image courtesy of
http://www.elekta.com/healthcare-professionals/products/elekta-oncology/treatmenttechniques/positioning-and-immobilization/bluebag.html.
Figure 2. LAP laser system in the CT/Sim. Image courtesy of www.lap-laser.com.
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Figure 3. Anterior-Posterior (AP) Beams Eye View of Treatment Isocenter
Figure 4. Right Lateral Beams Eye View of Treatment Isocenter
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Figure 5. Axial view of treatment isocenter. Green isodose line is 100%, blue isodose line is
98%, purple isodose line is 50%, and orange isodose line is 15%.
Figure 6. Coronal view of treatment isocenter. Green isodose line is 100%, blue isodose line is
98%, purple isodose line is 50%, and orange isodose line is 15%.
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Figure 7. Sagittal view of treatment isocenter. Green isodose line is 100%, blue isodose is 98%,
and purple isodose line is 50%.
Figure 8. Beams Eye View of the first arc field.
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Figure 9. Beams Eye View of the second arc Field.
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Figure 10. Dose Volume Histogram (DVH).