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Bret Conrad
June 26, 2013
June Case Study
Intensity Modulated Radiation Therapy of the Lower Esophagus
History of Present Illness: JK was an 80 year old male that had a history of Barrett’s
esophagus. He underwent a screening endoscopy in December of 2012 since it had been several
years since his last one. A mass was found and the patient was referred to Loyola University
Medical Center. The patient underwent an esophagogastroduodenoscopy/ endoscopic ultrasound
(EGD/EUS) on February 4, 2013 that revealed a mass at about 34-37 centimeters (cm) from the
incisors. The mass was occupying about 25 percent (%) of the luminal surface with ultrasonic
evidence of invasion into the adventitia. The pathology showed grade 2 adenocarcinoma of the
distal esophagus, stage 2B. An abnormal appearing subcarinal lymph node was found which
underwent a fine-needle aspiration (FNA), but was found to be benign. JK also underwent a
positron emission tomography (PET) scan on February 14, 2013, that showed the primary
esophageal mass uptake but did not reveal nodal or distant metastasis. The patient was a
candidate for surgery, and was not symptomatic at the time of consultation.
Past Medical History: JK had a past medical history of an elevated blood pressure, high
cholesterol, gastroesophageal reflux disease (GERD), and Barrett’s esophagus. Barrett’s
esophagus is the most common condition seen in patient’s that develop adenocarcinoma of the
esophagus.1
Social History: The patient’s social history showed that he was married with children. He was a
former smoker, smoking 2 packs a day for 30 years before quitting in 1982. He is retired and has
a family history of lung cancer.
Medications: The medications the patient was taking at the time of consult were Atorvastatin,
Benazepril, Nexium, Prochlorperazine, and Tamsulosin.
Diagnostic Imaging: The diagnostic imaging for this patient included an endoscopy in
December of 2012, an EGD/EUS on February 4, 2013, a FNA on a subcarinal lymph node, and a
PET scan on February 14, 2013.
Radiation Oncologist Recommendations: The recommendation from the radiation oncologist
was to administer neoadjuvant chemoradiation prior to surgical resection. This has been shown
to increase the patient’s median survival from 24 months with surgery alone to 49.4 months with
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chemoradiation followed by surgery.2 The patient agreed to undergo treatment, and expressed
understanding of the goals of treatment. The radiation oncologist discussed the rationale, risks,
benefits, complications, side effects, and alternatives to radiation therapy. The side effects that
were discussed included fatigue, dysphagia, nausea, vomiting, esophageal ulceration and
perforation, and poor wound healing.
The Plan (Prescription): The final prescription was to deliver radiotherapy to the esophagus
along with concurrent Carboplatin and Paclitaxel. For the stage 2B disease, the radiation
oncologist wanted to deliver 5040 centigray (cGy) to the gross disease with margin. The
radiation oncologist wanted to use the intensity-modulated radiation therapy (IMRT) technique.
Patient Setup/ Immobilization: The patient underwent a computed tomography (CT)
simulation on the Philips CT scanner. He was instructed to lie down in the supine position. His
shirt was removed and a gown was put on so he could be given tattoos. An alpha cradle was
placed under his thorax and head to prevent motion and ensure reproducibility every day. His
arms were raised above the head and molded in the alpha cradle because lateral beams would
probably be used (Figure 1).3 An angled sponge was placed under his knees for comfort and to
take pressure off of the back. A table pad was place under his buttocks for cushioning. After the
scan was taken, the patient was given 3 tattoos for localization and daily shifts. After the patient
left, the scan was transferred to the treatment planning system.
Anatomical Contouring: When the CT scan was received, the medical dosimetrist began
contouring the normal structures. In this case, the normal structures included the spinal cord,
right and left lungs, right and left kidneys, heart, liver, and carina. The carina was contoured only
for the radiation therapist’s assistance when they take their port films. When the stomach was
contoured, it was assigned a density of 0 since contrast was introduced for the CT scan (Figure
2). If the density was not overridden, the treatment planning system would assume it was bone.
The patient had very bad scoliosis, and his organs were not in the typical anatomical locations.
When the medical dosimetrists were done contouring the normal structures, the radiation
oncologist began contouring and review. The radiation oncologist double checked the normal
structure contours and then contoured the planning volumes. For this case, the planning
structures included a gross tumor volume (GTV), clinical target volume (CTV), and planning
target volume (PTV). Once the doctor was done, the medical dosimetrist continued the treatment
planning process. A few more contours had to be drawn on the scan, but these could not be
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drawn until the PTV was contoured. These two contours were the heart spare structure and the
cord spare structure. These are only contoured for IMRT patients, and they are used for
optimizing the plan. The heart spare structure is the heart minus the PTV with a margin, and the
cord spare is the spinal cord with a margin and extension posterior (Figure 3). These structures
are used so we can minimize the dose to those areas. Once the contours were finished the
medical dosimetrist began to develop the beams and energies.
Beam Isocenter/ Arrangement: When the patient was simulated a 3 point setup was used. The
medical dosimetrist made the isocenter shift from that setup. The isocenter was placed in the
middle of the PTV. The beam arrangement used was an anterior-posterior (AP) beam and 6
posterior obliques. This is a common technique at this facility, because the doctor caring for the
esophageal patients does not prefer a lot of low dose in the lungs. The gantry angles used were
190, 215, 240, 0, 120, 145, and 170. This arrangement spared the most dose in the lungs and
heart. The beam energy was 6 megavoltage (MV). This is also common for the IMRT patients.
The treatment plan was scheduled for the Varian 2100 linear accelerator. The prescription of
5040 cGy was entered into the plan and it was ready to be optimized.
Treatment Planning: The treatment planning was performed on the Eclipse treatment planning
system. The algorithm used was Anisotrophic Analytical Algorithm (AAA). The PTV to be
covered was rather large. In addition, the patient had severe scoliosis and his organs were
positioned differently than normal anatomy. The critical organs close to the PTV were both
lungs, the spinal cord, heart, and liver. The difficulty in optimizing this plan was the large
percentage of PTV in air (Figure 4). In Eclipse Treatment Planning System, the optimizer does
not take into account part of PTV being in air. Therefore, the optimizer assumes the PTV is
being covering by 100% of the dose, but when the beams actually calculate the coverage is less
than optimal. The normal critical structure doses in the optimizer were accurate, but the PTV
dose was not. Therefore the medical dosimetrist had to ensure the heart spare structure, cord
spare structure, and whole lung dose were in tolerance and then normalize the plan. The plan was
normalized to the 94% isodose line. This resulted in a plan with higher doses, but unfortunately
that was the only way to get more dose to the PTV. The overall hot spot (region of excess dose)
for the plan was 110%. The isodose lines were very conformal to the PTV in areas of all tissue
(Figure 5), however the coverage in areas of air was not optimal (Figure 6). Many different
optimizations were performed; however coverage of the PTV could not be increased. Increasing
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normalization resulted in more dose to the heart because the heart was in the PTV. The radiation
oncologist had to determine how high to normalize for better PTV coverage but also a higher
dose to the heart. The doctor decided on the 94% normalization after reviewing the dose volume
histogram (DVH) (Figure 7). The heart maximum dose was 5535 cGy with a mean dose of 2589
cGy, which was within the radiation oncologist’s tolerance. The cord maximum dose was 3825
cGy. The doctor evaluates that only 20% of both lungs receive 2000 cGy, which in this case was
18% receiving 2000 cGy. The only part of the DVH not optimal was the PTV coverage. The
DVH demonstrated less coverage but that is due to air in the PTV. The radiation oncologist was
not worried about that coverage as she was more worried about the coverage on the GTV, which
was between 99-100%.
Quality Assurance/ Physics Check: After the plan was finished, it was entered into the Rad
Calc 6.0 program. The difference between the Eclipse treatment planning system and Rad Calc
6.0 was only 0.6%. The radiation oncologist signed the prescription and the final plan. Since this
plan used IMRT, the physicist also performed a quality assurance (QA) on the treatment
machine. Once the QA passed, the physicist double checked and signed off on all of the
treatment fields. Before the actual treatments began, the radiation therapists took port films to
ensure accuracy and double checked for accurate monitor units.
Conclusion: This case study was very different from the previous esophageal cases. The main
challenge was that a large percentage of the PTV was in air. This made it very difficult for the
treatment planning system to optimize the plan. The optimizer calculated the PTV as optimal
coverage, however when the fields were calculated the coverage was poor. The medical
dosimetrists and radiation oncologist had to make important decisions about critical structure
doses and how much to normalize. Another component that made this plan different was the
patient’s severe scoliosis. The organs were in atypical positions in the body, making the field
shapes and sizes different than normal. This case study presented challenges as to whether IMRT
is better than 3 dimensional treatments. A great deal of time was spent working on this case and
unfortunately optimal PTV coverage was never obtained. However, the best plan was achieved
while sparing the normal structures.
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Figures
Figure 1. Patient positioning in CT simulation
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Figure 2. Contrast over-ride in stomach
Figure 3. Heart spare and spinal cord spare structures along with the PTV (Magenta)
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Figure 4. PTV overlapping air in lung
Figure 5. Isodose lines conformity in tissue (Yellow- 100%, Light Green- 95%)
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Figure 6. Isodose conformity in air
Figure 7. DVH
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References
1. Chao KS, Perez CA, Brady LW. Radiation Oncology Management Decisions. 3rd ed.
Philadelphia, PA: Lippincott Williams and Wilkins; 2011.
2. Van Hagen P, Hulshof MC, Van Lanschot JJ, et al. Preoperative chemoradiotherapy for
esophageal or junctional cancer. N Engl J Med. 2012;366:2074-2084.
http://www.nejm.org/doi/full/10.1056/NEJMoa1112088#t=abstract. Published May 31, 2012.
Accessed June 24, 2013.
3. Washington CM, Leaver D. Principles and Practice of Radiation Therapy. 3rd ed. St. Louis,
MO: Mosby Elsevier; 2010.