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Ellie Hawk
November 25, 2015
Clinical Practicum III
Final Clinical Project- IMRT
Esophagus and Upper Stomach Treatment Using Rapid Arc
The patient is a 61-year-old male with significant tobacco and alcohol use who now has
adenocarcinoma of the distal esophagus and upper stomach. He states he has not seen a physician
for over 40 years. SW presents with significant weight loss of 50 pounds and vomiting for 2
months, 30-40 times per day. A CT scan of the chest, abdomen, and pelvis in September 2015
displays involvement of numerous regional nodes and esophageal adenocarcinoma that extends
into the stomach. An endoscopy was performed in September 2015, but was not able to evaluate
the stomach due to the esophagus being strictured. A PET scan was attempted, but patient was
unable to complete due to claustrophobia, therefore leaving the patient incompletely staged. SW
presents with some small nodules in the lungs, an ill-defined liver lesion, and some lymph nodes
that are considered to be possibly metastatic.
Patient staging was deemed incomplete, although physicians believe SW’s stage to be T3
with possibly N2 to N3MX stage. The staging was determined off tumor volume, lymph node
involvement within and outside typical drainage pattern, along with no presence of obvious
distant disease. The tumor was determined to be a large obstructing mass, 34 cm from the
incisors, from a September 2015 endoscopy. A CT scan in September 2015 revealed thickening
of the mid to distal thoracic esophagus extending to the gastroesophageal junction. Enlarged
lymph nodes of the periesophageal and gastrohepatic ligament, and right-sided
tracheoesophageal groove lymph node measuring 11 mm were also observed. Due to his staging
possessing a value higher than N0, meaning there is lymph node involvement, lymph nodes were
to be included in treatment. In order to treat nodes, the gross target volume (GTV) was extended
past the esophageal mass to include surrounding lymph nodes. The GTV was measured to be
18cm x 7cm.
Chemoradiation was suggested for palliation of symptoms such as pain and esophageal
obstruction. A 6-week course of external beam radiation to the esophagus, upper stomach, and
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regional lymph nodes was prescribed. SW received 1.80 Gy for 25 fractions, totaling a
prescription dose of 45 Gy. The patient’s treatment was followed up with a boost of 1.8 Gy for 3
fractions to 5.4 Gy. The treatment schedule was developed in efforts to decrease tumor size to
the point where swallowing would resume. Possible acute side effects of treatment included
nausea, vomiting, fatigue, dysphagia, and odynophagia. Long-term side effects were described as
possible esophageal stricture, radiation pneumonitis, and/or cardiac issues due to the location of
treatment.
In September 2015 AW presented for a complex simulation of the esophageal radiation
fields to begin the radiation treatment process. After informed consent was obtained, he was
positioned head first supine on the CT simulator table in the supine position. Both of SW’s arms
were raised above his head in an indexed wing-board. A custom Vac-Lock mold was made to aid
in patient immobilization and treatment reproducibility. A thin sliced CT scan was then obtained.
The distal esophageal lesion was identified and the Radiation Oncologist set the isocenter using
the AW system, placing the isocenter in the targeted tumor volume. Isocenter coordinates were
then recorded, and appropriate marks were placed on the patient’s skin.
Figure 1: SW’s setup for daily treatment, patient in the supine position with both arms raised
above head with custom Vac-Lock mold made for position reproducibility.
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SW’s CT images from the simulation were transferred to the dosimetry computers so a
three-dimensional conformal treatment plan could be created, using RapidArc Intensity
Modulated Radiation Therapy. The esophageal lesion and abnormal lymph nodes were contoured
on consecutive slices by the Radiation Oncologist to generate a three-dimensional target volume.
Organs at risk (OR) within the treatment area were contoured by the Dosimetrist on the axial
slices of the patient’s treatment planning CT that was obtained during their simulation. Once
these structures are contoured they are a 3D volume as shown below on the patients Multi-Planar
view.
Figure 2: The multi-planar view that displays the 3D structures that are made by contouring
consecutive axial slices.
The rationale for contouring structures is to have the ability to monitor, display, and
evaluate their doses on the Dose-Volume-Histogram (DVH). The OR are evaluated on the DVH
to determine final field design, angles, and treatment doses. The physicians use QUANTEC as a
guideline on dose limitations to critical structures. Since the lungs, liver, kidneys, spinal cord,
heart, bowel, and stomach fall within the treatment area, and are dose limiting structures, they
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were contoured. This was to ensure their dose stayed minimal, and fell within the physicians
QUANTEC guidelines for acceptable dose to dose limiting structures. While contouring, a 1.5
cm margin was put on the GTV to create a PTV structure. A PTV OPTI was then created with a
0.1cm margin on the PTV. This structure was then used as the volume to be optimized to during
treatment planning.
To begin the treatment planning process the fields needed to be setup. The Arc Geometry
tool was used to create a plan that had a single isocenter and 2 full rotations, using complement
6X energy beams. The first beam traveled clockwise from 181° to 179° degrees with a collimator
angle of 10°, while the compliment beam traveled counterclockwise to travel from 179° to 181°
with a 350° collimator angle. Collimator angles must be used during RapidArc plans to prevent
leakage through the multi-leaf collimators (MLCs). There was no couch rotations used for this
treatment.
VMAT Optimization was used to apply objectives on the target volumes, and OR for
planning. The target volume, PTV OPTI, had upper and lower objectives applied. Initially, the
upper objective possessed a volume of 0% with a dose of 4,725 cGy, which is 105% of the
prescription with a priority ranking of 130 in efforts to keep the plan’s hot spot low. The lower
objective possessed a volume of 100% with a dose of 4,545 cGy, which is 101% of the
prescription with a priority ranking of 125 in efforts to ensure adequate coverage was provided to
the optimization structure. The plan began to calculate in which it was paused during Multi-
Resolution (MR) level 1, step 1 to make changes to planning objectives. The bowel space, heart,
kidneys, liver, lungs, and stomach all had planning objectives that were altered. These structures
were altered to prevent hot spots from falling into these structures, and reducing their overall
structure dose. Below are the OR with their final objectives used during treatment planning and
their QUANTEC dose limit guidelines that were followed.
OR Final Objective for
Treatment Planning
Dose Limit
Guideline
Volume (%)
Dose (cGy)
Priority (Gy)
Lungs, R 40 1,000 80 Total Lung:
5
Lung, L
60
40
60
500
1,000
500
50
80
50
V5<60%
V10<40%
V20<30%
V30<20%
Mean<18Gy
Liver Mean 950 50 V35<40%
Mean<20Gy
Kidney, R
Kidney, L
Mean
5
Mean
250
1,995
750
70
70
70
In at least one kidney:
V20<67%
Whole kidney:
<15Gy
Spinal Cord
No Objectives needed due to
location and low dose.
V50<1%
V45<5%
Heart Mean 2,545 50 Mean<30Gy
Bowel 0 4,580 90 Dmax<52
Stomach 0 4,598 100 V45<15%
Dmax<54
PTV
OPTI
Upper:
0
Lower:
100
4,725
4,545
130
135
GTV
PTV
No objectives used;
optimized to PTV OPTI
Table 1: Final planning objectives used during planning and the dose limit guidelines followed
during treatment planning.
Upon completion of planning and altering planning objectives, the axial slices and DVH
were used to evaluate dose distribution. By using the axial slices, isodose lines were evaluated to
determine how conformal the dose was to the PTV and how much dose the surrounding OR were
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receiving. The dose was extremely conformal to the desired PTV target volume, making it an
ideal treatment plan. The green 100% isodose line and PTV contour nearly lay on top of each
other, meaning the full-prescribed dose is being delivered to the PTV as desired. Since the PTV,
which is the GTV with a 1.5cm margin, is being fully covered by the 100% isodose line it is
clear that the GTV also has full coverage. The GTV is displayed in red with full coverage by the
green 100% isodose line with spots of 105% as shown by the pink isodose lines. OR contours
such as the right and left lungs, heart, and spinal cord are displayed on this isocenter slice. Dose
is being delivered to both lungs and the heart due to their proximity, but the volume being
irradiated and the dose being received by the OR is not deemed an issue since they are below
tissue tolerances. The spinal cord is far enough away from the target volume where only part of
the structure is receiving a minimal 50% of the prescribed dose, as displayed by the orange 50%
isodose line. Below you can view the GTV coverage along with the PTV coverage at isocenter.
Figure 3: Conformal dose distribution developed by the RapidArc treatment, that is sparring
surrounding OR.
The patient’s treatment plan had a hot spot of 108.7%, or 4,891.9 cGy verses the
prescribed 4,500 cGy. I am both satisfied and dissatisfied with the location of this hotspot. I like
that the hotspot only has a value of 108.7% and is relatively small. I also like that the hotspot
falls within the PTV, and not directly within any critical OR structures like the spinal cord,
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lungs, or heart that are nearby. I do not like that the location is not within the GTV, and is in the
last few superior slices of the PTV. I also do not like the hotspot’s location is near the carina and
esophagus. This could cause the patient to have worse side effects than necessary, like more
severe esophagitis or dysphagia. Along with the hotspot being in this slice, you are also able to
visualize the 100% isodose line breaking up. This is due to the beams traveling through air in the
carina, esophagus, and lungs. Although it is not ideal to have a 100% isodose line break up, it is
okay on this slice due to it being so superior within the field, and still providing full coverage to
the PTV as shown in pink. Below is the slice with the highest dose for SW treatment plan and
slight deterioration of the 100% isodose line.
Figure 4: Display of the hotspot with the treatment plan, and break up of the 100% isodose line
on superior slices of the PTV.
The DVH was also used to evaluate the plan prior to physician approval. The DVH
helped to determine dose to target volumes and OR. Below is the DVH for SW esophagus
treatment. Also included are the structure’s QUANTEC guidelines, rather they met their max or
mean dose criteria. All of the structures met their criteria besides both lungs, which met 3 of the
5 criteria guidelines. Both the right and left lung failed to meet the low dose tolerances for the
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lungs of V5<60% and V10<40%. They failed to meet criteria due to the target volumes location,
and dose having to fall into the lungs to provide the coverage needed to the GTV and PTV.
Image 5: DVH displaying the doses that the target volumes received and surrounding OR.
OR Dose Limit Guideline (Gy)
Final Dose (Gy)
Constraints Met?
Lungs, R
Lung, L
Total Lung:
V5<60%
V10<40%
V20<30%
V30<20%
Mean<18Gy
Total Lung:
V5= 88%
V10= 65%
V20=13%
V30=4.7%
Mean=13.5Gy
V5= 83%
V10= 66%
V20=10%
V30=1%
Mean=12Gy
Lungs, R
No: V5 and V10.
Yes: V20, V30, and
mean.
Lung, L
No: V5 and V10
Yes: V20, V30, and
mean.
Liver V35<40%
Mean<20Gy
V35=3%
Mean=10Gy
Yes.
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Kidney, R
Kidney, L
In at least one
kidney: V20<67%
Whole kidney: <15Gy
In at least one
kidney: V20=0%
Whole kidney: =2.5Gy
In at least one kidney:
V20=7.7%
Whole kidney:
=7Gy
Kidney, R
Yes.
Kidney, L Yes.
Spinal
Cord
V50<1%
V45<5%
V50=0%
V45=0%
Yes.
Heart Mean<30Gy Mean=26.8Gy Yes.
Bowel Dmax<52 Dmax=48.6Gy Yes.
Stomach V45<15%
Dmax<54
V45=13%
Dmax=47.8Gy
Yes.
PTV
OPTI
Only for planning purposes, not used on DVH to evaluate plan.
GTV 100% receiving Rx of 45Gy.
PTV 99% receiving Rx of 45Gy.
Table 2: OR and target volume’s final dose and rather they met their constraints set prior to
treatment planning.
From this project I was able to hone in on my RapidArc treatment planning skills. I was
able to accurately manipulate dose through planning objectives to make a conformal plan with a
low hotspot, and low dose to the surrounding OR. I learned while working with RapidArc you
must make small steps early within treatment planning. For example, the biggest changes to the
plan must be made during MR level 1, step 1. Dosimetrist must pause optimization during this
level since the treatment planning system has not began to fine tune the dose yet. During MR 1,
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step 1 the dose is being delivered through larger arc angles, therefore manipulations to OR
objectives will show a greater response.
I learned small steps are vital while planning with RapidArc because if you push to lower
a structures dose and end up losing coverage, it is challenging or nearly impossible to get the
coverage back without restarting your optimization. By taking small steps you are able to
evaluate dose without losing coverage. Once structures seem to have an ideal dose distribution,
you are able to run the calculations out on the plan and run intermediate dose. I learned to not
evaluate a plan until intermediate dose has been ran. Intermediate dose helps to reduce hotspot
values, sizes, and dose to structures and it is considered to be a fine-tuning process of the
treatment plan.
In short, this treatment planning project helped me to learn how a target volume may be
in a spot near many dose limiting OR, but RapidArc and patience while planning allows you to
develop a dynamic treatment plan with conformal dose distribution. The conformality of the dose
will accurately be able to deliver the prescribed dose to the target volume, while carving out dose
around the surrounding OR. RapidArc is a fascinating treatment planning tool and I look forward
to opportunities to advance my treatment planning skills and take on more complex plans with
more overlapping structures.
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