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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:

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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.