Angela Kempen

October Case Study

October 29, 2012

3D Conformal Radiation Therapy for Squamous Cell Carcinoma of the Vocal Cords

History of Present Illness: RW is a 77 year-old male who presents with a long history of

having a very hoarse voice. He has had previous direct laryngoscopy and biopsies which showed

dysplasia. He was seen by a physician in May and he was noted to have abnormal vocal cords.

He was recommended to have a direct laryngoscopy, but this procedure was postponed as a

result of developing bilateral pulmonary emboli. He was seen back by the same physician earlier

in the month of October and a direct laryngoscopy was done on 10/5/2012. The results of the

procedure revealed bilaterally abnormal vocal cords involving the vocal process to the

commissure. The cords have normal mobility. A biopsy revealed squamous cell carcinoma.

The patient was referred to Radiation Oncology for the consideration of radiation therapy.

Past Medical History: The patient suffers from severe chronic obstructive pulmonary disease

(COPD) and hypertension. He has dyslipidemia. In 2001, he experienced a myocardial

infarction (MI) and had a stent placed to circumflex the artery. The patient also suffered from a

transient ischemic attack (TIA), and was diagnosed with a pulmonary embolism (PE) in June of

2012. In addition, the patient has coronary artery disease.

Diagnostic Imaging Studies: The patient underwent a computed tomography (CT) scan of his

neck on 10/19/2012. The scan revealed exophytic tissue coming off the mid left true vocal cord

all the way through the anterior commissure and extending into the right true vocal cord to mid-

level. There is also some extra soft tissue density in the region of the anterior commissure along

with some minimal thickening of the adjacent aspects of the right and left true vocal cords. The

patient also had a flexible fiberoptic laryngoscopy done. The nasopharynx, oropharynx,

hypopharynx and larynx were examined. The findings showed bilaterally abnormal cords with

irregular heaped up tissue from the vocal process to the commissure. Mobility was normal. He

was staged as clinical stage I (T1b, N0, M0) early stage glottic larynx cancer, by American Joint

Committee on Cancer (AJCC).

Family History: The patient has a significant family history of cancer. Both his mother and

father died of cancer. Both of his brothers died of prostate cancer, one of his sisters died of lung

cancer and another sister died of breast cancer. He has a sister who is still alive, but living with

mantle cell lymphoma.

Social History: The patient is married and resides with his wife. They have three children. The

patient is a former pipe smoker of one pack per day for 40 years. He quit in 1987. He has

approximately two drinks a day.

Medications: The patient uses the following medications: Advair, albuterol, aspirin, Nitrotab,

palmetto fruit, senna, simvastatin, tiotropium, and warfarin.

Recommendations: The Radiation Oncologist recommended that the patient receive radiation

therapy for management of his early stage larynx cancer. This would be localized radiation

therapy to the larynx with no coverage of the lymph node region. The physician discussed the

rationale for radiation therapy with the patient. Toxicities during treatment were reviewed which

include, but are not limited to, fatigue, skin irritation, dysphagia, odynophagia, and hoarseness.

In addition, potential for late effects from treatment including thyroid cartilage necrosis and

injury to the soft tissues of the neck were discussed. The patient was in agreement to proceed.

The Plan (Prescription): The plan is for the patient to receive 6525 centigray (cGy) to the

larynx planning treatment volume (PTV) using a 3D-conformal technique.

Patient Setup/Immobilization: The patient was simulated in the supine position, with an

aquaplast mask used for immobilization of his head, neck and upper shoulder region. Arm pulls

were used in an attempt to move his shoulders as far down and away from his neck as possible.

A treatment planning computed tomography (TPCT) was completed with 2.5 millimeter (mm)

slices through the head and neck region.

Anatomical Contouring: The physician drew the gross tumor volume (GTV), clinical tumor

volume (CTV) and the larynx PTV. I contoured the spinal cord, right carotid and left carotid.

Beam Isocenter/Arrangement: I placed the isocenter in the middle of the larynx PTV. I then

added two lateral beams of 6 megavoltage (MV) photon energies. The straight lateral beams

were going through the patients shoulders, so I changed the right lateral to a right anterior

oblique (RAO) at 285 degrees with a collimator rotation of 340 degrees, and changed the left

lateral to a left anterior oblique (LAO) at 75 degrees with a collimator rotation of 20 degrees.

The physician then set his field size.

Treatment Planning: The physician wanted to the larynx PTV to receive 6525 cGy in 29

fractions at 225 cGy per fraction. The spinal cord was to be kept as low as reasonably

achievable. I calculated the beams and added 45 degree wedges with the heels facing anterior to

both the LAO and RAO beams to decrease hot spots. I still had a large hot spot superiorly, so I

copied the LAO field and added a 30 wedge with the heel facing superior to decrease the hot

spot. To cool the plan down even more, I copied the RAO field and closed some of the multi-

collimator leaves (MLC). I then weighted the beams to even out the prescription dose and make

the plan more conformal. The fields, wedge orientation and weighting of each beam can be seen

in Figure 1. I struggled to achieve 95% of the larynx PTV receiving full prescription dose, since

the fields were drawn so tight with very little margin. The physician was ok with this, but

wanted a bit more coverage anteriorly since that was were gross disease was located. A 4x3

centimeter (cm) piece of 0.5 cm bolus was added to increase dose in this area. The physician

prescribed to the 100% isodose line and approved the plan.

Figure 1: Field size, wedge orientation and beam weighting

Figure 2: Axial, sagittal and coronal slices

Figure 3: Axial slices showing isodose lines

Monitor Unit Check: Monitor unit (MU) calculations were performed to verify that the

treatment planning computer was calculating properly. MU check by Oncology Data Systems,

version 8.2.0, takes several factors into consideration in order to perform an accurate calculation

to determine the monitor units needed for treatment. The MU result is compared to the computer

MU calculation. The difference between the two should result in less than 5%, which it did for

this plan.

Quality Assurance Check: A physicist performed a second check of the treatment plan and

monitor unit check. It is critical to have an independent set of eyes look over the plan and

additional checks.

Conclusion: I chose this case study because it was challenging. The patient had a very short

neck and was unable to move his shoulders out of the treatment fields. Therefore, oblique

treatment fields were used. The physician drew his fields very tight with little margin around the

larynx PTV, which made it difficult to obtain adequate coverage of the larynx PTV. After

having a discussion with the physician, it was determined that eliminating hot spots and adding

the bolus to ensure the prescription dose adequately covered the gross disease was more

important than 95% of the larynx PTV receiving full prescription dose. I learned that a

discussion with the physician regarding exactly what he wants is extremely important in

treatment planning.

Figure 4: Dose Volume Histogram (DVH)