Angela Kempen

November Case Study

November 27, 2012

Intensity Modulated Radiation Therapy for Right Petroclival Meningioma of the Brain

History of Present Illness: KP is a 52 year-old woman who presented with approximately a 3-

year history of diplopia. A physician saw the patient at the end of July and examination revealed

third and sixth nerve palsy with pupillary asymmetry. Magnetic resonance imaging (MRI) was

performed which showed a large enhancing mass in the right petroclival region consistent with a

meningioma. There was encasement of the carotid artery and displacement of the brainstem.

There was extensive involvement of the cavernous sinus and the sella. The mass measured

approximately 4 centimeters (cm) in size. The patient was referred to the University of

Wisconsin Hospital and Clinic and met with a physician from their skull based team. The patient

was recommended to undergo a 2-stage procedure. She underwent a right orbital zygomatic

approach for the lesion on August 31, 2012, with debulking of the tumor. This showed a

meningioma without any features of atypia or anaplasia. The patient was allowed to recover

from that procedure and subsequently was taken back to the operating room for the second

procedure which was a right retro-sigmoid craniotomy and subtotal resection of a portion of the

petroclival part of the tumor. Again, she had a good recovery. She still has significant diplopia.

She has had no change in her vision. She has no focal muscular weakness. She has decreased

sensation on the right side of her face to light touch. She was having sensory seizures prior to

starting Keppra. Her seizures were sensory in nature. She states she would have odd smells or

tastes, and at times, seemed to hear things. She is having minimal headaches. She takes

occasional oxycodone primarily at night to help with pain. She has no problems with balance or

coordination. She indicates her cognitive function is stable. She has been asked to be seen for

the consideration of postoperative radiotherapy to address the residual tumor that was

unresectable. She has no previous history of malignancy. She has no previous history of

radiotherapy.

Past Medical History: The patient has hypertension. She also has anxiety and depression,

which may be related to her diagnosis.

Diagnostic Imaging Studies: A preoperative MRI was performed which showed a large

enhancing mass in the right petroclival region consistent with a meningioma. There was

encasement of the carotid artery and displacement of the brainstem. There was extensive

involvement of the cavernous sinus and the sella. The mass measured approximately 4

centimeters (cm) in size. A biopsy and excision was done on the right cavernous sinus, revealing

a World Health Organization (WHO) grade I meningioma. A postoperative MRI was done and

reviewed. This showed a subtotal resection, but not significant debulking of the right petroclival

meningioma. The mass effect on the brainstem was improved.

Family History: The patient’s mother and father are both deceased due to illnesses related to

smoking. She has three brothers who are alive and well.

Social History: The patient is married and resides with her husband. She is a former one pack a

day smoker, but quit in 2007. She rarely drinks alcohol.

Medications: The patient uses the following medications: acetaminophen, benzonatate,

cholecalciferol, citalopram, gluco sulfate NaCl-Chond, Levetiracetam, metoprolol, oxycodone

and psyllium.

Recommendations: The radiation oncologist recommended that the patient receive

postoperative radiotherapy to the area of the tumor with margins for this low-grade meningioma.

The goals of therapy, along with the risks of treatment were discussed with the patient and her

husband.

The Plan (Prescription): The plan is for the patient to receive a total dose of 50.4 Gy in 28

fractions using intensity modulated radiation therapy (IMRT).

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

Aquaplast mask used for immobilization of her head and neck region. A treatment planning

computed tomography (TPCT) was completed with 2.5 millimeter (mm) slices through her head

and upper neck region.

Anatomical Contouring: The TPCT was fused with an MRI scan, on MIM, for the physician to

contour his planning target volume (PTV). The physician contoured the right petroclival mass

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PTV, in addition to the optic chiasm and optic nerves. I contoured the brain, brainstem, eyes,

and lens and created a 1 cm ring around the right petroclival mass PTV, in addition to a normal

tissue volume.

Beam Isocenter/Arrangement: The patient was treated on a Varian 21EX linear accelerator

with 6 MV photon energies. The isocenter was placed in the middle of the right petroclival mass

PTV. I used an IMRT beam arrangement, consisting of five beams. I began on the right side of

the patient and set the first beam with a gantry angle of 200 degrees. I than placed four more

beams at gantry angles of 265, 295, 80 and 125 degrees around the patient.

Treatment Planning: The Varian Eclipse treatment planning system was used for this plan.

The physician provided a list of what he would like to achieve with this plan. His objectives

included at least 95% of the right petroclival mass PTV to receive 50.4 Gy in 28 fractions. He

wanted to keep the optic nerves less than 105% of the prescription dose, and the optic chiasm

less than 53 Gy. The brain and brainstem were to receive no more than 54 Gy. The eyes were to

be kept below 30 Gy and the lens below 7 Gy. I entered the above objectives into the

optimization parameters. I started to run the optimization and after the first trial, the right lens,

right optic nerve and brain were too hot. There were also significant hot spots outside of the

PTV. I entered additional parameters and increased the priority on those structures. In addition,

I increased the priority on the normal tissue volume to try and eliminate the hot spots outside the

PTV. It took a few more trials until I achieved a plan that met the physician’s objectives. The

plan was prescribed to the 99.8% isodose line and approved by the physician. The isodose lines

can be viewed in Figure 1 and Figure 2. Figure 3 shows the dose volume histogram for this plan.

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Figure 1: Axial, Sagittal, and Coronal slices

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Figure 2: Isodose distribution through axial slices

Monitor Unit Check: Independent monitor unit checks are not done at my facility for IMRT

treatment planning. These values are taken from the Mapcheck QA done on the linear

accelerator.

Quality Assurance Check: Mapcheck®, which is a Sun Nuclear diode array, was used in order

to verify the dose distribution of the plan. To calculate the measured output, the plan was run on

a MapCheck phantom on the linear accelerator where the output per field was taken. The fluence

of the IMRT plan is then computed onto a phantom in the Eclipse treatment planning system.

The treatment planning computer MU values are compared to the measured output obtained at

5cm depth from MapCheck. This value was then compared to the expected MU values,

ensuring that the plan is safe for treatment.

Conclusion: I chose this case study because it was the first brain IMRT case I have completed.

In the past, I created plans using volumetric intensity radiation therapy (VMAT) for brain cases.

However, with this patient, both VMAT and IMRT plans were calculated and the IMRT plan

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was superior. The main reason was integral brain dose. The brain dose was kept lower with the

IMRT plan, which the physician preferred. It was a great learning experience for me to be able

to plan this case using both techniques.

Figure 3: Dose Volume Histogram

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