1

Charles Poole

February Case Study

February 29, 2012

Intensity Modulated Radiotherapy of Recurrent Squamous Cell Carcinoma of the Oral

Cavity - Tongue

History of Present Illness: Patient JB is a 29 year old female who was diagnosed with

moderately differentiated squamous cell carcinoma of the oral cavity involving the left ventral

tongue in December 2010. Earlier in the summer of 2010, the patient observed a lesion on the

left front side of the tongue which was thought to be a canker sore and at the time assumed it

would heal. In September 2010, the lesion had not healed and had become an annoyance when

the patient consumed spicy or acidic foods or beverages. In October, the patient began applying

over-the-counter Anbesol® on the lesion to help with the mild discomfort. The patient became

increasingly concerned when the Anbesol® was not helping and subsequently went to a dentist.

The dentist referred JB to an oral surgeon for consultation and possible treatment of the lesion. In

late December 2010, a biopsy was done on the ventral part of the left tongue. The results of this

biopsy were determined to be moderately differentiated squamous cell carcinoma staged at T2,

N2c, M0. The lesion measured 1.2 cm x 1.5 cm on the left tongue. The lesion did not extend to

the base of tongue and it was primarily on the left lateral anterior part of the patients tongue. The

patient was referred to the head and neck surgery department at a regional hospital for further

evaluation, consultation, and treatment. In late December 2010, further staging with a positron

emission tomography (PET) scan and a computed tomography (CT) scan revealed evidence of

bi-lateral lymphadenopathy. The PET scan revealed lymph node involvement in the left

jugulodigastric and submandibular lymph node regions, as well as, left level II lymph node

region and the right low level IV lymph node region. In January 2011, the patient underwent

several procedures including a direct laryngoscopy, a hemiglossectomy, left modified neck

dissection, right modified neck dissection, left radial forearm free flap procedure for

reconstruction from head and neck surgery. It was determined that the nineteen lymph nodes

sampled on the right were negative and only one of twenty three lymph nodes sampled on the

left were positive. Also, all the surgical margins were negative. The patient was pathologically

stage as pT1, pN1. With this information, no further treatment was recommended. In the months

2

following the surgery JB recovered and was doing well until August of 2011 when a palpable

cervical lymph node was noticed at a follow up visit. JB subsequently, had another round of PET

and CT scans which revealed a slight increase in the size of several left neck lymph nodes and

negative right neck lymph nodes. In addition, the scans revealed residual increased

hypermetabolic activity in the previous left pharyngeal lymph nodes space. It was determined

that a second left modified radical neck dissection was to be performed. The results of that

dissection were that five left sided external jugular lymph nodes were negative and fifteen left

posterior neck lymph nodes were negative also. JB recovered well from the second neck

dissection until January of 2012 when the patient complained of left upper neck swelling.

On January 25, 2012, JB underwent a CT of the neck with contrast with revealed a necrotic

enhancing mass in the left cervical lymph node level II region. There were multiple other

necrotic appearing lymph nodes surrounding the mass posteriorly and inferiorly. The left parotid

gland demonstrated evidence of non-necrotic enhancing lymph nodes also. The main necrotic

mass was noted to be surrounding the common carotid artery and internal carotid arteries. On

January 27, 2012, JB had a PET / CT scan done which revealed an enlarged enhancing left neck

mass with a necrotic center which measured 4.5 cm x 7.1 cm x 6.3 cm. In addition, there was

enhancement in the left level IV lymph node region and also increase enhancement in the right

true vocal cord. There was suspicion of right true vocal cord paralysis. It was determined in the

following weeks through a nasolaryngoscopic examination that there was true vocal cord

paralysis on the left due to tumor involvement of the left vagus nerve. At this point, JB was

advised that the best course of treatment for this disease recurrence would be concurrent

chemoradiation therapy. In early February 2012, the patient was referred to radiation oncology

for a consultation of the patient’s history, symptoms, operative procedures, pathology reports,

and imaging studies. The radiation oncologist discussed the future course of treatment with JB

and due to the vocal cord involvement and the left vagus nerve involvement further surgery was

ruled out. The radiation oncologist discussed the chemoradiation treatment regimen and

informed the patient of short and long term side effects of this treatment. JB elected to proceed

with the recommendations made by the radiation oncologist.

Past Medical History: The patient has had a past medical history of cholelithiasis and

underwent surgery for cholecystectomy in May of 2010. The patient denied any other major

3

illnesses, injuries, or hospitalizations. JB reported no other chronic health problems. The patient

also reported no allergies or reactions to medications, food, or latex.

Social History: JB is employed in the small business sales division of Yahoo! Incorporated. JB

is not married and does not have children. The patient states she has never used tobacco and

drinks alcohol socially, only on occasion. JB reported that her mother has had a history of

cervical cancer that was treated 10 years ago and more recently is undergoing treatment for

peritoneal cancer. JB also reported a history of diabetes and heart disease in a maternal

grandfather and a paternal grandmother with a history of breast cancer.

Medications: JB uses the following medications: Lortab. Hydrocodone, extra strength Tylenol,

Aleve, and aspirin.

Diagnostic Imaging: On January 25, 2012, JB underwent a soft tissue neck CT with contrast

which revealed a massive necrotic rim enhancing mass located in the left neck at the level II to

III region with extension into the level V region. The superior to inferior extent of the main

necrotic mass measures approximately 5.5 cm. There are multiple necrotic appearing lymph

nodes surrounding the mass posteriorly and inferiorly. Also, there are other enlarged non-

necrotic enhancing lymph nodes surrounding the mass with involvement of the left parotid gland.

The mass abuts the left common carotid and internal carotid arteries. Additional findings

reported were adenopathy of one or two lymph nodes in the left supraclavicular region and a

right level III lymph node that is slightly enlarged measuring 1.4 cm in length. The patients left

tongue surgical region demonstrated normal post surgical changes with no abnormal soft tissue

thickening or enhancement in the region. On January 27, 2012, JB underwent a PET / CT scan of

the head and neck region which demonstrated high PET avidity in the aforementioned left neck

mass which was highly suspicious for malignancy. Other findings included increased activity in

a right level III lymph node and a new level IV lymph node measuring 1.1 cm in the left neck

that was suspicious for malignancy. Also, increased activity was reported in the right laryngeal

region which is suspicious for a second primary cancer or metastasis. There was no abnormal

increased activity in the tongue.

Recommendations: After review of the patients surgical history, pathological reports, and the

most recent imaging studies the patients current diagnosis is moderately differentiated squamous

cell carcinoma of the left oral tongue, post surgical resection, with pathologic staging of pT1,

4

pN1. After consultations with a medical oncologist, a radiation oncologist, and a multi-

disciplinary tumor board, it was recommended to JB that concurrent chemoradiation therapy

would be the best course of treatment for this disease recurrence in the left cervical neck. The

radiation oncologist recommended using Intensity Modulated Radiation Therapy (IMRT) for

treatment due to better homogeneous dose distribution and normal tissue sparring. The

dosimetric advantage of IMRT in the treatment of head and neck cancers is a significant

reduction of late salivary toxicity without adversely impacting tumor control and disease free

survival.1 Decreased salivary function or xerostomia is one of the most frequent and debilitating

long term side effects for radiation therapy of head and neck cancer.2 IMRT offers a dosimetric

advantage to prevent xerostomia.2

The Plan (prescription): The radiation oncologist’s plan after consultation with the medical

oncologist was to deliver concurrent chemoradiation therapy to the bi-lateral cervical neck area

focusing primarily on the left cervical neck recurrence, as well as, treating the bi-lateral

supraclavicular region involving the larynx. This treatment will take advantage of the dose

painting technique with IMRT. The treatment plan utilized one prescription of 70Gy at 2Gy per

fraction prescribed to the left neck (GTV) recurrent volume. By using an IMRT dose painting

technique, dose was prescribed to various volumes the radiation oncologist contoured bi-laterally

throughout the patient’s cervical neck based on pathologic findings and the most recent imaging

studies. These volumes were GTV, CTV 66, CTV 60, and CTV 54. The dose prescribed to these

contoured volumes was delivered over 35 fractions. The radiation therapy was delivered with

concurrent chemotherapy using cisplatin. The chemotherapy portion of this treatment regimen

was administered and managed under the direction of a medical oncologist.

Patient Setup / Immobilization: JB was CT simulated in the supine position with a large S-type

Aquaplast IMRT mask on an S-type board. A regular bite block was inserted into the patient’s

mouth for immobilization (Figure 1). The patient’s head was supported with an A-type headrest

and there was a sponge under the patient’s knees for support. The patient held onto a blue ring

with both hands placed on the patient’s abdomen (Figure 2).

Anatomical Contouring: The patient had a diagnostic CT scan with contrast performed on

January 25, 2012 (Figure 3) and a PET / CT scan performed on January 27, 2012 (Figure 4).

Both of these scans were fused with a CT simulation scan for radiation therapy treatment

5

planning by the medical dosimetrist. The radiation oncologist requested these datasets be fused

with the CT simulation dataset to assist in contouring the recurrent mass in the left cervical neck,

as well as, to identify the left and right cervical neck lymph nodes suspected for malignancy. A

contour of GTV was outlined from the PET scan which demonstrated a large mass with a

necrotic center. The positive glucose uptake in this left neck mass and the associated lymph

nodes in the left and right cervical neck suspected for malignancy were contoured. Additional

target volumes in the bi-lateral cervical neck and supraclavicular region were contoured by the

radiation oncologist and were labeled CTV 66, CTV 60 and CTV 54. All target volumes were

expanded by 0.3 cm and labeled as PTV’s accordingly. Each of these target volume expansions

were reviewed and edited by the physician to limit overlap with anatomical boundaries of the

right parotid gland, mandible, and oral cavity. Each expansion was also adjusted 0.4 cm inside

the skin surface to prevent excessive dose on the patient’s skin surface (Figure 5). The medical

dosimetrist contoured the organs at risk (OR) such as the spinal cord, right parotid, left parotid,

mandible, brain stem, oral cavity, and the esophagus. These OR’s were reviewed and adjusted by

the radiation oncologist and the medical dosimetrist was given a prescription objective sheet to

begin treatment planning.

Beam Isocenter / Arrangement: A single isocenter (Figure 6) was placed in the central portion

of all the treatment volumes midline and anterior to the spine by the medical dosimetrist for

IMRT planning (Figure 7-9). The IMRT plan utilized nine coplanar photon fields arranged

perpendicular to the patient with a gantry angle of 40° separating each field rotating clockwise

around the patient. The first field started at gantry angle 200° and the last field ended at gantry

angle 160°. There were no collimator or couch rotations for any of the nine fields and each field

had an energy of 6 MV. A low energy was used because the target volumes were near the surface

of the patient’s skin in the cervical neck region. The medical dosimetrist assigned the

prescription to the fields and put the IMRT objectives into the IMRT module of the radiation

treatment planning system (TPS). Once the treatment objectives were placed into the IMRT

module of the TPS, the computer determined the appropriate field sizes of each field to

accomplish the desired dose distributions around the target volumes.

Treatment Planning: The radiation oncologist outlined dose objectives to the target volumes

and OR dose constraints for this plan. The objective was to utilize the dose painting technique of

IMRT to escalate dose in certain target areas within a large irradiated volume while limiting dose

6

to other areas within that same volume (Figures 10-15). For each target volume, a uniform,

minimum, and maximum dose objective corresponding with the prescribed dose to each volume

was used in the IMRT module of the TPS corresponding to each prescription dose. In addition,

the OR dose constraints were put into the IMRT module of the TPS for plan optimization. The

initial OR objectives of the plan were: the right parotid mean dose was to be less than 23Gy, the

oral cavity maximum dose less than 55Gy, the esophagus maximum dose less than 50Gy, the

mandible maximum dose less than 72Gy, the brain stem maximum dose less than 50Gy, and the

spinal cord maximum dose less than 44Gy. The larynx dose and the left parotid maximum doses

were unachievable since these OR’s were overlapping with the target volumes. A normal tissue

objective was used to control peripheral dose outside of all the target volumes. The TPS used the

direct machine parameter optimization (DMPO) optimization feature with 117 segments to

accomplish the IMRT objectives and parameters. Once adequate prescription dose to each of the

target volumes was achieved, the medical dosimetrist reviewed the OR doses, the composite

isodose lines, and the Dose Volume Histogram (DVH). The radiation oncologist also reviewed

this plan (Figure 16-17) and assigned a normalization of 98% for the treatment plan. The monitor

units were reviewed and second checked with a QA computer program and were within

tolerance.

Conclusion: This plan presented the medical dosimetrist with some challenges utilizing a dose

painting technique. One challenge was to maintain adequate prescription coverage to each target

volume while limiting the dose to the OR’s. Since the left parotid gland was in the target volume,

the importance of sparing the right parotid gland was paramount. With IMRT, sparing the parotid

gland is achievable when the PTV overlapping the whole parotid gland is less than 20% of the

parotid gland volume.3

A good predictor of mean parotid dose is the percentage of overlap in the

whole parotid gland with any PTV.3 With more overlap, parotid gland sparing may be achieved

but, PTV dose coverage could be inadequate.3 Another challenge this plan presented was

controlling the dose escalation within the different target volumes. The CTV 66 volume

maximum dose had very tight constraints on it due to the adjacent volume of GTV receiving

approximately 6 percent higher dose. Maintaining dose limits to critical structures was difficult

and was not actually achieved in the case of the esophagus, mandible, and larynx. The dose

limits to the OR’s were difficult to achieve because these volumes were overlapping into the

target volumes being irradiated. The radiation oncologist reviewed these OR’s and determined

7

that the maximum doses to each OR was acceptable and coverage to the tumor volumes was a

priority. The primary objective of this plan was to treat the recurrence of this disease considering

how aggressive this disease has been.

Figure 1: CT simulation position with S-type Aquaplast IMRT mask and a bite block.

Figure 2: CT simulation with patient in supine position.

8

Figure 3: CT scan with contrast of the left cervical neck from January 25, 2012.

Figure 4: A PET / CT scan on January 27, 2012 showing an enhancing left neck mass.

9

Figure 5: Expanded target volumes adjusted inside the skin surface.

10

Figure 6: Isocenter Placement.

11

Figure 7: Isocenter placement in the axial view.

12

Figure 8: Isocenter placement in the sagittal view.

13

Figure 9: Isocenter placement in the coronal view.

14

Figure 10: IMRT dose painting technique for multiple target volumes.

15

Figure 11: IMRT dose painting technique for multiple target volumes.

16

Figure 12: IMRT dose painting technique for multiple target volumes.

17

Figure 13: IMRT dose painting technique for multiple target volumes.

18

Figure 14: IMRT dose painting technique for multiple target volumes.

19

Figure 15: IMRT dose painting technique for multiple target volumes.

20

Figure 16: Dose Volume Histogram (DVH).

21

Figure 17: Dose Volume Histogram (DVH).

22

References

1. Chao K, Ozyigit G, Tran B, Cengiz M, Dempsey J, Low D. Patterns of failure in patients

receiving definitive and postoperative IMRT for head-and-neck cancer. Int J Radiat Oncol Biol

Phys. 2003;55(2):312-321.

2. Graff P, Lapeyre M, Peiffert D, et al. Impact of intensity-modulated radiotherapy on health-

related quality of life for head and neck cancer patients: matched-pair comparison with

conventional radiotherapy. Int J Radiat Oncol Biol Phys. 2007;67(5):1309-1317.

3. Hunt M, Jackson A, Narayana A, Lee N. Geometric factors influencing dosimetric sparing of

the parotid glands using IMRT. Int J Radiat Oncol Biol Phys. 2006;66(1):296-304.