Oropharynx

Key Points

The oropharynx comprises the soft palate, tonsillar (faucial) pillars, tonsillar fossa, base of tongue, and pharyngeal walls.
The majority of oropharyngeal squamous cell carcinomas arise in the tonsil and base of tongue, particularly those that are associated with human papilloma virus (HPV).
The incidence of oropharyngeal carcinoma is rising in North America and Europe due to the increase in HPV-associated carcinoma afflicting mainly younger individuals (40 to 60 years of age) with no or minimal history of tobacco consumption (see Chapter 1).
Radiation alone is often the preferred modality of therapy for early-stage oropharyngeal carcinomas. Ipsilateral radiotherapy is highly successful in controlling tonsillar carcinomas confined to the fossa or with minimal extension to the soft palate.
Combination of radiation with chemotherapy (concurrent or induction) or cetuximab (antibody against epidermal growth factor receptor) is recommended for patients with locally advanced oropharyngeal carcinoma. The tumor volume, the general condition of the patients, and preference determine the specific choices.
Intensity-modulated radiation therapy is commonly used to spare normal tissues, principally to reduce the incidence and severity of xerostomia.
Patients with residual nodal disease after radiation or combined therapy are managed with neck dissection.
Patients with HPV-positive oropharyngeal carcinoma treated with established therapy regimens have very favorable prognoses.

Although the detail of radiation planning and delivery may differ among cancers arising from different anatomical subsites within the oropharynx, the treatment outcomes have been usually reported in aggregate. Therefore, this chapter begins by summarizing the general background outcome data before addressing individual subsites.

Background Data

Table 8.1 Outcomes of 1,042 Patients with Squamous Carcinoma of the Oropharynx Treated with Radiotherapy at the M.D. Anderson Cancer Center 1975 to 1998 (Analysis, 2005)

Primary Site		No. of Patients	5-yr Local Control (%)	5-yr Overall Survival^a (%)
	Soft palate	138	70	44
	Tonsillar fossa	324	76	56
	Base of tongue	383	77	49
	Pharyngeal wall	168	68	39
T stage^b
	T1	123	98	69
	T2	324	84	63
	T3	383	69	41
	T4	168	45	23
	Tx^c	44	95	80
Total		1,042	75	50
^a95% of surviving patients alive >5 yr. ^bFifth edition AJCC staging manual. ^cMost common presentation—tonsillectomy done prior to evaluation.

Table 8.2 First Site of Failure Distribution for Stage I and II Oropharynx Cancer Treated with Radiation at the M.D. Anderson Cancer Center (1970 to 1998)

	First Site of Failure
		*None*	L	R	LR	DM	*L and DM*	*R and DM*	*Total*
T stage	T1 and Tx	45	3	1	1	1	0	0	51
T stage	T2	87	21	5	1	8	1	1	124
Total		132	24	6	2	9	1	1	175
L, local recurrence; R, regional recurrence; LR, loco-regional recurrence; DM, distant metastases; L and DM, synchronous local recurrence and distant metastases; R and DM, synchronous regional recurrence and distant metastases.
Modified from Selek U, Garden AS, Morrison WH, et al. Radiation therapy for early-stage carcinoma of the oropharynx. Int J Radiat Oncol Biol Phys 2004;59:743-775.

Table 8.3 First Site of Failure Distribution for Stage T1, T2, and TX Oropharynx Cancer Treated with IMRT at the U.T.M.D. Anderson Cancer Center 2000 to 2002

	First Site of Failure
		*None*	L	R	LR	DM	*L and DM*	*R and DM*	*Total*
T stage	T1 and Tx	30	0	1	0	2	0	0	33
	T2	13	1	0	1	3	0	0	18
Total		43	1	1	1	5	0	0	51
L, local recurrence; R, regional recurrence; LR, loco-regional recurrence; DM, distant metastases; L and DM, synchronous local recurrence and distant metastases; R and DM, synchronous regional recurrence and distant metastases.
Modified from Garden AS, Morrison WH, Wong P-F, et al. Disease-control rates following intensity-modulated radiation therapy for small primary oropharyngeal carcinoma. Int J Radiat Oncol Biol Phys 2007;67:438-444.

Table 8.4 Survival of Patients with Oropharyngeal Carcinoma Based on Tumor HPV Status

First Author	Patient number	Marker	Overall Survival Rates (Positive vs. Negative)
Ang	223	p16^INK4A	84% vs. 51% (3-yr)
Fahkry	62	HPV	84% vs. 50% (3-yr)
Lassen	74	p16^INK4A	66% vs. 28% (5-yr)
Rischin	185	p16^INK4A	91% vs. 74% (2-yr)
Shi	111	HPV	88% vs. 67% (3-yr)
Data from Ang KK et al. N Engl J Med 2010;363:24-35; Fahkry C, et al. J Natl Cancer Inst Phys 2008;100:261-269; Lassen P, et al. J Clin Oncol 2009;27: 1992-1998; Rischin D, et al. J Clin Oncol 2010;28:4142-4148; Shi W, et al. J Clin Oncol 2009;27:6213-6221.

Table 8.5 Results of Intensity-Modulated Radiation Therapy for Cancer of the Oropharynx

First Author	Year	Patient Number	Median follow-Up (mo)	Disease Control Rate (%)
Feng	2005	94	36	94 (LRC-crude)
De Arruda	2006	50	18	98 (LC, 2-yr)
Yao	2006	66^a	27	99 (LRC, 3-yr)
Studer	2007	105^a	ND	88 (LC, 2-yr)
Garden	2007	51	45	94 (LRC, 2-yr)
Huang	2008	71	29	90 (LRC, 3-yr)
Sanguineti	2008	38	33	94 (LC, 3 -yr)
Eisbruch	2010	69	32	91 (LRC, 2-yr)
Mendenhall	2010	130	42	84 (LRC, 5-yr)
Daly	2010	107^a	29	92 (LRC, 3-yr)
LRC, locoregional control; LC local control; ND, not described
^aIncluded patients treated with definitive and postoperative radiation. Data from Feng M, et al. Radiother Oncol 2005;77:32-38; de Arruda FF, et al. Int J Radiat Oncol Biol Phys 2006;64:363-373; Yao M, et al. Am J Clin Oncol 2006;29:606-612; Studer G, et al. Strahlenther Onkol 2007;183:417-423; Garden AS, et al. Int J Radiat Oncol Biol Phys 2007;67:438-444; Huang K, et al.
Cancer 2008;113:497-507; Sanguineti G, et al. Int J Radiat Oncol Biol Phys 2008;72:737-746; Eisbruch A, et al. Int J Radiat Oncol Biol Phys 2010;76: 1333-1338; Mendenhall WM, et al. Laryngoscope 2010;120:2218-2222; Daly ME, et al. Int J Radiat Oncol Biol Phys 2010;76:1339-1346.

SOFT PALATE

Treatment Strategy

Primary radiotherapy is preferred for T1 to T2 N0 to N1 carcinomas. Superficial T1 lesions without lymphadenopathy may be amenable to local excision only.

Combination of radiation with systemic therapy is the treatment of choice for T3 and selected T4 or N2 to N3 tumors. As presented in Chapter 1, outside the protocol study setting, the three currently available treatment options established by randomized trials are radiation with concurrent cisplatin (either conventional fractionation plus three cycles of cisplatin or accelerated fractionation in 6 weeks plus two cycles of cisplatin), radiation with cetuximab (antibody against epidermal growth factor receptor), and a triple-agent induction chemotherapy regimen, referred to as TPF (docetaxel, cisplatin, and fluorouracil), followed by radiotherapy ± carboplatin. Radiation with concurrent high-dose cisplatin (100 mg/m², given every 3 weeks) has the longest track record and the strongest evidence-based results.

There is now a consensus that patients presenting with N2 to N3 nodal disease achieving a complete clinical and radiographic response do not require a planned neck dissection. The value of PET-CT scan obtained 10 to 12 weeks after the completion of therapy in determining the need for planned neck dissection for those with small, indeterminate residual nodal mass on CT scan is being investigated.

T4a tumors with bone invasion or extensive normal tissue destruction resulting in deformation and/or impaired functions are best treated with surgery and postoperative radiotherapy and, in the presence of extracapsular extension or positive margin, combined with concurrent cisplatin.

Primary Radiotherapy

Target Volume

The initial target volume is primary tumor with at least 2-cm margins and bilateral neck nodes, including the retropharyngeal and level II, III, and IV nodes. The target volume also includes ipsilateral level IB in the presence of level II node(s). For lateralized tumors, the target volume includes the ipsilateral tonsillar pillars, parapharyngeal space, and lateral aspect of the pterygoid muscle.

The boost volume encompasses the primary tumor and involved node(s) with 1- to 2-cm margins.

Setup and Field Arrangement for Conventional Radiotherapy Technique

Insertion of metal seeds at the borders of the tumor, when feasible, and marking of oral commissures and palpable nodes facilitate portal shaping. The patient is immobilized in a supine position with thermoplastic mask. An extended head and shoulder mask is used for conformal radiotherapy. With conventional technique, lateral parallel-opposed photon fields are used to treat the primary tumor and upper neck nodes (see Case Study 8-1).

Anterior border: at least 2 cm anterior to the tumor.
Superior border: at least 1.5 cm above the soft palate. If the primary tumor spreads into the tonsillar fossa, this border
is extended superiorly to encompass the medial pterygoid muscle to the pterygoid plate.
Posterior border: behind the mastoid tip when N0, behind the spinous processes when N+, or more posteriorly in the presence of large nodal mass.
Inferior border: just above the arytenoids except when the extent of nodal disease requires a lower inferior border.

Case Study 8-1

A 55-year-old man sought medical attention for a 6-month history of sore throat. Physical examination revealed a 3.5-cm exophytic tumor of the uvula and soft palate with minimal extension to the right anterior tonsillar pillar. The hard palate was not involved. There were no palpable neck nodes. Biopsy showed a moderately differentiated squamous cell carcinoma (SCC). Stage: T2 N0 M0. This patient was treated with primary radiotherapy according to the concomitant boost regimen. The fields were designed to encompass the primary tumor and upper neck nodes (Fig. 8.1). The boost volume covered the primary tumor with generous margins. The seed indicated the superior and anterior border of the tumor on the palate. The mid and lower neck nodes were treated through a matching anterior photon field with a midline block to shield the larynx. The dose to the primary tumor was 70.5 Gy in 41 fractions over 6 weeks. Areas of subclinical disease in the upper neck received 54 Gy in 30 fractions over 6 weeks. The mid and lower neck received 50 Gy in 25 fractions over 5 weeks. He had no evidence of disease 5 years after therapy. However, there was a slight retraction of the soft palate without functional repercussion.

Figure 8.1

A matching anterior appositional photon field is used to treat the mid and lower neck nodes when indicated. For the boost volume:

Lateral fields are reduced to cover the primary tumor with 1- to 2-cm margins (see Case Study 8-1). For selected T1 and small, superficial T2 tumors, it may be preferable to administer the boost dose with an intraoral cone when feasible (i.e., the lesion is accessible and the patient can tolerate an intraoral cone without gagging) to reduce treatment morbidity by limiting the dose to the mandible and soft tissues (see Case Study 8-2). In such cases, it is desirable to administer the boost dose first while the tumor is clearly visible and palpable. The introduction of intensity-modulated radiation therapy (IMRT), which can focus the boost dose to a small, well-defined volume, has reduced the need for intraoral cone irradiation.
Nodal metastases in the upper neck are encompassed in the lateral portals. Nodes in the mid or lower neck can receive boost dose with an appositional glancing photon field or electron portal.

Dose

For patients with T1 N0 and superficial T2 N0 tumors: conventional fractionation delivering 50 Gy in 25 fractions to the initial target volume followed by a boost dose of 16 Gy in 8 fractions by external beam or 15 Gy in 5 to 6 fractions given by intraoral cone.

For patients with larger T2 N0 to N1 tumors or T3 to T4 tumors who do not receive systemic treatment: concomitant boost schedule to total doses of 72 Gy in 42 fractions. The initial volume receives 1.8-Gy fractions to 54 Gy in 6 weeks. The boost volume receives an additional 1.5 Gy to a dose of 18 Gy given as second daily fractions during the last 2.5 weeks of the wide-field irradiations. The spinal cord dose is limited to 45 Gy or less.

For patients with T3 to T4 or N2 to N3 tumors who receive systemic therapy: options are (1) conventional fractionation (70 Gy in 35 fractions over 7 weeks) with three cycles of concurrent cisplatin or after TPF induction chemotherapy (± carboplatin), or (2) accelerated fractionation in 6 weeks,
either by concomitant boost regimen (72 Gy in 42 fractions as described above) or in 2-Gy fractions, 6 fractions per week (1 day a week of twice-a-day irradiation), when combined with two cycles of cisplatin or weekly cetuximab.

Case Study 8-2

A 38-year-old man sought medical attention because of a slight irritation behind the left jaw and blood-streaked saliva.

Physical examination revealed a 2.5-cm tumor at the junction of the soft palate and anterior faucial pillar on the left side (Fig. 8.2A). There was no palpable lymphadenopathy. Further examination was unremarkable. Biopsy of this lesion showed poorly differentiated carcinoma. Stage T2 N0 M0. He received treatment with an intraoral cone followed by external beam irradiation. A customized device was made to ensure reproducible cone positioning (Fig. 8.2B,C). A 3-cm cone was used to deliver irradiations with 125 KVp x-rays to a dose of 15 Gy in five fractions (Fig. 8.2D). The remaining therapy was given through an ipsilateral external beam portal. A combination of electrons and photons was used to administer 50 Gy in 25 fractions over 5 weeks. This patient was alive and well 6 years after completion of therapy.

Figure 8.2A-D

Intensity-Modulated Radiation Therapy

IMRT has now been widely adopted for the treatment of patients with oropharyngeal carcinomas because of its potential for exclusion of a large portion of at least one of the parotid glands from the high-dose volume, thereby reducing xerostomia without compromising the coverage of the primary tumor and draining lymphatics. The patient is immobilized in a supine position with an extended head and shoulder thermoplastic mask. Thin-cut CT scans are obtained in treatment position. The gross target volume (GTV), CTVs, and planning target volumes (PTVs) are outlined for dosimetric planning (see Case Study 8-3).

Gross Target Volume

GTV represents all areas determined from clinical examination and imaging studies to contain gross disease. It is very important to integrate the physical examination findings in treatment planning as CT scan may not detect superficial mucosal tumor extension.

Case Study 8-3

A 79-year-old woman presented with nasal voice, mild bilateral otalgia, and a globus sensation. Physical examination revealed a 2.5-cm exophytic lesion on the posterior aspect of the softpalate. A biopsy revealed moderately differentiated SCC. Staging workup included a CT scan of the head and neck, which showed a thickened soft palate and a 1.5 cm left level II node. She was treated with IMRT delivered in 30 fractions.

CTV_HD (66 Gy) encompassed the soft palate and left upper jugular involved node with margin. The remainder of left level II not included in CTV_HD and left level IB nodes were defined as CTV_ID. The retropharyngeal nodes and right level II nodal bed were delineated as CTV_ED (54 Gy).

Figure 8.3A-D show CTV_HD (red), CTV_ID (blue), and CTV_ED (yellow) on representative axial cuts from the level of the retropharyngeal nodes and soft palate superiorly and to the hyoid inferiorly. Figure 8.3E,F: show the isodose distributions on two axial images through the palate.

Figure 8.3A-D

The isocenter was placed above the thyroid notch, and the low neck was treated with a matching anterior beam. A larynx block was used for the first 40 Gy (Fig. 8.2G), and then a full midline block was added for 10 Gy. The left mid neck (level III) was boosted to 60 Gy with glancing photon fields. The patient remained well without disease 5 years later.

Figure 8.3E-G

Clinical Target Volumes

Three CTVs are generally delineated.

CTV_HD delineates volumes to receive the highest dose, which includes the primary and nodal GTVs with 0.5- to 1-cm margins. Margins should be more generous if the tumor borders are less well defined.
CTV_ID delineates volumes to receive an intermediate dose, which includes the remaining soft palate and the adjacent parapharyngeal space. CTV_ID covers the superior aspect of the tonsillar pillars for lateral tumors and, in the presence of positive node(s), the adjoining nodal compartment(s).
CTV_ED delineates volumes to receive an elective dose for potential subclinical disease. In the N0 neck, CTV_ED includes nodal levels II to IV and retropharyngeal nodes. When level II node is involved, CTV_ED also includes clinically uninvolved ipsilateral level IB nodes.

Dose

For patients with T1 N0 and superficial T2 N0 tumors: 66 Gy to CTV_HD, 60 Gy to CTV_ID, and 54 Gy to CTV_ED, given in 30 fractions over 6 weeks.

For patients with larger tumors who do not receive systemic therapy: options are (1) 70 Gy to CTV_HD, 63 Gy to CTV_ID, and 56 Gy to CTV_ED given in 35 fractions over 6 weeks (1 day a week of twice-a-day irradiation), (2) 70 Gy to CTV_HD, 60 Gy to CTV_ID, and 57 Gy to CTV_ED given in 33 fractions over 6.5 weeks, or (3) a concomitant type regimen, which requires two IMRT plans (see IMRT Section of Chapter 1).

For patients with T3 to T4 or N2 to N3 tumors who receive systemic therapy: options are (1) 70 Gy to CTV_HD, 60 Gy to CTV_ID, and 57 Gy to CTV_ED given in 35 fractions over 7 weeks combined with three cycles of concurrent cisplatin or after TPF induction chemotherapy (± carboplatin), (2) 70 Gy to CTV_HD, 63 Gy to CTV_ID, and 56 Gy to CTV_ED given in 35 fractions over 6 weeks (1 day a week of twice-a-day irradiation) when combined with two cycles of cisplatin or weekly cetuximab, or (3) 70 Gy to CTV_HD, 60 Gy to CTV_ID, and 57 Gy to CTV_ED given in 33 fractions over 6.5 weeks combined with high-dose cisplatin.

Postoperative Radiotherapy

Adjuvant radiotherapy is indicated in occasional patients treated with upfront surgery. The principles are similar to those for the treatment of retromolar trigone or posterior oral cavity tumors as presented in detail, including illustrative cases, in Chapter 6.

Target Volume

The initial target volume encompasses the entire surgical bed and all nodal areas of the neck. The boost volume encompasses areas of known disease location with 1- to 2-cm margins.

Setup and Field Arrangement

The general technique is the same as that described under Primary Radiotherapy.” Marking of the external surgical scar facilitates portal design. The anterior and superior field borders or CTVs are mainly determined by the local spread of the primary tumor and the extent of surgery (scar/flap). It is prudent to include 1- to 2-cm margins beyond the mucosal scar.

Background Data

Table 8.6 Local Control of Soft Palate Tumors by T Stage

Stage	No. of Patients	5 yr (%)
T1	53	90-92
T2	111	67-90
T3	93	58-67
T4	34	37-57
Adapted from Keus RB, et al. Radiother Oncol 1988;11:311-317; and Chera BS, et al. Head Neck 2008;30:1114-1119.

Table 8.7 Therapy Modality and Outcome by T Stage

	Stage
	Tx	T1	T2	T3	T4	*Total*
Primary Treatment	No. of Patients (No. Controlled)
Surgery	2 (2)	9 (9)	12 (11)	4 (4)	1 (0)	28 (26)
Radiation	4 (3)	24 (21)	79 (60)	30 (23)	13 (4)	150 (111)
Surgery + radiation	—	1 (1)	1 (0)	5 (3)	3 (2)	10 (6)
Total	6 (5)	34 (31)	92 (71)	39 (30)	17 (6)	183 (143)
Modified from Weber RS, Peters LJ, Wolf P, et al. Squamous cell carcinoma of the soft palate, uvula, and anterior faucial pillar. Otolaryngol Head Neck Surg 1988;99(1):16-23.

Dose

A dose of 60 Gy in 30 fractions to areas with high-risk features; that is, close or microscopically positive margins, perineural extension, vascular invasion, positive nodes, or extranodal extension. An additional boost dose of 6 Gy may be given when indicated, such as when multiple adverse features are present or when the interval between surgery and radiation is much longer than 6 weeks.
A dose of 56 Gy in 28 fractions to the surgical bed.
A dose of 50 Gy in 25 fractions to undissected regions to receive elective irradiation.

Timing of Postoperative Radiotherapy

It is desirable to commence postoperative radiotherapy as soon as possible after healing of surgical wounds. With good communication between surgical, radiation, and dental oncologists, simulation can usually take place 3 to 4 weeks after surgery, and radiotherapy can start within a week in most patients. When delayed wound healing postpones commencement of postoperative radiation to beyond 5 to 6 weeks, we administer accelerated fractionation, such as concomitant boost, by delivering twice-a-day irradiations for 5 treatment days, either once a week or daily toward the end of the radiation course, to reduce the potential hazard of prolonged cumulative treatment time.

TONSILLAR FOSSA

Treatment Strategy

Primary radiotherapy is preferred for T1 to T2 N0 to N1 carcinomas. Combination of radiation with systemic therapy is the treatment of choice for T3 and selected T4 or N2 to N3 tumors. As presented in Chapter 1, outside the protocol study setting, the three currently available treatment options established by randomized trials are radiation with concurrent cisplatin (either conventional fractionation plus three cycles of cisplatin or accelerated fractionation in 6 weeks plus two cycles of cisplatin), radiation with cetuximab (antibody against epidermal growth factor receptor), and a triple-agent induction chemotherapy regimen, referred to as TPF (docetaxel, cisplatin, and fluorouracil), followed by radiotherapy ± carboplatin. Radiation with concurrent high-dose cisplatin (100 mg/m², given every 3 weeks) has the longest track record and the strongest evidence-based results.

T4a tumors with bone invasion, laryngeal dysfunction, or severe trismus, for example, are best treated with surgery followed by adjuvant radiotherapy and, in the presence of extracapsular extension or positive margin, combined with concurrent cisplatin.

Case Study 8-4

A 47-year-old woman presented with a swollen right tonsil and, after some delay, underwent tonsillectomy. Histologic examination revealed invasive poorly differentiated SCC with lymphatic and perineural invasion. The final margins after additional resection were free. On presentation to our center, she had postsurgical changes without evidence of residual disease and was, therefore, staged as having a Tx (pT1) N0 tonsil carcinoma. We elected to treat this patient ipsilaterally with a wedged-pair technique, using “field-in-field” compensation (see Chapter 3). The total dose was 66 Gy in 33 fractions.

Figure 8.4 shows that the initial volume encompassed the tonsillar bed and upper neck, and was reduced after 50 Gy. This target (red) included the pterygoid muscle, parapharyngeal space, the lateral base of tongue, the lateral soft palate, and the ipsilateral retropharyngeal nodes. The boost volume encompassed the tonsillar bed only (green). An axial isodose distribution through the superior tonsillar region is shown. The initial wedged-pair fields were matched above the arytenoids to an anterior field that covered ipsilateral levels III and IV nodes to 50 Gy. She had no evidence of disease and had no sequelae 2 years after therapy.

Figure 8.4

Primary Radiotherapy

Target Volume

For the initial target volume:

T1 and T2 (with limited extension to the soft palate, and no base of tongue involvement), N0 to N1 tumors: primary lesion with 2-cm margins and ipsilateral retropharyngeal and level II to IV nodes (Case Study 8-4). The target volume also includes ipsilateral level IB in the presence of level II node(s).
T2 (with base of tongue or significant soft palate involvement), T3 and selected T4 or N2 to N3 tumors: tonsillar fossa, faucial pillars, soft palate, base of tongue, medial pterygoid muscle, and bilateral neck nodes (parapharyngeal-retropharyngeal, level II to IV, and ipsilateral level IB).

For the boost volume: primary tumor and involved node(s) with 1- to 2-cm margins.

Conventional Radiation Planning for Ipsilateral Treatment (for T1 to T2 N0 to N1 Tumors)

Insertion of metal seeds at the borders of the tumor, when feasible, and marking of oral commissures facilitate portal shaping. The patient is immobilized in a supine position
with thermoplastic mask for irradiation of the primary tumor and upper neck nodes with wedge-pair photon portals or IMRT.

Field borders for the initial target volume:

Anterior border: at least 2 cm anterior to the tumor.
Superior border: encompasses the insertion of the medial pterygoid muscle at the pterygoid plate.
Posterior border: 2 cm behind the mastoid tip and behind the edge of the sternocleidomastoid muscle.
Inferior border: just above the arytenoids.

A matching anterior photon portal is used to irradiate the mid and lower neck nodes.

For the boost volume, the field is reduced to cover initial gross disease with 1- to 2-cm margins (see Case Study 8-4).

Case Study 8-5

A 40-year-old woman presented after an excisional biopsy of an asymptomatic left neck mass. Histologic examination revealed SCC in a 2.3-cm lymph node. Staging workup did not reveal any residual nodal disease, but the left tonsil was firm. A biopsy of the tonsil done during examination under anesthesia revealed SCC. Stage was T1Nx (pN1). It was elected to treat her with ipsilateral IMRT.

Figure 8.5 shows axial isodose distributions through the superior tonsillar fossa and upper neck. The tonsillar region (red) received 66 Gy (Fig. 8.5A) and an additional rim of surrounding tissues (green) along with ipsilateral levels IB and II nodes received 60 Gy. The involved nodal bed defined from the prebiopsy imaging (blue) was prescribed a minimum dose of 63 Gy (Fig. 8.5B). The excision scar was wired for planning, and a 2-mm bolus was applied over the scar. The leftlow neck was treated with an appositional anterior field to 50 Gy, matched with an isocentric technique to the IMRT fields. She had no evidence of disease and had no sequelae 2 years after therapy.

Figure 8.5A,B

Intensity-Modulated Radiation Therapy Planning for Ipsilateral Treatment (for T1 to T2, N0 to N1 Tumors)

Clinical Target Volume

Three CTVs are generally delineated (see Case Studies 8-5 and 8-6).

CTV_HD delineates volumes to receive the highest dose, which includes the primary and nodal GTVs with 0.5- to 1-cm margins. The entire tonsillar fossa is generally encompassed from the maxillary tuberosity (superior) to the hyoid (inferior). An additional 1 cm is added if the GTV is at the edges of or beyond these cranial and caudal landmarks. CTV_HD also encompasses the glossopharyngeal sulcus and 1 cm of the ipsilateral base of tongue. Laterally, CTV_HD
covers the parapharyngeal space and 1 cm of the pterygoid muscle. Many patients present after tonsillectomy for small-volume tonsillar disease. In this situation, the medial pterygoid muscle should have 1 to 2 cm of coverage.
CTV_ID delineates volumes to receive an intermediate dose, which includes an additional 1-cm margin of coverage beyond the CTV_HD toward the pterygoid musculature laterally, and superiorly, the retromolar trigone, soft palate, and base of tongue. In the presence of positive node(s), CTV_ID encompasses the adjoining nodal compartment(s).
CTV_ED delineates volumes to receive an elective dose for subclinical disease. It is prudent to cover the medial pterygoid musculature to the pterygoid plates. In the N0 neck, CTV_ED includes nodal levels II to IV and retropharyngeal nodes. When level II node is involved, CTV_ED also includes clinically uninvolved ipsilateral level IB nodes.

Case Study 8-6

A 43-year-old man presented with a right upper neck mass. Excisional biopsy revealed SCC without obvious extracapsular extension. Postexcision CT scan did not reveal obvious disease. He underwent an examination under anesthesia and a right tonsillectomy. The right tonsil was found to contain SCC. Stage T1 Nx (1) M0. As the primary disease was conf ined to the tonsil, it was elected to prescribe ipsilateral IMRT.

CTV_HD (66 Gy) encompassed the tonsillar and nodal excision beds, CTV_ID (60 Gy) covered the remainder of level II and level IB nodes, and CTV_ED (54 Gy) delineated the ipsilateral retropharyngeal nodes, superior parapharyngeal space, and the medial pterygoid muscle up to the pterygoid plate.

Figure 8.6A-D

Figure 8.6 shows CTV_HD (aqua), CTV_ID (khaki), and CTV_ED (maroon) along with the isodose distributions on representative axial images at the level of the high retropharyngeal nodes (Fig. 8.6A), mid-tonsillar fossa (Fig. 8.6B

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