Postoperative Intensity-Modulated Radiation Therapy for Head and Neck Cancers: A Case-Based Review

Abstract

Postoperative radiation therapy targets of the head and neck region are often adjacent to nearby critical and avoidance structures. Therefore, intensity-modulated radiation therapy (IMRT) is preferred over previous techniques primarily due to (1) the ability to conform the high-dose regions around geometrically complex targets, (2) the ability to build steep dose gradients between targets and nearby critical structures, and (3) the ability to generate relative sparing of various surrounding nontarget normal structures from clinically significant doses without compromise of desired target coverage. Compared to clinical target volume delineation of intact regions (i.e., unoperated or unviolated neck), postoperative clinical target volumes are generally broader, in that they cross adjacent disturbed anatomic boundaries, are inclusive of surgical tracts and suture lines, and come nearer to the patient surface. Here we provide an expanded case-based illustration of our current approach to postoperative IMRT target volume delineation and treatment planning for various disease sites within the head and neck.

Case Examples

1.1 Case 1 (Fig. 10.1)

Fig. 10.1

A 63-year-old former smoker presented with a 3.5 cm painful mass of the left lateral border of the oral tongue (photograph). Biopsy of this mass showed moderately differentiated, invasive squamous carcinoma. Contrast-enhanced diagnostic CT of the neck (with puffed-cheek technique) demonstrated the primary mass (outlined in green) and revealed a radiographically positive lymph node in left level IIa due to peripheral enhancement and central hypodensity (arrow). There were no metastases on chest X-ray. Clinical stage was T2N1M0. He underwent primary surgical resection, including left partial glossectomy, left modified radical neck dissection (levels Ia through IV), and radial forearm free flap reconstruction of the left lateral tongue defect. Final surgical pathology revealed a 3.5 cm primary tumor, closest surgical margin was 2.0 cm, and there was no perineural or lymphovascular invasion. Two of 6 and 2 of four lymph nodes were positive for carcinoma in left neck levels Ib and IIa, respectively, each with extracapsular spread. The remainder of the left neck lymph nodes (levels IIb, III, and IV) were negative for carcinoma. Final pathologic stage was T2N2b. He was treated with postoperative chemoradiation (concurrent cis-platinum) using IMRT. Representative axial, sagittal, and coronal views from planning CT are shown. The primary tumor bed, free flap, and its attachments to the native tongue and positive neck levels (I and IIa) plus ~ 1 cm were delineated as high-risk CTV (CTV 60 Gy). The remainder of the oral tongue and operative bed of the left neck were treated to 57 Gy (intermediate risk), and the contralateral neck levels I–IV were treated electively to 54 Gy (standard risk). This was accomplished in a single integrated IMRT plan in 30 fractions. Representative isodose distributions are shown in multiple axial planes.

Case 1 Key Technical Points

• 1. At the time of simulation, the left neck suture line/surgical scar was marked with CT-compatible radiopaque wire, and 3 mm bolus was placed over the scar to ensure adequate surface dose to the scar. The left neck CTV contours were inclusive of the operative bed and surgical tracts and were taken out to the skin surface at the level of the scar.

• 2. A customized mouth-opening and tongue-depressing/tongue-immobilizing intraoral stent was used in this case. As demonstrated in the sagittal view, this provided physical separation of the tongue from the nontarget upper lip and hard palate.

• 3. In cancers of the oral tongue, in addition to targeting of the primary site tumor bed, we typically treat the remainder of the involved organ (entirety of the oral tongue) to operative bed or elective doses.

• 4. As demonstrated in the sagittal and coronal views, we ensured the CTVs were carried through the adjacent floor of the mouth, root of tongue, and submental region to the level of the hyoid.

• 5. The contralateral undissected (right) neck was treated electively to 54 Gy. The CTV for this unviolated/unoperated neck differed from that of the operated left neck, in that the right neck lymph node levels were delineated restricted by their anatomic boundaries (e.g., deep surface of the sternocleidomastoid and platysma), while in the left neck, the entirety of the sternocleidomastoid muscle was targeted as part of the operative bed target volume.

1.2 Case 2 (Fig. 10.2)

Fig. 10.2

A 65-year-old former smoker presented with a 4.0 cm painful expansile mass of the left lower alveolus (photograph). Biopsy of this mass showed poorly differentiated, invasive squamous carcinoma. Contrast-enhanced diagnostic CT of the neck (with puffed-cheek technique) demonstrated the primary mass interdigitated with multiple teeth and bone erosion (outlined in green). There were lymph node metastases seen on CT. There were no metastases seen on chest X-ray. Clinical stage was T4aN0M0. He underwent primary surgical resection, including left segmental mandibulectomy, left modified radical neck dissection (levels Ia through IV), and osseocutaneous fibular free flap reconstruction. Final surgical pathology revealed a 4.2 cm primary tumor with bone involvement, closest surgical margin was 1.0 cm, and there was perineural and lymphovascular invasion. One of 4 lymph nodes was positive for carcinoma in left neck level Ib, with extracapsular spread. The remainder of the left neck lymph nodes (levels IIa/b, III, and IV) were negative for carcinoma. Final pathologic stage was T4aN1. He was treated with postoperative chemoradiation (concurrent carboplatinum rather than cis-platinum due to profound baseline hypoacusis) using IMRT targeting the tumor bed, operative bed, and ipsilateral neck. A representative axial planning CT image with CTVs is shown. The primary tumor bed, free flap and its attachments, and positive neck level (Ib) plus margin were delineated as high-risk CTV (CTV 60 Gy). The remainder of the operative bed of the left neck and segment of the inferior alveolar nerve were treated to 57 Gy (intermediate risk). The left level Ib (area of ECE) was boosted to 66 Gy. This was accomplished in a single integrated IMRT plan in 30 fractions. Representative isodose distributions are shown in axial and sagittal plane.

Case 2 Key Technical Points

• 1. A customized mouth-opening and tongue-deviating intraoral stent was used in this case in order to displace the tip of the oral tongue, upper lip, and upper gingiva from the high-dose region.

• 2. The primary tumor bed, flap and its attachments, and bony cuts of the mandible were included in the CTV 60 Gy.

• 3. Given microscopic perineural invasion, the inferior alveolar nerve was targeted; the most proximal aspect of nerve coverage was to the interspace of the medial and lateral pterygoid muscles.

• 4. Given the surgical exposure associated with mandibulectomy and neck dissection, the tail of the left parotid was included in the operative bed target (CTV 57 Gy), as recurrences near a spared parotid in a pathologically involved neck have been described (10).

1.3 Case 3 (Fig. 10.3)

Fig. 10.3

A 63-year-old former smoker presented with a painful 1.7 cm mass centered in the right floor of the mouth, which was crossing midline (see photograph). Contrast-enhanced diagnostic CT of the neck demonstrated the primary mass (outlined in green) close to but not invading an adjacent mandibular torus. There were no lymph node metastases seen on CT. There were no metastases seen on chest X-ray. Clinical stage was T1N0M0. He underwent resection of the anterior floor of the mouth and bilateral neck dissection (levels II–IV) with radial forearm free flap reconstruction of the oral defect. Final pathology showed a 1.2 cm moderately differentiated tumor, 0.6 cm depth of invasion, no perineural or lymphovascular invasion, and free margins. There was a single lymph node involved in right level IB (without extracapsular extension) and a focus of metastatic carcinoma in the right submandibular gland, suspected to be direct spread down Wharton’s duct. He was treated with postoperative IMRT. Representative axial, sagittal, and coronal views from planning CT with CTVs are shown. The primary tumor bed, floor of the mouth, free flap and its attachments, and submandibular triangle plus margin were delineated as high-risk CTV (CTV 60 Gy). The remainder of the uninvolved operated bilateral neck above the junction was treated to 57 Gy (intermediate risk). Representative axial, sagittal, and coronal views from planning CT are shown with CTVs in color wash with accompanying dose distributions.

Case 3 Key Technical Points

• 1. A customized mouth-opening and tongue-elevating intraoral stent was used in this case in order to displace the mobile tongue, upper lip, and upper gingiva from the floor of the mouth.

• 2. For maximal, inferior constrictor muscle, larynx, and esophageal inlet sparing, a split-field IMRT technique utilizing half-beam block was used with the isocenter placed just above the arytenoids. The lower neck and supraclavicular fossae were treated using a low anterior neck field with a larynx block, which was extended to a full midline block after 40 Gy. Total dose to the bilateral midneck below the junction was 56 Gy in 28 fractions. A patched low-energy electron field was used to treat the central aspect of the neck surgical scar that fell under the larynx and full midline block.

1.4 Case 4 (Fig. 10.4)

Fig. 10.4

As 58-year-old smoker presented with hoarseness of voice and globus sensation. Biopsy of an anterior glottic mass revealed invasive squamous carcinoma. Contrast-enhanced CT neck demonstrated an enhancing mass in the anterior larynx, with full-thickness cartilage erosion with invasion of the anterior neck soft tissues (outlined in green). Bilateral cervical lymphadenopathy was seen (white arrows). There were no metastases on CXR. Final clinical stage was T4aN2cM0. He underwent total laryngectomy, with total thyroidectomy, and bilateral modified radical neck dissection and bilateral paratracheal dissections. Final pathology showed cartilage destruction and anterior soft tissue invasion, and surgical margins were free. There was multilevel adenopathy in the right neck with multiple positive nodes in levels II and III and a single involved node in left level II and with extracapsular spread of all positive nodes. He was treated with postoperative IMRT with concurrent cis-platinum. The tumor bed, larynx bed, reconstructed neopharynx and anastomosis, and bilateral positive nodal levels were treated to 60 Gy in 30 fractions. The remainder of the operative bed was treated to 57 Gy. Axial and sagittal planning CT images with CTVs and corresponding dose distributions are shown.

Case 4 Key Technical Points

• 1. At the time of simulation, the surgical scar was marked with CT-compatible radiopaque wire, and 3 mm bolus was placed over the scar both during simulation and treatment to ensure adequate surface dose to the scar and surgical tract.

• 2. Given anterior soft tissue invasion and multilevel adenopathy with extracapsular extension, generous HR-CTV delineation was pursued and generously included the anterior neck soft tissues, the entirety of the central compartment, positive nodal levels, and suprastomal region.

• 3. The tracheostoma was included in the lower-dose CTVs in this case. We consider including the stoma in the IR-CTV if there was extensive subglottic disease, narrow subglottic surgical margin, or low neck soft tissue invasion such as low neck nodes with extracapsular spread and in the HR-CTV if the location of the stoma is adjacent to preoperative disease. The risk of this location harboring disease is balanced with the risk of microstomia, which can be a severe late effect.

1.5 Case 5 (Fig. 10.5)

Fig. 10.5

A 68-year-old smoker presented with right-sided nasal obstructive symptoms and a right maxillary sinus mass. Transnasal endoscopic biopsy of this mass showed moderately differentiated invasive squamous carcinoma. Coronal views of an MRI of the face and a PET/CT demonstrated the primary tumor centered in the suprastructure of the maxillary sinus with extension to the lateral aspect of the nasal cavity as well as invasion through the floor of the orbit (outlined in green; white arrow). There were no lymph node metastases seen on MRI or PET/CT. There were no distant metastases on PET/CT. Clinical stage was T3N0M0. He underwent primary surgical resection, including subtotal maxillectomy and resection of the floor or orbit via lateral rhinotomy approach. The floor of the orbit was reconstructed with a titanium plate and the maxilla with an anterolateral thigh free flap. Final surgical pathology revealed a 4 cm primary tumor involving bone and invasion of the infraorbital nerve. The infraorbital nerve was dissected back to the foramen rotundum. Final surgical margins on the nerve and maxilla were clear. He was treated with postoperative IMRT, targeting the tumor bed, operative bed, and ipsilateral facial and upper neck lymphatics (levels IB–II). Representative axial and coronal planning CT images with CTVs in color wash and associated isodose lines are shown. The primary tumor bed, flap, reconstruction plate, floor of the orbit, right nasal cavity, and bony cuts of the maxilla were included in the CTV 60 Gy. The remainder of the operative bed was treated to 57 Gy. Right levels Ib and II were treated electively to 54 Gy. Treatment was accomplished in a single integrated IMRT plan in 30 fractions.

Case 5 Key Technical Points

• 1. A customized mouth-opening and tongue-depressing intraoral stent was used in this case in order to displace the lower oral cavity from the high-dose region.

• 2. Given gross neural spread along the infraorbital nerve, the most proximal aspect of nerve coverage was extended intracranially to include elective coverage of the trigeminal nerve ganglion (cavernous sinus).

• 3. IMRT facilitated excellent coverage of the high right nasal cavity and adjacent ethmoid sinuses and sparing of left optic structures.

1.6 Case 6 (Fig. 10.6)

Fig. 10.6

A 65-year-old man presented with persistent sinus congestion. A right-sided nasoethmoid tumor was discovered and biopsy showed olfactory neuroblastoma. Sagittal T1 MRI with gadolinium and a coronal contrast-enhanced CT showed this tumor to be 2.8 cm, widening the right posterior ethmoid sinus, crossing midline, and eroding the anterior skull base with dural involvement (outlined in green; white arrow). There were no lymph nodes or distant metastases, representing Kadish C disease. He underwent endonasal endoscopic ethmoidectomy with resection of tumor, cribriform plate, and adjacent frontal lobe dura. He was treated with postoperative IMRT, 60 Gy to the positive tumor bed and adjacent skull base and dura, 57 Gy to the operative bed and adjacent sinuses at risk, and 54 Gy electively to the draining lymphatics at risk (bilateral levels IB and II), all in a single integrated IMRT plan in 30 fractions. Axial, sagittal, and coronal planning CT images with CTVs and corresponding dose distributions are shown.

Case 6 Key Technical Points

• 1. A customized mouth-opening and tongue-depressing intraoral stent was used in this case in order to displace the lower oral cavity from the high-dose region.

• 2. IMRT utilizing multiple noncoplanar beam angles facilitated excellent coverage of the high nasoethmoid region, skull base, and dura of the anterior cranial fossa while generating a steep dose gradient near the adjacent critical structures of the central nervous system. The maximum dose to each optic nerve and optic chiasm was <54 Gy and the corneas were both <30 Gy. Mean dose to each parotid was <24 Gy.

1.7 Case 7 (Fig. 10.7)

Fig. 10.7

A 50-year-old man developed an asymptomatic left preauricular lump. FNA suggested pleomorphic adenoma. He underwent excisional biopsy revealing adenoid cystic carcinoma predominately cribriform type but with a focal solid component. There was intraoperative concern for residual disease near the mastoid tip and tumor adherence to the main trunk of the facial nerve. Post-biopsy diagnostic CT showed enhancing soft tissue just inferior and lateral to the stylomastoid foramen (white arrow). There were no lymph nodes or distant metastases on imaging. There were no cranial neuropathies. Clinical stage was TX(1)N0M0. He then underwent surgical resection consisting of lateral temporal bone resection with decompression of the facial nerve, superficial parotidectomy, and left supraomohyoid neck dissection. The tumor was completely resected and the facial nerve was dissected and preserved in its entirety. Final pathology showed a small focus of residual carcinoma and perineural and lymphovascular invasion. All lymph nodes were negative and surgical margins were free. He was then treated with postoperative IMRT, 60 Gy to the tumor bed (including the superficial parotid bed and stylomastoid foramen) and 57 Gy to the operative bed, which included the lateral temporal bone surgical site and facial nerve pathway in the descending facial canal and left upper neck. Axial, sagittal, and coronal planning CT images with CTVs and corresponding dose distributions are shown.

Case 7 Key Technical Points

• 1. A customized tongue-deviating intraoral stent was used in this case in order to displace the mobile tongue from the high- and intermediate-dose gradient. As seen in the axial image, the tongue was able to be displaced from the 35 Gy isodose line, which largely fell in the stent itself rather than the tongue.

• 2. At the time of simulation, the surgical scar was marked with CT-compatible radiopaque wire, and 3 mm bolus was placed over the scar to ensure adequate surface dose to the scar and surgical tract.

• 3. To ensure adequate coverage of the entire parotid bed, the anterior aspect of CTV 57 was extended to the level of the anterior edge of the masseter muscle and the deep border was taken down to the pharyngeal wall to ensure coverage of the deep lobe of parotid.

• 4. IMRT facilitated excellent coverage of the operative bed of the left temporal bone while minimizing dose to the underlying brain (left temporal lobe) as demonstrated in the coronal view.

1.8 Case 8 (Fig. 10.8)

Fig. 10.8

A 67-year-old presented with a painless pea-sized lump of the right side of the hard palate (photograph). Biopsy of this mass showed adenoid cystic carcinoma, tubular and cribriform type. Contrast-enhanced diagnostic CT of the neck demonstrated a 1.5 cm primary mass (white arrow) at the hard-soft palate junction. There were no metastases on chest X-ray. She underwent primary surgical resection, including right infrastructure maxillectomy and placement of a surgical obturator in the palate defect. Final surgical pathology revealed a 1.5 cm primary tumor, closest surgical margin was 1.0 cm, and there was perineural invasion. There was no bone invasion. She was treated with postoperative IMRT. The primary tumor bed and margin were delineated as high-risk CTV (CTV 60 Gy). The remainder of the adjacent palate and nasal floor were treated to 57 Gy (intermediate risk), and the right greater palatine nerve pathway was treated to 54 Gy at the proximal aspect of its targeted pathway. This was accomplished in a single integrated volumetric modulated arc plan in 30 fractions. Representative axial, sagittal, and coronal views from planning CT are shown with CTVs in color wash with accompanying dose distributions.

Case 8 Key Technical Points

• 1. The patient’s wax obturator was left in during simulation and treatment delivery to occupy the palate defect to help ensure adequate surface dose of the tumor bed.

• 2. A customized mouth-opening and tongue-depressing intraoral stent was used in this case in order to displace the lower oral cavity from the high-dose region of the palate.

• 3. Given perineural invasion and propensity for perineural spread of adenoid cystic carcinoma, the most proximal aspect of nerve coverage was extended to the skull base and inclusive of the pterygopalatine fossa.

• 4. IMRT facilitated excellent coverage of the palate and neural pathways at risk and sparing of bilateral major salivary glands and central nervous system structures (mean dose to the left and right parotid was each <6 Gy).

1.9 Case 9 (Fig. 10.9)

Fig. 10.9

An 80-year-old female presented with hoarseness of voice and right true vocal cord paresis, and a 5 cm right thyroid mass was discovered. Biopsy of the right thyroid mass showed papillary thyroid carcinoma. Contrast-enhanced diagnostic CT neck showed a necrotic mass in the right lobe of the thyroid with tracheal and esophageal invasion, involvement of the common party wall, and a positive right level II/III lymph node (white arrow). There were no distant metastases seen imaging. She underwent total thyroidectomy, bilateral paratracheal and superior mediastinal lymph node dissections, right neck dissection (levels II–V), partial esophageal muscularis resection, partial tracheal resection, and partial cricoid resection. Final pathology showed 5.0 cm papillary thyroid carcinoma with foci of squamoid and poorly differentiated components, cartilage invasion, extrathyroidal extension, 6 positive paratracheal lymph nodes with extracapsular extension, and a single positive lymph node in the right neck specimen. The inferior tracheal margin was clear but the superior tracheal margin was focally close (<1 mm) from the soft tissue edge. She was then treated with postoperative IMRT. The primary tumor bed, central compartment, and positive nodal levels were delineated as high-risk CTV (CTV 60 Gy). The remainder of the operative bed was in CTV 57 Gy (intermediate risk), and the undissected elective left midneck was included in CTV 54 Gy. The right aspect of the cricotracheal anastomosis was selected for an integrated boost to 63 Gy. This was accomplished in a 30 fraction plan. Representative axial, sagittal, and coronal views from planning CT are shown with CTVs in color wash with accompanying dose distributions.

Case 9 Key Technical Points

• 1. High-risk CTVs in this case included the entirety of the central compartment with generous coverage of the bilateral tracheoesophageal grooves, common party wall, laryngeal inlet on the right, cricoid cartilage, resected tracheal bed, resected esophageal muscularis bed, thyroid bed, anterior soft tissue of the low neck, paratracheal nodal bed, and positive nodal bed of the right neck.

• 2. Regarding radiation target volumes in the lateral neck, levels II–V were targeted in the node-positive neck (right side) and levels III–IV were targeted in the node-negative neck (left side). This allowed for sparing of the left major salivary glands. Mean dose to the left submandibular gland and that of left parotid gland were 12 and 6 Gy, respectively.