1. General Principles and Practical Pointsin Target Delineation: Oropharynx CaYong Chan Ahn, MD, PhDDept of Radiation OncologySamsung Medical CenterSungkyunkwan University School of Medicine

2. Anatomy 3. Tonguebase (Vallecula)TonsilAnt pillaFossaPost pillaSoft palate 4. Soft Palate Soft palate is thin, mobile muscle complexseparating nasopharynx from oropharynx. It is contiguous laterally with tonsillar pillars. Epithelium: Oral side is squamous Nasopharyngeal surface is respiratory 5. Tonsillar Fossa Boundaries: Ant -- ant tonsillar pillar (palatopharyngealmuscle) Post -- post tonsillar pillar (palatopharyngealmuscle) Inf -- glossotonsillar sulcus andpharyngoepiglottic fold Lat -- pharyngeal constrictor muscle and itsfascia, mandible, and lateral pharyngeal space 6. Tonguebase Boundaries: Ant -- circumvallate papillae Lat -- glossotonsillar sulci Post -- epiglottis Vallecula: Ttransition from tonguebase to epiglottis Tonguebase musculature is contiguouswith oral tongue. 7. Natural History& Patterns of Spread 8. Primary Lesion Spread is dictated by local anatomy, and eachanatomic site has its own peculiar patterns. Muscle invasion common (may spread alongmuscle or fascial planes) Bone and cartilage act as barrier to spread Parapharyngeal space invasion sup~infspread from base of skull to low neck Perineural invasion Vascular space invasion 9. Ant Tonsillar Pillar -- Primary Usually diagnosed early when superficial Usually with indistinct margins May be red, white, or mixture May develop central ulcer with rolledmargin Sup/Med -- to soft palate, post hard palate, andmaxillary gingiva. Ant/Lat -- to retromolar trigone, postgingivobuccal sulcus, buccal mucosa, adjacenttongue. 10. Ant Tonsillar Pillar -- Primary Advance lesions: Mandible invasion Skullbase and nasopharynx occurs lateassociated with medial pterygoid muscle andplate invasion (trismus and temporal pain). 11. Tonsillar Fossa -- Primary Initial lesions: Tend to be exophytic with central ulcerationplus an iniltrative component. Some develop submucosally -- neck nodeswith no obvious tonsillar lesion. Extension to posterior tonsillar pillar andoropharyngeal wall occurs early. Invasion into glossotonsillar sulcus andtonguebase occurs in 25%. 12. Tonsillar Fossa -- Primary Advance lesions: Penetrate to parapharyngeal space accessto skull base. Cranial nerve involvement is uncommon. May invade mandible, nasopharynx, andpyriform sinus. 13. Post Tonsillar Pilla -- Primary Early lesions are uncommon. May spread inferiorly alongpalatopharyngeal muscle to its insertionsinto middle pharyngeal constrictor,pharyngoepiglottic fold, and posteriorborder of thyroid cartilage. Also, lymphatic trunks of posterior tonsillarpillar are theoretically more likely to spreadto junctional (parapharyngeal) and level Vnodes. 14. Soft Palate -- Primary Nearly all lesions occur on oral side. Earliest tumors are red lesions with illdefined borders. White lesions may be leukoplakia,carcinoma in situ, or early invasivecarcinoma. Multiple sites involvement with normal-appearing intervening mucosa may occur. Most carcinomas are diagnosed while stillconfined to soft palate. 15. Soft Palate -- Primary Spread occurs first to tonsillar pillars andhard palate. Lateral spread may penetrate superiorconstrictor muscle and skull base and mayrarely extend to cranial nerves inparapharyngeal space. Involvement of lateral wall(s) ofnasopharynx may occur in advancedlesions. 16. Tonguebase -- Primary Usually remains in tongue unless it beginsat peripheral margin. Vallecular lesions: Post -- to lingual surface of epiglottis. Lat -- to lateral pharyngeal wall and anteriorwall of pyriform sinus along pharyngoepiglotticfold. Inf -- to preepiglottic space via thinhyoepiglottic ligament. 17. Tonguebase -- Primary Lateral tonguebase lesions: May invade glossotonsillar sulcus andeventually escape into neck (no effectivemusculature barrier). Advanced lesions spread to larynx, oraltongue, and parapharyngeal space. 18. Lymphatic Spread Predictors of LN meta: Histologic type Differentiation of tumor Primary lesion size Vascular space invasion Capillary lymphatics density Recurrence 19. Lymphatic Spread Subclinical disease in clinically (-) LN: Positive nodes by elective neck dissection Regional recurrence by F/U after no neck Tx 20. Subclinical Disease Defined as Disease statistically known to be present Cannot be seen or palpated in areasaccessible to physical examination Cannot be seen on highly efficient imagingstudies From barely detectable microscopic focus toundetected 2 cm node completely replaced bytumor 21. Incidence of Subclinical Disease 22. Lymphatic Spread Orderly progression Well-lateralized lesions spread toipsilateral neck Lesions on or near midline and lateralizedtongue base and nasopharyngeal lesions may spread to both sides, and tend to spreadto bulky side 23. Incidence of Subclinical Disease (%) 24. Lymphatic Spread Contralateral disease in clinically (+) LN: Large or multiple LN Lymphatic pathways obstruction by surgeryor RT Shunting is mainly through submental space Level II LN is most commonly involved incontralateral metastases from well-lateralizedlesions 25. Lymphatic Spread Skip metastasis can occur: If unusual LN site involvement (+) search for second primary Retrograde LN metastases in ipsilateralaxilla if lower neck LN involved 26. Lymphatic Spread Retropharyngeal LN involvement: Became easier with CT and MRI Risk of retropharyngeal adenopathy isrelated to clinically involved LN and primarysite 27. Lymphatic Spread(Oropharynx Cancer Summary)Tonguebase Tonsillar fossa Ant pillar Soft palate1st echelon II II Ib/II Ib/VcN(+) 75% 75% 45% 55%Contralateral 30% 10% 5% 15%Occult 40~50% 50~60% 10~15% 20% 28. Distant Metastasis Same for stage for stage regardless of Tx modality Related more to cN and involved LN location than: