Radiation Oncology/Toxicity/Larynx

Laryngeal toxicity
 * Lower dose to higher volume around larynx appears worse than higher dose just to glottis
 * There are no good NTCP studies for larynx. Western Ontario data suggests at most 50 Gy. MSKCC routinely constrains mean to 30-35 Gy (see PMID 17241750 below)
 * Laryngeal dose is much less with half-beam IMRT and matched low anterior field with laryngeal block compared with whole-field IMRT. Given this, consideration should be given to matched IMRT field with low anterior field and laryngeal block in appropriate clinical situations

Treatment Toxicity
 * Western Ontario
 * 2001 PMID 11801970 -- "Vocal function following radiation for non-laryngeal versus laryngeal tumors of the head and neck." (Fung K, Laryngoscope. 2001 Nov;111(11 Pt 1):1920-4.)
 * Retrospective. 13 patients with early glottic tumors and 17 patients with non-laryngeal tumors evaluated. Vocal function assessed with acoustic analysis, aerodynamic measurements, and videostroboscopy. Voice Handicap Index self-assessment. Mean dose laryngeal group 61 Gy vs. non-laryngeal group 50 Gy
 * Outcome: Non-laryngeal group had worse outcome in all measures
 * Conclusion: Patients treated with wide-field RT for non-laryngeal tumors have significantly worse vocal function (subjective and objective) compared with early glottic cancer patients
 * 2001 PMID 11771040 -- "Effects of head and neck radiation therapy on vocal function." (Fung K, J Otolaryngol. 2001 Jun;30(3):133-9.)
 * Retrospective. 30 patients, normal larynx, incidental RT, and NED >1 year. Videostroboscopic, aerodynamic, and acoustic analyses. Voice Handicap Index self-assessment. Comparison to age- and gender- matched controls
 * Outcome: Significant difference in many parameters. Voice acoustics worse at 50 Gy. Significant voice handicap in 27%. Younger patients greater handicap. Voice quality worsened with time.
 * Conclusion: Significant objective and subjective changes in vocal function in normal larynx with "incidental" irradiation

Treatment Planning
 * Memorial Sloan Kettering; 2007 PMID 17241750 -- "Choosing an intensity-modulated radiation therapy technique in the treatment of head-and-neck cancer." (Lee N, Int J Radiat Oncol Biol Phys. 2007 Aug 1;68(5):1299-309. Epub 2007 Jan 22.)
 * Planning comparison. 6 common H&N cases (nasopharynx, base of tongue, tonsil, supraglottic, hypopharynx, unknown primary). Extended whole-field IMRT (EWF-IMRT) vs split field IMRT with low anterior field (SF-IMRT)
 * Outcome: Target coverage comparable. Organs at risk comparable, except larynx if target volumes were not close
 * Conclusion: Different approach suggested based on clinical scenario. Typically, split-field IMRT for nasopharynx and oropharynx. If glottic larynx is a target (larynx, hypopharynx, and unknown primary), or if gross disease extends inferiorly close to glottic larynx, prefer whole-field IMRT


 * MD Anderson; 2005 PMID 15978743 -- "Intensity-modulated radiation therapy (IMRT) of cancers of the head and neck: comparison of split-field and whole-field techniques." (Dabaja B, Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1000-5. Epub 2005 Jun 22.)
 * Planning comparison. 13 patients with early-stage oropharynx. Whole-field IMRT (WF-IMRT) compared with half-beam IMRT matched to anterior beam (HB-IMRT). Planning per RTOG 0022
 * Outcome: PTV coverage comparable. Mean dose to OAR comparable, except larynx (WF-IMRT 47 Gy vs. HB-IMRT 18.7 Gy)
 * Conclusion: Acceptable plans with either approach. WF-IMRT has advantage if uncertainty about match line is a concern. HB-IMRT can achieve much lower larynx doses


 * University of Florida; 2004 PMID 14999801 -- "Unnecessary laryngeal irradiation in the IMRT era." (Amdur RJ, Head Neck. 2004 Mar;26(3):257-63; discussion 263-4.)
 * Review. IMRT dose much higher with IMRT than standard anterior low-neck field
 * Conclusion: Lateral opposed fields should not be extended to include larynx to avoid matching fields through lymphadenopathy. IMRT fields should not include normal larynx when laryngeal dose would be substantially lower with shielded anterior low-neck field