Carotid Sparing Modulated Radiotherapy (CSMRT) for Early Glottic Cancers: Single Institution Feasibility and Safety Assessment

Purpose/Objective(s)Early glottic cancers (cT1-2N0M0) have excellent outcome with radical radiotherapy alone. Conventional radiotherapy predisposes long term atherosclerosis risk. This single Institution protocol evaluated feasibility and safety of CSMRT for early glottic cancers. We also evaluated dosimetric data of CSMRT over conventional RT techniques.Materials/MethodsTwenty patients of early glottic squamous cell carcinomas evaluated with baseline fiber-optic laryngoscopy (FOL), CT scan neck and voice quality assessment. Voice quality was documented before CSMRT and at every 3 months by Institutional modified ELS (European Laryngology society) protocol. This included subjective and objective voice assessment in 5points scale. Standard contouring guidelines were followed including whole larynx in CTV and bilateral carotids were drawn and 3 mm PRV was added. CSMRT delivered 63-65.25 Gy in 28-29 fractions to T1 and T2 glottic cancers respectively by volumetric modulated arc therapy (VMAT). Between conventional and CSMRT dosimetric parameters like coverage, carotids mean, V50, V35, spinal cord Dmax, cricopharynx and thyroid Dmean were documented. Patients were followed up every 3 months for up to 2 years with periodic FOL and voice assessment and CT neck annually.Results20 patients (M:14, F:6) were treated over 4 years with median follow-up of 26 months and median age 60 years. Coverage remained similar in both plans with slight improvement in CSMRT (62.6 Gy vs 62 Gy). Carotid Dmean, V50 and V35 medians were 28 Gy,6 cc and 12 cc (CSMRT) and 52 Gy,26 cc and 50 cc (Conv) respectively. Median of Dmean for thyroid and cricopharynx were 20.8 Gy and 45 Gy (CSMRT) versus 38 Gy and 50 Gy (Conv). The only higher dose was for spinal cord Dmax in CSMRT (29 Gy vs 7 Gy). The treatment was well tolerated in CSMRT with grade 1 dysphagia (90%), grade 2 skin changes (15%), clinical hypothyroidism (3 patients). The voice quality worsened maximum at 3 months post CSMRT and median voice recovery at 6 months. Objective voice recording showed improvement before subjective. 70% patients needed steroids for 2-3 weeks duration. Till last follow up all patients were disease controlled and alive (local control 100%) All patients were on voice rehabilitation with professional speech therapist.ConclusionThis single Institution CSMRT protocol for early glottic cancers are safe and feasible. Oncological safety and better voice quality needs further validation with prospective protocol. Over a longer follow up correlation between carotid dosage and atherosclerotic events should be monitored.