NTCP modeling of subacute/late laryngeal edema scored by fiberoptic examination.
OBJECTIVE
Finding best-fit parameters of normal tissue complication probability (NTCP) models for laryngeal edema after radiotherapy for head and neck cancer.


METHODS
Forty-eight patients were considered for this study who met the following criteria: (1) grossly uninvolved larynx, (2) no prior major surgery except for neck dissection and tonsillectomy, (3) at least one fiberoptic examination of the larynx within 2 years from radiotherapy, (4) minimum follow-up of 15 months. Larynx dose-volume histograms (DVHs) were corrected into a linear quadratic equivalent one at 2 Gy/fr with alpha/beta = 3 Gy. Subacute/late edema was prospectively scored at each follow-up examination according to the Radiation Therapy Oncology Group scale. G2-G3 edema within 15 months from RT was considered as our endpoint. Two NTCP models were considered: (1) the Lyman model with DVH reduced to the equivalent uniform dose (EUD; LEUD) and (2) the Logit model with DVH reduced to the EUD (LOGEUD). The parameters for the models were fit to patient data using a maximum likelihood analysis.


RESULTS
All patients had a minimum of 15 months follow-up (only 8/48 received concurrent chemotherapy): 25/48 (52.1%) experienced G2-G3 edema. Both NTCP models fit well the clinical data: with LOGEUD the relationship between EUD and NTCP can be described with TD50 = 46.7 +/- 2.1 Gy, n = 1.41 +/- 0.8 and a steepness parameter k = 7.2 +/- 2.5 Gy. Best fit parameters for LEUD are n = 1.17 +/- 0.6, m = 0.23 +/- 0.07 and TD50 = 47.3 +/- 2.1 Gy.


CONCLUSIONS
A clear volume effect was found for edema, consistent with a parallel architecture of the larynx for this endpoint. On the basis of our findings, an EUD <30-35 Gy should drastically reduce the risk of G2-G3 edema.
Rancati
Tiziana
T
Prostate Program, Istituto Nazionale dei Tumori, Milan, Italy.
Fiorino
Claudio
C
Sanguineti
Giuseppe
G
D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy*; D005336:Fiber Optic Technology; D005500:Follow-Up Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007819:Laryngeal Edema / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology; D007828:Laryngoscopy; D007830:Larynx / Q000000981:diagnostic imaging / Q000528:radiation effects*; D016013:Likelihood Functions; D015233:Models, Statistical; D011336:Probability; D011446:Prospective Studies; D011832:Radiation Injuries; D011859:Radiography; D011879:Radiotherapy Dosage