A Nomogram to predict parotid gland overdose in head and neck IMRT.
OBJECTIVE
To generate a nomogram to predict parotid gland (PG) overdose and to quantify the dosimetric benefit of weekly replanning based on its findings, in the context of intensity-modulated radiotherapy (IMRT) for locally-advanced head and neck carcinoma (LAHNC).


METHODS
Twenty LAHNC patients treated with radical IMRT underwent weekly computed tomography (CT) scans during IMRT. The cumulated PG dose was estimated by elastic registration. Early predictors of PG overdose (cumulated minus planned doses) were identified, enabling a nomogram to be generated from a linear regression model. Its performance was evaluated using a leave-one-out method. The benefit of weekly replanning was then estimated for the nomogram-identified PG overdose patients.


RESULTS
Clinical target volume 70 (CTV70) and the mean PG dose calculated from the planning and first weekly CTs were early predictors of PG overdose, enabling a nomogram to be generated. A mean PG overdose of 2.5Gy was calculated for 16 patients, 14 identified by the nomogram. All patients with PG overdoses >1.5Gy were identified. Compared to the cumulated delivered dose, weekly replanning of these 14 targeted patients enabled a 3.3Gy decrease in the mean PG dose.


CONCLUSIONS
Based on the planning and first week CTs, our nomogram allowed the identification of all patients with PG overdoses >2.5Gy to be identified, who then benefitted from a final 4Gy decrease in mean PG overdose by means of weekly replanning.
Centre Eugene Marquis, Radiotherapy, de la Bataille Flandre Dunkerque, F-35000, Rennes, France. j.castelli@rennes.unicancer.fr.|Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France. j.castelli@rennes.unicancer.fr.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France. j.castelli@rennes.unicancer.fr.
J
J
Castelli
Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France.
A
A
Simon
Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France.
B
B
Rigaud
Centre Eugene Marquis, Radiotherapy, de la Bataille Flandre Dunkerque, F-35000, Rennes, France.
C
C
Lafond
Centre Eugene Marquis, Radiotherapy, de la Bataille Flandre Dunkerque, F-35000, Rennes, France.
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E
Chajon
Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France.
J D
JD
Ospina
Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France.
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P
Haigron
Centre Eugene Marquis, Medical oncology, Rennes, F-35000, France.
B
B
Laguerre
CHRU de Tours, Radiotherapy, Tours, F-37550, France.
A Ruffier
AR
Loubière
Centre Antoine Lacassagne, Radiotherapy, Nice, F-06100, France.
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K
Benezery
Centre Eugene Marquis, Radiotherapy, de la Bataille Flandre Dunkerque, F-35000, Rennes, France.|Rennes University 1, LTSI, Campus de Beaulieu, Rennes, F-35000, France.|INSERM, U1099, Campus de Beaulieu, Rennes, F-35000, France.
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de Crevoisier
D000368:Aged; D005260:Female; D005500:Follow-Up Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D049451:Nomograms; D058958:Organs at Risk / Q000528:radiation effects*; D010306:Parotid Gland / Q000528:radiation effects*; D011379:Prognosis; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
Adaptive radiotherapy; Head and neck; Nomogram; Parotid gland overdose