A Nomogram to predict parotid gland overdose in head and neck IMRT
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RESEARCH
Open Access
A Nomogram to predict parotid gland overdose in head and neck IMRT J. Castelli1,2,3*, A. Simon2,3, B. Rigaud2,3, C. Lafond1, E. Chajon1, J. D. Ospina2,3, P. Haigron2,3, B. Laguerre4, A. Ruffier Loubière5, K. Benezery6 and R. de Crevoisier1,2,3
Abstract Purposes: 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). Material and 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. Conclusion: 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. Keywords: Nomogram, Adaptive radiotherapy, Head and neck, Parotid gland overdose
Introduction During the course of intensity-modulated radiotherapy (IMRT) for head and neck cancer (HNC), large anatomical variations may result in delivered doses differing from the planned dose [1]. The literature shows that while dose variations in the clinical target volume appear extremely low [2–5], the percentage of patients with estimated PG overdoses ranges widely from 5 to 70 % [1, 5–10]. With the aim of correcting these PG overdoses, an adaptive radiotherapy (ART) strategy involving one or several replannings during treatment has been investigated [1, 2]. These replannings are, however, time* Correspondence: [email protected] 1 Centre Eugene Marquis, Radiotherapy, de la Bataille Flandre Dunkerque, F-35000 Rennes, France 2 Rennes University 1, LTSI, Campus de Beaulieu, Rennes F-35000, France Full list of author information is available at the end of the article
consuming, as a complete delineation can take up to 2.5 h [11–13] and may not be beneficial for all patients. It is therefore crucial to identify patients with PG overdose and evaluate how ART benefits each individual. Ideally, replanning decisions should be based on early and simple anatomical criteria, such as weight l
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