Impact of head and neck cancer adaptive radiotherapy to spare the parotid glands and decrease the risk of xerostomia.

Joel Castelli,Guillaume Louvel,Mohamed Nassef,Guillaume Cazoulat,Juan David Ospina,Enrique Chajon,Franck Jegoux,Renaud De Crevoisier,Karen Benezery,Antoine Simon,Olivier Henry,Pascal Haigron

doi:10.1186/s13014-014-0318-z

Abstract

BackgroundLarge anatomical variations occur during the course of intensity-modulated radiation therapy (IMRT) for locally advanced head and neck cancer (LAHNC). The risks are therefore a parotid glands (PG) overdose and a xerostomia increase.The purposes of the study were to estimate:- the PG overdose and the xerostomia risk increase during a “standard” IMRT (IMRTstd);- the benefits of an adaptive IMRT (ART) with weekly replanning to spare the PGs and limit the risk of xerostomia.Material and methodsFifteen patients received radical IMRT (70 Gy) for LAHNC. Weekly CTs were used to estimate the dose distributions delivered during the treatment, corresponding either to the initial planning (IMRTstd) or to weekly replanning (ART). PGs dose were recalculated at the fraction, from the weekly CTs. PG cumulated doses were then estimated using deformable image registration. The following PG doses were compared: pre-treatment planned dose, per-treatment IMRTstd and ART. The corresponding estimated risks of xerostomia were also compared. Correlations between anatomical markers and dose differences were searched.ResultsCompared to the initial planning, a PG overdose was observed during IMRTstd for 59% of the PGs, with an average increase of 3.7 Gy (10.0 Gy maximum) for the mean dose, and of 8.2% (23.9% maximum) for the risk of xerostomia. Compared to the initial planning, weekly replanning reduced the PG mean dose for all the patients (p < 0.05). In the overirradiated PG group, weekly replanning reduced the mean dose by 5.1 Gy (12.2 Gy maximum) and the absolute risk of xerostomia by 11% (p < 0.01) (30% maximum). The PG overdose and the dosimetric benefit of replanning increased with the tumor shrinkage and the neck thickness reduction (p < 0.001).ConclusionDuring the course of LAHNC IMRT, around 60% of the PGs are overdosed of 4 Gy. Weekly replanning decreased the PG mean dose by 5 Gy, and therefore by 11% the xerostomia risk.

Highlights

The treatment of unresectable Head & Neck Cancer (HNC) consists of a chemoradiotherapy [1,2]
Compared to the initial planning, a parotid glands (PG) overdose was observed during IMRTstd for 59% of the PGs, with an average increase of 3.7 Gy (10.0 Gy maximum) for the mean dose, and of 8.2% (23.9% maximum) for the risk of xerostomia
During the course of locally advanced head and neck cancer (LAHNC) intensity-modulated radiation therapy (IMRT), around 60% of the PGs are overdosed of 4 Gy

Summary

Introduction

The treatment of unresectable Head & Neck Cancer (HNC) consists of a chemoradiotherapy [1,2]. Large variations can be observed during the course of IMRT treatment, such as body weight loss [7,8], primary tumor shrinking [7], and PG volume reduction [9] Due to these anatomical variations and to the tight IMRT dose gradient, the actual administered dose may not correspond to the planned dose, with a risk of radiation overdose to the PGs (Figure 1) [10,11]. This dose difference clearly reduces the expected clinical benefits of IMRT, increasing the risk of xerostomia. Large anatomical variations occur during the course of intensity-modulated radiation therapy (IMRT) for locally advanced head and neck cancer (LAHNC). The purposes of the study were to estimate: - the PG overdose and the xerostomia risk increase during a “standard” IMRT (IMRTstd); - the benefits of an adaptive IMRT (ART) with weekly replanning to spare the PGs and limit the risk of xerostomia

Methods

Results

Conclusion