Parotid gland shrinkage during IMRT predicts the time to Xerostomia resolution
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RESEARCH
Open Access
Parotid gland shrinkage during IMRT predicts the time to Xerostomia resolution Giuseppe Sanguineti1,2, Francesco Ricchetti1,2, Binbin Wu1,2, Todd McNutt1,2 and Claudio Fiorino3*
Abstract Purpose: To assess the impact of mid-treatment parotid gland shrinkage on long term xerostomia during IMRT for oropharyngeal SCC. Methods and materials: All patients treated with IMRT at a single Institution from November 2007 to June 2010 and undergoing weekly CT scans were selected. Parotid glands were contoured retrospectively on the mid treatment CT scan. For each parotid gland, the percent change relative to the planning volume was calculated and combined as weighted average. Patients were considered to be xerostomic if developed GR2+ dry mouth according to CTCAE v3.0. Predictors of the time to xerostomia resolution or downgrade to 1 were investigated at both uni- and multivariate analysis. Results: 85 patients were selected. With a median follow up of 35.8 months (range: 2.4-62.6 months), the actuarial rate of xerostomia is 26.2% (SD: 5.3%) and 15.9% (SD: 5.3%) at 2 and 3 yrs, respectively. At multivariate analysis, mid-treatment shrink along with weighted average mean parotid dose at planning and body mass index are independent predictors of the time to xerostomia resolution. Patients were pooled in 4 groups based on median values of both mid-treatment shrink (cut-off: 19.6%) and mean WA parotid pl-D (cut-off: 35.7 Gy). Patients with a higher than median parotid dose at planning and who showed poor shrinkage at mid treatment are the ones with the outcome significantly worse (3-yr rate of xerostomia ≈ 50%) than the other three subgroups (3-yr rate of xerostomia ≈ 10%). Conclusion: For a given planned dose, patients whose parotids significantly shrink during IMRT are less likely to be long-term supplemental fluids dependent. Keywords: Parotid gland, IMRT, Shrinkage
Introduction Long-term dry mouth is a debilitating side effect of radiotherapy for head and neck cancer. More than a decade ago, Eisbruch et al. explored for the first time the existence of a direct relationship between the dose received by parotids and salivary output after radiotherapy [1]. After this early work, many studies investigated this issue, leading to a quite good consensus around the parallel behavior of parotids and the value of the mean dose to predict xerostomia [2]; consequently, this knowledge led to limit prospectively the dose to the parotid glands throughout IMRT. Data from randomized studies have confirmed the clinical validity of this approach [3]. * Correspondence: [email protected] 3 Department of Medical Physics, Ospedale San Raffaele, Milan, Italy Full list of author information is available at the end of the article
However, despite ‘dosimetric’ sparing of the parotids, 20-25% of patients still develop long-term xerostomia. Whether this reflects a different intrinsic radiosensitivity among patients, the added damage to other major/minor glands or the inability to correctly predict for the real dose delivered
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