Abstract
PurposeTo cover the microscopic tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3–4 cm are used for radiotherapy (RT) protocols. However, smaller margins of 2–3 cm might be reasonable when advanced diagnostic imaging is integrated into target volume delineation. Purpose of this study was to compare the dose distribution and deposition to the organs at risk (OAR) for different longitudinal margins using a DVH- and NTCP-based approach.MethodsTen patients with SCC of the middle or lower third were retrospectively selected. Three planning target volumes (PTV) with longitudinal margins of 4 cm, 3 cm and 2 cm and an axial margin of 1.5 cm to the gross target volume (GTV) were defined for each patient. For each PTV two treatment plans with total doses of 41.4 Gy (neoadjuvant treatment) and 50.4 Gy (definite treatment) were calculated. Dose to the lungs, heart, myelon and liver were then evaluated and compared between different PTVs.ResultsWhen using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, but not for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, a significant difference was calculated for Dmin, Dmean, Dmedian and V5-V35 of the lungs and for Dmax, Dmean and V5-V35 of the heart. Nevertheless, no difference was seen for median heart dose. An additional dose reduction for V10 of the heart was achieved for definite treatment plans when using a longitudinal margin of 3 cm. The NTCP-based risk of pneumonitis was significantly reduced by a margin reduction to 2 cm for neoadjuvant and definite treatment plans.ConclusionReduction of longitudinal margins from 4 cm to 3 cm can significantly reduce the dose to lungs and Dmean of the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of chemoradiation (CRT) for SCC in upcoming studies.
Highlights
Esophageal cancer (EC) is the eighth most common cancer in the world and more than 450.000 new cases are diagnosed each year [1]
An analysis of data from surgical resections identified microscopic intraepithelial and/ or subepithelial tumor extensions in 46% and 55% of patients, respectively, with less than 5% risk of positive resection margins at 3 cm [7]. To cover these areas that are at higher risk for microscopic tumor spread, radiotherapy (RT) for EC is typically done with large longitudinal safety margins, which lead to a significant dose exposure to the organs at risk (OAR)
Aim of this study is to evaluate the dosimetric effects of reduced longitudinal margins for neoadjuvant chemoradiation (nCRT) and definite chemoradiation (dCRT) of squamous cell carcinoma of the esophagus (SCC)
Summary
Esophageal cancer (EC) is the eighth most common cancer in the world and more than 450.000 new cases are diagnosed each year [1]. In the most recent study by van Hagen et al [10], which defined a new standard for nCRT in EC patients, the Planning Target Volume (PTV) was defined by adding longitudinal margins of 4 cm to the GTV. Today, when planning a neoadjuvant or dCRT for SCC the German S3-guideline [11] as well as the North American guidelines [5] recommend to define the clinical target volume (CTV) by adding a longitudinal safety margin of 3 cm to 4 cm and an axial margin of 1 cm to 1.5 cm to the GTV. To consider inter-fractional movement and anatomic changes due to breathing, another margin of 0.5–1.5 cm should be added to the CTV
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