Abstract
PurposeDose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions.Materials and methodsThis was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3 × 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided.ResultsIn all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found.ConclusionsThis planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions.
Highlights
Lung cancer is responsible for the highest number of cancer deaths in males and females worldwide
A recent multicenter planning study from Giglioli et al [13] showed that the general equivalent uniform planning target volume (PTV) dose varied between 105 and162 Gy if only the dose per fraction was specified without further specification on the dose prescription and normalization method, the dose inhomogeneity and PTV constraints
Contouring of the gross tumor volume (GTV) was performed in the lung window and an internal target volume (ITV) was generated as the encompassing of all tumor positions based on a four dimensional (4D) computed tomography (CT)
Summary
Lung cancer is responsible for the highest number of cancer deaths in males and females worldwide. Surgical resection is standard of care, but growing numbers of patients are medically inoperable due to their age and comorbidities. In patients with untreated early stage non-small cell lung cancer (NSCLC) the median survival is 13 months and the 5-year cancer-specific survival rate is 16% [1]. In these patients, being inoperable or refusing surgery, the standard of care is stereotactic body radiation therapy (SBRT) [2,3,4,5]. A recent multicenter planning study from Giglioli et al [13] showed that the general equivalent uniform planning target volume (PTV) dose varied between 105 and162 Gy if only the dose per fraction was specified without further specification on the dose prescription and normalization method, the dose inhomogeneity and PTV constraints
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