Evidence supports stereotactic body radiotherapy (SBRT) as a curative treatment option for inoperable early stage nonsmall-cell lung cancer (NSCLC) resulting in high rates of tumour control and low risk of toxicity. However, promising results are mainly derived from SBRT of peripheral pulmonary lesions, whereas SBRT for the central tumours can lead to severe radiation sequelae owing to the spatial proximity to the serial organs at risk. Robust data on the tolerance of mediastinal structures to high-dose hypofractionated radiation are limited; furthermore, there are many open questions regarding the efficiency, safety and response assessment of SBRT in inoperable, centrally located early stage NSCLC, which are addressed in a prospective multicentre study [sponsored by the European Organization for Research and Treatment of Cancer (EORTC 22113-08113-LungTech)]. In this review, we summarize the current status regarding SBRT for centrally located early stage NSCLC that leads to the rationale of the LungTech trial. Outline and some essential features of the study with focus on a summary of current experiences in dose/fraction-toxicity coherences after SBRT to the mediastinal structures that lead to LungTech normal tissue constraints are provided.Stereotactic body radiotherapy (SBRT) is a technique in which high doses of radiotherapy are very precisely delivered with steep dose gradients and a short overall treatment time (OTT). This achieves a very high biological dose.1 Evidence supports SBRT as a curative treatment option for inoperable early stage non-small-cell-lung cancer (NSCLC).2-5 Highprecision, hypofractionated dose delivery enables a significant reduction in both target volume size and exposure of normal tissue (NT) to high doses, resulting in a decreased toxicity risk and high rates of local control.6-8 However, promising results are mainly derived from the SBRT of small peripheral pulmonary lesions with low risk of treatment-related toxicity, as these tumours are surrounded by parallel organs at risk (OARs), specifically lung tissue. In contrast, the SBRT for central tumours can lead to severe, potentially life-threatening radiation sequelae owing to the spatial proximity to serial OARs. As robust, prospective and multicentre data on the tolerance of mediastinal structures to high-dose hypofractionated radiation is limited, there is generally caution in implementing SBRT for central lung tumours. Current published data are rather inconsistent regarding the definition of "central tumour", SBRT techniques, dose prescription and reporting, calculation algorithms, image guidance and evaluation of outcome. A recent systematic review has summarized the current limited evidence on this topic, mainly from singlecentre experiences, 9 but there are still many open questions
BackgroundThe EORTC has launched a phase II trial to assess safety and efficacy of SBRT for centrally located NSCLC: The EORTC 22113-08113—Lungtech trial. Due to neighbouring critical structures, these tumours remain challenging to treat. To guarantee accordance to protocol and treatment safety, an RTQA procedure has been implemented within the frame of the EORTC RTQA levels. These levels are here expanded to include innovative tools beyond protocol compliance verification: the actual dose delivered to each patient will be estimated and linked to trial outcomes to enable better understanding of dose related response and toxicity.MethodFor trial participation, institutions must provide a completed facility questionnaire and beam output audit results. To insure ability to comply with protocol specifications a benchmark case is sent to all centres. After approval, institutions are allowed to recruit patients. Nonetheless, each treatment plan will be prospectively reviewed insuring trial compliance consistency over time. As new features, patient’s CBCT images and applied positioning corrections will be saved for dose recalculation on patient’s daily geometry. To assess RTQA along the treatment chain, institutions will be visited once during the time of the trial. Over the course of this visit, end-to-end tests will be performed using the 008ACIRS-breathing platform with two separate bodies. The first body carries EBT3 films and an ionization chamber. The other body newly developed for PET- CT evaluation is fillable with a solution of high activity. 3D or 4D PET-CT and 4D-CT scanning techniques will be evaluated to assess the impact of motion artefacts on target volume accuracy. Finally, a dosimetric evaluation in static and dynamic conditions will be performed.DiscussionPrevious data on mediastinal toxicity are scarce and source of cautiousness for setting-up SBRT treatments for centrally located NSCLC. Thanks to the combination of documented patient related outcomes and CBCT based dose recalculation we expect to provide improved models for dose response and dose related toxicity.ConclusionWe have developed a comprehensive RTQA model for trials involving modern radiotherapy. These procedures could also serve as examples of extended RTQA for future radiotherapy trials involving quantitative use of PET and tumour motion.
Background and Purpose: Extensive radiation therapy quality assurance (RTQA) programs are needed when advanced radiotherapy treatments are used. As part of the RTQA four dimensional computed tomography (4DCT) imaging performance needs to be assessed. Here we present the RTQA data related to 4DCT procedures used within the context of stereotactic body radiotherapy (SBRT) of centrally located lung tumours. It provides an overview of the 4DCT acquisition methods and achievable accuracy of imaging lung tumour volumes. Materials and Methods: 3DCT and 4DCT images were acquired from a CIRS phantom with spheres of 7.5 and 12.5 mm radius using the institutional scan protocols. Regular asymmetric tumour motion was simulated with varying amplitudes and periods. Target volumes were reconstructed using auto-contouring with scanner specific thresholds. Volume and amplitudes deviations were assessed. Results: Although acquisition parameters were rather homogeneous over the eleven institutions analysed, volume deviations were observed. Average volume deviations for the 12.5 mm sphere were 15% (−4% to 69%) at end of inspiration, 2% (−2% to 9.0%) at end of expiration and 12% (0% to 36%) at mid-ventilation. For the 7.5 mm sphere deviations were 13% (−99% to 65%), 16% (−34% to 66%) and 1% (−13% to 20%), respectively. The amplitude deviation was generally within 2 mm although underestimations up to 6 mm were observed. Conclusions: The expiration phase was the most accurate phase to define the tumour volume and should be preferred for GTV delineation of tumours exhibiting large motion causing motion artefacts when using midventilation or tracking techniques. The large variation found among the institutions indicated that further improvements in 4DCT imaging were possible. Recommendations for 4DCT QA have been formulated.
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