Lungtech, a phase II EORTC trial of SBRT for centrally located lung tumours – a clinical physics perspective

Abstract

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.

Cleaning the dose falloff in lung SBRT plan

“…The novel treatment planning methodology proposed here involves a new optimization shell structure (OptiForR50) designed by expansion of the PTV according to Eqs. (8) and (14) and criterion specified in Eq. (15) in addition to more conventional shells structures.…”

“…[4][5][6] American association of physicists in medicine's (AAPM) task group report #101 states that steeper dose falloff outside the target helps minimize normal tissue toxicity and spare nearby organs at risk (OAR). 7 However, stereotactic radiotherapy faces multiple challenges from normal tissue toxicity, 8 tumor motion, 9 interplay between tumor motion and multileaf collimator (MLC) 10 among others. With recent technological advances, volumetric modulated arc therapy (VMAT) presents highly conformal dose distribution and fast delivery times.…”

The impact of technology on the changing practice of lung SBRT

“…Innovations in intra fraction management arguably belong to the second category and will be welcome for a subgroup of patients with very mobile tumours. Improved imaging for contouring of tumours and organs at risk is also desirable especially in central lung tumours [113] , but we are presently missing data about which structures drive toxicity and how much they should be spared. When this knowledge becomes available, advanced delivery techniques (such as proton therapy or MRI-guided RT (Menten et al [114] this issue)) may prove valuable for a larger group of patients.…”

Novel methodologies for dosimetry audits: Adapting to advanced radiotherapy techniques

“…For stereotactic techniques the key areas of interest in the dosimetry audit lie in the accuracy of the small field and potential FFF modelling, as well as the targeting accuracy. Stereotactic Body Radiotherapy (SBRT) and Stereotactic Radiosurgery (SRS) dosimetry audits have been performed by means of measurements in anthropomorphic phantoms [41] , [42] , [43] , [44] . Audit results are included in Table 2 .…”