Session Item

Purpose: The number of centers that are treating lung lesions with Stereotactic Body Radiation Therapy (SBRT) is increasing, but its technical implementation is still very heterogeneous. This study reports the results of the ESTRO 2021 survey on harmonization and standardization of SBRT planning. The study aimed toprovide insight into current practice and issue guidance for future developments and standard setting on the technical implementation of lung SBRT.

Methods: A survey was distributed online among ESTRO members and some European National associations of medical physicists. The questionnaire was designed based on recommendations given by Burns et al. (2008). Branching logic was used to minimize the number of unnecessary questions that respondents were presented with. Wherever possible closed questions and multiple choice questions were used to reduce the number of similar responses.  The length of the questionnaire was limited to 33 questions which focused on the center’s standard practice of lung SBRT and covered several aspects of delivery, prescription, planning details, motion management, IGRT and QA protocols.  

Results: A total of 309 answers were collected. After a thorough data cleaning 244 complete and unique answers were gathered. 39 repeated answers (different individuals from the same center or same individual answering two times) was used for robustness analysis. 39 countries participated, 88% of which were from Europe.  67% of respondents had at least 5 years experience, almost 50% treat between 50 and 250 patients per year. A C-arm linac was by far the most common treatment device. 98% of the participants treat lungs (80% of which even treat in the central zone) but a wide range of sites are also treated in SBRT regime (bone metastases, liver, prostate and pancreas were the most common indications).

The large majority (~75%) prescribes to the PTV asking to cover it with at least 95% of the prescription dose. The spectrum of  fractionation schemes is broad. Only one third of responders assess target homogeneity while conformity or gradient index are mainly used to assess conformity. 70% of the centers treat with VMAT and only 15% assess plan complexity. Various dose calculation engines are used and dose is almost equally reported to medium or water. 65% uses a grid spacing between 1 and 2mm, approximately 50% computes the dose on an averaged intensity projection CT and 90% manage the motion through the contouring of an ITV based mainly on MIP or sum of phases coming from a 4DCT scan. A large majority create the PTV adding isotropically 5mm to the ITV. The IGRT protocols are mainly based on pre-treatment CBCT (~55%) or 4DCBCT (~25%) with a broad spectrum of set-up correction recipes. Only 19% use implanted fiducials to treat lung lesions. The large majority of responders perform patient specific QA before the start of the treatment for every single patients most of which via direct measurements or independent software comparison. AAPM TG-101 (30%) and UK consortium guidelines (26%) are by far the two most common adopted guidelines. Only 35% of centers participated in an inter-centre credentialing in the last 5 years.

Conclusions: The survey revealed a fairly clear, but varied, picture regarding platform and delivery techniques, target volume, target coverage and movement management habits. The details on dose prescribing, dose planning and calculation showed a large dispersion, thus a general lack of consensus. Harmonization efforts should focus on these aspects.