Lattice radiotherapy: where less is more?

Abstract

We read with great interest the case report by Iori et al. who treated a large sarcomatoid lung cancer with lattice radiotherapy (LRT) (1). The authors reported good radiological response and patient reported symptom relief. We commend their efforts in implementing this emerging radiotherapy technique at their centre. We hope that this case report raises awareness and interest in the implementation of LRT in other institutions.LRT derived its basis from grid radiotherapy (GRID RT), where a wide radiation beam is passively filtered through a heavy metal block to deliver radiation in beamlets. This technique was popularized in the 1990s by Mohiuddin et al., with patients experiencing good clinical response despite partial irradiation of tumours, albeit at high doses (2). There were subsequently many pre-clinical and clinical studies exploring different aspects of GRID RT (3-5). However, the use of GRID RT remains limited to few centres worldwide. Possible reasons include difficulties with commissioning and delivering treatment with a GRID block or multileaf-collimator. As GRID RT is delivered as a static field, treating deep seated tumours may be difficult without unnecessary risk to adjacent organs at risk.Since the initial reports from Mohiuddin et al, we have seen technological advances in radiotherapy equipment and techniques over the past few decades. The early 2000s have seen the advent of intensity modulated radiotherapy that enabled us to deliver radiation via dose painting. Radiation techniques have also evolved with time and ablative doses can now be delivered via stereotactic body radiotherapy (SBRT). However, the lesions treatable with SBRT is often limited by size.So how do we marry the learnings of GRID RT and SBRT in the treatment of large tumours? LRT may be a potential solution. In essence, LRT takes dose painting to the extreme by delivering precise SBRT-like doses to spherical sub-volumes termed vertices, spread out within the tumour whilst simultaneously covering the entire tumour to a lower dose. In two recently reported studies, namely the LITE-SABR-M1 trial (6) as well as the LATTICE_01 study (7), we now have good clinical evidence supporting the use of this emerging radiotherapy technique.The LITE-SABR-M1 trial was a single-arm phase I trial conducted between October 2019 and August 2020 on 22 patients with tumours >4.5 cm. LRT technique was as described in the accompanying case report, except that the vertices received 66.7 Gy instead of 50 Gy. Importantly, concurrent systemic therapy was not allowed and a 2 week washout period was recommended before and after LRT. The authors reported a good safety profile with no treatment related grade 3 or more toxicity noted in the acute period. Patients also reported improvements in anxiety, depression, pain interferences, physical global health and physical function. Whilst not the primary endpoint, good radiological tumour responses were also