Lattice Radiation Therapy in clinical practice: A systematic review

Abstract

Purpose: Lattice radiation therapy (LRT) is an innovative type of spatially fractionated radiation therapy. It aims to increase large tumors control probability by administering ablative doses without an increased toxicity. Considering the rising number of positive clinical experiences, the objective of this work is to evaluate LRT safety and efficacy.

Method: Reports about LRT clinical experience were identified with a systematic review conducted on four different databases (namely, Medline, Embase, Scopus, and Cochrane Library) through the August 2022. Only LRT clinical reports published in English and with the access to the full manuscript text were considered as eligible. The 2020 update version PRISMA statement was followed.

Results: Data extraction was performed from 12 eligible records encompassing 7 case reports, 1 case series, and 4 clinical studies. 81 patients (84 lesions) with a large lesion ranging from 63.2 cc to 3713.5 cc were subjected to exclusive, hybrid, and metabolism guided LRT. Excluding two very severe toxicity with a questionable relation with LRT, available clinical experience seem to confirm LRT safety. When a complete response was not achieved 3-6 months after LRT, a median lesion reduction approximately ≥50 % was registered.

Conclusion: This systematic review appear to suggest LRT safety, especially for exclusive LRT. The very low level of evidence and the studies heterogeneity preclude drawing definitive conclusions on LRT efficacy, even though an interesting trend in terms of lesions reduction has been described.

Keywords: Abscopal effect; Bulky; LRT, Lattice Radiation Therapy; Lattice radiation therapy; Lattice radiotherapy; OAR, Organ At Risk; Radiation therapy; Radiotherapy; SFRT, Spatially Fractionated Radiation Therapy; Spatially fractionated radiotherapy; TCP, Tumor Control Probability.

Fig. 1

Fig. 1 shows the difference between the dose distribution of a conventional RT (on the left) and a LRT (on the right). In this example the conventional RT is a neoadjuvant irradiation of a rectal cancer, where the green area displays the isodose 25 Gy of the treatment plan. In is worth noting how the target irradiation is homogeneous. By contrast on the right it is illustrated a LRT treatment where the blue area represents the low dose regions (namely, the periphery or the valleys), while the red hotspots are the dose peaks (namely, the vertices). The right column shows how in LRT the irradiation is heterogeneous allowing delivering lower doses in the lesion periphery –i.e., near OARs-, while ablative doses are administered to the inner subvolumes. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

The figure shows the difference between the GRID RT (above) and the LRT (below). GRID RT is a 2D-dimensional approach where a group of parallel photon beams go through the target with a space disposition similar to a group of pens in a closed hand. By contrast, in LRT the photon beams are delivered with different directions. Hence, the LRT allows creating a three-dimensional array or matrix where the area of high and low doses alternates in all spatial directions.