Early clinical results of proton spatially fractionated GRID radiation therapy (SFGRT)

Abstract

Objective: Approximately 70 patients with large and bulky tumors refractory to prior treatments were treated with photon spatially fractionated GRID radiation (SFGRT). We identified 10 additional patients who clinically needed GRID but could not be treated with photons due to adjacent critical organs. We developed a proton SFGRT technique, and we report treatment of these 10 patients. Methods: Subject data were reviewed for clinical results and dosimetric data. 50% of the patients were metastatic at the time of treatment and five had previous photon radiation to the local site but not via GRID. They were treated with 15–20 cobalt Gray equivalent using a single proton GRID field with an average beamlet count of 22.6 (range 7–51). 80% received an average adjuvant radiation dose to the GRID region of 40.8Gy (range 13.7–63.8Gy). Four received subsequent systemic therapy. Results: The median follow-up time was 5.9 months (1.1–18.9). At last follow-up, seven patients were alive and three had died. Two patients who had died from metastatic disease had local shrinkage of tumor. Of those alive, four had complete or partial response, two had partial response but later progressed, and one had no response. For all patients, the tumor regression/local symptom improvement rate was 80%. 50% had acute side-effects of grade1/2 only and all were well-tolerated. Conclusion: In circumstances where patients cannot receive photon GRID, proton SFGRT is clinically feasible and effective, with a similar side-effect profile. Advances in knowledge: Proton GRID should be considered as a treatment option earlier in the disease course for patients who cannot be treated by photon GRID.

Divide and conquer: spatially fractionated radiation therapy

“…The treatment of 10 patients (large tumours) proton GRID therapy (1 cm-wide beams) with palliative intent has been reported (Ref. 31). The median time to last follow-up was around 6 months.…”

Proton minibeam radiation therapy: a promising therapeutic approach for radioresistant tumors

“…Indeed, ten patients with large tumors have already been treated with proton GRID therapy (1-cm wide beams) [34] with palliative intent. These patients had tumors that could not be treated with photons, standard broad-beam irradiation, or photon GRID due to the tolerance of normal tissues.…”

“…En effet, dix patients atteints de tumeurs de grande taille ont déjà été traités par protonthérapie GRID (faisceaux de 1 cm de large) [34] dans un but palliatif. Ces patients avaient des tumeurs qui ne pouvaient pas être traitées avec des photons, une irradiation standard à large faisceau ou une GRID aux photons en raison de la tolérance des tissus normaux.…”

History and current perspectives on the biological effects of high-dose spatial fractionation and high dose-rate approaches: GRID, Microbeam & FLASH radiotherapy

“…After initial studies over the years suggested that patients may benefit from GRID applications to their tumour, several new strategies for applying GRID with photons in IMRT treatment plans or with protons have emerged with advancing technological capabilities (36)(37)(38). These advanced GRID techniques allow for the delivery of spatial fractionation to deep seated bulky tumours and dose sparing to normal tissues.…”