High-dose spatially-fractionated radiation (GRID): a new paradigm in the management of advanced cancers

Abstract

Purpose: With the advent of megavoltage radiation, the concept of spatially-fractionated (SFR) radiation has been abandoned for the last several decades; yet, historically, it has been proven to be safe and effective in delivering large cumulative doses (> 100 Gy) of radiation in the treatment of cancer. SFR radiation has been adapted to megavoltage beams using a specially constructed grid. This study evaluates the toxicity and effectiveness of this approach in treatment of advanced and bulky cancers.

Methods and materials: From January 1995 through March 1998, 71 patients with advanced bulky tumors (tumor sizes > 8 cm) were treated with SFR high-dose external beam megavoltage radiation using a GRID technique. Sixteen patients received GRID treatments to multiple sites and a total of 87 sites were irradiated. A 50:50 GRID (open to closed area) was utilized, and a single dose of 1,000-2,000 cGy (median 1,500 cGy) to Dmax was delivered utilizing 6 MV photons. Sixty-three patients received high-dose GRID therapy for palliation (pain, mass, bleeding, or dyspnea). In 8 patients, GRID therapy was given as part of a definitive treatment combined with conventionally-fractionated external beam irradiation (dose range 5,000-7,000 cGy) followed by subsequent surgery. Forty-seven patients were treated with GRID radiation followed by additional fractionated external beam irradiation, and 14 patients were treated with GRID alone. Thirty-one treatments were delivered to the abdomen and pelvis, 30 to the head and neck region, 15 to the thorax, and 11 to the extremities.

Results: For palliative treatments, a 78% response rate was observed for pain, including a complete response (CR) of 19.5%, and a partial response (PR) of 58.5% in these large bulky tumors. A 72.5% response rate was observed for mass effect (CR 14.6%, PR 52.9%). The response rate observed for bleeding was 100% (50% CR, 50% PR) and for dyspnea, a 60% PR rate only. A relatively higher response rate (CR 23.3%, PR 60%) was observed in patients who received GRID treatment in the head and neck area. No grade 3 late skin, subcutaneous, mucosal, GI, or CNS complications were observed in any patient in spite of these high doses. In the 8 patients who received GRID treatment for definitive treatment, a clinical CR was observed in 5 patients (62.5%) and a pathological complete response was confirmed in the operative specimen in 4 patients (50%).

Conclusion: The efficacy and safety of using a large fraction of SFR radiation was confirmed by this study and substantiates our earlier results. In selected patients with bulky tumors (> 8 cm), SFR radiation can be combined with fractionated external beam irradiation to yield improved local control of disease, both for palliation and selective definitive treatment, especially where conventional treatment alone has a limited chance of success.