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

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.