Lattice radiotherapy (LRT) is a novel technique of delivering inhomogeneous doses of radiation to voluminous tumors. LRT derives from the conventional two-dimensional grid, with the application of new technology including 3-D radiation therapy and planning, Image Guided Radiation Therapy (IGRT) and adaptive therapy. This allows the delivery of very high doses of radiation to small spheres, called vertices, within the tumor volume while limiting the exposure to surrounding normal tissue. In addition, there is a hypothesis that LRT induces modulation of the immune response, potentiating bystander and abscopal effects. Fifty-six patients, 37 females and 19 males, with a variety of bulky tumors in different sites and pathologic diagnoses were treated with palliative intent using LRT from April 2010 to April 2019. Forty-seven patients received LRT combined with conventional fractionated radiation therapy and 9 of them received LRT combined with SBRT. Table 1 shows the number of patients with diagnosis and treatment sites. Ages ranged from 19 to 93 years, (median 72 years). The tumor volumes ranged from 41 cc to 1495 cc (median 219 cc average 285 cc). The number of lattice vertices ranged from 2 to 15 with an average of 1.2 cm diameter. The ratio of the total volume of the vertices with respect to the GTV volume was an average of 2%. All treatment was delivered using Linac-based volumetric modulated arc therapy (VMAT) using cone-beam CT prior to every fraction. Our preliminary results in unselected palliative patients with voluminous tumors show that LRT was well-tolerated in all patients, independent of the primary sites. All patients but one had a rapid tumor response, with minimal toxicity. The median overall survival for the entire group was 11 months. The survival at 1, 2, 3 and 5 years was 47%, 30%, 12% and 5%, respectively. Eighteen of the 56 patients (31%) are alive with a median survival of 26 months ranging from 4 to 83 months. Of these 18 patients alive, 8 of them (5 with cervical cancer and 3 with lung cancer) are alive with no evidence of disease (NED) with a median follow-up of 47 months. This lattice experience is consistent with the literature of case reports and small series using this technique. In the alive cohort, the majority of patients had either locally advanced cervical or lung cancer achieving a median survival of nearly four years. This modality of treatment has the potential to improve local control and achieve long remissions in these advanced cancer patients. The minimal toxicity encountered in this group supports the need for further investigation.Abstract 3184; Table 1Number of patients by site and diagnosis.DiagnosisnPelvisLungsRetro-peritoneumH/NExtremityAbdomenMediastinumNSCLC181611Gynecological (14 cervical ca)17161Gyn Sarcoma22Sarcoma6222RCC55H/N44Skin11Melanoma11Anal11Colon11TOTAL56201875321 Open table in a new tab