153 Lattice radiotherapy (LRT): Safely Dose Escalating Palliative Radiotherapy

Abstract

Introduction Lattice radiotherapy (LRT) is a novel technique of delivering inhomogeneous doses of radiation to voluminous tumours. LRT is relevant in the treatment of large tumour volumes where standard palliative radiotherapy doses are unlikely to achieve meaningful tumour and symptom control, and dose escalation to the entire PTV is likely to carry a significant risk of increased toxicity. For lattice radiotherapy, a 3D-array of focal hot spots called vertices are created within the tumour PTV. The vertices are postulated to produce more efficient immunogenic cell death whilst the remainder of the PTV is covered by a standard palliative dose. Method We have successfully used hybrid lattice radiotherapy to treat a 55-year-old gentleman with rapid recurrence of his thoracic lung adenocarcinoma following previous pneumonectomy. He developed multiple embolic infarcts following 2 cycles of chemoimmunotherapy. Lattice radiotherapy was offered to optimise local control. The target PTV was treated with 30 Gy in 10 fractions daily with an additional four 10Gy lattice vertices volumes within the PTV volume (1909.67 cc) on day one. Each vertex was 1 cm in diameter and positioned >= 2 cm from other vertices (in 3D) and OARs. (See diagram). [Formula presented] Results The entire treatment was delivered successfully and at 4-weeks post treatment, the patient remained alive with grade 2 oesophagitis and intermittent worsening of tumour related chest pain requiring an increased need for PRN opiates. There was no clinical or biochemical evidence of tumour lysis. Conclusion Lattice radiotherapy has a huge potential role in helping select patients with large volume tumours achieve effective palliation of symptoms. Current evidence is strongly supportive of its tolerability, which our patient demonstrates. Future strategies to optimise its success include combining it with immunotherapy to harness its immunogenic potential, and also the integration of FDG PET to guide the location of the vertices within the tumour PTV. Disclosure No significant relationships.