ESTRO 2024 - Abstract Book

S1916

Clinical - Mixed sites, palliation

ESTRO 2024

Federico Iori 1 , Patrizia Ciammella 1 , Sebastiano Finocchi Ghersi 1 , Andrea Botti 2 , Valeria Trojani 2 , Mauro Iori 2 , Cinzia Iotti 1 1 Azienda USL-IRCCS di Reggio Emilia, Radiation Oncology Unit, Reggio Emilia, Italy. 2 Azienda USL-IRCCS di Reggio Emilia, Medical Physics Unit, Reggio Emilia, Italy

Purpose/Objective:

Lattice Radiation Therapy (LRT) is an innovative irradiation technique developed to improve large neoplastic lesions response with a toxicity similar to a conventional palliative radiotherapy. LRT aims delivering ablative doses by an inhomogeneous target irradiation, where the areas of high and low doses alternate as peaks and valleys [1]. Although the LITE SABR M1 study highlighted the short-term safety of exclusive LRT (i.e., LRT delivered with several simultaneous integrated boosts) as suggested by a recent systematic review, no clear data about exclusive LRT efficacy is currently available [2, 3]. Thus, the purpose of this work is to investigate exclusive LRT efficacy in patients affected by a symptomatic voluminous lesion, concurrently reporting treatment related toxicity.

Material/Methods:

We reviewed all patients treated with an exclusive LRT at our institution until March 2023. Patients were considered eligible if they had had at least 1-week systemic therapy washout before and after exclusive LRT administration. The primary endpoint was the Objective Response Rate (ORR) at the 3-month CT, in accordance with RECIST 1.1 criteria. The secondary endpoints were the assessment of median lesions reduction at 90 days, concurrently investigating treatment related toxicity according to the CTCAE v5.0 scale.

Results:

From December 2021 to March 2023, 20 metastatic palliative patients with a median age of 69 years (range 18-85 years) were treated (10 males and 10 females). Median Karnofsky Performance Status was 80 (IQR1-3: 80-90). All patients were symptomatic due to a voluminous cancer lesion, in progression despite systemic therapies, and with no room for SBRT, debulking surgery, or further chemotherapy. Lesions were located in the cranium (n=1; 5%), the thorax (n=7; 35%), the abdomen (n=3; 15%), the pelvis (n=4; 20%) and the extremities (n= 5; 25%). With reference to lesions histology, there were NSCLC (n= 5; 25%), sarcoma (n=5; 25%), renal cell carcinoma (n=3; 15%), ovarian cancer (n=2; 10%), melanoma (n=2; 10%), rectal cancer (n=1; 10%), and glioblastoma (n=1; 10%). Median lesions volume (GTV) resulted 475.4 cc (IQR1-3: 269.8-997.1 cc), for a median PTV of 796.4 cc (IQR1-3: 490.4-1582.9 cc). The LRT treatment consisted in 5 consecutive LRT fractions for a total dose of 20 Gy prescribed to the PTV, with several simultaneous integrated boosts up to 66.70 Gy (hotspots), delivered to discrete sub-volumes, geometrically located inside the GTV. An in-house algorithm that maximizes hotspots generation and their disposition according to target shape and dimension, automatically performed this process. Per plan, a median number of 4 arcs (range: 4-6) was used, with a median hotspots number of 12 (IQR1-3: 9-17), and a vertices diameter of 1-1.5 cm. At 90 days follow up, only 14 patients were alive and underwent the 3-month reassessment CT. The ORR was 64% with a median lesion reduction of 54% (IQR1-3: 27-69%). The patients with partial response (PR), stable disease (SD), and progressive disease (PD) were 9, 5, and 0, respectively, according to RECIST1.1 criteria. Patients with PR reported a median lesion reduction of 66% (IQR1-3: 55-72%). All patients had an immediate antalgic benefit after LRT, with an improvement in Patient Acceptable Symptom State (PASS). No > G3 treatment related toxicity was recorded during the 3-month follow up period. No death was related to LRT administration.