ESTRO 2025 - Abstract Book

S2847

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

2980

Digital Poster Dosimetric comparison of IMRT and VMAT Lattice radiation therapy (LRT) as a boost for locally advanced non-small cell lung carcinoma. Balaji Subramanian Sitaraman, Thuraya Al-Hajri, Khalsa Al Shukaili, Zakiya Al-Rahbi, Binukumar Johnson, Ahmed Al Habsi RADIATION ONCOLOGY, ROYAL HOSPITAL, MUSCAT, Oman Purpose/Objective: LRT-based Spatially fractionated Radiotherapy (SFRT) is suggested as an alternative to stereotactic body radiotherapy for escalating the dose to the primary lung tumor. SFRT, with its enhanced bystander effects, can improve outcomes for patients with Locally advanced non small cell lung carcinoma(LA-NSCLC) receiving immunotherapy. In an era of evolving immunotherapeutics, radiation-induced abscopal effects can be improved while respecting doses to the central airways, pulmonary veins, spinal cord, and heart. The current dosimetric study compares the quality of IMRT, and VMAT LRT plans which adhere to the recently proposed guidelines. Material/Methods: Ten patients with LA-NSCLC treated with conventionally fractionated radiotherapy were retrospectively selected for the study. IMRT and VMAT LRT plans with 1.5cm diameter lattice points spaced 3cm center to the center were generated for each patient using an identical CT data set to deliver 18Gy in 1 fraction. Contouring, constraints, and planning were aligned with those described recently (1). Maximum, minimum, and doses of 90%,50%,10%,and5% (e.g., D90%(%) -Minimum dose to X% of the GTV expressed as a percentage of the prescribed dose) of the GTV and total MU were compared. Dosimetric data was analyzed with descriptive statistics and the Mann-Whitney test to compare the significance of dosimetric parameters in both techniques. Results: GTV for our patients ranged from 135.9 to 419cm3 (Median:219.5cm3). Total number of lattice points ranged from 2-5. For VMAT and IMRT-LRT, the plans achieved comparable results for maximum, minimum, and D90%, D50%, D10%, and D5%. There was no variation in both techniques for heterogeneity(D10%/D90%). BODY-GTV V30%(cm3) was better with VMAT plans(p<0.05). Additionally, by its design, LRT delivers a minimal dose to surrounding organs at risk.

Conclusion: The present study suggests that VMAT-based LRT reduces low-dose exposure to healthy tissues beyond the target volume. Moreover, VMAT-based LRT may be an alternative to SBRT for safe dose escalation in large-volume lung tumors close to critical organs at risk. VMAT based SFRT boost merits evaluation in a prospective clinical trial.