ESTRO meets Asia 2024 - Abstract Book

S330

Physics – Motion management and adaptive radiotherapy

ESTRO meets Asia 2024

Anatomical change which causes by radiotherapy side effects is commonly seen among the patients. This study aims to define the influencing factors for ART, predicting an effective replan time frame in order to maximize the clinical benefits of ART.

Material/Methods:

91 H&N patients who underwent re-planning during their course of radiotherapy in year 2021 to 2023 were included in this study. The fractionation regime of their Volumetric Modulated Arc Therapy (VMAT) plan was range from 33 to 35 fractions with 2.00 to 2.12Gy per fraction. Patient’s weight loss and anatomical variation at neck area were investigated. MIM Precise Art software was used to capture the projected parotid glands mean dose and spinal cord maximum dose. The dosimetric impact caused by anatomical and positioning variation was then determined.

Results:

30 patients underwent re-simulation within 4 th week of radiotherapy treatment for the early needs of adaptive planning. 61 patients re-simulated after the 20 th fractions. The result depicted an average of 5.6 % of weight loss which was regardless of patient nutrition intake and swallowing difficulty/toxicity. Only small number of patients experienced weight loss of more than 10%. Left and right neck anatomical change which compared the last CBCT before re-planning with the CT planning images, varied between 0.5 to 1 cm. The projected spinal cord maximum dose did not reflect the same trend as anatomical change, and this could be due to patient positioning and setup especially when immobilization mask no longer well-fitted. The highest change in spinal cord dose was 12.8% (range from 0.1%-12.8%) from its original planned dose. The result depicted an average of 5.6 % of weight loss which was regardless of patient nutrition intake and swallowing difficulty/toxicity. Only small number of patients experienced weight loss of more than 10%. Left and right neck anatomical change which compared the last CBCT before re-planning with the CT planning images, varied between 0.5 to 1 cm. The projected spinal cord maximum dose did not reflect the same trend as anatomical change and this could be due to patient positioning and setup especially when immobilization mask no longer well-fitted. The highest change in spinal cord dose was 12.8%

Conclusion:

Weight loss and neck anatomical variation which can be detected by the radiation therapists would be the primary influencing factors on the H&N adaptive radiotherapy, followed by the dosimetric change of parotid glands and spinal cord. Close monitoring on anatomical variation in H&N radiotherapy patients should be started on the 3 rd week of treatment in order to track and trace the ideal time for re-simulation.

Keywords: H&N, Anatomical and positioning variation

References:

1. Metin F. et al. Evaluation of triggered adaptive Re-planning in Routine Practice. Front. Oncol. (2020) 10:579917

2. E. Brown et al. Head and neck adaptive radiotherapy: predicting the time to replan. Asia Pac J Clin Oncol. (2016); 12(4):460-467

3. Barragan-Montero et al. Dosimetrically triggered adaptive radiotherapy for head and neck cancer: Considerations for the implementation of clinical protocols. Radiation Oncology Physics.