Author: Mohamed Bahaaeldin Mohamed Afifi, Lili Chen, Xiaoming Chen, Ahmed A. Eldib, Chang Ming Charlie Ma, Robert A. Price 👨🔬
Affiliation: Fox Chase Cancer Center, Radiological Sciences and Medical Imaging Department, College of Applied Medical Sciences, Prince Sattam bin Abdulaziz University. 🌍
Purpose: Reirradiation of recurrent cancer or a newly developed lesion in a proximal location poses a challenge for radiation treatments. This is occasionally encountered in many modern clinics and efforts are needed to ensure the non-exceedance of the dose constraints of the different critical organs. In this work, we present our adaptive radiotherapy approach to spare those preirradiated structures.
Methods: Adaptive radiotherapy treatments are conducted in our department using Ethos CBCT-based system since February 2023. CT images for patients with prior treatments were fused to the patient’s previous planning CT images. The region of prior irradiation was delineated by resampling the previous dose distribution into the patient’s new CT images. New limits for normal structures were derived based on the allowed remining dose after what was received in previous treatments. We proposed the generation of a target alignment structure comprising the clinical target volume united with a bony landmark and any implanted fiducials. We also generated a prior-irradiation alignment structure that represents a union of the region of prior treatment and a bony landmark. Those two alignment structures will serve as a guide for positioning the target and defining the preirradiated area while utilizing the Ethos propagation function during the adaptive session.
Results: For Stereotactic 5 fraction treatment of liver lesions, we were able to keep the radiation confined to certain liver sectors to ensure that a volume more than or equal to 700cc was not irradiated by a dose more than 21Gy. For lesions near the small bowel, it was shown in some fractions that the adaptive plan was meeting the maximum dose limit which was going to be exceeded if the original scheduled plan was used for patient treatment.
Conclusion: Adaptive planning can aid in monitoring the preirradiated sites and help in avoiding over-irradiation of critical organs.