ESTRO 2024 - Abstract Book

S4075

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Dose accumulation using DIR in the management of multiple SABR reRt in Hepatocellular Carcinoma

AHAMED BADUSHA MOHAMED YOOSUF 1,2 , Mohd Zahri Bin Abdul Aziz 3 , Mohd Syahir Mansor 3 , Gokula Kumar Appalanaido 3 , Salem Alshehri 1,2 , Mamdouh Alqathami 1,2,4 1 King Abdullah Specialized Children Hospital, Oncology, Riyadh, Saudi Arabia. 2 King Abdullah International Medical Research Centre, Clinical Research, Riyadh, Saudi Arabia. 3 Advanced Medical & Dental Institute, Radiation Oncology, Penang, Malaysia. 4 King Saud Bin Abdulaziz University for Health Sciences, Radiological Sciences, Riyadh, Saudi Arabia

Purpose/Objective:

Stereotactic ablative radiotherapy (SABR), or delivery of a highly biologically effective dosage to recurring tumors previously treated with radiotherapy (RT), has emerged as a feasible treatment option for patients who have failed earlier RT or are not surgical candidates. However, multiple re-irradiations pose new obstacles and raise the issue of a safe tolerated dose to nearby organs at risk (OAR). In clinical practice, the physical summation of doses for OARs from each irradiation is often utilized to assess accumulation of doses in individual organs at risk. The alignment of anatomic structures in the second or subsequent treatment with re-irradiation may shift noticeably due to factors such as tumor growth, changes in patient weight, surgery, or rigidity after past treatment. Image registration methods are becoming increasingly crucial in measuring delivered dosage and modifying treatment to patient changes as radiation therapy progresses towards more adaptive procedures. We hypothesized that deformable registration will allow us to calculate an accurate cumulative dose to OARs from multiple re-irradiations. The purpose of this study was to compare the cumulative dose to OARs using deformable image registration (DIR) with MIMs software to the physical sum dose in the management of stereotactic (Cyberknife) based re-irradiation (reRt) in hepatocellular carcinoma (HCC).

Material/Methods:

Between June 2016 and March 2022, 10 HCC patients and 31 treatment plans for recurrent or residual tumors who received multiple re-irradiation treatments (minimum - 2 treatments; maximum - 5 treatments) using CyberKnife based stereotactic radiotherapy utilizing DIR method were studied. The median total prescribed radiation doses at initial treatment and subsequent re-irradiation were 49 Gy (range, 18-60 Gy in 3 to 5 fractions) and 48 Gy (range, 10 - 54 Gy in 1 to 5 fractions), respectively. The DIR was used to superimpose the dose distribution of the previous treatments onto the latest retreatment plan. The maximum, minimum, and mean doses for various OARs were calculated using physical dose summation and DIR. The Dice Similarity Coefficient (DSC) was utilized in the DIR assessment, as specified by AAPM TG132. Furthermore, radiobiological impacts were considered using EQD2 calculations.

Results:

Table 1 lists the dose summation indices determined for various OARs. The small bowel had the lowest DSC values (0.20 ± 0.05), whereas the left kidney had the highest similarities (0.93 ± 0.1). The dosimetric impact of DIR was most clearly observed in situations where the small bowel volume was significantly altered at reRT compared to the initial course of radiation.