ESTRO meets Asia 2024 - Abstract Book

S56

Interdisciplinary – Brachytherapy

ESTRO meets Asia 2024

Purpose/Objective:

High dose rate interstitial brachytherapy (HDR IBT) stands as a pioneering and extensively utilized technique for liver tumor management, owing to its capacity to deliver maximal radiation doses to the target while minimizing exposure to surrounding healthy tissues and organs at risk (OARs). This study aims to evaluate the dosimetric parameters of adjacent OARs—namely, the central liver structure (CLS), right chest wall (RCW), and right diaphragm (RD)—in HDR IBT for liver malignancies, utilizing the Iridium-192 (Ir 192) source. This evaluation is extremely important for clinical reference to preserve the OAR functionality based on clinical data from our center.

Material/Methods:

Computed tomography (CT) imaging was employed for treatment planning and subsequent retrospective analysis of dose distributions in the OARs among 55 patients who underwent a total of 89 HDR IBT treatment sessions. Data sourced from the Oncentra treatment planning system (TPS) facilitated statistical analysis of dosimetric variables, encompassing single and multiple fractionations of the prescribed dose ranging from 15 to 25 Gy, administered via HDR IBT for liver tumors.

Results:

Dosimetric analyses of OARs in this investigation were produced based on RTOG 0438, the liver SBRT protocol, and relevant literature. The recommended D50% values for CLS spanned from 10.11 Gy to 61.25 Gy, while D0.2cc values ranged from 27.31 Gy to 150.84 Gy across single and multiple fractionations, respectively. Similarly, recommended D50% values for RCW were ≤ 9.47 Gy and 11.46 Gy, with corresponding D0.2cc values of ≤ 31.54 Gy and 163.01 Gy, respectively. Lastly, recommended D50% values for RD were ≤ 17.63 Gy and 26.30 Gy, alongside D0.2cc values of ≤ 72.19 Gy and 297.14 Gy for both single and multiple fractionations, within the prescribed dose range of 15–25 Gy.

Conclusion:

In this study, we found that the higher doses received by the organs at risk (OAR) during high dose rate interstitial brachytherapy (HDR IBT) for liver cancer are not because of the size of the tumor or the dose given. This means that giving a higher dose is not always necessary for planning the best treatment. Instead, using what has been learned from clinical experience and following the guidelines about how much dose to give to the tumor and OARs in HDR IBT is important. When we looked at treatments given in either one or multiple sessions to 55 patients, we noticed that the smallest measured area (D0.2cc) of the three OARs received a high dose, which was quite different from the dose received by half of the volume (D50%) of these areas. This difference points out the importance of carefully managing the dose. To help with this, we suggest specific dose limits for each OAR: for the central liver structure (CLS), the total dose for half of its volume (D50%) should be between 10.11 Gy and 61.25 Gy, and the highest dose received by the smallest area (D0.2cc) should be between 27.31 Gy and 150.84 Gy, depending on if the treatment is given in one or multiple sessions. For the right chest wall (RCW), D50% should be no more than 9.47 Gy and 11.46 Gy, and D0.2cc should not exceed 31.54 Gy and 163.01 Gy, respectively. Lastly, for the right diaphragm (RD), D50% should be no more than 17.63 Gy and 26.30 Gy, with D0.2cc not exceeding 72.19 Gy and 297.14 Gy for treatments given in one or multiple sessions across the 15 – 25 Gy dose range. These recommendations aim to make the treatment effective while keeping the nearby tissues safe, showing the careful balance needed in planning HDR IBT for liver cancer.

Keywords: liver cancer, HDR IBT, dosimetry.