Comparison of two iodine-125 brachytherapy implant techniques for the treatment of lung tumor: Preplanning and intraoperative planning

Abstract

Purpose

To compare preplanning and intraoperative planning methods of lung tumor brachytherapy based on postimplant CT images and dosimetric outcomes.

Methods and Materials

Detailed postimplant evaluations of iodine-125 seed implants were performed in 15 patients using a preplanning technique and in 15 patients treated with an intraoperative planning technique. The implant details, dosimetric parameters, and implant quality indices were compared. Furthermore, the dose to the lung and the incidence of complications were compared.

Results

The planning target volume was similar in both groups (p = 0.496). The median V_100%, V_150%, and V_200% values (the percent of the planning target volume receiving 100%, 150%, and 200% of the prescription dose) for the intraoperative planning technique were 95.65%, 76.47%, and 59.80%, respectively. The median V_100%, V_150%, and V_200% values for the preplanning methodology were 88.86%, 69.23%, and 28.30%, respectively (p < 0.01). The median values of the coverage index, c1, conformity index, and plan quality index were higher in the intraoperative planning group than in the preplanning group (p < 0.05). The overdose volume index and dose nonhomogeneity ratio were higher in the intraoperative group (p < 0.05), and the dose homogeneity index was lower in the intraoperative group (p < 0.05) than in the preplanning group. No significant differences were observed in the reference dose (V_REF), external index, or lung doses between the two groups. The incidences of pneumothorax and hemoptysis were minimal in both groups.

Conclusion

These data showed that the intraoperative planning method was superior to the preplanning method for the treatment of lung tumors.

Introduction

CT-guided iodine-125 (I-125) seed stereotactic brachytherapy (SBT) has been used for many years in the treatment of lung tumors (1). Our previous studies showed that I-125 brachytherapy could enhance the clinical efficacy and improve the overall survival of patients with advanced nonsmall cell lung cancer (NSCLC) (2). We compared the dosimetric differences between SBT and stereotactic body radiation therapy (SBRT) for the treatment of non-small cell lung cancer. Our data showed that, compared with SBRT, SBT can generate a comparable dose within the planning target volume (PTV), while the organs at risk (OARs) only receive a very low dose (3). However, the plans were generated in the preplanning model. Preplanning refers to a treatment plan created a few days before implantation that includes determining the number of I-125 seeds and needle locations. Although the treatment planning system (TPS) can generate perfect treatment planning using patients' CT images gained several days before implantation, it is impossible to mirror the preplan in the operating room (OR). This method has some limitations. First, when CT images are obtained several days before implantation, the tumor volume and shape might change between the preplanning period and the time of implantation. Second, it is difficult to replicate the patient position and images acquired during the preimplant planning study in the OR. Third, because of lung movement, rib obstruction and the need to avoid vascular structures, the treatment plan should be revised during surgery. Implantation in full accordance with the preplan is usually impossible.

To overcome these disadvantages, we turned to permanent prostate brachytherapy for inspiration. In 2000, the American Brachytherapy Society noted that, “Ideally, one should strive for online, real-time intraoperative dosimetry to allow for adjustment in seed placement to achieve the intended dose” (4). Many institutions have performed and refined intraoperative treatment planning with a goal of achieving this ideal [5], [6], [7]. Beginning in February 2017, we attempted to use this treatment planning approach for the treatment of lung tumors. To compare preplanning and intraoperative planning methods of lung tumor brachytherapy, we evaluated the dosimetry differences in 30 consecutive patients who were treated with the preplanning or intraoperative planning methods.