MR‐guided 125I seed implantation treatment for maxillofacial malignant tumor

Abstract Purpose This study assessed the therapeutic efficacy of postoperative magnetic resonance (MR)‐guided interstitial 125I seed implantation for treatment of oral and maxillofacial malignant tumors. Methods and Materials A total of 127 patients with oral or maxillofacial malignant tumors were included in this study who received interstitial 125I treatment after the surgery resection. Before implantation, all the patients received MR scans to assess the lesion scope, extent, and nature. 125I implantation target regions were based on the pre‐operative imaging. 125I seeds were delivered to target regions via puncture needles under the real‐time guidance of MR. Computed tomography (CT)or MR was performed immediately after implantation and again every 3 months later. Results After successful 125I implantation, all patients were also examined regularly to detect tumor recurrence, lymphatic, and distant metastases. To date, CT or MR verification showed that 13/127 patients experienced tumor recurrence or lymphatic metastasis or distant metastasis. No seeds migration was observed, no serious treatment‐related complications affected patient quality of life, and no important organ (such as major cervical vessels, spinal cord, etc.) injuries were observed. Conclusion Our results show that MR‐guided 125I implantation is an effective approach to site‐specific treatment for oral and maxillofacial tumor, which could potentially reduce postoperative complications and tumor recurrence rates, increase patient survival, and improve quality of life.

125 I brachytherapy is clinically efficient against malignancies, which can reduce complications from the conventional external beam radiotherapy and improve patient quality of life. [10][11][12] To achieve optimal clinical therapeutic effects, the 125 I implantation plan implemented in the present study was designed by a treatment planning system (TPS) with patient imaging data. 125 I was delivered to a pre-operatively designated target region under real-time magnetic resonance imaging (MR) guidance. 13 Accordingly, the target region received stable, short-range radiation, with scarce damage to normal tissues. 14,15 During conventional computed tomography (CT)-guided surgery, artifacts from the metal puncture needle used for 125 I implantation can interfere with lesion images. The present study used MR due to its enhanced sensitivity without artifacts compared to CT. The MR-guided technique was proved to have good therapeutic effects in the treatment of lung and liver cancers. 16

2.C | 125 I implantation
Before surgery, all the patients received MR scans to assess lesion scope, extent, and nature. We designated the target regions according to MR (Fig. 2). Radioactive 125 I seeds were delivered to these target regions via puncture needles under real-time MR guidance (Fig. 3) according to the Paris principles at the depth of 10 mm, and the space between each implantation was 1 cm. Postoperation CT scans were input into the TPS to detect seed locations and distributions. If seeds were poorly positioned, the radiotherapy efficacy could be reduced, then a group of extra seeds was implanted. The MPD was 60 Gy, D90 was >80 Gy, and V150 was <50%.

2.D | Post-implantation verification and reexamination
CT scans were performed 48 h after implantation, and the data were added to the TPS. The verification of implanted seed locations and distributions was accomplished by comparing pre-implantation and post-implantation data of CT and MR. 18,19 Once the "cold spots" (the pre-designed regions with no seeds) were found, the re-implantation would be conducted in time. Then patients were observed every 3 months to assess the therapy efficacy. If there were no abnormalities during the first postoperative year, patients were assessed every 6 months thereafter. In addition to the routine physical examination, cervical ultrasound was performed to detect the possible lymph node metastasis. For adenoid cystic carcinomas, chest X rays were performed to detect lung metastases. For those patients suspicious for regional recurrence, CT scans were performed and compared with pre-operative MR.

2.E | Quality of life evaluation
The quality of life (QOL) of these patients was assessed by using the

| RESULTS
The average follow-up period was 54.6, and 36 months was the minimum for a case to be included in the series. In total, 127 patients received 125 I implantation in our study ( Table 1). The number of seeds varied from 10 to 145 (average, 40.79). No "cold spots" were discovered. Post-implantation CT verifications showed that all seed distributions and positions were consistent with pre-operatively designated target areas. There were no cases of seed migration.
Only 13/127 cases experienced tumor recurrence or metastasis ( Fig. 4), with a local control rate of 89.76% (

| DISCUSSION
Surgical excision is the conventional treatment for oral and maxillofacial malignant tumors. 20,21 Postoperative radiotherapy is usually applied for high-grade malignant tumors and nerve-involved tumors. 22 Compared with surgical resection alone, surgical excision plus postoperative radiotherapy can greatly increase oral and maxillofacial malignancy local control and long-term survival rates. 5,23 However, the conventional external beam radiotherapy can seriously damage normal tissues, leading to oral mucositis, hemorrhage, xerostomia, radiation caries and orradionecrosis of the jaws. 11,24 Precision radiotherapy aims to improve radiation curative effects and reduce side effects by targeting lesions with more precise radiation doses and protect normal tissues. The 125 I radionuclide has low photon energy, and a short effective penetration distance in tissues, 25,26 and 125 I is now commonly used as a supplementary therapy for malignant tumors, including lung, rectal, liver, breast, and cervical cancers, osteosarcomas, and others. [27][28][29][30] The curative effects of brachytherapy are mainly determined by the precise assessment of target lesion positioning, precise distribution of the radiation dose and an accurate radiation plan. The most critical aspect of the treatment plan is the precise implantation of radioactive seeds to protect normal tissues. While CT-guided implantation was used widely in the past, 31-34 MR has higher spatial and density resolutions and can clearly show lesion shape, size, and anatomic relationship with the surrounding tissues. MR can also reconstruct three-dimensional images by basing on cross-sections, providing more accurate targeting. In addition, the scattering of the metal puncture needle could hindered exact positioning of lesions at CT-guided radioactive 125 I implantation. 35,36 As MR has enhanced sensitivity compared to CT, it can provide real-time guidance during radioactive 125 I implantation, and allow puncture needle insertion at a safe and exact angle, depth, and position, and prevent important structures from injury. MR imaging can also be used for verification after implantation. Once "cold spots" are discovered, seeds can be re-added immediately. Then MR can be used to monitor radioactive seeds distribution and assess treatment efficacy. accurately, without major negative impacts to normal tissues. During follow-up, seed distributions remained consistent with pre-operative treatment plans, no seed migration was observed, and the local tumor control was satisfactory. MR guidance therefore enables additional therapeutic opportunities for patients. However, MR application is still restricted due to high device and examination expenses, and interference by pulsing blood vessels near lesions.
Novel technological developments are needed to overcome these limitations.
Importantly, the factors such as tumor type, patient clinical characteristics, biological features, and pathological results must be considered in order to pinpoint ideal target regions for 125 I implantation.
In our study, 13

CONF LICT OF I NTEREST
The author have no other relevant conflicts of interest to disclose.