Thymoma is a rare disease in clinic. It can be divided into malignant tumor and benign tumor according to whether it is aggressive or not. Type A thymic tumors are generally considered benign because of less aggressive. However, studies have shown that some patients with type A thymoma can have occurred recurrence and distant metastasis even after complete resection (15), indicating that they still have the characteristics of malignant tumor. Therefore, all thymomas are now considered as malignant tumors (16).For the treatment of this disease, according to the current domestic and international guidelines and expert consensus, radical surgical resection is considered as the first-line recommended plan for patients with stage I to IIIA. Postoperative adjuvant radiotherapy and chemotherapy can further reduce the probability of recurrence and metastasis according to the stage. Curran (17) et al. calculated that postoperative adjuvant radiotherapy can reduce the local recurrence rate of invasive thymocytoma after complete resection from 28–5% by multiple studies. For patients in stage IIIB-IV, the treatment is complex. It is currently recommended to perform induced radiotherapy and chemotherapy for patients who cannot be surgically excised immediately. Then the possibility of surgical excision will be evaluated after the mass is reduced. A number of articles have suggested that the indications for surgery are: no extensive invasion of intrathoracic organs, no invasion to the main vessels or the heart, technically resectable, and resistant to surgical treatment, as assessed by imaging (18–23). The principle of operation is to complete resection as far as possible. The standard operation is median sternal cleavage and total thymectomy. Dai et al. (24) believe that tumor reduction surgery has a poor prognosis and does not significantly improve the survival of patients, unless when other treatment methods are not feasible. The patient in this case was initially diagnosed as type A thymoma, stage IIIB. Imaging examination suggested that the tumor was huge and had mediastinal pleural invasion. The surgeon's assessment remained that it was difficult to completely remove the tumor and the risk was very high.
Preoperative inductive therapy is thought to shrink the size of the tumor, reduce the stage, and gain the opportunity of surgical resection thereby, which includes neoadjuvant chemotherapy and neoadjuvant concurrent chemoradiotherapy, while the clinical data of neoadjuvant radiotherapy alone are few. The effective rate of chemotherapy for patients with thymoma is between 60% and 90% (25). Rea et al. (26) treated 32 patients with invasive thymoma with neoadjuvant chemotherapy, and the final complete surgical resection rate was 75%, and the 10-year overall survival rate was 61%. The European Organization for Research and Treatment for Cancer (EORTC) Lung Cancer Collaborative Group, treated 16 patients with advanced thymoma with combined chemotherapy, the median survival was 4.3 years (27). Thymoma is considered to be moderately sensitive to radiation(28). Wright et al. reviewed 10 cases with stage Ⅲ- ⅣA thymoma, these patients were all treated with induced chemoradiation, eventually 8 cases were complete resection, 5 years survival rate was 69% (29). In addition, a number of studies have shown that concurrent chemoradiotherapy has a good effect on inoperable locally advanced thymic tumors, with a total response rate of 69%-92% (30–32). At present, the International Thymoma Collaboration Group (ITMIG) recommends a dose of 40 ~ 64Gy for concurrent radiotherapy(33). 3D CRT, IMRT or VMAT technologies are recommended. The adverse reactions of normal organs to radiotherapy are related to the location and size of the tumor, previous treatment and the physical condition of the patient. The thymus gland is located between the two lungs, adjacent to the heart, and conventional radiotherapy techniques are likely to cause adverse reactions. Studies have shown that the radiation dose of more than 30Gy may lead to side reactions such as radiation pneumonia and radiation pericarditis, and with the increase of dose, the incidence of ADR also increased further (34, 35). The patient in this case was older and weak, with poor pulmonary function due to long-term smoking history, pulmonary infection and bilateral pleural effusion. In addition, the patient’s tumor was huge, surrounding the heart. After evaluation, the patient could be intolerant to conventional chemoradiotherapy.
125I seed which release gamma rays, can continuously kill tumor cells at a close range when implanted in tumor tissue. Compared with traditional radiotherapy, the biggest advantage of the technology is that the tissue dose is inversely proportional to the particle distance, meaning that the dose in the tumor target area close to the particle is higher, while the dose in the normal organs far away from the particle is lower(36, 37), thus reducing the adverse reactions of the normal organs. According to the statistics of some studies, the dose received in the target area of 125I particles is usually 2–3 times of the maximum prescribed dose of external radiation (38), which is more in line with the requirements of "conformal and intensity-modulated" radiotherapy. At present, this technique is widely used in China and has achieved good efficacy in the treatment of a variety of solid tumors. Moreover, it has been written into the guidelines for the diagnosis and treatment of prostate cancer of the European Association of Urology (39–43). In the treatment of thymoma, many articles have reported its effectiveness and safety (8–10). After multi-disciplinary consultation and discussion, combined with the opinions of the patient and his family members, the patient decided to receive 125I seed implantation therapy.
3D printing technology can create a personalized guidance template according to the patient's image,to guide the implantation of 125I seeds. Zhang Hongtao and Xu Junma et al. (44, 45) compared the preoperative and postoperative dosimetric parameters of patients with particle implantation guided by 3D printing templates, the result was no significant difference. They believe that the dose of particle implantation guided by 3D printing templates could be accurately controlled. Freehand implantation mainly depends on the experience of the operator. Postoperative particle position and dose cannot be consistent with the preoperative plan, and the dose in the target area is not uniform, which can easily lead to a poor tumor control and recurrence, and a higher risk of damage to normal tissues and organs (46). Based on this, this patient decided to receive 125I seed implantation guided by 3D printing template. The operation of this patient went smoothly, the dose was 120Gy. Having used the BCCA implantation quality evaluation criteria for postoperative planning verification, the result of the implantation quality evaluation was excellent. Three months later, the patient's chest CT reexamination showed that the tumor had almost completely regressed. The pleural effusion disappeared, and the symptoms of chest tightness, shortness of breath and fatigue of the patient were basically relieved. The patient has survived for more than 3 years.