Journal of Cancer Research and Therapeutics

ORIGINAL ARTICLE
Year
: 2020  |  Volume : 16  |  Issue : 2  |  Page : 203--208

Experimental study on radiation damage of125I seeds implanted in canine gastric wall tissue


Zaishuang Ju1, Zhe Wang1, Lin Wang2, Jianxin Li2, Zhong Wu1, Xiang Li1, Fuguang Wang1, Ruoyu Wang1,  
1 Department of Medical Oncology, Affiliated Zhongshan Hospital of Dalian University; The Key Laboratory of Biomarker High Throughput Screening and Target Translation of Breast and Gastrointestinal Tumor, Dalian University, Dalian, P. R. China
2 Department of Thoracic Surgery, Affiliated Zhongshan Hospital of Dalian University, Dalian, P. R. China

Correspondence Address:
Ruoyu Wang
Department of Medical Oncology, Affiliated Zhongshan Hospital of Dalian University, Dalian 116001
P. R. China

Abstract

Objective: The objective of the study was to investigate the radiation damage to125 I seeds implanted in canine gastric wall tissue. Materials and Methods: Eight beagles were randomly assigned to either the treatment or control group, with four beagles per group. For each beagle in the treatment group, six125 I seeds were implanted in the gastric wall in two rows, spaced at 1.0 cm, with a seed activity of 0.5 mCi and a half-life of 60.2 d. For each beagle in the control group, six 125 I seeds were similarly implanted as a cold source. After implantation, the beagles were scanned by computed tomography (CT) (slice thickness: 2 mm), the region of interest was labeled along the seed boundaries, and postoperative doses were verified. One beagle per group was sacrificed at the 1, 2, 3, and 4 half-lives to be used as gross specimens for observing histological and ultrastructural changes using light microscopy and electron microscopy, respectively. Results: Beagles from the treatment group who had125 I radioactive seeds implanted in their stomach walls had the most radiation damage after two half-lives, damage repair began after three half-lives, and the damage was stabilized and further repaired after four half-lives. In the control group, only mild inflammatory reactions were observed around the seeds. Conclusion: Appropriate and well-planned implantation of125 I radioactive seeds in beagle stomach walls is safe and reliable.



How to cite this article:
Ju Z, Wang Z, Wang L, Li J, Wu Z, Li X, Wang F, Wang R. Experimental study on radiation damage of125I seeds implanted in canine gastric wall tissue.J Can Res Ther 2020;16:203-208


How to cite this URL:
Ju Z, Wang Z, Wang L, Li J, Wu Z, Li X, Wang F, Wang R. Experimental study on radiation damage of125I seeds implanted in canine gastric wall tissue. J Can Res Ther [serial online] 2020 [cited 2020 Jul 5 ];16:203-208
Available from: http://www.cancerjournal.net/text.asp?2020/16/2/203/285191


Full Text



 Introduction



After more than 40 years of development since thefirst brachytherapy using125 I seeds as the radiation source at the Memorial Hospital of the US in 1965, brachytherapy with125 I radioactive seeds has become standard treatment for prostate cancer in developed countries.[1] It is now widely used in intra- and postoperative radiotherapy for many other tumors.[2],[3],[4],[5] In China, this treatment strategy is regarded as the third type of technology by the Ministry of Health and has been widely used to locally treat lung cancer, head-and-neck cancer, spinal metastasis, and lymph node metastasis, with good clinical efficacy.[6] However, research on125 I seeds has been inadequate, and their safety and level of tissue damage remain unclear. Thus, in this study, we implanted125 I seeds in beagles' stomach walls for gross observation of the implanted gastric walls at different time points postimplantation to study the changes at the cellular, tissue, and ultrastructural levels. This study aims to provide a basis for safely applying125 I seeds in clinics.

 Materials and Methods



Animals

Eight adult beagles (four males and four females, weighing 15.4–18.6 kg, with an average of 16 kg) were procured from the Animal Center of the Medical College of Dalian University (license number: SCXK GO 2008-002) and randomly assigned to either the treatment or control group, with four animals per group.

Seed source and seed implantation equipment

Treatment group:125 I-sealed seed source (particle activity [apparent activity]: 0.5 mCi and half-life: 59.4 d). Control group: Sealed125 I seed source (cold source). Both the seed sources were purchased from Ningbo Jun'an Pharmaceutical Technology Co., Ltd. The implantation gun and needles and radiation protective clothing, including apron, gloves, glasses, thyroid shielding, and skirts, were purchased from Beijing Astro Technology Co., Ltd. The seed implantation plan system was purchased from the Image Center of Beijing University of Aeronautics and Astronautics.

Seed implantation

Eight beagles were weighed in the morning and then anesthetized by intraperitoneally injecting pentobarbital sodium (1 mg/kg body weight). Under complete anesthesia, open surgery was performed in the sterile animal laboratory to expose the whole stomach. On the middle and upper areas of the anterior gastric wall,125 I seeds were implanted through suturing in two rows, with 1-cm spacing between the seeds and the rows, using six seeds per animal [Figure 1]. Then, the incision was closed. The treatment group was implanted with the125 I-sealed seed source with the above-described activity as a radiation source, whereas the control group was implanted with the sealed seed source as a cold source.{Figure 1}

Postoperative treatment and plan validation

Immediately after surgery, anterior and lateral X-ray digital radiography (DR) was performed to verify the position and number of implanted seeds. A computed tomography (CT) scan was performed (slice thickness: 2 mm), and the CT images were exported to the treatment planning system, through which the region of interest was outlined along the implanted seed boundaries for postoperative dose verification. The beagles were administered gentamicin sulfate (160,000 units) orally for 3 consecutive days. The beagles' general conditions were monitored and compared with their conditions before implantation. The beagles were raised in separated cages under standard feeding conditions.

Main observation indicators

Two months after surgery, X-ray DR was again performed on the animals to verify the implanted seeds' positions and numbers. At 2, 4, 6, and 8 months (which, respectively, corresponded to 1, 2, 3, and 4 half-life/lives of the radioactive seeds) after surgery, one beagle per group was killed through air embolism through cardiac puncture. Open surgery was performed to expose the whole stomach to observe general morphological changes on the anterior gastric wall. The entire gastric wall layer at the center of the seed implantation was then placed in either 1% formaldehyde or 2% glutaraldehyde fixative. Hematoxylin and eosin-stained sections were produced to observe tissue and cellular changes under light microscopy and ultrastructural changes in the cells by electron microscopy (JEM-200EX transmission electron microscope, Japan).

 Results



General status

Eight beagles manifested poor appetite within 12 h after surgery. Normal diet behaviors and activities similar to those preoperation were resumed 12 h after surgery.

Dosimetric results

The doses indicated by postoperative immediate verification planning on the four beagles in the treatment group are shown in [Table 1] [Figure 2] and [Figure 3].{Table 1}{Figure 2}{Figure 3}

The doses indicated by postoperative immediate verification planning on the four beagles in the control group were 0 Gy.

Imaging observation

Six seeds were implanted in the stomach walls of each beagle in both the groups. Two months after implantation, the beagles were evaluated by DR [Figure 4], which showed that the seed distributions for the animals in both the groups were highly similar to those at preoperative planning, except in two cases. For one treatment group case, only four seeds were retained on the gastric wall [Figure 5], whereas two seeds were displaced, with an 8.3% displacement rate (2/24). In addition, in one control group case, five seeds were retained on the gastric wall, whereas one seed was displaced, with a 4.17% displacement rate (1/24).{Figure 4}{Figure 5}

Gross specimens

Treatment group

At 2 months postsurgery, areas of edema and a thickened stomach wall centered at the125 I seeds were formed, with a hard texture and seeds embedded within. Fibrous thickening occurred at the serosa, and gastric mucosal folds disappeared, but no ulcers or perforations were observed.

At 4 months postsurgery, seeds were embedded in the stomach wall, the areas of edema and stomach wall thickening centered at the125 I seeds had slightly subsided, and the gastric mucosal folds had disappeared, whereas adhesion between the serosa and the spleen was tight. After careful blunt dissection, suspected but unconfirmed perforation was observed on the gastric wall [Figure 6].{Figure 6}

Six and 8 months postsurgery, seeds were embedded in the stomach wall, the areas of edema and stomach wall thickening centered at the125 I seeds had subsided completely, and the gastric mucosal folds had disappeared, similar to those observed at one half-life [Figure 7].{Figure 7}

Control group

At 2, 4, 6, and 8 months after surgery, the seeds were well-embedded in the gastric wall, and the serosa and stomach wall mucosa showed no noticeable abnormalities.

Pathology results by light microscopy

Treatment group

Two months after surgery, nodular tissue and cell aggregates were seen on the serosa and muscularis, and fibrous tissue proliferated at the gastric muscularis and surrounding areas, with obvious peripheral chronic inflammatory infiltration of mostly lymphocytes. Mucosal cells were in disarray, but the mucosal surface looked intact.

Four months postsurgery, a mild inflammatory response was seen near the gastric serosa, and small nodular lesions and fibroblast proliferation were present within the muscularis. Edema became more profound under the mucosa and was worse than that at 2 months postsurgery. Obvious edema occurred for the cells at the site of adhesion to the spleen, appearing as balloon-like lesions [Figure 8].{Figure 8}

Six months postsurgery, small blood vessel proliferation under the stomach wall mucosa was significant, and some small vessel walls had thickened, with hyaline degeneration and noticeable submucosal plasma cell infiltration.

Eight months postsurgery, nodular tissue and cell aggregates were seen within the gastric wall serosa and mucosa, accompanied by fibrous tissue hyperplasia within the serosa, mucosa and surrounding areas, peripheral infiltration of chronic inflammatory cells, and more profound vascular hyperplasia [Figure 9].{Figure 9}

Control group

Two months postsurgery, a few inflammatory cells, mostly lymphocytes, had infiltrated the gastric wall incision site, especially around the sutured sites.

Four, 6, and 8 months postsurgery, inflammatory cells had mostly disappeared compared with those at 2 months, whereas fibroblasts had increased. The gastric mucosa showed no noticeable abnormalities.

Electron microscopy results

Treatment group

Two months postsurgery, granular materials formed within the gastric myometrial cell cytoplasm, with an intracytoplasmic aggregation of many endosomes. Cytoplasmic mitochondria were partially swollen, and chromosomes aggregated on the side of the nucleus.

Four months postsurgery, fibroblast hyperplasia occurred to the serosa, and the gastric muscularis cell nuclei were oval shaped, with intact nuclear membranes and chromatin marginalization. Intercellular connections were tight, mitochondria were partially observed with edema and sporadic vacuolization, mucosal cells were rich in cytoplasm, and edema on the mitochondria and endoplasmic reticulum had changed significantly [Figure 10].{Figure 10}

Six months postsurgery, many serosal fibroblasts were tightly arranged in sheets or bundles, gastric muscularis cells were oval shaped, with increased mitochondria and endoplasmic reticulum numbers, nuclei were normal, and chromatin marginalization was rare within the nuclei. Irregularly shaped cells were observed in the mucosa, with many mitochondrial vacuoles and endoplasmic reticular edema, profound chromatin aggregation and marginalization, and fewer changes than those seen at 4 months postsurgery.

Eight months postsurgery, fibroblasts on the serosal surface were tightly arranged in sheets and bundles but more dispersed than those at 6 months postsurgery. Mitochondrial vacuolization occurred, and nuclei were intact, with marginalized chromosomes. Endosomes were observed but less abundantly than previously seen [Figure 11]. Within the muscularis cells, large endosomes were seen locally, and muscularis cells were mostly normal, with increased brown granular substances in the cytoplasm and chromatin marginalization in the nuclei as seen previously. The mucosal cell shape was more regular than previously seen, and string-shaped collagen fibers were seen around the cells. Several vacuolated mitochondria were present in the cytoplasm, and many endoplasmic reticula were observed, with reduced marginalized intact chromatin within the nucleus.{Figure 11}

Control group

At 2, 4, 6, and 8 months postsurgery, the gastric mucosa and serosa showed no noticeable abnormalities.

 Discussion



Gastric cancer is a highly common digestive system malignancy. Gastric cancer incidence ranks the second or third in China and the fifth worldwide.[7],[8],[9] Intraperitoneal recurrence is the main reason why radical surgery fails in gastric cancer. The 1-year survival of gastric cancer is reported to be approximately 40%, and the 5-year survival is approximately 21%. Adjuvant radiotherapy and chemotherapy can improve the 5-year survival of gastric cancer patients.[10],[11],[12] The routine prescribed postoperative adjuvant external radiation dose is 45 Gy/5 weeks at 95% planning target volume, and a 45-Gy external beam dose is far from reaching the lethal dose needed to kill the tumor cells. Interstitially implanting125 I seeds can increase the local dose; however, the physical, chemical, and radiological changes induced by the implanted125 I seeds at low radioactive dose rates likely differ from those induced by the conventionally segmented X-ray external radiation therapy at a high radioactive dose rate.

Basic research on this topic has rarely been reported. Wang et al.[13] reported that 30 and 60 days after implanting125 I seeds in rabbit stomach walls, the serosal and muscularis tissues exhibited degeneration and necrosis, with a multinucleated giant cell response, and the tissue damage severity gradually reduced from the seed source to the periphery. Tissues that were 5 mm peripheral to the seed source were involved, whereas tissues at 2 mm peripheral to the seed source mainly showed degeneration and necrosis. On the 120th and 180th days, chronic inflammatory cell infiltration was observed, and on the 180th day, pathological damages were concentrated in the serosa and muscularis, while the mucosa was normal, with an injury depth of 1–2 mm. Wang's results were similar to ours. In this study, at one half-life after implantation, local fibrosis was observed centered at the seed site, and fibroblast proliferation was seen in the gastric serosa. After two half-lives, the spleen almost invaded the stomach wall, and after separation, gastric perforation was observed. Under light microscopy, edema was observed on the mucosal surface in addition to large-scale serosal fibroblast proliferation, indicating acute radiation reactions on the mucosal surface. After three half-lives, light microscopy showed plasma cells on the mucosal surface, whereas electron microscopy showed increased numbers of organelles within the cells, suggesting increased tissue repair responses. After four half-lives, electron microscopy indicated that organelle activities further increased, and chromatin marginalization lessened, suggesting decreased apoptosis and that damage to the tissues and cells from radiation stabilized after repair. The results of these two studies were mostly consistent.

Clinically, Zou et al.[14] reported that among 76 cases of Stage II and III gastric cancer, the 3- and 5-year survival rates of the radical surgery + 125 I seed group were 61.9% and 42.86%, respectively, higher than those (11.76% and 0%, respectively) of the radical surgery group. Primary side effects included abdominal pain and abdominal distension, but without gastrointestinal fistula formation, indicating high efficacy, low toxicity, and low side effects from the seed implantation. Haiyan et al.[15] reported that among 15 gastric cancer cases with pancreatic invasion treated with palliative gastrectomy surgery coupled with125 I brachytherapy, 5 (33%) achieved complete remission, 9 (60%) achieved partial remission, 1 (7%) showed no change, and 0 showed progressive disease. However, pancreatic fistula occurred in one case, which was cured after conservative treatment. In this study, after two half-lives, spleen–stomach adhesion was observed near the stomach walls on the gross specimens, and after blunt separation, the spleen had almost infiltrated through the stomach wall. Gastric perforation was observed after careful dissection, suggesting that after125 I seed implantation, irregular gastric peristalsis may cause spleen–stomach adhesions and even gastric perforations. Therefore, in clinical treatment, muscular organ characteristics, such as gastric irregular peristalsis and inclination of deformation, should be considered to avoid damaging the stomach and surrounding organs. Fistula or perforation in hollow organ after seed implantation might compose of several reasons. (1) Radiation activity of seed is the most important factor. Needless to say, high activity seed would destroy the balance of tissue repairment and damage, so that fistula or perforation would be showed up. (2) Gross Tumor Volume (GTV) prescribe dose is also another key factor. (3) Gastric wall movement is an unexpected factor, by which seed could be rearranged after implantation. Therefore, hot area could be established. All of those might contribute to fistula or perforation.

Dosimetry and radiation biological applications of125 I seeds in gastric cancer have rarely been reported.[16],[17] The dosimetric parameters for125 I seed implantation recommended by the American Association of Physicists in the Medicine Working Group Report No. 43 indicate that the brachytherapeutic dose is 140 Gy. In this study, the main reason that gastric perforation occurred in one beagle was that D80 = 240 Gy, resulting in the implanted seed being displaced, which led to a decreased central dose and increased peripheral dose. Although many factors affect the maximum tolerated dose in the gastric wall, our results suggest that in clinical postoperative validation, various doses for different tumor volumes and irradiation doses for peripheral tissues should be assessed to determine possible side effects.

 Conclusion



We demonstrated that after 3–4 half-lives, radiation damage from125 I seed implantation in beagle stomach walls was repaired and stabilized; however, these results require further clinical verification. Some shortcomings of this study include its small sample size and the fact that different seed numbers, seed activity, and seed arrangement affect local responses to the radiation damage, which should be investigated in future basic and clinical studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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