The effects of high dose and highly fractionated radiation on distraction osteogenesis in the murine mandible

Investigation of differences of sacral and vertebral bone mineral densities before and after radiotherapy in patients with locally advanced rectal cancer

PURPOSE

Radiotherapy is a treatment method performed using ionizing radiation on cancer patients either alone or with surgery and/or chemotherapy. Although modern radiotherapy techniques provide a significant advantage in protecting healthy tissues, it is inevitable that normal tissues are also located in the areas targeted by radiations. In this study, we aimed to examine the bone mineral density changes in bone structures commonly included in the irradiated area such as, L5 vertebra, sacrum, and femur heads, in patients who have received pelvic radiotherapy; and the relationship between these changes with radiation dose.

MATERIAL AND METHODS

Patients included in the study had been previously diagnosed with rectal cancer, which were operated or not. Preoperative or postoperative pelvic radiotherapy was planned for all patients. In terms of convenience when comparing with future scans, all densitometry and CT scans were performed with the same devices. Fifteen patients were included in the study. In order to determine the dose of radiation each identified area had taken after radiotherapy, the sacrum, L5 vertebra, bilateral femoral heads, and L1 regions were contoured in the CT scans in which treatment planning was done. Sagittal cross-sectional images were taken advantage of while these regions were being contoured.

RESULTS

Bone mineral density was evaluated with CT and dual-energy X-ray absorptiometry before and after the treatment. The regions that have theoretically been exposed to irradiation, such as L5, sacrum, left to right femur were found to have significant difference in terms of bone density. According to CT evaluation, there was a significant decrease in bone intensity of L5, sacrum, left and right femurs. Dual-energy X-ray absorptiometry assessment revealed that the whole of the left femoral head, left femur neck and Ward's region were significantly affected by radiotherapy. However, there was no significant difference in the sacrum and L5 vertebra before and after radiotherapy.

CONCLUSION

More accurate results could be achieved if the same study was conducted on a larger patient population, with a longer follow-up period. When the reduction in bone density is at maximum or a cure is likely in a long-term period, bone mineral density could be determined by measurements performed at regular intervals.

Radioprotection With Amifostine Enhances Bone Strength and Regeneration and Bony Union in a Rat Model of Mandibular Distraction Osteogenesis

BACKGROUND

Using distraction osteogenesis (DO) to regenerate robust endogenous bone could greatly enhance postoncologic reconstruction of head and neck cancer. However, radiation (XRT) corrosive effects still preclude DO's immense potential. We posit that adjunctive pretreatment with the radioprotectant amifostine (AMF) can optimize wound healing and allow for successful DO with quantifiable enhancements in bony union and strength despite previous surgical bed irradiation.

METHODS

Two groups of murine left hemimandibles were exposed to a human equivalent radiation dosage fractionated over 5 daily doses of 7 Gy. AMF-XRT-DO (n = 30) received AMF before radiation, whereas XRT-DO (n = 22) was untreated. All animals underwent left hemimandibular osteotomy and external fixator placement, followed by distraction to a 5.1-mm gap. Left hemimandibles were harvested and mechanically tested for parameters of strength, yield, and breaking load.

RESULTS

Radiation-related complications such as severe alopecia were significantly increased in XRT-DO compared with the AMF-treated group (P = 0.001), whereas infection and death were comparable (P = 0.318). Upon dissection, bony defects were grossly visible in XRT-DO distraction gap compared with AMF-XRT-DO, which exhibited significantly more complete unions (P = 0.004). Those results were significantly increased in the specimens prophylactically treated with AMF (yield: 39.41 N vs 21.78 N, P = 0.023; breaking load: 61.74 N vs 34.77 N, P = 0.044; respectively).

CONCLUSIONS

Our study revealed that AMF enhances biomechanical strength, regeneration, and bony union after radiation in a murine model of DO. The use of prophylactic AMF in combination with DO offers the promise of an alternative reconstructive option for patients afflicted with head and neck cancer.

Osteoradionecrosis of the Jaws: Clinico-Therapeutic Management: A Literature Review and Update

Osteoradionecrosis is one of the most serious oral complications of head and neck cancer treatment. It is a severe delayed radiation-induced injury, characterized by bone tissue necrosis and failure to heal for at least 3 months. In most cases osteoradionecrosis gradually progresses, becoming more extensive and painful that leads to infection and pathological fracture. The present paper provides a literature review and update on the risk factors underlying osteoradionecrosis, its clinical and diagnostic particulars, prevention and most widely accepted treatment options including the latest treatment modalities. Lastly, a new early management protocol is proposed based on the current clinical criteria relating to osteonecrosis secondary to treatment with bisphosphonates, together with the adoption of new therapies supported by increased levels of evidence.

Development of mandibular osteoradionecrosis in rats: Importance of dental extraction

OBJECTIVES

To develop an animal model of mandibular osteoradionecrosis (ORN) using a high-energy radiation source (as used in human therapeutics) and to assess the role of tooth extraction on ORN development.

MATERIALS AND METHODS (STUDY DESIGN)

Ten animals were irradiated with a single 35- or 50-Gy dose. Three weeks later, the second left mandibular molar was extracted from three animals in each group. Nine weeks after irradiation, the animals were euthanized, with an injection of contrast agent in the bloodstream to highlight vascularization. Mandibles were harvested and studied using micro-CT, histology, tartrate-resistant acid phosphatase activity and scanning electron microscopy.

RESULTS

This study demonstrates that a single 50-Gy dose associated with molar extraction is necessary for ORN development. In these conditions, absence of healing of the mucosa and bone, dental effects, fibrosis, an increase in osteoclast activity and a decrease in vascularization were observed. We also determined that molar extraction increases the impact of the cellular effects of radiation.

CONCLUSION

The mandibular ORN animal model was validated after 50-Gy irradiation and molar extraction. The results of this study therefore support an animal ORN model and tissue engineering strategies will now be developed to regenerate bone for patients with head and neck cancer.

A Histomorphometric Analysis of Radiation Damage in an Isogenic Murine Model of Distraction Osteogenesis

PURPOSE

The devastation radiation therapy (XRT) causes to endogenous tissue in patients with head and neck cancer can be a prohibitive obstacle in reconstruction of the mandible, demanding a better understanding of XRT-induced damage and options for reconstruction. This study investigated the cellular damage caused by radiation in an isogenic murine model of mandibular distraction osteogenesis (DO). The authors posited that radiation would result in fewer osteocytes, with increased empty lacunae and immature osteoid.

MATERIALS AND METHODS

Twenty Lewis rats were randomly assigned to a DO group (n = 10) or a XRT/DO group (n = 10). These groups underwent an osteotomy and mandibular DO across a 5.1-mm gap. XRT was administered to the XRT/DO group at a fractionated human equivalent dose of 35 Gy before surgery. Animals were sacrificed on postoperative day 40 and mandibles were harvested and sectioned for histologic analysis.

RESULTS

Bone that underwent radiation showed a significantly decreased osteocyte count and complementary increase in empty lacunae compared with non-XRT bone (P = .019 and P = .000). In addition, XRT bone exhibited increased immature osteoid and decreased mature woven bone compared with nonradiated bone (P = .001 and P = .003, respectively). Furthermore, analysis of the ratio of immature osteoid to woven bone volume exhibited a significant increase in the XRT bone, further showing the devastating damage from XRT (P = .001).

CONCLUSION

These results clearly show the cellular diminution that occurs as a result of radiation. This foundational study provides the groundwork on which to investigate cellular therapies in an immuno-privileged model of mandibular DO.

Comparing calvarial transport distraction with and without radiation and fat grafting

The purpose of this study is to: a) assess transport distraction to reconstruct cranial defects in radiated and non-radiated fields b) examine adipose grafting's effect on the bony regenerate and overlying wound, and c) elucidate sources of bone formation during transport distraction osteogenesis. Twenty-three male New Zealand white rabbits (3 months; 3.5 kg) were used, 10 non-irradiated and 13 irradiated (17 treatment, 6 control) with a one-time fraction of 35 Gy. A 16 × 16 mm defect was abutted by a 10 × 16 mm transport disc 5 weeks after irradiation, and 11 animals were fat grafted at the distraction site. Latency (1 day), distraction (1.5 mm/day), and consolidation (4 weeks) followed. Fluorochromes were injected subcutaneously and microCT, fluorescence, and histology assessed. In distracted animals without fat grafting, bone density measured 701.87 mgHA/ccm and 2271.95 mgHA/ccm in irradiated and non-irradiated animals. In distracted animals with fat grafting, bone density measured 703.23 mgHA/ccm and 2254.27 mgHA/ccm in irradiated and non-irradiated animals. Fluorescence revealed ossification emanating from the dura, periosteum, and transport segment with decreased formation in irradiated animals. Transport distraction is possible for cranial reconstruction in irradiated fields but short-term osseous fill is significantly diminished. Adipose grafting enhances wound healing in previously irradiated fields but does not enhance ossification.

Distraction osteogenesis following low-dose hyperfractionated irradiation in the rat mandible

PURPOSE

The investigators hypothesized that low-dose hyperfractionated radiation would impair mandibular distraction osteogenesis (DO) in a murine mandibular model.

MATERIALS AND METHODS

Male Sprague-Dawley rats underwent fractionated radiation (30 Gy) of the left mandible. After a 2-week recovery period, an external frame distractor was applied and gradual distraction of the mandible was performed. Tissue was harvested after a 28-day consolidation period. Gross, radiologic, and histologic evaluations were undertaken. Control animals underwent surgery for an identical time frame without preoperative radiation.

RESULTS

Animals subjected to preoperative radiation (n = 10) showed suboptimal bone formation, including bone atrophy, incomplete bridging of the distraction gap, and gross bony defects or nonunion, compared with controls (n = 10). Although physical lengthening was achieved, irradiation consistently led to a detrimental effect on the normal process of DO.

CONCLUSION

This set of experiments establishes a valuable rodent model to evaluate the effects of radiation on DO and may help to formulate strategies to optimize DO before it is widely applied in oncologic reconstruction.