A new finite element approach for near real‐time simulation of light propagation in locally advanced head and neck tumors

Background and Objectives

Several clinical studies suggest that interstitial photodynamic therapy (I‐PDT) may benefit patients with locally advanced head and neck cancer (LAHNC). For I‐PDT, the therapeutic light is delivered through optical fibers inserted into the target tumor. The complex anatomy of the head and neck requires careful planning of fiber insertions. Often the fibers' location and tumor optical properties may vary from the original plan therefore pretreatment planning needs near real‐time updating to account for any changes. The purpose of this work was to develop a finite element analysis (FEA) approach for near real‐time simulation of light propagation in LAHNC.

Methods

Our previously developed FEA for modeling light propagation in skin tissue was modified to simulate light propagation from interstitial optical fibers. The modified model was validated by comparing the calculations with measurements in a phantom mimicking tumor optical properties. We investigated the impact of mesh element size and growth rate on the computation time, and defined optimal settings for the FEA. We demonstrated how the optimized FEA can be used for simulating light propagation in two cases of LAHNC amenable to I‐PDT, as proof‐of‐concept.

Results

The modified FEA was in agreement with the measurements (P = 0.0271). The optimal maximum mesh size and growth rate were 0.005–0.02 m and 2–2.5 m/m, respectively. Using these settings the computation time for simulating light propagation in LAHNC was reduced from 25.9 to 3.7 minutes in one case, and 10.1 to 4 minutes in another case. There were minor differences (1.62%, 1.13%) between the radiant exposures calculated with either mesh in both cases.

Conclusions

Our FEA approach can be used to model light propagation from diffused optical fibers in complex heterogeneous geometries representing LAHNC. There is a range of maximum element size (MES) and maximum element growth rate (MEGR) that can be used to minimize the computation time of the FEA to 4 minutes. Lasers Surg. Med. 47:60–67, 2015. © 2015 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.     

儿童股骨远端骨肉瘤保留骨骺的定制肿瘤型假体重建术

 目的 介绍儿童股骨远端骨肉瘤保留骨骺的定制肿瘤型假体重建术,并探讨其工作原理、手术操作技巧、早期临床疗效以及并发症的防治。方法 2012年8月至2013年7月期间,应用肿瘤瘤段骨切除、保留骨骺的定制肿瘤型假体重建术治疗股骨远端骨肉瘤的儿童患者3例,均为男性,年龄8岁、9岁和15岁。术前给予新辅助化疗1~2周期,化疗结束后根据X线、CT 和MR等检查结果评价化疗疗效,对于化疗效果好且符合保留骨骺手术条件者采用此术式治疗。首先通过CT、MRI确定病变范围,根据影像学检查结果利用计算机辅助定制保留骨骺的肿瘤型假体以及模具,待假体定制完毕后行肿瘤瘤段骨切除、保留骨骺的定制肿瘤型假体重建术,术后指导患者进行功能锻炼,切口愈合1周后给予术后的规范化化疗,并进行长期随访。 结果 3例患者手术时间分别为3 h、4 h和6 h,术中出血量分别为300 ml、500 ml和2 200 ml。对3例患者术后随访时间 为12~24个月,根据美国骨肿瘤学会评分系统（Musculoskeletal Tumor Society,MSTS）,术后3个月功能评分分别为24分、26分和13分,短期随访显示患者肢体功能良好。1例患者出现假体感染,经保守治疗（抗炎补液、切口换药等）无效后行大腿截肢术,余2例患者未出现假体松动等其他并发症。2例患者双下肢长度相差均< 2 cm。结论 通过严格掌握保留骨骺保肢手术的适应证,配合术前及术后的新辅助化疗,保留骨骺的定制肿瘤型假体重建术为儿童股骨远端骨肉瘤的保肢治疗提供了新的选择方案,其疗效安全、可靠,且具有手术操作简单、手术时间短、术后恢复快等优点,但长期疗效尚需进一步观察。     

Hyperbaric oxygen therapy improves angiogenesis and bone formation in critical sized diaphyseal defects

Besides the use of autologous bone grafting several osteoconductive and osteoinductive methods have been reported to improve bone healing. However, persistent non‐union occurs in a considerable number of cases and compromised angiogenesis is suspected to impede bone regeneration. Hyperbaric oxygen therapy (HBO) improves angiogenesis. This study evaluates the effects of HBO on bone defects treated with autologous bone grafting in a bone defect model in rabbits. Twenty‐four New‐Zealand White Rabbits were subjected to a unilateral critical sized diaphyseal radius bone defect and treated with autologous cancellous bone transplantation. The study groups were exposed to an additional HBO treatment regimen. Bone regeneration was evaluated radiologically and histologically at 3 and 6 weeks, angiogenesis was assessed by immunohistochemistry at three and six weeks. The additional administration of HBO resulted in a significantly increased new bone formation and angiogenesis compared to the sole treatment with autologous bone grafting. These results were apparent after three and six weeks of treatment. The addition of HBO therapy to autologous bone grafts leads to significantly improved bone regeneration. The increase in angiogenesis observed could play a crucial role for the results observed. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:513–520, 2015.     

Reduced tonicity stimulates an inflammatory response in nucleus pulposus tissue that can be limited by a COX‐2‐specific inhibitor

In intervertebral disc herniation with nucleus pulposus (NP) extrusion, the elicited inflammatory response is considered a key pain mechanism. However, inflammatory cytokines are reported in extruded herniated tissue, even before monocyte infiltration, suggesting that the tissue itself initiates the inflammation. Since herniated tissue swells, we investigated whether this simple mechanobiological stimulus alone could provoke an inflammatory response that could cause pain. Furthermore, we investigated whether sustained‐release cyclooxygenase‐2 (COX2) inhibitor would be beneficial in such conditions. Healthy bovine NP explants were allowed to swell freely or confined. The swelling explants were treated with Celecoxib, applied either as a bolus or in sustained‐release. Swelling explants produced elevated levels of interleukin‐6 (IL‐6) and prostaglandin E₂ (PGE₂) for 28 days, while confined explants did not. Both a high concentration bolus and 10 times lower concentration in sustained release completely inhibited PGE₂ production, but did not affect IL‐6 production. Swelling of NP tissue, without the inflammatory system response, can trigger cytokine production and Celecoxib, even in bolus form, may be useful for pain control in extruded disc herniation. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1724–1731, 2015.