Anatomic reconstruction and functional rehabilitation of oromandibular defects with rigid internal fixation

Monte Carlo simulation and film dosimetry for electron therapy in vicinity of a titanium mesh

Titanium (Ti) mesh plates are used as a bone replacement in brain tumor surgeries. In the case of radiotherapy, these plates might interfere with the beam path. The purpose of this study is to evaluate the effect of titanium mesh on the dose distribution of electron fields. Simulations were performed using Monte Carlo BEAMnrc and DOSXYZnrc codes for 6 and 10 MeV electron beams. In Monte Carlo simulation, the shape of the titanium mesh was simulated. The simulated titanium mesh was considered as the one which is used in head and neck surgery with a thickness of 0.055 cm. First, by simulation, the percentage depth dose was obtained while the titanium mesh was present, and these values were then compared with the depth dose of homogeneous phantom with no titanium mesh. In the experimental measurements, the values of depth dose with titanium mesh and without titanium mesh in various depths were measured. The experiments were performed using a RW3 phantom with GAFCHROMIC EBT2 film. The results of experimental measurements were compared with values of depth dose obtained by simulation. In Monte Carlo simulation, as well as experimental measurements, for the voxels immediately beyond the titanium mesh, the change of the dose were evaluated. For this purpose the ratio of the dose for the case with titanium to the case without titanium was calculated as a function of titanium depth. For the voxels before the titanium mesh there was always an increase of the dose up to 13% with respect to the same voxel with no titanium mesh. This is because of the increased back scattering effect of the titanium mesh. The results also showed that for the voxel right beyond the titanium mesh, there is an increased or decreased dose to soft tissues, depending on the depth of the titanium mesh. For the regions before the depth of maximum dose, there is an increase of the dose up to 10% compared to the dose of the same depth in homogeneous phantom. Beyond the depth of maximum dose, there was a 16% decrease in dose. For both 6 and 10 MeV, before the titanium mesh, there was always an increase in dose. If titanium mesh is placed in buildup region, it causes an increase of the dose and could lead to overdose of the adjacent tissue, whereas if titanium mesh is placed beyond the buildup region, it would lead to a decrease in dose compared to the homogenous tissue.

Estimation of dose enhancement to soft tissue due to backscatter radiation near metal interfaces during head and neck radiothearpy - A phantom dosimetric study with radiochromic film

The objective of this study was to investigate the dose enhancement to soft tissue due to backscatter radiation near metal interfaces during head and neck radiotherapy. The influence of titanium-mandibular plate with the screws on radiation dose was tested on four real bones from mandible with the metal and screws fixed. Radiochromic films were used for dosimetry. The bone and metal were inserted through the film at the center symmetrically. This was then placed in a small jig (7 cm × 7 cm × 10 cm) to hold the film vertically straight. The polymer granules (tissue-equivalent) were placed around the film for homogeneous scatter medium. The film was irradiated with 6 MV X-rays for 200 monitor units in Trilogy linear accelerator for 10 cm × 10 cm field size with source to axis distance of 100 cm at 5 cm. A single film was also irradiated without any bone and metal interface for reference data. The absolute dose and the vertical dose profile were measured from the film. There was 10% dose enhancement due to the backscatter radiation just adjacent to the metal-bone interface for all the materials. The extent of the backscatter effect was up to 4 mm. There is significant higher dose enhancement in the soft tissue/skin due to the backscatter radiation from the metallic components in the treatment region.

Increased plate and osteosynthesis related complications associated with postoperative concurrent chemoradiotherapy in oral cancer

BACKGROUND

Plate osteosynthesis is a widely used technique in head and neck reconstructive surgery. The objective of this study was to determine whether postoperative chemoradiotherapy, which was recently introduced for high-risk head and neck cancer, affects plate and osteosynthesis related complications.

METHODS

Fifty-two consecutive patients, who had undergone plate osteosynthesis for mandibular reconstruction between October 2003 and September 2006, were included in the study. The patients were divided into 3 groups: (1) surgery alone (n = 19), (2) surgery with postoperative radiotherapy (n = 14), and (3) surgery with concurrent chemoradiotherapy (n = 19). Outcome measures included any bone or plate related complications.

RESULTS

The plate and osteosynthesis related complications occurred in 10.5% of patients in surgery-alone group, 28.6% in surgery with postoperative radiation group, and 63.2% in surgery with postoperative concurrent chemoradiotherapy group. The differences in the complication rates among these 3 groups were statistically significant (p = .003). In univariate analysis, postoperative radiation (p = .007) and concurrent chemotherapy (p = .003) were found to be significantly associated with complications. In multivariate analysis, only concurrent chemotherapy was found to be statistically significant (p = .002) with odds ratio of 7.72.

CONCLUSION

Postoperative concurrent chemoradiotherapy significantly increases plate and osteosynthesis related complications in oral cancer.

Comparative study of locking plates in mandibular reconstruction after ablative tumor surgery: THORP versus UniLOCK system

PURPOSE

This retrospective study compared 2 types of rigid locking plates (THORP and UniLOCK; Stratec Medical, Oberdorf, Switzerland) in 107 patients undergoing reconstruction for bridging mandibular defects following ablative tumor surgery.

PATIENTS AND METHODS

From January 1993 to December 2000, 107 patients were reconstructed following ablative tumor surgery with 57 THORP plates and 50 UniLOCK plates. Study follow-up ranged from 18 to 87 months (average, 32 months). Complications were categorized into delayed wound healing, infection, plate exposure, and plate fracture, taking into account the type and timing of reconstruction.

RESULTS

Overall type and number of complications show no statistically significant differences between THORP and UniLOCK groups. Infection was the most frequent type of complication (THORP, 30; UniLOCK, 32). Others included delayed wound healing (THORP, 13; UniLOCK, 12), plate exposure (THORP, 8; UniLOCK, 7), and plate fracture (THORP, 5; UniLOCK, 1). Plates were removed in 22 THORP and 11 UniLOCK plates. The most frequent reason for plate removal in both groups was infection. Other reasons for plate removal include tumor recurrence, plate fracture, plate exposure, or a combination of reasons.

CONCLUSIONS

THORP and UniLOCK plates do not present statistically significant differences in the parameters studied. Nevertheless, the UniLOCK group had slightly better results. Considering that the THORP system is much bulkier and its screws bigger, our results lead to the conclusion that bridging osteosynthesis with a 2.4 UniLOCK system is adequate for plate reconstruction of mandibular defects.

Effect of mandibular titanium reconstructive plates on radiation dose

BACKGROUND

The effects of the mandibular titanium alloy plates on the radiation-tissue interactions are not clearly defined. Photon beam radiation may be modified after striking a metal plate used to reconstruct the mandible after oncologic surgery. The purpose of this study was to determine, in a human mandible model, the effects of a titanium alloy plate on the radiation dose received at the bone/titanium (plate and screws) interface and bone/soft tissue interface.

METHODS

We used an adult male human head and neck ex vivo model. A medical grade titanium alloy 6-hole plate, 2.4 mm, was fixed in the midline of the mandible. The mandible was then irradiated using 6 MV photon beams. Thermoluminescent dosimeters were used to measure the radiation doses anterior and posterior to the mandible. The experiment was then repeated without the plate and screws.

RESULTS

The difference between the average doses received by the mandible reconstructed with plate/screws and a mandible without plate/screws was +2.1% at the buccal aspect of the mandible and +3.0% at the lingual aspect; respective P values were.741 and .323. Thus, these differences were not statistically significant.

CONCLUSION

In this study, we did not observe any significant influence of titanium alloy plate/screws on the radiation doses received by tissues anterior or posterior to the mandible.

Effect of metal reconstruction plates on cobalt-60 dose distribution: a predictive formula and clinical implications

PURPOSE

We sought to create a predictive formula for the dose perturbations caused by head and neck reconstruction plates in the delivery of postoperative radiotherapy with 60Co beams.

MATERIALS AND METHODS

The dose perturbation effects of Vitallium and Titanium reconstruction plates and flat metal plates of aluminum (13Al), stainless steel (26Fe), tin (50Sn) and lead (82Pb) irradiated with a 60Co beam were measured in polystyrene phantoms using a film dosimetry system. We then used these results to create formulas to predict the effect of a metal reconstruction plate dependent upon its effective atomic number.

RESULTS

Percentage dose increases secondary to back scattering were 10% at 1 mm in front of the Vitallium plate and 40% at the plate while the percentage dose decrease was 29% at the plate and 10% 1 mm behind the plate. For the Titanium plate, the percentage dose increase was 5% at 1 mm in front the plate and 25% at the plate while the percentage dose decrease was 20% at the plate and 5% 1 mm behind the plate. For flat plates the percentage dose increases and decreases, respectively, at the plate surfaces were: 13Al (8%, 6%), 26Fe (35%, 16%), 50Sn (60%, 24%), and 82Pb (85%, 13%). A second order polynomial predicting the back scatter and shadowing effects was created, Y = a + bZ + cZ2, where Z is the effective atomic number of the plate while a, b, and c are the following constants: for back scatter a = 0.854 +/- 0.082, b = 0.0212 +/- 0.0044, c = -0.00011 +/- 0.00004 and for shadowing a = 1.108 +/- 0.021, b = -0.0141 +/- 0.0011, c = 0.00014 +/- 0.00001.

CONCLUSIONS

It is possible to predict the effect of a metal reconstruction plate upon the delivered postoperative radiotherapy dose. The dose perturbations around the plate only exist for a few millimeters, but this is substantially greater than the thickness of a normal tissue or tumor cell. Perhaps a coating of a low effective atomic number, biologically inert, substance might allow for greater dose homogeneity and decrease the risks of plate failure or tumor recurrence.

Mandibular reconstruction using a titanium plate: the impact of radiation therapy on plate preservation

PURPOSE

To evaluate the soft tissue and bone tolerance of radiation therapy (RT) in patients undergoing radical composite resection and mandibular reconstruction using a bridging titanium plate with myocutaneous flap closure.

METHODS AND MATERIALS

From 1990 to 1994, 47 patients with primary or recurrent oral cavity or oropharyngeal carcinomas were treated with radical composite resection and mandibular reconstruction using a bridging titanium plate with myocutaneous flap closure. Eleven patients received no RT (no RT), 10 patients received RT greater than 10 months from the time of surgery (remote RT), and 26 patients received RT within 12 weeks of surgery (perioperative RT). The radiation dose to the reconstructed mandible ranged from 45 to 75 Gy (median 63 Gy). The effect of the titanium plate on the radiation dose was measured using film dosimetry and soft tissue and bone-equivalent materials. The median follow-up was 17 months (range: 3-50 months).

RESULTS

Late complications included four patients with osteomyelitis or necrosis, two plate exposures requiring flap revision, one chronic infection, two cases of chronic pain, two fistulae, and one case of trismus and malocclusion. The crude incidence of late complications by treatment was: (a) no RT: 3 of 11 patients (27%); (b) remote RT: 2 of 10 patients (20%); and (c) perioperative RT: 9 of 26 patients (35%). One patient in the no-RT group lost the plate due to chronic pain. Five patients in the perioperative RT group also had plate loss, four due to osteomyelitis and/or necrosis, and one due to pain related to a recurrent tumor. No patients in the remote RT group had plate loss. The actuarial prosthesis preservation rate at 2 years was 88% for the no RT, 100% for the remote RT, and 57% for the perioperative RT groups (p = 0.05). Phantom dose measurements showed that for parallel opposed 6 MV photon beams, there was no significant increase in the dose proximal or distal to the plate in either a soft tissue- or bone-equivalent phantom.

CONCLUSIONS

The impact of radiation therapy on plate preservation after mandibular reconstructive surgery using a titanium plate may be dependent on the timing of RT relative to surgery. Significantly more mandibular reconstruction plates were lost when the involved mandible received RT in the perioperative period than when RT was delivered beyond 10 months from surgery or when no RT was given. The use of alloplastic implants such as titanium plates in conjunction with myocutaneous flap coverage for mandibular reconstruction is attractive because it allows immediate reconstruction of the defect and promotes a good functional and cosmetic result; however, administration of perioperative RT may result in a higher plate failure rate.

The AO system for primary mandibular reconstruction

We reviewed the records of 27 patients who underwent primary mandibular reconstruction with AO plates to investigate the outcome and complications of this procedure. Immediate soft-tissue flap coverage was required in 26 patients. Early complications were seen in 44% of the patients, with the highest incidence after irradiation (P = 0.02). Late complications were mostly related to tumor recurrence (12). Late complications not associated with recurrence were persistent pain (2), minor infections (3), plate exposure (3), and plate fracture (1). Good to excellent cosmetic results were obtained in all but 1 patient. Full mastication was not possible for any of our patients, and therefore function was not fully restored. Speech and deglutition were mostly influenced by the amount of soft-tissue resection. Mean follow-up was 20 months (range 3 to 52). At last evaluation, 12 patients were alive and free of disease, and 15 were dead of disease or other causes. Our results show that primary mandibular reconstruction with rigid plates is a safe, effective, and reliable technique to restore mandibular continuity and cosmesis. For lateral defects, this method is a viable alternative to free vascularized osseocutaneous flaps.

Advantages of mandibular reconstruction with the titanium hollow screw osseointegrating reconstruction plate (THORP)

Alloplastic reconstruction following segmental mandibulectomy is a simple way to maintain mandibular segmental relationships, partially preserving form and function for many patients. This study is a retrospective review of 40 patients who had mandibular reconstruction with metal plates over a 6-year period (April 1986 through August 1992). The results of reconstruction with titanium hollow-screw osseointegrating reconstruction plates (THORP [n = 12]) and solid screw (SS) steel and titanium plates (n = 28) are compared. One THORP has been removed as compared to 14 SS plates. While the improved results with THORP may be attributable in part to its advanced design, the success of soft-tissue reconstruction and tumor extirpation are important factors in the early outcome seen in this series. Longer follow-up is needed to determine if THORP can serve as a permanent implant. THORP is the authors' method of choice for alloplastic mandibular reconstruction.

Experience with AO reconstruction plates after partial mandibular resection involving its continuity

A report is presented on experience with the use of 54 plates, without primary bone grafts, after resections for malignant tumours involving the continuity of the mandible, in 52 patients. There were complications in 27 cases: postoperative infection or soft tissue dehiscence occurred 20 times, chronic soft tissue perforation once, screw loosening twice, and plate fracture four times. Adjuvant radiotherapy and/or chemotherapy had no effect on the incidence of the complications. Seventeen of the plates (a good 30%) had to be removed prematurely due to the complications. Major deformity did not always occur if relative stabilization had developed through cicatrix formation. Thirty-seven plates (barely 70%) remained: in 19 cases until the death of the patient, in 3 cases until recurrence, in 12 cases until bone grafting, and in 3 cases they were still in situ up to 65 months. In principle, reconstruction plates have proven themselves. However, application and soft tissue coverage need great care and a great deal of experience.