The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 88, Issue 5

Scientific Articles | May 01, 2006

Spinal Implants and Radiation Therapy: The Effect of Various Configurations of Titanium Implant Systems in a Single-Level Vertebral Metastasis Model

Murat Pekmezci, MD¹; Bahar Dirican, PhD²; Bülent Yapici, MSc³; Muharrem Yazici, MD¹; Ahmet Alanay, MD¹; Salih Gürdalli, PhD³

¹ Department of Orthopedics, Hacettepe University, Sihhiye, Ankara 06100, Turkey. E-mail address for M. Yazici: yazioglu@hacettepe.edu.tr
² Department of Radiation Oncology, Gulhane Military Medical School, Etlik, Ankara 06018, Turkey
³ Department of Radiation Oncology, Hacettepe University, Ankara 06100, Turkey

View Disclosures and Other Information

Note: The authors thank Ergun Karaagaoglu, PhD, for his contribution to the statistical analyses in this study.

In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Johnson and Johnson, Turkey. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at Hacettepe University Faculty of Medicine, Ankara, Turkey

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2006 May 01;88(5):1093-1100. doi: 10.2106/JBJS.D.02901

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Abstract

Background: The combination of surgery and radiation therapy is a common clinical practice in the treatment of spinal tumors. Although it is known that metallic implants disturb radiation therapy beams, it is not known what kind of dose distributions appear with spinal irradiation in the presence of a spinal implant. The aim of the present study was to investigate the effect of various spinal implant constructs on the dose of radiation delivered to the spinal canal in a single-level metastasis model.

Methods: We performed four spinal implant reconstructions on standard sawbones spine models: posterior instrumentation without anterior column reconstruction, posterior instrumentation with anterior column reconstruction with use of a titanium cage, anterior instrumentation with anterior column reconstruction with use of a titanium cage, and anterior instrumentation with anterior column reconstruction with use of chest tubes filled with bone cement. Irradiation with two different radiation therapy units (a cobalt-60 teletherapy unit and a linear accelerator) was performed twice for each model in a posterior-to-anterior direction, and thermoluminescent dosimeters were used to measure the dose changes in the anterior, middle, and posterior portions of the spinal canal.

Results: Compared with the sawbones-only model, the posterior instrumentation reconstructions resulted in a 5% to 7% decrease in the radiation dose delivered to the spinal canal with both radiation therapy units, whereas the anterior instrumentation reconstructions resulted in a 1% decrease in the dose delivered with the linear accelerator unit and a =2% increase in the dose delivered with the cobalt-60 teletherapy unit. When thermoluminescent dosimeters in the middle of the spinal canal were evaluated individually, anterior instrumentation with anterior column reconstruction with use of bone cement-filled chest tubes resulted in a 5.5% increase in the radiation dose delivered with the cobalt-60 teletherapy unit, whereas all of the other instrumentation models resulted in a <1% disturbance in the radiation dose delivered with both radiation therapy units.

Conclusions: The posterior instrumentation systems did not result in the delivery of an increased dose of radiation to the spinal cord, suggesting that current radiation therapy regimens may be performed without additional harm. The anterior instrumentation systems also appeared to be relatively safe when irradiation was performed with the linear accelerator unit. However, when irradiation was performed with use of the cobalt-60 teletherapy unit, there was an increase in the dose of radiation delivered to the spinal canal in the presence of the anterior instrumentation systems, particularly the anterior column reconstruction with use of bone cement-filled chest tubes. These dose-perturbation characteristics might be important to consider during the calculation of radiation therapy protocols for patients who are going to receive high doses or recurrent treatments that would reach the tolerance limits of the spinal cord.

Figures in this Article

Because of its extensive blood supply, the spine is the most common site of skeletal metastases¹. Spinal metastases usually present with intractable pain, neurological deficit, or pathological fracture. Treatment strategies for metastatic spinal disease include chemotherapy, radiation therapy, and surgery. Surgery often is combined with radiation therapy for several reasons. First, because of the unique anatomy of the spine, once a tumor is outside the confines of the vertebral body, the resection becomes intralesional. Second, in order for the radiation therapy to be effective, the size of the tumor should be reduced to oxygenate its core so that the lethal effects of the ionizing radiation can be enabled. Third, in cases of impending neurological deficit, surgery may produce an immediate effect whereas radiation therapy requires a latent period of days. When used in combination, surgery should precede radiation therapy because of the high rate of wound complications following radiation therapy; in the study by Ghogawala et al.², the rate of wound complications was 32% (nine of twenty-eight) among patients who had radiation before surgery, compared with 12% (four of thirty-four) among patients who had surgery before radiation. However, this introduces another problem, namely, the calculation of the radiation dose delivered to the patient. It has long been known that metallic implants disturb radiation beams^3-8. It has been demonstrated that metallic implants decrease the radiation dose behind them and increase the dose in front secondary to the so-called interface effect³. To the best of our knowledge, there has been only one study that has investigated the radiation dose perturbation effect of spinal implants, and that study demonstrated that the dose changes around the spinal cord were clinically unimportant⁹.

The purposes of the present study were to investigate the effect of various spinal constructs on the radiation dose delivered to the spinal canal, to determine whether there is any difference among instrumentation types and combinations, and to determine whether these dose distributions are affected by the energy level of the radiation beam.

Materials and Methods

Materials and Methods | Results | Discussion | References

Sawbones, which are morphological replicas of the human spine, were used to simulate the spatial orientation of spinal implants with each other and the spine elements accurately. Titanium spinal implants were chosen because they are commonly the implant of choice for tumor patients in daily practice¹⁰. A single-level vertebral body metastasis scenario (L1 metastasis) was selected as the most common indication for a combination of radiation therapy and surgery. The present study was designed to focus only on the dose changes in the spinal canal.

The implants and materials that were used in the study included the titanium ISOLA (AcroMed, Raynham, Massachusetts) for posterior instrumentation; the Kaneda system (Kaneda CI; AcroMed, Neuchatel, Switzerland) for anterior instrumentation; the Harms mesh cage (DePuy Orthopädie, a Johnson and Johnson Company, Sulzbach, Germany) for vertebral body replacement; and polymethylmethacrylate cement (Surgical Simplex P; Howmedica, Limerick, Ireland). Four different instrumentation models were configured: (1) T12-L2 posterior instrumentation without anterior column reconstruction (the PI model), (2) T12-L2 posterior instrumentation, L1 corpectomy, and anterior column reconstruction with a Harms cage (the PI-Ca model); (3) T12-L2 anterior instrumentation, L1 corpectomy, and anterior column reconstruction with a Harms cage (the AI-Ca model); and (4) T12-L2 anterior instrumentation, L1 corpectomy, and anterior column reconstruction with chest tubes filled with bone cement interposition (the AI-Ce model) (Figs. 1-A through 1-D)¹¹. Portions of three chest tubes filled with bone cement were applied together as an anterior support. Since the interface effect depends on the density (atomic number) of the tissue or implant and the atomic number of the plastic chest tube is smaller than that of the polymethylmethacrylate, we did not expect the chest tube to increase the backscattering capacity of the cement bars^3-8. A sawbones-only model (without instrumentation) was irradiated as a control.

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Figs. 1-A, 1-B, 1-C, and 1-D: Figs. 1-A through 1-D Photographs illustrating the instrumentation models that were used in the study. Fig. 1-A The PI model involved posterior instrumentation with pedicle screws (6.5 × 45 mm) and rods (6.35 mm). Fig. 1-B The PI-Ca model involved posterior instrumentation with pedicle screws (6.5 × 45 mm) and rods (6.35 mm) and anterior column reconstruction with a titanium cage (50 mm in height; 22 × 28-mm oval). Fig. 1-C The AI-Ca model involved anterior instrumentation with pedicle screws (6.5 × 45 mm) and rods (6.35 mm) and anterior column reconstruction with an anterior titanium cage (50 mm in height; 22 × 28-mm oval). Fig. 1-D The AI-Ce model involved anterior instrumentation with pedicle screws (6.5 × 45 mm) and rods (6.35 mm) and anterior column reconstruction with chest tubes (size 28G; 50 mm in length) filled with polymethylmethacrylate bone cement.

The radiation dose at different points over the sawbones spine model was measured with use of lithium fluoride thermoluminescent dosimeter chips and a commercial thermoluminescent dosimeter reader (Victoreen 2800, Cleveland, Ohio). In each group, the thermoluminescent dosimeter measurements were repeated twice to check the variables that can affect the measured dose. The thermoluminescent dosimeter chips were calibrated individually before each irradiation. Four different points were selected on the sawbones spine: (1) ventral to the L1 vertebral lamina (the posterior aspect of the canal), (2) the center of the spinal canal at the level of the L1 vertebra (the middle aspect of the canal), (3) dorsal to the posterior wall of the L1 vertebra (the anterior aspect of the canal), and (4) dorsal to the posterior wall of the L2 vertebra (Fig. 2).

Following the placement of the thermoluminescent dosimeters, the spine model was placed in water to simulate soft tissues surrounding the normal spine⁹. Each model was then irradiated with two different radiation therapy units—an isocentric cobalt-60 teletherapy unit (Theretron 780 C; Nordion, Kanata, Ontario, Canada) representing low energy and a linear accelerator unit (Elekta SL-25, West Sussex, United Kingdom) representing high energy—with use of a single nonfractionated dose and a single lateral port at distances of 80 and 100 cm, respectively. The field size was 8 × 10 cm, with an absorbed dose of 50 cGy aimed at the L1 corpus (Table I).

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TABLE I Irradiation Conditions

	Machine^*
	⁶⁰Co	LINAC
Mode	?-Photon	X-ray
Energy	1.25 MeV	6 MV
Source-to-surface distance (cm)	80	100
Field size (cm)	8 × 10	8 × 10
Build up (cm)	0.5	1.5

⁶⁰Co = irradiation with cobalt-60 teletherapy unit, and LINAC = irradiation with linear accelerator unit

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TABLE I Irradiation Conditions

	Machine^*
	⁶⁰Co	LINAC
Mode	?-Photon	X-ray
Energy	1.25 MeV	6 MV
Source-to-surface distance (cm)	80	100
Field size (cm)	8 × 10	8 × 10
Build up (cm)	0.5	1.5

⁶⁰Co = irradiation with cobalt-60 teletherapy unit, and LINAC = irradiation with linear accelerator unit

The sawbones models were irradiated with the two energy levels on two occasions. The beam was directed from posterior to anterior in order to simulate common clinical practice¹². The average of two measurements for each reference point was accepted as the measured absolute dose for that level. In order to evaluate whether there were any significant differences in dose disturbances between the implant designs, the average of all measurements at each reference point was evaluated for each implant system. In addition to measured absolute doses, the percent change in dose induced by each implant system was calculated with the following formula: Percent change=Dose_implant-Dose_sawbone
onlyDose_sawbone
only where Dose_Implant stands for the average dose measured at the reference points when a specific implant system was in place, and Dose_{sawbone only} stands for the average dose measured when there was only sawbones.

Statistical Methods

The overall results were compared with use of the Friedman test, whereas the results of individual groups were compared with use of the Wilcoxon signed-rank test. The level of significance was set at p < 0.05. All analyses were performed with use of the SPSS software program (version 10.0; SPSS, Chicago, Illinois).

Results

Materials and Methods | Results | Discussion | References

Cobalt-60 irradiation resulted in a measured dose of 59.78 cGy in the spinal canal of the sawbones-only model. The posterior instrumentation (PI) system resulted in a decrease in the measured dose to 56.10 cGy. The posterior instrumentation and anterior cage reconstruction (PI-Ca) system demonstrated a similar result, with a measured dose of 55.81 cGy. The anterior instrumentation and anterior cage reconstruction (AI-Ca) system resulted in a dose of 60.11 cGy. Finally, the anterior instrumentation and anterior cement reconstruction (AI-Ce) system resulted in a dose of 61.00 cGy (Table II). The percent change in dose was calculated with use of the measured absolute doses. Cobalt-60 irradiation resulted in a 6.2% decrease in the dose with the posterior instrumentation (PI) system, a 6.6% decrease with the posterior instrumentation and anterior cage reconstruction (PI-Ca) system, a 0.6% increase with the anterior instrumentation and anterior cage reconstruction (AI-Ca) system, and a 2.0% increase with the anterior instrumentation and anterior cement reconstruction (AI-Ce) system (Fig. 3).

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TABLE II Average Doses Measured Within the Canal with the Cobalt-60 and Linear Accelerator Irradiation at 50 cGy

	Dose^*(cGy)
Instrumentation Model	⁶⁰Co	LINAC
Sawbones only	59.78	56.69
Posterior instrumentation (PI)	56.10	53.47
Posterior instrumentation + anterior titanium cage reconstruction (PI-Ca)	55.81	53.68
Anterior instrumentation + anterior titanium cage reconstruction (AI-Ca)	60.11	56.35
Anterior instrumentation + anterior cement-filled chest tube reconstruction (AI-Ce)	61.00	56.32

⁶⁰Co = irradiation with cobalt-60 teletherapy unit, and LINAC = irradiation with linear accelerator unit

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TABLE II Average Doses Measured Within the Canal with the Cobalt-60 and Linear Accelerator Irradiation at 50 cGy

	Dose^*(cGy)
Instrumentation Model	⁶⁰Co	LINAC
Sawbones only	59.78	56.69
Posterior instrumentation (PI)	56.10	53.47
Posterior instrumentation + anterior titanium cage reconstruction (PI-Ca)	55.81	53.68
Anterior instrumentation + anterior titanium cage reconstruction (AI-Ca)	60.11	56.35
Anterior instrumentation + anterior cement-filled chest tube reconstruction (AI-Ce)	61.00	56.32

⁶⁰Co = irradiation with cobalt-60 teletherapy unit, and LINAC = irradiation with linear accelerator unit

Linear accelerator irradiation produced an average dose of 56.69 cGy in the sawbones-only model. This dose decreased to 53.47 cGy with the posterior instrumentation (PI) system and to 53.68 cGy with the posterior instrumentation and anterior cage reconstruction (PI-Ca) system. The measured doses with the anterior instrumentation and anterior cage reconstruction (AI-Ca) and anterior instrumentation and anterior cement reconstruction (AI-Ce) systems were 56.35 and 56.32 cGy, respectively (Table II). Linear accelerator irradiation resulted in a 5.7% decrease in the radiation dose with the posterior instrumentation (PI) system, a 5.3% decrease with the posterior instrumentation and anterior cage reconstruction (PI-Ca) system, a 0.6% decrease with the anterior instrumentation and anterior cage reconstruction (AI-Ca) system, and a 0.7% decrease with the anterior instrumentation and anterior cement reconstruction (AI-Ce) system (Fig. 3).

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Fig. 2: Location of the reference points in the spinal canal, including the anterior aspect of the canal (1), the middle aspect of the canal (2), the posterior aspect of the canal (3), and the adjacent level (4).

The dose-attenuation effect of both posterior instrumentation models was significant (p < 0.05), whereas the dose-attenuation effect of the anterior instrumentation and anterior cage reconstruction (AI-Ca) system was not significantly different from the sawbones-only model (p > 0.05) with either cobalt-60 or linear accelerator irradiation, with the numbers available (Table III). Although the dose-concentration effect of the anterior instrumentation and anterior cement reconstruction (AI-Ce) system with cobalt-60 irradiation was significant (p < 0.05), the dose-attenuation effect of the same system with linear accelerator irradiation was not (p > 0.05), with the numbers available (Table III). The dose-attenuation effects of the posterior instrumentation (PI) and posterior instrumentation and anterior cage reconstruction (PI-Ca) systems were not significantly different from each other (p > 0.05) (Table III). However, the dose patterns of the posterior instrumentation and anterior cage reconstruction (PI-Ca) and anterior instrumentation and anterior cage reconstruction (AI-Ca) systems were significantly different from each other (p < 0.05) (Table III). Finally, the difference between the dose patterns of the anterior instrumentation and anterior cage reconstruction (AI-Ca) and anterior instrumentation and anterior cement reconstruction (AI-Ce) systems was not significant (p > 0.05), with the numbers available (Table III).

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TABLE III Results of the Statistical Analysis^*

	P Value
	⁶⁰Co	LINAC
PI vs. SB	0.03	0.02
PI-Ca vs. SB	0.01	0.01
AI-Ca vs. SB	0.33	0.29
AI-Ce vs. SB	0.04	0.40
PI vs. PI-Ca	0.33	0.33
PI-Ca vs. AI-Ca	0.01	0.02
AI-Ca vs. AI-Ce	0.09	0.62

⁶⁰Co = irradiation with cobalt-60 teletherapy unit; LINAC = irradiation with linear accelerator unit; SB = sawbones only; PI = posterior instrumentation without an anterior column reconstruction; PI-Ca = posterior instrumentation, L1 corpectomy, and anterior column reconstruction with Harms cage; AI-Ca = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with Harms cage; and AI-Ce = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with bone cement-filled chest-tube interposition

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TABLE III Results of the Statistical Analysis^*

	P Value
	⁶⁰Co	LINAC
PI vs. SB	0.03	0.02
PI-Ca vs. SB	0.01	0.01
AI-Ca vs. SB	0.33	0.29
AI-Ce vs. SB	0.04	0.40
PI vs. PI-Ca	0.33	0.33
PI-Ca vs. AI-Ca	0.01	0.02
AI-Ca vs. AI-Ce	0.09	0.62

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Fig. 3: Illustration depicting the percent dose changes at the spinal canal with different implant combinations at two energy levels. PI = posterior instrumentation without anterior column reconstruction; PI-Ca = posterior instrumentation, L1 corpectomy, and anterior column reconstruction with a Harms cage; AI-Ca = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with a Harms cage; AI-Ce = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with chest tubes filled with bone cement; Co 60 = irradiation with the cobalt-60 teletherapy unit; and LINAC = irradiation with the linear accelerator unit.

Although the difference between the anterior instrumentation and anterior cage reconstruction (AI-Ca) and anterior instrumentation and anterior cement reconstruction (AI-Ce) systems was not significant, the p value of 0.09 prompted us to evaluate the individual reference points within these systems. Linear accelerator irradiation of both systems resulted in dose attenuation of <1% at all reference points. On the other hand, cobalt-60 irradiation resulted in variable changes in the dose patterns in the form of either a decrease (attenuation) or an increase (concentration) in dose. All reference points had dose changes of <1%, except for the middle of the spinal canal in the anterior instrumentation and anterior cement reconstruction (AI-Ce) system, which had a 5.5% increase in dose (Fig. 4).

Discussion

Materials and Methods | Results | Discussion | References

Radiation therapy is an effective modality for the treatment of spinal tumors; however, it is associated with serious complications, the most important of which is myelopathy. Individual patient sensitivity plays an important role in radiation tolerance; however, the occurrence of myelopathy essentially depends on the total radiation dose¹³. Although several regimens for conventional external-beam radiation therapy have been developed, delivering a total dose of 4500 cGy¹⁴, it has been reported that myelopathy can occur with doses of as low as 3350 cGy¹⁵. Therefore, there is no safe dose regarding the amount of radiation delivered to the spinal cord for the purposes of obtaining clinically satisfactory results while avoiding spinal cord complications.

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Fig. 4: Illustration depicting the percent dose changes at the reference points in AI-Ca and AI-Ce systems with cobalt-60 and linear LINAC irradiation. AI-Ca = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with Harms cage; AI-Ce = anterior instrumentation, L1 corpectomy, and anterior column reconstruction with chest tubes filled with bone cement; Co = irradiation with Cobalt-60 teletherapy unit; and Li = irradiation with linear accelerator unit.

The current approach to the treatment of a spinal metastasis is radiation therapy, either alone or in combination with surgery. When used in combination, surgery should precede radiation therapy because of the high rate of wound complications when surgery is performed after radiation therapy². The presence of surgical hardware complicates the calculation of the safe and effective dose for the patient's treatment protocol. Metallic implants attenuate the dose applied as a function of the difference between the atomic numbers of the tissues and implants^3-8. When a radiation beam meets a structure with a high atomic number, some of the formed electrons are reflected back, resulting in concentration of the dose in front of the implant. In a similar manner, some of the electrons that are formed cannot pass through the implant, resulting in attenuation of the dose behind the implant³. It is difficult to predict dose changes in cases of spinal instrumentation when multiple metallic implants interact with each other in multiple planes. In this scenario, the spinal cord is subject to either attenuation or backscatter or, most likely, both.

In the sawbones-only model, we measured doses that were higher than the administered dose because the radiation beams have build-up points at different depths where the target dose is formed. Beyond the build-up point, the dose gradually diminishes. Since the target area usually lies much deeper, the actual administered dose is increased to obtain the target dose at the desired depth. Our study demonstrated that all implant combinations resulted in a dose disturbance in some manner. The posterior instrumentation model that we studied produced an attenuation effect of 5% to 7% that was independent of the energy level of the beam. The reduction was approximately double the rate observed by Liebross et al.⁹. The ISOLA system that we used has narrower interrod distance when compared with the Texas Scottish Rite Hospital system (Medtronic Sofamor Danek, Memphis, Tennessee) used by Liebross et al. Therefore, the rods of the ISOLA system might have produced a shield effect over the canal, which may have enhanced the attenuation effect. We also demonstrated that, with the numbers available, the addition of a cage to a posterior instrumentation system (the PI-Ca model) did not significantly alter the dose delivered to the spinal canal with either radiation therapy unit when compared with the posterior instrumentation (PI) model (Table III).

In order to determine whether there was a difference between the anterior and posterior instrumentation systems in terms of spine irradiation, the anterior instrumentation and anterior cage reconstruction (AI-Ca) and posterior instrumentation and anterior cage reconstruction (PI-Ca) groups were compared. The posterior instrumentation (PI-Ca) system resulted in a decrease in the dose delivered to the canal (p < 0.02) (Table III). Since both systems did not result in an increase in the dose delivered to the canal, we propose that they can be used interchangeably in terms of the risk of spinal myelopathy.

We also looked for the effect of the materials used for anterior column reconstruction on the radiation therapy dose and compared the anterior instrumentation and anterior cage reconstruction (AI-Ca) and anterior instrumentation and anterior cement reconstruction (AI-Ce) groups. Linear accelerator irradiation resulted in a negligible (<1%) attenuation effect with both systems. Cobalt-60 irradiation demonstrated a backscatter effect, which was =2% with both systems; however, the anterior instrumentation and anterior cement reconstruction (AI-Ce) system resulted in a backscatter effect that was three times the size of that of the anterior instrumentation and anterior cage reconstruction (AI-Ca) system. Statistical analysis demonstrated that only the combination of the anterior instrumentation and anterior cement reconstruction (AI-Ce) system and cobalt-60 irradiation resulted in a significant (p = 0.04) change in the dose delivered to the spinal canal, whereas the combinations of all of the other anterior systems and radiation therapy units caused no significant change in dose, with the numbers available (Table III).

Further evaluation of individual reference points revealed a 5.5% increase in dose at the thermoluminescent dosimeter that was located at the center of the spinal canal during cobalt-60 irradiation of the anterior instrumentation and anterior cement reconstruction (AI-Ce) model (Fig. 4). Although the clinical importance of this dose concentration at the center of the spinal canal is unknown, it might be reasonable to consider this effect during radiation therapy planning for a patient with anterior instrumentation and cement reconstruction.

The present study had some limitations. First, the density of the sawbones was lower than that of a cadaveric spine and the sawbones likely did not behave as a human spine. However, we believe that this difference in densities does not affect the validity of our conclusions because our evaluation was based on the dose differences between the models. Second, we performed only two separate measurements with each construct. This number of repetitions may seem inadequate; however, in order to increase the accuracy of our measurements, we calibrated each thermoluminescent dosimeter individually instead of performing a group calibration. Also, the literature suggests that two or three measurements are usually sufficient^7,8,16.

In conclusion, our results demonstrate that spinal implants have variable effects on the dose delivered to the spinal canal, depending on the implant construction and the energy level of the radiation beam. Knowledge of these dose-perturbation characteristics may be helpful when calculating the radiation therapy protocols for such patients who are going to receive very high doses that would reach the tolerance limits of the spinal cord. ?

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Topics

radiation therapy ; cobalt ; chest tubes ; neoplasm metastasis ; reconstructive surgical procedures ; spinal canal ; titanium ; teleradiotherapy procedure ; spinal cage ; vertebrae

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Murat Pekmezci, Bahar Dirican, Bülent Yapici, Muharrem Yazici, Ahmet Alanay, Salih Gürdalli; Spinal Implants and Radiation Therapy: The Effect of Various Configurations of Titanium Implant Systems in a Single-Level Vertebral Metastasis Model. The Journal of Bone & Joint Surgery. 2006 May;88(5):1093-1100.

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