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Effects of radiotherapy on mandibular reconstruction plates
Effects of Radiotherapy on Mandibular Reconstruction Plates Manuel H. Castillo, MD, Terry M. Button, MS, Ralph Doerr, MD, Maritza I. Homs, MD, Charles W. Pruett, MO, John I. Pearce, MSc, Buffalo,New York
The radiation dose in the vicinity of metal mandibular implants was measured using lithium fluoride ( T L D - 1 0 0 ) thermoluminescent dosimeters. Dosimeters were positioned in contact with Vitallium | and stainless steel (AO) reconstruction plates. Simple transmission was measured with a solid state detector removed from the implant at a depth of 2.5 cm in a polystyrene phantom. The measurements were made for a 6 mV photon beam from a linear accelerator. At points in front of, but in contact with the
metal implants, the dose was greater by 23 percent for Vitallium and 17 percent for stainless steel than that with no implant. At contact behind the implant, the dose was reduced considerably: 14 per-
cent for Vitailium and 13 percent for stainless steel. At remote points behind the implant, the dose was reduced due to attenuation.
p
rimary reconstruction of mandibular defects after ablative surgery remains a challenge to the head and neck surgeon. Several reconstructive modalities have been prescribed to achieve immediate reconstruction that is cosmetically and functionally acceptable. Due to the unacceptable results of wires and pins and the limitations of immediate bone grafting, the search for a successful system has been a persistent one [1-4]. A good alternative for reconstruction is the use of three-dimensional bendable metal plates, as described by Schmoker [5], to achieve continuity and maintain normal function and aesthetics [6-9]. The use of metal plates in mandibular reconstruction has become increasingly popular because of good functional and cosmetic results. A significant number of these patients will require postoperative radiotherapy. From the Department of Surgery, State University of New York at Buffalo and Roswell Park Memorial Institute, Buffalo, New York 14203. Requests for reprints should be addressed to Manuel H. Castillo, MD, Department of Surgery, Veterans' Administration Medical Center, 3495 Bailey Avenue, Buffalo, New York 14215. Presented at the 34th Annual Meeting of the Society of Head and Neck Surgeons, New Orleans, Louisiana, May 22-26, 1988.
The purpose of our study was to determine the interface of metal and tissue between Vitallium and stainless steel reconstruction plates during radiotherapy. MATERIAL AND M E T H O D S The radiation dose in the vicinity of metal mandibular implants was measured using lithium fluoride (TLD100) thermoluminescent dosimeters. These dosimeters are useful for measuring local tissue dose due to their small size (3 by 3 by 1 mm), sensitivity, and near tissue equivalence. Radiation stimulates electrons in the dosimeter material to be trapped in excited states. Heating the dosimeter allows these electrons to return to the valence bond with the subsequent emission of visible light. This light can be detected and converted to an electric current with a photomultiplier tube. The total resulting charge collected over a selected heating range is proportional to the dose delivered to the thermoluminescent dosimeter. A commercial thermoluminescent dosimeter reader was used. Since 6 mV photons are commonly employed for head and neck irradiation, measurements were made using a 6 mV linear accelerator. For this energy, the maximum dose is achieved at a soft-tissue depth of 1.5 cm. Thermoluminescent dosimeters were positioned at this depth and in contact with the metal implants in a water phantom. The dosimeters were sealed in contact with either a Vitallium (Luhr) reconstruction plate or a stainless steel (Synthes) reconstruction plate with a thin Mylar ~ sheet. Simple transmission through the metal implants was measured with a solid state detector (Victoreen) removed from the implant at a depth of 2.5 cm in a polystyrene phantom. RESULTS We investigated the alterations of the local dose distribution caused by the presence of the metal implant. At points above, but in contact with the metal implants, the dose was greater than that with no implant, presumably due to electron contamination. In the case of Vitallium, the increase was approximately 23 4- 10 percent, whereas for stainless steel, the increase was 17 4- 6 percent. The reduction was 14 4- 5 percent for Vitallium and 13 4- 1 percent for stainless steel. At points removed beneath the implant, the dose was decreased due to simple attenuation. These data demonstrate that the thicker stainless steel implant reduces the underlying dose more than Vitallium. The dose to overlying soft tissue in contact with the implant may be significantly greater than the prescribed dose, typically 7,000 cGy, increasing the risk of soft-tissue necrosis.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 156
OCTOBER 1988
261
CASTILLO ET AL
The dose at contact and at points removed beneath the implant was considerably reduced due to attenuation, measuring -3.9 4- 0.5 percent for Vitallium and -6.6 49.5 percent for stainless steel. COMMENTS Surgical access to oral and pharyngeal lesions often necessitates mandibulotomy. Composite resections, including a segment of mandible, remains a cornerstone procedure in oncologic head and neck surgery. Multiple techniques have been described to achieve proper immobilization of the bone fragments and osteosynthesis. One such technique is the use of wires and pins. The following sequence of events is critical to the successful completion of this process: hematoma formation, granulation, growth of connective fibrous tissue, collagen invasion, mineralization, ostcoblasts forming osteoid, and bone remodeling [I0]. However, this technique results in callus formation by secondary bone healing in a significant number of patients. Callus formation is caused by failure to prevent motion, inferring a lack of total stability. Wires contribute to callus formation by allowing bending and rotation of the fragments and not providing rigid fixation. The sequelae of wire and pin placement are fibrous union, angulation, shortening, and rotational deformity. Gaisford et al [1] described an 85 percent removal rate of the Kischner wire prosthesis due to postoperative complications, whereas Sako and Marchetta [2] reported 66 percent. Resection of significant portions of the mandible further contributes to functional and cosmetic disabilities. All of these resections will lead to various degrees of malocclusion, temporomandibular joint dysfunction, and facial asymmetry. To improve functional and cosmetic results, finding better ways of mandibular fixation and bridging of defects became necessary. The concept of mandibular plating arose from this need [11]. In 1970, Allgower et al [12] developed a dynamic compression plate that achieved effective compression osteosynthesis. Spiessel [13] further refined it to permit more accurate stabilization of the bone fragments. At the present time, plates with different characteristics and materials are available. These plates are designed for reconstruction, bridging of defects, and compression and will maintain an accurate anatomic reduction if perfect alignment is achieved prior to plate implantation. Stainless steel, Vitallium, and titanium are the materials most commonly used in the plates. Each metal has different degrees of biocompatibility, mechanical and tensile strength, ductility, and fatigue limit. The immediate rigid immobilization, fixation, and compression afforded by the plates induces primary bone healing and eliminates callus formation [14,15]. Immediate restoration of function, form, and contour, as well as access to the airway and oral cavity for examination, care, hygiene, mastication, and physiotherapy, can thus be obtained. Another advantage is that occlusion is maintained without the need for maxillomandibular fixation. Postoperative management of oncologic patients who have received these implants frequently involves adjuvant 262
THE AMERICAN JOURNAL OF SURGERY
radiotherapy to the resected area. Dramatic dose hetereogeneity exists in the region of metal-tissue interfaces [16]. Physical, geometric, and radiobiologic factors can combine to produce exceptionally high local doses [13]. Scher et al [17] reported that irradiation of an implanted stainless steel plate will cause two different effects on the dose adjacent to the plate. They found an overdosage region in front of the plate equivalent to 120 percent of the prescribed dose and an underdosage region behind the plate receiving 80 percent of the prescribed dose. The increase in patient surface dose resulting from high-energy photon beam contamination by electrons and scattered photons has been well documented [1820]. This contamination results from the interaction of photons with flattening filters, collimators, trimmers, shadow trays, cross hair, air, and the patient. This additional dose is heightened through interaction with high anatomic number (Z) materials. Similar effects are to be expected for medium Z implants. It is common for head and neck patients to receive a total midplane dose of 7,000 cGy, usually delivered bilaterally in the mandible region. Metal implants can significantly alter the expected local dose distribution. The dose to overlying soft tissue in contact with the implant may be significantly greater than 7,000 cGy, increasing the risk of soft-tissue necrosis. In addition, the dose to points beneath the implant will be less than expected due to attenuation. The contact radiologic properties of Vitallium and stainless steel appear to be similar (difference not statistically significant), and measured characteristics overlap within the dispersion of the measurements. Because of the greater thickness required for stainless steel as compared with Vitallium, larger dose reduction to underlying removed points are observed due to simple attentuation. Therefore, we conclude that Vitallium has a slight radiologic advantage over stainless steel. In our clinical experience, soft-tissue necrosis and plate exposure have been successfully prevented by interposition of viable muscle between the plate and the skin, as well as by making the radiation oncologist aware of the implant. We believe that further studies are warranted to evaluate alternative methods of compensating for the increased dose on top of the implant. The possible reduction of contact dose above these implants through the use of low Z coating also deserves investigation.
REFERENCES 1. Gaisford JC, Hanna BC, Gutman D. Management of mandibular fragments following resection. Hast Reconstr Surg 1968; 28: 192-206. 2. Sako K, Marchetta FC. The use of metal prosthesis following anterior mandibulectomy and neck dissection for carcinoma of the oral cavity. Am J Surg 1962; 104: 715-20. 3. Behringer WH, Schweiger JW. Mandibular replacement after resection for tumor. Laryngoscope 1977; 87: 1922-31. 4. Boyne PJ. Restoration of osseous defects and maxillofacial casualties. J Am Dent Assoc 1969; 78: 767-76. 5. Schmoker RR. Mandible reconstruction using a special plate: animal experiments and clinical appearance. J Maxillofac Surg 1983; 11: 99106. 6. Gullane P J, Holmes H. Mandibular reconstruction: new concepts.
VOLUME 156
OCTOBER 1988
RADIOTHERAPY AND MANDIBULAR RECONSTRUCTION PLATES
Arch Otolaryngol Head Neck Surg 1986; 112: 714-9. 7. Strelzow VV. Mandibular reconstruction using implantable stabilization plates. Arch Otolaryngol Head Neck Surg 1983; 109: 333-7. 8. Maisel RH. Reconstruction of the mandible. Laryngoscope 1983; 93: 1122-6. 9. Chow JM, Hill JM. Primary mandibular reconstruction using the AO reconstruction globe. Laryngoscope 1986; 96: 768-73. 10. Coutelier L. Recherches Sur la Guerison des Fractures. Brussels: Arscia, 1969. 11. Luhr HG. Zur stabilen osteosynthese bei unterkieferfrakturen. (Stabile osteosynthesis in mandibular fractures). Dtsch Zahnarztl Z 1968; 23: 754. 12. Allg0wer M, Perren SM, Matter P. A new method for internal fixation: the dynamic compression plate (DCP). Injury 1970; 2: 40. 13. Spiessel B. Grundsatzliches zur knochentransplantation. Fortschr Kiefer Gesichtschir 1976; 20: 14.
14. Sehenk R, WiUenegger H. Histologie der primateren knochenheilung. Arch Klin Chir 1963; 19: 593. 15. Rahn A. Direct and indirect bone healing after operative fracture treatment. Otolaryngol Clin North Am 1987; 20: 425-40. 16. Gibbs FA, Palos B, Giffinet DR. The metal interface effect in irradiation of the oral cavity. Radiology 1976; 119: 705-7. 17. Scher N, Poe D, Reft C, Kuchnil P, Weichselbaum R, Panje WR. Radiotherapy of the resected mandible following stainless steel plate fixation. Laryngoscope 1988; 98: 561-3. 18. Johns HE, Bates LM, Watson HE. Depth dose data and diaphragm design for the saskatchewan 1,000 curie cobalt unit. Br J Radiol 1952; 25: 302. 19. Gray L. Relative surface doses from supervoltage radiation. Radiology 1973; 109: 437. 20. Machie TR, Scrimger JW. Contamination of a 15 mV photon beam by electrons and scattered photons. Radiology 1982; 144: 403.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 156
OCTOBER 1988
263
The radiation dose in the vicinity of metal mandibular implants was measured using lithium fluoride ( T L D - 1 0 0 ) thermoluminescent dosimeters. Dosimeters were positioned in contact with Vitallium | and stainless steel (AO) reconstruction plates. Simple transmission was measured with a solid state detector removed from the implant at a depth of 2.5 cm in a polystyrene phantom. The measurements were made for a 6 mV photon beam from a linear accelerator. At points in front of, but in contact with the
metal implants, the dose was greater by 23 percent for Vitallium and 17 percent for stainless steel than that with no implant. At contact behind the implant, the dose was reduced considerably: 14 per-
cent for Vitailium and 13 percent for stainless steel. At remote points behind the implant, the dose was reduced due to attenuation.
p
rimary reconstruction of mandibular defects after ablative surgery remains a challenge to the head and neck surgeon. Several reconstructive modalities have been prescribed to achieve immediate reconstruction that is cosmetically and functionally acceptable. Due to the unacceptable results of wires and pins and the limitations of immediate bone grafting, the search for a successful system has been a persistent one [1-4]. A good alternative for reconstruction is the use of three-dimensional bendable metal plates, as described by Schmoker [5], to achieve continuity and maintain normal function and aesthetics [6-9]. The use of metal plates in mandibular reconstruction has become increasingly popular because of good functional and cosmetic results. A significant number of these patients will require postoperative radiotherapy. From the Department of Surgery, State University of New York at Buffalo and Roswell Park Memorial Institute, Buffalo, New York 14203. Requests for reprints should be addressed to Manuel H. Castillo, MD, Department of Surgery, Veterans' Administration Medical Center, 3495 Bailey Avenue, Buffalo, New York 14215. Presented at the 34th Annual Meeting of the Society of Head and Neck Surgeons, New Orleans, Louisiana, May 22-26, 1988.
The purpose of our study was to determine the interface of metal and tissue between Vitallium and stainless steel reconstruction plates during radiotherapy. MATERIAL AND M E T H O D S The radiation dose in the vicinity of metal mandibular implants was measured using lithium fluoride (TLD100) thermoluminescent dosimeters. These dosimeters are useful for measuring local tissue dose due to their small size (3 by 3 by 1 mm), sensitivity, and near tissue equivalence. Radiation stimulates electrons in the dosimeter material to be trapped in excited states. Heating the dosimeter allows these electrons to return to the valence bond with the subsequent emission of visible light. This light can be detected and converted to an electric current with a photomultiplier tube. The total resulting charge collected over a selected heating range is proportional to the dose delivered to the thermoluminescent dosimeter. A commercial thermoluminescent dosimeter reader was used. Since 6 mV photons are commonly employed for head and neck irradiation, measurements were made using a 6 mV linear accelerator. For this energy, the maximum dose is achieved at a soft-tissue depth of 1.5 cm. Thermoluminescent dosimeters were positioned at this depth and in contact with the metal implants in a water phantom. The dosimeters were sealed in contact with either a Vitallium (Luhr) reconstruction plate or a stainless steel (Synthes) reconstruction plate with a thin Mylar ~ sheet. Simple transmission through the metal implants was measured with a solid state detector (Victoreen) removed from the implant at a depth of 2.5 cm in a polystyrene phantom. RESULTS We investigated the alterations of the local dose distribution caused by the presence of the metal implant. At points above, but in contact with the metal implants, the dose was greater than that with no implant, presumably due to electron contamination. In the case of Vitallium, the increase was approximately 23 4- 10 percent, whereas for stainless steel, the increase was 17 4- 6 percent. The reduction was 14 4- 5 percent for Vitallium and 13 4- 1 percent for stainless steel. At points removed beneath the implant, the dose was decreased due to simple attenuation. These data demonstrate that the thicker stainless steel implant reduces the underlying dose more than Vitallium. The dose to overlying soft tissue in contact with the implant may be significantly greater than the prescribed dose, typically 7,000 cGy, increasing the risk of soft-tissue necrosis.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 156
OCTOBER 1988
261
CASTILLO ET AL
The dose at contact and at points removed beneath the implant was considerably reduced due to attenuation, measuring -3.9 4- 0.5 percent for Vitallium and -6.6 49.5 percent for stainless steel. COMMENTS Surgical access to oral and pharyngeal lesions often necessitates mandibulotomy. Composite resections, including a segment of mandible, remains a cornerstone procedure in oncologic head and neck surgery. Multiple techniques have been described to achieve proper immobilization of the bone fragments and osteosynthesis. One such technique is the use of wires and pins. The following sequence of events is critical to the successful completion of this process: hematoma formation, granulation, growth of connective fibrous tissue, collagen invasion, mineralization, ostcoblasts forming osteoid, and bone remodeling [I0]. However, this technique results in callus formation by secondary bone healing in a significant number of patients. Callus formation is caused by failure to prevent motion, inferring a lack of total stability. Wires contribute to callus formation by allowing bending and rotation of the fragments and not providing rigid fixation. The sequelae of wire and pin placement are fibrous union, angulation, shortening, and rotational deformity. Gaisford et al [1] described an 85 percent removal rate of the Kischner wire prosthesis due to postoperative complications, whereas Sako and Marchetta [2] reported 66 percent. Resection of significant portions of the mandible further contributes to functional and cosmetic disabilities. All of these resections will lead to various degrees of malocclusion, temporomandibular joint dysfunction, and facial asymmetry. To improve functional and cosmetic results, finding better ways of mandibular fixation and bridging of defects became necessary. The concept of mandibular plating arose from this need [11]. In 1970, Allgower et al [12] developed a dynamic compression plate that achieved effective compression osteosynthesis. Spiessel [13] further refined it to permit more accurate stabilization of the bone fragments. At the present time, plates with different characteristics and materials are available. These plates are designed for reconstruction, bridging of defects, and compression and will maintain an accurate anatomic reduction if perfect alignment is achieved prior to plate implantation. Stainless steel, Vitallium, and titanium are the materials most commonly used in the plates. Each metal has different degrees of biocompatibility, mechanical and tensile strength, ductility, and fatigue limit. The immediate rigid immobilization, fixation, and compression afforded by the plates induces primary bone healing and eliminates callus formation [14,15]. Immediate restoration of function, form, and contour, as well as access to the airway and oral cavity for examination, care, hygiene, mastication, and physiotherapy, can thus be obtained. Another advantage is that occlusion is maintained without the need for maxillomandibular fixation. Postoperative management of oncologic patients who have received these implants frequently involves adjuvant 262
THE AMERICAN JOURNAL OF SURGERY
radiotherapy to the resected area. Dramatic dose hetereogeneity exists in the region of metal-tissue interfaces [16]. Physical, geometric, and radiobiologic factors can combine to produce exceptionally high local doses [13]. Scher et al [17] reported that irradiation of an implanted stainless steel plate will cause two different effects on the dose adjacent to the plate. They found an overdosage region in front of the plate equivalent to 120 percent of the prescribed dose and an underdosage region behind the plate receiving 80 percent of the prescribed dose. The increase in patient surface dose resulting from high-energy photon beam contamination by electrons and scattered photons has been well documented [1820]. This contamination results from the interaction of photons with flattening filters, collimators, trimmers, shadow trays, cross hair, air, and the patient. This additional dose is heightened through interaction with high anatomic number (Z) materials. Similar effects are to be expected for medium Z implants. It is common for head and neck patients to receive a total midplane dose of 7,000 cGy, usually delivered bilaterally in the mandible region. Metal implants can significantly alter the expected local dose distribution. The dose to overlying soft tissue in contact with the implant may be significantly greater than 7,000 cGy, increasing the risk of soft-tissue necrosis. In addition, the dose to points beneath the implant will be less than expected due to attenuation. The contact radiologic properties of Vitallium and stainless steel appear to be similar (difference not statistically significant), and measured characteristics overlap within the dispersion of the measurements. Because of the greater thickness required for stainless steel as compared with Vitallium, larger dose reduction to underlying removed points are observed due to simple attentuation. Therefore, we conclude that Vitallium has a slight radiologic advantage over stainless steel. In our clinical experience, soft-tissue necrosis and plate exposure have been successfully prevented by interposition of viable muscle between the plate and the skin, as well as by making the radiation oncologist aware of the implant. We believe that further studies are warranted to evaluate alternative methods of compensating for the increased dose on top of the implant. The possible reduction of contact dose above these implants through the use of low Z coating also deserves investigation.
REFERENCES 1. Gaisford JC, Hanna BC, Gutman D. Management of mandibular fragments following resection. Hast Reconstr Surg 1968; 28: 192-206. 2. Sako K, Marchetta FC. The use of metal prosthesis following anterior mandibulectomy and neck dissection for carcinoma of the oral cavity. Am J Surg 1962; 104: 715-20. 3. Behringer WH, Schweiger JW. Mandibular replacement after resection for tumor. Laryngoscope 1977; 87: 1922-31. 4. Boyne PJ. Restoration of osseous defects and maxillofacial casualties. J Am Dent Assoc 1969; 78: 767-76. 5. Schmoker RR. Mandible reconstruction using a special plate: animal experiments and clinical appearance. J Maxillofac Surg 1983; 11: 99106. 6. Gullane P J, Holmes H. Mandibular reconstruction: new concepts.
VOLUME 156
OCTOBER 1988
RADIOTHERAPY AND MANDIBULAR RECONSTRUCTION PLATES
Arch Otolaryngol Head Neck Surg 1986; 112: 714-9. 7. Strelzow VV. Mandibular reconstruction using implantable stabilization plates. Arch Otolaryngol Head Neck Surg 1983; 109: 333-7. 8. Maisel RH. Reconstruction of the mandible. Laryngoscope 1983; 93: 1122-6. 9. Chow JM, Hill JM. Primary mandibular reconstruction using the AO reconstruction globe. Laryngoscope 1986; 96: 768-73. 10. Coutelier L. Recherches Sur la Guerison des Fractures. Brussels: Arscia, 1969. 11. Luhr HG. Zur stabilen osteosynthese bei unterkieferfrakturen. (Stabile osteosynthesis in mandibular fractures). Dtsch Zahnarztl Z 1968; 23: 754. 12. Allg0wer M, Perren SM, Matter P. A new method for internal fixation: the dynamic compression plate (DCP). Injury 1970; 2: 40. 13. Spiessel B. Grundsatzliches zur knochentransplantation. Fortschr Kiefer Gesichtschir 1976; 20: 14.
14. Sehenk R, WiUenegger H. Histologie der primateren knochenheilung. Arch Klin Chir 1963; 19: 593. 15. Rahn A. Direct and indirect bone healing after operative fracture treatment. Otolaryngol Clin North Am 1987; 20: 425-40. 16. Gibbs FA, Palos B, Giffinet DR. The metal interface effect in irradiation of the oral cavity. Radiology 1976; 119: 705-7. 17. Scher N, Poe D, Reft C, Kuchnil P, Weichselbaum R, Panje WR. Radiotherapy of the resected mandible following stainless steel plate fixation. Laryngoscope 1988; 98: 561-3. 18. Johns HE, Bates LM, Watson HE. Depth dose data and diaphragm design for the saskatchewan 1,000 curie cobalt unit. Br J Radiol 1952; 25: 302. 19. Gray L. Relative surface doses from supervoltage radiation. Radiology 1973; 109: 437. 20. Machie TR, Scrimger JW. Contamination of a 15 mV photon beam by electrons and scattered photons. Radiology 1982; 144: 403.
THE AMERICAN JOURNAL OF SURGERY
VOLUME 156
OCTOBER 1988
263