In/ .I Radrarion Oncology Biol Phys.. Vol. 23, PP. 639-645 Pnnted in the U.S.A. All rights resewed.
0360-3016192 $5.00 + .OO Copyright 0 1992 Pergamon Press Ltd.
??Special Feature
DEVICES JOHANNES
VALUABLE
H. A. M. KAANDERS,
IN HEAD
AND NECK RADIOTHERAPY
M.D.,* TERENCE J. FLEMING, D.D.S.,+
MOSHE H. MAOR,
M.D.*
AND LESTER
J. PETERS,
K. KIAN ANG, M.D.,*
M.D.*
The University of Texas M.D. Anderson Cancer Center, Houston, TX
Normal tissue reactions limit the use of radiotherapy in the management of patients with head and neck neoplasms. Customized intraoral stents can help prevent unnecessary irradiation of various normal tissues thus reducing severity of reactions. Two basic types of devices, referred to as shielding and positional stents, are presented. The fabrication and the application of such devices are illustrated through five case reports. Recommendations on use of these tools and the possibility of combining these means with methods to improve dose distribution within the target volume containing air gaps are provided. Close collaboration between the attending radiotherapist and dentist is essential for designing appropriate devices for individual patients. However, when properly designed and used, these stents are effective in reducing treatment morbidity. Intraoral stents, Head and neck cancer, Radiotherapy, Complications. A shielding device serves to reduce the radiation dose ad-
INTRODIJYIION
ministered to normal tissues by incorporating shielding material, whereas a positional device serves to displace normal tissues out of the treatment fields. An ancillary function of positional stents is to facilitate the use of internal bolus to fill surgical cavities. Five examples of intraoral stents to illustrate their use are presented in this paper.
Radiotherapy of head and neck cancers requires meticulous planning because of the presence of multiple critical tissues and organs and the complex pathways of spread of many tumors. These anatomical constraints impose a challenge to deliver radiation doses sufficient to obtain a high tumor control probability while keeping the incidence of serious complications acceptable. Two classes of normal tissue reactions limit the delivery of radiation treatment. First, acute mucosal reactions limit the rate (weekly dose) at which fractionated radiotherapy can be delivered. Such reactions, if excessive, may cause unplanned treatment interruption, thereby diminishing the efficacy of treatment by allowing tumor clonogens to repopulate. Second, late side effects such as soft tissue or bone necrosis, limit the total radiation dose that can be administered. In a substantial number of head and neck patients, it is possible to reduce normal tissue reactions by the use of simple, custom-made intraoral devices designed to exclude uninvolved tissues from the treatment portals or to provide shielding of tissues within the treatment volume. Patients with primary cancer of the oral cavity, oropharynx, paranasal sinuses, and salivary glands are most suitable for the use of such devices. In general, these devices can be categorized into two basic types: shielding or positional.
METHODS
AND MATERIALS
All stents were designed after consultation between the attending radiotherapist and dentist with regard to the set-up of radiation fields and the tissues to be spared. With this knowledge, oral impressions were taken in the appropriate maxillo-mandibular jaw relationship and the resulting dental casts were mounted on a dental articulator in the correct treatment position. The stent was initially sculptured in dental baseplate wax. The resulting wax model was verified in the patient and adjustments were made as necessary. Issues assessed during the try-in session were: (a) adequacy and reproducibility of the stent with regard to tissue positioning; (b) ease of insertion and removal; (c) patient tolerance and stability in the treatment position; (d) simplicity of design; (e) safety (especially with reference to aspiration).
* Dept. of Radiotherapy. +Dept. of Dental Oncology. Reprint requests to: K. Kian Ang, M.D., Department of Radiotherapy, M.D. Anderson Cancer Center, 15 1.5 Holcombe Blvd., Box 97, Houston, TX 7703 1.
This investigationwas supported in part by grant CA06294 awarded by the National Cancer Institute, United States Department of Health and Human Services. Accepted for publication 3 January 1992. 639
640
I. J. Radiation Oncology 0 Biology 0 Physics
After approval, the wax model was duplicated in methyl methacrylate following the same procedures used in complete denture fabrication. Transparent methyl methacrylate was preferred, particularly when shielding alloy was added to the stent. In cases no. 1, no. 2, and no. 5 where a Lipowitz alloy, i.e., Cerrobend,* was used following processing of the acrylic resin stent, a void of appropriate contour was cut into the plastic to retain the protective metal. This void is readily cut by utilizing common dental equipment, a dental lathe and acrylic resin finishing burs, routinely used in contouring the acrylic resin of partial or complete removable dentures. Because the melting temperature of the alloy is 158°F (70”(Z), the molten alloy could be poured directly into the void without concern for heat damage causing any dimentional changes to the plastic. After cooling, the alloy was coated with at least 0.5 cm of acrylic resin to minimize electron backscatter and to prevent contact of metal with the mucosal surface. Earlier non-published studies completed by the Department of Radiation Physics at this cancer center utilized a film phantom and a buildup type ionization chamber in connection with an electrometer to determine the thickness of Cerrobend required for protection for the various therapeutic ionizing beams. Those studies also measured the radiation dose received by those tissues adjacent to the stent. These study results have been used in the evolution of the Cerrobend containing stents herein described. Occasionally, it was necessary to modify the stent in the later stages of treatment because of trismus or severe reactions of unshielded mucosa which was accomplished by judicial reduction of the acrylic bulk. RESULTS Case no. 1: A 37-year-old woman presented with a 1.5 cm mass at the left angle of the mandible. The head and neck exam was otherwise unremarkable and the facial nerve function was intact. Material for cytology was obtained by fine needle aspiration and was interpreted as pleomorphic adenoma. At surgery, the tumor was found to be mainly located in the deep lobe of the parotid gland. It was well encapsulated and was dissected out along with the surrounding normal parotid tissue. The facial nerve was preserved. Pathologic examination revealed an acinic cell carcinoma measuring 2.4 cm in maximum diameter. All gross tumor was resected but tumor cells extended to the surgical margin. For this reason, postoperative radiotherapy was recommended. The left parotid bed was treated with an ipsilateral appositional field using a combination of 20 MeV electrons and 18 MV photons weighted 4: 1, respectively. A dose of 56 Gy was delivered in 2 Gy fractions, specified at the
* Cerro Metal Product,
Bellefort,
PA.
Volume 23, Number 3, 1992
90% isodose line. To reduce the dose to the underlying brain during the electron treatments 2 cm of beveled bolus was placed over the superior part of the field. After a dose of 44 Gy the field was reduced off the spinal cord, and treatment to the postauricular and posterior cervical area was completed with 12 MeV electrons. A custom-made intraoral stent containing Cerrobend was used to shield the tongue and contralateral oral mucosa from the electron beam treatments by positioning between the alveolar processes and the tongue, displacing the tongue toward the contralateral side. The stent was held in place by the teeth fitting in the ridge on the lateral side (Figures IA-C). Although the Cerrobend was sufficiently thick to reduce the transmitted dose to approximately 10% when treating with electrons, it would have increase the dose directly behind the stent when treating with high energy photons due to the forward scatter of secondary electrons. For this reason when the patient was treated with photons to maintain the treatment field geometry a duplicate stent without the lead-alloy was used. Because 80% of the dose was delivered by electrons, there was still a significant protection of the tongue and contralateral oral mucosa such that mucositis in these areas could be prevented. Figure 1D shows a port-film with the stent in position. Case no. 2: A 66-year-old woman presented with a right buccal mucosa lesion. On physical examination she was found to have an infiltrative tumor measuring approximately 3.5 cm in largest diameter, extending anteriorly almost to the oral commissure. The tumor was 1.Oto 1.5 cm thick without apparent skin involvement. There were two right submandibular nodes palpable, the largest measuring 2 cm in diameter. Biopsy revealed squamous cell carcinoma. The patient underwent resection of the tumor and a right modified neck dissection. Pathologic examination revealed a well-differentiated squamous cell carcinoma of the buccal mucosa with microscopic extension into the skeletal muscle and skin of the cheek. Nine lymph nodes were recovered in the surgical specimen and four of these contained metastatic squamous cell carcinoma with extension beyond the capsule. The patient was given postoperative radiotherapy. The tumor bed and right upper neck were treated with an ipsilateral appositional 13 MeV electron field to a given dose of 60 Gy in 30 fractions. The ipsilateral mid- and lower jugular nodes and the posterior cervical chain were encompassed by a 9 MeV electron field. These areas were treated to a given dose of 50 Gy in 25 fractions. The scar extending into the mid-neck was given a 4 Gy boost with 6 MeV electrons. A variation of the stent as described in case # 1 was used for this patient. As in the previous case, the stent containing Cerrobend was placed between the alveolar processes and the tongue, serving to displace the tongue and
Devices in head and neck radiotherapy 0 J. H. A. M. KAANDERS
641
et al.
(A)
((3
(B)
(D)
Fig. 1. Intraoral stent for shielding the tongue and contralateral oral mucosa during ipsilateral radiation treatment for a parotid gland tumor. (A) Lateral view: the flange on the lateral side of the stent containing occlusal registration. (8) Stent insertion. (C) Device in treatment position. (D) Port film showing the position of the stent in relation to the radiation field.
In this case, the right oral commissure needed to be included in the field and thus, fall off was required anteriorly. In order to shield the contralateral part of both lips and the left oral commissure, the stent protruded anteriorly (Figures 2A-C). Case no. 3: A 49-year-old woman presented with a three-month history of enlarging neck masses. On examination she was found to have a 3 cm exophytic lesion on the left side of the base of the tongue, extending laterally to the glossopharyngeal sulcus. Mobility of the tongue was normal. There were three palpable nodes in the neck (a 3.5 X 3 cm right upper jugular node, a 2.5 X 2 cm left jugulo-digastric node, and a 2 X 2 cm left mid-jugular node). Biopsy of the primary lesion revealed squamous cell carcinoma. The patient received radiotherapy followed by neck dissection. The primary tumor and upper neck nodes were to shield the tongue and contralateral
oral mucosa.
treated with lateral parallel-opposed portals using Cobalt60 photons to a dose of 45 Gy in 25 fractions delivered to the isocenter. Reduction off the spinal cord was made and therapy was continued with 6 MV photons to a tumor dose of 54 Gy in 30 fractions. The posterior cervical strips were supplemented with electron beams. The mid- and lower jugular nodes were treated through an anterior appositional Cobalt-60 field and supplemented with a smaller posterior field to a tumor dose of 54 Gy in 30 fractions. During the last 2.5 weeks of this basic treatment, the primary tumor and palpable nodes were boosted to a total tumor dose of 72 Gy. The boost was delivered in 1.5 Gy per fraction given as second daily treatments using the concomitant boost technique ( 1). Figures 3A-B show the stent for this patient. It consisted of a horizontal tongue positioner with protrusions fitting the occlusal surfaces of the mandibular and maxillary teeth which served to separate the upper and lower jaws. The
642
I. J. Radiation Oncology 0 Biology0 Physics
(A)
Volume 23, Number 3, 1992
left soft and hard palate extending to the left maxillary tuberosity. The neck had no palpable nodes. The patient subsequently underwent a wide resection of the tumor with partial palatectomy and partial maxillectomy. Pathologic examination showed an adenoid cystic carcinoma measuring 3 cm in largest diameter. The surgical margins were close; therefore, he was referred for postoperative radiotherapy. He was treated in the supine position with right and left lateral parallel-opposed 6 MV photon fields which encompassed the surgical bed and upper neck. A dose of 60 Gy, in 2 Gy fractions, was delivered to the isocenter. A field reduction was made after 44 Gy. A modification of the stent as described in the previous case was used. It served to open the mouth and depress most of the oral tongue out of the radiation field. The surgical procedure left a relatively large air cavity which could compromise the dose homogeneity in the target
(B)
(A)
Fig. 2. Intraoral stent for protection of the tongue and contralateral oral mucosa and commissure during ipsilateral radiation treatment for a tumor of the buccal mucosa. (A) Lateral view. (B) Stent mounted on an articulator. (C) Anterior end of the stent protrudes through the mouth for shielding part of the lips and the left oral commissure.
tongue was depressed by the horizontal portion such that it could be treated with adequate margins without encompassing the palate, upper gums, and most of the buccal mucosa. Case no. 4: A 4 1-year-old man sought medical attention because of a two-year history of a slowly enlarging soft palate mass. On physical examination he was found to have a 4 cm submucosal soft tissue mass involving the
(8) Fig. 3. Device to open the mouth and depress the tongue. (A) Stent mounted on maxillary and mandibular casts. (B) Portal film showing the position of the tongue held down by the depressor and the mouth kept open by the stent so that the palate, gum, and most of the buccal mucosa were excluded from the field.
Devices in head and neck radiotherapy 0 J. H. A. M.
KAANDERS
643
et al.
(El
(C)
F)
Fig. 4.(A) Surgical defect after left partial palatectomy and partial maxillectomy in a patient with an adenoid cystic carcinoma. (B) A balloon-supporting stent: the lower blade serves to depress the tongue and the cradle supports a water-filled balloon. (C) Side view of the position of the balloon. (D) Stent in position: a space was created to facilitate filling of balloon. (E) Stent and balloon in position. (F) Simulation film: the tongue blade was marked by a radiopaque wire and the balloon was filled with contrast material to indicate the position of the device relative to the normal tissues; the lateral orbital canthi and oral commissures were also marked; the solid and dotted black lines represent the large and boost fields, respectively.
644
I. J. RadiationOncology 0 Biology0 Physics
(A)
Volume23, Number3, 1992 volume (Figure 4A). For this reason, a balloon filled with water (tissue equivalent for radiation absorption) was placed in the surgical defect. In order to support the balloon, a cradle was added on top of the tongue-depressing part (Figures 4B-C). A space was provided between the upper incisors and the blade to insert the balloon (Figures 4D-E). Figure 4F shows the position of the balloon filled with contrast material on the patient’s simulation film. Case no. 5: A 76-year-old woman presented with a lesion on the right side of the upper lip. On examination there was a slightly raised, erythematous lesion extending from the vermilion of the upper lip to the nasal ala with upward retraction of the lip (Figure 5A). The lesion was 2.2 cm in largest dimension and involved almost the entire thickness of the lip. The inner mucosal lining was, however, intact. There were no palpable lymph nodes in the neck. A biopsy of this lesion showed basal cell carcinoma of which the patient received radiation therapy. The tumor and a l-cm margin of normal tissue were encompassed by an appositional 9 MeV electron field. A lead cut-out was used for skin collimation and a bolus of l-cm thickness was placed over the skin to ensure an adequate dose at the surface of the tumor. Also, a bolus was placed in the right nostril to enhance the dose homogeneity. A dose of 50 Gy was given in 25 fractions, specified at the 90% isodose line which was followed by an implant with radium needles. A stent was placed over the upper and lower alveolar processes to open the mouth and separate the lips, thereby excluding the lower lip from the radiation field (Figures 5B-C). It also displaced the tongue posteriorly so that it was out of the range of the electron beam. To shield the gum, the part of the stent that was between the upper lip and the alveolar ridge was filled with Cerrobend. Overdosage to the mucosa of the upper lip by backscatter was prevented by acrylic coating. At the completion of electron beam treatment, confluent mucositis occurred at the upper lip mucosa, whereas no appreciable reaction was observed on the mucosa of the gum.
DISCUSSION The 5 case histories presented here demonstrate the use of dental prosthetic devices to displace or protect normal tissues during radiotherapy in head and neck cancer patients. In Case four, the use of water bolus to reduce dose inhomogeneity resulting from a large air cavity in the treatment volume is also illustrated. Although it is rela-
Fig. 5.(A) A woman with a slightly raised lesion extending from the vermillion of the upper lip to the nasal ala with upward retraction of the lip. (B) The stent used mounted on an articulator. The upper part of the stent that separated the upper lip from the alveolar process contained Cerrobend to shield the latter. (C) The stent in treatment position. The lower flange held the lower lip away from the radiation field.
Devices in head and neck radiotherapy 0 J. H. A. M.
tively simple to construct these stents using materials familiar to dentists and maxillofacial prosthodontists (2, 4) it is crucial that the attending radiotherapist and the dentist or prosthodontist work closely to design the devices on an individual basis in order to obtain an optimally functioning product. This procedure can be completed in 2 to 3 days. To secure adequate positioning and optimal shielding, the devices should be customized. If desired, radiopaque material can be placed in the stent to enhance identification on simulation films or port films and thus verify its proper position. If a lead-alloy is used for shielding purposes, care should be taken to minimize electron back scatter (3). This can be accomplished by coating the alloy with acrylic resin of 0.5 cm thickness. The thickness of the alloy needed for effective shielding depends on the energy of the electrons used (5). The advantage of the positional stents as described in Cases three and four over the more traditionally used cork and tongue blade is three-fold. First, it is easier to reproduce the position of the customized stent on each treatment session because it is adjusted to and fits the occlusal surfaces of the upper and lower molars and premolars. In contrast, a cork with tongue blade hinges on the incisors
KAANDERS
et al.
645
only. In edentulous patients, the stent can be shaped over the alveolar ridges, thus assuring a more reliable position. Second, the positional stent secures more adequate depression of the tongue. Finally, the stent can be modified to support a water-filled balloon as shown in Case four. The tongue-depressing stent is useful to treat cancers of the tongue and floor of mouth where the tongue itself is part of the target volume, as well as of tumors of the palate, nasal cavity, and paranasal sinuses where one wishes to spare the tongue. Variations on this stent can be used if desired, for example, to protrude the upper or lower lip in order to bring these structures out of the radiation field. The shielding stents as described in Cases one and two are used with ipsilateral treatment of well lateralized tumors of the oral cavity (buccal mucosa, retromolar trigone), parotid gland, lip, and sometimes skin of the cheek. In our experience, both types of devices have been effective in reducing the intensity and/or volume of radiation-induced mucositis and in improving radiation distribution. In view of the known detrimental effect of treatment interruption in the radiotherapy of head and neck cancer, we strongly recommend the use of devices of this type whenever possible.
REFERENCES 1. Ang, K. K.; Peters, L. J.; Weber, R. S.; Maor, M. H.; Morrisen, W. H.; Wendt, C. D.; Brown, B. W. Concomitant boost radiotherapy schedules in the treatment of carcinoma of the oropharynx and nasopharynx. Int. J. Radiat. Oncol. Biol. Phys. 19: 1339-1345; 1990. 2. Fleming, T. J.; Rambach, S. C. A tongue-shielding radiation stent. J. Prosthet. Dent. 49: 389-392; 1983. 3. Khan, F. M. Electron beam therapy. In: Khan, F. M., ed.
The physics of radiation therapy. Baltimore, MD: Williams & Wilkins; 1984: 337-34 1. 4. Knudson, R. C.; Williams, E. 0. Radiographically detectable intraoral positional radiation stent. J. Prosthet. Dent. 61: 1-3; 1989. 5. Purdy, J. A.; Choi, M. C.; Feldman, A. Lipowitz metal shielding thickness for dose reduction of 6-20 MeV electrons. Med. Phys. 7: 251-253; 1980.
0360-3016192 $5.00 + .OO Copyright 0 1992 Pergamon Press Ltd.
??Special Feature
DEVICES JOHANNES
VALUABLE
H. A. M. KAANDERS,
IN HEAD
AND NECK RADIOTHERAPY
M.D.,* TERENCE J. FLEMING, D.D.S.,+
MOSHE H. MAOR,
M.D.*
AND LESTER
J. PETERS,
K. KIAN ANG, M.D.,*
M.D.*
The University of Texas M.D. Anderson Cancer Center, Houston, TX
Normal tissue reactions limit the use of radiotherapy in the management of patients with head and neck neoplasms. Customized intraoral stents can help prevent unnecessary irradiation of various normal tissues thus reducing severity of reactions. Two basic types of devices, referred to as shielding and positional stents, are presented. The fabrication and the application of such devices are illustrated through five case reports. Recommendations on use of these tools and the possibility of combining these means with methods to improve dose distribution within the target volume containing air gaps are provided. Close collaboration between the attending radiotherapist and dentist is essential for designing appropriate devices for individual patients. However, when properly designed and used, these stents are effective in reducing treatment morbidity. Intraoral stents, Head and neck cancer, Radiotherapy, Complications. A shielding device serves to reduce the radiation dose ad-
INTRODIJYIION
ministered to normal tissues by incorporating shielding material, whereas a positional device serves to displace normal tissues out of the treatment fields. An ancillary function of positional stents is to facilitate the use of internal bolus to fill surgical cavities. Five examples of intraoral stents to illustrate their use are presented in this paper.
Radiotherapy of head and neck cancers requires meticulous planning because of the presence of multiple critical tissues and organs and the complex pathways of spread of many tumors. These anatomical constraints impose a challenge to deliver radiation doses sufficient to obtain a high tumor control probability while keeping the incidence of serious complications acceptable. Two classes of normal tissue reactions limit the delivery of radiation treatment. First, acute mucosal reactions limit the rate (weekly dose) at which fractionated radiotherapy can be delivered. Such reactions, if excessive, may cause unplanned treatment interruption, thereby diminishing the efficacy of treatment by allowing tumor clonogens to repopulate. Second, late side effects such as soft tissue or bone necrosis, limit the total radiation dose that can be administered. In a substantial number of head and neck patients, it is possible to reduce normal tissue reactions by the use of simple, custom-made intraoral devices designed to exclude uninvolved tissues from the treatment portals or to provide shielding of tissues within the treatment volume. Patients with primary cancer of the oral cavity, oropharynx, paranasal sinuses, and salivary glands are most suitable for the use of such devices. In general, these devices can be categorized into two basic types: shielding or positional.
METHODS
AND MATERIALS
All stents were designed after consultation between the attending radiotherapist and dentist with regard to the set-up of radiation fields and the tissues to be spared. With this knowledge, oral impressions were taken in the appropriate maxillo-mandibular jaw relationship and the resulting dental casts were mounted on a dental articulator in the correct treatment position. The stent was initially sculptured in dental baseplate wax. The resulting wax model was verified in the patient and adjustments were made as necessary. Issues assessed during the try-in session were: (a) adequacy and reproducibility of the stent with regard to tissue positioning; (b) ease of insertion and removal; (c) patient tolerance and stability in the treatment position; (d) simplicity of design; (e) safety (especially with reference to aspiration).
* Dept. of Radiotherapy. +Dept. of Dental Oncology. Reprint requests to: K. Kian Ang, M.D., Department of Radiotherapy, M.D. Anderson Cancer Center, 15 1.5 Holcombe Blvd., Box 97, Houston, TX 7703 1.
This investigationwas supported in part by grant CA06294 awarded by the National Cancer Institute, United States Department of Health and Human Services. Accepted for publication 3 January 1992. 639
640
I. J. Radiation Oncology 0 Biology 0 Physics
After approval, the wax model was duplicated in methyl methacrylate following the same procedures used in complete denture fabrication. Transparent methyl methacrylate was preferred, particularly when shielding alloy was added to the stent. In cases no. 1, no. 2, and no. 5 where a Lipowitz alloy, i.e., Cerrobend,* was used following processing of the acrylic resin stent, a void of appropriate contour was cut into the plastic to retain the protective metal. This void is readily cut by utilizing common dental equipment, a dental lathe and acrylic resin finishing burs, routinely used in contouring the acrylic resin of partial or complete removable dentures. Because the melting temperature of the alloy is 158°F (70”(Z), the molten alloy could be poured directly into the void without concern for heat damage causing any dimentional changes to the plastic. After cooling, the alloy was coated with at least 0.5 cm of acrylic resin to minimize electron backscatter and to prevent contact of metal with the mucosal surface. Earlier non-published studies completed by the Department of Radiation Physics at this cancer center utilized a film phantom and a buildup type ionization chamber in connection with an electrometer to determine the thickness of Cerrobend required for protection for the various therapeutic ionizing beams. Those studies also measured the radiation dose received by those tissues adjacent to the stent. These study results have been used in the evolution of the Cerrobend containing stents herein described. Occasionally, it was necessary to modify the stent in the later stages of treatment because of trismus or severe reactions of unshielded mucosa which was accomplished by judicial reduction of the acrylic bulk. RESULTS Case no. 1: A 37-year-old woman presented with a 1.5 cm mass at the left angle of the mandible. The head and neck exam was otherwise unremarkable and the facial nerve function was intact. Material for cytology was obtained by fine needle aspiration and was interpreted as pleomorphic adenoma. At surgery, the tumor was found to be mainly located in the deep lobe of the parotid gland. It was well encapsulated and was dissected out along with the surrounding normal parotid tissue. The facial nerve was preserved. Pathologic examination revealed an acinic cell carcinoma measuring 2.4 cm in maximum diameter. All gross tumor was resected but tumor cells extended to the surgical margin. For this reason, postoperative radiotherapy was recommended. The left parotid bed was treated with an ipsilateral appositional field using a combination of 20 MeV electrons and 18 MV photons weighted 4: 1, respectively. A dose of 56 Gy was delivered in 2 Gy fractions, specified at the
* Cerro Metal Product,
Bellefort,
PA.
Volume 23, Number 3, 1992
90% isodose line. To reduce the dose to the underlying brain during the electron treatments 2 cm of beveled bolus was placed over the superior part of the field. After a dose of 44 Gy the field was reduced off the spinal cord, and treatment to the postauricular and posterior cervical area was completed with 12 MeV electrons. A custom-made intraoral stent containing Cerrobend was used to shield the tongue and contralateral oral mucosa from the electron beam treatments by positioning between the alveolar processes and the tongue, displacing the tongue toward the contralateral side. The stent was held in place by the teeth fitting in the ridge on the lateral side (Figures IA-C). Although the Cerrobend was sufficiently thick to reduce the transmitted dose to approximately 10% when treating with electrons, it would have increase the dose directly behind the stent when treating with high energy photons due to the forward scatter of secondary electrons. For this reason when the patient was treated with photons to maintain the treatment field geometry a duplicate stent without the lead-alloy was used. Because 80% of the dose was delivered by electrons, there was still a significant protection of the tongue and contralateral oral mucosa such that mucositis in these areas could be prevented. Figure 1D shows a port-film with the stent in position. Case no. 2: A 66-year-old woman presented with a right buccal mucosa lesion. On physical examination she was found to have an infiltrative tumor measuring approximately 3.5 cm in largest diameter, extending anteriorly almost to the oral commissure. The tumor was 1.Oto 1.5 cm thick without apparent skin involvement. There were two right submandibular nodes palpable, the largest measuring 2 cm in diameter. Biopsy revealed squamous cell carcinoma. The patient underwent resection of the tumor and a right modified neck dissection. Pathologic examination revealed a well-differentiated squamous cell carcinoma of the buccal mucosa with microscopic extension into the skeletal muscle and skin of the cheek. Nine lymph nodes were recovered in the surgical specimen and four of these contained metastatic squamous cell carcinoma with extension beyond the capsule. The patient was given postoperative radiotherapy. The tumor bed and right upper neck were treated with an ipsilateral appositional 13 MeV electron field to a given dose of 60 Gy in 30 fractions. The ipsilateral mid- and lower jugular nodes and the posterior cervical chain were encompassed by a 9 MeV electron field. These areas were treated to a given dose of 50 Gy in 25 fractions. The scar extending into the mid-neck was given a 4 Gy boost with 6 MeV electrons. A variation of the stent as described in case # 1 was used for this patient. As in the previous case, the stent containing Cerrobend was placed between the alveolar processes and the tongue, serving to displace the tongue and
Devices in head and neck radiotherapy 0 J. H. A. M. KAANDERS
641
et al.
(A)
((3
(B)
(D)
Fig. 1. Intraoral stent for shielding the tongue and contralateral oral mucosa during ipsilateral radiation treatment for a parotid gland tumor. (A) Lateral view: the flange on the lateral side of the stent containing occlusal registration. (8) Stent insertion. (C) Device in treatment position. (D) Port film showing the position of the stent in relation to the radiation field.
In this case, the right oral commissure needed to be included in the field and thus, fall off was required anteriorly. In order to shield the contralateral part of both lips and the left oral commissure, the stent protruded anteriorly (Figures 2A-C). Case no. 3: A 49-year-old woman presented with a three-month history of enlarging neck masses. On examination she was found to have a 3 cm exophytic lesion on the left side of the base of the tongue, extending laterally to the glossopharyngeal sulcus. Mobility of the tongue was normal. There were three palpable nodes in the neck (a 3.5 X 3 cm right upper jugular node, a 2.5 X 2 cm left jugulo-digastric node, and a 2 X 2 cm left mid-jugular node). Biopsy of the primary lesion revealed squamous cell carcinoma. The patient received radiotherapy followed by neck dissection. The primary tumor and upper neck nodes were to shield the tongue and contralateral
oral mucosa.
treated with lateral parallel-opposed portals using Cobalt60 photons to a dose of 45 Gy in 25 fractions delivered to the isocenter. Reduction off the spinal cord was made and therapy was continued with 6 MV photons to a tumor dose of 54 Gy in 30 fractions. The posterior cervical strips were supplemented with electron beams. The mid- and lower jugular nodes were treated through an anterior appositional Cobalt-60 field and supplemented with a smaller posterior field to a tumor dose of 54 Gy in 30 fractions. During the last 2.5 weeks of this basic treatment, the primary tumor and palpable nodes were boosted to a total tumor dose of 72 Gy. The boost was delivered in 1.5 Gy per fraction given as second daily treatments using the concomitant boost technique ( 1). Figures 3A-B show the stent for this patient. It consisted of a horizontal tongue positioner with protrusions fitting the occlusal surfaces of the mandibular and maxillary teeth which served to separate the upper and lower jaws. The
642
I. J. Radiation Oncology 0 Biology0 Physics
(A)
Volume 23, Number 3, 1992
left soft and hard palate extending to the left maxillary tuberosity. The neck had no palpable nodes. The patient subsequently underwent a wide resection of the tumor with partial palatectomy and partial maxillectomy. Pathologic examination showed an adenoid cystic carcinoma measuring 3 cm in largest diameter. The surgical margins were close; therefore, he was referred for postoperative radiotherapy. He was treated in the supine position with right and left lateral parallel-opposed 6 MV photon fields which encompassed the surgical bed and upper neck. A dose of 60 Gy, in 2 Gy fractions, was delivered to the isocenter. A field reduction was made after 44 Gy. A modification of the stent as described in the previous case was used. It served to open the mouth and depress most of the oral tongue out of the radiation field. The surgical procedure left a relatively large air cavity which could compromise the dose homogeneity in the target
(B)
(A)
Fig. 2. Intraoral stent for protection of the tongue and contralateral oral mucosa and commissure during ipsilateral radiation treatment for a tumor of the buccal mucosa. (A) Lateral view. (B) Stent mounted on an articulator. (C) Anterior end of the stent protrudes through the mouth for shielding part of the lips and the left oral commissure.
tongue was depressed by the horizontal portion such that it could be treated with adequate margins without encompassing the palate, upper gums, and most of the buccal mucosa. Case no. 4: A 4 1-year-old man sought medical attention because of a two-year history of a slowly enlarging soft palate mass. On physical examination he was found to have a 4 cm submucosal soft tissue mass involving the
(8) Fig. 3. Device to open the mouth and depress the tongue. (A) Stent mounted on maxillary and mandibular casts. (B) Portal film showing the position of the tongue held down by the depressor and the mouth kept open by the stent so that the palate, gum, and most of the buccal mucosa were excluded from the field.
Devices in head and neck radiotherapy 0 J. H. A. M.
KAANDERS
643
et al.
(El
(C)
F)
Fig. 4.(A) Surgical defect after left partial palatectomy and partial maxillectomy in a patient with an adenoid cystic carcinoma. (B) A balloon-supporting stent: the lower blade serves to depress the tongue and the cradle supports a water-filled balloon. (C) Side view of the position of the balloon. (D) Stent in position: a space was created to facilitate filling of balloon. (E) Stent and balloon in position. (F) Simulation film: the tongue blade was marked by a radiopaque wire and the balloon was filled with contrast material to indicate the position of the device relative to the normal tissues; the lateral orbital canthi and oral commissures were also marked; the solid and dotted black lines represent the large and boost fields, respectively.
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Volume23, Number3, 1992 volume (Figure 4A). For this reason, a balloon filled with water (tissue equivalent for radiation absorption) was placed in the surgical defect. In order to support the balloon, a cradle was added on top of the tongue-depressing part (Figures 4B-C). A space was provided between the upper incisors and the blade to insert the balloon (Figures 4D-E). Figure 4F shows the position of the balloon filled with contrast material on the patient’s simulation film. Case no. 5: A 76-year-old woman presented with a lesion on the right side of the upper lip. On examination there was a slightly raised, erythematous lesion extending from the vermilion of the upper lip to the nasal ala with upward retraction of the lip (Figure 5A). The lesion was 2.2 cm in largest dimension and involved almost the entire thickness of the lip. The inner mucosal lining was, however, intact. There were no palpable lymph nodes in the neck. A biopsy of this lesion showed basal cell carcinoma of which the patient received radiation therapy. The tumor and a l-cm margin of normal tissue were encompassed by an appositional 9 MeV electron field. A lead cut-out was used for skin collimation and a bolus of l-cm thickness was placed over the skin to ensure an adequate dose at the surface of the tumor. Also, a bolus was placed in the right nostril to enhance the dose homogeneity. A dose of 50 Gy was given in 25 fractions, specified at the 90% isodose line which was followed by an implant with radium needles. A stent was placed over the upper and lower alveolar processes to open the mouth and separate the lips, thereby excluding the lower lip from the radiation field (Figures 5B-C). It also displaced the tongue posteriorly so that it was out of the range of the electron beam. To shield the gum, the part of the stent that was between the upper lip and the alveolar ridge was filled with Cerrobend. Overdosage to the mucosa of the upper lip by backscatter was prevented by acrylic coating. At the completion of electron beam treatment, confluent mucositis occurred at the upper lip mucosa, whereas no appreciable reaction was observed on the mucosa of the gum.
DISCUSSION The 5 case histories presented here demonstrate the use of dental prosthetic devices to displace or protect normal tissues during radiotherapy in head and neck cancer patients. In Case four, the use of water bolus to reduce dose inhomogeneity resulting from a large air cavity in the treatment volume is also illustrated. Although it is rela-
Fig. 5.(A) A woman with a slightly raised lesion extending from the vermillion of the upper lip to the nasal ala with upward retraction of the lip. (B) The stent used mounted on an articulator. The upper part of the stent that separated the upper lip from the alveolar process contained Cerrobend to shield the latter. (C) The stent in treatment position. The lower flange held the lower lip away from the radiation field.
Devices in head and neck radiotherapy 0 J. H. A. M.
tively simple to construct these stents using materials familiar to dentists and maxillofacial prosthodontists (2, 4) it is crucial that the attending radiotherapist and the dentist or prosthodontist work closely to design the devices on an individual basis in order to obtain an optimally functioning product. This procedure can be completed in 2 to 3 days. To secure adequate positioning and optimal shielding, the devices should be customized. If desired, radiopaque material can be placed in the stent to enhance identification on simulation films or port films and thus verify its proper position. If a lead-alloy is used for shielding purposes, care should be taken to minimize electron back scatter (3). This can be accomplished by coating the alloy with acrylic resin of 0.5 cm thickness. The thickness of the alloy needed for effective shielding depends on the energy of the electrons used (5). The advantage of the positional stents as described in Cases three and four over the more traditionally used cork and tongue blade is three-fold. First, it is easier to reproduce the position of the customized stent on each treatment session because it is adjusted to and fits the occlusal surfaces of the upper and lower molars and premolars. In contrast, a cork with tongue blade hinges on the incisors
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only. In edentulous patients, the stent can be shaped over the alveolar ridges, thus assuring a more reliable position. Second, the positional stent secures more adequate depression of the tongue. Finally, the stent can be modified to support a water-filled balloon as shown in Case four. The tongue-depressing stent is useful to treat cancers of the tongue and floor of mouth where the tongue itself is part of the target volume, as well as of tumors of the palate, nasal cavity, and paranasal sinuses where one wishes to spare the tongue. Variations on this stent can be used if desired, for example, to protrude the upper or lower lip in order to bring these structures out of the radiation field. The shielding stents as described in Cases one and two are used with ipsilateral treatment of well lateralized tumors of the oral cavity (buccal mucosa, retromolar trigone), parotid gland, lip, and sometimes skin of the cheek. In our experience, both types of devices have been effective in reducing the intensity and/or volume of radiation-induced mucositis and in improving radiation distribution. In view of the known detrimental effect of treatment interruption in the radiotherapy of head and neck cancer, we strongly recommend the use of devices of this type whenever possible.
REFERENCES 1. Ang, K. K.; Peters, L. J.; Weber, R. S.; Maor, M. H.; Morrisen, W. H.; Wendt, C. D.; Brown, B. W. Concomitant boost radiotherapy schedules in the treatment of carcinoma of the oropharynx and nasopharynx. Int. J. Radiat. Oncol. Biol. Phys. 19: 1339-1345; 1990. 2. Fleming, T. J.; Rambach, S. C. A tongue-shielding radiation stent. J. Prosthet. Dent. 49: 389-392; 1983. 3. Khan, F. M. Electron beam therapy. In: Khan, F. M., ed.
The physics of radiation therapy. Baltimore, MD: Williams & Wilkins; 1984: 337-34 1. 4. Knudson, R. C.; Williams, E. 0. Radiographically detectable intraoral positional radiation stent. J. Prosthet. Dent. 61: 1-3; 1989. 5. Purdy, J. A.; Choi, M. C.; Feldman, A. Lipowitz metal shielding thickness for dose reduction of 6-20 MeV electrons. Med. Phys. 7: 251-253; 1980.
