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Oral Medicine

Authors : Dr. Suraj Agarwal, Dr. Samta Goel Mittal

Abstract

Complete medical and dental careshould be involveto prevent radiotherapy’searly and late complications.Therefore, interdisciplinary care andconsultations with leading physicians are necessary. Optimal control of sideeffects of oncological therapy can beobtained only by preliminary preparationof the patient’s oral cavity precedingprincipal treatment, explaining himthe importance of prophylactic activityand the necessity of taking care of oralhygiene rigorously. Precise clinical examinationand taking aorthopantomogramenable the dentist to plan oral cavitysanitation. This article provides you with general dental considerations for patient’s undergoing radiotherapy for head and neck carcinomas.

Keywords: Chemotherapy, Radiotherapy, Radiation Prosthesis, Orthopantomogram

INTRODUCTION

The current, therapeutic approach towards head and neck cancers is a multifaceted regimen comprising of surgery, chemotherapy, immunotherapy, radiotherapy and dental therapy. The dental professional plays a crucial role in the care of head and neck cancer patients. A detailed oral examination is thus mandatory prior to cancer treatment to -
 
  1. Reduce the risk of complications arising due to treatment
  2. Reduce the risk of infection involving the dentition and the mucosa
  3. Minimize and manage complications arising due to hyposalivation

I. General dental considerations1,2
  1. Pre treatment intervention is directed at maintaining the bone and mucosal integrity, periodontal health and salivary gland function. Regardless the anticipated treatment, a detailed general examination must be performed using the following guidelines.
  2. The patient's detailed history must be obtained to assess the past and present oral problems. Special attention must be paid to the presence and condition of prosthesis if any.
  3. Mucosa in all the areas must be thoroughly examined, palpated, and any abnormality must be recorded.
  4. Periodontal examination must include full mouth probing and assessment of the loss of attachment. Loss of attachment is greater in irradiate fields and hence attachment loss must be considered in pre radiotherapy treatment planning.
  5. Alveolar bone levels must be quantified using bitewing radiographs and tooth mobility if present must be graded on a scale ranging from 0 to 4.
  6. The entire extent of the tumor is visualized clinically and the margins must be palpated.
  7. Any area of anesthesia or paraesthesia must be recorded.
  8. A panoramic radiograph is obligatory to evaluate the entire extent of the lesion and bone destruction. This may be supplemented with Periapical, Occlusal and bite wing views as and when required.
  9. A vitality test for all the teeth must be performed using an electric pulp tester.
  10. The TMJ and muscles of mastication must be examined and the inter incisal opening must be recorded.
  11. Saliva production must be measured prior to the treatment; a culture for patients with infections is indicated during the course of therapy. A shift to cariogenic flora dominated by S.mutans, lactobacilli, Candida and gram negative bacilli is a sure indication of fluoride therapy.
  12. Prior to commencement of treatment, all teeth must be scaled and root planed. Any potential source of irritation must be eliminated. All non vital teeth that cannot be restored must be extracted well in advance before beginning with radiotherapy to prevent Osteoradionecrosis.

II. Dental considerations for patients undergoing radiotherapy1,2

Tumoricidal doses of radiation invariably cause some amount of destruction to the normal tissues. The severity of this damage is related to the type and amount of radiation used, fractionation and the duration of treatment.

It is obligatory for all patients undergoing radiotherapy to take a dental examination. Patient education and counseling plays a vital role in enabling them to comply with the treatment procedures. All possible short term and long term sequelae must be explained to the patient in an attempt to have them comprehend the problem. Once this is done all the procedures to reduce the toxic effects of radiation on the tissues are carried out.

Any tooth that is involved by periodontal disease, trauma or caries that cannot be restored must be extracted prior to radiotherapy. Adequate healing takes place in not less than 10 days following the extraction. More traumatic extraction require more time for healing. If surgical resection of the tumor is planned prior to radiation therapy, then in such cases necessary dental extractions and alveoloplasties can be carried out at the time of surgery itself. This provides adequate time for healing and eliminates the need for additional anesthesia. Those teeth that are not in the line of radiation field must be managed more conservatively.

It is of paramount importance to preserve as many teeth as possible because this aids in good post operative rehabilitation of the patient. The retained teeth are to be protected by periodic application of fluorides and prophylaxis. Radiation prosthesis may be made to protect the important structures from the radiation field. Dental extractions or surgeries carried out after radiotherapy carry a risk of developing osteoradionecrosis. However certain studies have found that post radiation extraction be carried out with adequate antibiotic coverage using lignocaine free local anesthesia and an atraumatic technique has a zero percent incidence of osteoradionecrosis.

Radiation therapy prosthesis:

Radiation therapy prostheses are the ones that are used in the various modalities of treatment to deviate the normal structures from the path of radiation beam. In certain cases it may also be used to hold the tumor in the path of the beam, in the same place during every cycle. The objectives of using radiation therapy prosthesis are as follows,
 
  1. To outline and define the fields of radiation
  2. To assist in directing the beam to the desired site
  3. To provide protection to the contagious normal tissues.
  4. To displace the tongue, lips or cheeks away from the path of radiation
  5. To serve as carrier for radium sources
  6. To facilitate patient set up
  7. To permit duplication of patient arrangement
  8. To simplify dosimetry in the tumor and normal tissues

Types of radiation therapy prosthesis:

Drane&Rahn have classified radiation prosthesis into three types: locator, carriers and stents. It may also be classified as tissue displacers, carriers and cone locating devices. The ideal requirements for a shield or a stent to achieve the goal of therapeutic success are as follows.
 
  1. The prosthesis must be comfortable to the patient.
  2. It should be light in weight, stable and self retaining.
  3. The appliance must be break resistant and easy to repair and clean.
  4. It must require minimal adjustments when it is being used,
  5. It must allow easy visualization of the tissues and must be easy to place and remove.
 
Figure 1: Radiation therapy prosthesis


While as already mentioned, tissue displacers ensure that tissues which have to be irradiated are positioned in the field and tissues be spared are displaced, a carrier appliance is indicated when a radioactive source is administered by means of beads or capsule or needles. Radium and Cesium 137 are frequently used as beads or needles in Brachytherapy. Cone locating devices on the other hand, position the radiation beam precisely on the tumor, thus simplifying intra oral radiation therapy technique.

III. Prosthodontic considerations for post radiotherapy patients1,2

Prosthodontic therapy for post radiotherapy patients has always been a matter of controversy. Indiscriminate use of prosthesis without the proper knowledge of the new oral environment created by radiotherapy can be disastrous to the patient. The time for placement of prosthesis after radiotherapy is subjective. However a period of 1 year after the completion of radiation is considered to be a good time to begin with prosthetic rehabilitation. While some patients may be able to wear their dentures comfortably within a few months, mucosal edema and inflammation may cause pain and discomfort for others.

The clinician must try to obtain as much information as possible from the radiotherapist, surgeon and the patient, to completely evaluate all the physical signs. The status of the oral tissues is an important point to be considered in the prosthetic treatment planning. Severe reduction in the salivary secretion will result in loss of lubrication and retentive properties of the denture. Subtle signs like telangiectasia and scarring indicate tissue friability and are potential sites for tissue breakdown. Tissue undercuts, sharp ridges and any bony exostosis are also possible sites of tissue breakdown and must be considered strictly before treatment planning. Thus all the necessary adjustments and alterations must be incorporated into the prosthesis to accommodate the irritated tissues.

The following Prosthodontic principles must be always followed to minimize the morbidity caused due to construction of prosthesis.
 
  1. All procedures must be atraumatic and non-irritating.
  2. Master impressions must be completely extended and made with non pressure technique. The trays must not be overextended in reflex areas like the muco-buccal fold and mylohyoid ridges.
  3. Impression material used must be non-irritating. Metallic pastes are contraindicated due to their drying effect on the mucosa. Eugenol is an irritant and must be used with caution. Plaster is rigid and liberates heat while setting, so it can cause abrasion of the tissues. Low fusing compounds, rubber/ silicon based impression materials are recommended to prevent tissue injury.
  4. While maxilla-mandibular relations may be recorded by routine methods, use of monoplane occlusion scheme with acrylic teeth is recommended.
  5. Proper overjet and overbite must be provided to prevent cheek, tongue or lip biting.
  6. Any soft tissue/bony undercut must be blocked or relieved.
  7. Heat cure acrylic can be used as a denture base while ensuring minimal residual monomer. Silicone soft liners help to reduce trauma, but are non wettable especially in an already dry mouth.
  8. Final insertion and post insertion care are very critical. All occlusal pressure spots must be relieved. The patient must be seen every day for the next two weeks and any early sign of denture related trauma must be identified and treated. Once the patient is comfortable, a three month follow up is sufficient unless some other complications develop.

Patient Positioning and Treatment Planning 3

Before planning a therapy the treatment position must be chosen, such as on CT or simulation, taking into accounts the technical restriction of the equipment to be used throughout the process. The position should be reasonably comfortable for the patient but compatible with treatment requirements. For all techniques used, the appropriate support devices, such as headrests, chestboards, armpoles, footrests or firm blocks in a range of standard shapes, should be available in each planning and treatment room. The use of soft pillows or cushions is not recommended where accuracy is required, but may be appropriate for large field palliative treatments. The use of thin foam mattresses under the patient will compromise accuracy (Griffith et al 1991), but should be considered for patient comfort where palliation is undertaken, to enable the patient to lie for the treatment exposure.

Depending on the technique being used and the degree of accuracy required the types of couch section/s supporting the patient on planning should have the same degree of rigidity as the couch sections to be used during treatment. Immobilizing patients with head and neck tumors is essential as high doses must be given accurately to small volumes while avoiding adjacent radiosensitive organs such as the brainstem, eye and cervical cord. Patient receiving such therapy often requires a treatment shell made from a thin transparent plastic such as Uvex. This shell is molded to the patient's skin, following every surface contour. Field size entry and exit points can be drawn on the shells rather than the patient’s skin. The shell is molded to the patient's skin. The shell also helps to maintain the patient’s position during treatment with the maximum support and comfort.
 
Figure 2: Uvex Treatment Shell Figure 3: Uvex Treatment Shell molded to patient’s skin


The shell is made by first taking a 'negative' impression of the patient in the treatment position. This used to be done with plaster of Paris. Polyformsoftened in hot water is often used today since it is easier to handle, cleaner, and quicker to set. The Polyform impression is filled with a thick layer of 'Plaster of Paris' a 'positive' model of the treatment area is obtained and this is used in vacuum machine to mould the uvex to the model. In this way a clear plastic shell is made that fits over the patient and clips onto a headrest. The fields, beam entry and exit positions can be marked on the shell will require drilling out as skin sparing is required. 3

Before making a shell the patient must be in the desired treatment position. Patient receiving radiotherapy to middle ear tumors are irradiated with their neck extended so that the posterior beam of a wedged pair avoids the contra lateral eye. Patient with tumors of the glottis or tonsil have their neck in a neutral position so that the cord remains parallel to the posterior border of the opposed pair. Any patient position adopted for planning should be reproducible by means of reference marks giving adequate three-dimensional information. There are two main criteria for achieving correct three-dimensional orientation of the patient on both the treatment and planning table. -
 
  • Straightness of the longitudinal or caudo-cephalic axis.
  • Degree of lateral rotation of the part of the body to be treated.

In order to set the patient correctly in the beam in all three dimensions, two other factors are important.
 
  1. The method used to center the patient in the isocentric axis laterally and longitudinally.
  2. The method used to set the patient at the correct height in relation to the isocentre.

All of these procedures are subject to inaccuracy depending on the method used. Treatment fields will always appear to be correct on setting -up according to surface marks and the specified machine parameters.
 
Figure 4: Patient Positioning for tumor parotid or
middle ear and for tumor of tonsil or glottis


Assessment of accuracy and reproducibility by portal verification/placement 4

To assess the accuracy, with which treatment fields are placed in relation to the target volume, as delineated on planning films, a means of checking the daily treatment field orientation is required. Routine use of portal or field films or electronic portal imaging devices provides verification, on a two-dimensional image, of the anatomy actually irradiated by a field. For a series of patient treated by a particular method, daily or less frequent visual checks, from portal films or digital images, can show the accuracy trends for that treatment method, so that practice can be monitored and analyzed, and accuracy predicted for each technique. Disadvantage of portal system is poor image quality, which is due to inherent lack of contrast at megavoltage energies. At these energies, the major interaction process is Compton scattering, so the intrinsic contrast between soft tissue and bone is severely limited.

Recently CEA and Kodak have introduced new portal film cassette systems with much improved contrast. The image quality is such that highly acceptable portal films should be obtainable in most clinical situations.

Simulation and beam verification 5

With the patient in the treatment position the field entry and exit positions can be marked. This can be done form surface anatomy with radiographs to check the field positions. For treatment more complex than single or parallel opposite fields a simulator is often used.

Simulator is an isocentrically mounted diagnostic x-ray unit that will mimic the geometrical arrangements of any therapy machine. The simulator couch is identical to the therapy couch so that the patient maintains the same position. The couch can be rotated through 360° parallel to the floor (couch angle) and the height adjusted to provide a full range of focus source distances. The diagnostic x-ray unit can provide check radiographs of the intended treatments and has fluoroscopic capability so that the fields can be visually moved or contrast studies performed.

Simulators rotate isocentrically 360° around the tumor volume (gantry angle) and the x-ray head rotates to provide any required 'head twist'. The patient is placed on the couch in the treatment position and the anterior or posterior field aligned. This is performed either clinically or with the aid of the fluoroscopic screening facility using sketch reference points. Contrast media can be used to visualize or identify skin and other soft tissue. The tumor volume is localized in the coronal plane and a verification x-ray taken. A radio-opaque ruler or ring is included to calculate the magnification.

Thorough, independent checking and simulator verification are essential to ensure the correct implementation of a treatment plan. A variety of tools have been designed for this work. Sherouse and Chancy have described a virtual simulator that provides a beam's eye-view (BEV) or specified observer view for a treatment setup.A set of simple 2-dimentional (2D) Kinetic models, used for the same purpose, has been described by Seaby and Thomas.

According to this model simulator, for a visual check of a treatment field set-up the target would be set at the appropriate angles to tilt and turn. The gantry, turntable and collimator angles for treatment would then be set as specified by the treatment plan and the target viewed along a line of sight joining the center of the target volume and the center of the collimators, i.e. the central axis. A check is made that on;
 
  1. The sides of the collimator appear parallel to those of the target.
  2. The orientation of the wedge filter agrees with the plan.

According to A.W. Seaby, M Thomas, and C Craven, there are considerable limitations to the use of this model. In particular, viewing the target is difficult for some positions of the gantry and impossible for others. In addition, the accuracy with which the target is orientated is approximately 1°. The test includes a judgment of whether or not the lines defining two collimator edges are parallel to the long edges defining the target volume. Increasing the scale of the model would improve the accuracy with which the angle of a component could be set. However, the increased size and weight would make lit a much less convenient tool to use at the planning and checking stations.

Despite these limitations, the model has proved useful for treatment planning and training by allowing the visualization of the treatment set-up from the source of x-ray or an observer viewpoint. The models are particularly helpful for the detection of any problem with the orientation of a wedge filter.
 
Figure 5: Checking alignment of the field with target volume by line of sight


PRINCIPLES OF TREATMENT PLANNING 6

Steps in the planning sequence

Treatment planning consists of several basic principles, applied in sequence after tumor diagnosis and staging.

1. Selecting an appropriate technique

The site, size, shape and stage of the tumor as assessed on completion of diagnostic procedures including clinical/surgical and radiological finding determines the type of technique and whether or not radical treatment can be delivered. When a radical treatment is appropriate, the technique chosen is dependent on various factors. These include the size and location of the tumor and the practice of the department or individual consultants for treating particular tumors. The .site of and proximity of a tumor to critical organs influences the degree of treatment complexity required to achieve a radical treatment.

2. Selecting a patient position compatible with the treatment site and the technique envisaged, including the type and arrangement of any supports or accessories

The position to be adopted for the first stage of planning must be the one, which will be used during treatment. Therefore this position must be;
 
  1. Acceptable to the patient, who must be immobile for the duration of each procedure.
  2. Reproducible from one occasion to another.
  3. Compatible with applying treatment beams to the region to be treated.
  4. Compatible with any special requirement for the treatment machine likely to be used.

3. Collecting information about the size, shape of the region of the patient, which contains the tumor and geographically relating the tumor to this and to critical organs in the proximity.

Localizations procedures, for tumors suitable for the application of radical treatments, are used to assess the exact tumor size and position. Computerized tomography (CT) has become the radiological medium of choice for tumor assessment, although magnetic resonance imaging (MRI) is increasingly used.

Ultrasound is also occasionally used for specific purposes such as assessing chest wall thickness is breast planning. The use of simple radiotherapy simulator is common. This together with clinical findings and/or diagnostic radiographs presently appears to be adequate for identifying the target tissue for some routine treatments.

Localization using CT scans.- the scanner (and the patient) must be specially set up for radiotherapy planning scans for information to be valid under treatment conditions. The superior accuracy of localization using CT planning compared with conventional radiography has long been proven.

4. Applying information about the available treatment machines and radiation sources/beams to the patient, to plan a detailed technique for dose prescription and delivery.

5. Performing check procedures on the plan and patient to verify the adequacy or the plan when applied to the patient. Within the planning program, the construction of beam direction shells and manufacture of shielding blocks also take place as required.

Refrences
  1. Myers EN, Suen JY, Myers JN, Hanna EYN. Cancers of the head and neck. 4thedition. Saunders, 2003; pp128-46.
  2. Maxymiw, Wood. Post radiation dental extraction without hyperbaric oxygen.Oral Surg Oral Med Oral Pathol Oral RadiolEndod 1991;72:270-274.
  3. Griffitis SC, Short CA. In: Radiotherapy Principles to Practice, 2nd edition.Churchill Livingston, 2004: pp137-160.
  4. Stewart S, Kam KC. In: Treatment of Oral Cancer, 2nd edition. John Wiley andSons, 1990: pp827-849.
  5. Langmark KA, Goss V. Characterization of new portal film system forradiotherapy verification. Br J Radiol 1990;72:479-484.
  6. Seaby AW, Thomas M, Craven C. A Model Simulator for RadiotherapyTreatment Planning and checking. Br J Radiol 1999;72:293-295.