radiation therapy of head and neck tumors n.
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  1. RADIATION THERAPY OF HEAD AND NECK TUMORS Dr. Vinit Shah Junior Resident Prosthodontics FODS, KGMU

  2. Contents • PART - I • Introduction • Physical principles • Interaction of radiation and tissues • Fractionation • Brachytherapy • Indications for treatment of head and neck tumours • Use of prosthetic stents and splints during therapy • Radiation effects • Part - II • Dental management – dentulous patients • Osteoradionecrosis • Prosthetic management – edentulous patients • Implants in irradiated tissues • Irradiation of existing implants • Conclusion

  3. Introduction John Beumer III, Tohomas A. Curtis, and Russel Nishimura: • Radiation therapy is defined as the therapeutic use of ionizing radiation. • Two categories of radiation ; • Electromagnetic • Particulate • Electromagnetic wave of wavelength less than 1 angstrom are called photons. • They have neither mass nor charge. Measured in electron volt. eg x- rays and gamma rays. • Particulate radiation have mass and are charged negatively (electrons), positively ( protons, alpha particles) or are neutral (neutrons)

  4. Interactions of Radiation and Tissues • Radiation absorption by tissues • Biologic effects • Reoxygenation • Repopulation • Accelerated repopulation

  5. Radiation absorption by tissue Direct ionizing Indirect Ionizing

  6. INTERACTIONS OF RADIATION AND TISSUES • When Charged particles have sufficient energy , they are directly ionizing. ( pass through target matter, and disrupt the atomic structure by producing chemical and biological changes). • Photons and neutrons (uncharged particle) are indirectly ionizing .(give up their energy to produce fast moving charged particles.)

  7. Biologic effect • The primary effect of radiation is confined to the intranuclear structures such as DNA and mitotic apparatus. • Damage to intranuclear structures may be; 1. lethal 2. sublethal(may not be apparent until atleast one cellular division is attempted). • If enough time passes between the sublethal event and cellular division, the damage may be corrected, process known as repair of sublethal damage.

  8. Reoxygenation • The indirect action of photon beam on target tissues is dependent on the level of oxygenation concept known as reoxygenation. • Anoxic tissues - 3 times more resistant to radiation effects oxygen+ organic free radicals = organic peroxides • This reaction leaves more hydroxyl free radical which can then interact with target molecules that would otherwise react with hydrogen to form inactive molecules of water.

  9. Redistribution • The radiation effect on individual cells may vary according to the position they occupies in the cell cycle at the time of irradiation. • More vulnerable during G1 and in mitotic phase • Relatively radioresistant at the beginning and the end of DNA synthesis. • Radiation given during these phases, increased cell killing, known as redistribution.

  10. Repopulation and accelerated repopulation • In a given enough overall treatment time, cell in the irradiated tissue can proliferate and repopulate known as repopulation. • It has been observed that any cytotoxic agent, including radiation, can trigger colonogenic surviving cells to divide faster than before. This is called accelerated repopulation. • Estimated to occur about 4 weeks after the initiation of the treatment. • Thus in order to keep pace with the more rapid growth of tumor cell, a more rapid delivery of treatment may be needed.

  11. Isoeffect Models • Biologically Equivalent Treatment Schedules • As dose increases, tissue changes become more profound and irreversible  increased complications. • Important variables: • Number of fractions • Dose per fraction • Total dose • Time period

  12. FRACTIONATION • Radiation therapy is delivered in the series of treatment or fractions. “Conventional fractionation” (in US) • total dose - 6500 to 7200cGy • daily fractions -180-200cGy • period- 7weeks • given Monday through friday

  13. FRACTIONATION Advantages: • Allows regular reoxygenation of the tumor during the course of treatment, making it more radiosensitive. • Offers radiation to effect more tumor cells during the radiosensitive phase of their cell cycle. • Normal cell seems to recover more completely between fractions from sublethal damage than do tumor cells.

  14. BRACYTHERAPY • Method of radiation treatment in which sealed radioactive source is used to deliver the dose to a short distance by interstitial(direct insertion into tissue), intracavitary(placement within a cavity) or surface application(molds). (Boost for advanced tumors or primarily for small lesions) • Most commonly used radioisotope in head and neck regions are iridium 192, cesium137 and radium 226. • Radiation sources may be form of needles, narrow tubes, wires or small beads.

  15. Advantages – • Rapid decrease in dose with distance from radiation source (inverse square law). • Thus a high radiation dose can be given to the tumor while sparing surrounding normal tissues. • Also dose rate is low relative to external beam therapy, it can be considered a highly fractionated form of irradiation • Thus continuous low dose irradiation tends to synchronize the cell cycle and allows sublethal damage repair.

  16. Disadvantages – • Inhomogeneity. • Requires the operator to have adequate technical and conceptual skills to achieve good dose distribution. • Exposure to room personnel and to therapist specially with the use of radium needles.

  17. Indications for treatment of head and neck tumors • Decision regarding the use of radiation and/or surgery for the control of primary lesion is a function of the location and extent of the tumor. • carcinoma of nasopharynx, base of tongue, soft palate, tonsillar fossaradiation therapy is the treatment of choice because of surgical morbidity, difficult access, and high risk of regional lymph node involvement.

  18. Carcinoma of salivary gland and alveolar ridge should be treated surgically followed by radiotherapy due to potential for bony infiltration. • Early carcinoma of glottic larynx and tongue are equally well controlled by radiation or surgery but radiation offer a better functional result • Hard deeply infiltrated carcinoma of tongue are less likely to be controlled by radiation. (Due to fixation to the vocal cord) ( superficial / exophytic lesions have higher cure rate with radiation than deeply infiltrated lesions)

  19. Prosthetic devices in Radiation Therapy These are used to optimize the delivery of radiation while reducing the associated morbitity.

  20. Positioning stents • Used to rearrange tissue topography within the radiation field and displace normal tissues outside the radiation field. Useful in; • tongue and floor of the mouth lesions. • inferior positioning of tongue and mandible enabling to lower the radiation field. (sparing to parotid gland – more salivary output )

  21. For dentulous patients. • Interocclusal stent prepared that extends lingually from both occlusal tables with a flat plate ff acrylic resin. • Serves to depress the tongue • A hole is made in the anterior horizontal segment • Serves as an orientation hole for reproducible tongue position.

  22. For edentulous patients • Impressions • Interocclusal record at half/ two-thirds of maximum opening • Mounting • Base plate wax attached to mandibular record base to form the portion which will depress the tongue. • Occlusal index for comfort and stability

  23. Per oral cone positioning device • use to boost radiation over Small superficial lesions (T1 or T2 in sizes) in accessible locations in the oral cavity. • The tumor site > adjacent vital structures • useful in; • lesions like floor of mouth, hard palate, soft palate, or tongue. (Spares vital adjacent tissues such as mandible, teeth and salivary gland.)

  24. Shielding • Helpful if patient is to receive unilateral dose of radiation. • Useful in; • Buccal mucosa, skin and alveolar ridge. • It has been reported that; 1 cm thickness of Cerrobend alloy will prevent transmission of 95%of an 18 Mev electron beam radiation exposure to normal structures.

  25. Lipowitz metal or cerrobend alloy is commonly used to shield. • Cerrobend Alloy: • Low fusing alloy • 50% bismuth • 26.7% lead • 13.3% tin • 10% cadmium

  26. Recontouring tissues to simplify dosimetry • Use of a stent to flatten the lip and corner of the mouth, thereby placing the entire lip in the same plane to deliver uniform dosage of radiation. Useful in; • treating skin lesions associated with upper and lower lips.

  27. Positioning a radioactive source Radioactive source (cesium132 or iridium 192). Preloaded After loaded • Preloaded (RS position within prosthesis prior to carrier insertion) medical staffs receives some exposure. • After loading technique, isotopes are threaded into the hollow tubing after the carrier is in predesigned location reduces the radiation exposure to medical staff.

  28. Templates used in direct implantation Direct implantation of the radioactive source in the tumor. useful in; Lesion of the tongue and anterior floor of the mouth. • Used to position the source and also determine the proper depth of insertion. • Once prosthesis is secured , tissue conditioning material is flowed over the implants to maintain them in proper position during the treatment period.

  29. Tissue bolus devices • Irregular tissue = uneven radiation dose • A bolus is a tissue equivalent material placed directly onto or into irregular tissue contours to produce a more homogenous dose distribution. commonly used materials are- saline, wax, acrylic resins. This method optimizes the dosimetry by restoring tissue density throughout the defect and ensures uniform delivery of radiation and also protects friable healing tissue such as skin graft.

  30. Following orbital exenteration and maxillectomy • Irregular contours and air spaces • Tissues at greatest risk of radiation injury: skin grafts, areas of thin mucosa over bone and brain tissue

  31. Radiation effects • Oral mucous membrane • Taste • Olfaction • Edema • Trismus • Salivary glands • Bone • Periodontium • Teeth

  32. Radiation effects ORAL MUCOUS MEMBRANE- • Initially an erythema appears, epithelium becomes thin, less keratinized, vascularity decreases and mucosa becomes more fibrotic leading to extensive ulceration and desquamation. • Pain and dysphagia resulting in weight loss . • Mucositis begins to appear 2-3 weeks after the start of therapy and reaches peak toward the end of therapy. • Soft palate> hypopharynx> floor of the mouth > buccal mucosa> base of the tongue> dorsum of tongue • Healing is rapid and usually complete in 2-3 weeks.

  33. After therapy, changes in tissues in the field of therapy predispose to tissue breakdown and delayed healing • Epithelium thin and less keratinized • Submucosa less vascular and fibrotic • These changes make fabrication and tolerance of prosthesis difficult.

  34. Taste Taste bud shows signs of degeneration and atrophy at 1000 cGy and at cancericidal dose the architecture of taste bud is completely obliterated. • Alteration in taste are discovered during the second week and continue throughout the course of treatment. • Perception of bitter and acid flavors are more impaired than salt and sweet. • Taste gradually return to normal levels after therapy is completed. • Xerostomia  decreased recovery of taste

  35. Olfaction • Since the olfactory epithelium is high in nasal passage and not included within the radiation field, the sense of smell is less affected.

  36. Edema • Edema of tongue, buccal mucosa, submental and submandibular area is occasionally clinically significant. • Apparent during the early postradiation period when scaring and fibrosis are common (Impairs patency of both lymphatic and venous channel resulting in obstruction.) • Occasionally, edema reaches proportion which compromise tongue mobility, impairs salivary control, make denture utilization and speech articulation more difficult.

  37. Trismus • Most noticeable following treatment of nasopharyngeal, parotid, palatal and nasal sinus tumors in which TMJ and muscles of mastication are in radiation field. • Maximum mouth opening may be reduced upto 10-15mm. • Treatment • Exercise • Dynamic bite openers

  38. Salivary gland • Saliva changes in volume, viscosity, pH, inorganic and organic constituents, predisposing to caries, periodontal disease, impairment of taste acuity, poor tolerance of prosthetic restoration, and difficulty in swallowing.

  39. Bone • Bone is 1.8 times as dense as soft tissue , thus, it absorbs a large proportion of radiation than does a comparable volume of soft tissue. • Mandible absorbs more than maxilla because of increased density, plus reduced vascularity accounts for increase incident of osteoradionecrosis.

  40. Periodontium • Periodontal ligament thickens and fibres become disoriented. • Exhibit decreased cellularity and vascularity • cementum capacity for repair and regeneration is also compromised.

  41. Teeth • Evidence in changes of crystalline structure of enamel, dentin, or cementum following RT is unclear. • Pulp shows decrease in vascular elements, with accompanying fibrosis and atrophy. • Pulpal response to infection, trauma, and various dental procedures appears compromised. Level as low as 2500 cGy can have marked effect on tooth development. Exposure • before calcification completion - tooth bud may be damaged . • At later stage of development - may arrest growth.

  42. Composition of oral flora • Radiation field that include substantial portions of salivary glands leads to significant changes in the composition of oral flora. • Increase in the population of streptococcus mutans, lactobacillus and actinomyces predisposing to dental caries. • Brown has reported upto 100 fold increase in fungal populations. • Post therapy candidiasis of corner of mouth and beneath prosthetic appliance is common.

  43. Contents • PART - I • Introduction • Physical principles • Interaction of radiation and tissues • Fractionation • Brachytherapy • Indications for treatment of head and neck tumours • Use of prosthetic stents and splints during therapy • Radiation effects • Part - II • Dental management – dentulous patients • Osteoradionecrosis • Prosthetic management – edentulous patients • Implants in irradiated tissues • Irradiation of existing implants • Conclusion

  44. Dental management –dentulous patients • Criteria for pre-radiation Extraction- • Following factors should be considered before making decisions regarding extraction or retention of teeth. • They are divided into 2 categories: • .Dental Disease Factors - Condition of residual dentition -Dental compliance of patient • Radiation Delivery Factors -Urgency of treatment -Mode of therapy - Radiation fields -Mandible versus maxilla - Dose to bone

  45. Condition of residual ridge • Dentition in optimal condition (high risk dental procedures will not have to be performed in the post treatment period). • Extraction of all teeth with questionable prognosis before radiation. • Periodontal status in healthy condition. (Furcation involvement of mandibular molar teeth in the radiation field is ground for preradiation extraction) .

  46. Dental compliance of the patient Becomes difficult to maintain after treatment; • reduced salivary output. • Trismus, • impaired motor functions, • and surgical morbidities (The patient’s oral hygiene at initial examination is often a reliable indicator of future performance.)

  47. Radiation delivery factors • Urgency of treatment • Mode of therapy • Radiation fields • Mandible versus maxilla • Dose to bone

  48. Urgency of treatment • The status and behavior of tumor may preclude pre-radiation dental extractions, since delay secondary healing could significantly compromise control of disease. • The dentist, radiation therapist and patient must accept the risk of complications and must attempt to maintain oral health at optimum level. Control of tumor obviously is the most important consideration.

  49. Mode of therapy • When external beam therapy is used in combination with radioactive sources implanted( brachytherapy) - dose to adjacent tissues is reduced and more confined. • When external radiation is the sole mean of radiation delivery - close scrutiny of the dentition is mandatory.

  50. Radiation field • Nasopharynx and posterior soft palate, (includes both parotid glands) – xerostomia and postradiation caries. • Lateral tongue and floor of mouth, (encompass the entire body of mandible ) - osteoradionecrosis is high. • Tonsillar, soft palate , or retromolar trigone carcinomas, (major salivary glands and a significant portion of body of mandible.) - caries and osteoradionecrosis is high in this group.