RADIOTHERAPY

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RADIOTHERAPY : 

RADIOTHERAPY

INTRODUCTION : 

INTRODUCTION The modality of treatment of cancer are surgery, radiotherapy and chemotherapy. Operating team must first ascertain all relevant information about tumor and patient. Key tumor variables are histological type and stage. Those related to patient are age, general health, occupation, and social support. Both surgery and radiotherapy are local treatments, either in combination or individually both often effect a cure.

DEFINITION OF RADIOTHERAPY From dictionary of cancer terms, NATIONAL CANCER INSTITUTE, U.S National institutes of health. : 

DEFINITION OF RADIOTHERAPY From dictionary of cancer terms, NATIONAL CANCER INSTITUTE, U.S National institutes of health. Definition: (ray-dee-oh-THER-a-pee) The use of high-energy radiation from x-rays, gamma rays, neutrons, and other sources to kill cancer cells and shrink tumors. Treatment with ionizing radiation has been recognized as a valuable modality in management of cancer for a century. Local treatment modality. Complementary with surgery.

RATIONALE FOR RADIOTHERAPY : 

RATIONALE FOR RADIOTHERAPY PURPOSE: To eradicate tumors at primary site and in some cases regional lymph nodes. PRINCIPLE ADVANTAGE: Spares normal tissue function. for example: preservation of natural voice in advance laryngeal cancer.

HOW RADIOTHERAPY WORKS : 

HOW RADIOTHERAPY WORKS Radiation causes damage to DNA in both normal and malignant cells. Cells unable to repair this damage by time of next division,then they die in MITOSIS. Cancer cells divide more frequently. Malignant cells repair less efficiently.

MOLECULAR BIOLOGY : 

MOLECULAR BIOLOGY APOPTOSIS or programmed cell death, occurs at INTERPHASE and has been identified following radiation exposure. Rapid phenomena characterized by chromatin condensation and degradation. Effects individual cells which are scattered through out a tumor. Stimuli for APOPTOSIS include irradiation, chemotherapy, viral infection, cytokines, and hypoxia. Apoptosis process regulated by genes such as p53 and bcl-2. Wild type p53 promotes apoptosis. bcl-2 in contrast can prevent apoptosis.

Tumor suppressor p53 is a critical component of signaling pathway that results in G1 arrest.P53 dubbed as “GUARDIAN OF THE GENOME”.GROWTH FACTORS also effect radiation response of both normal tissues and tumors.Tumor necrosis factor alpha, keratinocyte growth factor, platelet derived growth factor, basic fibroblast growth factor etc enhance radiation response of some tumor cell lines and protecting haematopoietic cell lines. : 

Tumor suppressor p53 is a critical component of signaling pathway that results in G1 arrest.P53 dubbed as “GUARDIAN OF THE GENOME”.GROWTH FACTORS also effect radiation response of both normal tissues and tumors.Tumor necrosis factor alpha, keratinocyte growth factor, platelet derived growth factor, basic fibroblast growth factor etc enhance radiation response of some tumor cell lines and protecting haematopoietic cell lines.

RELATIONSHIP BETWEEN CURE AND COMPLICATION : 

RELATIONSHIP BETWEEN CURE AND COMPLICATION Basic principle of radiotherapy: 1.To achieve high radiation dose into tumors. 2.Minimizing dose into surrounding normal tissues. 3.To avoid complications as far as possible.

For these reasons, THERAPEUTIC RATIO is low. Therapeutic ratio is the relationship between the dose that is required for cure and the dose which causes unacceptable damage.In general terms A tumor is more likely to be cured if a higher dose is given. Similarly, complications are more likely if a higher dose is used. This is shown graphically. : 

For these reasons, THERAPEUTIC RATIO is low. Therapeutic ratio is the relationship between the dose that is required for cure and the dose which causes unacceptable damage.In general terms A tumor is more likely to be cured if a higher dose is given. Similarly, complications are more likely if a higher dose is used. This is shown graphically.

In head neck region situation is more complex.1.Squamous cancer is less radiosensitive than others such as lymphomas. - Requires high doses of cure. 2.Radiotherapy in head neck region requires greater technical precision. - Close juxtaposition of critical radiosensitive organs such as eyes, brainstem, salivary glands and mucosa. : 

In head neck region situation is more complex.1.Squamous cancer is less radiosensitive than others such as lymphomas. - Requires high doses of cure. 2.Radiotherapy in head neck region requires greater technical precision. - Close juxtaposition of critical radiosensitive organs such as eyes, brainstem, salivary glands and mucosa.

Likelyhood of an uncomplicated cure diminishes beyond a certain critical dose level. Central part of both curves is quite steep.- relatively small increase in dose may greatly increase the likelyhood of cure or greatly increase risk of complications.Aim of any modification in treatment technique is to ENHANCE THERAPEUTIC RATIO. : 

Likelyhood of an uncomplicated cure diminishes beyond a certain critical dose level. Central part of both curves is quite steep.- relatively small increase in dose may greatly increase the likelyhood of cure or greatly increase risk of complications.Aim of any modification in treatment technique is to ENHANCE THERAPEUTIC RATIO.

T N M Classification : 

T N M Classification T : primary tumour TX : primary tumour cannot be assessed T0 : no evidence of primary tumour Tis : carcinoma in situ T1 : tumour 2cm or less in greater dimension T2 : tumour more than 2cm but no more than 4cm in greatest dimension. T3 : tumour more than 4cm in greatest dimension. T4 : Lip : tumour invades adjacent structures, e.g. through cortical bone, inferior alveolar nerve, floor of mouth, skin of face. Oral cavity : tumour invades adjacent structures e.g. through cortical bone , into deep (extrinsic) muscle of tongue, maxillary sinus, skin (superficial erosion alone of bone/tooth socket by gingival primary is not sufficient to classify a tumour as T4)

Slide 15: 

N – Regional lymph nodes. NX N0 – No regional lymph node metastasis N1 – Metastasis in a single ipsilateral lymph node, 3 cm or less in greatest dimension N2 – Metastasis in a single ipsilateral lymph node, more than 3 cm but not more than 6 cm in greatest dimension, or in multiple ipsilateral lymph nodes, none more than 6 cm in greatest dimension, or in bilateral or contralateral lymph nodes, none more than 6 cm in greatest dimension. N2a: Metastasis in a single ipsilateral lymph node, more than 3 cm but not more than 6 cm in greatest dimension. N2b: Metastasis in multiple ipsilateral lymph nodes ,none more than 6 cm in greatest dimension. N2c: Metastasis in bilateral or contralateral lymph nodes, none more than 6 cm in greatest dimension.

Slide 16: 

N3 – Metastasis in a lymph node, more than 6 cm in greatest dimension. note: midline nodes are considered ipsilateral nodes. M – DISTANT METASTASIS MX – Presence of distant metastasis cannot be assessed. M0 – No distant metastasis. M1 – Distant metastasis.

Stage grouping: : 

Stage grouping: Stage 0 Tis N0 M0 Stage I T1 N0 M0 Stage II T2 N0 M0 Stage III T1 N1 M0 T2 N1 M0 T3 N0,N1 M0 Stage IV A T4 N0,N1 M0 Any T1,2,3 N2 M0 Stage IV B T1,2,3 N2 M0 Stage IV C T Any N M1 Source: Hermanek, p, sobin LH (eds): TNM classification of malignant tumors, 4rth edn, 2nd revision. International union against cancer. Springer, Berlin,. Heidelberg, New york: 1992.

COMBINED MODALITY TREATMENT : 

COMBINED MODALITY TREATMENT Decided at initial assessment to use radiotherapy in combination with surgery either preoperatively or postoperatively. Uses of radiotherapy with curative intent: 1. Radiotherapy alone as principle treatment. 2. Radiotherapy planned in conjunction with surgery. -preoperatively -postoperatively 3. Pathology guided post operative radiotherapy 4. Salvage radiotherapy for recurrence after surgery.

Radiotherapy alone as principle treatment:Sometimes radiotherapy is used both as definitive treatment and as an adjunct to surgery.Example: a patient with a small tonsillar carcinoma and bulky cervical lymph nodes.Radiotherapy alone has little chance of sterilizing a large lymph node mass and greatest probability of tumor control in the neck is with a radical neck dissection with post operative radiotherapy.In contrast, for small tumor in oropharynx radical radiotherapy may be less morbid than composite resection. : 

Radiotherapy alone as principle treatment:Sometimes radiotherapy is used both as definitive treatment and as an adjunct to surgery.Example: a patient with a small tonsillar carcinoma and bulky cervical lymph nodes.Radiotherapy alone has little chance of sterilizing a large lymph node mass and greatest probability of tumor control in the neck is with a radical neck dissection with post operative radiotherapy.In contrast, for small tumor in oropharynx radical radiotherapy may be less morbid than composite resection.

PREOPERATIVE AND POSTOPERATIVE RADIOTHERAPY : 

PREOPERATIVE AND POSTOPERATIVE RADIOTHERAPY Radiotherapy is best at eradicating small volumes of diseases and more likely to fail if there is large bulky tumors. Two modalities combined usefully, the advantage of each overcoming the shortcomings of other. PREOPERATIVE RADIOTHERAPY Tumors will shrink prior to surgery making operation easier. Sterilizing majority of viable cells , risk of tumor dissemination at time of surgery was reduced. Advantages -Blood supply may be better than after surgery, leading improved oxygenation. -tumor seeding during surgery decreased. Disadvantage -loss of definitive tumor staging and lower doses given concerning increase in surgical morbidity.

POSTOPERATIVE RADIOTHERAPY : 

POSTOPERATIVE RADIOTHERAPY Considered preferable. -proper pathological staging of tumors and nodes. -introduction of free flaps in reconstructive surgery. -following surgery only microscopic tumor left behind, relatively easy to cure with radiation. INDICATIONS -Large infiltrating tumors. -compromised margins of surgical resection. -perineural spread. -extension of tumor into deep soft tissues or bone destruction. -multiple lymph nodes, large lymph nodes, and extracapsular nodal spread.

Slide 22: 

As a General rule : -Every attempt should be made to begin radiation therapy approximately 4-6 weeks postoperatively. -Therefore it is important that extractions or dental restorations if required, must be done at or close to the time of ablative surgery so that all surgical wounds can heal during the same interval.

ADJUVANT RADIOTHERAPY : 

ADJUVANT RADIOTHERAPY Given following definitive treatment which has apparently removed the malignancy. Reduced chances of recurrence. Elective post operative irradiation following complete surgical excision of tumor. Prophylactic irradiation of clinically negative neck. Irradiation of known residual disease following incomplete surgery is not considered adjuvant.

Advantages of surgery versus radiotherapy for early stage head and neck cancer : 

Advantages of surgery versus radiotherapy for early stage head and neck cancer PRO SURGERY Relatively quick, expeditions treatment. Ability to assess prognosis through pathologic assessment of specimen (e.g margins) and alter treatment accordingly Avoids risk of xerostomia. Preserves ability to use radiotherapy in future, if needed. Avoids risk of radiation carcinogenesis.

Slide 25: 

PRO RADIOTHERAPY avoids prolong general anaesthesia. Lower risk of systemic complications. Ability to preserve normal anatomic structures Treatment can be given on outpatient basis , and many can continue to work during treatment.

TYPES OF RADIATION TREATMENT : 

TYPES OF RADIATION TREATMENT External beam Radiotherapy. Interstitial or Intracavitary Brachytherapy. Unsealed Radionuclide Therapy.

EXTERNAL BEAM RADIOTHERAPY : 

EXTERNAL BEAM RADIOTHERAPY Also known as TELETHERAPY. Beam of radiation directed by a machine to tumor bearing part of patient. Variety of different types of radiations are in current use. TYPES OF EXTERNAL BEAM RADIOTHERAPY. Photons [x-ray or gamma rays] particles[ e.g. electrons] -common in use

Radiations used in therapy classified by their energy levels.Measured in volts.Least energetic have energy upto 100,000v or 100kv{superficial}TYPES OF PHOTON RADIATION BEAMX-ray Photons. -superficial, e.g 100kv -orthovoltage, e.g 300kv -megavoltage,e.g 6 mvGamma Photons. -cobalt ~2mv. : 

Radiations used in therapy classified by their energy levels.Measured in volts.Least energetic have energy upto 100,000v or 100kv{superficial}TYPES OF PHOTON RADIATION BEAMX-ray Photons. -superficial, e.g 100kv -orthovoltage, e.g 300kv -megavoltage,e.g 6 mvGamma Photons. -cobalt ~2mv.

Advantages of megavoltage radiotherapy : 

Advantages of megavoltage radiotherapy Principle advantage- Increased dose at depth. Skin sparing. Better precision. -edges of linear accelerator beams much more precisely defined. -less penumbra * narrower margins can safely be used around tumor. Diminished bone absorption.

Radioactive isotopes emitting megavoltage gamma rays. : 

Radioactive isotopes emitting megavoltage gamma rays. Gamma rays emitted by some radiation isotopes are of Radio megavoltage quality. Beam from radium ‘bomb’ –earliest form of high energy external beam treatment. After world war II, radium superseaded by artificial radioactive isotopes eg cesium and cobalt. Cobalt radiation. -more penetrating, -penumbra, from a linear accelerator, -low technology equipment, -cheaper, -requires less maintenance.

PARTICLE BEAM IRRADIATION : 

PARTICLE BEAM IRRADIATION Types of particle beam. -Electrons. -Neutrons. -Protons.

Electron beam irradiation : 

Electron beam irradiation Uniform dose upto a certain depth of penetration and then dose falls of very rapidly. Thus ,used to treat superficial parts. For example; used to boost the dose to nodal mass overlying spinal cord. Following initial photon treatment to a cord tolerance dose. Superior to orthovoltage as fall off dose at depth is more rapid. Shows skin sparing effect. Not preferably absorbed by bone or cartilage.

NEUTRON BEAM THERAPY : 

NEUTRON BEAM THERAPY Other form of particle radiation widely used. Despite radiobiological predictions that neutron would be advantageous ,clinical trials fail to demonstrate anticipated benefit. PROTON BEAM THERAPY Limited applications. Not widely available. Current U.K facility in liverpool. -used exclusively for ocular melanoma.

INTERSTITIAL RADIOTHERAPY : 

INTERSTITIAL RADIOTHERAPY Also known as BRACHYTHERAPY. Sealed sources of radioactive isotopes either implanted into tumor. OR placed in natural body cavity. For example; maxillary antrum or nasopharynx {intracavitary therapy} RADIUM NEEDLES -removable implants. -long half life, removed after 1 week. -superseaded initially by cesium and later by iridium. RADON NEEDLES -short half life elements. -permanently implanted. -superseaded by gold or iodine.

-Oral cavity is the most common site for Interstitial implantation. - many oral tumors, being small, relative well demarcated. - anatomically accessible.-Interstitial therapy treats small, localized volume with rapid fall off dose remote from implant.-Enables higher radiation dose.-Diminishes doses to adjacent structures such as bone and salivary glands.-Clinical experience suggests control rates better for suitable tumors.-Previously thick rigid needles were used as principle type.-More versatile flexible systems introduced. -iridium wire implants. -can be cut to any length. -radiation protection easier. : 

-Oral cavity is the most common site for Interstitial implantation. - many oral tumors, being small, relative well demarcated. - anatomically accessible.-Interstitial therapy treats small, localized volume with rapid fall off dose remote from implant.-Enables higher radiation dose.-Diminishes doses to adjacent structures such as bone and salivary glands.-Clinical experience suggests control rates better for suitable tumors.-Previously thick rigid needles were used as principle type.-More versatile flexible systems introduced. -iridium wire implants. -can be cut to any length. -radiation protection easier.

ADVANTAGES OF IRIDIUM WIRE IMPLANTS : 

ADVANTAGES OF IRIDIUM WIRE IMPLANTS Insertion of applicators into which radioactive sources are subsequently put {AFTER LOAD}. No radiation exposure to staff. Radiation far less penetrating. DISADVANTAGES Relatively short half life. Reuse impracticable. Increased cost.

Newer use of Brachytherapy : 

Newer use of Brachytherapy Treatment of recurrent neck nodes which have previously been irradiated. Intraoperative insertion of tubes of subsequent after loading. Tubes covered with well vascularised mucocutaneous flap. Tumor irradiated without over dosing.

USES OF UNSEALED SOURCES : 

USES OF UNSEALED SOURCES Radioactive isotopes can be used in form of drugs given orally or intravenously. These drugs are then concentrated by metabolic pathway in malignant tissue, enabling larger radiation doses to be given to tumor. Example: treatment of differentiated thyroid carcinoma of follicular cell origin with radioactive iodine.

VOLUMES TO BE TREATED : 

VOLUMES TO BE TREATED Should be enough to cover bulk of tumor defined by clinical examination and imaging. Allow reasonable margin for microscopic infiltration. Size of margin treated around tumors varies. At some centers clinically uninvolved nodes irradiated prophylactically. ONE MAY CHOOSE -to over treat proportion of patient. -ensuring maximum number of patients cured at first time. OR -minimize initial treatment. -sparing side effects.

Shrinking Field Technique : 

Shrinking Field Technique Used in treatment of large volume. To treat some part prophylactically. Large volume is covered. Adequate to treat sub clinical disease. Their volume reduced to cover bulk of disease. Boosted to a high dose.

FRACTIONATION OF RADIOTHERAPY : 

FRACTIONATION OF RADIOTHERAPY Units of radiation measurement. In physical terms, radiation dose prescribed using S.I units; The GRAY (Gy). Named after pioneering British Radiobiologist L.H.GRAY. Gray =Gy =S.I unit. Centigray =cGy =0.01 Gy. Rad =cGy.

Slide 42: 

In biological terms, other factors must be mentioned to describe dose to a tumor; -number of fractions. -fraction size. -interval between fractures. -overall time. -volume treated. -radiation quality (e.g photons or neutrons) -beam energy.

Radiobiologic principles explaining why fractionation allows tumor control without local necrosis: : 

Radiobiologic principles explaining why fractionation allows tumor control without local necrosis: Repair Reoxygenation Repopulation Redistribution

Slide 44: 

REPAIR: series of enzymatic processes reflecting intracellular mechanism for healing intracellular radiation damage. -desirable in normal tissue but not in tumor. REOXYGENATION: there is gradient of oxygenation and hypoxia within a tumor. -with radiation more radiosensitive oxygenated cells are killed sparing hypoxic cells. -it represents process by which the oxygen is restored to remaining hypoxic cells.

Slide 45: 

REPOPULATION: refers ability of various cell population to divide in interval between radiation therapy. -it is important to complete any planned course as quickly as possible. REDISTRIBUTION: reflects the relative variability of cell radio sensitivity throughout the cell cycle. -cells are considered to be most radiosensitive during MITOTIC PHASE (late G2 and M) and most radio resistant in late S phase.

CONVENTIONAL FRACTIONATION : 

CONVENTIONAL FRACTIONATION Maximum amount of radiation given as single dose is limited by NORMAL TISSUE TOLERANCE. Total dose divided in small doses, called FRACTIONS, given for e.g, daily, the maximum dose tolerated by normal tissues increases. Cure becomes more likely. Despite variation in total dose, number of fractions per week, total number of fractions and overall time, results are similar. The shorter course treatment is standard in some BRITISH CENTERS, but the longer is regarded as the International Conventional Fractionation schedule in international circles. One of the largest clinical trial organized by BRITISH INSTITUTE OF RADIOLOGY, showed no significant differences comparing short with a long overall treatment time.

Slide 47: 

Acute mucosal reaction is more severe with short regimen, more protracted fractionation is recommended when a large area of mucosa require radiation. As brain tissue is more likely to be damaged if large doses per fractionation are used, a protracted schedule is preferred if any of the central nervous system is included within the treated volume.

CONVENTIONAL AND ALTERNATIVE FRACTIONATION SCHEDULE : 

CONVENTIONAL AND ALTERNATIVE FRACTIONATION SCHEDULE Conventional : 60 Gy in 30x2 Gy fractions over 42 days. Hypo fractionation : Smaller number of fractions each larger than 2 Gy. Hyper fractionation: Larger number of fractions each smaller than 2 Gy. Acceleration : Shortened overall time. Split course : Gap to allow acute reactions to settle.

EXPERIMENTAL FRACTIONATION : 

EXPERIMENTAL FRACTIONATION Hyper fractionation. -when number of fractions is increased beyond conventional levels and the dose per fraction is reduced correspondingly. - in order to keep the overall treatment duration same, treatments need to be given more than once( twice or thrice) a day. - with multiple treatments per day, the inter fraction interval becomes critical. - to allow for repair of sub lethal damage in normal tissues the minimum safe inter fraction interval is usually as 6 hours. Acceleration. -when the overall treatment time is reduced.

C H A R T(Continuous, Hyper fractionated, Accelerated radiation therapy) : 

C H A R T(Continuous, Hyper fractionated, Accelerated radiation therapy) This gives a radical course of treatment an just 12 days, using 3 fractions per day, 7 days per week. The short overall time overcome the REPOPULATION OF MALIGNANT CELLS. Reduced fraction size is used to prevent increased late tissue damage.

Split courses : 

Split courses Acute mucosal reaction may be dose limiting. In an attempt to overcome this problem, radiotherapy course is divided into two halves. Separated by gap of about 2 weeks, allowing mucosal reaction to settle. Disadvantages. -gap gives time for remaining tumor cells to divide rapidly and repopulate the tumor. -split courses produce inferior results to continuous schedules.

Slide 52: 

If an unplanned gap in treatment occurs, perhaps because of machine breakdown or inter current illness; tumor cells repopulation threaten develops. In these circumstances:- - the total dose may be increased by increasing the size number of remaining fractions. - treat to same planned total dose with the same fraction size in same overall time treating with multiple fractions per day.

PLANNING AND QUALITY CONTROL OF RADIATION THERAPY` : 

PLANNING AND QUALITY CONTROL OF RADIATION THERAPY` SELECTING THE TREATMENT VOLUME. PREPARATION OF SHELL. SIMULATION. BEAM SHAPING. WEDGES AND COMPENSATORS. ISODOSE PLANS. TREATMENT VARIFICATION.

Selecting the treatment volume : 

Selecting the treatment volume Precise technical details of treatment must be decided before it is commenced. Factors determining volume to be treated: Extent of tumor (known from clinical and radiological examination), Knowledge of natural history of that tumor type, Usual patterns of spread. In head and neck it is important to confine the treatment to this volume, In order to protect vulnerable structures such as eye, lacrimal and salivary glands, the brain stem and spinal cord.

Preparation of a shell : 

Preparation of a shell For accurate treatment of target volume, the patient needs to lie still during treatment. To ensure this, patient’s head is immobilized in a plastic shell. Such shells, sometimes called MASKS. MOULDS or CASTS, are prepared individually for each patient. Skilled technical staff required.

Slide 56: 

Simulation Treatment simulator is a diagnostic x-ray machine with image intensifier facilities. Rotates around the patient, like treatment unit with exactly matching geometry. Treatment field of appropriate size is chosen using image intensifier. Radiograph is taken showing position of selected field and any areas to be shielded, in relation to tumor and normal structures.

Beam shaping : 

Beam shaping Blocks are introduced into beam to produce irregularly shaped field to shield any vulnerable structures. Standard blocks OR customized blocks can be used. Modern linear accelerators equipped with multi leaf collimators which allow automatic beam shaping. Position of beam and any blocked areas are marked on to shell to guide radiographers during treatment.

Wedges and compensators : 

Wedges and compensators Aim of treatment planning is to ensure that target volume containing tumor receives a high and uniform dose. Beyond depth absorbed dose is maximum (about 1 cm for 4mv photons), the dose received from one beam decreases as it penetrates further into patient. Two or more beams are often used. Fired at different angles and intersect at tumor, which therefore receives the highest dose. To achieve uniform dose, METAL WEDGES may be inserted in head of treatment unit into beam to attenuate dose differentially across its width.

Isodose plans : 

Isodose plans A computer is used to create a map or plan of the radiation dose distribution within the patient. Usually this plan is of one cross section through the middle of tumor, although in complicated cases several sections at different levels are required. Plan shows outline of patient and position of tumor and any adjacent vulnerable structures. Position of treatment fields is indicated and contour lines are drawn joining points which receive the same dose (ISODOSE LINES).

Slide 60: 

ISODOSE PLAN is checked to ensure:- -tumor is contained within high dose volume. -receives an adequate and uniform dose -dose received by any critical structure is within limits of tolerance.

Treatment verification : 

Treatment verification During first treatment session, radiographs may be taken using beam from treatment unit. These verification or check films are compared with simulator films to ensure:- 1.treatment field positioned as planned. 2.any blocks are correctly located. Modern linear accelerator are equipped with portal verification equipment so that each field can be checked daily for accuracy before it is administrated.

COMPLICATIONS : 

COMPLICATIONS ACUTE:- during or immediately after a course of treatment. -skin reactions. -cutaneous erythema. -blistering or moist desquamation. -hyperpigmentation. -mucosal reactions. -xerostomia. -mucositis.

Slide 63: 

Late effects:-which may come on in subsequent months or years. -Dental and bone effects. -bone and soft tissue necrosis. -xerostomia. -periodontal disease. -Wide spread radiation caries. -Osteoradionecrosis. -Skin and soft tissue effects. -telengiectasia. -atrophy. -hypopigmentation and fibrosis. -Neurological effects. -Hypothyroidism -Visual problems. -dry eyes, corneal ulcerations, cataracts, retinal damage.

Pre irradiation Dental Care. : 

Pre irradiation Dental Care. All non restorable teeth in direct beam of radiation, significant periodontal disease should be EXTRACTED. Sharp bone margins removed as irradiated bone does not remodel spontaneously. All remaining teeth should be restored. Complete oral hygiene instructions. Custom trays provided to permit application of 0.4% stannous fluoride, 1% sodium fluoride gel or 1% AFP gel.

Post Irradiation Dental care : 

Post Irradiation Dental care Dentures should not be used in irradiated area for 1 year after radiotherapy. Oral hygiene , fluoride therapy is recommended. Saliva substitute may be used to lubricate mouth. Endodontic therapy should be undertaken if post irradiation pulpitis develops. No attempts should be made to raise flaps or obtain linear closure. Antibiotics should be administered and L.A without adrenaline should be used.

RADIOSENSITIVITY and CELL TYPE : 

RADIOSENSITIVITY and CELL TYPE Different cells from various organs of same individual respond to irradiation quite differently. Most radiosensitive cells are those that- 1.Have high mitotic rate. 2.Undergo many future mitoses. 3.Most primitive in differentiation. EXCEPTIONS 1.Lymphocytes 2.Oocytes. ---very radiosensitive even though they are highly differentiated and non dividing.

Mammalian cells divided into five categories of radiosensitivity on histological basis. : 

Mammalian cells divided into five categories of radiosensitivity on histological basis. VEGETATIVE INTERMITOTIC CELLS- -Most radiosensitive. -These are stem cells, retain their primitive properties. EXAMPLES- precursor cells such as those in SPERMATOGENIC AND ERYTHROBLASTIC SERIES. - basal cells of oral mucous membrane. DIFFERENTIATING INTERMITOTIC CELLS- -Divide regularly. -Undergo some differentiation between divisions. EXAMPLES- dividing cells of inner enamel epithelium. - cells of hematopoietic series in intermediate stage of differentiation. - spermatocytes and oocytes.

Slide 68: 

MULTIPOTENTIAL CONNECTIVE TISSUE CELLS- -Intermediate radiosensitivity. -divide irregularly. -capable of limited differentiation. EXAMPLES- vascular endothelial cells, fibroblasts, mesenchymal cells. REVERTING POSTMITOTIC CELLS- -Generally radio resistant. -Divide infrequently. -Generally specialized in function. EXAMPLES- acinar and ductal cells of salivary glands and pancreas, parenchymal cells of liver, kidney, and thyroid.

Slide 69: 

FIXED POSTMITOTIC CELLS- -most resistant to direct action of radiation. -highly differentiated cells, once mature, incapable of division. EXAMPLES- neurons, striated muscle cells, squamous epithelial cells(differentiated and are close to surface of oral mucous membrane), erythrocytes.

Radio sensitivity Of Normal Cells And Tissues : 

Radio sensitivity Of Normal Cells And Tissues RADIO SENSITIVE (2500r or less kills or seriously injures cells). Lymphocytes and lymphoblasts. Bone marrow (myeloblasts and erythroblastic cells) Epithelium of intestine and stomach. germ cells (ovary and testis)

Slide 71: 

RADIO RESPONSIVE(2500-5000r kills or injures cells). Epithelium of skin and skin appendages. Endothelium of blood vessels. Salivary glands. Bone and cartilage (growing). Conjunctiva, cornea and lens of eye. Collagen and elastic tissue (fibroblasts themselves are resistant)

RADIO RESISTANT (over 5000r necessary to kill or injure many cells) : 

RADIO RESISTANT (over 5000r necessary to kill or injure many cells) Kidney. Liver. Thyroid. Pancreas. Pituitary. Adrenal and parathyroid glands. Mature bone cartilage. Muscle. Brain and other nervous tissue.

CONCLUSION : 

CONCLUSION Radiation therapy is a local treatment modality. May be used alone for the treatment for head and neck cancer, or it may be used after surgery for combined modality treatment of patients with high risk cancer. Many of the problems associated with radiotherapy can be minimized with adequate pre therapy care and with aggressive maintenance of oral hygiene.