Cell Skin Cancer

[a radiologist places x-rays on a screen tobe read.] [narrator:] the management of cancer involvesthe services of several disciplines. utilizing the judgment and skills of the surgeon. the pathologist. the internist. and the radiation therapist. at the very outset, it is important to determinewhich modality of treatment, or combination, will most likely benefit the patient. and whether treatment is to be given withintent to cure, or for palliation.

radiation doses and treatment schedules varygreatly depending upon therapeutic aims. and the radiation therapist, like the surgeonand chemotherapist, is guided by the classic dictum, "first do no harm". the objective: to deliver a cancerocidal doseto the tumor with the least possible damage to the surroundingtissues. in outlining a treatment plan, the therapistconsiders many factors. the general status of the patient. the type and location of the tumor. its volume. its expected response to radiation.

these and other physical and biological factorswill govern the selection of the appropriate type of radiation. isodose charts showing the penetration ofthe beam for a given energy, will help verify the suitability of the radiationfor the particular location of the tumor. radiation therapy uses a variety of equipment, providing a wide spectrum of wavelengths and penetration characteristics. this low voltage, 100 kilovolt unit is suitable for treating superficial, thin lesions, such as this basal cell carcinoma. the 100 kilovolt unit produces soft x-raysof low penetration,

which deposit most of their energy in the first few centimeters of tissue. generators in the 250 to 300 kilovolt rangeproduce x-rays of somewhat greater penetration, useful for treating superficial thick lesions;as for example, this tumor of the carotid gland. megavolt -- million volt equipment -- produces still harder, more penetrating radiation. a two million volt machine, such as this resonant transformer, is suitable for treating deeper lesions. here, used to irradiate paraaortic lymph node metastases, in a patient with a testicular carcinoma. six million volt x-rays are produced by thislinear accelerator. with a betatron, 35 or even 45 million electronvolt x-rays can be obtained. the penetration achieved with these high energiespermits treatment at depths beyond the effective

reach of lower energy beams as seen in thiscomparison. as noted earlier, the energy from a low-voltage,100 kev unit is quickly absorbed. and does not penetrate much beyond the superficialtissues. with approximately eight percent of the maximumdose measurable at a depth of 10 cm. approximately 35 percent of the maximum dosereaches this level with 250 kev radiation. the two million volt generator delivers approximately50 percent of its maximum dose at this depth. the six million volt linear accelerator delivers70 percent, and the 35 mev betatron delivers a full 85to 90 percent of its dose maximum at 10 centimeters. isodose charts used by the therapist in planningtreatment show the dose distribution in percentages

of the maximum dose for a given energy atvarious depths below the skin's surface. each chart identifies the modality, the sourceskin distance, and the field size. the penetration of these high energy beams permits effective irradiation of deep-seated tumors. in addition, at higher energies, the edgesof the beam are sharp because these highly energetic x-rays are not significantly scatteredby the irradiated tissues, either backward or laterally, as is the case with low-energy radiation wherethere is significant scatter outside the field. the more sharply defined edges of the highenergy beam confine the radiation more precisely to the treated area.

another advantage of high-energy radiationis that the maximum dose is not reached at the skin's surface, but at varying depthsbeneath it... so that skin reactions are not a limitingfactor. high energy ionizing radiation in the megavoltrange can also be obtained with relatively simple equipment using radioactive isotopessuch as cobalt-60. the cobalt-60 unit emits gamma radiations, which are similar in penetration to x-raysproduced by a three million volt generator. the gamma radiation from isotopes is indistinguishable from electrically-produced x-rays of the same energy.

of all high energy installations in use today,more than 80 percent are cobalt-60 units. here, used to treat the patient with hodgkins disease. the quantity of emitted radiation is expressed in roentgens, a unit of measure of ionization in air. however, the amount of energy absorbed intissue is measured in rads, the unit of radiation-absorbed does. one rad equalling 100 ergs of energy absorbed per gram of tissue. absorbed dose, however, varies with tissuecomposition and radiation energy. as illustrated in this x-ray film, at lowenergies -- 250 kev or less -- there is a significant difference in absorption betweensoft tissue and bone. because of the greater absorption of energyby the denser, skeletal tissues.

at higher energies, this absorption differential does not exist, and the amount of energy absorbed by bone and soft tissue is about equal. this allows treatment to cancerocidal dosesin the vicinity of bone without producing bone damage because of increased absorption. this side-by-side comparison shows the differencein absorption at low and high energies. the effects of radiation are initiated bythe interaction of the x-rays or gamma rays with the orbital electrons of the tissue atoms. the displaced electrons and scattered photonscause increasingly large numbers of ionizations as they penetrate the tissue.

the released electrons act as chemically reactivereducing substances, forming free radicals and producing chemical damage, including damageto dna. damage to dna may be reparable, or may resultin cell death, clinically observable as tumor shrinkage. the initial manifestation of cell death oftenoccurs at the time of mitosis. this cell, which has previously been irradiated,is about to divide. at first it appears normal. however, as cell division proceeds, the chromosomestend to clump together, and a chromosome bridge can be seen to connect the two potential daughtercells.

this abortive division is one of a numberof manifestations of lethal cell damage following irradiation. in general, the sensitivity of a cell to theeffects of radiation seems largely related to its mitotic activity. cells which are mitotically most active areusually the most radiosensitive, illustrated here by this poorly differentiated,squamous cell carcinoma of the nasal pharynx. among the most radiosensitive tumors are themalignant lymphomas and leukemias. undifferentiated, squamous cell carcinomas and germinal tumors such as seminomas and dysgerminomas.

moderately radiosensitive are the well-differentiated squamous cell carcinomas of the skin and mucus membranes, adenocarcinomas, and some sarcomas. relatively radio-resistant tumors includeosteogenic sarcomas, malignant melanomas, and some gliomas. radiosensitivity of a tumor however, is notnecessarily related to curability, since tumors with a high degree of radiosensitivityare often those which also show marked anaplasia, aggressive growth, and wide dissemination. in fact, the chances for cure of a cancerby irradiation depend mainly

on its location, its size and accessibility, its biological behavior, and probably on immunological factors. the general condition of the patient is ofconsiderable importance, and can significantly influence the patient's tolerance to irradiation. cancer of the cervix is a classic examplein which radiation therapy is given with the intent to cure. with irradiation as the principal treatmentmodality, recent five-year survival rates free of disease were reported by a major institution as follows. [graph titled 5 year survival rates/cancer of the cervix is shown.] this patient was initially examined by herreferring gynecologist,

who biopsied a lesion on the cervix. examination of the biopsy specimen showed a moderately differentiated, squamous cell carcinoma. and she was referred to the radiation therapist for consultation. the cystoscopic examination and intravenousurogram were within normal limits. blood count and chemistries were also normal. vaginal examination revealed a normal-sized, slightly anteflexed uterus with a tumor involving the external cervical os and extending into the left fornix. on rectal/vaginal examination, the lesionis felt to involve the medial aspect of the

left parametrium without reaching the pelvicwall, classifying this as a stage 2b tumor. in order to plan the treatment, certain measurements are needed. the anterior/posterior diameter is measured and recorded on plotting paper. the contour of the pelvis is then obtainedwith lead tape, and is also traced... and superimposed on the appropriate isodose chart. treatment will be given through two opposed fields.

the dose contribution of the anterior fieldis plotted. and then that of the posterior. this will result in a relatively homogenousdose distribution in the volume to be treated, avoiding regions of overdosage or underdosage. compounding of the doses contributed by eachfield results in these summation curves. the limits of the treatment field are outlinedon the skin and entered in the patient's treatment chart. she will receive daily treatments of 200 rads through both the anterior and posterior fields, until a tumor dose of about 4,000 rads has been reached,

well within the tolerance of the normal pelvictissue. fractionating the total dose into small incrementsover a protracted period results in greater dose tolerance and favors recovery of thenoncancerous tissues. the field size is optically simulated, using a beam collimator, which is adjustedto conform with a treatment field. and the treatment is started. if there are no interruptions in the treatment schedule, the goal of 4,000 rads will be obtained inapproximately four weeks. on the last day of cobalt therapy, the leftparametrium has returned to almost normal consistency.

and the lesion at the cervical os is now visible as a small, whitish area of neurotic tumor tissue. treatment will be completed with intravaginal and intrauterine radium therapy. this permits delivery of a very high doseto the central, most resistant part of the lesion. and simultaneously increases the dose to thelateral, pelvic tissues. a tumor dose of the level attained by thismethod cannot be reached by external radiation alone. after cervical dilatation, a tandem is inserted into the uterine canal. followed by colpostats placed into the lateralfornices. the position of the radium-containing applicatorsis verified radiographically. these films permit calculation of the exactdose delivered to the tumor and adjacent structures.

examination after completion of the full courseof treatment shows the healed cervix. radiation therapy with a goal of palliationis exemplified in this patient with a six- month history of difficulty inswallowing solid foods, and recent weight loss. the esophagram demonstrated a mid-thoracic, obstructive lesion, which on biopsy proved to be a squamous cellcarcinoma. treatment will be given by rotating beam technique. on a contour of the patient's chest, radii are drawn from the axis of rotation to theskins surface. the axis is located at the exact center ofthe tumor. the radii will be used in the computation of the summation curves.

these indicate a maximum dose region surroundingthe tumor, and a much lower dose to the adjacent organs. the chances for cure in carcinoma of the esophagusare statistically very small since metastases are frequently present when the cancer isdiagnosed. nevertheless, one can usually obtain significantpalliation with radiation therapy. this split-screen comparison shows the grossly normal appearance of the esophagus, approximately one month after the end of treatment. in addition to its use as a primary modalityof treatment, radiation therapy can be effective in combination with other types of therapy.

for example, children with wilms tumor showa higher survival rate when radiation therapy is used, in addition to surgery and chemotherapy. in this post-operative patient, irradiationmay limit metastatic spread by destroying any cancer cells which may have been leftbehind in the renal bed. in some cases of this disease, preoperativeirradiation is given in an effort to destroy tumor cells which might be disseminated at nephrectomy. in recent years, the combination of surgery,radiation, and chemotherapy has resulted in a dramatic increase in survival rates in wilm'stumor. radiation therapy also has a major role inthe treatment of many other types of cancer.

in a patient with carcinoma of the larynx,with a lesion limited to one or both chords and no fixation, radiation therapy can offera cure and has the advantage of preserving the voice. this patient received a course of cobalt-60therapy over a period of 43 days. one month after completion of treatment, laryngoscopyshowed no evidence of residual tumor. as with all patients treated by irradiation, this man is now seen regularly for follow-up examination. [physician:] mr. benkowsky, you feel well? [mr. benkowsky:] yes sir. [physician:] how long has it been now? aboutfive years since [inaudible] -- [mr. benkowsky:] five years -- five years,longer than that...

[physician:] mm-hmm. and your voice staysstrong? [mr. benkowsky:] oh yes. strong enough allthe time. [physician:] and how about the swallowing? [mr. benkowsky:] the swallowing is okay. [physician:] you want to take your denturesout and put them into this? [mr. benkowsky:] oh sure, i'll do that. ican do that. [mr. benkowsky:] yes. [physician:] now open your mouth up wide.now stick your tongue out and let me see it. all right. now say "e".

[mr. benkowsky:] "e". [physician:] say "e" again. [mr. benkowsky:] "e" . [physician:] very good. that's fine. [narrator:] whether used with the intent tocure, or with the intent to palliate... alone, or in combination with other treatment modalities, radiation therapy has a major role in the management of cancer. in fact, at some time in the course of treatment,at least 50 percent of patients with cancer can benefit from radiation therapy.

about half of these treated for cure, andhalf for palliation. [radiation equipment is switched on and aregular ticking/knocking sound is heard.] [images of different types of cancers pre- and post-treatment are shown.] [images fade out; ticking stops.]