Click here to view next page of this article


New Advances in Radiation Therapy

When we speak about radiation oncology, on the biological level. What weíre trying to do is kill a cancer cell. What one has to realize is radiation is effective only in microscopic disease for the most part, and itís not effective during the entire time period that the radiation is being given. The reason is, if you look at the biology of cancer, and you think about the dividing cell, the majority of a cancer mass does not divide at any one time, only about 10% of the cancer.

The clinical implication of this is that one sees the maximum effect of radiation, not during the time of radiation but within three to four weeks after a patient completed radiation therapy. The reason we give a small dose initially of 180 to 200 rads is that lower doses, the cell has the ability to repair the damage of the radiation and that is called the sublethal effect. That is this little slope you see here.

When angiogenesis takes place, and there is a vascularity, what happens is the vasculature oxygenates the center of the tumor mass and what we have found over the years, is the more oxygenated the cancer mass is, the greater the likelihood the cancer will die and here you have a comparison of what happens when cell are in a toxic background or no oxygen and when there is oxygen present.

When a patient goes to radiation oncology, the treatment plan is always to give the patient, for example in cervical cancer both external beam radiation therapy and intracavitary or brachy therapy. The reason that patientís receive external beam radiation therapy is to control the pelvis or what we call regional control. What you are treating is the tumor bed as well as the lymphatics in the pelvis. When a patient receives an implant or brachy therapy.

When patientís go down to radiation, they are simulated, what they do when they simulate the patient is basically develop a treatment plan or go ahead and plan out what region they are treating with regard to the external beam radiation therapy. In gynecologic oncology, we usually treat the pelvis, and when we treat the pelvis, the field is usually 15 x 15 cm and the reason is because you want to incorporate the pelvis and the internal iliac obturator nodes as well as part of the external iliac nodes. Occasionally, with ovarian cancer, what one will see is patientís will receive whole abdomen radiation therapy. In the 1970s, whole abdomen was quite frequently given to patientís and what happened was we saw a 30% bowel complication.

It all depends really on what your treatment field and what you are trying to accomplish. For example, here is the tumor as you can see, if you go from front to back, is that there is less of a margin with regard to the amount of radiation that is being delivered to periphery, so what happens is that there is a higher complication rate giving APPA versus 360 degree rotation. For radiation to be effective with regard to cancer, the size of the cancer becomes extremely important, as you can see here, is if there is greater than a 2 cm nodule, 5000 to 6000 centigrade is required to kill the cancer.

How can you cure cervical cancer? Because you have a gross mass present, you only can give 4500 centigrade to 5000 centigrade to the pelvis, how do we give enough radiation to kill a cancer that is on the cervix. That is done by what we call brachy therapy and brachy therapy is giving a high dose of radiation directly to the cancer and these are the implants. Modern day implants are based on what we call the Manchester system. Historically what we used to do in Stockholm, we used to put two radiation sources right against the cervix at tandem.

The radiation sources used for an implant nowadays are cesium, cesium 137 is used and has a half life of 30 years, so itís not necessary to calculate the dose with regard to the radiation implant every year, because these are long lived isotopes. We used to use radium or radium 226, the problem with radium 226, it has a very long half life of 1620 years, but in addition, in itís decay, gave off radon gas and when the sources would crack.

Occasionally, in a morbidly obese patient, who has endometrial cancer, what the radiation oncologist will do is place Hayman capsules. What Hayman capsules are, are small radiation sources that usually contain cesium that are 5 to 10 mg of cesium, they place the sources actually into the uterus to radiate the surface of the uterus. The problem here clinically is that the ability to cure the cancer decreases about 15 to 20%. So when we give radiation therapy, our goal is to give external beam radiation therapy 4000 to 4500 centigrade and implant.

Usually an elderly patient or an obese patient will receive radiation therapy, a younger patient with an early stage disease will receive a radical hysterectomy. We also treat the periaortic area with radiation therapy for cervical cancer, the dose we give 4000 to 5500 however, the five year survival varies and it varies with regard to the size of the lymph node and the amount of disease present. Five year survival with radiation therapy to the periaortic area.

Endometrial cancer, it varies. It varies from institution to institution. The determination of whether a patient receives radiation for endometrial cancer depends if there is, one, deep myometrial invasion; two high grade of tumor, grade three or three lymph node involvement or stage III. Those are the determining factors whether patient will receive adjuvant therapy with endometrial cancer.