Basic
principles of Radiobiology
1. The
critical target for radiation injury for most cell types is DNA.
2. Inonizing
radiation in sufficient dosage will produce cell death and then loss of
clonogenic capacity
3.
Disruption of plasma membranes is the other form of cell damage
4. Unit of
dosage: Gray (1 joule/kg); 1 Gray = 100 rad; centigray (cGy) is the unit
of current pratice, 1 cGy = 1 rad.
5.
Fractionation: A single dose of radiation (eg 600cGy) will result in
fewer surviving cells than the same total dose given in several smaller
fractions ( eg 300 cGy x 3). But, fractionated radiation provides chance
of repair of normal tissue damage between fractions.
6.
Radiosensitivity correlates with the presence of oxygen. Keep Hb ³ 10
will enhance the radiation sensitivity.
7.
hyperthermia: 42 - 43 C sensitizes cell to radiation.
Radiation
Techniques: radiation therapy is delivered in three ways
1.
Teletherapy ( External beam):given with megavoltage or supervoltage
equipment
1) Photons:
a quantum of high-energy electromagnetic radiation to cause ionization.
Photon may be gamma ray or x-rays
2)
Electrons: generated from betatrons or high-energy accelerators. For
superficial lesion
2.
Brachytherapy:
Radiation
Therapy in Gynecologic Malignancies
A. Cervical
Cancer:
1.
Indications:
1) When
surgery is not possibile: stage ³ IIb, age > 70 y/o, general condition
not suitable for surgery, contraindication of anesthesia
2) Adjuvant
therapy of radical hysterectomy:
parametrium
involvement (+),
pelvic lymph
node metastases (+),
cervicix
invasion depth > 2/3,
section
margin with cancer,
Section
margin with CIN III in patient receiving neoadjuvant chemotherapy (bulky
tumor)
inadequate
surgical margin
3) Recurrent
cancer (local recurrence): often combined with chemotherapy, single or
combination regimen.
4)
Palliation in advanced disease: short courses, eg 2000 cGy in 5
fractions, 3000 cGy in 10 fractions
5)
Interstitial implants (& COBRT): to provide small volume boost in
patients after external therapy, also in recurrent focus of previous
radiation therapy ( central, sidewall)
2.
Irradiation administration:
1) External
radiation: dose is limited due to the adjacent normal organ.
Brachy
therapy: to achieve a higher cintral tumor dose
2) Treatment
dosage: 4000-5000 cGy for local control of microscopic tumor, 6000 cGy
or more to obvious tumor
3) Reference
points:
Point A: 2
cm later and 2 cm superior to the external cx os
Point B: 3
cm later to point A and corresponds to the pelvic sidewall
4) The
summated dose to point A for adequate central control is 7500 - 8500
cGy. The dose to point B is 4500 - 6500 cGy for parametrium and sidewall
control
5) Box
technique: may spare rectum and sigmoid colon and small bowel to reduce
side-effect
6) Extented
field: to cover para-aortic lymph node, up to T-12. used in PA L/N (+)
7) Drainage
of pyometra before radiation to prevent sepsis from rupture of pyometra
3. Toxicity:
1) Late
complication (5-15%)
Hematuria,
radiation cystitis: Tx with normal siline irrigation, hyperbaric
oxygenation
Hemorrhagic
proctitis: Tx with cort-enema
Fistula:
rectovaginal fistula is most often, Tx with colostomy. Vesicovaginal
fistula, Tx with long term foley catherization and repair, PCN.
Stricture:
of ureter, PCN if hydronephrosis occurs.
perforation
of hallo organ: rectum, sigmoid, small bowel, pyometra.
2) Acute
toxicity:
a) Abdominal
cramping and diarrhea in (60%) : Tx with antidiarrhea medications (eg.
kaopectin)
b) Anorexia,
nausea, vomiting (75%): Tx with novamin, primperan, zofran
c) General
fatigue (100%): supportive Tx
d)
thrombocytopenia and neutropenia (10%): Isolation to prevent secondary
infection, prophylactic antibiotics, G-CSF.
e)
Pneumonitis (15%): most often self-limiting and resolves spontaneously
f) Liver
damage(40%): GOT, Alk-p elevation: observation and supportive Tx
g) Abdominal
bloating (10%): symptomatic relief
B.
Endometrial Cancer:
1. Adjuvant
therapy: myometrial invasion ³ 1/2
2. Localized
endometrial cancer --- curative intent
3.
Toxicities are same as in cervical cancer
C. Ovarian
Cancer:
1.
Indication:
1) For
selected patient of ovarian cancer, eg focal residual tumor in p’t of
poor liver and renal function and chemotherapy is not suitable
2) Improving
local control of microscopic lesion in some specific condition
2.
Irradiation administration:
1) Whole
abdominopelvic radiation; moving-strip techniqe, open-field technique
2) Acute
toxicity was similar for both techniques. Late complication s were nore
frequent with the strip technique.
3) Open
technique was more favored
3. Toxicity:
1) Abdominal
cramping and diarrhea in (60%) : Tx with antidiarrhea medications (eg.
kaopectin)
2) Anorexia,
nausea, vomiting (75%): Tx with novamin, primperan, zofran
3) General
fatigue (100%): supportive Tx
4)
thrombocytopenia and neutropenia (10%): Isolation to prevent secondary
infection, prophylactic antibiotics, G-CSF.
5)
Pneumonitis (15%): most often self-limiting and resolves spontaneously
6) Liver
damage(40%): GOT, Alk-p elevation: observation and supportive Tx
7) Abdominal
bloating (10%): symptomatic relief
D. Combined
Operative Brachy Radiation Therapy (COBRT): for focal residual tumor
(mainly CX Ca) after a debulking surgery (most often exenteration
surgery) in patient who had reciieved full dose external radiation
E. Vulva
Cancer:
1.
Indication:
1) In
patient of advanced diseses to reduced the postoperative locoreginal
failure
2) Poor
candidate of surgery or anesthesia
3)
Inguinopelvic irradiation is used for adjuvant therapy in patient of
positive node.
4) Local
irradiation when the surgical margin or deep margin ( periosteum) is not
adequate
2. Radiation
Administration:
1) 4500 -
5000 cGy for microscopic disease, 6000 - 6400 cGy for macroscopic lesion
2) Fraction
size should be minimized to 160 - 175 cGy to reduced radiarion sequelae
3) 5-FU or
cisplatin can be used as radiation sensitizer
4) Electron
beam is used in superficial lesion
3. Toxicity:
1) Acute
moist desquamation
2) Late
complication: lymphedema, atrophy and fibrosis of skin and subcutaneous
tissues
3) Hip
fracture
F. Vaginal
Cancer: advanced stage
The
side-effect and its management of radiation therapy
* Radiation
Cystitis (hemorrhagic cystitis)的處理原則:
1. 2
combined antibiotics
2. on 3 way
foley
3. Ringer
lactate solution irrigation(最好是冰的)180ml/hr
4.
照會骨科for高壓氧治療(Hyperbaric Oxygenation HBO)
*
Hemorrhagic proctitis
1. On low
residual dilt or soft diet.
2. Cort-enema
for sectum suppositary retention