This document provides an overview of principles of radiation therapy. It defines key terminology like radiation oncology, dosimetry, and radiation physicists. It describes different types of radiation including photons, electrons, and other particles. It explains how radiation is delivered through linear accelerators and other systems. It also covers topics like dose calculations, fractionation schedules, and the goals of delivering precise radiation doses to tumor volumes while sparing surrounding healthy tissues.

1. Principles of Radiation Therapy
“𝐘𝐨𝐮 𝐜𝐚𝐧’𝐭 𝐰𝐚𝐢𝐭 𝐮𝐧𝐭𝐢𝐥 𝐥𝐢𝐟𝐞
𝐢𝐬𝐧’𝐭 𝐡𝐚𝐫𝐝 𝐚𝐧𝐲𝐦𝐨𝐫𝐞
𝐛𝐞𝐟𝐨𝐫𝐞 𝐲𝐨𝐮 𝐝𝐞𝐜𝐢𝐝𝐞 𝐭𝐨 𝐛𝐞
𝐡𝐚𝐩𝐩𝐲!” (Nightbirde)
Nightbirde was
diagnosed with
cancer in 2020

2. 2

3. Terminology
• Radiation oncology is a specialty focused primarily on the treatment of malignancies
• Radiation therapists are the individuals who actually operate the radiation equipment
and deliver radiation treatments
• Dosimetry - is the discipline of calculating the radiation dose absorbed by the patient and
the calculations are based on the depth dose measurements of the radiation beams used to
treat an actual patient
• Radiation physicists - supervise and review the work of dosimetrists
• Radiation Unit
– Gray (Gy) - The current Standard International unit for absorbed dose
– One Gy = 100 rad = 1 joule/kg
– Clinically, the radiation doses for
• Curative treatment = 70 to 85 Gy
• Palliative treatment = 30 to 40 Gy
3

4. Radiation
• Energy emitted from a source that is transmitted through an intervening medium
or space and absorbed by another body
• Transmission is in the form of waves but wave/particle duality under quantum
physics
• Classified as
– Non-ionizing
• EM radiation at or below the UV spectrum is nonionizing
• longer wavelength/lower frequency lower energy
• May cause injury to humans but the injury is generally limited to thermal damage i.e. burns.
– Ionizing
• short wavelength/high frequency higher energy
• has sufficient energy to produce ions in matter at the molecular level
• can result significant damage to DNA and denaturation of proteins
4

5. 5

6. • Radiation therapy is the focused delivery of energy in tissue to accomplish controlled
biologic damage
• Ionizing radiation used for therapy may be
• defined by their wave lengths
Photons (x-rays)
• used in external beam therapy
• emitted by the electrons outside the nucleus
– produced when a stream of electrons collides with a high atomic number target (tungsten)
located in the head of a linear accelerator
Gamma rays
• emitted by the excited nucleus itself
– originate from unstable atom nuclei and are emitted during decay of radioactive materials
(radionuclides) which are widely used in brachytherapy
6

7. • defined by their masses
• produced by linear accelerators or other high energy generators and are usually delivered
by external beam
• electrons, neutrons, protons, helium ions, heavy charged ions, and pi mesons
– Except for electrons (β-rays), which are available in all modern radiation oncology centers, and
protons, other particles have limited clinical we
• Electron beams: negatively charged and deposit most of their energy near the surface
(used to treat relatively superficial targets )
• Proton beams: positively charged particles that are much heavier than electrons
– Protons scatter minimally as they interact with matter, deposit increasing amounts of energy as
they slow down, and then stop at a depth related to their initial energy (Bragg peak effect)
• So they are use deep targets → deep pelvic and paraaortic lymph nodes, while sparing unnecessary
dosing and injury to anterolateral organs, such as the bowel and kidneys
– major advantage of proton therapy is the lack of an exiting dose through normal tissues. Proton
therapy use for gynecologic malignancies is primarily investigational
• Neutron beams: neutral particles that tend to deposit most of their energy in a single
intranuclear event
7

8. 8

9. • Radiation delivery system
– Gamma Knife
– Linac (linear accelerator)
– CyberKnife
– Novalis ExacTrac Robotic system
– Tomotherapy (aka helical tomotherapy)
9

10. Radiation source
• Radionuclides (radioisotopes)
– undergo nuclear decay and can emit:
• (1) positively charged alpha particles,
• (2) negatively charged beta particles (electrons),
and
• (3) gamma rays
• Linear Accelerator (Linac)
– can produce both photon and electron
beams
– Photon-therapy mode: for deep-seated
tumors
– Electron-therapy mode: for superficial lesions
• The unit for electron beam energy is MeV
(million electron volts)
• Cobalt machine
– Uses cobalt-60
– Produces 1.33 Mv gamma rays
– short half life, require replacement every 4 to
5 yrs
10

11. 11

12. Linear Accelerator
• The patient lies on the treatment couch
(Q.The gantry (G), couch, and head (H)
– These components can all rotate 360
degrees, which allows multiple fields and
angles to achieve optimal dose delivery to
a tumor
• A kV x-ray source (X} is used in
conjunction with an image intensifier 0-
kV) for image guided radiotherapy
(IGRT)
• Another image intensifier (1-MV) is used
for standard port imaging
12

13. Electromagnet Radiation Energy Deposition
• Radiation energy must be deposited in the cancer cells to
initiate radiation damage
• When electromagnetic radiation impacts target tissues, energy
is transferred in 3 ways
– is dominant if the incident energy is low (< 100 kV)
– radiation interacts with an inner orbital electron
– dominates in mid- to high energy ranges (1 MV to 20 MV) and is
the most important in clinical radiation therapy
– interaction occurs with an outer orbital electron
 Both photoelectric effect (A) and Compton effect (B) result in
creation of fast electrons, which then initiate the biologic
process of radiation damage
– occurs when a photon beam with very high energy (beyond 20
MV) strikes the electromagnetic field of the nucleus
– impact of radiation on the atom’s nuclear forces produces a
positron-electron pair
– When a positron later combines with a free electron in these
tissues, two photons are created, which can then lead to radiation
damage 13
MV - million electron volts

14. Depth dose Curve
• A depth dose curve specifically illustrates the dose distribution of a given radiation beam as it penetrates tissues
• Controlled biologic damage
– selective radiation dose distribution within malignant tissue than within the surrounding, a innocent bystander" normal tissues
– achieved by using radiation beams with differing physical properties to define the spatial distribution of an absorbed dose when
these beams strike tissue
– Objective: to minimize side effects (acute, delayed & late)
• Ideally, an absorbed radiation dose is as conformal as possible
– Perfect conformality is achieved when
• targeted malignant tissue absorbs 100% of the prescribed dose while
• adjacent normal tissues absorb 0%
• As the energy increases, the depth of maximum dose (Dmax or D100) increases
• The energy and penetrating power of ionizing radiation increase as the photon frequency increases and
wavelength decreases
• With Electron beam therapy - maximum dose lies close to the surface
– So indicated for superficial targets (metastatic cancer to the inguinal lymph nodes
• With Photon beam (high-energy) therapy - maximum dose is deposited below the surface
– Beyond this point. the dose gradually diminishes as energy is absorbed by the deep surrounding tissues
– This explains the so-called. skin-sparing effect of high energy photons
– Indicated for pelvic malignancy (usually treated with at least 6-MV photon beams)
Dosimetry
• Calculation of radiation dose to be absorbed by the target
• are based on the depth dose measurements of the radiation beams used to treat an actual patient
• dose distribution is usually displayed as a colorful map overlaid on the radiologic images of the patient
14

15. Inverse square law
• radiation intensity from a point source is inversely proportional
to the square of the distance away from the radiation source
– Dose ∝ (1÷ distance2)
– Example: dose at 2 cm will be one-fourth of the dose at 1 cm
15

16. • The exact mechanism of cell death due to radiation is still an
area of active investigation
16
Mechanism of injury Description
Double strand break of
DNA
• DNA injuries involve its strands, bases, and cross-links
Single strand breaks - are easily repaired
the most important lesion is the double strand break → This breakage leads to irreversible
loss of the reproductive integrity of the cell and eventual cell death
Ionizing
• Directly ionizing ➔ Fast electrons may directly strike DNA to create damage
o seen in particulate radiation
• Indirectly ionizing (most common)
o contribute to ~ 2/3rd of cell biologic damage
o fast electron may interact with water to create a hydroxyl radical, which subsequently
interacts with DNA to cause injury

17. Cell Death after radiation
• two pathways
– Apoptosis (programmed cell death)
• aka interphase death
– Mitotic catastrophe
• the most common mechanism
•  premature or inappropriate entry of cells
into mitosis
Four R’s of Radiation Biology
• four mechanisms by which cells
respond to radiation
1) Repair
– Repair of sublethal damage repair
(SLDR) and potentially lethal damage
repair (PLDR)
2) Reassortment
o redistributes surviving cells over cell-
cycle phases thus avoiding repeated
irradiation in resistant phases
o Cells in mitosis (M) and G2 are most
sensitive to radiation
o Conversely, cells in G1 and S (DNA synthesis) phases
are less sensitive
o When exposed to radiation, those cells that are in the
G2/M phase are killed. During
reassortment, surviving cell populations
restart their progression through the mitotic cycle
3) Repopulation
– The last process seen in SLDR
– tissue's response to replenish the cell pool
4) Reoxygenation
– Cells located within 100 microns of blood capillaries
are oxygenated, and beyond 100 microns, cells are
hypoxic
– After radiation, the oxygenated cells are killed by
chemical intermediates described earlier
– Following cell death, the tumor shrinks and allows
hypoxic cells to be positioned within the oxygen
diffusion range of blood capillaries and become
oxygenated
17

18. Linear quadratic Theory and the Alpha/Beta Ratio
• a simple relationship between cell survival and delivered
dose
• alpha/beta ratio reflects the response of normal tissues to
radiation
• Alpha portion of the curve
– probability of cell death is proportional to the radiation dose
• Cell survival is proportional to dose
– Early-responding tissues have a high alpha/beta ratio
– Eg - bone marrow, reproductive organs, and GI mucosa
• Beta portion
– indicates that the probability of cell death is proportional to
the square of the dose
– late-responding tissues
– Eg - lung, kidney, spinal cord, and brain
– Show clinical reactions only weeks to months after
completion of a radiation therapy course
18

19. • Main issues in radiotherapy
– Target tumor related
• en-bloc
• a volume of cancerous tissue
• its local extensions
• its regional lymphatics
– Avoid side effect
• Minimize normality of tissue quality
19

20. Radiation Fractionation Schemes
• Parameters that affect the efficacy and safety of a radiation
course include
o Total radiation dose applied,
o Size of each radiation “fraction” (treatment),
o Time between treatments (“ fractionation schedule”), and
o Elapsed time to deliver the total prescribed dose
1) Standard Fractionation - Conventional radiation
therapy
• Delivery of dose over the shortest feasible elapsed time to
maximize efficacy
– So that cells being killed > surviving cancer cells that can
proliferate and repopulate
• But, it has deleterious consequences on normal tissues
– concern for delayed injury is less when short courses of
radiation are administered with palliative intent
• Radiation delivered with curative intent is generally
administered in daily treatments (Monday through Friday)
of 1.8 Gy to 2.0 Gy.
• Cumulative doses range from 45 Gy to treat microscopic
disease to 70 Gy or more to treat gross disease
2) Altered Fractionation
• Aimed at increasing local tumor control
with lower long-term complications
• Two major strategies
– Hyper fractionation: smaller dose per
fraction
• total dose are increased, but overall treatment
time is relatively unchanged
– Accelerated fractionation:
• dose per fraction is unchanged, overall treatment
duration is reduced, and the total dose is
unchanged or decreased
• The usual weekend break is either shortened or
eliminated
• severe acute reactions are frequent
– Hypofractionation: dose per fraction is
increased, number of fractions and total dose
are reduced, and the overall treatment time is
decreased
• Comparison by RadiationTherapy
Oncology Group (RTOG)
– showed similar local control, survival rates,
and toxicity compared with standard
fractionation
20

21. RadiationTherapy
Basic steps of radiotherapy
, stage
: Scan to confirm extent of the disease and therapy
• CT scan With IV contrast enhancement - to optimally delineate size and
location of all tumor target volumes
• MRI - often useful as an adjunct to the planning CT to help delineate the
relevant tumor and normal tissue anatomy
• Fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT
– To rule out distant metastases, detect involved LNs that were apparently normal
on CT alone
21

22. : localize the tumor or planning of radiation fields - anatomic areas that will
receive a tumoricidal dose (four volumes)
• (1) a gross tumor volume (GTV): encompasses any gross disease
• (2) a clinical target volume (CTV): incorporates any areas at risk for microscopic tumor
spread;
• (3) a planning target volume (PTV): accounts for uncertainties in treatment planning or
delivery such as patient motion or daily set-up error; and
• (4) a volume that defines the normal organs at risk (OAR): will be exposed, albeit to a lesser
radiation dose
: Prescribe the radiation dose and therapy techniques
• prescribed as definitive, palliative, or adjuvant therapy
• Will it be integrated with surgery and chemotherapy?
• Tool that is particularly helpful in the radiation planning and optimization process
– dose volume histogram (DVH)
– computer-generated radiation dose map
– Intensity-modulated radiation therapy (IMRT)
22

23. Intent of Radiotherapy can be
• as primary treatment for many gynecologic malignancies
– Curative intent - Cervix, vulva, vagina, uterus
• postoperatively if the probability of tumor recurrence is high
– Adjunctive to surgery - Cervix, vulva, vagina, uterus
• in the relief of symptoms caused by metastasis of any
gynecologic cancer
– Palliative intent - Metastasis causing symptoms: bleeding, pain,
obstruction
23

24. • Based on placement of radioactive source, radiotherapy is classified as
– Radiation from a source outside the patient
– indicated when an area to be irradiated is large
Includes
a) Three-dimensional conformal radiation therapy (3DCRT)
b) Intensity-modulated radiation therapy (IMRT)
c) Image-guided radiation therapy (IGRT)
d) Stereotactic radiosurgery (SRS) and stereotactic radiation therapy (SRT)
e) Stereotactic body radiation therapy (SBRT)
f) Proton therapy
– Radioactive sources may be placed in the
– sealed or unsealed radioisotopes are inserted into the cancer or its immediate vicinity
– indicated only for small rumor volumes (<3 to 4 cm)
– Typically practiced after external beam radiation therapy has decreased a large tumor volume
24

25. • a radiation treatment technique that maximizes tumor damage while minimizing injury to the
surrounding normal tissues
• Used to treat many different types of cancer
• Highly accurate type of conformal radiation therapy.
• Shapes and divides multiple beams of radiation into tiny beams (beamlets) that vary in dose
• Used for most cancer types, especially for curative treatment.
• Volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) are specialised forms of
IMRT that deliver radiation continuously as the treatment machine rotates around the body
NB: 3DCRT & IMRT have better conformality of the dose distribution
• Uses a treatment machine that takes x-rays or CT scans at the start of each session to check that
you are in the correct position for treatment.
• Positioning can be very finely adjusted to deliver treatments with millimetres accuracy
• Commonly used with many types of radiation therapy to any area of the body
• May also be recommended for areas likely to be affected by movement, such as the lungs from
breathing
25

26. • Specialised type of radiation therapy
• Combines many small radiation fields to give precisely targeted radiation.
• SRS is delivered as one high dose and SRT is delivered as a small number of high
doses.
• Used to treat small cancers in the brain while minimising the radiation reaching
healthy brain tissue.
• A custom-made mask is worn to keep the head still.
• Despite the name, SRS is not surgery and does not involve any surgical cuts
• Sometimes called stereotactic ablative body radiation therapy (SABR)
• Similar to SRS, this method delivers tightly focused beams of high-dose radiation
precisely onto the tumor from many different angles.
• Uses a hypo fractionated regimen of five or fewer fractions (10 to 20 Gy per
fraction)
• Commonly used - lung, liver, and spine
• SBRT should be used with extreme caution in the pelvis
• ➔ Using IGRT, SBRT and IMRT – It is possible to have a "real-time" approaches to
overcome technical factors such as patient or organ motion and tumor size and shape
changes during a treatment course
26

27. • Uses radiation from protons rather than x-rays
• Protons are tiny parts of atoms with a positive charge that release most of
their radiation within the cancer.
• Proton therapy is useful when the cancer is near sensitive areas, such as
the brainstem or spinal cord, especially in children.
• Special machines called cyclotrons and synchrotrons are used to generate
and deliver the protons.
• Proton therapy is not yet available in Australia (as at November 2019), but
there is funding in special cases to allow Australians to travel overseas for
treatment
27

28. Internal RadiationTherapy (Brachytherapy)
• involves placing radiation sources as close as possible to the tumor site
• Classifications
1) Based on location of radioactive source
– Interstitial: placement of catheters or needles directly into the c:ancer and surrounding tissues
– Intracavitary: sealed radioactive sources such as iridium-192 are inserted into a body cavity such as uterus
– Intraluminal, Endovascular
2) Based on duration
– Temporary brachytherapy
• radioisotopes are removed from the patient after a period of time, ranging from minutes to days
• All intracavitary and some interstitial implants are temporary
– Permanent brachytherapy
• radioactive source – implanted & left to gradually decay
• Other types of internal radiation therapy
– Radionuclide therapy [Eg - radioactive iodine]
• Radioactive material - taken orally as a capsule / liquid or given by injection
– selective internal radiation therapy (SIRT)
• aka Radioembolisation
• tiny pellets called microspheres, are injected through catheter -inserted to hepatic artery
28

29. Routine gynecologic intracavitary implantation
• standard equipment
– For uterus: tandem (T)
– Vaginal applicator: ovoids (O)
• In gynecologic oncology, brachytherapy with T&O is indicated for
cervical cancer.
• For uterine cancer, vaginal brachytherapy with a cylinder is used
to treat the vaginal apex or length of the vagina, which is the
most common site of disease recurrence after hysterectomy
After loading - Manual versus Remote
• Manual after loading
– this method increased hospital staff radiation exposure
• Remote after loading
– commonly practiced today
– This remote control system delivers a single miniaturized iridium
source from a protective safe through connecting cables to the
holding devices previously inserted into the patient
– Following treatment, the radioactive source is automatically
retracted back into the safe
29

30. Low Dose rate versus High Dose rate Brachytherapy
Low Dose rate
• Delivered over the course of many
days and requires prolonged
hospitalization
• Dose rates from 0.4 Gy to 2 Gy/hr
• Example
– Intracavitary implant for cervical
cancer: 30 to 40 Gy delivered
continuously over several days
High Dose rate
• Treatment is shortened to minutes.
• Rates higher than 12 Gy/hr.
• avoids lengthy inpatient
hospitalization
• minimizes patient immobility and
thromboembolic events
• Example
– Intracavitary implant for cervical
cancer: 30 to 40 Gy delivered 3 to 5
weekly fractions
• become more popular
30
• Long-term analysis shows similar local tumor control and late complication rates in patients treated
for cervical cancer with both HDR and LOR

31. Tumor Control Probability
Factors affecting response to radiation
• Tumor’s size (Volume of initial tumor)
– Large tumors are more difficult to control with radiation than smaller ones
• Intrinsic radiosensitivity
– determined by its pathologic type
o Highly sensitive: Lymphoma, dysgerminoma, small cell cancer, embryonal cancer
o Moderately sensitive: Squamous carcinoma, adenocarcinoma
o Poorly sensitive: Osteosarcoma, glioma, melanoma
– Even cancers with a similar histology may have variable responses to radiation.This may be explained by
heterogeneity within a given tumor and by the cancer cell’s ability to repair radiation damage
• TreatmentTime
– When protracted time intervals are required to complete a fractionated radiation therapy course, tumor
control probability decreases, especially in rapidly proliferating epithelial cancers
– Shorter duration – better response
• Cell cycle position
• Tumor Hypoxia
– major factor leading to poor local tumor control and poor survival rates
31

32. • To overcome tumor hypoxia, many strategies have been devised and vary
in efficacy.
– Hyberbaric oxygen in conjugation with radiotherapy
– Carbogen and nicotinamide (ARCON)
• accelerated radiotherapy with carbogen and nicotinamide (ARCON) improves tumor control
in patients with anemia but is not commonly used
– Bioreductive agents
• tirapazamine (TPZ) - hypoxic cell sensitizers
– High-linear-energy-transfer radiation
– Hyperthermia
– ensure adequate oxygen carrying capacity, a hemoglobin level of at least 12 gldL
• Erythropoietin vs transfusion
• higher rates of thromboembolism with erythropoietin use
32

33. Radiotherapy + Surgery
• Radiation therapy can be given
– before, after, or at the time of surgery
• surgical resection and its associated morbidity can often be minimized
• Advantages of preoperative adjuvant radiation
– decrease the potential or locoregional and distant tumor dissemination and the likelihood of positive surgical margins
– to avoid extensive surgery in locally advanced cancer (eg – vulvovaginal ca)
– In unresectable cancers, it can transform them into suitable candidates for a surgical attempt
• Purpose of adjuvant radiation
– Decrease a high probability for local recurrence if positive margins, lymph node metastases, lymphovascular invasion, and high-
grade disease
– Cervical ca with lymphovascular invasion, deep stromal invasion, or large tumor size
– Uterine ca: stage IB or greater disease
– Intermediate risk: older age, lymphovascular invasion, deep myometrial invasion, or intermediate- or high-grade disease
– In these cases, it is ideally delivered 3 to 6 weeks following surgery
• Intraoperative radiation therapy (lORT) is infrequent
33

34. Radiotherapy + chemotherapy
• increase local disease control and decrease distant metastasis.
• can be administered in a concurrent or alternating fashion to maximize tumoricidal effects
and minimize overlapping toxicities and complications
• interactions into four groups:
– (1) Spatial cooperation (independent action), (2) additivity, (3) supra-additivity, and (4)
subadditivity
• For gynecologic cancers, platinum compounds are most commonly used with radiation
therapy
– Both radiation and cisplatin cause single- and double-strand DNA breaks and base damage
– Although most lesions are repaired, if a cisplatin-induced DNA adduct lies close to a radiation
induced single-strand break, then the damage is irreparable and leads to cell death
34

35. • Nucleoside analogues (fludarabine and gemcitabine)
– enhance the effects of radiation-induced cell killing
– inhibit DNA synthesis by blocking cells at the G1/S checkpoint
• The remaining cell population is synchronized at the G2/M junction, the most radiation-sensitive
phase of the cell cycle
– Clinically, in a Phase III study of cervical cancer patients, the progression-free survival
and overall survival rates improved in patients randomized to receive gemcitabine,
cisplatin, and radiation followed by adjuvant gemcitabine compared with cisplatin and
radiation alone
– However, inclusion of gemcitabine is still considered investigational for cervical cancer
treatment
• Taxanes (paclitaxel and docetaxel)
– enhance the effects of radiation by causing microtubule dysfunction and blocking cells at
the G2/M junction
– Taxanes have been administered with platinum agents and radiation therapy in small
nonrandomized trials involving patients with locally advanced cervical cancer
35

36. • Effects of radiation on tissues are generally of two types:
– Loss of mature functional cells by apoptosis (programmed cell death)
• This usually occurs within 24 hours of radiation
– Loss of cellular reproductive capacity
• The severity depends upon the total dose of radiation, length of time over which
radiotherapy is delivered and the radiosensitivity of the particular cell types
• Usually lost cells are replaced by proliferation of surviving stem cells or progenitor cells
• In general, radiation therapy is less well tolerated if
– (1) the irradiated tissue volume is large,
– (2) the radiation dose is high,
– (3) the dose per fraction is large, and
– (4) the patient’s age is advanced
36

37. • Furthermore, the radiation damage to normal tissues can be
exacerbated by factors such as
– prior surgery, concurrent chemotherapy, infection, diabetes mellitus,
hypertension, and inflammatory bowel disease
• In general, if tissues with a rapid proliferation rate such as
epithelium of the small intestine or oral cavity are irradiated, acute
clinical symptoms develop within a few days to weeks
• This contrasts with muscular, renal, and neural tissues, which have
low proliferation rates and may not display signs of radiation
damage for months to years after treatment
37

38. Tissue Response to radiation
Epithelium & Parenchyma o Atrophy (Main), necrosis, ulceration, fibrosis
Skin o skin necrosis > moist desquamation > dry desquamation > Erythema
o during a 6 to 7 week radiation therapy
Vagina o acute vaginal mucositis
o delayed reactions : atrophic vaginitis, formation of vaginal synechiae or telangiectasia, and most commonly, vaginal
stricture.
Ovary and Pregnancy
Outcomes
o depend on radiation dose and patient age
o For example, a dose of 4 Gy may sterilize 30 percent of young women, but 100 percent of those older than 40
o Symptoms of ovarian failure mirror those of natural menopause, and symptom treatment is similar in those who are
candidates
o To minimize radiation exposure to the ovaries, gonads may be surgically repositioned, termed transposition
Bladder o Acute cystitis symptoms within 2 to 3 weeks o beginning treatment
Small Bowel o particularly vulnerable to acute early damage from radiation therapy
o After a single dose of 5 to 10 Gy, crypt cells are destroyed, and villi become denuded
o An acute malabsorption syndrome ensues to cause nausea, diarrhea, vomiting, and cramping
Rectosigmoid o diarrhea, tenesmus, and mucoid discharge
o antidiarrheal medications, low-residue diet, steroid-retention or sucralfate enemas, and hydration are management
mainstays
Kidney o acute radiation nephropathy
Bone o Fractures, pain
HematologicToxicity o deplete bone marrow hematopoietic stem cells that include erythrocyte, leukocyte, and platelet precursors
o if platelet < 35,000 andWBC < 1000 → then radiation may be held until these values rise
o For anemia, transfusion is recommended
o To spare bone marrow injury, IMRT may be beneficial
38

39. Ovarian transposition before pelvic radiation
 performed to preserve fertility or prevent early
menopause
 in reproductive-age patients who are undergoing
pelvic or low abdominal radiation therapy and
who will not be treated with gonadotoxic
chemotherapy
 Not candidates
– Menopausal patients
– Patients over 40 years old with poor ovarian
reserve
– patients with cancers at moderate or high risk for
ovarian metastasis
 Route
– Laparotomy
– Laparoscopy – preferred
 Outcome
– Ovarian function: 33 – 93%
– Pregnancy: 3%
39
Procedure
 The ovarian ligaments (1) and the mesovarium (2)
are divided
 If mobility is inadequate, a relaxing incision on the
peritoneum inferior to the ovary (3) may be
needed
 ovaries are mobilized to a level cephalad to the
anterior superior iliac spine without tension
 Transpose ovaries at least 1.12 cm higher than the
iliac crest plane

40. Pregnancy Outcomes
• Exposure to radiotherapy in childhood or adulthood does not significantly
raise the risk for a congenital anomaly or genetic disease in their offspring
• However, prior childhood abdominopelvic radiation can affect pregnancy
outcomes
– Adverse effects include elevated rates of abortion, low birthweight, stillbirth, and
preterm birth
– Proposed explanations include
• reduced uterine volume,
• endometrial and myometrial atrophy, fibrosis, and
• impaired uterine blood flow
40

41. Pelvic organ tolerance
• The uterine corpus, cervix and vagina tolerate very high dose
of radiation
o 20-30,000 cGy/2 wks surface doses are tolerated
• 1 Centi-gray (cGy) = 10−2 Gy
• Bladder, rectum, recto sigmoid and sigmoid are more
susceptible to RT
• Pelvic irradiation spares significant portion of small bowel
41

42. Radiation therapy side effects
Complications of radiotherapy
• Increased incidence of spontaneous mutations
– the doubling dose is ~100Gy(experiment in mice)
– 1- 6% of spontaneous mutations in humans
• Permanent sterility
– 250-600 Gy in acute exposure,0.2 Gy/yr in
protracted exposure
• Poor wound healing, fistula formation
• Radiation induced soft tissue necrosis
• Reduced bladder capacity, hematuria,
ureteral/urethral stricture
• Hematochezia, bowel obstruction, tenesmus,
fecal incontinence, fistula formation
• Dryness and shortening of vagina, dyspareunia,
decreased libido
42
Short-term
side effects
Long-term or
late side effects
Fatigue ✓
Skin problems ✓
Appetite loss ✓
Nausea ✓
Mouth and throat problems ✓
Bladder problems ✓ ✓
Bowel problems ✓ ✓
Hair loss ✓ ✓
Lymphoedema ✓ ✓
Tissue hardening (fibrosis) ✓
Sexuality and intimacy issues ✓ ✓
Infertility ✓

43. 43

44. • Fetal effects-depend on GA, dose ,dose rate
– IUGR ,abortion , still birth ,neonatal death , gross congenital
malformations
– 0.5Gy/entire gestation,<=0.05Gy/mn(safe
– 10Gy exposure during sensitive period(10 days-26wks) >therapeutic
abortion
• Childhood cancer
44

45. • A secondary cancer may develop as a
result of prior radiation therapy.
• The accepted criteria for the diagnosis
of radiation induced cancer
– Cancer located within the previously
irradiated region
– Histology differ from that of the original
malignancy
– there should be a latent period of at least a
few years
• Latency for leukemia is less than 10 years,
whereas for solid tumors may take decades
• Risk factor
o Receiving higher radiation doses
o Those exposed at an earlier age
o susceptibility of specific tissue types to radiation
induced carcinogenesis
1. High: Bone marrow, female breast, thyroid
2. Moderate: Bladder, colon, stomach, liver, ovary
3. Low: Bone, connective tissue, muscle, cervix, uterus,
rectum
• Mechanisms
– (1) mutations, including alterations in the structure
of single genes or chromosomes;
– (2) changes in gene expression, without mutations;
and
– (3) oncogenic viruses, which, in turn, may cause
neoplasia
• Prevention
– irradiation of smaller fields with advanced
technologies such as IMRT compared with larger
field 2-D external beam radiation may reduce the
incidence of radiation-induced malignancies
45