Cancer management by Radiotherapy

Cancer management by Radiotherapy or Radiation therapy


Radiation may be particulate or electromagnetic
Radiotherapy kills tumour cells by generating high energy molecular movement Tumour susceptibility is related to tumour oxygenation and radiosensitivity of the individual cells
Radiotherapy may be used as a primary, neoadjuvant, adjuvant or palliative therapy to causes damage to normal as well as tumour cells resulting in local and systemic complications
.This is the therapeutic use of ionising radiation for the treatment of malignant conditions

What are the types of radiation


Particulate type : which does not penetrate the tissue deeply and is used predominantly to treat cutaneous and subcutaneous conditions like as­
• Protons
Alpha particles and pimesons

Electromagnetic type

 Which penetrates tissue deeply and is therefore used to treat deep tumour tissue such as X-Rays and Gamma rays

What are the Mechanism of action of Radiotherapy

Radiation kills cells by causing high-energy interactions between molecules by.
• DNA damage is via release of kinetic energy from free radicals an oxygen dependent process
, Causes deletions and strand breaks within the DNA
May trigger apoptosis in some cells due to severe DNA damage
, Cells are most sensitive during S phase
Killing cells leads to stimulation of other cells to divide, ie to enter the S phase by
• Repair normal cells take 4 hours to recover (6+ hours for CNS), malignant cell take longer
• Re-population: more cells are stimulated to divide due to death of others
after about 3-4 weeks of standard fractionated treatment
• Re-distribution: pushes cells into the S phase - more radiosensitive
• Re-oxygenation: oxygen is a radiation sensitizer; cell death facilitates re-oxgenation increases cytotoxicity
The degree of tumour destruction by radiotherapy is related to  

  Radiosensitivity of tumours as
Sensitive: seminoma, Hodgkin's lymphoma

Resistant: tendency to repair DNA damage eg melanoma
• Similar tumour types tend to have similar radiosensitivity eg all carcinoma
• Slow-growing tumours may not respond or respond slowly to radiotherapy
Tolerance of normal tissue: surrounding tissue may be very sensitive to treatment (eg nervous tissue, small bowel), which limits the amount of radiotherapy be delivered
Tumour size: larger tumours have areas of low oxygen tension and necrosis and more resistant. They require more cycles and larger treatment volumes with 
normal tissue to higher doses of radiation

What are the methods of Administration of radiotherapy

Locally ie the source can be implanted into tissue to be treated (eg brachiotherapy for prostate cancer) or into a cavity eg uterus
Systematically (eg iodine-131 for thyroid cancer
External beam radiation via linear accelerator
Fractionation describes the number of individual treatments and their time course the therapeutic ratio is the relationship between the amount of radiation tolerated by normal tissues and that delivered to the tumour.
.for radical treatments, aim tor maximum possible dose in the smallest volume which will
encompass all of the tumour and likely occult spread. This is called the treatment volume and it comprise
Macroscopic tumour Bological margin (0.5-1 cm
Technical margin (allows for minute variations in positioning and set up
The site is accurately localized by imaging and permanent skin markings applied to ensure
reproducibility at subsequent sessions
Complex multifield arrangements divide the tumour into cubes. The radiation is targeted to divided the dose between surrounding normal tissues, because different tissues can tolerate amounts of radiation (eg liver is more resilient than kidney). It is usually delivered intermittently , allowing normal tissues to recover. This takes at least 4 hours, while malig­nant tissues take longer.
Improved imaging techniques now allow precise targeting of a tumour shape, which is if it is located near sensitive structures. Techniques are being refined so that there is
an increase in the number of sessions that can be given within a short period of treatment time

Treatment time

 Is known as accelerated radiotherapy (eg multiple sessions per day for 2 weeks
Sterotactic radiotherapy is commonly used for brain tumours. The patient's head is placed
in a frame and an accurate 3-D image of the tumour is obtained using high-resolu­tion MRI. The beam of radiation is focused on the tumour but rotation of delivery means surrounding normal tissues receive minimal doses

Radiation Therapy Planning

Radiation therapy is delivered in a homogeneous dose to a well­ defined region that includes tumor and/or surrounding tissue at risk for subclinical disease

 The first step in planning is to define the target to be irradiated as well as the dose-limiting organs in the vicinity. Treatment planning includes evaluation of alternative treatment techniques. which is done through a process referred to as simulation. Once the beam distribution is determined that will best achieve homogenous delivery to the target volume and minimize the dose to the normal tissue. immobilization devices and mark­ings or tattoos on the patient's skin are used to ensure that each daily treatment is given in the same way. Conventional fractionation­  is 1.8 to 2 Gy per day, administered 5 days each week for 3 to7weeks
 Radiation therapy
 May be used as the primary modality for primary modality or palliation in certain patients with metastatic disease, mostly patients with bony metastases. In this condition. radiation is recommended for symptomatic metastases only. However. lytic metastases in weight-bearing bones such as the femur, tibia, or humerus also are considered for irradiation. Another condition in which radiation might be appropriate is spinal cord compression due to metastases to the vertebral body extending posteriorly to the spinal canal
The goal of adjuvant radiation therapy is to decrease local­
regional recurrence rates

Adjuvant radiation therapy can be given

before surgery after surgery, or in selected cases during surgery

 Preoperative radiation therapy

 It may minimize seeding of the tumor during surgery and it allows for smaller treatment fields because the operative bed has not been contam­inated with tumor cells. Finally. radiation therapy for inoperable tumors may achieve adequate reduction to make them operable

The disadvantages
 Are an increased risk of postoperative wound healing problems
 and the difficulty in planning subsequent radiation therapy in the patients who have positive surgical margins

  postoperative radiation therapy
 It is usually given 3 to 4 weeks after surgery to allow for wound healing. The advantage of postoperative radiation therapy is that the surgi­cal specimen can be evaluated histologically and radiation therapy can be reserved for patients who are most likely to benefit from it
What are the uses of radiotherapy

 ,Used either as primary treatment adjuvant treatment neoadjuvant treatment or as palliative treatment

Primary treatment

 As in sensitive tumours
Better cosmetic and functional result inoperable patients or patients with high mortality/morbidity with surgery
Patient not fit for surgery
  Adjuvant radiotherapy
Can be given at site of disease (control of margins - mark surgical site with clips for easy identification) or at site of potential metastatic spread

Neoadjuvant radiotherapy
• Pre-operatively, can downstage tumours eg rectal tumour
Can reduce risk of seeding at operation
Does not cause additional surgical morbidity if performed within 4 week of surgery

Palliation radiotherapy
Palliative radiotherapy aims for symptom relief, from either primary or metastatic disease (cg relief of bone pain, bleeding, dyspnoea, cord compression vena caval obstruction)
• It is given as short courses of treatment, with simple set-ups, to minimise toxicity
Single fractions are often used to control bone pain

What are the Complications of radiotherapy

Local complications

• Itching and dry skin
• Ulceration
• Bleeding
• Radiation enteritis
• Fibrosis and stricture formation
• Delayed wound healing
• Osteoradionecrosis

Systemic complications

• Lethargy
• Loss of appetite
• Premature menopause
• Acute leukaemia
• Myelosuppression
• Hypothyroidism/renal failure - after many years treatment


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