Australian Doctor 20th June 2025 | Page 34

radiotherapy. Brachytherapy uses

an active radiation source to deliver the dose of radiotherapy either inserted into the tumour directly

RADIOTHERAPY INTENT AND RATIONALE

THE intent, rationale, schedule, dose

or into a body cavity. There are two

and fractionation of radiotherapy are

main types of brachytherapy. In the

decided after consideration of several

first, called low dose rate brachyther-

factors( see box 2).

apy, the source is inserted into the

Treatment intent is a significant

organ permanently. This is most

factor, with higher doses and more

commonly used to treat prostate

treatments( fractions) prescribed over

cancer. Once inserted, the source is

several weeks in the curative setting.

not a radiation risk, as the distance the radiation travels in the body is

This is to deliver the highest tolerable dose to eradicate the tumour, while

small and the source decays over

accepting some short-term toxicities

time. The second is called high dose

and minimal late toxicities. Lower

rate brachytherapy, where the source

doses and shorter courses of treatment

is inserted and then removed. This

are recommended in the palliative set-

technique poses additional radiation

ting; this is to deliver a dose to achieve

safety issues, as the source cannot

symptom control and minimise the

be turned‘ off’ but can be placed in a

patient’ s time away from home. There

shielded safe when not required.

are generally fewer side effects with

A key principle of radiotherapy

the lower dose and shorter course.

is that while individual cells cannot

Significant late toxicity, regardless of

be targeted, they can essentially be selected through a process of fractionation. This describes dividing up the total course of radiotherapy

Figure 2. More accurate planning for radiotherapy using visualised soft tissue structures.

intent, is undesirable.

The radiation dose delivered to the patient in the treatment setting is in a unit known as the gray( Gy). Most

over a number of days / weeks. When

curative schedules of radiotherapy

the radiation is delivered, the cancer

are delivered at 2Gy / day five days per

cell is likely to have defective DNA

week, a total dose of about 50-70Gy.

repair and is therefore destroyed.

Some tumour sites, such as head / neck

Normal cells are expected to have

cancer, require a higher dose of 70Gy,

normal DNA repair and can there-

while a localised low-grade lymphoma

fore heal between each fraction of

requires a dose of 24Gy.

radiotherapy.

In the palliative setting, higher

Fractionation also aids poten-

doses of radiotherapy are delivered

tial redistribution of cells in the cell

per fraction to decrease the overall

cycle to a more radiosensitive phase.

treatment time burden for the patient

The oxygenation status of a tumour

and because a higher total dose is not

is also an important predictor of

required, as total tumour eradication

response to radiotherapy; the more

is not the intent.

oxygenated the tumour, the greater

Safe delivery of radiation ther-

the DNA damage from radiotherapy.

apy requires a multidisciplinary team

Fractionation improves this by pro-

approach, including radiation oncolo-

gressively shrinking the tumour to

gists, medical physicists and radiation

improve oxygenation. Transiently

therapists. The radiation oncologist

open blood vessels may also be more likely to be open over multiple fractions of radiotherapy as opposed to a single treatment. Repopulation of both cancerous and normal tissue occurs, so treatment breaks are

Figure 3. Multiple small beams of radiation can be shaped by the treating machine to create a more conformal dose distribution.

assesses the patient and prescribes the radiotherapy; the physicist ensures the prescribed radiation dose is being delivered correctly by the machines; and the radiation therapist positions the patient and ensures the accurate

generally avoided unless the patient

delivery of treatment. The role of the

experiences significant toxicities.

excision, and is non-invasive com-

of modalities to achieve an optimal

dications to radiotherapy, although

physicist is especially important, as

INDICATIONS AND CONTRA­ INDICATIONS

UNLIKE other cancer therapies,

pared with surgical resection. For these reasons, radiotherapy is estimated to be of benefit in about 50 % of patients with cancer. 4

Most tumours can be treated with

outcome.

The decision to use radiotherapy for a particular cancer is made by a multidisciplinary team. Team meetings are based around tumour sub-

retreatment of previously irradiated tissue needs to be performed with caution. This is because previously irradiated tissue will retain some irreversible tissue effects from the

radiation cannot be seen or sensed.

WHAT CAN A PATIENT EXPECT?

SEVERAL steps are followed before

radiotherapy can be used to treat

radiotherapy either on its own( defin-

types, and a range of professionals,

radiotherapy. The benefit of radio-

a patient starts with radiation therapy.

tumours from the vertex of the scalp

itively) or in conjunction with surgi-

including surgeons, pathologists,

therapy is always weighed up against

This multi-step planning process takes

all the way to the tip of the toe. It

cal resection, chemotherapy, targeted

radiologists, radiation oncologists,

the risks, as with any other medical

time, so it may be a while before the

has the advantages of not being lim-

therapy, immunotherapy or hor-

medical oncologists and allied health

procedure.

patient starts treatment. In emergency

ited by the blood brain barrier or by

mone therapy( adjuvantly). Many

staff, will attend.

The indications for radiotherapy

cases, this process may occur on the

structures that may impair surgical

cancer types require a combination

There are no absolute contrain-

appear in box 1.

same day, but a wait of several weeks