Radiation Therapy for Prostate Cancer: External Beam & SBRT Guide

What is radiation therapy for prostate cancer?

Radiation therapy uses high-energy rays or particles to kill prostate cancer cells. It is a curative treatment option for localized prostate cancer (Stage I-III) and can also be used for advanced disease (palliative treatment for bone metastases).

Radiation works by damaging the DNA of cancer cells, preventing them from dividing and growing. Unlike surgery, radiation does not require incisions or anaesthesia, and there is no recovery from the procedure itself (though side effects occur).

External beam radiation therapy (EBRT) – IMRT, 3D-CRT

External beam radiation therapy delivers radiation from a machine outside the body, targeting the prostate. Modern techniques improve precision and reduce side effects.

3D-Conformal Radiation Therapy (3D-CRT):

• Basic technique using 3D imaging to shape radiation beams
• Less precise than IMRT
• Now largely replaced by IMRT

Intensity-Modulated Radiation Therapy (IMRT):

• Advanced technique that varies the intensity of radiation beams
• Allows higher doses to the prostate while sparing surrounding organs (bladder, rectum)
• Standard of care for prostate cancer EBRT
• Typical schedule: 5 days/week for 8-9 weeks (total 40-45 treatments)

Image-Guided Radiation Therapy (IGRT):

• Uses daily imaging (CT or X-ray) to ensure accurate targeting
• Often used with IMRT
• Accounts for prostate movement (bladder filling, rectal gas)

Stereotactic body radiation therapy (SBRT) – high-dose, fewer treatments

SBRT (also called CyberKnife or stereotactic ablative radiotherapy – SABR) delivers very high doses of radiation in just 1-5 treatments.

Key features:

• Extremely precise targeting (sub-millimetre accuracy)
• High dose per fraction (7-10 Gy vs. 1.8-2.0 Gy for conventional)
• Only 1-5 treatments (typically 5 treatments over 1-2 weeks)
• Requires fiducial markers (gold seeds placed in the prostate)

Advantages:

• Convenience – fewer visits (1-2 weeks vs. 8-9 weeks)
• Biologically more effective for some tumours (high dose per fraction)
• Excellent cancer control rates (similar to conventional EBRT)

Disadvantages:

• Higher risk of urinary side effects (some studies)
• Requires fiducial placement (minor procedure)
• Not suitable for very large prostates or high-risk patients (may require hormone therapy)

Proton therapy – more precise, less scatter

Proton therapy uses protons (charged particles) instead of X-rays. Protons deposit most of their energy at a specific depth (Bragg peak), minimising radiation to tissues beyond the target.

Potential advantages:

• Less radiation to surrounding organs (bladder, rectum, bowel)
• May reduce long-term side effects (though evidence is limited)
• Ideal for young patients or those with genetic predisposition

Disadvantages:

• Much more expensive than IMRT or SBRT
• Limited availability (only specialised centres)
• Not clearly superior to IMRT in clinical trials

Evidence:

• No large randomised trial has shown proton therapy is better than IMRT
• Cost-effectiveness is questionable (2-3x more expensive)
• May benefit select patients (young, favourable anatomy)

Treatment process – simulation, planning, daily treatments

Step 1: Simulation (planning session):

• You lie on the treatment table in the position you will be treated
• A CT scan is performed to map the prostate and surrounding organs
• Small tattoos (dots) may be placed for daily positioning
• For SBRT: Fiducial markers (gold seeds) are placed in the prostate 1 week before simulation
• For IMRT: A full bladder and empty rectum are required for each treatment

Step 2: Treatment planning (1-2 weeks):

• A radiation oncologist and medical physicist design the treatment plan
• The plan optimises dose to the prostate while minimising dose to bladder, rectum, and bowel

Step 3: Daily treatments:

• Each treatment takes 10-15 minutes (actual radiation time: 1-2 minutes)
• You lie on the table; imaging confirms prostate position
• Painless – you will not feel the radiation
• You can go about your normal activities after treatment

Side effects – urinary, bowel, fatigue, erectile dysfunction

Radiation side effects are generally temporary but can be long-term in some men:

Urinary side effects (most common):

• Frequency and urgency: Needing to urinate more often (peaks during treatment, resolves by 3 months)
• Dysuria (painful urination): Burning sensation (temporary)
• Hematuria (blood in urine): Usually mild
• Late effects (months to years): Urethral stricture (rare), radiation cystitis (chronic inflammation)

Bowel side effects:

• Diarrhoea, rectal urgency, frequency: Common during treatment, usually resolves
• Rectal bleeding (proctitis): Late effect (6-24 months after treatment) – occurs in 5-10% of men, usually mild
• Fecal incontinence: Rare (<1%)

Fatigue:

• Cumulative during treatment (worsens over weeks)
• Resolves 4-8 weeks after treatment ends

Erectile dysfunction (ED):

• Rate: 20-40% at 5 years (lower than surgery)
• Onset is gradual (months to years after radiation, vs. immediate after surgery)
• Treatment: PDE-5 inhibitors (Viagra, Cialis) – often effective

Hormone therapy side effects (if combined with ADT):

• Hot flashes, fatigue, decreased libido, erectile dysfunction
• Usually temporary (duration of hormone therapy)

Success rates – biochemical recurrence-free survival

Radiation therapy has excellent cancer control outcomes, comparable to surgery:

• Low-risk (Gleason 6): 10-year biochemical recurrence-free survival: 85-95%
• Intermediate-risk (Gleason 7): 10-year biochemical recurrence-free survival: 75-85%
• High-risk (Gleason 8-10): 10-year biochemical recurrence-free survival: 60-75% (with hormone therapy)

PSA nadir after radiation:

• PSA declines slowly over 18-36 months
• Nadir (lowest PSA) should be <0.5 ng/mL
• Rise >2.0 ng/mL above nadir is Phoenix criteria for recurrence

Radiation vs. surgery – comparison table

Feature	Radiation (IMRT/SBRT)	Surgery (Radical Prostatectomy)
Invasive	No incisions, no anaesthesia	Requires incisions and anaesthesia
Hospital stay	None (outpatient)	1-2 days
Recovery time如何看待None (but side effects during treatment)	2-4 weeks return to work, 6-8 weeks full recovery
Catheter	None	7-10 days
Erectile dysfunction	20-40% at 5 years (gradual onset)	20-50% at 2 years (immediate)
Urinary incontinence	<5% (late onset, rare)	5-10% at 12 months
Bowel side effects	5-10% rectal bleeding (proctitis)	<1% (rare)
Dry ejaculation	No (semen production preserved)	Yes (100%)
Convenience	5 days/week for 8-9 weeks (or 5 treatments for SBRT)	One-time procedure

Interactive FAQ – Radiation therapy for prostate cancer

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Disclaimer: This information is for educational purposes. Radiation therapy decisions should be made with a radiation oncologist. Consult a specialist at Vivekananda Hospital for personalised treatment recommendations.