Prostate cancer is one of the most common malignancies affecting men worldwide.
Fortunately, it is also one of the cancers with the highest cure rates when diagnosed early.
Today, radiotherapy plays a central role in the management of localized, locally advanced, and even selected metastatic prostate cancer.
But treating prostate cancer is far more complex than simply delivering radiation.
Every millimeter matters.
Every image matters.
Every fraction matters.
Understanding the Disease
The prostate is a walnut-sized gland located below the bladder and in front of the rectum. It surrounds the proximal urethra and contributes to seminal fluid production.
Because of its anatomical location, the prostate lies very close to several critical organs:
– Rectum
– Bladder
– Urethra
– Femoral heads
– Penile bulb
– Neurovascular bundles
– Small bowel (in selected patients)
This proximity makes radiotherapy particularly challenging.
The goal is simple:
Deliver a curative dose to the prostate while minimizing toxicity to surrounding healthy tissues.
Who Needs Radiotherapy?
Radiotherapy is recommended for:
• Localized prostate cancer
• Locally advanced disease
• Biochemical recurrence after prostatectomy
• Positive surgical margins
• Oligometastatic disease (SBRT)
• Palliative treatment for painful bone metastases
Treatment decisions depend on:
– PSA level
– Gleason Score / ISUP Grade Group
– Clinical T Stage
– MRI findings
– PSMA PET/CT (when available)
– Patient age
– Performance status
– Life expectancy
Simulation (CT Planning)
Planning begins with CT Simulation.
This is one of the most critical steps.
Patients are usually instructed to:
Have a comfortably full bladder. Empty the rectum before simulation.The reason is simple.
The bladder and rectum change prostate position every day.
Reproducible preparation improves treatment accuracy.
Immobilization
Patients are typically positioned:
– Supine
– Head on a standard headrest
– Knee support
– Foot fixation
Comfort is essential because the patient must maintain the same position throughout treatment.
MRI Fusion
Modern prostate planning rarely relies on CT alone.
MRI provides superior soft tissue contrast.
Fusion of MRI with planning CT allows more accurate delineation of:
– Prostate
– Seminal vesicles
– Dominant intraprostatic lesions
– Apex
– Base
This significantly improves contour accuracy.
Contouring
Radiation Oncologists contour:
GTV
Usually not visible on CT.
MRI often identifies the dominant lesion.
CTV
May include:
– Entire prostate
– Proximal seminal vesicles
– Entire seminal vesicles (high-risk patients)
– Pelvic lymph nodes when indicated
PTV
Margins compensate for:
– Setup error
– Internal organ motion
– Bladder filling
– Rectal volume changes
Typical margins:
– 5 mm
Posterior margin:
– 3 mm
when daily IGRT is available.
Organs at Risk (OARs)
Critical structures include:
– Rectum
– Bladder
– Femoral heads
– Penile bulb
– Bowel bag
– Urethra (for SBRT)
Each has strict dose constraints to minimize toxicity.
Treatment Techniques
Modern prostate radiotherapy is delivered using:
– 3DCRT
– IMRT
– VMAT
VMAT has become the standard in many centers because it offers:
– Better conformity
– Faster treatment
– Improved OAR sparing
Image Guidance (IGRT)
The prostate is not a fixed organ.
Its position changes daily due to:
– Bladder filling
– Rectal gas
– Patient movement
Therefore, daily IGRT is essential.
Common methods include:
– CBCT
– kV imaging
– Fiducial markers
– Surface Guidance
– Electromagnetic transponders (Calypso)
Without daily verification, target coverage may be compromised.
Prescription Dose
Dose depends on the clinical scenario.
Common schedules include:
Conventional Fractionation:
≈74–80 Gy in 37–40 fractions.
Moderate Hypofractionation:
≈60 Gy in 20 fractions.
Ultra-Hypofractionation (SBRT):
≈36.25–40 Gy in 5 fractions.
Several randomized trials have demonstrated excellent outcomes with hypofractionation.
Why Hypofractionation Works
Unlike many tumors, prostate cancer has a low alpha/beta ratio (~1.5 Gy).
This means it is particularly sensitive to larger doses per fraction.
As a result, fewer fractions with higher dose per fraction can achieve excellent tumor control without increasing late toxicity when carefully planned.
Androgen Deprivation Therapy (ADT)
Many intermediate- and high-risk patients receive hormonal therapy in combination with radiotherapy.
ADT reduces testosterone levels, making cancer cells more sensitive to radiation and improving long-term disease control.
Acute Side Effects
During treatment, patients may experience:
– Increased urinary frequency
– Dysuria
– Nocturia
– Mild diarrhea
– Rectal irritation
– Fatigue
These symptoms are usually temporary and manageable.
Late Toxicity
Potential late effects include:
– Rectal bleeding
– Urinary incontinence
– Urethral stricture
– Erectile dysfunction
Modern IMRT and VMAT have significantly reduced these complications.
Adaptive Radiotherapy
With CBCT and MRI-LINAC, clinicians can adapt treatment when bladder or rectal anatomy changes significantly.
Adaptive radiotherapy represents the future of prostate treatment.
Follow-Up
After treatment:
PSA levels gradually decline.
Unlike surgery, PSA does not immediately become undetectable.
A temporary PSA Bounce may occur and should not always be interpreted as recurrence.
Long-term follow-up is essential.
Conclusion
Prostate radiotherapy is one of the greatest examples of precision medicine.
Every stage—from patient preparation and CT simulation to MRI fusion, contouring, inverse planning, image guidance, and dose delivery—requires meticulous attention to detail.
Success depends not only on advanced technology but also on the coordinated work of radiation oncologists, medical physicists, dosimetrists, radiation therapists, nurses, and engineers.
Because in prostate radiotherapy…
Every millimeter counts, and every fraction is another step toward cure.
— From Radiotherapy World Academy
References
– NCCN Guidelines: Prostate Cancer
– ESTRO Guidelines for Prostate Radiotherapy
– ASTRO Clinical Practice Guidelines
– EAU Guidelines on Prostate Cancer
– Khan FM. The Physics of Radiation Therapy
– Podgorsak EB. Radiation Oncology Physics