When prostate cancer returns after initial local treatment, such as a radical prostatectomy, it is known as a biochemical recurrence. This means the prostate-specific antigen (PSA) level, which should have dropped to an undetectable level after surgery, begins to rise again. Salvage radiation therapy (SRT) is a second-line treatment designed to eliminate residual or recurrent cancer cells presumed to be localized in the prostatic fossa or prostate bed. SRT is called “salvage” because it is administered after the primary therapy has failed. This treatment aims to prevent the further progression and spread of the disease.
When Salvage Radiation Becomes Necessary
The primary trigger for considering salvage radiation is a biochemical recurrence, formally defined as a confirmed PSA level of \(0.2 \text{ ng/mL}\) or higher following radical prostatectomy, often confirmed by a second rising value. Physicians must first determine if the recurrence is localized to the pelvic area or if it has already spread elsewhere in the body. The timing of treatment initiation is a significant factor in predicting successful outcomes.
Clinical evidence shows that starting radiation when the PSA level is very low significantly improves the chance of long-term control. Treatment initiated when the pre-radiation PSA is \(\leq 0.5 \text{ ng/mL}\) yields better results than starting at higher levels. Early intervention at these low PSA levels is associated with a reduced risk of the cancer spreading to distant sites.
Imaging is used to confirm that the recurrence is localized and to define the treatment area. Advanced scans, such as Prostate-Specific Membrane Antigen (PSMA) Positron Emission Tomography (PET) scans, are valuable in this setting. PSMA PET scans can detect small clusters of cancer cells in the prostate bed or nearby lymph nodes, guiding the radiation oncologist in defining the target volume.
Planning and Technical Delivery of Treatment
Salvage radiation relies on advanced planning and delivery methods to maximize the dose to the target while sparing surrounding healthy tissue. The modern standard uses Intensity-Modulated Radiation Therapy (IMRT). IMRT shapes the radiation beam to conform closely to the treatment area’s contours, reducing the dose delivered to nearby sensitive organs like the bladder and rectum.
The process begins with a simulation, where the patient undergoes a planning Computed Tomography (CT) scan, often supplemented by an MRI, while positioned exactly as they will be for daily treatment. The radiation oncologist outlines the clinical target volume, which always includes the prostate bed and may include pelvic lymph node regions for higher-risk patients. The total radiation dose, typically delivered over six to seven weeks, is calculated in Gray (Gy), with a common prescribed dose ranging from 66 to 70 Gy.
To ensure daily accuracy, Image-Guided Radiation Therapy (IGRT) is employed. IGRT involves taking daily imaging, such as Cone-Beam CT scans, just before treatment to verify the exact position of the area. This guidance allows the radiation therapist to make minute adjustments, compensating for small internal movements. This precision is essential for the safe delivery of the prescribed dose with minimal impact on adjacent organs.
Expected Results and Long-Term Monitoring
The primary measure of success is achieving long-term biochemical control, meaning the PSA level drops to a very low or undetectable level and remains stable. Success rates are strongly influenced by the PSA level at the start of treatment; the lower the pre-treatment PSA, the higher the probability of successful control. Patients treated at a PSA of \(0.5 \text{ ng/mL}\) or less often see long-term progression-free survival rates between 60% and 80%.
Factors that predict a less favorable outcome include a high Gleason score (8 to 10) from the original surgery or evidence of cancer spread into the seminal vesicles. Achieving a PSA nadir (lowest point) of \(0.1 \text{ ng/mL}\) or less after SRT is the most favorable indicator of long-term success. Post-treatment monitoring involves checking PSA levels at regular intervals to confirm control.
To enhance radiation efficacy, hormone therapy, known as Androgen Deprivation Therapy (ADT), is often administered concurrently. ADT lowers male hormones (androgens) that fuel prostate cancer growth, making cells more susceptible to radiation. A short course of ADT, typically lasting four to six months, is recommended for patients with a higher risk of recurrence. The combination of ADT and radiation improves long-term disease control and survival outcomes compared to radiation alone for certain patient groups.
Managing Treatment-Related Side Effects
Radiation delivery to the prostate bed can affect nearby organs in the pelvis, leading to both acute and chronic side effects. Acute side effects occur during or shortly after the six- to seven-week treatment course and generally resolve within a few weeks to months. These effects are categorized into genitourinary and gastrointestinal issues due to the proximity of the bladder and rectum.
Genitourinary side effects include increased urinary frequency, urgency, and painful urination (dysuria). These symptoms are managed with medications that help relax the bladder or treat any inflammation. Gastrointestinal side effects commonly involve rectal irritation, manifesting as loose stools, diarrhea, or a feeling of incomplete emptying (proctitis). Dietary modifications and anti-diarrheal medications help alleviate these symptoms.
Chronic side effects persist or develop months to years after treatment ends. Long-term genitourinary issues may include worsening pre-existing urinary incontinence or, less commonly, blood in the urine (hematuria). Chronic gastrointestinal issues, such as occasional rectal bleeding (hematochezia) or persistent changes in bowel habits, occur in a smaller percentage of patients. Modern IMRT and IGRT techniques help minimize the incidence of severe long-term complications.