Late toxicity after post-prostatectomy intensity modulated radiation therapy: Evaluating normal-tissue sparing...

Area of Science:

• Radiation Oncology
• Urologic Oncology
• Medical Physics

Background:

• Dose-volume histogram (DVH) toxicity relationships are not well-defined for men receiving radiation therapy after radical prostatectomy (RP).
• Evaluating existing guidelines is crucial for minimizing late toxicity in this population.

Purpose of the Study:

• To assess the ability of Radiation Therapy Oncology Group (RTOG) study 0534 and institutional intact normal-tissue sparing guidelines to minimize late toxicity.
• To evaluate the relationship between dose to the bladder trigone and late toxicity.

Main Methods:

• 164 men received intensity-modulated radiation therapy (IMRT) to the prostate bed post-RP.
• Dose-volume histogram (DVH) parameters for the rectum and bladder were analyzed against late gastrointestinal (GI) and genitourinary (GU) toxicity (Grade 2+).
• RTOG 0534 and institutional intact prostate RT guidelines were evaluated for adherence.

Main Results:

• At a median follow-up of 33 months, 4-year freedom from Grade 2+ GI and GU toxicity was 91%.
• RTOG 0534 guidelines were not met in 65% (rectum) and 41% (bladder) of cases; institutional intact prostate guidelines were not met in 21% (rectum) and 25% (bladder).
• No tested parameters, including dose to the bladder trigone or adherence to proposed normal tissue goals, were significantly associated with late toxicity (P > .1).

Conclusions:

• Over 90% of men experienced no Grade 2+ late toxicity 4 years after post-RP IMRT.
• No specific dose constraints or parameters evaluated were found to be associated with late toxicity.
• In the absence of established postoperative DVH guidelines, utilizing intact prostate guidelines is a reasonable approach.