Early results of urethral dose reduction and small safety margin in intensity-modulated radiation therapy (IMRT) for localized prostate cancer using a real-time tumor-tracking radiotherapy (RTRT) system

Abstract

BackgroundWe prospectively assessed the utility of intensity-modulated radiation therapy (IMRT) with urethral dose reduction and a small margin between the clinical target volume (CTV) and the planning target volume (PTV) for patients with localized prostate cancer.MethodsThe study population was 110 patients in low- (14.5%), intermediate- (41.8%), and high-risk (43.6%) categories. Three gold fiducial markers were inserted into the prostate. A soft guide-wire was used to identify the urethra when computed tomography (CT) scan for treatment planning was performed. A dose constraint of V70 < 10% was applied to the urethral region. Margins between the CTV-PTV were set at 3 mm in all directions. Patients were treated with 70 Gy IMRT in 30 fractions (D95 of PTV) over 7.5 weeks. The patient couch was adjusted to keep the gold markers within 2.0 mm from their planned positions with the use of frequent on-line verification.ResultsThe median follow-up period was 31.3 (3.2 to 82.1) months. The biochemical relapse-free survival (bRFS) rates at 3 years were 100%, 93.8% and 89.5% for the low-, intermediate-, and high-risk patients, respectively. The incidences of acute adverse events (AEs) were 45.5% and 0.9% for grades 1 and 2, respectively. The late AEs were grade 1 cystitis in 10.0% of the patients, rectal bleeding in 7.3%, and urinary urgency in 6.4%. Only three patients (2.7%) developed grade 2 late AEs.ConclusionsOn-line image guidance with precise correction of the table position during radiotherapy achieved one of the lowest AEs rates with a bRFS equal to the highest in the literature.

Target margins in radiotherapy of prostate cancer

“…They noted similar rectal toxicity in-between two cohorts. Shimizu et al 65 reported on 110 patients treated with real-time tracking of fiducial markers and a PTV margin of 3 mm. They noted low adverse events with favourable relapse-free survival suggesting that the small margins did not compromise prostate coverage with their localization protocol.…”

Urethra-sparing stereotactic body radiotherapy for prostate cancer: how much can the rectal wall dose be reduced with or without an endorectal balloon?

“…≈1.5Gy) compared with the nearby organs at risk (OAR); rectum, urethra and bladder, with α/β values of 3–5 Gy [ 2 , 3 ]. A treatment strategy, such as intentionally under-dosing areas of potentially lower tumor burden, for example the periurethral transitional zone of the prostate, may be used to reduce the risk of radiation induced urinary toxicity [ 4 – 6 ]. However, the risk of rectal toxicity is a major concern when designing prostate dose-escalation studies.…”

Acute Urinary Morbidity Following Stereotactic Body Radiation Therapy for Prostate Cancer with Prophylactic Alpha-Adrenergic Antagonist and Urethral Dose Reduction

“…Previous studies of urethral sparing with both EBRT and brachytherapy have demonstrated unacceptable levels of local recurrence ( 26 ). Urethral dose reduction (UDR) aims to reduce the risk of late urinary toxicity without significantly increasing the risk of local recurrence ( 27 ). Urethral catheter (UC) placement prior to simulation is a commonly used technique to identify the prostatic urethra.…”