Treatment outcome and compliance to dose-intensified linac-based SBRT for unfavorable prostate tumors using a novel real-time organ-motion tracking

Abstract

Purpose/objectives To report preliminary data on treatment outcome and compliance to dose-intensified organ sparing SBRT for prostate cancer using a novel electromagnetic transmitter-based tracking system (RayPilotÒ System) to account for intra-fractional organ motion. Material/methods Thirteen patients with intermediate unfavorable (9) and selected high-risk (4) prostate cancer underwent dose-escalated SBRT in 4 or 5 fractions (BED1.5 = 279 Gy and 253 Gy, respectively). The VMAT treatment consisted in two 6FFF or 10FFF full arcs optimized to have the 95% isodose covering at least 95% of the PTV (2 mm isotropic expansion of the CTV). Whenever the real-time tracking registered a displacement that exceeded 2 mm during the setup and/or the beam delivery, the treatment was interrupted and the prostate motion was promptly corrected. The incidence of treatment-related genitourinary (GU) and gastrointestinal (GI) toxicity, patient QoL and PSA outcomes were computed from the start of treatment to the last follow-up date. Results All patients completed the treatment in the expected time (10.2 +/− 4.2 minutes) and their compliance to the procedure was excellent. No clinically significant acute Grade 2 or higher GI (rectal) and GU side effects were observed within 90 days from the treatment completion. The median IPSS increased from 8 at baseline to 12 one-month after treatment and settled to 6 at 3 months. EPIC-26 scores in the urinary domain decreased from a median baseline of 86 pre-treatment to 79 at one-month and returned to baseline at a later timepoint (median score of 85 at 3 months). EPIC-26 scores in the bowel domains did not show significant changes within 3 months following RT. The prostate was found within 1 mm from its initial position in 78% of the beam-on time, between 1 and 2 mm in 20%, and exceeded 2 mm only in 2%, after correction for motion which was performed in 45% of the fractions, either during setup or beam delivery. Conclusions Our preliminary findings show that dose intensified SBRT for unfavorable prostate tumors does not come at the cost of an increased toxicity, provided that a reliable technique for real time prostate monitoring is ensured. Fast FFF beams contributed to reduce intra-fractional motion. These observations need to be confirmed on a larger scale and a longer follow up.

Intrafraction Prostate Motion Management During Dose-Escalated Linac-Based Stereotactic Body Radiation Therapy

“…In the context of extreme hypofractionation, even a single fraction with unexpected organ motion can lead to potentially detrimental dosimetric and clinical consequences. The excellent early toxicity rates, compliance, and biochemical outcomes seen in the present series ( 23 ) suggest that treatment was delivered accurately and precisely.…”

“…Patient population and treatment planning protocol have been described previously ( 23 ). Briefly, patients were immobilized in the supine position with arms over their chest using the FeetFix system (CIVCO Medical Solutions, Iowa, US) attached to the couch for ankle fixation.…”

The MIRAGE Trial—Optical Illusion or the Future of Prostate Stereotactic Radiotherapy?

“…However, a few single-arm prospective studies have reported lower acute GU and GI toxicity using small clinical target volume to PTV margin using conventional methods. [5][6][7] Another approach to reducing GU toxicity can be to improve urethra delineation, which can be a reason for reduced GU toxicity in the MIRAGE MRI group. 1 A phase-2 study involving 170 patients treated on CT-based LINACs reported acute grade 2 GU toxicity of 18% with urethra-sparing SBRT using a 5-mm margin all around except posteriorly (3 mm).…”

“…As highlighted by the Kishan et al study, no randomized data support using 2-mm PTV margins for prostate SBRT. However, a few single-arm prospective studies have reported lower acute GU and GI toxicity using small clinical target volume to PTV margin using conventional methods . Another approach to reducing GU toxicity can be to improve urethra delineation, which can be a reason for reduced GU toxicity in the MIRAGE MRI group .…”

Stereotactic Body Radiation Therapy in Prostate Cancer: Where Do We Stand?

“…Furthermore, late grade ≥3 genitourinary and gastrointestinal toxicity were found in 2.3% and 0.9% patients, respectively. Lucchini et al 61 assessed dose-intensified linac-based SBRT using novel real-time organ motion tracking in unfavorable prostate cancer (n = 13). The patients were delivered SBRT in 4 or 5 fractions, and preliminary findings revealed that RTOG grade ≥3 genitourinary toxicity was observed in 2% and 2% patients in the 2 groups, respectively, with no treatment-related deaths.…”