Evaluating the potential benefit of reduced planning target volume margins for low and intermediate risk patients with prostate cancer using real-time electromagnetic tracking

Abstract

PurposeThe aim of this study is to quantify and describe the feasibility, clinical outcomes, and patient-reported outcomes of reduced planning target volume (PTV) margins for prostate cancer treatment using real-time, continuous, intrafraction monitoring with implanted radiation frequency transponder beacons.Methods and materialsFor this prospective, nonrandomized trial, the Calypso localization system was used for intrafraction target localization in 31 patients with a PTV margin reduced to 2 mm in all directions. A total of 1333 fractions were analyzed with respect to movement of the prostate, pauses and interruptions, and dosimetric data. Pre- and posttreatment quality-of-life scores were tracked at baseline, during treatment, and up to 24 months after treatment.ResultsThe mean time of daily treatment was 10 minutes, with 96.1% of all treatments falling within a 20-minute treatment window standard. On average, beacon motion exceeded 3 mm during active treatment only 1.76% of the time. The average length of treatment interruption was 34.2 seconds, with an average of 1 interruption every 3.39 fractions. The displacement or excursion of the prostate was the greatest in the superior or inferior dimension (0.11 mm and 0.09 mm, respectively) and anterior or posterior dimension (0.07 mm and 0.13 mm, respectively), followed by the left or right dimension (0.05 mm and 0.06 mm, respectively). At 6 months, patients demonstrated a smaller change in Expanded Prostate Cancer Index Composite scores than the ProtecT comparator group (decreased short-term morbidity). However, in the Bowel and Urinary domains at 12 and 24 months, there was no significant difference.ConclusionsOur data confirm and support that the use of Calypso tracking with intensity modulated radiation therapy reliably provides minimal disruption to daily treatments and overall time of treatment, with the PTV only moving outside of a 3-mm margin < 2% of the time. The use of a 3-mm PTV margin provides adequate dosimetric coverage while minimizing genitourinary and gastrointestinal toxicity.

Intrafraction motion tracking for MR-Linac prostate radiotherapy

“…Both studies showed that the intrafraction motion variance will continue to increase over time and are in good agreement with our results. Our findings are consistent with studies that assessed intrafraction motion with electromagnetic transponders [92], kV imaging [10,19], cine-MR [16] and transperineal ultrasound [68].…”

Impact of immobilisation and image guidance protocol on planning target volume margins for supine craniospinal irradiation

“…Reduction in PTV margins can potentially reduce irradiated volumes and low dose spills considerably and may translate to clinical benefit. The reduction in PTV margins can reduce toxicities associated with radiation therapy as has been shown in some other disease sub-sites [ 18 , 19 ]. The standardization of IGRT protocol may reduce the chances of target miss during treatment with improving quality assurance of the whole process bettering outcome.…”

Reducing PTV margins for prostate SBRT with motion compensation and gating techniques

“…It has been shown that PTV margins as low as 3 mm can be utilized for prostate treatments with the Calypso system. 8 When used in combination with endo‐rectal balloons (ERBs) that limit the prostate motion, the PTV expansion can be reduced to 2 mm. 9 Continual monitoring of the prostate position is also possible utilizing MRI Linacs, with a typical image refresh rate of ∼4 Hz.…”