Real‐time intrafraction prostate motion during linac based stereotactic radiotherapy with rectal displacement

Abstract

BackgroundKilovoltage Intrafraction Monitoring (KIM) is a method which determines the three‐dimensional position of the prostate from two‐dimensional kilovoltage (kV) projections taken during linac based radiotherapy treatment with real‐time feedback. Rectal displacement devices (RDDs) allow for improved rectal dosimetry during prostate cancer treatment. This study used KIM to perform a preliminary investigation of prostate intrafraction motion observed in patients with an RDD in place.MethodsTen patients with intermediate to high‐risk prostate cancer were treated with a Rectafix RDD in place during two boost fractions of 9.5–10 Gy delivered using volumetric modulated arc therapy (VMAT) on Clinac iX and Truebeam linacs. Two‐dimensional kV projections were acquired during treatment. KIM software was used following treatment to determine the displacement of the prostate over time. The displacement results were analyzed to determine the percentage of treatment time the prostate spent within 1 mm, between 1 and 2 mm, between 2 and 3 mm and greater than 3 mm from its initial position.Results KIM successfully measured displacement for 19 prostate stereotactic boost fractions. The prostate was within 1 mm of its initial position for 84.8%, 1–2 mm for 14%, 2–3 mm 1.2% and ≥3 mm only 0.4% of the treatment time.ConclusionsIn this preliminary study using KIM, KIM was successfully used to measure prostate intrafraction motion, which was found to be small in the presence of a rectal displacement device.Trial registrationThe Hunter New England Human Research Ethics Committee reference number is 14/08/20/3.01.

Clinical Assessment of Prostate Displacement and Planning Target Volume Margins for Stereotactic Body Radiotherapy of Prostate Cancer

“…Larger required margins have been reported as well, up to 4.4 mm SI and 5.2 mm AP based on pre-and post-treatment imaging during SBRT (25), and 5.4 mm (SI) and 5.0 mm (AP) based on Calypso data during conventional fractionation (27). Notably, some studies have noted translations as small as 0.01 ± 0.23 mm (LR), 0.11 ± 0.64 mm (AP), and 0.21 mm ± 0.12 (SI) with incorporation of a rectal distension device and realtime kV infraction monitoring (20). A strength of the present study, however, is the large patient cohort, as the majority of prior published studies have included fewer than 100 patients, and many with fewer than 50 patients.…”

“…Variables affecting intra-fractional target motion include bladder and rectal filling, treatment time, target size, and tissue density (15)(16)(17)(18). Rectal and bladder filling are generally the greatest contributors to prostate displacement, and as a result, prostate displacement tends to be greatest in the superior-inferior (SI) and anterior-posterior (AP) directions (9,(17)(18)(19)(20). Motions can be transient, such as those created by movement of gas through the rectum, or sustained, such as continuous filling of the bladder and rectum (11).…”

“…Multiple image-guided motion management strategies exist (22), and a wide range of required prostate radiotherapy margins have been proposed based on varied techniques. However, the numbers of patients included in studies to estimate required margins are relatively modest, and proposed margins based on data from the intra-fractional, interarc kilovoltage (kV) imaging method is lacking (8,9,16,19,20,(23)(24)(25)(26)(27).…”

Extreme hypofractionated proton radiotherapy for prostate cancer using pencil beam scanning: Dosimetry, acute toxicity and preliminary results

“…This motion can cause the target to be missed or disruption of dose distribution. Legge et al 12 demonstrated with kilovoltage intrafraction monitoring that the intrafraction motion of the prostate is greater than 3 mm only in 0.4% of cases. Curtis et al evaluated necessary PTV margins according to the frequency of image acquisition.…”

Application of rectal retractor for postprostatectomy salvage radiotherapy of prostate cancer: A case report and literature review

“…Also, studies have been investigated the impact of a RR on the intrafraction prostate motion during VMAT using cone‐beam CT (CBCT) and kilovoltage intrafraction monitoring (KIM). As demonstrated in these studies, intrafraction prostate motion was reduced by a RR . Thus, advantages in terms of low cost, rectal dose sparing, reproducibility of the rectal wall position, and prostate stabilization can be achieved with RR.…”