Real-time prostate motion assessment: image-guidance and the temporal dependence of intra-fraction motion

Abstract

BackgroundThe rapid adoption of image-guidance in prostate intensity-modulated radiotherapy (IMRT) results in longer treatment times, which may result in larger intrafraction motion, thereby negating the advantage of image-guidance. This study aims to qualify and quantify the contribution of image-guidance to the temporal dependence of intrafraction motion during prostate IMRT.MethodsOne-hundred and forty-three patients who underwent conventional IMRT (n=67) or intensity-modulated arc therapy (IMAT/RapidArc, n=76) for localized prostate cancer were evaluated. Intrafraction motion assessment was based on continuous RL (lateral), SI (longitudinal), and AP (vertical) positional detection of electromagnetic transponders at 10 Hz. Daily motion amplitudes were reported as session mean, median, and root-mean-square (RMS) displacements. Temporal effect was evaluated by categorizing treatment sessions into 4 different classes: IMRTc (transponder only localization), IMRTcc (transponder + CBCT localization), IMATc (transponder only localization), or IMATcc (transponder + CBCT localization).ResultsMean/median session times were 4.15/3.99 min (IMATc), 12.74/12.19 min (IMATcc), 5.99/5.77 min (IMRTc), and 12.98/12.39 min (IMRTcc), with significant pair-wise difference (p<0.0001) between all category combinations except for IMRTcc vs. IMATcc (p>0.05). Median intrafraction motion difference between CBCT and non-CBCT categories strongly correlated with time for RMS (t-value=17.29; p<0.0001), SI (t-value=−4.25; p<0.0001), and AP (t-value=2.76; p<0.0066), with a weak correlation for RL (t-value=1.67; p=0.0971). Treatment time reduction with non-CBCT treatment categories showed reductions in the observed intrafraction motion: systematic error (Σ)<0.6 mm and random error (σ)<1.2 mm compared with ≤0.8 mm and <1.6 mm, respectively, for CBCT-involved treatment categories.ConclusionsFor treatment durations >4-6 minutes, and without any intrafraction motion mitigation protocol in place, patient repositioning is recommended, with at least the acquisition of the lateral component of an orthogonal image pair in the absence of volumetric imaging.

Observation of intrafraction prostate displacement through the course of conventionally fractionated radiotherapy for prostate cancer

“…There was a tendency for large IFPDs (≥3 mm) to increase with elapsed time. Our results were consistent with previous studies [1][2][3][4][5][6][7][8][9][10][11]. In our present study, an IFPD of ≥3 mm in each direction was detected in only ~2-3 % of all obtained TLS images (2,336 images).…”

“…To determine the optimal planning target volume (PTV) margins in non-realtime IGRT for prostate cancer, knowledge of intrafraction prostate displacement (IFPD) is necessary. Many previous studies, including non-real-time tracking studies and realtime tracking studies have pointed out the characteristics of IFPD as follows: (1) IFPD is larger in cranio-caudal (CC) and antero-posterior (AP) directions compared to the left-right (LR) direction [1][2][3][4][5][6][7][8][9][10][11], (2) individual differences in IFPD are significant [3][4][5]10], (3) IFPD increases with elapsed time in each fraction [6][7][8][9][10][11], and (4) large IFPDs are observed in a small proportion of all treatment time [1,[9][10][11]. Although these characteristics of IFPD have been clarified, institutional IFPD data should be assessed because significant differences in clinical practice may exist (e.g.…”

ACR Appropriateness Criteria for external beam radiation therapy treatment planning for clinically localized prostate cancer, part II of II

“…As the EBRT time increases, the risk of significant intrafraction prostate motion increases. Cramer et al 9 evaluated intrafraction prostate motion during intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) using electromagnetic transponders and recommended patient repositioning when treatment duration exceeds 4 to 6 minutes. Shelton et al 10 observed a similar relationship between treatment duration and intrafraction prostate motion, with shorter treatment times achieved with VMAT (compared with IMRT), which resulted in a 30% to 40% reduction in intrafraction prostate motion.…”

The effect of prostate motion during hypofractionated radiotherapy can be reduced by using flattening filter free beams

“…The pattern of an individual patient is unpredictable and any of the six motion patterns can occur during each fraction. In any case, the positional uncertainty increases with time [12][13][14][15][16]. The increased dose per fraction and thereby increased treatment time for hypofractionation could lead to larger positional uncertainty due to the prostate motion.…”