Analysis of intra-fraction prostate motion and derivation of duration-dependent margins for radiotherapy using real-time 4D ultrasound

Abstract

Background and purpose: During radiotherapy, prostate motion changes over time. Quantifying and accounting for this motion is essential. This study aimed to assess intra-fraction prostate motion and derive duration-dependent planning margins for two treatment techniques. Material and methods: A four-dimension (4D) transperineal ultrasound Clarity® system was used to track prostate motion. We analysed 1913 fractions from 60 patients undergoing volumetric-modulated arc therapy (VMAT) to the prostate. The mean VMAT treatment duration was 3.4 min. Extended monitoring was conducted weekly to simulate motion during intensity-modulated radiation therapy (IMRT) treatment (an additional seven minutes). A motion-time trend analysis was conducted and the mean intra-fraction motion between VMAT and IMRT treatments compared. Duration-dependent margins were calculated and anisotropic margins for VMAT and IMRT treatments were derived. Results: There were statistically significant differences in the mean intra-fraction motion between VMAT and the simulated IMRT duration in the inferior (0.1 mm versus 0.3 mm) and posterior (−0.2 versus −0.4 mm) directions respectively (p ≪ 0.01). An intra-fraction motion trend inferiorly and posteriorly was observed. The recommended minimum anisotropic margins are 1.7 mm/2.7 mm (superior/inferior); 0.8 mm (left/right), 1.7 mm/2.9 mm (anterior/posterior) for VMAT treatments and 2.9 mm/4.3 mm (superior/inferior), 1.5 mm (left/right), 2.8 mm/4.8 mm (anterior/posterior) for IMRT treatments. Smaller anisotropic margins were required for VMAT compared to IMRT (differences ranging from 1.2 to 1.6 mm superiorly/inferiorly, 0.7 mm laterally and 1.1-1.9 mm anteriorly/posteriorly). Conclusions: VMAT treatment is preferred over IMRT as prostate motion increases with time. Larger margins should be employed in the inferior and posterior directions for both treatment durations. Duration-dependent margins should be applied in the presence of prolonged imaging and verification time.

A study of the clinical, treatment planning and dosimetric feasibility of dose painting in external beam radiotherapy of prostate cancer

“…In this department, audits have shown 95% agreement between offline ‘experts’ and online matching by radiographers to within less than 3 mm [28] . Results were broadly in agreement with the study by Grimwood [11] and Pang [9] suggesting margins of 2–3 mm are appropriate. As this is essentially a manual method, automated matching, when available, may reduce this further.…”

“…Image guidance for FLAME, PIVOTALboost and DELINEATE was achieved using fiducial markers with daily cone beam CT (CBCT). However, since prostate motion can take place following imaging [9] the performance of a trans-perineal ultrasound system for real time image guided radiotherapy (IGRT) [10] in relation to DIL margins was evaluated. In view of the high dose gradients, small size of the DILs and their proximity to OARs, measurement was used to verify that the planned dose distributions could be accurately delivered.…”

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

“…Incomplete capturing of larger displacements could result in underestimation of required margins. However, as our recorded mean displacements were similar to-if not slightly larger thanmany studies using continuous or more frequent monitoring (such as CyberKnife, Calypso Beacon transponders, cine-MRI, and real-time ultrasound studies) (20,24,26,43,44), this may not be the case. The lack of rotational data is another potential study limitation; however, data from the recent phase II TROG 15.01 SPARK trial of continuous kV intra-fraction monitoring suggest that rotational changes appear to fall within PTV margins used to account for translational motion, and the authors conclude that CTV-to-PTV expansions should focus on accounting for translational displacements (45).…”

“…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).…”

Partial prostate re-irradiation for the treatment of isolated local recurrence of prostate cancer in patients previously treated with primary external beam radiotherapy: short-term results of a monocentric study

“…All patients received a total dose of 35 Gy in seven daily fractions of 5 Gy, five fractions/week, which translates into a CA) was used to delineate GTV on planning CT. Clinical Target Volume (CTV) was defined as the GTV plus 3 mm[14]. The Planning Target Volume (PTV) included the CTV and a margin of 3 mm[15]. On each slice, contouring of organs at risk was also performed: rectum, bladder, penile bulb and femoral heads.…”