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

Abstract

BackgroundExtreme hypofractionation requires tight planning margins, high dose gradients, and strict adherence to planning criteria in terms of patient positioning and organ motion mitigation. This study reports the first clinical experience worldwide using a novel electromagnetic (EM) tracking device for intrafraction prostate motion management during dose-escalated linac-based stereotactic body radiation therapy (SBRT).MethodsThirteen patients with organ-confined prostate cancer underwent dose-escalated SBRT using flattening filter-free (FFF) volumetric modulated arc therapy (VMAT). The EM tracking device consisted of an integrated Foley catheter with a transmitter. Patients were simulated and treated with a filled bladder and an empty rectum. Setup accuracy was achieved by ConeBeam-CT (CBCT) matching, and motion was tracked during all the procedure. Treatment was interrupted when the signals exceeded a 2 mm threshold in any of the three spatial directions and, unless the offset was transient, target position was re-defined by repeating CBCT. Moreover, the displacements that would have occurred without any intrafraction organ motion management (i.e. no interruptions and repositionings) were simulated.ResultsIn 31 out of 56 monitored fractions (55%), no intervention was required to correct the target position. In 25 (45%) a correction was mandated, but only in 10 (18%), the beam delivery was interrupted. Total treatment time lasted on average 10.2 minutes, 6.7 minutes for setup, and 3.5 minutes for beam delivery. Without any intrafraction motion management, the overall mean treatment time and the mean delivery time would have been 6.9 minutes and 3.2 minutes, respectively. The prostate would have been found outside the tolerance in 8% of the total session time, in 4% of the time during the setup, and in 14% during the beam-on phase. Predominant motion pattern was posterior and its probability increased with time, with a mean motion ≤ 2 mm occurring within 10 minutes.ConclusionsEM real-time tracking was successfully implemented for intrafraction motion management during dose-escalated prostate SBRT. Results showed that most of the observed displacements were < 2 mm in any direction; however, there were a non-insignificant number of fractions with motion exceeding the predefined threshold, which would have otherwise gone undetected without intrafraction motion management.

Electromagnetic Transmitter-Based Prostate Gating for Dose-Escalated Linac-Based Stereotactic Body Radiation Therapy: An Evaluation of Intrafraction Motion

“…To the best of our knowledge, this is the largest study reporting data on intrafraction prostate motion during LINAC-based SBRT evaluated with a novel electromagnetic (EM) tracking device consisting of an integrated Foley catheter with a transmitter connected to a receiver placed on a treatment table. We confirm, based on a larger population, the technical and clinical feasibility of such an approach, as already shown by Panizza et al [16].…”

“…Table 4 shows the results in terms of the % of time the CTV was outside the CTV-to-PTV margin (2 mm) for the whole population and for the three identified groups of patients. In our analysis, we were interested in verifying if the CTV-to-PTV margins (2 mm) that we applied according to the available literature [16] were safe enough in our daily clinical practice. For this reason, we calculated the amount of time we were obliged to stop the treatment during its delivery because of a displacement of the target outside the given margin (before deciding whether to restart the treatment or redo the CBCT procedure).…”

“…In this retrospective study, we report our experience with a novel electromagnetic (EM)-GPS-transmitter-based device consisting of an integrated Foley catheter with a transmitter connected to a receiver placed on a treatment table. We decided to adopt this system as it could be adopted without any surgical intervention or definitive implantation of intraprostatic coils [16]. In particular, we report the results in terms of the real-time tracking of prostate organ motion during dose-escalated LINAC-based PCa SBRT.…”

Stereotactic body radiation therapy (SBRT) for prostate cancer: Improving treatment delivery efficiency and accuracy

“…Recently, Panizza et al [12] evaluated the intrafraction prostate motion with a novel electromagnetic tracking device during the delivery of two 10 MV FFF arcs. They observed displacements below 2 mm in most of the cases within 10 min, with an increased probability of motion with time.…”

“…Nowadays, prostate volumetric modulated arc therapy (VMAT)-SBRT treatments are commonly planned with multiple flattening filter free (FFF) arcs, generally two [8] , [9] , [10] , [11] , [12] , [13] , [14] but even up to four [15] , thus requiring intrafraction motion monitoring.…”