Analysis of inter- and intra fractional partial bladder wall movement using implanted fiducial markers

Abstract

BackgroundCurrent adaptive and dose escalating radiotherapy for muscle invasive bladder cancer requires knowledge of both inter-fractional and intra-fractional motion of the bladder wall involved. The purpose of this study is to characterize inter- and intra-fractional movement of the partial bladder wall using implanted fiducial markers and a real-time tumor-tracking radiotherapy system.MethodsTwo hundred fifty one sessions with 29 patients were analysed. After maximal transurethral bladder tumor resection and 40 Gy of whole bladder irradiation, up to six gold markers were implanted transurethrally into the bladder wall around the tumor bed and used for positional registration. We compared the systematic and random uncertainty of positions between cranial vs. caudal, left vs. right, and anterior vs. posterior tumor groups. The variance in intrafractional movement and the percentage of sessions where 3 mm and 5 mm or more of intrafractional wall movement occurring at 2, 4, 6, 8, 10, and at more than 10 min until the end of a session were determined.ResultsThe cranial and anterior tumor group showed larger interfractional uncertainties in the position than the opposite side tumor group in the CC and AP directions respectively, but these differences did not reach significance. Among the intrafractional uncertainty of position, the cranial and anterior tumor group showed significantly larger systematic uncertainty of position than the groups on the opposite side in the CC direction. The variance of intrafractional movement increased over time; the percentage of sessions where intrafractional wall movement was larger than 3 mm within 2 min of the start of a radiation session or larger than 5 mm within 10 min was less than 5%, but this percentage was increasing further during the session, especially in the cranial and anterior tumor group.ConclusionsMore attention for intrafractional uncertainty of position is required in the treatment of cranial and anterior bladder tumors especially in the CC direction. The optimal internal margins in each direction should be chosen or a precise intrafractional target localization system is required depending on the tumor location and treatment delivery time in the setting of partial bladder radiotherapy.

Image-guided Adaptive Radiotherapy for Bladder Cancer

“…As the bladder tumour is relatively rigid and non-elastic compared with non-tumourbearing bladder regions, it may be minimal [32,107]. One conclusion that can be drawn from this work is that despite these limitations when GTV is present on the superior and anterior regions of the bladder, larger positional variation should be expected than when GTV is present at other regions of the bladder [34,36,41,106,107].…”

“…Consensus drawn from studies assessing inter-fraction change is that bladder motion occurs predominantly in the cranial direction (as a result of bladder filling) and [32] Cine-MR motion up 57 mm identified over 28 min Gronborg et al, 2015 [33] Intra-fractional motion over 10 min captured by 5 mm Nishioka et al, 2017 [34] Motion predominantly superior and anterior direction; Intra-fractional motion over 10 min captured by 5 mm Dees-Ribbers et al, 2014 [13] Motion between a full bladder and an empty bladder protocol does not differ Yee et al, 2010 [35] Inter-fraction motion predominantly anterior direction 0 Fiducial marker Chai et al, 2010 [36] Sondergaard et al, 2010 [37] GTV deformation and motion assessed using lipiodol Non-ART PTV: CTV þ15 mm PoD-PTVs: Small ¼ smallest bladder (as seen on planning CT/CBCTs) þ 5 mm Medium ¼ halfway between small and large Large ¼ PTVcomp of CT and CBCTs þ5 mm Alternative method PoD-PTVs: Small ¼ PTVcomp of 2 smallest bladder (as seen on planning CT/CBCTs) þ 5 mm Medium and large as above Small PoD-PTV generated using 2 smallest volumes as seen on planning and CBCT days 1e5 was selected more frequently than initial method Online re-optimisation using PTV; Iso: bladder þ5 mm Aniso: bladder þ7 mm (S), 5 mm (A,R,L,I,P) Pop: bladder þ14 mm (A,S), 9 mm (P), 5 mm (R,L,I)…”

Adaptation Time as a Determinant of the Dosimetric Effectiveness of Online Adaptive Radiotherapy for Bladder Cancer

“…Additional studies have shown an impact of time on the movement of tumors or structures near the bladder during the patient on-couch time. The maximum bladder wall movements from the start of a treatment session increased intrafractionally with time, as found in the study by Nishioka using implanted fiducial markers and stereoscopic fluoroscopy [34]. Eijkelenkamp et al analyzed the deformations of the GTV in dependence on adaptation time from repeated imaging on an MR-Linac during five dose fraction [35].…”

Implementación y uso clínico de la radioterapia adaptativa. Informe del grupo de trabajo de radioterapia adaptativa de la Sociedad Española de Física Médica (SEFM)

“…Hallan movimientos intrafracción de la pared vesical discretamente menores para los pacientes tratados con la vejiga llena, en tanto que los cambios interfracción son solo ligeramente mayores, variando R y v para estos últimos desde 1 mm en la parte caudal hasta 12 mm en la craneal-anterior. Nishioka et al, 142 evalúan los movimientos inter e intrafracción de la parte de la pared en la que está localizado el tumor mediante marcadores de oro en la pared vesical. Hallan, al igual que en Dees-Ribbers et al 141 , que los mayores movimientos fueron en las direcciones cráneo-caudal (de −13.6 mm a 10.8 mm) y antero-posterior (de −10.0 mm a 7.7 mm) para el movimiento interfracción (cuantil 95%), aunque los valores de R y v hallados son menores, alrededor de 5 mm.…”