Dose deviations induced by respiratory motion for radiotherapy of lung tumors: Impact of CT reconstruction, plan complexity, and fraction size

Abstract

A thorax phantom was used to assess radiotherapy dose deviations induced by respiratory motion of the target volume. Both intensity modulated and static, non-modulated treatment plans were planned on CT scans of the phantom. The plans were optimized using various CT reconstructions, to investigate whether they had an impact on robustness to target motion during delivery. During irradiation, the target was programmed to simulate respiration-induced motion of a lung tumor, using both patient-specific and sinusoidal motion patterns in three dimensions. Dose was measured in the center of the target using an ion chamber. Differences between reference measurements with a stationary target and dynamic measurements were assessed. Possible correlations between plan complexity metrics and measured dose deviations were investigated. The maximum observed motion-induced dose differences were 7.8% and 4.5% for single 2 Gy and 15 Gy fractions, respectively. The measurements performed with the largest target motion amplitude in the superiorinferior direction yielded the largest dosimetric deviations. For 2 Gy fractionation schemes, the summed dose deviation after 33 fractions is likely to be less than 2%.Measured motion-induced dose deviations were significantly larger for one CT reconstruction compared to all the others. Static, non-modulated plans showed superior robustness to target motion during delivery. Moderate correlations between the modulation complexity score applied to VMAT (MCSv) and measured dose deviations were found for 15 Gy SBRT treatment plans. Correlations between other plan complexity metrics and measured dose deviations were not found. K E Y W O R D S complexity, interplay, lung, radiotherapy, SBRT, VMAT

Selection Strategy of Jaw Tracking in VMAT Planning for Lung SBRT

“…In addition, the intra-fraction motion of the target may cause a dose deviation between the calculated and delivered dose due to dose blurring and interplay effects between MLC and tumor motion (29)(30)(31), especially for a small-sized target (32,33). Besides, the above results could also be affected by other factors, such as the plan complexity and tumor shapes (34)(35)(36).…”

Positron emission tomography guided dose painting by numbers of lung cancer: Alanine dosimetry in an anthropomorphic phantom

“…The degree of tumour motion depends on several factors [30] , [31] , [32] , but one should expect that larger, more advanced tumours suitable for dose painting are less affected than smaller tumours. Larger tumour displacements will lead to larger dose discrepancies, although the summed dose deviation due to respiratory motion after many treatment fractions might not be clinically relevant [33] . Respiratory gated treatment might be preferable in terms of preserving the sharp dose gradients seen in the TPS.…”

Análisis dosimétrico de paciente específico considerando movimiento respiratorio en cáncer de pulmón

“…Según diferentes publicaciones donde se ha analizado la cuestión: (Jiang et al, 2003), (Gurjar et al, 2017), (Kishore et al, 2020), (Sande et al, 2020), (Berbeco et al, 2006), (Jafari & Alalawi, 2017), incluir en los controles de calidad de paciente específico dichas variables conlleva a que la diferencia dosimétrica (resultado de la comparación entre cálculo en el sistema de planeación y el suministro de dosis en el acelerador) sea mayor a la obtenida en condiciones donde no se contemplan. Desde estas perspectivas, se hace necesario que el sistema de planeación considere dos aspectos: correcciones por cambio de medio (homogeneidad) y los efectos físicos producidos por el movimiento (heterogeneidad y efecto interacción) aun teniendo claro que el sistema de planeación realiza cálculos en condiciones estáticas (Jiang et al, 2003), (Bortfeld et al, 2004), (Stambaugh et al, 2013).…”

“…Estas incluyen incertidumbres debido al limitante de la exactitud de la medida presentada por el desconocimiento real de la dosis. Por tanto, según estos autores la exactitud de los valores obtenidos será más cercana a las condiciones reales de tratamiento del paciente a pesar del aumento de la diferencia dosimétrica (Jiang et al, 2003), (Gurjar et al, 2017), (Kishore et al, 2020), (Sande et al, 2020), (Berbeco et al, 2006), (Jafari & Alalawi, 2017).…”

“…Para ello, la técnica SBRT-VMAT resulta pertinente, pero esta se caracteriza por presentar dosis heterogéneas dentro del volumen de interés (está permitido no exceder el 140% de la dosis prescrita) (Hurkmans et al, 2014). Por otra parte, la interacción entre los movimientos de la MLC y el objetivo de interés, podrían generar errores en la distribución de la dosis calculada versus la entregada; estos efectos han sido estudiados por varios autores (Jiang et al, 2003), (Bortfeld et al, 2004), (Stambaugh et al, 2013), (Sande et al, 2020), (Kubo et al, 2018) y se describen como sigue.…”