Gated rapidarc using KV images acquired during dose delivery for liver stereotactic treatment

Abstract

Purpose In this paper, we used the Intrafration Motion Review technique (IMR, Varian medical system), which allows simultaneous kV/MV utilization to analyse the liver motion during gated RapidArc stereotactic treatment. Materials and methods Eight liver cancer patients with implanted fiducial markers were treated using the gated RapidArc technique with a Varian Novalis Truebeam linear accelerator. Four 4D computed tomography (CT) scans were acquired using Real time Position Management (RPM) system to study the reproducibility of liver motion. The cine 4D CT images were separated into 10 phases CT series based on respiratory motion information. A Maximum Intensity Projection (MIP) and an Average Intensity Projection (Ave-IP) CT series were generated. The Internal Target Volume (ITV) was outlined in the MIP CT series. The Planning Target Volume (PTV) was created by adding a 5 mm margin from the ITV. The fiducials were marked in the exhalation and/or in the inhalation phase making possible the intrafraction verification. The treatment planning is realized in the Ave-IP CT series. The patient's alignment is set based on markers using daily cone beam CT (CBCT). During the treatment, kV images were acquired at each exhalation or inhalation phase when the respiratory signal cross the upper and lower gating threshold defined during the respiratory learning process. The positions of the fiducials markers were compared with their expected positions. Results The average (±SD) conformity index CIPTV = (VPTV95% (cc)/ VPTV (cc)) * (VPTV95% (cc)/ Viso95% (cc)) was 0.93 ± 0.02 and homogeneity index HIPTV = (D2% - D98%)/Dmedian was 0.09 ± 0.02. The average MU/Gy was 147 ± 25. The room occupation's time was 53, 30, 20, 24, 24 min respectively for the five first fractions. The average kV images acquired per fraction were 35 with a maximum of 74 images and a minimum of 12 images. The average gating errors of the fiducials in the Superior–Inferior (SI) direction during the intrafraction was 0,91 mm with a maximum of 6 mm. Conclusion For tumor motion, monitoring intra-fraction by IMR ensures with certainty the PTV irradiation estimates with a systematic checking of the position of the target volume (fiducials) when this one come inside the region of treatment. In this paper, we used the Intrafration Motion Review technique (IMR, Varian medical system), which allows simultaneous kV/MV utilization to analyse the liver motion during gated RapidArc stereotactic treatment. Eight liver cancer patients with implanted fiducial markers were treated using the gated RapidArc technique with a Varian Novalis Truebeam linear accelerator. Four 4D computed tomography (CT) scans were acquired using Real time Position Management (RPM) system to study the reproducibility of liver motion. The cine 4D CT images were separated into 10 phases CT series based on respiratory motion information. A Maximum Intensity Projection (MIP) and an Average Intensity Projection (Ave-IP) CT series were generated. The Internal Target Volume (ITV) was outlined in the MIP CT series. The Planning Target Volume (PTV) was created by adding a 5 mm margin from the ITV. The fiducials were marked in the exhalation and/or in the inhalation phase making possible the intrafraction verification. The treatment planning is realized in the Ave-IP CT series. The patient's alignment is set based on markers using daily cone beam CT (CBCT). During the treatment, kV images were acquired at each exhalation or inhalation phase when the respiratory signal cross the upper and lower gating threshold defined during the respiratory learning process. The positions of the fiducials markers were compared with their expected positions. The average (±SD) conformity index CIPTV = (VPTV95% (cc)/ VPTV (cc)) * (VPTV95% (cc)/ Viso95% (cc)) was 0.93 ± 0.02 and homogeneity index HIPTV = (D2% - D98%)/Dmedian was 0.09 ± 0.02. The average MU/Gy was 147 ± 25. The room occupation's time was 53, 30, 20, 24, 24 min respectively for the five first fractions. The average kV images acquired per fraction were 35 with a maximum of 74 images and a minimum of 12 images. The average gating errors of the fiducials in the Superior–Inferior (SI) direction during the intrafraction was 0,91 mm with a maximum of 6 mm. For tumor motion, monitoring intra-fraction by IMR ensures with certainty the PTV irradiation estimates with a systematic checking of the position of the target volume (fiducials) when this one come inside the region of treatment.