Clinical Application Of Dibh Amplitude Gated Technique For Stereotactic Body Radiotherapy (Sbrt) Lung And Liver Oligometastases

The purpose of this analysis is to report the clinical implementation and our initial experience with DIBH amplitude based motion management for SBRT in patients with lung and liver oligometastases. The main challenge in planning is to minimize the internal organ motion to reduce the PTV size and hence dose to surrounding normal tissue. Diaphragmatic motion is a good internal surrogate and closely correlates with the motion of the external surrogate marker used in the RPM gating. 8 consecutive patients treated with DIBH-Amplitude-based SBRT were included in this prospective study (table 1). All patients were coached for 3-4 days in order to achieve a reproducible breath hold in terms of amplitude and duration. Simulation CT scans were acquired in free breathing and DIBH phases. A pretreatment 4D-CBCT in free-breathing phase was acquired and orthogonal fluoroscopy images of the treatment site were also acquired in free breathing and DIBH phases. Acquired imaging data was imported into TPS and target delineation was performed in accordance with the ongoing RTOG BR001 protocol. Treatment planning was performed with co-planar 6MV FFF 2-3 Arc VMAT technique and evaluated as per acceptance criteria of RTOG BR001. The dose was escalated in consecutive patients from BED10 of 75 Gy10 up to 132 Gy10. Patient-specific pre-treatment QA was performed for all patients. Pre-treatment and intra-treatment positioning verification was performed with DIBH CBCT for all patients for each treatment fraction and corrected on a 6D treatment couch. Breath-hold for across all patients varied from 25-45 seconds. Maximum Tumor motion measured during fluoroscopy in free-breathing varied from 8 mm to 15 mm and in DIBH it came down to 1-3 mm, which allowed a reduction in PTV margins from 5mm to 3mm. The Dose gradient index for all DIBH SBRT plans varied from 0.73 to 1.4 cm. Total MU’s varied from 1794 to 4765, with total treatment time per session varying from 11.33 minutes to 41.28 minutes and beam-on time varying from 120 seconds to 537 seconds. DIBH Amplitude Gated SBRT reduced the target motion by freezing the target in the DIBH amplitude phase, which allowed a reduction in the PTV margin. DIBH amplitude based SBRT is a precise and reliable motion management technique for SBRT lung and liver. The Treatment time of DIBH gated SBRT can be reduced with treatment techniques like FFF and Gated VMAT/IMRT for moving tumours in Liver and Lung. The main limitation of DIBH Amplitude gated SBRT is the breath-hold time of the patient. The DIBH process is time-consuming and dependent on specialized training as compared to free breath SBRT.Abstract 3741; Table 1Sr. NoTreatment SiteDose/FX (Gy/FX)FXBEDMaximum Tumour Motion in FluoroscopyFree breath (mm)DIBH (mm)1R Lung-Central50 GY/10FX10 Fx75922Liver60 Gy/10FX10 FX961423L Lung-Peripheral50 GY/5FX5 Fx1001324Liver60 Gy/8FX8 Fx1051325Liver60 Gy/8FX8 Fx1051326L Abdominal Wall45 Gy/3FX3 Fx112.5827L Chest Wall45 Gy/3FX3 Fx112.5818Liver60 Gy/5FX5 Fx13291 Open table in a new tab