Verification of planning target volume settings in volumetric modulated arc therapy for stereotactic body radiation therapy by using in-treatment 4-dimensional cone beam computed tomography.

To evaluate setup error and tumor motion during beam delivery by using 4-dimensional cone beam computed tomography (4D CBCT) and to assess the adequacy of the planning target volume (PTV) margin for lung cancer patients undergoing volumetric modulated arc therapy for stereotactic body radiation therapy (VMAT-SBRT). Fifteen lung cancer patients treated by single-arc VMAT-SBRT were selected in this analysis. All patients were treated with an abdominal compressor. The gross tumor volumes were contoured on maximum inspiration and maximum expiration CT datasets from 4D CT respiratory sorting and merged into internal target volumes (ITVs). The PTV margin was isotropically taken as 5 mm. Registration was automatically performed using "pre-3D" CBCT. Treatment was performed with a D95 prescription of 50 Gy delivered in 4 fractions. The 4D tumor locations during beam delivery were determined using in-treatment 4D CBCT images acquired in each fraction. Then, the discrepancy between the actual tumor location and the ITV was evaluated in the lateral, vertical, and longitudinal directions. Overall, 55 4D CBCT sets during VMAT-SBRT were successfully obtained. The amplitude of tumor motion was less than 10 mm in all directions. The average displacements between ITV and actual tumor location during treatment were 0.41 ± 0.93 mm, 0.15 ± 0.58 mm, and 0.60 ± 0.99 mm for the craniocaudal, left-right, and anteroposterior directions, respectively. The discrepancy in each phase did not exceed 5 mm in any direction. With in-treatment 4D CBCT, we confirmed the required PTV margins when the registration for moving target was performed using pre-3D CBCT. In-treatment 4D CBCT is a direct method for quantitatively assessing the intrafractional location of a moving target.

Takahashi W ，Yamashita H ，Kida S ，Masutani Y ，Sakumi A ，Ohtomo K ，Nakagawa K ，Haga A ... -  《-》

Evaluation of interfractional variation of the centroid position and volume of internal target volume during stereotactic body radiotherapy of lung cancer using cone-beam computed tomography.

Sun Y ，Ge H ，Cheng S ，Yang C ，Zhu Q ，Li D ，Tian Y ... -  《Journal of Applied Clinical Medical Physics》

ITV versus mid-ventilation for treatment planning in lung SBRT: a comparison of target coverage and PTV adequacy by using in-treatment 4D cone beam CT.

Bellec J ，Arab-Ceschia F ，Castelli J ，Lafond C ，Chajon E ... -  《Radiation Oncology》

Effect of immobilization and performance status on intrafraction motion for stereotactic lung radiotherapy: analysis of 133 patients.

To assess intrafractional geometric accuracy of lung stereotactic body radiation therapy (SBRT) patients treated with volumetric image guidance. Treatment setup accuracy was analyzed in 133 SBRT patients treated via research ethics board-approved protocols. For each fraction, a localization cone-beam computed tomography (CBCT) scan was acquired for soft-tissue registration to the internal target volume, followed by a couch adjustment for positional discrepancies greater than 3 mm, verified with a second CBCT scan. CBCT scans were also performed at intrafraction and end fraction. Patient positioning data from 2047 CBCT scans were recorded to determine systematic (Σ) and random (σ) uncertainties, as well as planning target volume margins. Data were further stratified and analyzed by immobilization method (evacuated cushion [n=75], evacuated cushion plus abdominal compression [n=33], or chest board [n=25]) and by patients' Eastern Cooperative Oncology Group performance status (PS): 0 (n=31), 1 (n=70), or 2 (n=32). Using CBCT internal target volume was matched within ±3 mm in 16% of all fractions at localization, 89% at verification, 72% during treatment, and 69% after treatment. Planning target volume margins required to encompass residual setup errors after couch corrections (verification CBCT scans) were 4 mm, and they increased to 5 mm with target intrafraction motion (post-treatment CBCT scans). Small differences (<1 mm) in the cranial-caudal direction of target position were observed between the immobilization cohorts in the localization, verification, intrafraction, and post-treatment CBCT scans (p<0.01). Positional drift varied according to patient PS, with the PS 1 and 2 cohorts drifting out of position by mid treatment more than the PS 0 cohort in the cranial-caudal direction (p=0.04). Image guidance ensures high geometric accuracy for lung SBRT irrespective of immobilization method or PS. A 5-mm setup margin suffices to address intrafraction motion. This setup margin may be further reduced by strategies such as frequent image guidance or volumetric arc therapy to correct or limit intrafraction motion.

Li W ，Purdie TG ，Taremi M ，Fung S ，Brade A ，Cho BC ，Hope A ，Sun A ，Jaffray DA ，Bezjak A ，Bissonnette JP ... -  《-》

Evaluation of the cone beam CT for internal target volume localization in lung stereotactic radiotherapy in comparison with 4D MIP images.

Wang L ，Chen X ，Lin MH ，Xue J ，Lin T ，Fan J ，Jin L ，Ma CM ... -  《-》