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Abstract: Background and purpose: To evaluate the feasibility and validity of cone beam computed tomography (CBCT) and active breath control (ABC) by long breath-holding in hypofraction radiotherapy of liver tumor. Methods and materials: Twenty-four patients received hypofraction radiotherapy of liver tumor with long breath-holding at end-inhale; four prescriptions were used: 6Gy×7 (n =8), 10Gy×4 (n =7), 5Gy×9 (n =6), 4Gy×10 (n =3). For each fraction, all patients received pre-correction CBCT scans with ABC, some patients received post-correction and post-treatment CBCT. The interfraction and intrafraction liver positioning errors on medial–lateral (ML), cranial–caudal (CC) and anterior–posterior (AP) directions were obtained. The theoretic margin from clinical target volume (CTV) to planning target volume (PTV) was calculated based on post-treatment error. The dosimetric parameters of PTV and normal tissue were compared between ABC and free breathing (FB). Results: The interfraction error in liver positioning showed system errors (Σ) of 3.18mm (ML), 6.80mm (CC) and 3.05mm (AP); random error (σ) of 3.03mm (ML), 6.78mm (CC) and 3.62mm (AP). These errors were significantly reduced with CBCT guided online correction. The intrafraction systematic error was 0.72mm (ML), 2.21mm (CC), 1.49mm (AP), and random error was 2.30mm (ML), 3.58mm (CC), 2.49mm (AP). Dosimetric parameters such as PTV, the liver’s volume included by 23, 30Gy isodose curve (V23, V30), mean dose to normal liver (MDTNL) and mean dose to cord were significantly larger for FB (P <0.05). Conclusion: Liver radiotherapy with long time breath-holding at end-inhale is an effective method to reduce liver motion, PTV and dose to normal tissue. Interfraction and intrafraction liver positioning errors were substantial. CBCT guided online correction of positioning error is recommended for liver radiotherapy with end-inhale ABC. [Copyright &y& Elsevier]

Abstract: Purpose: To study the inter- and intrafraction tumor reproducibility with active breath control (ABC) utilizing cone-beam computed tomography (CBCT), and compare validity of registration with two different regions of interest (ROI). Methods and materials: Thirty-one lung tumors in 19 patients received conventional or stereotactic body radiotherapy with ABC. During each treatment, patients had three CBCT scanned before and after online position correction and after treatment. These CBCT images were aligned to the planning CT using the gray scale registration of tumor and bony registration of the thorax, and tumor position uncertainties were then determined. Results: The interfraction systematic and random translation errors in the left–right (LR), superior–inferior (SI) and anterior–posterior (AP) directions were 3.6, 4.8, and 2.9mm; 2.5, 4.5, and 3.5mm, respectively, with gray scale alignment; 1.9, 4.3, 2.0mm and 2.5, 4.4, 2.9mm, respectively, with bony alignment. The interfraction systematic and random rotation errors with gray scale and bony alignment groups ranged from 1.4° to 3.0° and 0.8° to 2.3°, respectively. The intrafraction systematic and random errors with gray scale registration in LR, SI, AP directions were 0.9, 2.0, 1.8mm and 1.5, 1.7, 2.9mm, respectively, for translation; 1.5°, 0.9°, 1.0° and 1.2°, 2.2°, 1.8°, respectively, for rotation. The translational errors in SI direction with bony alignment were significantly larger than that of gray scale (p <0.05). Conclusions: With CBCT guided online correction the interfraction positioning errors can be markedly reduced. The intrafraction errors were not diminished by the use of ABC. Rotation errors were not very remarkable both inter- and intrafraction. Gray scale alignment of tumor may provide a better registration in SI direction. [Copyright &y& Elsevier]

Abstract: Background and purpose: Online adaptive correction in image-guided intensity-modulated radiotherapy appeared to be a promising approach for precision radiation treatment in head and neck tumors. This protocol was designed to evaluate the clinical feasibility and effect of online cone beam computed tomography (CBCT) guidance in IMRT of nasopharyngeal cancer (NPC). Methods and materials: The Elekta Synergy system, which integrates an X-ray volumetric imager (XVI), was used to deliver radiation treatment for 22 cases of NPC. The acquired CBCT was registered to the planning CT for online and offline analysis. The systematic and random setup errors, as well as planning target volume (PTV) margin, were calculated at different correction threshold levels. The impact of online setup correction on dosimetry was evaluated by simulation of pre-correction errors. Results: The correction-of-setup-errors frequencies for 1, 2 and 3mm thresholds were 41.3–53.9%, 12.7–21.2% and 6.3–10.3%, respectively. Online correction was effective at the 2mm threshold level for all three axes. The pre-correction systematic errors for the whole group ranged 1.1–1.3mm, and the random errors were also 1.1–1.3mm. After online correction, the systematic and random errors ranged 0.4–0.5mm and 0.7–0.8mm, respectively, in the three directions. The PTV margins for the pre-correction, pretreatment and post-treatment positions were 3.5–4.2mm, 1.6–1.8mm and 2.5–3.2mm, respectively, in three directions. Analysis of hypothetical dosimetric change due to a translational isocenter shift of 3mm showed that if no correction was applied, the mean maximum dose to both the brain stem and spinal cord would be increased by 10Gy, the mean dose to the left and right parotids would be increased by 7.8 and 8.5Gy, respectively, and the dose to target volumes would be decreased: 4Gy for 95% GTV and 5.6Gy for 95% CTV60. Conclusions: CBCT-based online correction increased the accuracy of IMRT for NPC and reduced irradiated margins, by decreasing both the systematic and random errors. Online CBCT correction reduces the radiation dose to normal tissue and creates room for further dose escalation of tumors. [Copyright &y& Elsevier]

Abstract: Purpose: To study the intrafraction tumour position error utilizing cone beam CT (CBCT) in patients receiving radiotherapy. Methods and materials: Fifty-four patients were treated with Elekta Synergy S system, including 19 head and neck, 25 thoracic and 10 abdominal-pelvic tumours. All patients received CBCT after initial setup and some of them received CBCT after correction and after treatment. CBCT were registered to planning CT and errors of isocenter position on the left-to-right (LR), superior–inferior (SI) and anterior–posterior (AP) directions were analyzed. Results: After treatment the systematic (Σ) and random uncertainty (σ) increased, the increments of tumour Σ were 0.1–0.3, 0.2–0.5 and 0.2–0.6mm, respectively, while the increments of σ were 0.1–0.3, 0.2–0.4 and 0.1–0.4mm, respectively, for the head and neck, thoracic and abdominal-pelvic tumours. Based on 380 paired pre- and post-treatment CBCT, the intrafraction errors (mean±SD) in the LR, SI and AP directions were −0.1±0.9, −0.3±1.0 and −0.2±0.7mm, respectively, for head and neck tumours, −0.1±1.2, −0.1±1.9 and 0.1±1.3mm, respectively, for thoracic tumours, −0.1±1.1, 0.2±1.4 and −0.1±1.5mm, respectively, for abdominal-pelvic tumours. Isotropic planning margins of 3.4, 6.1 and 5.4mm were generated with linear addition of internal margin (IM) to CTV for the head and neck, thoracic and abdominal-pelvic tumours, respectively, while margins were only 2.4, 4.4 and 3.9mm, respectively, if IM was added in quadrature. Conclusions: Utilizing CBCT measurements before and after treatment to detect intrafraction tumour position errors was clinically feasible. The detected intrafraction errors could be applied to improve the accuracy of radiation delivery. [Copyright &y& Elsevier]