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Background: Radioembolization with Yttrium-90 (90 Y) microspheres is becoming a more widely used transcatheter treatment for unresectable hepatocellular carcinoma (HCC). Using post-treatment 90 Y positron emission tomography/computerized tomography (PET/CT) scans, the distribution of microspheres within the liver can be determined and quantitatively assessed. We studied the radiation dose of 90 Y delivered to liver and treated tumors.Methods: This retrospective study of 56 patients with HCC, including analysis of 98 liver tumors, measured and correlated the dose of radiation delivered to liver tumors and normal liver tissue using glass microspheres (TheraSpheres®) to the frequency of complications with modified response evaluation criteria in solid tumors (mRECIST). 90 Y PET/CT and triphasic liver CT scans were used to contour treated tumor and normal liver regions and determine their respective activity concentrations. An absorbed dose factor was used to convert the measured activity concentration (Bq/mL) to an absorbed dose (Gy).Results: The 98 studied tumors received a mean dose of 169 Gy (mode 90–120 Gy; range 0–570 Gy). Tumor response by mRECIST criteria was performed for 48 tumors that had follow-up scans. There were 21 responders (mean dose 215 Gy) and 27 non-responders (mean dose 167 Gy). The association between mean tumor absorbed dose and response suggests a trend but did not reach statistical significance (p = 0.099). Normal liver tissue received a mean dose of 67 Gy (mode 60–70 Gy; range 10–120 Gy). There was a statistically significant association between absorbed dose to normal liver and the presence of two or more severe complications (p = 0.036).Conclusion: Our cohort of patients showed a possible dose–response trend for the tumors. Collateral dose to normal liver is non-trivial and can have clinical implications. These methods help us understand whether patient adverse events, treatment success, or treatment failure can be attributed to the dose that the tumor or normal liver received.

PurposeTo assess intra‐ and inter‐fractional motions of liver and lung tumors using active breathing control (ABC).Methods and MaterialsNineteen patients with liver cancer and 15 patients with lung cancer treated with stereotactic body radiotherapy (SBRT) were included in this retrospective study. All patients received a series of three CTs at simulation to test breath‐hold reproducibility. The centroids of the whole livers and of the lung tumors from the three CTs were compared to assess intra‐fraction variability. For 15 patients (8 liver, 7 lung), ABC‐gated kilovoltage cone‐beam CTs (kV‐CBCTs) were acquired prior to each treatment, and the centroids of the whole livers and of the lung tumors were also compared to those in the planning CTs to assess inter‐fraction variability.ResultsLiver intra‐fractional systematic/random errors were 0.75/0.39 mm, 1.36/0.97 mm, and 1.55/1.41 mm at medial‐lateral (ML), anterior‐posterior (AP), and superior‐inferior (SI) directions, respectively. Lung intra‐fractional systematic/random errors were 0.71/0.54 mm (ML), 1.45/1.10 mm (AP), and 3.95/1.93 mm (SI), respectively. Substantial intra‐fraction motions (>3 mm) were observed in 26.3% of liver cancer patients and in 46.7% of lung cancer patients. For both liver and lung tumors, most inter‐fractional systematic and random errors were larger than the corresponding intra‐fractional errors. However, these inter‐fractional errors were mostly corrected by the treatment team prior to each treatment based on kV CBCT‐guided soft tissue alignment, thereby eliminating their effects on the treatment planning margins.ConclusionsIntra‐fractional motion is the key to determine the planning margins since inter‐fractional motion can be compensated based on daily gated soft tissue imaging guidance of CBCT. Patient‐specific treatment planning margins instead of recipe‐based margins were suggested, which can benefit mostly for the patients with small intra‐fractional motions.

Purpose The purposes of this work are to (a) investigate whether the use of auto‐planning and multiple iterations improves quality of head and neck (HN) radiotherapy plans; (b) determine whether delivery methods such as step‐and‐shoot (SS) and volumetric modulated arc therapy (VMAT) impact plan quality; (c) report on the observations of plan quality predictions of a commercial feasibility tool. Materials and methods Twenty HN cases were retrospectively selected from our clinical database for this study. The first ten plans were used to test setting up planning goals and other optimization parameters in the auto‐planning module. Subsequently, the other ten plans were replanned with auto‐planning using step‐and‐shoot (AP‐SS) and VMAT (AP‐VMAT) delivery methods. Dosimetric endpoints were compared between the clinical plans and the corresponding AP‐SS and AP‐VMAT plans. Finally, predicted dosimetric endpoints from a commercial program were assessed. Results All AP‐SS and AP‐VMAT plans met the clinical dose constraints. With auto‐planning, the dose coverage of the low dose planning target volume (PTV) was improved while the dose coverage of the high dose PTV was maintained. Compared to the clinical plans, the doses to critical organs, such as the brainstem, parotid, larynx, esophagus, and oral cavity were significantly reduced in the AP‐VMAT (P < 0.05); the AP‐SS plans had similar homogeneity indices (HI) and conformality indices (CI) and the AP‐VMAT plans had comparable HI and improved CI. Good agreement in dosimetric endpoints between predictions and AP‐VMAT plans were observed in five of seven critical organs. Conclusion With improved planning quality and efficiency, auto‐planning module is an effective tool to enable planners to generate HN IMRT plans that are meeting institution specific planning protocols. DVH prediction is feasible in improving workflow and plan quality.

To monitor tumor motion during stereotactic body radiotherapy (SBRT) for patients with liver cancer, an integrated ultrasound and kilo-voltage cone-beam computed tomography (KV-CBCT) system has been proposed. The presence of an ultrasound probe may interfere with the radiation beams. The purpose of this study is to minimize this interference by altering orientations of the ultrasound probe and directions of radiation beams while not compromising the quality of SBRT plans. Ten patients, who received SBRT of liver cancer, were randomly selected for this study. To simulate the presence of an ultrasound probe, a virtual probe was oriented either parallel or vertical to the longitudinal axis of the patient's body and was added on the surface of the patient's body at the nearest location to the tumor. For both the parallel and vertical probe orientations, 2 new SBRT (Probe-Para and Probe-Vert) plans that minimize the interference between the probe and radiation beams were created for each patient. These SBRT plans were compared to the original clinically accepted SBRT plans, with a treatment goal of 37.5 Gy to the planning target volume (PTV) in 3 fractions. Specific dosimetric endpoints were evaluated, including doses to 95% (D95), of the PTV plan conformal index (CI), homogeneity index (HI), and relevant endpoint doses to organs at risk. For 2 patients with superficially located tumors, no clinically acceptable SBRT plans could be produced without the interference between the probe and radiation beams. For the remaining 8 patients, the Probe-Para plans allowed 7 patients to be treated with coplanar radiation beams (without moving the treatment couch during treatment) and 1 patient to be treated with non-coplanar beams (by moving the treatment couch during treatment). The Probe-Vert plans allowed 2 patients to be treated with coplanar beams and 6 patients to be treated with non-coplanar beams. The average D95 of the PTV were 38.63 Gy ± 0.14 (р = 0.65) for Probe-Para plans, 38.48 Gy ± 0.31 (р = 0.33) for Probe-Vert plans, and 38.72 Gy ± 0.14 for clinical SBRT plans. There were no significant differences (p > 0.05) in CI and HI of all SBRT plans. The endpoint doses to the liver, heart, esophagus, right kidney, and stomach also had no significant differences (p > 0.05). Except for superficial lesions, real-time ultrasound monitoring during liver SBRT is clinically feasible. Placing the ultrasound probe parallel to the longitudinal axis of the patient allows a greater probability of utilizing preferred coplanar beams.