Takeaki Ishihara

Efficacy of stereotactic body radiotherapy for hepatocellular carcinoma with portal vein tumor thrombosis/inferior vena cava tumor thrombosis: evaluation by comparison with conventional three-dimensional conformal radiotherapy

This study aimed to evaluate the efficacy of stereotactic body radiotherapy (SBRT) compared with three-dimensional conformal radiotherapy (3DCRT). Forty-three patients with portal vein tumor thrombosis (PVTT)/inferior vena cava tumor thrombosis (IVCTT) treated with SBRT (27 with CyberKnife (CK) and 16 with TrueBeam (TB)) from April 2013 to December 2014, and 54 treated with 3DCRT from June 2008 to March 2013 were evaluated. Dosimetric parameters, response to radiotherapy (RT) and survival outcomes were compared in total SBRT vs. 3DCRT, CK vs. 3DCRT and TB vs. 3DCRT, respectively. The median biologically effective dose 10 (BED10) values in total SBRT, CK, TB and 3DCRT were 73.4 Gy10, 75.0 Gy10, 60.5 Gy10 and 58.5 Gy10, respectively (P < 0.001 in total SBRT vs. 3DCRT, P < 0.001 in CK vs. 3DCRT, P = 0.004 in TB vs. 3DCRT). The tumor response rates were 67%, 70%, 62% and 46%, respectively (P = 0.04, P = 0.04, P = 0.25). The 1-year overall survival rates were 49.3%, 56.7%, 38.1% and 29.3%, respectively (P = 0.02, P = 0.02, P = 0.30), and the 1-year local progression rates were 20.4%, 21.9%, 18.8% and 43.6%, respectively (P = 0.01, P = 0.04, P = 0.10). The use of SBRT made it possible to achieve a higher BED10 compared with the use of 3DCRT. Improvements in local control and survival were achieved in the CK group and the total SBRT group. Our results suggest that SBRT may have the potential to be the standard RT technique for the treatment of PVTT/IVCTT.

Dosimetric factors predicting radiation pneumonitis after CyberKnife stereotactic body radiotherapy for peripheral lung cancer

Objective: The aims of this study were to investigate the frequency of symptomatic radiation pneumonitis (RP) after CyberKnife lung stereotactic body radiotherapy (SBRT) and to evaluate predictive factors of symptomatic RP. Methods: 56 patients with peripheral non-small-cell lung cancer were treated using the CyberKnife® VSI™ System (Accuracy Inc., Sunnyvale, CA) between May 2013 and September 2015. Total radiation doses ranged from 48 to 56 Gy, as delivered in four equal fractions. Symptomatic RP was defined as a grade of ≥2. Predictive factors for symptomatic RP were evaluated using univariate and multivariate analyses. Results: With a median follow-up duration of 12.5 months (range, 3–27 months), symptomatic RP was observed in 6 (10.7%) of the 56 patients. In the univariate analysis, percent vital capacity (p < 0.05), maximum tumour diameter (p < 0.05), gross tumour volume (p < 0.05), planning target volume (p < 0.01), mean lung dose (p < 0.01) and a normal lung volume receiving 5–50 Gy of radiation (V5–50) (p < 0.01) were identified as significant predictive factors for symptomatic RP. In the multivariate analysis, only a V25 >3.4% (p = 0.011) was identified as a significant predictive factor of symptomatic RP. Conclusion: The incidence of symptomatic RP after CyberKnife SBRT was almost identical to the incidences reported in the linear accelerator-based SBRT. A significant association was observed between a V25 >3.4% and the risk of developing symptomatic RP. Advances in knowledge: This is the first report that has investigated prognostic factors for symptomatic RP after CyberKnife SBRT for lung cancer. The newly developed scoring system may help to predict symptomatic RP.

[18F]Fluorodeoxyglucose uptake by positron emission tomography predicts outcomes for oropharyngeal and hypopharyngeal cancer treated with definitive radiotherapy

ABSTRACT This study evaluated the prognostic significance of the maximum standardized uptake value of the primary site (pSUVmax) in 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) scans of patients with oropharyngeal or hypopharyngeal cancer who were treated using definitive radiotherapy. The study included 86 patients who were primarily treated with radiotherapy for oropharyngeal or hypopharyngeal cancer. Sixty-nine patients underwent concurrent chemotherapy. The associations between pre-treatment pSUVmax and treatment outcomes were evaluated. The most appropriate pSUVmax cut-off value for predicting disease-free survival (DFS) and local control (LC) was selected using receiver operating characteristic (ROC) curves. The median follow-up time for surviving patients was 60 months, while the median survival time in the entire patient cohort was 55 months. A pSUVmax cut-off value of 9.0 showed the best discriminative performance. Five-year OS and DFS rates were 65.9% and 60.0%, respectively. In univariate analyses, pSUVmax (p = 0.009), T-stage (p = 0.001), N-stage (p = 0.039), and clinical stage (p = 0.017) were identified as significant prognostic predictors for DFS. The multivariate analysis did not identify any statistically significant factors, but the association between pSUVmax and DFS was borderline significant (p = 0.055). Interestingly, pSUVmax was predictive of local controllability in T1–T2 disease (p = 0.024), but there was no significant association for T3–T4 disease (p = 0.735). In this study, pSUVmax was predictive of DFS and LC in patients with oropharyngeal or hypopharyngeal cancer that was treated with definitive radiotherapy. pSUVmax was strongly associated with LC in T1–T2 disease.

Comparison of dosimetric parameters in the treatment planning of magnetic resonance imaging–based intracavitary image-guided adaptive brachytherapy with and without optimization using the central shielding technique

Abstract This study aimed to compare dosimetric parameters between non-optimized and optimized treatment planning (NOP and OP, respectively) of magnetic resonance imaging (MRI) –based intracavitary (IC) image-guided adaptive brachytherapy (IGABT) using the central shielding (CS) technique for cervical cancer. Fifty-three patients treated with external beam radiotherapy using CS and MRI-based IGABT with the IC approach alone were evaluated. The total high-risk clinical target volume (HR-CTV) D90 was aimed at >70 Gy equivalent dose in 2 Gy fractions (EQD2). In the small HR-CTV group (≤30 cm3), the mean D90s for NOP/OP were 98.6/80.7 Gy. In the large (30.1–40 cm3) and extensive (>40 cm3) HR-CTV groups, the mean D90s were 81.9/77.5 and 71.1/73.6 Gy, respectively. The mean D2cc values for organs at risks (OARs) in OP were acceptable in all groups, despite the high bladder D2cc in the NOP. The correlation between HR-CTV at first brachytherapy (BT) and NOP D90 was stronger than that between HR-CTV at first BT and OP D90. The targeted HR-CTV D90 and dose constraints of D2cc for OARs were both achieved in 16 NOP/47 OP patients for the bladder, 39/50 for the rectum, and 47/50 for the sigmoid colon (P < 0.001, P = 0.007, and P = 0.34, respectively). For small tumors, the role of optimization was to reduce the D2cc for OARs while maintaining the targeted D90. However, optimization was of limited value for extensive tumors. Methods of optimization in IGABT with CS for cervical cancer should be standardized while considering its effectiveness and limitations.

Stereotactic body radiotherapy for second primary lung cancer and intra-parenchymal lung metastasis in patients previously treated with surgery: evaluation of indications and predictors of decreased respiratory function

Abstract Background: The adaptation criteria for administration of stereotactic body radiotherapy (SBRT) to patients with lung cancer who previously underwent surgery and subsequently developed a second primary lung cancer (SPLC) or intra-parenchymal lung metastasis (IPLM) are controversial, unlike the criteria for repeat surgery. We aimed to evaluate the feasibility of SBRT for these patients. Factors associated with decreased respiratory function were also evaluated. Material and methods: Sixty-nine patients with 89 lesions who underwent SBRT between 2008 and 2017 were analyzed. Of these, 29 were diagnosed with SPLC while the remaining 40 had IPLM. The distribution of histological types was as follows: squamous cell carcinoma (n = 13 lesions); adenocarcinoma (n = 25); non-small cell carcinoma (n = 1); unknown histological type (n = 49). The prescribed doses to the planning target volume (PTV) were 50 Gy in five fractions for 85 lesions and 60 Gy in 10 fractions for four lesions at PTV mean. Results: Over a median follow-up period of 55 months, the 4-year overall survival and local control rates were 50.3% and 87.6%, respectively. Six patients experienced grade 2 radiation pneumonitis and one experienced grade 3. Two patients experienced grade 5 pulmonary fibrosis. Decreased respiratory function was observed in 10 patients (15.1%). On multivariate analysis, the presence of pulmonary disease before SBRT was the only statistically significant factor associated with decreased respiratory function. Conclusions: SBRT is safe and feasible in patients with SPLC or IPLM previously treated surgically. Pre-existing pulmonary disease was a predictive factor for decreased respiratory function.

Application of dual-energy CT to suppression of metal artefact caused by pedicle screw fixation in radiotherapy: a feasibility study using original phantom

The objective of the present study was the determination of the potential dosimetric benefits of using metal-artefact-suppressed dual-energy computed tomography (DECT) images for cases involving pedicle screw implants in spinal sites. A heterogeneous spinal phantom was designed for the investigation of the dosimetric effect of the pedicle-screw-related artefacts. The dosimetric comparisons were first performed using a conventional two-directional opposed (AP-PA) plan, and then a volumetric modulated arc therapy (VMAT) plan, which are both used for the treatment of spinal metastases in our institution. The results of Acuros® XB dose-to-medium (Dm) and dose-to-water (Dw) calculations using different imaging options were compared with experimental measurements including the chamber and film dosimetries in the spinal phantom. A dual-energy composition image with a weight factor of  -0.2 and a dual-energy monochromatic image (DEMI) with an energy level of 180 keV were found to have superior abilities for artefact suppression. The Dm calculations revealed greater dosimetric effects of the pedicle screw-related artefacts compared to the Dw calculations. The results of conventional single-energy computed tomography showed that, although the pedicle screws were made from low-Z titanium alloy, the metal artefacts still have dosimetric effects, namely, an average (maximum) Dm error of 4.4% (5.6%) inside the spinal cord for a complex VMAT treatment plan. Our findings indicate that metal-artefact suppression using the proposed DECT (DEMI) approach is promising for improving the dosimetric accuracy near the implants and inside the spinal cord (average (maximum) Dm error of 1.1% (2.0%)).

Investigation of the efficacy and safety of CyberKnife hypofractionated stereotactic radiotherapy for brainstem metastases using a new evaluation criterion: ‘symptomatic control’

Abstract The treatment of brainstem metastases remains a challenge as the brainstem itself is considered a neurological organ at risk. We aimed to investigate the efficacy and safety of CyberKnife hypofractionated stereotactic radiotherapy (HFSRT) for brainstem metastases, and to examine the balance between efficacy and safety for the management of neurological symptoms. A total of 26 lesions [pons (n = 18), medulla (n = 4) and midbrain (n = 4)] in 20 patients treated with CyberKnife hypofractionated stereotactic radiotherapy were retrospectively analyzed. The total radiation doses (18–30 Gy) were delivered in 3 or 5 equal fractions. The median follow-up was 6.5 (range, 0.5–38.0) months. The 6- and 12-month local control rates were 100% and 90%, respectively. Symptomatic failures, defined as the worsening and appearance of neurological symptoms due to the brainstem lesion after CyberKnife HFSRT, were observed in 6 patients [local failure (n = 1) and adverse events (n = 5). The symptomatic control and overall survival rates were 90% and 72% (after 6 months), respectively, and 76% and 53% (after 12 months), respectively. Longer symptomatic control was associated with site of lesion origin, and longer overall survival was associated with a graded prognostic assessment score of >2. To our knowledge, this is the second study to investigate the efficacy and safety of CyberKnife HFSRT for brainstem metastases. The local control rate was comparable with that of prior stereotactic radiosurgery studies. We propose a new evaluation criterion—‘symptomatic control’—to evaluate the efficacy and safety of brainstem radiotherapy.

Radiotherapy for brainstem gliomas in children and adults: A single‐institution experience and literature review

To evaluate the treatment results of radiotherapy (RT) in children and adults with brainstem gliomas (BSGs) and review the previous literature.

SU-E-T-145: Beam Characteristics of Flattening Filter Free Beams Including Low Dose Rate Setting

Purpose: In commissioning of volumetric modulated arc therapy (VMAT), it is necessary to evaluate the beam characteristics of various dose rate settings with potential to use. The aim of this study is to evaluate the beam characteristics of flattened and flattening filter free (FFF) including low dose rate setting. Methods: We used a Varian TrueBeam with Millennium 120 MLC. Both 6 and 10 MV beams with or without flattening filter were used for this study. To evaluate low-dose rate FFF beams, specially-designed leaf sequence files control out-of-field MLC leaf pair at constant dose rate ranging from 80 to 400 MU/min. For dose rate from 80 MU/min to the maximum usable value of all energies, beam output were measured using ionization chamber (CC04, IBA). The ionization chamber was inserted into water equivalent phantom (RT3000-New, R-tech), and the phantom was set with SAD of 100cm. The beam profiles were performed using the 2D diode array (Profiler2, Sun Nuclear). The SSD was set to 90cm and a combined 30cmx30cmx9cm phantom which consisted of solid water slabs was put on the device. All measurement were made using 100MU irradiation for 10cmx10cm jaw-defined field size with a gantry angle of 0°. Results: In all energies, the dose rate dependences with beam output and variation coefficient were within 0.2% and 0.07%, respectively. The flatness and symmetry exhibited small variations (flatness ≤0.1 point and symmetry≤0.3 point at absolute difference). Conclusion: We had studied the characteristics of flattened and FFF beam over the 80 MU/min. Our results indicated that the beam output and profiles of FFF of TrueBeam linac were highly stable at low dose rate setting.