Interfractional target changes in brain metastases during 13-fraction stereotactic radiotherapy

Background The risk for radiation necrosis is lower in fractionated stereotactic radiotherapy (SRT) than in conventional radiotherapy, and 13-fraction SRT is our method of choice for the treatment of brain metastases ≥ around 2 cm or patients who are expected to have a good prognosis. As 13-fraction SRT lasts for at least 17 days, adaptive radiotherapy based on contrast-enhanced mid-treatment magnetic resonance imaging (MRI) is often necessary for patients undergoing 13-fraction SRT. In this study, we retrospectively analyzed interfractional target changes in patients with brain metastases treated with 13-fraction SRT. Methods Our analyses included data from 23 patients and 27 metastatic brain lesions treated with 13-fraction SRT with dynamic conformal arc therapy. The peripheral dose prescribed to the planning target volume (PTV) was 39–44.2 Gy in 13-fractions. The gross tumor volume (GTV) of the initial SRT plan (initial GTV), initial PTV, and modified GTV based on the mid-treatment MRI scan (mid-treatment GTV) were assessed. Results The median initial GTV was 3.8 cm3 and the median time from SRT initiation to the mid-treatment MRI scan was 6 days. Compared to the initial GTV, the mid-treatment GTV increased by more than 20% in five lesions and decreased by more than 20% in five lesions. Interfractional GTV volume changes of more than 20% were not significantly associated with primary disease or the presence of cystic components/necrosis. The mid-treatment GTV did not overlap perfectly with the initial PTV in more than half of the lesions. Conclusions Compared to the initial GTV, the mid-treatment GTV changed by more than 20% in almost one-third of lesions treated with 13-fraction SRT. As SRT usually generates a steep dose gradient as well as increasing the maximum dose of PTV compared to conventional radiotherapy, assessment of the volume and locational target changes and adaptive radiotherapy should be considered as the number of fractions increases.

Gamma Knife Radiosurgery of Distal Aneurysm: A Case Series

A series of 3 patients (35–60 years old) with bleeding distal aneurysm not associated with AVM who underwent radiosurgery by gamma knife are reported. One isocentre centralized over the aneurysm was used; peripheral dose 24–28.8 Gy was applied. Control angiography 20–36 months after gamma knife surgery (GKS) demonstrated obliteration of both the aneurysm and the feeding artery, without deterioration of the neurological symptoms. Our case series implies that GKS might serve as a safe mini-invasive technique in the treatment of selected distal aneurysms.

Evaluation of Peripheral Dose for Varian Trilogy Linear Accelerator

Objective To measure and evaluate the peripheral dose(PD) for Trilogy linear accelerator in different setup condition and investigate the feasibility of the diode dosimetric system to measure the peripheral dose.Methods Peripheral dose were measured using a CC13 ionization chamber and the diode dosimetric system in a set of solid water phantom. Measurements were performed for different depths, field sizes, physical and virtual wedge, radiation beam energy and up at distance of 1cm to 31cm beyond the field edges. PD is separated into PDleakage and PDscatter by measure peripheral dose with or without scattering phantom. CRIS phantom was used for this research with the diode dosimetric system at the interest points of the breast, thyroid, and lens.Results All the measure data were normalized to isocenter. The measured PD decreases exponentially as a function of distance up to 31cm from the edge. PD shows no significant relevant to depth and it increases with the increased field size. As the physics wedge angle increase, PD increases about 1%, but enhanced dynamic wedge decreased 2-3% compared with open field. As the beam energy increase, PD decreased. All PD data difference less than 1% between CC13 ionization chamber and diode. The PD of CRIS phantom for Volume Modulated ARC Therapy (VMAT) is minimum and the mean dose for breast、thyroid and lens is 6.72 mGy、2.90 mGy and 2.37 mGy respectively.Conclusion The diode dosimetric system provides an sufficient assessment in peripheral regions of 6MV X-ray beam. PD changes because of field size、depth、beam energy etc and the assessment of PD would be helpful to evaluate the dose received by the relevant critical structures near the treatment field. Furthermore it is advantaged to use external shielding for critical organs.

Venous outflow restriction as a predictor of cavernous sinus dural arteriovenous fistula obliteration after Gamma Knife surgery

OBJECTIVEGamma Knife surgery (GKS) obliterates 65%–87% of cavernous sinus dural arteriovenous fistulas (CSDAVFs). However, the hemodynamic effect on GKS outcomes is relatively unknown. The authors thus used the classification scheme developed by Suh et al. to explore this effect.METHODSThe authors retrospectively (1993–2016) included 123 patients with CSDAVFs who received GKS alone at the institute and classified them as proliferative type (PT; n = 23), restrictive type (RT; n = 61), or late restrictive type (LRT; n = 39) after analyzing their pre-GKS angiography images. Treatment parameters, the presence of numerous arterial feeders, and venous drainage numbers were compared across the CSDAVF types. Patients’ follow-up MR images were evaluated for the presence of complete obliteration. A Kaplan-Meier analysis was conducted to determine the correlation between CSDAVF types and outcomes.RESULTSThe 36-month probability of complete obliteration was 74.3% for all patients, with no significant differences across types (p = 0.56). PT had the largest radiation volume (6.5 cm3, p < 0.001), the most isocenters (5, p = 0.015) and venous drainage routes (3, p < 0.001), and the lowest peripheral dose (16.6 Gy, p = 0.011) and isodose level coverage (64.3%, p = 0.006). CSDAVFs presenting with ocular patterns were less likely to be completely obliterated (hazard ratio 0.531, p = 0.009). After adjustment for age, CSDAVFs with more venous drainage routes were less likely to be completely obliterated (hazard ratio 0.784, p = 0.039).CONCLUSIONSGKS is an equally effective treatment option for all 3 CSDAVF types. Furthermore, the number of venous drainage routes may help in predicting treatment outcomes and making therapeutic decisions.

Enhancement of the Dose on 12 MV Linac with Free Flattening Filter Mode

Purpose: In the last years, some studies investigated dosimetric benefits of a free flattening filter for the photon mode in the radiotherapy field. This study aims to provide a theoretical study published and analysis of basic dosimetric properties for a Saturne 43 Linac head to implement free flattening filter beams clinically.Material and Methods: This is the first Monte Carlo study for the head of Saturne 43 with replacement flattening filter mode investigating beam dosimetric characteristics, including central axis absorbed doses, beam profiles and photon energy spectra. The later ones were analyzed for flattening filter and replacement flattening filter beams using BEAMnrc and DOSXYZnrc Monte Carlo codes for 10 × 10 cm2, 5 × 5 cm2 and 2 × 2 cm2 square field sizes.Results: A 3.94-fold increase of dose rate and electron contaminating increased by 246.4 % with the replacement flattening filter mode for field size of 10 × 10 cm2. Reduction was made by replacement flattening filter beam in the peripheral dose up to 30%, and the time was reduced more than 50 %.Conclusion: Results obtained from our study revealed that some characteristic dosimetries such as the maximum increase in depth dose rate, decrease in out-of-depth dose, and reducing time can be beneficial for the unflattened beam to be used in the radiotherapy for the advanced techniques.

Hepatocellular carcinoma with tumor thrombus in portal vein branch: Transarterial chemoembolization combined with Iodine125 brachytherapy versus transarterial chemoembolization combined with sorafenib.

e15646 Background: Patients with hepatocellular carcinoma (HCC) accompanied with portal vein tumor thrombus (PVTT) have a poor prognosis. Although transarterial chemoembolization (TACE) plus sorafenib (TACE-S) could lead to an improved survival than TACE alone in HCC patients with first- or second-branch PVTT (branch PVTT), the survival was very limited. We compared the safety and efficacy of TACE plus Iodine125 brachytherapy (TACE-I) with TACE-S in patients with unresectable HCC and branch PVTT. Methods: The medical records of consecutive patients with HCC and branch PVTT who underwent TACE-I (TACE-I group) or TACE-S (TACE-S group) from January 2015 to December 2017 were retrospectively evaluated. Iodine125 seeds were implanted into the PVTT under CT guidance 3-5 days after the initial TACE. The matched peripheral dose of Iodine125 brachytherapy was set to be 120-140 Gy. Sorafenib was administered 400 mg twice daily. Outcomes of patients who underwent TACE-I, including adverse events, treatment responses, time to progression (TTP), and overall survival (OS), were compared with those of patients who underwent TACE-S. Results: One hundred and twenty patients were included in the analysis; 62 patients underwent TACE-I and 58 underwent TACE-S. The overall incidence of adverse events was significantly lower in TACE-I group than in TACE-S group (58.1% vs. 93.1%, P < .001), and incidence of grade 3 or higher adverse events also was significantly lower in TACE-I group than in TACE-S group (3.2% vs. 27.6%, P < .001). PVTT OR rates at 12 weeks (58.1% vs. 13.8%, P < .001) and at 24 weeks after the treatment (68.9 % vs. 10.9%, P < .001) in TACE-I group were higher than those in TACE-S group. TACE-I led to significantly longer TTP (median, 11.2 months vs. 6.2 months, P < .001) and OS (median, 20.9 months vs. 14.0 months, P < .001) than TACE-S. In uni- and multivariable analyses, TACE-I treatment, PVTT extent, tumor size ≥10 cm, PVTT OR at 12 weeks, and intrahepatic tumor OR at 12 weeks were independent prognostic factors for OS. Conclusions: TACE-I had less side effects and may improve OS than TACE-S for HCC patients with branch PVTT.

Monte Carlo Study of Unflattened Photon Beams Shaped by Multileaf Collimator

Introduction: This study investigates basic dosimetric properties of unflattened 6 MV photon beam shaped by multileaf collimator and compares them with those of flattened beams.Materials and Methods: Monte Carlo simulation model using BEAM code was developed for a 6MV photon beam based on Varian Clinic 600 unique performance linac operated with and without a flattening filter in beam line. Dosimetric features including lateral profiles, central axis depth dose, photon and electron spectra were calculated for flattened and unflattened cases, separately.Results: An increase in absolute depth dose with a factor of more than 2.4 was observed for unflattened beam which was dependent on depth. PDDs values were found to be lower for unflattened beam for all field sizes. Significant decrease in calculated mlc leakage was observed when the flattening filter was removed from the beam line. The total scatter factor, SCP was found to show less variation with field sizes for unflattened beam indicating a decrease in head scatter. The beam profiles for unflattened case are found to have lower relative dose value in comparison with flattened beam near the field edge, and it falls off faster with distance.Conclusion: Our study showed that increase in the dose rate and lower peripheral dose could be considered as realistic advantages for unflattened 6MV photon beams.