Contrast-enhanced radiotherapy is an innovative treatment that combines the selective accumulation of heavy elements in tumors with stereotactic irradiations using medium energy X-rays. The radiation dose enhancement depends on the absolute amount of iodine reached in the tumor and its time course. Quantitative, postinfusion iodine biodistribution and associated brain perfusion parameters were studied in human brain metastasis as key parameters for treatment feasibility and quality. Twelve patients received an intravenous bolus of iodinated contrast agent (CA) (40 mL, 4 mL/s), followed by a steady-state infusion (160 mL, 0.5 mL/s) to ensure stable intratumoral amounts of iodine during the treatment. Absolute iodine concentrations and quantitative perfusion maps were derived from 40 multislice dynamic computed tomography (CT) images of the brain. The postinfusion mean intratumoral iodine concentration (over 30 minutes) reached 1.94±0.12 mg/mL. Reasonable correlations were obtained between these concentrations and the permeability surface area product and the cerebral blood volume. To our knowledge, this is the first quantitative study of CA biodistribution versus time in brain metastasis. The study shows that suitable and stable amounts of iodine can be reached for contrast-enhanced radiotherapy. Moreover, the associated perfusion measurements provide useful information for the patient recruitment and management processes.
Background: In most clinical trials, gold fiducial markers are implanted in the prostate to tune the table position before each radiation beam. Yet, it is unclear if a cone-beam computed tomography (CBCT) should be performed before each beam to monitor a possible variation of the organs at risk (OARs) fullness, especially in case of rectoprostatic spacer implantation. The present study aimed at assessing the inter-and intra-fraction movements of prostate, bladder and rectum in patients implanted with a hyaluronic acid spacer and undergoing prostate stereotactic body radiotherapy (SBRT). Methods: Data about consecutive patients undergoing prostate SBRT were prospectively collected between 2015 and 2019. Inter-and intra-fraction prostate displacements and volume variation of organs at risk (OARs) were assessed with CBCTs. Results: Eight patients were included. They underwent prostate SBRT (37.5Gy, 5 fractions of 7.5Gy) guided by prostate gold fiducial markers. Inter-fraction variation of the bladder volume was insignificant. Intra-fraction mean increase of the bladder volume was modest (29 cc) but significant (p < 0.001). Both inter-and intra-fraction variations of the rectum volume were insignificant but for one patient. He had no rectal toxicity. The magnitude of table displacement necessary to match the prostate gold fiducial marker frequently exceeded the CTV/PTV margins (0.4 cm) before the first (35%) and the second arc (15%). Inter-and intra-fraction bladder and rectum volume variations did not correlate with prostate displacement. Conclusion: Major prostate position variations were reported. In-room kV fiducial imaging before each arc seems mandatory. Intra-fraction imaging of the OARs appears unnecessary. We suggest that only one CBCT is needed before the first arc.
Purpose:
Synchrotron stereotactic radiotherapy (SSRT) is an innovative treatment combining the selective accumulation of heavy elements in tumors with stereotactic irradiations using monochromatic medium energy x‐rays from a synchrotron source. Phase I/II clinical trials on brain metastasis are underway using venous infusion of iodinated contrast agents. The radiation dose enhancement depends on the amount of iodine in the tumor and its time course. In the present study, the reproducibility of iodine concentrations between the CT planning scan day (Day 0) and the treatment day (Day 10) was assessed in order to predict dose errors.
Methods:
For each of days 0 and 10, three patients received a biphasic intravenous injection of iodinated contrast agent (40 ml, 4 ml/s, followed by 160 ml, 0.5 ml/s) in order to ensure stable intra‐tumoral amounts of iodine during the treatment. Two volumetric CT scans (before and after iodine injection) and a multi‐slice dynamic CT of the brain were performed using conventional radiotherapy CT (Day 0) or quantitative synchrotron radiation CT (Day 10). A 3D rigid registration was processed between images. The absolute and relative differences of absolute iodine concentrations and their corresponding dose errors were evaluated in the GTV and PTV used for treatment planning.
Results:
The differences in iodine concentrations remained within the standard deviation limits. The 3D absolute differences followed a normal distribution centered at zero mg/ml with a variance (∼1 mg/ml) which is related to the image noise.
Conclusion:
The results suggest that dose errors depend only on the image noise. This study shows that stable amounts of iodine are achievable in brain metastasis for SSRT treatment in a 10 days interval.
Purpose:
Iodine‐enhanced radiotherapy is an innovative treatment combining the selective accumulation of an iodinated contrast agent in brain tumors with irradiations using monochromatic medium energy x‐rays. The aim of this study is to compare dynamic stereotactic arc‐therapy and iodineenhanced SSRT.
Methods:
Five patients bearing brain metastasis received a standard helical 3D‐scan without iodine. A second scan was acquired 13 min after an 80 g iodine infusion. Two SSRT treatment plans (with/without iodine) were performed for each patient using a dedicated Monte Carlo (MC) treatment planning system (TPS) based on the ISOgray TPS. Ten coplanar beams (6×6 cm2, shaped with collimator) were simulated. MC statistical error objective was less than 5% in the 50% isodose. The dynamic arc‐therapy plan was achieved on the Iplan Brainlab TPS. The treatment plan validation criteria were fixed such that 100% of the prescribed dose is delivered at the beam isocentre and the 70% isodose contains the whole target volume. The comparison elements were the 70% isodose volume, the average and maximum doses delivered to organs at risk (OAR): brainstem, optical nerves, chiasma, eyes, skull bone and healthy brain parenchyma.
Results:
The stereotactic dynamic arc‐therapy remains the best technique in terms of dose conformation. Iodine‐enhanced SSRT presents similar performances to dynamic arc‐therapy with increased brainstem and brain parenchyma sparing. One disadvantage of SSRT is the high dose to the skull bone. Iodine accumulation in metastasis may increase the dose by 20–30%, allowing a normal tissue sparing effect at constant prescribed dose. Treatment without any iodine enhancement (medium‐energy stereotactic radiotherapy) is not relevant with degraded HDVs (brain, parenchyma and skull bone) comparing to stereotactic dynamic arc‐therapy.
Conclusion:
Iodine‐enhanced SSRT exhibits a good potential for brain metastasis treatment regarding the dose distribution and OAR criteria.
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