Quantification of residual dose estimation error on log file-based patient dose calculation

PurposeThe log file-based patient dose estimation includes a residual dose estimation error caused by leaf miscalibration, which cannot be reflected on the estimated dose. The purpose of this study is to determine this residual dose estimation error.Methods and materialsModified log files for seven head-and-neck and prostate volumetric modulated arc therapy (VMAT) plans simulating leaf miscalibration were generated by shifting both leaf banks (systematic leaf gap errors: ±2.0, ±1.0, and ±0.5 mm in opposite directions and systematic leaf shifts: ±1.0 mm in the same direction) using MATLAB-based (MathWorks, Natick, MA) in-house software. The generated modified and non-modified log files were imported back into the treatment planning system and recalculated. Subsequently, the generalized equivalent uniform dose (gEUD) was quantified for the definition of the planning target volume (PTV) and organs at risks.ResultsFor MLC leaves calibrated within ±0.5 mm, the quantified residual dose estimation errors that obtained from the slope of the linear regression of gEUD changes between non- and modified log file doses per leaf gap are in head-and-neck plans 1.32 ± 0.27% and 0.82 ± 0.17 Gy for PTV and spinal cord, respectively, and in prostate plans 1.22 ± 0.36%, 0.95 ± 0.14 Gy, and 0.45 ± 0.08 Gy for PTV, rectum, and bladder, respectively.ConclusionsIn this work, we determine the residual dose estimation errors for VMAT delivery using the log file-based patient dose calculation according to the MLC calibration accuracy.     

Dosimétrie rénale du 177Lu-Dotatate : mise en place au sein du Groupement hospitalier Est des Hospices Civils de Lyon

IntroductionThe kidney is considered as a critical dose-limiting organ with ¹⁷⁷Lu-Dotatate. Renal dosimetry could play a role in optimizing treatment. We present a feedback on the implementation of renal dosimetry in our medical center.Material and methodThe renal dosimetry of the 1st administration of ¹⁷⁷Lu-Dotatate (approximately 7.4 GBq) has been performed for seven patients. The reference dosimetry strategy included 4 post-therapeutic SPECT/CT at 6 h, 24 h, 72 h and 168 h and anatomical renal volume delineation (VOI). Alternative dosimetric strategies consisted of 72 h or 168 h time point eviction (time sampling A or B) and delimitation of 1 or 3 spherical VOIs (3 mL each) per kidney (“1 sVOI” or “3 sVOI” methods). The quantitative scintigraphic processing was performed by 4 operators using Dosimetry Toolkit®. The renal dose was calculated with OLINDA/EXM® 2.0.ResultsThe calculated mean absorbed renal dose was 3.68 ± 0.68 Gy with the reference method, with no significant impact of interoperator variability (P = 0.41). It was in satisfactory agreement with time sampling A or B. The “1 sVOI” and “3 sVOI” methods overestimated the renal dose (5.01 ± 0.94 Gy and 4.91 ± 0.79 Gy respectively), with a significant impact on interoperator variability (P < 0.05), despite a reduction in processing time.ConclusionThe main logistic constraint of ¹⁷⁷Lu-Dotatate renal dosimetry in our center is the time-consumption due to SPECT/CT acquisitions. A possible approach supported by our preliminary results is a reduction in the number of scintigraphic acquisitions.     

Dose distribution homogeneity in two TBI techniques—Analysis of 208 irradiated patients conducted in Stanislaw Leszczynski Memorial Hospital,Katowice

BackgroundTo analyze and compare dose distribution homogeneity in selected points (especially in the chest wall region) for patients irradiated with two different TBI techniques to achieve a uniform total dose (excluding lungs area) specified in the range of 11.4–14.0 Gy.Material and methodsFrom August 2000 to December 2009, a group of 158 patients was treated by the use of 15 MV photon irradiation consisting of six fractions: four opposed lateral and two anterior–posterior/posterior–anterior (AP/PA). Patients were irradiated with the fraction dose of 2 Gy twice a day for 3 consecutive days. The prescribed dose to PC point (specified at intersection of the beam axis with the mid-plane of the patient irradiated laterally) was 12 Gy. Since January 2010 until closing the study, another group of 50 patients was treated according to a modified protocol. The treatment was carried out in six lateral fractions only, twice a day, for three following days and a lateral lung shield was used for a part of total irradiation time. The measurements of doses in 20 selected points of patient's body were carried out by means of MOSFET detectors.ResultsThe modified TBI technique allows to achieve an expected homogenous dose in the points of interest similar to that obtained by using the initial protocol. The calculated and measured in vivo doses met the specified range of 11.4–14 Gy for both applied TBI protocols.ConclusionsOur results indicate that for all patients the homogenous dose distribution in the specified range was achieved.     

Ascorbic acid 2-glucocide reduces micronucleus induction in distant splenic T lymphocytes following head irradiation

PurposeEvidence from in vivo studies suggests there are enhanced radiation effects in abscopal regions after local head gamma ray irradiation. Splenocyte apoptosis and T lymphocyte micronuclei were induced at higher rates than what would be estimated given the dose at a shielded, distant position. In addition, we evaluated the radio-protective effects of ascorbic acid, acting as a radical scavenger on enhanced radiation effects in the shielded spleen following local head irradiation.Methods and materialsThe heads of C3H mice were exposed to γ-rays (10–20 Gy), while the other parts of the body were shielded with a 5 cm-thick lead block. The effective dose for the spleen was calculated at 1.0–2.0 Gy. Splenocytes were isolated 24 h after cranial irradiation and their apoptosis was measured with an Elisa kit (Roche). The induction of T lymphocyte micronuclei was studied using the cytokinesis-block micronucleus assay. The ascorbic acid glucoside, 2-O-alpha-d-glucopyranosyl-l-ascorbic acid (AA-2G), was orally administered to mice 1 h before whole body irradiation. The radio protective effects of AA-2G were estimated by comparing the induction of splenocyte damage (by apoptosis) and micronucleus induction.ResultsThe splenocyte damage, as measured by the above two methods, was more excessive than what would be expected given exposure to 1.0–2.0 Gy of radiation. Our results suggest that the effects were enhanced in a distant, non-irradiated organ after localized irradiation. Plasma ascorbic acid concentrations were increased 8–10× over control. Treatment with ascorbic acid slightly protected mouse splenocytes from the induction of apoptosis by the enhanced effects of radiation in the abscopal region. However, ascorbic acid significantly inhibited micronucleus induction in splenic T lymphocytes following local head irradiation.ConclusionsOur results suggest that ascorbic acid effectively scavenged radiation-induced radicals and protected against the enhanced effects of radiation in an abscopal region after local head gamma ray irradiation.     

Étude dosimétrique de préparations de médicaments radiopharmaceutiques au 68Ga

AimProduction of ⁶⁸Ga-radiopharmaceuticals is a rapidly growing field in France. However, operators may already be involved in other radiopharmaceutical activities. It is thus necessary to know the exposure of this new activity.Material and methodsFor passive dosimetry, a radiophotoluminescent (RPL) dosimeter, a thermoluminescent (TLD) chip, 2 TLD rings and a passive dosimeter for crystalline were used. For active dosimetry, an extremity dosimeter and a whole body dosimeter were used. This study was performed during semi-automatized production of ⁶⁸Ga-investigational medicinal products. Values were normalized to 500MBq manipulated (median activity using a 1850MBq ⁶⁸Ga-generator), 60 radiosynthesis (maximum enrollment ability of our center) and 2 operators. A LB123 proportional counter was used for quantification of external exposition to 10MBq ⁶⁸Ge and internal exposition by inhalation was theoretically assessed. ⁶⁸Ga emission attenuation by collective protection equipments was also discussed.ResultsConsidering passive dosimetry, the equivalent dose to extremities was 21.75 ± 0.34 mSv, the whole-body effective dose was 0.189 ± 0.011 mSv and the dose to crystalline was 0.925 ± 0.009 mSv. Considering active dosimetry, the equivalent dose to extremities was 8,75 ± 0.12 mSv and the whole-body effective dose was 0,088 ± 0.009 mSv. Total exposure to ⁶⁸Ge was 1.75 μSv.ConclusionIn our hands, ⁶⁸Ga is a directly transposable activity in radiopharmacies already equipped for ¹⁸F because of a dosimetry complying with regulatory limits and suitable radiation protection of collective equipments.     

Whole body protection against lethal ionizing radiation in mice by REC-2001: A semi-purified fraction of Podophyllum hexandrum

The current study has concentrated on assessment of the radioprotective potential of REC-2001, a semi-purified fraction of rhizomes of Podophyllum hexandrum, in Swiss albino Strain ‘A’ mice exposed to 10 Gy whole-body gamma radiation. Animals were treated with 10 and 15 mg/kg b wt (i.p.) of REC-2001 1 h prior to exposure to a lethal dose of γ-radiation (10 Gy) and observed upto 30 days. For analysis of maximum tolerable dose (MTD), LD₅₀ and acute toxic dose, different concentrations of the extract were administered to animals and their mortality and morbidity status was observed upto 72 h and one week, respectively. Dose reduction factor (DRF) was determined by exposing REC-2001 pre-treated mice to supra-lethal doses of γ-radiation. Endogenous spleen colony forming units (CFU), DNA strand breaks in thymocytes (alkaline halo assay) and lipid degradation was studied to understand the mechanism of radioprotection . A single dose of REC-2001 (10 and 15 mg/kg b wt i.p.) exhibited >90% survival in the pre-treated irradiated group versus no survival in radiation control group. Single doses of upto 75 mg/kg b wt (i.p.) did not cause any mortality (MTD) in mice. REC-2001, a dose of 90 mg/kg b wt, resulted in 50% mortality (LD₅₀), while the LD₁₀₀ was 115 mg/kg b wt REC-2001 exhibited a DRF of 1.62. CFU counts in the REC-2001 treated group were found significantly high (5.33/spleen) as compared to controls. Exposure of thymocytes to 10 Gy radiation resulted in increased halo diameter (45±3 μm) in comparison to untreated controls (8±1 μm). REC-2001 administration (500 μg/ml) decreased the halo diameter to 15±2 μm. Radiation-induced lipid degradation was also inhibited by REC-2001. The present study has revealed that REC-2001 is a promising radioprotective fraction that can be effectively used against lethal doses of γ-radiation after further investigations in higher animal models.     

Évaluation de l’exposition des travailleurs du service de radioimmunoanalyse du Bénin aux rayonnements ionisants de l’iode 125

Occupational radiation dose of staff handling ¹²⁵I assessment at the Benin radioimmunoassay laboratory, have been undertaken from October 2012 to April 2013 to determine level of radiation safety. Equivalent dose to skin, whole body and extremities, were measured by the mean of thermoluminescence dosimetry. Firstly, three permanent workers and two students were provided with finger ring dosimeters to wear at index finger base of both hands. Ring dosimeters were used for four months. Secondly, three permanent workers and three students were provided with badge dosimeters to wear at the chest level. Badge dosimeters were renewed monthly for six months. The exposed ring and badge dosimeters were evaluated in Ghana. Permanent workers highest average equivalent dose received at index finger base of both hands was 142.75 ± 89.54, microSV/2 months and that of students was 34.69 ± 29.23, microSV/2 months. Workers skin exposure was below one third of prescribed dose limits for permanents workers (500mSv/yr) and students (150mSv/yr). Whole body exposure, expressed in mSv/month, of permanent workers and students, respectively ranged from 0.12 to 0.23 and from 0.11 to 0.16. Radio-immuno-assay laboratory workers are weakly exposed to ionizing radiation. They are safe from deterministic effect risk.     

Fast protocol for radiochromic film dosimetry using a cloud computing web application

PurposeTo investigate the feasibility of a fast protocol for radiochromic film dosimetry to verify intensity-modulated radiotherapy (IMRT) plans.Method and materialsEBT3 film dosimetry was conducted in this study using the triple-channel method implemented in the cloud computing application (Radiochromic.com). We described a fast protocol for radiochromic film dosimetry to obtain measurement results within 1 h.Ten IMRT plans were delivered to evaluate the feasibility of the fast protocol. The dose distribution of the verification film was derived at 15, 30, 45 min using the fast protocol and also at 24 h after completing the irradiation. The four dose maps obtained per plan were compared using global and local gamma index (5%/3 mm) with the calculated one by the treatment planning system. Gamma passing rates obtained for 15, 30 and 45 min post-exposure were compared with those obtained after 24 h.ResultsSmall differences respect to the 24 h protocol were found in the gamma passing rates obtained for films digitized at 15 min (global: 99.6% ± 0.9% vs. 99.7% ± 0.5%; local: 96.3% ± 3.4% vs. 96.3% ± 3.8%), at 30 min (global: 99.5% ± 0.9% vs. 99.7% ± 0.5%; local: 96.5% ± 3.2% vs. 96.3 ± 3.8%) and at 45 min (global: 99.2% ± 1.5% vs. 99.7% ± 0.5%; local: 96.1% ± 3.8% vs. 96.3 ± 3.8%).ConclusionsThe fast protocol permits dosimetric results within 1 h when IMRT plans are verified, with similar results as those reported by the standard 24 h protocol.     

Dose-dependent effect of radiation on angiogenic and angiostatic CXC chemokine expression in human endothelial cells

Blood vessel growth is regulated by angiogenic and angiostatic CXC chemokines, and radiation is a vasculogenic stimulus. We investigated the effect of radiation on endothelial cell chemokine signaling, receptor expression, and migration and apoptosis. Human umbilical vein endothelial cells were exposed to a single fraction of 0, 5, or 20 Gy of ionizing radiation (IR). All vasculogenic chemokines (CXCL1–3/5–8) increased 3–13-fold after 5 or 20 Gy IR. 20 Gy induced a marked increase (1.6–4-fold) in angiostatic CXC chemokines. CXCR4 expression increased 3.5 and 7-fold at 48 h after 5 and 20 Gy, respectively. Bone marrow progenitor cell chemotaxis was augmented by conditioned media from cells treated with 5 Gy IR. Whereas 5 Gy markedly decreased intrinsic cell apoptosis (0 Gy = 16% ± 3.6 vs. 5 Gy = 4.5% ± 0.3), 20 Gy increased it (21.4% ± 1.2); a reflection of pro-survival angiogenic chemokine expression. Radiation induces a dose-dependent increase in pro-angiogenic CXC chemokines and CXCR4. In contrast, angiostatic chemokines and apoptosis were induced at higher (20 Gy) radiation doses. Cell migration improved significantly following 5 Gy, but not 20 Gy IR. Collectively, these data suggest that lower doses of IR induce an angiogenic cascade while higher doses produce an angiostatic profile.     

Effect of storage conditions of blood on radiation-induced chromosomal aberrations and apoptosis in human lymphocytes

To evaluate the effect of storage conditions of blood on the direct relationship between radiation-induced chromosome aberrations and apoptosis in human peripheral blood lymphocytes, whole blood was irradiated with 3 Gy X-rays. Directly after irradiation, a sample of blood was analyzed for chromosome damage and proliferation index, after phytohaemagglutinin stimulation and incubation at 37 °C for 56 h. Blood samples were stored for 48 h at 4 and 20 °C with or without phytohaemagglutinin and analyzed for cell viability and apoptosis at 0, 24 and 48 h storage time. After 48 h of storage, unstimulated cultures were stimulated to proliferate. These samples and cultures stimulated immediately before storage were incubated at 37 °C for 56 h and analyzed for chromosome damage and proliferation index. Metaphases were examined for the presence of dicentrics, excess acentrics, and rings. Storage at 20 °C without phytohaemagglutinin for 48 h increases significantly the yield of apoptosis and decreases significantly the yield of dicentrics. During 48 h of storage time the presence of phytohaemagglutinin and the temperature of 4 °C protected the irradiated lymphocytes from apoptosis allowing accurate estimation of the real yield of radiation-induced chromosome damage. Therefore these blood-storage conditions enable analysis in metaphase and may offer some advantages for biodosimetry of absorbed radiation dose.     

Sparing dysphagia/aspiration related structures using novel hybrid volumetric modulated arc therapy

PurposeStudies using split field IMRT to spare dysphagia/aspiration related structures (DARS) have raised concern regarding dose uncertainty at matchline. This study explores the utility of hybrid VMAT in sparing the DARS and assesses matchline dose uncertainty in postoperative oral cavity cancer patients and compares it with VMAT.Methods & materialsTen postoperative oral cavity cancer patients were planned with h-VMAT and VMAT using the same planning CT dataset. PTV and DARS were contoured using standard delineation guidelines. In h-VMAT 80% of the neck dose was planned using AP/PA technique and then VMAT optimization was done for the total PTV by keeping the corresponding AP/PA plan as the base dose. Planning goal for PTV was V_95% ≥ 95% and for DARS, adequate sparing. Plans and dose volume histograms were analyzed using dosimetric indices. Absolute point and portal dose measurements were done for h-VMAT plans to verify dose at the matchline.ResultsCoverage in both the techniques was comparable. Significant differences were observed in mean doses to DARS (Larynx: 24.36 ± 2.51 versus 16.88 ± 2.41 Gy; p < 0.0006, Pharyngeal constrictors: 25.16 ± 2.41 versus 21.2 ± 2.1 Gy; p < 0.005, Esophageal inlet: 18.71 ± 2 versus 12.06 ± 0.79 Gy; p < 0.0002) favoring h-VMAT. Total MU in both the techniques was comparable. Average percentage variations in point dose measurements in h-VMAT done at +3.5 and −3.5 positions were (1.47 ± 1.48 and 2.28 ± 1.35%) respectively. Average gamma agreement for portal dose measured was 97.07%.Conclusionh-VMAT achieves better sparing of DARS with no matchline dose uncertainty. Since these patients have swallowing dysfunction post-operatively, attempts should be made to spare these critical structures as much as possible.     

Implementation of a dose–response curve for γ-radiation in the Portuguese population by use of the chromosomal aberration assay

An in vitro dose–response curve following exposure to γ-radiation was determined at the IST/ITN, by use of the chromosomal aberration assay. This is the first study of this kind carried out among the Portuguese population. Un-irradiated and γ-irradiated peripheral blood lymphocytes from 16 healthy donors were cultured. A total of 22,395 metaphases were analyzed for frequency and distribution of dicentrics and centric rings, as a function of the radiation dose. The dose–response data for dicentrics and dicentrics plus centric rings were fitted by use of a linear–quadratic model: Y_dic = (0.0011 ± 0.0006) + (0.0105 ± 0.0035)D + (0.0480 ± 0.0019)D² and Y_{dic + rings} = (0.0011 ± 0.0006) + (0.0095 ± 0.0036)D + (0.0536 ± 0.0020)D². Also, calibration curves related to age and gender were determined, but no significant differences were found. Following the establishment of the dose–response curves, a validation experiment was carried out with three individuals. Real and estimated doses, obtained with the dose–response curves, were in agreement. These results give us confidence to apply both dose–response calibration curves in future biological dosimetry requirements.     

Characterization of irregular electron beam for boost dose after whole breast irradiation

Irradiating a tumor bed with boost dose after whole breast irradiation helps reducing the probability of local recurrence. However, the success of electron beam treatment with a small area aiming to cover a superficial lesion is a dual challenge as it requires an adequate dosimetry beside a double check for dose coverage with an estimation of various combined uncertainty of tumor location and losing lateral electron equilibrium within small field dimensions.Aim of workthis work aims to measure the electron beam fluence within different field dimensions and the deviation from measurement performed in standard square electron applicator beam flatness and symmetry, then to calculate the average range of the correction factor required to overcome the loss of lateral electron equilibrium.Material and methodthe electron beam used in this work generated from the linear accelerator model ELEKTA Precise and dosimetry system used were a pair of PTW Pin Point ion chambers for electron beam dosimetry at standard conditions and assessment of beam quality at a reference depth of measurement, with an automatic water phantom, then a Roos ion chamber was used for absolute dose measurement, and PTW 2Darray to investigate the beam fluence of four applicators 6, 10, 14 and 20 cm² and 4 rectangular cutouts 6 × 14, 8 × 14, 6 × 17 and 8 × 17 cm², the second part was clinical application which was performed in a precise treatment planning system and examined boost dose after whole breast irradiation.Resultsrevealed that lower energy (6MeV and 8MeV) showed the loss of lateral electron equilibrium and deviation from measurements of a standard applicator more than the high energy (15 MeV) which indicated that the treatment of superficial dose with 6MeV required higher monitor unit to allow for the loss of lateral electron equilibrium and higher margin as well.     

Patient radiation biological risk in computed tomography angiography procedure

Computed tomography angiography (CTA) has become the most valuable imaging modality for the diagnosis of blood vessel diseases; however, patients are exposed to high radiation doses and the probability of cancer and other biological effects is increased. The objectives of this study were to measure the patient radiation dose during a CTA procedure and to estimate the radiation dose and biological effects.The study was conducted in two radiology departments equipped with 64-slice CT machines (Aquilion) calibrated according to international protocols. A total of 152 patients underwent brain, lower limb, chest, abdomen, and pelvis examinations. The effective radiation dose was estimated using ImPACT scan software. Cancer and biological risks were estimated using the International Commission on Radiological Protection (ICRP) conversion factors.The mean patient dose value per procedure (dose length product [DLP], mGy·cm) for all examinations was 437.8 ± 166, 568.8 ± 194, 516.0 ± 228, 581.8 ± 175, and 1082.9 ± 290 for the lower limbs, pelvis, abdomen, chest, and cerebral, respectively. The lens of the eye, uterus, and ovaries received high radiation doses compared to thyroid and testis. The overall patient risk per CTA procedure ranged between 15 and 36 cancer risks per 1 million procedures. Patient risk from CTA procedures is high during neck and abdomen procedures. Special concern should be provided to the lens of the eye and thyroid during brain CTA procedures. Patient dose reduction is an important consideration; thus, staff should optimize the radiation dose during CTA procedures.     

In vivo skin dose measurement using MOSkin detectors in tangential breast radiotherapy

The purpose of this study is to measure patient skin dose in tangential breast radiotherapy. Treatment planning dose calculation algorithm such as Pencil Beam Convolution (PBC) and in vivo dosimetry techniques such as radiochromic film can be used to accurately monitor radiation doses at tissue depths, but they are inaccurate for skin dose measurement. A MOSFET-based (MOSkin) detector was used to measure skin dose in this study. Tangential breast radiotherapies (“bolus” and “no bolus”) were simulated on an anthropomorphic phantom and the skin doses were measured. Skin doses were also measured in 13 patients undergoing each of the techniques. In the patient study, the EBT2 measurements and PBC calculation tended to over-estimate the skin dose compared with the MOSkin detector (p < 0.05) in the “no bolus radiotherapy”. No significant differences were observed in the “bolus radiotherapy” (p > 0.05). The results from patients were similar to that of the phantom study. This shows that the EBT2 measurement and PBC calculation, while able to predict accurate doses at tissue depths, are inaccurate in predicting doses at build-up regions. The clinical application of the MOSkin detectors showed that the average total skin doses received by patients were 1662 ± 129 cGy (medial) and 1893 ± 199 cGy (lateral) during “no bolus radiotherapy”. The average total skin doses were 4030 ± 72 cGy (medial) and 4004 ± 91 cGy (lateral) for “bolus radiotherapy”. In some cases, patient skin doses were shown to exceed the dose toxicity level for skin erythema. Hence, a suitable device for in vivo dosimetry is necessary to accurately determine skin dose.