Monte Carlo dose verification for a single-isocenter VMAT plan in multiple brain metastases

The purpose of this study was to verify the accuracy of dose calculation algorithms of a treatment planning system for a single-isocenter volumetric modulated arc therapy (VMAT) plan in multiple brain metastases, by comparing the dose distributions of treatment planning system with those of Monte Carlo (MC) simulations. We used a multitarget phantom containing 9 acrylic balls with a diameter of 15.9 mm inside a Lucy phantom measuring 17 × 17 × 17 cm³. Seven VMAT plans were created using the multitarget phantom: 1 multitarget plan (MTP) and 6 single target plans (STP). Three of the STP plans had a large jaw field setting, almost equivalent to that of the MTP, while the other plans had a jaw field setting fitted to each planning target volume. The isocenter for all VMAT plans was set to the center of the phantom. The VMAT dose distributions were calculated using the analytical anisotropic algorithm (AAA) and were also recalculated through Acuros XB (AXB) and MC simulations under the same irradiation conditions. The AAA and AXB methods tended to overestimate dosage compared with the MC method in the MTP and in STPs with large jaw field settings. The dose distribution in single-isocenter VMAT plans for multiple brain metastases was influenced by jaw field settings. Finally, we concluded that MC-VMAT dose calculations are useful for 3D dose verification of single-isocenter VMAT plans for multiple brain metastases.     

Dependence of volume dose indices on dose calculation algorithms for VMAT-SBRT plans for peripheral lung tumor

The purpose of this study was to investigate the dependence of volume dose indices on dose calculation algorithms for volumetric modulated arc therapy (VMAT) for stereotactic body radiotherapy (SBRT) plans to treat peripheral lung tumors by comparing them with those of Monte Carlo (MC) calculations. VMAT-SBRT plans for peripheral lung tumors were created using the Eclipse treatment planning system (TPS) for 24 patients with nonsmall cell lung cancer. VMAT dose distributions for gross tumor volume (GTV), internal target volume (ITV), and planning target volume (PTV) were calculated using the analytical anisotropic algorithm (AAA), the Acuros XB (AXB) algorithm, and a MC algorithm. VMAT dose distributions of the 3 algorithms were compared using their volume dose indices from dose volume histograms (DVHs), a dose difference map, and 3-dimensional gamma analysis. The DVHs for GTV and ITV from AAA, AXB, and MC were in good agreement. The difference between the ITV and PTV volume dose indices from AAA and MC increased as D₉₈, D₉₅, D₈₀, D₅₀, and D₂. In particular, the difference between D₉₈ for PTV from AAA and MC was up to 48%. A >5% difference between D₉₅ for PTV from AAA and MC was 11 patients, but only 2 patients for ITV. The volume dose indices for AXB were near those of MC. AAA tended to overestimate the PTV volume dose indices compared to AXB and MC. Thus, we propose that the volume dose indices for the ITV be used because they are independent of dose calculation algorithms.     

Comparison between Acuros XB and Brainlab Monte Carlo algorithms for photon dose calculation

Purpose

The Acuros? XB dose calculation algorithm by Varian and the Monte Carlo algorithm XVMC by Brainlab were compared with each other and with the well-established AAA algorithm, which is also from Varian.

Methods

First, square fields to two different artificial phantoms were applied: (1) a “slab phantom” with a 3?cm water layer, followed by a 2?cm bone layer, a 7?cm lung layer, and another 18?cm water layer and (2) a “lung phantom” with water surrounding an eccentric lung block. For the slab phantom, depth–dose curves along central beam axis were compared. The lung phantom was used to compare profiles at depths of 6 and 14?cm. As clinical cases, the CTs of three different patients were used. The original AAA plans with all three algorithms using open fields were recalculated.

Results

There were only minor differences between Acuros and XVMC in all artificial phantom depth doses and profiles; however, this was different for AAA, which had deviations of up to 13% in depth dose and a few percent for profiles in the lung phantom. These deviations did not translate into the clinical cases, where the dose–volume histograms of all algorithms were close to each other for open fields.

Conclusion

Only within artificial phantoms with clearly separated layers of simulated tissue does AAA show differences at layer boundaries compared to XVMC or Acuros. In real patient CTs, these differences in the dose–volume histogram of the planning target volume were not observed.     

Evaluation of beam modeling for small fields using a flattening filter-free beam

The characteristics of a flattening filter-free (FFF) beam are different from those of a beam with a flattening filter. For small-field dosimetry, the beam data needed by the radiation treatment planning system (RTPS) includes the percent depth dose (PDD), off-center ratio (OCR), and output factor (OPF) for field sizes down to 3 × 3 cm² to calculate the beam model. The purpose of this study was to evaluate the accuracy of calculations for the FFF beam by the Eclipse^? treatment planning system for field sizes smaller than 3 × 3 cm² (2 × 2 and 1 × 1 cm²). We used 6X and 10X FFF beams by the Varian TrueBeam^? to produce. The AAA and AXB algorithms of the Eclipse were used to compare the Monte Carlo (MC) calculation and the measurements from three dosimeters, a diode detector, a PinPoint dosimeter, and EBT3 film. The PDD curves and the penumbra width in the OCR calculated by the Eclipse, measured data, and those from the MC calculations were in good agreement to within ±2.8 % and ±0.6 mm, respectively. However, the difference in the OPF values between AAA and AXB for a field size of 1 × 1 cm² was 5.3 % for the 6X FFF beam and 7.6 % for the 10X FFF beam. Therefore, we have to confirm the small field data that is included for the RTPS commission procedures.     

Accuracy of dose calculation algorithms for virtual heterogeneous phantoms and intensity-modulated radiation therapy in the head and neck

This study verified the dose calculation accuracy of the analytical anisotropic algorithm (AAA), Acuros XB version 10 (AXB10), and version 11 (AXB11) installed in an Eclipse treatment planning system, by comparing with Monte Carlo (MC) simulations. First, the algorithms were compared in terms of dose distributions using four types of virtual heterogeneous multi-layer phantom for 6 and 15 MV photons. Next, the clinical head and neck intensity-modulated radiation therapy (IMRT) dose distributions for 6 MV photons were evaluated using dose volume histograms (DVHs) and three-dimensional gamma analysis. In percentage depth doses (PDDs) for virtual heterogeneous phantoms, AAA overestimated absorbed doses in the air cavity, bone, and aluminum in comparison with MC, AXB10, and AXB11. The PDDs of AXB10 almost agreed with those of MC and AXB11, except for the air cavity. The dose in the air cavity was higher for AXB10 than for AXB11, because their electron cutoff energies are set at 500 and 200 keV, respectively. For head and neck IMRT dose distributions, the D₉₅ in the clinical target volume (CTV) for AAA was almost the same as that for AXB10 and was approximately 7 % larger than that for MC. Comparing each approach with MC using a criterion of 3 %/3 mm, the pass rates for AXB10, AXB11, and AAA were 92.4, 94.7, and 90.4 % in the CTV, respectively. In conclusion, AAA produces dose errors in heterogeneous regions, while AXB11 provides calculation accuracy comparable to MC. AXB10 overestimates the dose in regions that include an air cavity.     

Dosimetric comparison of analytical anisotropic algorithm and the two dose reporting modes of Acuros XB dose calculation algorithm in volumetric modulated arc therapy of carcinoma lung and carcinoma prostate

Volumetric Modulated Arc Therapy (VMAT) is an important modality for radical radiotherapy of all major treatment sites. This study aims to compare Analytical Anisotropic Algorithm (AAA) and the two dose-reporting modes of Acuros XB (AXB) algorithm -the dose to medium option (D_m) and the dose to water option (D_w) in Volumetric Modulated Arc Therapy (VMAT) of carcinoma lung and carcinoma prostate. We also compared the measured dose with Treatment Planning System calculated dose for AAA and the two dose reporting options of Acuros XB using Electronic Portal Imaging Device (EPID) and ArcCHECK phantom. Treatment plans of twenty patients each who have already undergone radiotherapy for cancer of lung and cancer of prostate were selected for the study. Three sets of VMAT plans were generated in Eclipse Treatment Planning System (TPS), one with AAA and two plans with Acuros-D_m and Acuros-D_w options. The Dose Volume Histograms (DVHs) were compared and analyzed for Planning Target Volume (PTV) and critical structures for all the plans. Verification plans were created for each plan and measured doses were compared with TPS calculated doses using EPID and ArcCHECK phantom for all the three algorithms. For lung plans, the mean dose to PTV in the AXB-D_w plans was higher by 1.7% and in the AXB-D_m plans by 0.66% when compared to AAA plans. For prostate plans, the mean dose to PTV in the AXB-D_w plans was higher by 3.0% and in the AXB-D_m plans by 1.6% when compared to AAA plans. There was no difference in the Conformity Index (CI) between AAA and AXB-D_m and between AAA and AXB-D_w plans for both sites. But the homogeneity worsened in AXB-D_w and AXB-D_m plans when compared to AAA plans for both sites. AXB-D_w calculated higher dose values for PTV and all the critical structures with significant differences with one or two exceptions. Point dose measurements in ArcCHECK phantom showed that AXB-D_m and AXB-D_w options showed very small deviations with measured dose distributions than AAA for both sites. Results of EPID QA also showed better pass rates for AXB-D_w and AXB-D_m than AAA for both sites when gamma analysis was done for 3%/3 mm and 2%/2 mm criteria. With reference to the results, it is always better to choose Acuros algorithm for dose calculations if it is available in the TPS. AXB-D_w plans showed very high dose values in the PTV when compared to AAA and AXB-D_m in both sites studied. Also, the volume of PTV receiving 107% dose was significantly high in AXB-D_w plans compared to AXB-D_m plans in sites involving high density bones. Considering the results of dosimetric comparison and QA measurements, it is always better to choose AXB-D_m algorithm for dose calculations for all treatment sites especially when high density bony structures and complex treatment techniques are involved. For patient specific QA purposes, choosing AXB-D_m or AXB-D_w does not make any significant difference between calculated and measured dose distributions.     

Volumetric evaluation of an alternative bladder point in brachytherapy for locally advanced cervical cancer

Purpose

To evaluate an alternative dose point, so-called ALG (for Alain Gerbaulet), for the bladder in comparison to the International Commission on Radiation Units and Measurements (ICRU) point and D2cm³ (minimal dose to maximally exposed 2 cm³) in a large cohort of patients with locally advanced cervical cancer treated with external beam radiotherapy followed by image-guided pulsed dose rate brachytherapy.

Methods and materials

For each patient, the ALG point was constructed 1.5 cm above the ICRU bladder, parallel to the tandem (coronal and sagittal planes). The dosimetric data from 162 patients were reviewed.

Results

Average doses to ALG and bladder points were 19.40 Gy?±?7.93 and 17.14?±?8.70, respectively (p?=?0.01). The 2 cm³ bladder dose averaged 24.40?±?6.77 Gy. Ratios between D2cm³ and dose points were 1.37?±?0.46 and 1.68?±?0.74 (p?<?0.001) for ALG and ICRU points, respectively. Both dose points appeared correlated with D2cm³ (p?<?0.001) with coefficients of determination (R²) of 0.331 and 0.399 respectively. The estimated dose to the ICRU point of the rectum was 12.77?±?4.21 and 15.76?±?5.94 for D2cm³ (p?<?0.0001). Both values were significantly correlated (p?<?0.0001, R²?=?0.485).

Conclusion

The ALG point underestimates the D2cm³, but its mean on a large cohort is closer to D2cm³ than the dose to ICRU point. However, it shows great variability between cases and the weak strength of its correlation to D2cm³ indicates that it is not a good surrogate for individual volumetric evaluation of the dose D2cm³.     

PET SUV correlates with radionuclide uptake in peptide receptor therapy in meningioma

Purpose

To investigate whether the tumour uptake of radionuclide in peptide receptor radionuclide therapy (PRRT) of meningioma can be predicted by a PET scan with ⁶⁸Ga-labelled somatostatin analogue.

Methods

In this pilot trial, 11 meningioma patients with a PET scan indicating somatostatin receptor expression received PRRT with 7.4?GBq ¹⁷⁷Lu-DOTATOC or ¹⁷⁷Lu-DOTATATE, followed by external beam radiotherapy. A second PET scan was scheduled for 3?months after therapy. During PRRT, multiple whole-body scans and a SPECT/CT scan of the head and neck region were acquired and used to determine the kinetics and dose in the voxel with the highest radionuclide uptake within the tumour. Maximum voxel dose and retention of activity 1?h after administration in PRRT were compared to the maximum standardized uptake values (SUV_max) in the meningiomas from the PET scans before and after therapy.

Results

The median SUV_max in the meningiomas was 13.7 (range 4.3 to 68.7), and the maximum fractional radionuclide uptake in voxels of size 0.11?cm3 was a median of 23.4?×?10^?6 (range 0.4?×?10^?6 to 68.3?×?10^?6). A strong correlation was observed between SUV_max and the PRRT radionuclide tumour retention in the voxels with the highest uptake (Spearman’s rank test, P?max and the therapeutic uptake (r?=?0.95) and between SUV_max and the maximum voxel dose from PRRT (r?=?0.76). Observed absolute deviations from the values expected from regression were a median of 5.6?×?10^?6 (maximum 9.3?×?10^?6) for the voxel fractional radionuclide uptake and 0.40?Gy per GBq (maximum 0.85?Gy per GBq) ¹⁷⁷Lu for the voxel dose from PRRT.

Conclusion

PET with ⁶⁸Ga-labelled somatostatin analogues allows the pretherapeutic assessment of tumour radionuclide uptake in PRRT of meningioma and an estimate of the achievable dose.     

Normal liver tissue change after proton beam therapy

Purpose

Normal liver tissue changes after proton beam therapy (PBT) were investigated in patients at 1 and 2 years after the therapy.

Materials and methods

Changes in normal liver tissue volume were examined. The dose distribution of the normal liver tissue was also simulated on the follow-up CTs.

Results

The normal liver tissue volume was 1149?±?215 cm³ before treatment, 1089?±?188 cm³ at 1 year, and 1080?±?236 cm³ at 2 years after treatment. The normal liver tissue volume was increased in 10 and decreased in 20 patients at 2 years and was smaller than that before the treatment in total (P?=?0.03). The simulated volume that received more than 30 Gray equivalent [V30 (cm³)] at 1 year was 258?±?187 cm³ and that at 2 years (244?±?171 cm³) was smaller than that before treatment (297?±?140 cm³) (P?=?0.03).

Conclusions

The changes in the shape and volume of normal liver tissue are not constant, which cause a large dose distribution discrepancy in the normal liver for 2 years. Therefore, careful consideration of the dose distribution of normal liver tissue is required when planning re-irradiation.

     

CT pulmonary angiography using organ dose modulation with an iterative reconstruction algorithm and 3D Smart mA in different body mass indices: image quality and radiation dose

Objective

To investigate the differences in imaging quality and radiation dose in CT pulmonary angiography (CTPA) by organ dose modulation and 3D Smart mA modulation in different body mass indices (BMIs) with an adaptive statistical iterative reconstruction (ASiR-V) algorithm.

Methods

Three hundred female patients who underwent CTPA were equally divided into three groups: A (18.5 kg/m^2?≦?BMI?<?24.9 kg/m²), B (24.9 kg/m^2?≦?BMI?<?29.9 kg/m²) and C (29.9 kg/m^2?≦?BMI≦?34.9 kg/m²). The groups were randomly subdivided into two subgroups (n?=?50): A1–A2, B1–B2 and C1–C2. The patients in subgroups A1, B1 and C1 underwent organ dose modulation with the ASiR-V algorithm. The other patients underwent 3D Smart mA modulation. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of all images were calculated after CTPA. Images were then subjectively evaluated using a 5-point scale. The volume CT dose index and dose-length product (DLP) were recorded and their means calculated. The DLP was converted to the effective dose (ED).

Results

In group A, the SNR, CNR, and subjective image scores showed no statistical differences (P?>?0.05). The ED in subgroup A1 was 33.36% lower than that in A2. In group B and C, the variables showed no significant differences between the subgroups B1 and B2 (P?>?0.05), and the subgroups C1 and C2 (P?>?0.05), respectively. The ED in subgroup B1 and C1 was 36.15 and 38.22% lower than that in B2 and C2, respectively.

Conclusions

Using organ dose modulation and applying the ASiR-V algorithm can more effectively reduce the radiation dose in CTPA than in 3D Smart mA modulation, while maintaining image quality.

     

The phenomenon of drop in output at larger field sizes for telecobalt units

It is known that the output factors (OPFs) for external-beam radiotherapy units increase with field size due to increased scattered radiation from the collimator system. Saturation in the OPF value is generally reported beyond approximately 30 × 30 cm². For the first time, to the best of our knowledge, we report on a drop in OPF values, although marginal, measured for a telecobalt machine beyond the 38 × 38 cm² field size. We believe that reporting and explaining the results will lead to a better understanding of the scatter composition of the radiation from telecobalt machines. This also has the potential to impact the estimation of low dose regions in patients, in addition to being a purely scientific inquiry. We used Monte Carlo (MC) simulations to validate the measured values. The MC data showed that the decrease in OPF was due to decreased scatter from the machine head.     

Improving TBI lung dose calculations: Can the treatment planning system help?

Lung toxicity is a serious concern during total body irradiation (TBI). Therefore, evaluation of accurate dose calculation when using lung blocks is of utmost importance. Existing clinical treatment planning systems can perform the calculation but there are large inaccuracies when calculating volumetric dose at extended distances in the presence of high atomic number materials. Percent depth dose and absolute dose measurements acquired at 400 cm SSD with a cerrobend block were compared with calculated values from the Eclipse treatment planning system using AAA and Acuros. The block was simulated in 2 ways; (1) manually drawing a contour to mimic the block and (2) creating a virtual block in the accessory tray. Although the relative dose distribution was accurately calculated, larger deviations of around 50% and 40% were observed between measured depth dose and absolute dose with AAA and Acuros, respectively. Deviations were reduced by optimizing the relative electron density in the contoured block or the transmission factor in the virtual block.     

Small bowel toxicity after high dose spot scanning-based proton beam therapy for paraspinal/retroperitoneal neoplasms

Purpose

Mesenchymal tumours require high-dose radiation therapy (RT). Small bowel (SB) dose constraints have historically limited dose delivery to paraspinal and retroperitoneal targets. This retrospective study correlated SB dose–volume histograms with side-effects after proton radiation therapy (PT).

Patients and methods

Between 1997 and 2008, 31 patients (mean age 52.1 years) underwent spot scanning-based PT for paraspinal/retroperitoneal chordomas (81?%), sarcomas (16?%) and meningiom (3?%). Mean total prescribed dose was 72.3 Gy (relative biologic effectiveness, RBE) delivered in 1.8–2 Gy (RBE) fractions. Mean follow-up was 3.8 years. Based on the pretreatment planning CT, SB dose distributions were reanalysed.

Results

Planning target volume (PTV) was defined as gross tumour volume (GTV) plus 5–7 mm margins. Mean PTV was 560.22 cm³. A mean of 93.2?% of the PTV was covered by at least 90?% of the prescribed dose. SB volumes (cm³) receiving doses of 5, 20, 30, 40, 50, 60, 70, 75 and 80 Gy (RBE) were calculated to give V5, V20, V30, V40, V50, V60, V70, V75 and V80 respectively. In 7/31 patients, PT was accomplished without any significant SB irradiation (V5?=?0). In 24/31 patients, mean maximum dose (Dmax) to SB was 64.1 Gy (RBE). Despite target doses of >?70 Gy (RBE), SB received >?50 and >?60 Gy (RBE) in only 61 and 54?% of patients, respectively. Mean SB volumes (cm³) covered by different dose levels (Gy, RBE) were: V20 (n?=?24): 45.1, V50 (n?=?19): 17.7, V60 (n?=?17): 7.6 and V70 (n?=?12): 2.4. No acute toxicity ≥ grade 2 or late SB sequelae were observed.

Conclusion

Small noncircumferential volumes of SB tolerated doses in excess of 60 Gy (RBE) without any clinically-significant late adverse effects. This small retrospective study has limited statistical power but encourages further efforts with higher patient numbers to define and establish high-dose threshold models for SB toxicity in modern radiation oncology.     

Heterogeneity-corrected vs -uncorrected critical structure maximum point doses in breast balloon brachytherapy

Recent studies have reported potentially clinically meaningful dose differences when heterogeneity correction is used in breast balloon brachytherapy. In this study, we report on the relationship between heterogeneity-corrected and -uncorrected doses for 2 commonly used plan evaluation metrics: maximum point dose to skin surface and maximum point dose to ribs. Maximum point doses to skin surface and ribs were calculated using TG-43 and Varian Acuros for 20 patients treated with breast balloon brachytherapy. The results were plotted against each other and fit with a zero-intercept line. Max skin dose (Acuros) = max skin dose (TG-43) ? 0.930 (R² = 0.995). The average magnitude of difference from this relationship was 1.1% (max 2.8%). Max rib dose (Acuros) = max rib dose (TG-43) ? 0.955 (R² = 0.9995). The average magnitude of difference from this relationship was 0.7% (max 1.6%). Heterogeneity-corrected maximum point doses to the skin surface and ribs were proportional to TG-43-calculated doses. The average deviation from proportionality was 1%. The proportional relationship suggests that a different metric other than maximum point dose may be needed to obtain a clinical advantage from heterogeneity correction. Alternatively, if maximum point dose continues to be used in recommended limits while incorporating heterogeneity correction, institutions without this capability may be able to accurately estimate these doses by use of a scaling factor.     

Dose attenuation effect of hip prostheses in a 9-MV photon beam: commercial treatment planning system versus Monte Carlo calculations

Purpose The purpose of this study was to investigate the dosimetric effect of various hip prostheses on pelvis lateral fields treated by a 9-MV photon beam using Monte Carlo (MC) and effective path-length (EPL) methods. Material and methods The head of the Neptun 10 pc linac was simulated using the MCNP4C MC code. The accuracy of the MC model was evaluated using measured dosimetric features including depth dose values and dose profiles in a water phantom. The Alfard treatment planning system (TPS) was used for EPL calculations. A virtual water phantom with dimensions of 30 × 30 × 30 cm³ and a cube with dimensions of 4 × 4 × 4 cm³ made of various metals centered in 12 cm depth was used for MC and EPL calculations. Various materials including titanium, Co-Cr-Mo, and steel alloys were used as hip prostheses. Results Our results showed significant attenuation in absorbed dose for points after and inside the prostheses. Attenuations of 32%, 54% and 55% were seen for titanium, Co-Cr-Mo, and steel alloys, respectively, at a distance of 5 cm from the prosthesis. Considerable dose increase (up to 18%) was found at the water–prosthesis interface due to back-scattered electrons using the MC method. The results of EPL calculations for the titanium implant were comparable to the MC calculations. This method, however, was not able to predict the interface effect or calculate accurately the absorbed dose in the presence of the Co-Cr-Mo and steel prostheses. Conclusion The dose perturbation effect of hip prostheses is significant and cannot be predicted accurately by the EPL method for Co-Cr-Mo or steel prostheses. The use of MC-based TPS is recommended for treatments requiring fields passing through hip prostheses.     

Treatment planning after hydrogel injection during radiotherapy of prostate cancer

Purpose

Imaging for treatment planning shortly after hydrogel injection is optimal for practical purposes, reducing the number of appointments. The aim was to evaluate the actual difference between early and late imaging.

Patients and methods

Treatment planning computed tomography (CT) was performed shortly after injection of 10 ml hydrogel (CT1) and 1–2 weeks later (CT2) for 3 patients. The hydrogel was injected via the transperineal approach after dissecting the space between the prostate and rectum with a saline/lidocaine solution of at least 20-ml. Hydrogel volume and distances between the prostate and rectal wall were compared. Intensity-modulated radiotherapy (IMRT) plans up to a dose of 78 Gy were generated (rectum V₇₀?<?20?%, rectum V₅₀?<?50?%; with the rectum including hydrogel volume for planning).

Results

A mean planning treatment volume of 104 cm³ resulted for a prostate volume of 37 cm³. Hydrogel volumes of 30 and 10 cm³ were determined in CT1 and CT2, respectively. Distances between the prostate and rectal wall at the levels of the base, middle, and apex were 1.7 cm, 1.6 cm, 1.5 cm in CT1 and 1.3 cm, 1.2 cm, 0.8 cm in CT2, respectively, corresponding to a mean decrease of 24, 25, and 47?%. A small overlap between the PTV and the rectum was found only in 1 patient in CT2 (0.2 cm³). The resulting mean rectum (without hydrogel) V₇₅, V₇₀, V₆₀, V₅₀ increased from 0?%, 0?%, 0.6?%, 10?% in CT1 to 0.1?%, 1.2?%, 6?%, 20?% in CT2, respectively.

Conclusion

Treatment planning based on imaging shortly after hydrogel injection overestimates the actual hydrogel volume during the treatment as a result of not-yet-absorbed saline solution and air bubbles.     

The impact of radiological equipment on patient radiation exposure during endovascular aortic aneurysm repair

Objectives

To compare the patient radiation dose during endovascular aortic aneurysm repair (EVAR) using different types of radiological systems: a mobile fluoroscopic C-arm, mobile angiographic and fixed angiographic equipment.

Methods

Dose–area products (DAP) were obtained from a retrospective study of 147 consecutive patients, subjected to 153 EVAR procedures during a 3.5-year period. On the basis of these data, entrance surface dose (ESD) and effective dose (ED) were calculated. EVARs were performed using a fluoroscopic C-arm, mobile or fixed angiographic equipment in 79, 26 and 48 procedures, respectively.

Results

Fluoroscopy times were essentially equivalent for all the systems, ranging from 15 to 19?min. The clinical outcomes were not significantly different among the systems. Statistically significant differences among radiological equipment grouping were found for DAP (mobile C-arm: 32?±?20?Gy?cm²; mobile angiography: 362?±?164?Gy?cm²; fixed angiography: 464?±?274?Gy?cm²; P?<?10^?6), for ESD (mobile C-arm: 0.18?±?0.11?Gy; mobile angiography: 2.0?±?0.8?Gy; fixed angiography: 2.5?±?1.5?Gy; P?<?10^?6) and ED (mobile C-arm: 6.2?±?4.5?mSv; mobile angiography: 64?±?26?mSv; fixed angiography: 129?±?76?mSv; P?<?10^?6).

Conclusions

Radiation dose in EVAR is substantially less with a modern portable C-arm than with a fixed or mobile dedicated angiographic system.

Key Points

? Fluoroscopy during endovascular aortic aneurysm repair can impart a substantial radiation dose. ? Radiation doses during EVAR are higher when using mobile/fixed angiographic systems. ? Mobile C-arm fluoroscopy imparts a lower dose with an equivalent clinical outcome. ? Procedures need to be dose-optimised when using mobile/fixed angiographic systems.     

Effects of bone marrow or mesenchymal stem cell transplantation on oral mucositis (mouse) induced by fractionated irradiation

Background and purpose

Oral mucositis is a severe and dose limiting early side effect of radiotherapy for head-and-neck tumors. This study was initiated to determine the effect of bone marrow- and mesenchymal stem cell transplantation on oral mucositis (mouse tongue model) induced by fractionated irradiation.

Material and methods

Daily fractionated irradiation (5?×?3 Gy/week) was given over 1 (days 0–4) or 3 weeks (days 0–4, 7–11, 14–18). Each protocol was terminated (day 7 or 21) by graded test doses (5 dose groups, 10 animals each) in order to generate complete dose–effect curves. The incidence of mucosal ulceration, corresponding to confluent mucositis grade 3 (RTOG/EORTC), was analyzed as the primary, clinically relevant endpoint. Bone marrow or mesenchymal stem cells were transplanted intravenously at various time points within these fractionation protocols.

Results

Transplantation of 6?×?10⁶, but not of 3?×?10⁶ bone marrow stem cells on day ??1, +?4, +?8, +?11 or +?15 significantly increased the ED₅₀ values (dose, at which an ulcer is expected in 50?% of the mice); transplantation on day +?2, in contrast, was ineffective. Mesenchymal stem cell transplantation on day ??1, 2 or +?8 significantly, and on day +?4 marginally increased the ED₅₀ values.

Conclusion

Transplantation of bone marrow or mesenchymal stem cells has the potential to modulate radiation-induced oral mucositis during fractionated radiotherapy. The effect is dependent on the timing of the transplantation. The mechanisms require further investigation.