Clinical implications of different calculation algorithms in breast radiotherapy: A comparison between pencil beam and collapsed cone convolution

BackgroundThis investigation focused on the clinical implications of the use of the Collapsed Cone Convolution algorithm (CCC) in breast radiotherapy and investigated the dosimetric differences as respect to Pencil Beam Convolution algorithm (PBC).Material and methods15 breast treatment plans produced using the PBC algorithm were re-calculated using the CCC algorithm with the same MUs. In a second step, plans were re-optimized using CCC algorithm with modification of wedges and beam weightings to achieve optimal coverage (CCCr plans). For each patient, dosimetric comparison was performed using the standard tangential technique (SWT) and a forward-planned IMRT technique (f-IMRT).ResultsThe CCC algorithm showed significant increased dose inhomogeneity. Mean and minimum PTV doses decreased by 1.4% and 2.8% (both techniques). Mean V95% decreased to 83.7% and 90.3%, respectively for the SWT and f-IMRT. V95% was correlated to the ratio of PTV and lung volumes into the treatment field. The re-optimized CCCr plans achieved similar target coverage, but high-dose volume was significantly larger (V107%: 7.6% vs 2.3% (SWT), 7.1% vs 2.1% (f-IMRT). There was a significantly increase in the ipsilateral lung volume receiving low doses (V5 Gy: 31.3% vs 26.2% in SWT, 27.0% vs 23.0% in f-IMRT). MUs needed for PTV coverage in CCCr plans were higher by 3%.ConclusionsThe PBC algorithm overestimated PTV coverage in terms of all important dosimetric metrics. If previous clinical experience are based on the use of PBC model, especially needed is discussion between medical physicists and radiation oncologists to fully understand the dosimetric changes.     

Multi-institutional comparison of secondary check of treatment planning using computer-based independent dose calculation for non-C-arm linear accelerators

PurposeThis report covers the first multi-institutional study of independent monitor unit (MU)/dose calculation verification for the CyberKnife, Vero4DRT, and TomoTherapy radiotherapy delivery systems.MethodsA total of 973 clinical treatment plans were collected from 12 institutions. Commercial software employing the Clarkson algorithm was used for verification after a measurement validation study, and the doses from the treatment planning systems (TPSs) and verification programs were compared on the basis of the mean value ± two standard deviations. The impact of heterogeneous conditions was assessed in two types of sites: non-lung and lung.ResultsThe dose difference for all locations was 0.5 ± 7.2%. There was a statistically significant difference (P < 0.01) in dose difference between non-lung (−0.3 ± 4.4%) and lung sites (3.5 ± 6.7%). Inter-institutional comparisons showed that various systematic differences were associated with the proportion of different treatment sites and heterogeneity correction.ConclusionsThis multi-institutional comparison should help to determine the departmental action levels for CyberKnife, Vero4DRT, and TomoTherapy, as patient populations and treatment sites may vary between the modalities. An action level of ±5% could be considered for intensity-modulated radiation therapy (IMRT), non-IMRT, and volumetric modulated arc radiotherapy using these modalities in homogenous and heterogeneous conditions with a large treatment field applied to a large region of homogeneous media. There were larger systematic differences in heterogeneous conditions with a small treatment field because of differences in heterogeneity correction with the different dose calculation algorithms of the primary TPS and verification program.     

Feasibility of setting up generic alert levels for maximum skin dose in fluoroscopically guided procedures

PurposeThe feasibility of setting-up generic, hospital-independent dose alert levels to initiate vigilance on possible skin injuries in interventional procedures was studied for three high-dose procedures (chemoembolization (TACE) of the liver, neuro-embolization (NE) and percutaneous coronary intervention (PCI)) in 9 European countries.MethodsGafchromic® films and thermoluminescent dosimeters (TLD) were used to determine the Maximum Skin Dose (MSD). Correlation of the online dose indicators (fluoroscopy time, kerma- or dose-area product (KAP or DAP) and cumulative air kerma at interventional reference point (K_a,r)) with MSD was evaluated and used to establish the alert levels corresponding to a MSD of 2 Gy and 5 Gy. The uncertainties of alert levels in terms of DAP and K_a,r, and uncertainty of MSD were calculated.ResultsAbout 20–30% of all MSD values exceeded 2 Gy while only 2–6% exceeded 5 Gy. The correlations suggest that both DAP and K_a,r can be used as a dose indicator for alert levels (Pearson correlation coefficient p mostly >0.8), while fluoroscopy time is not suitable (p mostly <0.6). Generic alert levels based on DAP (Gy cm²) were suggested for MSD of both 2 Gy and 5 Gy (for 5 Gy: TACE 750, PCI 250 and NE 400). The suggested levels are close to the lowest values published in several other studies. The uncertainty of the MSD was estimated to be around 10–15% and of hospital-specific skin dose alert levels about 20–30% (with coverage factor k = 1).ConclusionsThe generic alert levels are feasible for some cases but should be used with caution, only as the first approximation, while hospital-specific alert levels are preferred as the final approach.     

Adaptive SBRT by 1.5 T MR-linac for prostate cancer: On the accuracy of dose delivery in view of the prolonged session time

PurposeAdaptive Stereotactic Body Radiotherapy (SBRT) of prostate cancer (PC) by online 1.5 T MRi-guidance prolongs session-time, due to contouring and planning tasks, thus increasing the risk of prostate motion. Hence, the interest to verify the adequacy of the delivered dose.Material and methodsFor twenty PC patients treated by 35 Gy (D_p) in five fractions, daily pre- and post- delivery MRi scans were respectively used for adapt-to-shape (ATS) optimization, and re-computation of the delivered irradiation (D_rec). Two expansion recipes, from Clinical (CTV) to Planning target volume (PTV), which slightly differed in the posterior margin were used for groups I and II, of ten patients each. Plans had to assure D_95% ≥ 95%D_p to PTV, and D_1cc ≤ D_p to rectum, bladder, penile bulb, and urethral planning-risk-volume (urethral-PRV). The adequacy of the delivered dose was estimated by inter-fraction average (ifa) of dose-volume metrics computed from D_rec. A cumulative dose (D_sum) was calculated from the five daily D_rec deformed onto the simulation MRi.ResultsFor each patient, CTV coverage resulted in D_95% > 95%D_p when estimated as ifa by D_rec. No significant difference for D_95% and D_99% metrics to CTV resulted between groups I and II. D_1cc was < D_p for rectum, urethral-PRV, and penile bulb, whereas < 103.5%D_p for the bladder.Significant correlations resulted between metrics computed by D_sum and as ifa by D_rec, by both linear-correlation analysis, and Receiver-Operating-Characteristic curve analysis.ConclusionsOur results for PC-SBRT confirm the adequacy of the delivered dose by ATS with 1.5 T MR-linac, and the consistency between dose-volume metrics computed by D_rec and D_sum.     

Variation of the prescription dose using the analytical anisotropic algorithm in lung stereotactic body radiation therapy

PurposeThe aim of the present investigation was to evaluate the dosimetric variation regarding the analytical anisotropic algorithm (AAA) relative to other algorithms in lung stereotactic body radiation therapy (SBRT). We conducted a multi-institutional study involving six institutions using a secondary check program and compared the AAA to the Acuros XB (AXB) in two institutions.MethodsAll lung SBRT plans (128 patients) were generated using the AAA, pencil beam convolution with the Batho (PBC-B) and adaptive convolve (AC). All institutions used the same secondary check program (simple MU analysis [SMU]) implemented by a Clarkson-based dose calculation algorithm. Measurement was performed in a heterogeneous phantom to compare doses using the three different algorithms and the SMU for the measurements. A retrospective analysis was performed to compute the confidence limit (CL; mean ± 2SD) for the dose deviation between the AAA, PBC, AC and SMU. The variations between the AAA and AXB were evaluated in two institutions, then the CL was acquired.ResultsIn comparing the measurements, the AAA showed the largest systematic dose error (3%). In calculation comparisons, the CLs of the dose deviation were 8.7 ± 9.9% (AAA), 4.2 ± 3.9% (PBC-B) and 5.7 ± 4.9% (AC). The CLs of the dose deviation between the AXB and the AAA were 1.8 ± 1.5% and −0.1 ± 4.4%, respectively, in the two institutions.ConclusionsThe CL of the AAA showed much larger variation than the other algorithms. Relative to the AXB, larger systematic and random deviations still appeared. Thus, care should be taken in the use of AAA for lung SBRT.     

Development of a deformable phantom for experimental verification of 4D Monte Carlo simulations in a deforming anatomy

PurposeTo verify the accuracy of 4D Monte Carlo (MC) simulations, using the 4DdefDOSXYZnrc user code, in a deforming anatomy. We developed a tissue-equivalent and reproducible deformable lung phantom and evaluated 4D simulations of delivered dose to the phantom by comparing calculations against measurements.MethodsA novel deformable phantom consisting of flexible foam, emulating lung tissue, inside a Lucite external body was constructed. A removable plug, containing an elastic tumor that can hold film and other dosimeters, was inserted in the phantom. Point dose and position measurements were performed inside and outside the tumor using RADPOS 4D dosimetry system. The phantom was irradiated on an Elekta Infinity linac in both stationary and moving states. The dose delivery was simulated using delivery log files and the phantom motion recorded with RADPOS.ResultsReproducibility of the phantom motion was determined to be within 1 mm. The phantom motion presented realistic features like hysteresis. MC calculations and measurements agreed within 2% at the center of tumor. Outside the tumor agreements were better than 5% which were within the positional/dose reading uncertainties at the measurement points. More than 94% of dose points from MC simulations agreed within 2%/2 mm compared to film measurements.ConclusionThe deformable lung phantom presented realistic and reproducible motion characteristics and its use for verification of 4D dose calculations was demonstrated. Our 4DMC method is capable of accurate calculations of the realistic dose delivered to a moving and deforming anatomy during static and dynamic beam delivery techniques.     

A multi-institutional study of secondary check of treatment planning using Clarkson-based dose calculation for three-dimensional radiotherapy

PurposeAs there have been few reports on quantitative analysis of inter-institutional results for independent monitor unit (MU) verification, we performed a multi-institutional study of verification to show the feasibility of applying the 3–5% action levels used in the U.S. and Europe, and also to show the results of inter-institutional comparisons.MethodsA total of 5936 fields were collected from 12 institutions. We used commercial software employing the Clarkson algorithm for verification after a validation study of measurement and software comparisons was performed. The doses generated by the treatment planning systems (TPSs) were retrospectively analyzed using the verification software.ResultsMean ± two standard deviations of all locations were 1.0 ± 3.6%. There were larger differences for breast (4.0 ± 4.0%) and for lung (2.5 ± 5.8%). A total of 80% of the fields with differences over 5% of the action level involved breast and lung targets, with 7.2 ± 5.4%. Inter-institutional comparisons showed various systematic differences for field shape for breast and differences in the fields were attributable to differences in reference point placement for lung. The large differences for breast and lung are partially attributable to differences in the methods used to correct for heterogeneity.ConclusionsThe 5% action level may be feasible for verification; however, an understanding of larger differences in breast and lung plans is important in clinical practice. Based on the inter-institutional comparisons, care must be taken when determining an institution-specific action level from plans with different field shape settings and incorrectly placed reference points.     

Validation of 4D Monte Carlo dose calculations using a programmable deformable lung phantom

PurposeTo validate the accuracy of 4D Monte Carlo (4DMC) simulations to calculate dose deliveries to a deforming anatomy in the presence of realistic respiratory motion traces. A previously developed deformable lung phantom comprising an elastic tumor was modified to enable programming of arbitrary motion profiles. 4D simulations of the dose delivered to the phantom were compared with the measurements.MethodsThe deformable lung phantom moving with irregular breathing patterns was irradiated using static and VMAT beam deliveries. Using the RADPOS 4D dosimetry system, point doses were measured inside and outside the tumor. Dose profiles were acquired using films along the motion path of the tumor (S-I). In addition to dose measurements, RADPOS was used to record the motion of the tumor during dose deliveries. Dose measurements were then compared against 4DMC simulations with EGSnrc/4DdefDOSXYZnrc using the recorded tumor motion.ResultsThe agreements between dose profiles from measurements and simulations were determined to be within 2%/2 mm. Point dose agreements were within 2σ of experimental and/or positional/dose reading uncertainties. 4DMC simulations were shown to accurately predict the sensitivity of delivered dose to the starting phase of breathing motions. We have demonstrated that our 4DMC method, combined with RADPOS, can accurately simulate realistic dose deliveries to a deforming anatomy moving with realistic breathing traces. This 4DMC tool has the potential to be used as a quality assurance tool to verify treatments involving respiratory motion. Adaptive treatment delivery is another area that may benefit from the potential of this 4DMC tool.     

Use of a second-dose calculation algorithm to check dosimetric parameters for the dose distribution of a first-dose calculation algorithm for lung SBRT plans

PurposeTo verify lung stereotactic body radiotherapy (SBRT) plans using a secondary treatment planning system (TPS) as an independent method of verification and to define tolerance levels (TLs) in lung SBRT between the primary and secondary TPSs.MethodsA total of 147 lung SBRT plans calculated using X-ray voxel Monte Carlo (XVMC) were exported from iPlan to Eclipse in DICOM format. Dose distributions were recalculated using the Acuros XB (AXB) and the anisotropic analytical algorithm (AAA), while maintaining monitor units (MUs) and the beam arrangement. Dose to isocenter and dose-volumetric parameters, such as D₂, D₅₀, D₉₅ and D₉₈, were evaluated for each patient. The TLs of all parameters between XVMC and AXB (TL_AXB) and between XVMC and AAA (TL_AAA) were calculated as the mean ± 1.96 standard deviations.ResultsAXB values agreed with XVMC values within 3.5% for all dosimetric parameters in all patients. By contrast, AAA sometimes calculated a 10% higher dose in PTV D₉₅ and D₉₈ than XVMC. The TL_AXB and TL_AAA of the dose to isocenter were −0.3 ± 1.4% and 0.6 ± 2.9%, respectively. Those of D₉₅ were 1.3 ± 1.8% and 1.7 ± 3.6%, respectively.ConclusionsThis study quantitatively demonstrated that the dosimetric performance of AXB is almost equal to that of XVMC, compared with that of AAA. Therefore, AXB is a more appropriate algorithm for an independent verification method for XVMC.     

Generating and using patient-specific whole-body models for organ dose estimates in CT with increased accuracy: Feasibility and validation

The estimation of patient dose using Monte Carlo (MC) simulations based on the available patient CT images is limited to the length of the scan. Software tools for dose estimation based on standard computational phantoms overcome this problem; however, they are limited with respect to taking individual patient anatomy into account. The purpose of this study was to generate whole-body patient models in order to take scattered radiation and over-scanning effects into account. Thorax examinations were performed on three physical anthropomorphic phantoms at tube voltages of 80 kV and 120 kV; absorbed dose was measured using thermoluminescence dosimeters (TLD). Whole-body voxel models were built as a combination of the acquired CT images appended by data taken from widely used anthropomorphic voxel phantoms. MC simulations were performed both for the CT image volumes alone and for the whole-body models. Measured and calculated dose distributions were compared for each TLD chip position; additionally, organ doses were determined.MC simulations based only on CT data underestimated dose by 8%–15% on average depending on patient size with highest underestimation values of 37% for the adult phantom at the caudal border of the image volume. The use of whole-body models substantially reduced these errors; measured and simulated results consistently agreed to better than 10%.This study demonstrates that combined whole-body models can provide three-dimensional dose distributions with improved accuracy. Using the presented concept should be of high interest for research studies which demand high accuracy, e.g. for dose optimization efforts.     

Development of a four-dimensional Monte Carlo dose calculation system for real-time tumor-tracking irradiation with a gimbaled X-ray head

PurposeTo develop a four-dimensional (4D) dose calculation system for real-time tumor tracking (RTTT) irradiation by the Vero4DRT.MethodsFirst, a 6-MV photon beam delivered by the Vero4DRT was simulated using EGSnrc. A moving phantom position was directly measured by a laser displacement gauge. The pan and tilt angles, monitor units, and the indexing time indicating the phantom position were also extracted from a log file. Next, phase space data at any angle were created from both the log file and particle data under the dynamic multileaf collimator. Irradiation both with and without RTTT, with the phantom moving, were simulated using several treatment field sizes. Each was compared with the corresponding measurement using films. Finally, dose calculation for each computed tomography dataset of 10 respiratory phases with the X-ray head rotated was performed to simulate the RTTT irradiation (4D plan) for lung, liver, and pancreatic cancer patients. Dose-volume histograms of the 4D plan were compared with those calculated on the single reference respiratory phase without the gimbal rotation [three-dimensional (3D) plan].ResultsDifferences between the simulated and measured doses were less than 3% for RTTT irradiation in most areas, except the high-dose gradient. For clinical cases, the target coverage in 4D plans was almost identical to that of the 3D plans. However, the doses to organs at risk in the 4D plans varied at intermediate- and low-dose levels.ConclusionsOur proposed system has acceptable accuracy for RTTT irradiation in the Vero4DRT and is capable of simulating clinical RTTT plans.     

A retrospective comparison of organ dose and effective dose in percutaneous vertebroplasty performed under CT guidance or using a fixed C-arm with a flat-panel detector

PurposeTo compare the organ-dose and effective-dose (E) delivered to the patient during percutaneous vertebroplasty (PVP) of one thoracic or lumbar vertebra performed under CT guidance or using a fixed C-arm.MethodsConsecutive adult patients undergoing PVP of one vertebra under CT-guidance, with optimized protocol and training of physicians, or using a fixed C-arm were retrospectively included from January 2016 to June 2017. Organ-doses were computed on 16 organs using CT Expo 2.4 software for the CT procedures and PCXMC 2.0 for the fixed C-arm procedures. E was also computed with both software. Dosimetric values per anatomic locations for all procedures were compared using the paired Mann-Whitney-Wilcoxon test.ResultsIn total, 73 patients were analysed (27 men and 46 women, mean age 78 ± 10 years) among whom 35 (48%) underwent PVP under CT guidance and 38 (52%) PVP using a fixed C-arm. The median E was 11.31 [6.54; 15.82] mSv for all PVPs performed under CT guidance and 5.58 [3.33; 8.71] mSv for fixed C-arm and the differences was significant (p<0.001). For lumbar PVP, the organ doses of stomach, liver and colon were significantly higher with CT-scan than with the fixed C-arm: 97% (p=0.02); 21% (p=0.099) and 375% (p=0.002), respectively. For thoracic PVP, the lung organ dose was significantly higher with CT-scan than with the fixed C-arm (127%; p<0.001) and the oesophagus organ doses were not significantly different (p = 0.626).ConclusionThis study showed that the E and the organ dose on directly exposed organs were both higher for PVP performed under CT-guidance than with the fixed C-arm.     

Implementation and evaluation of a transit dosimetry system for treatment verification

PurposeTo evaluate a formalism for transit dosimetry using a phantom study and prospectively evaluate the protocol on a patient population undergoing 3D conformal radiotherapy.MethodsAmorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. The measured EPID dose map was back-projected using the planning CT images to calculate dose at pre-specified points within the patient using commercially available software, EPIgray (DOSIsoft, France). This software compared computed back-projected dose with treatment planning system dose. A series of tests were performed on solid water phantoms (linearity, field size effects, off-axis effects). 37 patients were enrolled in the prospective study.ResultsThe EPID dose response was stable and linear with dose. For all tested field sizes the agreement was good between EPID-derived and treatment planning system dose in the central axis, with performance stability up to a measured depth of 18 cm (agreement within −0.5% at 10 cm depth on the central axis and within −1.4% at 2 cm off-axis). 126 transit images were analysed of 37 3D-conformal patients. Patient results demonstrated the potential of EPIgray with 91% of all delivered fields achieved the initial set tolerance level of Δ_D of 0 ± 5-cGy or %Δ_D of 0 ± 5%.ConclusionsThe in vivo dose verification method was simple to implement, with very few commissioning measurements needed. The system required no extra dose to the patient, and importantly was able to detect patient position errors that impacted on dose delivery in two of cases.     

An assessment of a 3D EPID-based dosimetry system using conventional two- and three-dimensional detectors for VMAT

PurposeTo provide a 3D dosimetric evaluation of a commercial portal dosimetry system using 2D/3D detectors under ideal conditions using VMAT.MethodsA 2D ion chamber array, radiochromic film and gel dosimeter were utilised to provide a dosimetric evaluation of transit phantom and pre-treatment ‘fluence’ EPID back-projected dose distributions for a standard VMAT plan. In-house 2D and 3D gamma methods compared pass statistics relative to each dosimeter and TPS dose distributions.ResultsFluence mode and transit EPID dose distributions back-projected onto phantom geometry produced 2D gamma pass rates in excess of 97% relative to other tested detectors and exported TPS dose planes when a 3%, 3 mm global gamma criterion was applied. Use of a gel dosimeter within a glass vial allowed comparison of measured 3D dose distributions versus EPID 3D dose and TPS calculated distributions. 3D gamma comparisons between modalities at 3%, 3 mm gave pass rates in excess of 92%. Use of fluence mode was indicative of transit results under ideal conditions with slightly reduced dose definition.Conclusions3D EPID back projected dose distributions were validated against detectors in both 2D and 3D. Cross validation of transit dose delivered to a patient is limited due to reasons of practicality and the tests presented are recommended as a guideline for 3D EPID dosimetry commissioning; allowing direct comparison between detector, TPS, fluence and transit modes. The results indicate achievable gamma scores for a complex VMAT plan in a homogenous phantom geometry and contributes to growing experience of 3D EPID dosimetry.     

Determination of the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams

PurposeTo determine the surface dose of a water phantom using a semiconductor detector for diagnostic kilovoltage x-ray beams.MethodsAn AGMS-DM+ semiconductor detector was calibrated in terms of air kerma measured with an ionization chamber. Air kerma was measured for 20 x-ray beams with tube voltages of 50–140 kVp and a half-value layer (HVL) of 2.2–9.7 mm Al for given quality index (QI) values of 0.4, 0.5, and 0.6, and converted to the surface dose. Finally, the air kerma and HVL measured by the AGMS-DM+ detector were expressed as a ratio of the surface dose for 10 × 10 and 20 × 20 cm² fields. The ratio of both was represented as a function of HVL for the given QI values and verified by comparing it with that calculated using the Monte Carlo method.ResultsThe air kerma calibration factor, CF, for the AGMS-DM+ detector ranged from 0.986 to 1.016 (0.9% in k = 1). The CF values were almost independent of the x-ray fluence spectra for the given QI values. The ratio of the surface dose to the air kerma determined by the PTW 30,013 chamber and the AGMS-DM+ detector was less than 1.8% for the values calculated using the Monte Carlo method, and showed a good correlation with the HVL for the given QI values.ConclusionIt is possible to determine the surface dose of a water phantom from the air kerma and HVL measured by a semiconductor detector for given QI values.     

Monte Carlo simulation of the dose distribution of ICRP adult reference computational phantoms for acquisitions with a 320 detector-row cone-beam CT scanner

PurposeThe purpose of this study was to develop and validate a Monte Carlo (MC) simulation tool for patient dose assessment for a 320 detector-row CT scanner, based on the recommendations of International Commission on Radiological Protection (ICRP). Additionally, the simulation was applied on four clinical acquisition protocols, with and without automatic tube current modulation (TCM).MethodsThe MC simulation was based on EGS4 code and was developed specifically for a 320 detector-row cone-beam CT scanner. The ICRP adult reference phantoms were used as patient models. Dose measurements were performed free-in-air and also in four CTDI phantoms: 150 mm and 350 mm long CT head and CT body phantoms. The MC program was validated by comparing simulations results with these actual measurements acquired under the same conditions. The measurements agreed with the simulations across all conditions within 5%. Patient dose assessment was performed for four clinical axial acquisitions using the ICRP adult reference phantoms, one of them using TCM.ResultsThe results were nearly always lower than those obtained from other dose calculator tools or published in other studies, which were obtained using mathematical phantoms in different CT systems. For the protocol with TCM organ doses were reduced by between 28 and 36%, compared to the results obtained using a fixed mA value.ConclusionsThe developed simulation program provides a useful tool for assessing doses in a 320 detector-row cone-beam CT scanner using ICRP adult reference computational phantoms and is ready to be applied to more complex protocols.     

Dosimetric impact of Acuros XB on cervix radiotherapy using RapidArc technique: a dosimetric study

BackgroundAcuros XB (AXB) may predict better rectal toxicities and treatment outcomes in cervix carcinoma. The aim of the study was to quantify the potential impact of AXB computations on the cervix radiotherapy using the RapidArc (RA ) technique as compared to anisotropic analytical algorithm (AA) computations.Materials and methodsA cohort of 30 patients previously cared for cervix carcinoma (stages II–IIIB) was selected for the present analysis. The RA plans were computed using AA and AXB dose computation engines under identical beam setup and MLC pattern.ResultsThere was no significant (p > 0.05) difference in D_95% and D_98% to the planning target volume (PTV); moreover, a significant (p < 0.05) rise was noticed for mean dose to the PTV (0.26%), D_50% (0.26%), D_2% (0.80%) and V_110% (44.24%) for AXB computation as compared to AA computations. Further, AXB estimated a significantly (p < 0.05) lower value for maximum and minimum dose to the PTV. Additionally, there was a significant (p < 0.05) reduction observed in mean dose to organs at risk (OARs) for AXB computation as compared to AA, though the reduction in mean dose was non-significant (p > 0.05) for the rectum. The maximum difference observed was 4.78% for the rectum V_50Gy, 1.72%, 1.15% in mean dose and 2.22%, 1.48% in D_2% of the left femur and right femur, respectively, between AA and AXB dose estimations.ConclusionFor similar target coverage, there were significant differences observed between the AAA and AXB computations. AA underestimates the V_50Gy of the rectum and overestimates the mean dose and D_2% for femoral heads as compared to AXB. Therefore, the use of AXB in the case of cervix carcinoma may predict better rectal toxicities and treatment outcomes in cervix carcinoma using the RA technique.     

Validation of a dose tracking software for skin dose map calculation in interventional radiology

PurposeValidate the skin dose software within the radiation dose index monitoring system NEXO[DOSE]® (Bracco Injeneering S.A., Lausanne, Switzerland). It provides the skin dose distribution in interventional radiology (IR) procedures.MethodsTo determine the skin dose distribution and the Peak Skin Dose (PSD) in IR procedures, the software uses exposure and geometrical parameters taken from the radiation dose structured report and additional information specific to each angiographic system. To test the accuracy of the software, GafChromic® XR-RV3 films, wrapped under a cylindrical PMMA phantom, were irradiated with different setups. Calculations and films results are compared in terms of absolute dose and geometric accuracy, using two angiographic systems (Philips Integris Allura FD20, Siemens AXIOM-ArtisZeego).ResultsCalculated and film measured PSD values agree with an average difference of 7% ± 5%. The discrepancies in dose evaluation increase up to 33% in lower dose regions, because the algorithm does not consider the out-of-field scatter contribution of the neighboring fields, which is more significant in these areas. Regarding the geometric accuracy, the differences between the simulated dose spatial distributions and the measured ones are<3 mm (4%) in simple tests and 5 mm (5%) in setups closer to clinical practice. Moreover, similar results are obtained for the two studied angiographic system vendors.ConclusionsNEXO[DOSE]® provides an accurate skin dose distribution and PSD estimate. It will allow faster and more accurate monitoring of patient follow-up in the future.     

Setup accuracy and dose attenuation of a wooden immobilization system for lung stereotactic body radiotherapy

BackgroundWe evaluated the setup error and dose absorption of an immobilization system with a shell and wooden baseplate (SW) for lung stereotactic body radiotherapy (SBRT).Materials and methodsSetup errors in 109 patients immobilized with an SW or BodyFix system (BF) were compared. Dose attenuation rates of materials for baseplates were measured with an ion-chamber. Ionization measurements were performed from 90° to 180° gantry angle in 10° increments, with the ball water equivalent phantom placed at the center of the wood and carbon baseplates whose effects on dose distribution were compared using an electron portal imaging device.ResultsThe ratio for the anterior-posterior, cranial-caudal, and right-left of the cases within 3-mm registered shifts in interfractional setup error were 90.9%, 89.2%, and 97.4% for the SW, and 93.2%, 91.6%, and 98.0% for the BF, respectively. For intrafractional setup error, 98.3%, 97.4%, and 99.1% for the SW and 96.6%, 95.8%, and 98.7% for the BF were within 3-mm registered shifts, respectively. In the center position, the average (minimum/maximum) dose attenuation rates from 90° to 180° for the wooden and carbon baseplates were 0.5 (0.1/2.8)% and 1.0 (–0.1/10.1)% with 6 MV, respectively. The gamma passing rates of 2%/2 mm for the wooden and carbon baseplates were 99.7% and 98.3% (p < 0.01).ConclusionsThe immobilization system with an SW is effective for lung SBRT since it is comparable to the BF in setup accuracy. Moreover, the wooden baseplate had lower radiation attenuation rates and affected the dose distribution less than the carbon baseplate.