Energy spectrum and dose enhancement due to the depth of the Lipiodol position using flattened and unflattened beams

Aim

Lipiodol was used for stereotactic body radiotherapy combining trans arterial chemoembolization. Lipiodol used for tumour seeking in trans arterial chemoembolization remains in stereotactic body radiation therapy. In our previous study, we reported the dose enhancement effect in Lipiodol with 10× flattening-filter-free (FFF). The objective of our study was to evaluate the dose enhancement and energy spectrum of photons and electrons due to the Lipiodol depth with flattened (FF) and FFF beams.

Dosimetry of the left anterior descending coronary artery in left breast cancer patients treated with postoperative external radiotherapy

Aim

To evaluate the dose distribution to the left anterior descending (LAD) coronary artery in patients treated with postoperative three-dimensional conformal radiotherapy (3DCRT).

Is volumetric modulated arc therapy with constant dose rate a valid option in radiation therapy for head and neck cancer patients?

Background

Intensity-modulated radiotherapy (IMRT) improves dose distribution in head and neck (HN) radiation therapy. Volumetric-modulated arc therapy (VMAT), a new form of IMRT, delivers radiation in single or multiple arcs, varying dose rates (VDR-VMAT) and gantry speeds, has gained considerable attention. Constant dose rate VMAT (CDR-VMAT) associated with a fixed gantry speed does not require a dedicated linear accelerator like VDR-VMAT. The present study explored the feasibility, efficiency and delivery accuracy of CDR-VMAT, by comparing it with IMRT and VDR-VMAT in treatment planning for HN cancer.

Local control rates in stereotactic body radiotherapy (SBRT) of lung metastases associated with the biologically effective dose

AimTo evaluate dose differences in lung metastases treated with stereotactic body radiotherapy (SBRT), and the correlation with local control, regarding the dose algorithm, target volume and tissue density.BackgroundSeveral studies showed excellent local control rates in SBRT for lung metastases, with different fractionation schemes depending on the tumour location or size. These results depend on the dose distributions received by the lesions in terms of the tissue heterogeneity corrections performed by the dose algorithms.Materials and methodsForty-seven lung metastases treated with SBRT, using intrafraction control and respiratory gating with internal fiducial markers as surrogates (ExacTrac, BrainLAB AG), were calculated using Pencil Beam (PB) and Monte Carlo (MC) (iPlan, BrainLAB AG).Dose differences between both algorithms were obtained for the dose received by 99% (D_99%) and 50% (D_50%) of the planning treatment volume (PTV). The biologically effective dose delivered to 99% (BED_99%) and 50% (BED_50%) of the PTV were estimated from the MC results. Local control was evaluated after 24 months of median follow-up (range: 3–52 months).ResultsThe greatest variations (40.0% in ΔD_99% and 38.4% in ΔD_50%) were found for the lower volume and density cases. The BED_99% and BED_50% were strongly correlated with observed local control rates: 100% and 61.5% for BED_99% > 85 Gy and <85 Gy (p < 0.0001), respectively, and 100% and 58.3% for BED_50% > 100 Gy and <100 Gy (p < 0.0001), respectively.ConclusionsLung metastases treated with SBRT, with delivered BED_99% > 85 Gy and BED_50% > 100 Gy, present better local control rates than those treated with lower BED values (p = 0.001).     

Hippocampal dose during Linac-based stereotactic radiotherapy for brain metastases: An observational study

IntroductionAim of the present study is to evaluate homolateral and contralateral hippocampus (H-H, C-H, respectively) dose during Fractionated Stereotactic Radiotherapy (FSRT) or Radiosurgery (SRS) for brain metastases (BM).Materials & methodsPatients with BM < 5, size ≤ 30 mm, KPS ≥ 80 and a life expectancy > 3 months, were considered for SRS/FSRT (total dose 15–30 Gy, 1–5 fractions). For each BM, a Flattening Filter Free (FFF) Volumetric Modulated Arc Therapy (VMAT) plan was generated with one or two arcs. Hippocampi were not considered during optimizations phase and were contoured and evaluated retrospectively in terms of dose: the Dmedian, Dmean, D0.1cc and the V1Gy, V2Gy, V5Gy and V10Gy were analyzed.ResultsFrom April 2014 to December 2015, 81 BM were treated with FFF-FSRT/SRS. For the H-H, the average values of Dmedian, Dmean and D0.1cc were 1.5Gy, 1.54Gy and 2.2Gy, respectively, while the V1Gy, V2Gy, V5Gy and V10Gy values were 25%, 8.9%, 8.9% and 2.1%, respectively. For the C–H, the average Dmedian, Dmean and D0.1 cc were 0.7Gy, 0.7Gy, 0.9Gy, respectively, while the average values of V1Gy, V2Gy, V5Gy and V10Gy were 18%, 10.2%, 2.8% and 1.4%, respectively. Tumor dimension, tumor cranial-caudal length and the distance between BM and H-H were correlated to Dmedian, Dmean and D0.1cc. For C-H, only the distance from PTV was correlated with a dose reduction.ConclusionDuring FFF-FSRT/SRS, hippocampus received a negligible dose. Despite its clinical significance is still under evaluation, in patients with a long life expectancy, H-H should be considered during Linac-based FSRT/SRS.     

Advanced optimization methods for whole pelvic and local prostate external beam therapy

PurposeRadiation treatment planning inherently involves multiple conflicting planning goals, which makes it a suitable application for multicriteria optimization (MCO). This study investigates a MCO algorithm for VMAT planning (VMAT–MCO) for prostate cancer treatments including pelvic lymph nodes and uses standard inverse VMAT optimization (sVMAT) and Tomotherapy planning as benchmarks.MethodsFor each of ten prostate cancer patients, a two stage plan was generated, consisting of a stage 1 plan delivering 22 Gy to the prostate, and a stage 2 plan delivering 50.4 Gy to the lymph nodes and 56 Gy to the prostate with a simultaneous integrated boost. The single plans were generated by three planning techniques (VMAT–MCO, sVMAT, Tomotherapy) and subsequently compared with respect to plan quality and planning time efficiency.ResultsPlan quality was similar for all techniques, but sVMAT showed slightly better rectum (on average D_mean −7%) and bowel sparing (D_mean −17%) compared to VMAT–MCO in the whole pelvic treatments. Tomotherapy plans exhibited higher bladder dose (D_mean +42%) in stage 1 and lower rectum dose (D_mean −6%) in stage 2 than VMAT–MCO. Compared to manual planning, the planning time with MCO was reduced up to 12 and 38 min for stage 1 and 2 plans, respectively.ConclusionMCO can generate highly conformal prostate VMAT plans with minimal workload in the settings of prostate-only treatments and prostate plus lymph nodes irradiation. In the whole pelvic plan manual VMAT optimization led to slightly improved OAR sparing over VMAT–MCO, whereas for the primary prostate treatment plan quality was equal.     

Dosimetric evaluation of image based brachytherapy using tandem ovoid and tandem ring applicators

Aim

The aim of the study is to evaluate the differences in dosimetry between tandem-ovoid and tandem-ring gynaecologic brachytherapy applicators in image based brachytherapy.

Monte Carlo calculation of photo-neutron dose produced by circular cones at 18 MV photon beams

Aim

The aim of this study is to calculate neutron contamination at the presence of circular cones irradiating by 18 MV photons using Monte Carlo code.

Voxel-by-voxel correlation between radiologically radiation induced lung injury and dose after image-guided,intensity modulated radiotherapy for lung tumors

PurposeTo correlate radiation dose to the risk of severe radiologically-evident radiation-induced lung injury (RRLI) using voxel-by-voxel analysis of the follow-up computed tomography (CT) of patients treated for lung cancer with hypofractionated helical Tomotherapy.Methods and materialsThe follow-up CT scans from 32 lung cancer patients treated with various regimens (5, 8, and 25 fractions) were registered to pre-treatment CT using deformable image registration (DIR). The change in density was calculated for each voxel within the combined lungs minus the planning target volume (PTV). Parameters of a Probit formula were derived by fitting the occurrences of changes of density in voxels greater than 0.361 g cm⁻³ to the radiation dose. The model’s predictive capability was assessed using the area under receiver operating characteristic curve (AUC), the Kolmogorov-Smirnov test for goodness-of-fit, and the permutation test (P_test).ResultsThe best-fit parameters for prediction of RRLI 6 months post RT were D₅₀ of 73.0 (95% CI 59.2.4–85.3.7) Gy, and m of 0.41 (0.39–0.46) for hypofractionated (5 and 8 fractions) and D₅₀ of 96.8 (76.9–123.9) Gy, and m of 0.36 (0.34–0.39) for 25 fractions RT. According to the goodness-of-fit test the null hypothesis of modeled and observed occurrence of RRLI coming from the same distribution could not be rejected. The AUC was 0.581 (0.575–0.583) for fractionated and 0.579 (0.577–0.581) for hypofractionated patients. The predictive models had AUC>upper 95% band of the P_test.ConclusionsThe correlation of voxel-by-voxel density increase with dose can be used as a support tool for differential diagnosis of tumor from benign changes in the follow-up of lung IMRT patients.     

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.     

Postoperative endometrial carcinoma treated with external beam irradiation plus vaginal-cuff brachytherapy. Is there a dose relationship with G2 vaginal complications?

AimTo analyse the possible relationship between the EQD2_(α/β=3Gy) at 2 cm³ of the vagina and late toxicity in vaginal-cuff-brachytherapy (VBT) after external-beam-irradiation (EBRT) for postoperative endometrial carcinoma (EC).Materials and methodsFrom 2014 to 2016, 62 postoperative EC patients were treated with EBRT + VBT. The median EBRT dose was 45 Gy (44 Gy–50.4 Gy). VBT involved a single 7 Gy dose. Toxicity was prospectively evaluated using the RTOG score for the rectum and bladder and the objective LENT-SOMA criteria for the vagina. EQD2_{(α/β = 3Gy)} at 2 cm³ of the most exposed part of the vagina was calculated by the sum of the EBRT + VBT dose. Statistics: Boxplot, Student’s t and Chi-square tests and ROC curves.ResultsMean follow-up: 39.2 months (15–68). Late toxicity: bladder:0 patient; rectum:2 patients-G1; Vagina: 26 patients-17G1, 9G2; median EQD2_(α/β=3Gy) at 2 cm³ in G0-G1 patients was 70.4 Gy(SD2.36), being 72.5 Gy(SD2.94) for G2p. The boxplot suggested a cut-point identifying the absence of G2: 100 % of G2p received >68 Gy, ROC curves showed an area under the curve of 0.72 (sensitivity of 1 and specificity of 0.15).ConclusionsDoses >68 Gy EQD2_(α/β=3Gy) at 2 cm³ to the most exposed area of the vagina were associated with late G2 vaginal toxicity in postoperative EC patients treated with EBRT + VBT suggesting a very good dose limit to eliminate the risk of G2 late toxicity. The specificity obtained indicates the need for prospective analyses.     

Sensitivity and stability of optically stimulated luminescence dosimeters with filled deep electron/hole traps under pre-irradiation and bleaching conditions

PurposeWe aimed to evaluate the characteristics of optically stimulated luminescence dosimeters (OSLDs) with fully filled deep electron/hole traps, and determine the optimal bleaching conditions for these OSLDs to minimize the changes in dose sensitivity or linearity according to the accumulated dose.MethodsInLight nanoDots were used as OSLDs. The OSLDs were first pre-irradiated at a dose greater than 5 kGy to fill the deep electron and hole traps, and then bleached (OSLD_full). OSLD_full characteristics were investigated in terms of the full bleaching, fading, regeneration of luminescence, dose linearity, and dose sensitivity with various bleaching conditions. For comparison, OSLDs with un-filled deep electron/hole traps (OSLD_empty) were investigated in the same manner.ResultsThe fading for OSLD_full exhibited stable signals after 10 min, for 1 and 10 Gy. The mean supra-linear index values for OSLD_full were 1.001 ± 0.001 for doses from 2 to 10 Gy. Small variations in dose sensitivity were obtained for OSLD_full within standard deviations of 0.85% and 0.71%, whereas those of OSLD_empty decreased by 2.3% and 4.2% per 10 Gy for unfiltered and filtered bleaching devices, respectively.ConclusionsUnder the bleaching conditions determined in this study, clinical dosimetry with OSLD_full is highly stable, minimizing the changes in dose sensitivity or linearity for the clinical dose.     

Gated carbon-ion scanning treatment for pancreatic tumour with field specific target volume and organs at risk

ObjectiveTo assess the feasibility of treatment planning for pancreatic tumours subject to respiratory motion using field-specific target volumes (FTV) and field-specific organs at risk (FOAR) using four-dimensional computed tomography (4DCT).MethodsFourteen pancreatic cancer patients underwent 4DCT. Radiation oncologists contoured the gross tumour volume (GTV), clinical target volume (CTV), spinal cord, duodenum, kidneys, and stomach. The gating duty cycle was set to 30 % around exhalation. FTV and FOAR were calculated using the 4DCT dataset. Planning target volumes (PTV) and planning organs at risk volumes (PRV) were defined as equal to FTV and FOAR, respectively. A dose of 55.2 Gy relative biological effectiveness (RBE) was planned to target the PTV from four beam angles. A single field uniform dose (SFUD) plan was selected. The dose distribution, including intrafractional motion changes, was generated.ResultsThe mean volume of target receiving 95 % of the planned doses was 96.4 ± 4.1 % to the GTV and 94.7 ± 0.9 % to the CTV. The highest dose to 2 cc of duodenal volume was 27.5 Gy (RBE). The volume of the stomach receiving ⩾30 Gy (RBE) was <7.0 cc in all patients. All metrics for OARs satisfied dose constraints.ConclusionDose to the CTV was covered sufficiently by the 4DCT-generated FTV, and dose to OARs was reduced by 4DCT-generated FOAR. This methodology may prevent adverse reactions while preserving local tumour control.     

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.