Organ motion quantification and margins evaluation in carbon ion therapy of abdominal lesions

PurposeIn image-guided particle radiotherapy of abdominal lesions, respiratory motion hinders treatment accuracy. In this study, 2D cineMRI data were used to quantify the tumor (GTV) motion and to evaluate the clinical approach based on deriving an internal target volume (ITV) from a planning 4DCT for gating treatments.MethodsSeven patients with abdominal lesions were treated with carbon-ion therapy at the National Centre of Oncological Hadron-therapy (Italy). The MR scan was performed on the same day of the 4DCT acquisition. For four patients, an additional MR was acquired approximately after 1 week. The cineMRI combined with deformable image registration algorithm was used to quantify tumor motion. Afterwards, two ITVs were defined considering (1) all phases (ITV_FB) and (2) only phases within the gating window (ITV_G), and then compared with the clinical (4DCT-derived) ITVs (ITV_CG and ITV_CFB).ResultsTumor residual motion estimated by cineMRI data in the two MRI sessions resulted not significantly different from 4DCT, although cineMRI accounted for cycle-to-cycle variations. The ITV normalized for the GTV median values were higher for ITV_FB with respect to ITV_G, ITV_CFB and ITV_CG. The Hausdorff distances with respect to the GTV were up to 10.55 mm, 3.13 mm, 5.56 mm and 2.51 mm, for ITV_FB, ITV_G, ITV_CFB and ITV_CG, respectively. According to both metrics, ITV_CG and ITV_G were not found significantly different.ConclusionsCineMRI acquisitions allowed to quantify organ motion without delivering additional dose to the patient and to verify treatment margins in gated carbon-ion therapy of abdominal lesions.     

A novel tool for assessing the correlation of internal/external markers during SGRT guided stereotactic ablative radiotherapy treatments

IntroductionAn in-house developed tool was implemented and validated to investigate the skin surface, hepatic dome, and target displacement for stereotactic ablative radiotherapy (SABR) of thoracic/abdominal lesions using a Surface Guided Radiation Therapy (SGRT) system combined with 4D- images.Materials and methodsFourteen consecutive patients with tumors near the hepatic dome undergoing SABR treatments were analyzed. For each patient, a planning 4D-CT and five 4D-CBCT images were acquired. The C-RAD technology was also used to register/monitor the position of the skin reference point (SRP) as an external marker representative of patient breathing. The 4D images were imported in the developed tool, and the absolute maximum height (P_max,dome) of the hepatic dome on the ten respiratory phases was semi-automatically detected. Similarly, the contour of the skin surface was extracted in correspondence with the SRP position. The tool has been validated using an ad hoc modified moving phantom with pre-selected amplitudes and numbers of cycles. The Pearson correlation coefficients and Bland-Altman plots were calculated.ResultsThere was a strong correlation between the skin motion amplitude based on 4D-CBCT and the C-RAD in all the patients (0.90 ± 0.08). Similarly, the mean ± SD of Pearson correlation coefficients of skin and P_max,dome movements registered by 4D-CT and 4D-CBCT were 0.90 ± 0.05 and 0.94 ± 0.05, respectively. The mean ± SD of Pearson correlation coefficients comparing the skin and P_max,dome displacements within each imaging modality were 0.88 ± 0.05 and 0.90 ± 0.05 for 4D-CT and 4D-CBCT, respectively. The SRP displacement during the set-up imaging and the treatment delivery were similar in all the investigated patients. Similar results were obtained for the ad hoc modified phantom in the preliminary validation phase.ConclusionThe strong correlation between the tumor/ hepatic dome and skin displacements confirms that the SGRT approach can be considered appropriate for intra- and inter-fraction motion management in SABR therapy.     

Dosimetric impact of contrast-enhanced 4d computed tomography for stereotactic body radiation therapy of hepatocelluar carcinoma

BackgroundA purpose of the study was to investigate the dosimetric impact of contrast media on dose calculation using average 4D contrast-enhanced computed tomography (4D-CECT) and delayed 4D-CT (d4D-CT) images caused by CT simulation contrast agents for stereotactic body radiation therapy (SBRT) of liver cases.Materials and methodsFifteen patients of liver SBRT treated using the volumetric modulated arc therapy (VMAT) technique were selected retrospectively. 4D-CECT, and d4D-CT were acquired with the Anzai gating system and GE CT. For all patients, gross target volume (GTV) was contoured on the ten phases after rigid registration of both the contrast and delayed scans and merged to generate internal target volume (ITV) on average CT images. Region of interest (ROI) was drawn on contrast images and then copied to the delayed images after rigid registration of two average CT datasets. The treatment plans were generated for contrast enhanced average CT, delayed average CT and contrast enhanced average CT with electron density of the heart overridden.ResultsNo significant dosimetric difference was observed in plans parameters (mean HU value of the liver, total monitor units, total control points, degree of modulation and average segment area) except mean HU value of the aorta amongst the three arms. All the OARs were evaluated and resulted in statistically insignificant variation (p > 0.05) using one way ANOVA analysis.ConclusionsContrast enhanced 4D-CT is advantageous in accurate delineation of tumors and assessing accurate ITV. The treatment plans generated on average 4D-CECT and average d4D-CT have a clinically insignificant effect on dosimetric parameters.     

Tracking,gating, free-breathing,which technique to use for lung stereotactic treatments? A dosimetric comparison

BackgroundThe management of breath-induced tumor motion is a major challenge for lung stereotactic body radiation therapy (SBRT). Three techniques are currently available for these treatments: tracking (T), gating (G) and free-breathing (FB).AimTo evaluate the dosimetric differences between these three treatment techniques for lung SBRT.Materials and methodsPretreatment 4DCT data were acquired for 10 patients and sorted into 10 phases of a breathing cycle, such as 0% and 50% phases defined respectively as the inhalation and exhalation maximum. GTV_ph, PTV_ph (=GTV_ph + 3 mm) and the ipsilateral lung were contoured on each phase.For the tracking technique, 9 fixed fields were adjusted to each PTV_ph for the 10 phases. The gating technique was studied with 3 exhalation phases (40%, 50% and 60%). For the free-breathing technique, ITV_FB was created from a sum of all GTV_ph and a 3 mm margin was added to define a PTV_FB. Fields were adjusted to PTV_FB and dose distributions were calculated on the average intensity projection (AIP) CT. Then, the beam arrangement with the same monitor units was planned on each CT phase.The 3 modalities were evaluated using DVHs of each GTV_ph, the homogeneity index and the volume of the ipsilateral lung receiving 20 Gy (V_20Gy).ResultsThe FB system improved the target coverage by increasing D_mean (75.87_(T)–76.08_(G)–77.49_(FB)Gy). Target coverage was slightly more homogeneous, too (HI: 0.17_{(T and G)}–0.15_(FB)). But the lung was better protected with the tracking system (V_20Gy: 3.82_(T)–4.96_(G)–6.34_(FB)%).ConclusionsEvery technique provides plans with a good target coverage and lung protection. While irradiation with free-breathing increases doses to GTV, irradiation with the tracking technique spares better the lung but can dramatically increase the treatment complexity.     

Evaluation of four-dimensional cone beam computed tomography ventilation images acquired with two different linear accelerators at various gantry speeds using a deformable lung phantom

We evaluated four-dimensional cone beam computed tomography (4D-CBCT) ventilation images (VI_CBCT) acquired with two different linear accelerator systems at various gantry speeds using a deformable lung phantom.The 4D-CT and 4D-CBCT scans were performed using a computed tomography (CT) scanner, an X-ray volume imaging system (Elekta XVI) mounted in Versa HD, and an On-Board Imager (OBI) system mounted in TrueBeam. Intensity-based deformable image registration (DIR) was performed between peak-exhale and peak-inhale images. VI_CBCT- and 4D-CT-based ventilation images (VI_CT) were derived by DIR using two metrics: one based on the Jacobian determinant and one on changes in the Hounsfield unit (HU). Three different DIR regularization values (λ) were used for VI_CBCT. Correlations between the VI_CBCT and VI_CT values were evaluated using voxel-wise Spearman’s rank correlation coefficient (r).In case of both metrics, the Jacobian-based VI_CBCT with a gantry speed of 0.6 deg/sec in Versa HD showed the highest correlation for all the gantry speeds (e.g., λ = 0.05 and r = 0.68). Thus, the r value of the Jacobian-based VI_CBCT was greater or equal to that of the HU-based VI_CBCT. In addition, the ventilation accuracy of VI_CBCT increased at low gantry speeds.Thus, the image quality of VI_CBCT was affected by the change in gantry speed in both the imaging systems. Additionally, DIR regularization considerably influenced VI_CBCT in both the imaging systems. Our results have the potential to assist in designing CBCT protocols, incorporating VI_CBCT imaging into the functional avoidance planning process.     

Deep inspiration breath hold in post-operative radiotherapy for right breast cancer: a retrospective analysis

BackgroundThe aim of our study is to determine whether deep inspiration breath hold (DIBH) is effective for reducing exposure of the heart, left coronary artery (LAD) and both lungs in right breast radiotherapy.Materials and methodsWe have analyzed 10 consecutive patients with right-sided breast cancer (BC), simulated during free breathing (FB) and in DIBH modality. For all patients we contoured breast PTV and organs at risk (right and left lungs, heart, LAD) on both CT scans (FB and DIBH). Finally, 5 patients were treated with IMRT and 5 with VMAT techniques.ResultsAll patients were able to end the treatments in DIBH modalities regardless of the longer treatment time in comparison to FB. The maximum and mean dose to the heart are lower in the DIBH modality. The mean values of the heart mean dose were 1.76 Gy in DIBH and 2.19 Gy in FB. The mean heart maximum dose in DIBH and FB were, respectively, 9.3 Gy and 11 Gy. Likewise, the maximum dose to the LAD is lower in DIBH; 2.57 Gy versus 3.56 Gy in FB. Noteworthy, 3 patients with hepatomegaly treated with the DIBH technique showed a higher ipsilateral lung dose than FB, but a decrease of liver dose.ConclusionWe report that the use of DIBH for right-sided BC allows the dose to the heart, LAD and to the liver to be reduced in case of hepatomegaly. This technique is well tolerated by patients, when adequately trained, and could be considered effective even in right sided BC.     

Parathyroid Cystic Adenoma: A Systematic Review and Meta-Analysis

ObjectiveTo review diagnostic imaging modalities for parathyroid cystic adenomas (PCA). Since PCAs are a rare (0.5%-1%) subclass of parathyroid adenomas, and due to their cystic component, imaging modalities known to be efficient for diagnosing solid adenomas might fail in localizing them.MethodsWe conducted a systematic review using the PubMed and Cochrane databases for English articles on PCAs published between 1995 and 2020. A meta-analysis of the retrieved data was performed.ResultsOverall, 39 studies, reporting on a total of 160 patients, were included in the analysis. Two thirds (68%) of the patients were female, with a mean age of 53.9 years. A single cystic adenoma was detected in 98.1% of cases. The mean blood calcium corrected for albumin level was 12.6 ± 2.7 mg/dL, and the mean parathyroid hormone level was 565.5 ± 523.8 pg/mL. The mean PCA sizes as measured by ultrasound (US), computed tomography (CT), and ex vivo measurement were 4.8 ± 3.6, 5.2 ± 3.2, and 3.5 cm, respectively. The median weight was 8.1 g. PCA was detected in 86% of US examinations; 100% of US-guided fine needle aspiration, 4-dimensional computed tomography (4D-CT), or magnetic resonance imaging examinations; and 61% of 99m-technetium sestamibi scan with single-photon emission computed tomography ((99m)Tc-SPECT). (99m)Tc-SPECT showed a significantly lower diagnostic rate than US (odds ratio, 3.589), US-guided fine needle aspiration, CT combined with 4D-CT, and the combination of US, CT, 4D-CT, and magnetic resonance imaging (P < .001).ConclusionAlthough US and 4D-CT showed a significantly high rate in diagnosing PCA, (99m)Tc-SPECT showed a lower PCA diagnostic rate. These findings suggest that larger cystic lesions suspected as PCAs should be further evaluated using 4D-CT rather than (99m)Tc-SPECT.     

Resolution enhancement for lung 4D-CT based on transversal structures by using multiple Gaussian process regression learning

PurposeFour-dimensional computed tomography (4D-CT) plays a useful role in many clinical situations. However, due to the hardware limitation of system, dense sampling along superior–inferior direction is often not practical. In this paper, we develop a novel multiple Gaussian process regression model to enhance the superior-inferior resolution for lung 4D-CT based on transversal structures.MethodsThe proposed strategy is based on the observation that high resolution transversal images can recover missing pixels in the superior-inferior direction. Based on this observation and motived by random forest algorithm, we employ multiple Gaussian process regression model learned from transversal images to improve superior–inferior resolution. Specifically, we first randomly sample 3 × 3 patches from original transversal images. The central pixel of these patches and the eight-neighbour pixels of their corresponding degraded versions form the label and input of training data, respectively. Multiple Gaussian process regression model is then built on the basis of multiple training subsets obtained by random sampling. Finally, the central pixel of the patch is estimated based on the proposed model, with the eight-neighbour pixels of each 3 × 3 patch from interpolated superior-inferior direction images as inputs.ResultsThe performance of our method is extensively evaluated using simulated and publicly available datasets. Our experiments show the remarkable performance of the proposed method.ConclusionsIn this paper, we propose a new approach to improve the 4D-CT resolution, which does not require any external data and hardware support, and can produce clear coronal/sagittal images for easy viewing.     

Performance of the irregular surface compensator compared with four-field box and intensity modulated radiation therapy for gynecologic cancer

PurposeA retrospective planning study was undertaken to evaluate the dosimetric advantages of the irregular surface compensator (ISC) technique, a forward planning technique with electronic compensation algorithm available on Varian Eclipse treatment planning system. This was extensively compared to the conventional four-field box (4FB) and intensity modulated radiation therapy using 5 fields (IMRT5F) on gynecologic cancer patients.MethodsTwenty-two patients were enrolled. The prescribed dose was 50.4 Gy in 28 fractions to the primary target including pelvic lymph nodes. 4FB treatment plans were generated, then fluence of anterior and posterior fields were modified to generate ISC plans. IMRT5F were inversely optimized with equally spaced five coplanar fields. Dose-volume parameters were evaluated for the comparison of three planning techniques. The MU and delivery time were also estimated.ResultsIn terms of target coverage, the conformity and homogeneity index of ISC (1.67 and 1.03, respectively) were superior to those of 4FB (2.43 and 1.06, respectively) but slightly inferior to those of IMRT5F (1.10 and 1.02, respectively). ISC also illustrated an overall improvement in normal organ saving. Compared to 4FB, the mean dose of the rectum was reduced by about 4.0–5.0 Gy with ISC and IMRT5F. The volume receiving large doses was reduced for bladder with statistical significance with ISC and more with IMRT5F relative to 4FB. The mean number of MU per fraction were 200.86 (4FB), 446.09 (ISC) and 895.59 (IMRT5F).ConclusionThe ISC technique has the superior target coverage and healthy tissue sparing in comparison with conventional 4FB and comparable normal organ saving compared to IMRT5F. The ISC can be an available option for gynecologic radiotherapy.     

Dose delivery accuracy on helical tomotherapy for 4-dimensional tumor motion — a phantom study

BackgroundThe advances in image guidance and capability of highly conformal dose deliveries made possible the use of helical tomotherapy (HT) for lung cancer treatment. To determine the effect of respiratory motion on the delivered dose in HT, film dosimetry using a dynamic phantom was performed. This was a phantom study to determine the effect of motion on the delivered dose in HT.Materials and methods4D computed tomography (4DCT) was acquired for various target motions of CIRS dynamic phantom (CIRS Inc., Norfolk, USA) with 2.5cm diameter spherical target of volume 8.2 cc moving in the COS⁴ motion pattern. AveIP images and treatment plans were generated in the HT planning system. Target excursions during treatment delivery were changed in the superior-inferior, anteroposterior and lateral directions. The breathing cycle time was varied from 4 to 5 sec. and also the delivery interruptions were introduced. A film was exposed for each delivery and gamma analysis was performed.ResultsThe gamma pass rate (GPR) with 3%, 2 mm criteria for the target motion in the S-I direction showed a significant reduction from 97.5% to 54.4% as the motion increased from 3 mm to 8 mm (p = 0.03). For the target motion in S-I = 8 mm, L-R = A-P = 3 mm, the percentage decrease in the GPR was 74% (p = 0.001) for three interruptions.ConclusionThe ITV based approach in HT is ideal for a shallow breathing situation when the tumor excursions were confined to 5 mm in the S-I and 3 mm in L-R and A-P directions.     

Impact of acuros XB algorithm in deep-inspiration breath-hold (DIBH) respiratory techniques used for the treatment of left breast cancer

AimTo investigate the impact of Acuros XB (AXB) algorithm in the deep-inspiration breath-hold (DIBH) technique used for treatment of left sided breast cancer.BackgroundAXB may estimate better lung toxicities and treatment outcome in DIBH.Materials and MethodsTreatment plans were computed using the field-in-field technique for a 6 MV beam in two respiratory phases - free breathing (FB) and DIBH. The AXB-calculations were performed under identical beam setup and the same numbers of monitor units as used for AAA-calculation.ResultsMean Hounsfield units (HU), mass density (g/cc) and relative electron density were -782.1 ± 24.8 and -883.5 ± 24.9; 0.196 ± 0.025 and 0.083 ± 0.032; 0.218 ± 0.025 and 0.117 ± 0.025 for the lung in the FB and DIBH respiratory phase, respectively. For a similar target coverage (p > 0.05) in the DIBH respiratory phase between the AXB and AAA algorithm, there was a slight increase in organ at risk (OAR) dose for AXB in comparison to AAA, except for mean dose to the ipsilateral lung. AAA predicts higher mean dose to the ipsilateral lung and lesser V_20Gy for the ipsilateral and common lung in comparison to AXB. The differences in mean dose to the ipsilateral lung were 0.87 ± 2.66 % (p > 0.05) in FB, and 1.01 ± 1.07% (p < 0.05) in DIBH, in V_20Gy the differences were 1.76 ± 0.83% and 1.71 ± 0.82% in FB (p < 0.05), 3.34 ± 1.15 % and 3.24 ± 1.17 % in DIBH (p < 0.05), for the ipsilateral and common lung, respectively.ConclusionFor a similar target volume coverage, there were important differences between the AXB and AAA algorithm for low-density inhomogeneity medium present in the DIBH respiratory phase for left sided breast cancer patients. DIBH treatment in conjunction with AXB may result in better estimation of lung toxicities and treatment outcome.     

Advanced dose calculation algorithms in lung cancer radiotherapy: Implications for SBRT and locally advanced disease in deep inspiration breath hold

PurposeEvaluating performance of modern dose calculation algorithms in SBRT and locally advanced lung cancer radiotherapy in free breathing (FB) and deep inspiration breath hold (DIBH).MethodsFor 17 patients with early stage and 17 with locally advanced lung cancer, a plan in FB and in DIBH were generated with Anisotropic Analytical Algorithm (AAA). Plans for early stage were 3D-conformal SBRT, 45 Gy in 3 fractions, prescribed to 95% isodose covering 95% of PTV and aiming for 140% dose centrally in the tumour. Locally advanced plans were volumetric modulated arc therapy, 66 Gy in 33 fractions, prescribed to mean PTV dose. Calculation grid size was 1 mm for SBRT and 2.5 mm for locally advanced plans. All plans were recalculated with AcurosXB with same MU as in AAA, for comparison on target coverage and dose to risk organs.ResultsLung volume increased in DIBH, resulting in decreased lung density (6% for early and 13% for locally-advanced group).In SBRT, AAA overestimated mean and near-minimum PTV dose (p-values < 0.01) compared to AcurosXB, with largest impact in DIBH (differences of up to 11 Gy). These clinically relevant differences may be a combination of small targets and large dose gradients within the PTV.In locally advanced group, AAA overestimated mean GTV, CTV and PTV doses by median less than 0.8 Gy and near-minimum doses by median 0.4–2.7 Gy.No clinically meaningful difference was observed for lung and heart dose metrics between the algorithms, for both FB and DIBH.ConclusionsAAA overestimated target coverage compared to AcurosXB, especially in DIBH for SBRT.     

Local control and failure patterns after intensity modulated radiotherapy with reduced target volume delineation after induction chemotherapy for patients with T4 nasopharyngeal carcinoma

BackgroundThe delineation of target volume after induction chemotherapy(IC) for nasopharyngeal carcinoma(NPC) is currently controversial. In this study, we aimed to analyze the long-term local control(LC) and failure patterns of T4 NPC treated with reduced target volume radiotherapy after IC.MethodsFrom September 2007 to January 2013, 145 patients with T4 NPC were retrospectively reviewed. All patients received at least 1 cycle of IC followed by intensity modulated radiotherapy(IMRT). The gross tumor volume(GTV) was delineated according to the post-IC images for intracavity tumors and lymph nodes. The LC and overall survival (OS) rates were calculated using the Kaplan-Meier method. The location and extent of local failures were transferred to the pretreatment planning computed tomography (CT) for dosimetric analysis.ResultsWith a median follow-up time of 95 months (range, 16–142 months), 23 local failures were found. The estimated 10-year LC and OS rates were 81.1%and 54.8% respectively. Among the 20 local failures with available diagnostic images, 18(90%) occurred within the 95% isodose lines and were considered in-field failures and 2(10%) were marginal. There was no outside-field failure.ConclusionsIn-field failure was the major pattern of local failure for T4 NPC. IMRT with reduced target volume after IC seems to be feasible. Further researches exploring optimal volume and radiation dose for local advanced NPC in the era of IC are warranted.     

Normal lung tissue complication probability in MR-Linac and conventional radiotherapy

PurposeTo study normal lung tissue (NLT) complications in magnetic resonance (MR) image based linac and conventional radiotherapy (RT) techniques.Materials and MethodsThe Geant4 toolkit was used to simulate a 6 MV photon beam. A homogenous magnetic field of 1.5 Tesla (T) was applied in both perpendicular and parallel directions relative to the radiation beam.Analysis of the NLT complications was assessed according to the normal lung tissue complication probability (NTCP), the mean lung dose (MLD), and percentage of the lung volume receiving doses greater than 20 Gy (V₂₀), using a sample set of CT images generated from a commercially available 4D-XCAT digital phantom.ResultsThe results show that the MLD and V₂₀ were lower for MR-linac RT. The largest reduction of MLD and V₂₀ for MR-linac RT configurations were 5 Gy and 29.3%, respectively.ConclusionMR-linac RT may result in lower NLT complications when compared to conventional RT.     

Dosimetric impact of 4DCT artifact in carbon-ion scanning beam treatment: Worst case analysis in lung and liver treatments

IntroductionWe evaluated the impact of 4DCT artifacts on carbon-ion pencil beam scanning dose distributions in lung and liver treatment.Methods & materials4DCT was performed in 20 liver and lung patients using area-detector CT (original 4DCT). 4DCT acquisition by multi-detector row CT was simulated using original 4DCT by selecting other phases randomly (plus/minus 20% phases). Since tumor position can move over the respiratory range in original 4DCT, mid-exhalation was set as reference phase. Total prescribed dose of 60 Gy (RBE) was delivered to the clinical target volume (CTV). Reference dose distribution was calculated with the original CT, and actual dose distributions were calculated with treatment planning parameters optimized using the simulated CT (simulated dose). Dose distribution was calculated by substituting these parameters into the original CT.ResultsFor liver cases, CTV-D95 and CTV-Dmin values for the reference dose were 97.6 ± 0.5% and 89.8 ± 0.6% of prescribed dose, respectively. Values for the simulated dose were significantly degraded, to 88.6 ± 14.0% and 46.3 ± 26.7%, respectively. Dose assessment results for lung cases were 84.8 ± 12.8% and 58.0 ± 24.5% for the simulated dose, showing significant degradation over the reference dose of 95.1 ± 1.5% and 87.0 ± 2.2%, respectively.Conclusions4DCT image quality should be closely checked to minimize degradation of dose conformation due to 4DCT artifacts. Medical staff should pay particular attention to checking the quality of 4DCT images as a function of respiratory phase, because it is difficult to recognize 4DCT artifact on a single phase in some cases     

Voluntary breath-hold reduces dose to organs at risk in radiotherapy of left-sided breast cancer

AimTo compare the dose to organs at risk with free breathing (FB) or voluntary breath-hold (VBH) during radiotherapy of patients with left sided breast cancer.BackgroundRadiotherapy reduces the risk of breast-cancer-specific mortality but the effects on other organs increase non-cancer-specific mortality. Radiation exposure to the heart, in particular in patients with left sided breast cancer, can be reduced by breath hold methods that increase the distance between the heart and the radiation field.Materials and MethodsThree-dimensional conformal radiotherapy (3D-CRT) dose plans for the left breast and organs at risk including the heart, left anterior descending coronary artery (LAD) and ipsilateral lung were compared with FB and VBH in ten patients with left sided breast cancer.ResultsThe mean doses to the heart and LAD were reduced by 50.4 % (p < 0.001) and 58.8 % (p = 0.006), respectively, in VBH relative to FB. The mean dose to the ipsilateral lung was reduced by 13.8 % (p = 0.11) in VBH relative to FB. The planning target volume (PTV) coverage was at least 95 % in both FB and VBH (p = 0.78).ConclusionThe VBH technique significantly reduces the dose to organs at risk in 3D-CRT treatment plans of left sided breast cancer.     

Effect of accounting for interfractional CTV shape variations in PTV margins on prostate cancer radiation treatment plans

PurposeThe aim of this study was to account for interfractional clinical target volume (CTV) shape variation and apply this to the planning target volume (PTV) margin for prostate cancer radiation treatment plans.MethodsInterfractional CTV shape variations were estimated from weekly cone-beam computed tomography (CBCT) images using statistical point distribution models. The interfractional CTV shape variation was taken into account in the van Herk’s margin formula. The PTV margins without and with the CTV shape variation, i.e., standard (PTV_ori) and new (PTV_shape) margins, were applied to 10 clinical cases that had weekly CBCT images acquired during their treatment sessions. Each patient was replanned for low-, intermediate-, and high-risk CTVs, using both margins. The dose indices (D98 and V70) of treatment plans with the two margins were compared on weekly pseudo-planning computed tomography (PCT) images, which were defined as PCT images registered using a deformable image registration technique with weekly CBCT images, including contours of the CTV, rectum, and bladder.ResultsThe percentage of treatment fractions of patients who received CTV D98 greater than 95% of a prescribed dose increased from 80.3 (PTV_ori) to 81.8% (PTV_shape) for low-risk CTVs, 78.8 (PTV_ori) to 87.9% (PTV_shape) for intermediate-risk CTVs, and 80.3 (PTV_ori) to 87.9% (PTV_shape) for high-risk CTVs. In most cases, the dose indices of the rectum and bladder were acceptable in clinical practice.ConclusionThe results of this study suggest that interfractional CTV shape variations should be taken into account when determining PTV margins to increase CTV coverages.     

Definition of the margin of major coronary artery bifurcations during radiotherapy with electrocardiograph-gated 4D-CT

PurposeThe aim was to measure the cardiac motion-induced displacements of major coronary artery bifurcations utilizing electrocardiography (ECG)-gated four-dimensional computed tomography (4D-CT) and to determine the margin of coronary artery bifurcations.MethodsThirty-seven female patients who underwent retrospective ECG-gated 4D-CT in inspiratory breath hold (IBH) were enrolled. The left main coronary artery bifurcation (LM), the obtuse marginal branch bifurcation (OM), the first diagonal branch bifurcation (D₁), the second diagonal branch bifurcation (D₂), the caudal portion of the left anterior descending branch (APX), the first right ventricular artery bifurcation (V) and the acute marginal branch bifurcation (AM) were contoured. The center of the contour of the coronary arterial bifurcations at end systole was defined as the standard, and the margin were then calculated.ResultsThe margin in the left–right (LR), cranio-caudal (CC), and anterior-posterior (AP) coordinates were as follows: LM 3, 3, and 3 mm; D₁ 6, 3, and 3 mm; D₂ 3, 3, and 3 mm; APX 4, 4, and 4 mm; OM 4, 6, and 5 mm; V 6, 8, and 7 mm; and AM 6, 8, and 7 mm, respectively.ConclusionCoronary artery bifurcations should be considered a separate organ at risk (OAR), and different margin should be provided due to the differences resulting from motion displacement. The maximum margin in the LR, CC, and AP coordinates of left coronary artery bifurcations were 6, 6, and 5 mm, and those of the right coronary artery bifurcations were 6, 8, and 7 mm, respectively.     

Evaluation of the rectal V30 parameter in patients diagnosed with postoperative endometrial cancer

BackgroundThe present paper reports on analysis of 184 patients who were diagnosed with endometrial cancer. The main objective of this study was to address parameter V_rec(30Gy) which determines a volume of the rectum irradiated with a dose of 30 Gy during radiotherapy.Materials and methodsAll patients were irradiated with an IMRT technique on linear accelerators. The planning target volume (PTV) contour was determined by a radiation oncologist. The clinical target volume (CTV) was drawn on CT images obtained in a prone position. For statistical analysis, appropriate tests (e.g. the Shapiro-Wilk, Wilcoxon) were used.Results and discussionThe performed analysis showed that the recommended condition for V_rec(30Gy) is met only in 3% of patients and the observed median value exceeds 90%. The obtained results were compared with the studies in which the V_rec(30Gy) values were related to various radiotherapy techniques.ConclusionsThe analysis showed that the condition for V_rec(30Gy) is satisfied in the case of only 3% of patients. Due to the difficulty with meeting the condition, it should be reconsidered based on real results.     

Set-up errors in head and neck cancer patients treated with intensity modulated radiation therapy: Quantitative comparison between three-dimensional cone-beam CT and two-dimensional kilovoltage images

ObjectivesTo compare the patient set-up error detection capabilities of three-dimensional cone beam computed tomography (3D-CBCT) and two-dimensional orthogonal kilovoltage (2D-kV) techniques.Methods3D-CBCT and 2D-kV projections were acquired on 29 head-and-neck (H&N) patients undergoing Intensity Modulated Radiotherapy (IMRT) on the first day of treatment (time 0) and after the delivery of 40 Gy and 50 Gy. Set-up correction vectors were analyzed after fully automatic image registration as well as after revision by radiation oncologists. The dosimetric effects of the different sensitivities of the two image guidance techniques were assessed.ResultsA statistically significant correlation among detected set-up deviations by the two techniques was found along anatomical axes (0.60 < ρ < 0.72, p < 0.0001); no correlation was found for table rotation (p = 0.41). No evidence of statistically significant differences between the indications provided along the course of the treatment was found; this was also the case when full automatic versus manually refined correction vectors were compared. The dosimetric effects analysis revealed slight statistically significant differences in the median values of the maximum relative dose to mandible, spinal cord and its 5 mm Planning Organ at Risk Volume (0.95%, 0.6% and 2.45%, respectively), with higher values (p < 0.01) observed when 2D-kV corrections were applied.ConclusionA similar sensitivity to linear set-up errors was observed for 2D-kV and 3D-CBCT image guidance techniques in our H&N patient cohort. Higher rotational deviations around the table vertical axis were detected by the 3D-CBCT with respect to the 2D-kV method, leading to a consistent better sparing of organs at risk.