Differences In Dosimetric Parameters Research Articles

Clinical feasibility of deep learning-based auto-segmentation of target volumes and organs-at-risk in breast cancer patients after breast-conserving surgery

BackgroundIn breast cancer patients receiving radiotherapy (RT), accurate target delineation and reduction of radiation doses to the nearby normal organs is important. However, manual clinical target volume (CTV) and organs-at-risk (OARs) segmentation for treatment planning increases physicians’ workload and inter-physician variability considerably. In this study, we evaluated the potential benefits of deep learning-based auto-segmented contours by comparing them to manually delineated contours for breast cancer patients.MethodsCTVs for bilateral breasts, regional lymph nodes, and OARs (including the heart, lungs, esophagus, spinal cord, and thyroid) were manually delineated on planning computed tomography scans of 111 breast cancer patients who received breast-conserving surgery. Subsequently, a two-stage convolutional neural network algorithm was used. Quantitative metrics, including the Dice similarity coefficient (DSC) and 95% Hausdorff distance, and qualitative scoring by two panels from 10 institutions were used for analysis. Inter-observer variability and delineation time were assessed; furthermore, dose-volume histograms and dosimetric parameters were also analyzed using another set of patient data.ResultsThe correlation between the auto-segmented and manual contours was acceptable for OARs, with a mean DSC higher than 0.80 for all OARs. In addition, the CTVs showed favorable results, with mean DSCs higher than 0.70 for all breast and regional lymph node CTVs. Furthermore, qualitative subjective scoring showed that the results were acceptable for all CTVs and OARs, with a median score of at least 8 (possible range: 0–10) for (1) the differences between manual and auto-segmented contours and (2) the extent to which auto-segmentation would assist physicians in clinical practice. The differences in dosimetric parameters between the auto-segmented and manual contours were minimal.ConclusionsThe feasibility of deep learning-based auto-segmentation in breast RT planning was demonstrated. Although deep learning-based auto-segmentation cannot be a substitute for radiation oncologists, it is a useful tool with excellent potential in assisting radiation oncologists in the future.Trial registration Retrospectively registered.

Dosimetric Comparisons of Simulation Techniques for Left-Sided Breast Cancer in the COVID-19 Era: Techniques to Reduce Viral Transmission and Respect the Therapeutic Ratio.

BackgroundThe COVID-19 pandemic challenges our ability to safely treat breast cancer patients and requires revisiting current techniques to evaluate optimal strategies. Potential long-term sequelae of breast radiation have been addressed by deep inspiration breath-hold (DIBH), prone positioning, and four-dimensional computed tomography (4DCT) average intensity projection (AveIP)-based planning techniques. Dosimetric comparisons to determine the optimal technique to minimize the normal tissue dose for left-sided breast cancers have not been performed.MethodsTen patients with left-sided, early-stage breast cancer undergoing whole breast radiation were simulated in the prone position, supine with DIBH, and with a free-breathing 4DCT scan. The target and organs at risk (OAR) contours were delineated in all scans. Target volume coverage and OAR doses were assessed. One-way analysis of variance (ANOVA) and Kruskal-Wallis one-way ANOVA were used to detect differences in dosimetric parameters among the different treatment plans. Significance was set as p < 0.05.ResultsWe demonstrate differences in heart and lung dose by the simulation technique. The mean heart doses in the prone, DIBH, and AveIP plans were 129 cGy, 154 cGy, and 262 cGy, respectively (p=0.02). The lung V20 in the prone, DIBH, and AveIP groups was 0.5%, 10.3% and 9.5%, respectively (p <0.001). Regardless of technique, lumpectomy planning target volume (PTV) coverage did not differ between the three plans with 95% of the lumpectomy PTV volume covered by 100.4% in prone plans, 98.5% in AveIP plans, and 99.3% in DIBH plans (p=0.7).ConclusionsProne positioning provides dosimetric advantages as compared to DIBH. When infection risks are considered as in the current coronavirus disease 2019 (COVID-19) pandemic, prone plans have advantages in reducing the risk of disease transmission. In instances where prone positioning is not feasible, obtaining an AveIP simulation may be useful in more accurately assessing heart and lung toxicity and informing a risk/benefit discussion of DIBH vs free breath-hold techniques.

Dosimetry of local failure with single dose 19 Gy high-dose-rate brachytherapy for prostate cancer

Purpose/objectiveLong-term follow up of single dose high-dose rate brachytherapy (HDR BT) for localised prostate cancer has revealed higher than expected rates of biochemical and local failure. This study aimed (i) to investigate the pattern of relapse within the prostate with reference to the initial site of disease in those patients; and (ii) to examine if there were any relationships between the HDR BT dosimetric parameters to these areas of recurrence. Materials/methodsA retrospective review of treatment records of patients who received 19 Gy single fraction of HDR BT was carried out. A matched pair analysis used one control for each biochemical recurrence case matched with pre-treatment Clinical target volume (CTV) size, Gleason score, T stage, risk category and presence of an identifiable dominant intraprostatic nodule (DIL) for each biochemical recurrence case identified.For all datasets, the pre HDR BT DILs were delineated on the diagnostic pre-treatment T2-weighted MRI and planning CT images. For patients with local recurrence post HDR BT, the recurrent nodules were contoured on the diagnostic T2-weighted MRI and choline PET which were registered to the original HDR BT planning CT.Dosimetric parameters of CTV, planning target volume (PTV), DIL and organs at risk (OARs) were evaluated. Wilcoxon signed-rank test was performed to investigate if there were any significant differences in dosimetric parameters between cases and controls. Cox regression analysis was performed to explore if there were any clinical and dosimetric parameters predicting for biochemical progression free survival (bPFS), local recurrence free survival (LR-PFS) and DIL recurrence free survival (DIL-PFS). ResultsBetween 2013 and 2018, 180 patients received 19 Gy HDR-BT monotherapy. With a median follow up of 36 months, 19 (10.6%) patients developed biochemical recurrence. Of the 19 patients with biochemical failure, 13 had a local recurrence, including 7 who occurred at the site of DIL.Thirty-eight intermediate/high risk patients were included in the matched pair analysis. No statistically significant differences were found in all CTV, PTV, DIL and OAR dosimetric parameters between cases and controls (p > 0.05).For the Cox regression analysis, none of the covariates investigated were found to be statistically significant factors to predict for bPFS, LC-PFS and DIL-PFS. ConclusionNo associations between biochemical recurrences and HDR BT dosimetry were identified in our cohort of patients receiving 19 Gy single fraction HDR BT. A large proportion of recurrences occurred at the site of original disease. HDR BT for intermediate/high risk prostate cancer should be undertaken using a minimum of two fractions.

Improved Ipsilateral Breast and Chest Wall Sparing With MR-Guided 3-fraction Accelerated Partial Breast Irradiation: A Dosimetric Study Comparing MR-Linac and CT-Linac Plans

PurposeExternal beam accelerated partial breast irradiation (APBI) is subject to treatment uncertainties that must be accounted for through planning target volume (PTV) margin. We hypothesize that magnetic resonance–guided radiation therapy with reduced PTV margins enabled by real-time cine magnetic resonance image (MRI) target monitoring results in better normal tissue sparing compared with computed tomography (CT)-guided radiation therapy with commonly used clinical PTV margins. In this study, we compare the plan quality of ViewRay MRIdian Linac forward planned intensity modulated radiation therapy and TrueBeam volumetric modulated arc therapy for a novel 3-fraction APBI schedule. Methods and MaterialsTargets and organs at risk (OARs) were segmented for 10 patients with breast cancer according to NSABP B39/RTOG 0413 protocol. A 3 mm margin was used to generate MR PTV3mm and CT PTV3mm plans, and a 10 mm margin was used for CT PTV10mm. An APBI schedule delivering 24.6 Gy to the clinical target volume and 23.4 Gy to the PTV in 3 fractions was used. OAR dose constraints were scaled down from existing 5-fraction APBI protocols. Target and OAR dose-volume metrics for the following data sets were analyzed using Wilcoxon matched-pairs signed-rank test: (1) MR PTV3mm versus CT PTV3mm plans and (2) MR PTV3mm versus CT PTV10mm. ResultsAverage PTVs were 84.3 ± 51.9 cm3 and 82.6 ± 55 cm3 (P = .5) for MR PTV3mm and CT PTV3mm plans, respectively. PTV V23.4Gy, dose homogeneity index, conformity index (CI), and R50 were similar. There was no meaningful difference in OAR metrics, despite MR PTV3mm being larger than the CT PTV3mm in 70% of the patients. Average PTVs for MR PTV3mm and CT PTV10mm plans were 84.3 ± 51.9 cm3 and 131.7 ± 74.4 cm3, respectively (P = .002). PTV V23.4Gy was 99% ± 0.9% versus 97.6% ± 1.4% (P = .03) for MR PTV3mm and CT PTV10mm, respectively. Dose homogeneity index, CI, and R50 were similar. MR PTV3mm plans had better ipsilateral breast (V12.3Gy, 34.8% ± 12.7% vs 44.4% ± 10.9%, P = .002) and chest wall sparing (V24Gy, 8.5 ± 5.5 cm3 vs 21.8 ± 14.9 cm3, P = .004). ConclusionsMR- and CT-based planning systems produced comparable plans when a 3 mm PTV margin was used for both plans. As expected, MR PTV3mm plans produced better ipsilateral breast and chest wall sparing compared with CT PTV10mm. The clinical relevance of these differences in dosimetric parameters is not known.

An Inverse Dose Optimization Algorithm for Three-Dimensional Brachytherapy.

PurposeTo investigate an implementation method and the results of an inverse dose optimization algorithm, Gradient Based Planning Optimization (GBPO), for three-dimensional brachytherapy.MethodsThe GBPO used a quadratic objective function, and a dwell time modulation item was added to the objective function to restrict the dwell time variance. We retrospectively studied 4 cervical cancer patients using different applicators and 15 cervical cancer patients using the Fletcher applicator. We assessed the plan quality of GBPO by isodose lines for the patients using different applicators. For the 15 patients using the Fletcher applicator, we utilized dose-volume histogram (DVH) parameters of HR-CTV (D100%, V150%) and organs at risk (OARs) (D0.1cc, D1cc, D2cc) to evaluate the difference between the GBPO plans and the IPSA (Inverse Planning Simulated Annealing) plans, as well as the GBPO plans and the Graphic plans.ResultsFor the 4 patients using different applicators, the dose distributions are conformable. For the 15 patients using the Fletcher applicator, when the dwell time modulation factor (DTMF) is less than 20, the dwell time deviation reduces quickly; however, after the DTMF increased to 100, the dwell time deviation has no remarkable change. The difference in dosimetric parameters between the GBPO plans and the IPSA plans is not statistically significant (P>0.05). The GBPO plans have a higher D100% (3.57 ± 0.36, 3.38 ± 0.34; P<0.01) and a lower V150% (55.73 ± 4.06, 57.75 ± 3.79; P<0.01) than those of the Graphic plans. The differences in other DVH parameters are negligible between the GBPO plans and the Graphic plans.ConclusionsThe GBPO plans have a comparable quality as the IPSA plans and the Graphic plans for the studied cervical cancer cases. The GBPO algorithm could be integrated into a three-dimensional brachytherapy treatment planning system after studying more sites.

Assessing tumor centrality in lung stereotactic ablative body radiotherapy (SABR): the effects of variations in bronchial tree delineation and potential for automated methods

Accurate delineation of the proximal bronchial tree (PBT) is crucial for appropriate assessment of lung tumor centrality and choice of Stereotactic Ablative Body Radiotherapy (SABR) dose prescription. Here, we investigate variabilities in manual PBT delineation and their potential to influence assessing lesion centrality. A fully automatic, intensity-based tool for PBT contouring and measuring distance to the target is also described. This retrospective analysis included a total of 61 patients treated with lung SABR. A subset of 41 patients was used as a training dataset, containing clinical PBT contour and additional subsequently generated manual contours. The tool was optimized and compared against manual contours in terms of volume, distance to the target and various overlap/similarity metrics. The remaining 20 patients were used as a validation dataset to investigate the dosimetric effects of variations between manual and automatic PBT contours. Considerable interobserver variability was observed, particularly in identifying the superior and inferior borders of the PBT. Automatic PBT contours were comparable to manual contours with average Dice of 0.63 to 0.79 and mean distance to agreement of 1.78 to 3.34 mm. No significant differences in dosimetric parameters were found between automatically and manually generated contours. A moderate negative correlation was found between PBT maximum dose and distance to the lesion (p < 0.05). Variability in manual PBT delineation may result in inconsistent assessment of tumor centrality. Automatic contouring can help standardize clinical practice, support investigations into the link between SABR outcomes and lesion proximity to central airways and the development of predictive toxicity models that incorporate precise measurements of tumor location in relation to high-risk organs.

Assessing cumulative dose distributions in combined external beam radiotherapy and intracavitary brachytherapy for cervical cancer by treatment planning based on deformable image registration.

BackgroundThis study aimed to validate the feasibility of deformable image registration (DIR) in assessing the cumulative dose distributions in combined external beam radiotherapy (EBRT) and intracavitary brachytherapy (ICBT) for cervical cancer.MethodsThis retrospective study included 23 patients with stage IIB disease treated with combined EBRT to the whole pelvis (50.4 Gy in 28 fractions) using an intensity-modulated radiotherapy technique with 6-MV X-ray, followed by three-dimensional (3D) ICBT (28 Gy in 4 fractions). Tumor gross target volume at diagnosis (GTV-Tinit), tumor gross target volume before brachytherapy, high-risk clinical target volume (HR-CTV), intermediate-risk clinical target volume (IR-CTV), and parametrium and organs at risk were recontoured on computed tomography images of EBRT and ICBT, respectively. The dose-volume parameters were also determined. The DIR results were reviewed using MIM Maestro (Reg Review) and modified by function (Reg Refine). To evaluate the accuracy of DIR, DIR-based cumulative dose-volume histogram (DVH) parameters and simple DVH parameter addition were compared using Wilcoxon rank-sum tests.ResultsThe cumulative dose distributions of EBRT and four ICBT sessions were successfully illustrated using DIR. The mean tumor diameters were 68.35 cm3 at diagnosis and 29.63 cm3 at ICBT initiation. The mean tumor regression was 56.6%. The median minimum dose covering 90% (D90) of HR-CTV, GTV-Tinit, IR-CTV, and parametrium were 69.58±4.94, 68.81±7.98, 59.28±3.78, and 60.97±1.1 Gyα/β=10, respectively, for DIR and 69.11±5.68, 68.49±8.62, 58.89±3.59, and 61±1.49 Gyα/β=10, respectively, with conventional simple DVH parameter addition.No statistically significant differences in dosimetric parameters were observed between the two methods.ConclusionsAlthough there were limitations in the DIR accuracy, DIR-based dose accumulation was significantly beneficial in visually showing the cumulative dose distribution in the target area to clinicians in combined radiotherapy for cervical cancer in routine clinical practice.

Dose distribution of brachytherapy for locally advanced (stage IIB) cervical cancer

PurposeThe aim of the study was to compare the dose distributions of combined intracavitary and interstitial (IC/IS) brachytherapy with 3-catheter IC brachytherapy in treating locally advanced (stage IIB) cervical cancer. Methods and MaterialsIn total, 46 patients were included, each with stage IIB cervical cancer, local lesion sizes ≥5 cm, and tumors that had not regressed after 45 Gy/25 F external intensity-modulated radiotherapy. To identify the dosimetric advantage of delivering a local boost to high-risk (HR)-cervix in IC/IS, patients were divided into two groups: IC/IS and IC/IS + HR-cervix. The differences in dosimetric parameters were compared between the two groups. Comparisons were then made between the parameters of the four planning methods: IC (Point A), IC (three dimensional [3D]), IC/IS, and IC/IS + HR-cervix. ResultsIn patients with IC/IS implants, the relative uterine tandem dwell time was significantly extended in the IC/IS + HR-cervix group, and the V150 and V200 volumes of HR-cervix were increased (all p < 0.001), whereas the D90 and D100 values of the IC/IS + HR-cervix group were lower than those in the IC/IS group. In pairwise comparisons, HR-cervix V150 and V200 values were lowest in the IC/IS group, followed by the IC (3D), IC/IS + HR-cervix, and IC (Point A) groups. All differences were statistically significant (p < 0.05), with the exception of IC/IS vs. IC (3D). ConclusionsWhen treating locally advanced cervical cancer (stage IIB, local residual volume ≥5 cm after external radiotherapy), the IC/IS + HR-cervix optimization method can meet the HR clinical target volume D90 dose requirement, normal tissue dose limits, and can escalate doses to local areas of the cervix.

A pilot study on dosimetric and radiomics analysis of urethral strictures following HDR brachytherapy as monotherapy for localized prostate cancer.

A cohort of high dose-rate (HDR) monotherapy patients was analyzed to (i) establish the frequency of non-malignant urethral stricture; (ii) explore the relation between stricture formation with the dose distribution along the length of the urethra, and MRI radiomics features of the prostate gland. A retrospective review of treatment records of patients who received 19 Gy single fraction of HDR brachytherapy (BT) was carried out. A matched pair analysis used one control for each stricture case matched with pre-treatment International Prostate Symptom Score (IPSS) score, number of needles used and clinical target volume volume for each stricture case identified.For all data sets, pre-treatment T2 weighted MRI images were used to define regions of interests along the urethra and within the whole prostate gland. MRI textural radiomics features-energy, contrast and homogeneity were selected. Wilcoxon signed-rank test was performed to investigate significant differences in dosimetric parameters and MRI radiomics feature values between cases and controls. From Nov 2010 to July 2017, there were 178 patients treated with HDR BT delivering 19 Gy in a single dose. With a median follow-up of 28.2 months, a total of 5/178 (3%) strictures were identified.10 patients were included in the matched pair analysis. The urethral dosimetric parameters investigated were not statistically different between cases and controls (p > 0.05). With regards to MRI radiomics feature analysis, significant differences were found in contrast and homogeneity between cases and controls (p < 0.05). However, this did not apply to the energy feature (p = 0.28). In this matched pair analysis, no association between post-treatment stricture and urethral dosimetry was identified. Our study generated a preliminary clinical hypothesis suggesting that the MRI radiomics features of homogeneity and contrast of the prostate gland can potentially identify patients who develop strictures after HDR BT. Although the sample size is small, this warrants further validation in a larger patient cohort. Urethral stricture has been reported as a specific late effect with prostate HDR brachytherapy. Our study reported a relatively low stricture rate of 3% and no association between post-treatment stricture and urethral dosimetry was identified. MRI radiomics features can potentially identify patients who are more prone to develop strictures.

Possibility of Interchanging Patients for Beam-Matched Linear Accelerators from the Same Vendor

The purpose of this study is to investigate the possibility of interchanging patients on beam-matched linear accelerators (linacs), by evaluating the dosimetric variation and the dose delivery accuracy of volumetric modulated arc therapy (VMAT). Two VitalBeam linacs installed recently in our center were included in this study. For dosimetric data comparison, beam data, such as percentage depth doses (PDDs), beam profiles, output factors, multi-leaf collimator (MLC) leaf transmission factors, and the dosimetric leaf gap (DLG), for 6-MV and 10-MV beams were measured on both linacs. Sixty patients (20 head and neck, 20 lung, and 20 prostate cancers) were selected to evaluate the dosimetric parameters and the delivery accuracy of the VMAT plans created for various treatment sites. All the VMAT plans were generated using the Eclipse treatment planning system (TPS) with the same optimizer algorithm. The dose differences between two beam-matched linacs for planning target volumes (PTVs) and organs at risk (OARs) were recorded and analyzed. Patient-specific dosimetric quality assurance (DQA) using the Electronic Portal Image Device (EPID) were performed, and the measured planar doses were compared with those calculated by using the TPS though absolute dose gamma evaluation using 2%/2 mm and 2%/3 mm criteria. The differences in all dosimetric beam data between the two beam-matched linacs were all within 1% for the 6-MV and the 10-MV beams. For all 60 cases of three treatment sites, no notable differences were observed in the dosimetric comparison and the DVH variation between the beam-matched linacs. The average differences in dosimetric parameters of PTV and OARs were all within 1%. Furthermore, all passing rates of measured doses on the beam-matched linacs were higher than 93% and 97% for the 2%/2 mm and the 2%/3 mm criteria, respectively. Our overall dosimetric variation in beam data and VMAT plans remains within the tolerance of clinical acceptability. Pretreatment verification results were also clinically acceptable, showing good agreement with the calculated doses. Therefore, this study demonstrated the possibility of swapping patients in a VMAT plan without any modification and re-planning between two beam-matched linacs.

Simulation of an HDR Prostate Boost with Stereotactic Intensity-Modulated Proton Versus Photon Radiation Therapy: A Dosimetric Comparison Study

To compare the dose escalation potential of intensity modulated proton stereotactic body radiation therapy (SBPT) versus photon stereotactic body radiation therapy (SBXT) using prostate brachytherapy dose-prescription metrics. Nineteen patients treated with external radiation-only for prostate cancer at our institution were selected and stratified by prostate size (< 30; n = 6, 30-50; n = 7, > 50 cc; n = 6). Initial CT simulation scans were used for re-planning with SBPT and SBXT modalities. Clinical target volume (CTV), defined as the prostate gland only, was delineated by CT and planning MRI. For SBXT, the planning target volume (PTV) was generated by a 2mm isotropic expansion (except 0mm posteriorly). For SBPT, robust optimization was utilized to account for setup (2mm) and proton range uncertainties (2.5%). A prescription dose of 19 Gy in 2 fractions was used to simulate a high-dose rate brachytherapy (HDR-B) boost regimen.1 Treatment planning goals were designed to mimic dose distributions of HDR-B.2-3 Target doses were maximized to the upper limit of OAR dose constraints for each SBXT and SBPT plan. Pairs of plans were compared within patients. The median difference in dosimetric parameters examined in brachytherapy were compared using the Mann-Whitney U test. Spearman’s rank correlation was used to determine if dosimetric parameters were associated with prostate size. Mean CTV volume was 47cc (range 15-123 cc). All SBXT and SBPT plans met OAR dose constraints (rectum V75% < 1cc, bladder V75% < 5cc and urethra V125% < 1cc). The median conformity index (CI) for SBPT and SBXT was 2.1 and 1.3 (P< 0.001), respectively, whereas gradient index (GI) was 2.4 and 4.2 (P < 0.01). Prostate volume receiving 100% of the dose (V100) was significantly greater for SBXT vs SBPT plans but with a median difference of only 2% (P < 0.01). The median V125 (82% vs 73%) and V200 (11% vs 2%) was significantly greater for SBPT vs SBXT with a median difference of 8% (P < 0.001) and 7% (P < 0.001), respectively. Median V150 was 49% for both cohorts. V125 and V200 were significantly correlated with increasing prostate size as demonstrated by a Spearman’s correlation coefficient of 0.5 (P = 0.02) and 0.5 (P = 0.04), respectively. Median dose to 2cc of the bladder neck was significantly lower with SBPT vs SBXT (17.2 Gy vs 27.4 Gy, P < 0.05). In comparison to SBXT, SBPT better mimics the high dose distributions that are achievable with HDR-B while meeting OAR constraints. Both V125 and V200 for the prostate were significantly greater with SBPT compared to SBXT, and were correlated with increasing prostate size. However, SBPT plans had decreased conformity compared to SBXT. These results are relevant for future trial design, particularly in high risk prostate cancer patients not amenable to brachytherapy boost.

Performance Evaluation of a Transmission Reference Detector for Commissioning Beam Data in a Wedge Field

The purpose of this study is to evaluate the performance of a “stealth chamber” as a novel reference detector for measuring the commissioning beam data for a wedge field. The stealth chamber is a transmission ionization chamber intended to be used as a reference chamber for relative dosimetry. The percentage depth doses (PDDs) and the dose profiles of 6-, 8-, and 10-MV photon beams of four wedge filters were measured using the stealth and the CC13 chambers as reference detectors. The PDD and the profile measurements were performed under various field sizes ranging from 4 × 4 cm2 to 20 × 20 cm2. For the evaluate of the performance of the stealth chamber in fields with a physical wedge, all measurement data obtained using the stealth chamber as a reference detector were compared with those measured using two CC13 chambers as both field and reference detectors. For the PDDs, the differences in dosimetric parameters such as the depth of maximum dose (dmax) and the PDD at 10 cm (D10) and 5 cm (D5) were analyzed for both reference detectors. In addition, the root-mean-square error (RMSE) was calculated to measure the agreement of the profiles at dmax and a 10 cm depth. The percentage differences in D10 and D5 between both detectors were less than 1% for all energies and fields with four wedges. Furthermore, the RMSEs of the profiles at dmax and 10-cm depth in both chambers were within 1% for all energies and fields except for the 60° wedge angle. This study found that the use of a stealth chamber to measure the commissioning beam data for a wedge field is feasible, although a relatively large difference in the PDD was observed in the build-up region. However, we recommend careful verification of the PDDs and dose profiles for large field size and wedge angle before clinical use.

Optimization of tangential fields arrangement in the breast cancer 3D conformal radiation therapy

Introduction: The incidence of breast cancer increases with the rate of 1-2% at the world. Radiation therapy is one of the available choices for breast cancer treatment. The single isocentre half-beam block technique is considered as a standard technique to avoid hot and cold spots within the PTV. The major advantage of half beam technique is that the both contralateral breast and lung are completely spared. Also, using this technique, we don’t have any field matching problem. But, Lateral and medial movement of isocenter in conjunction of supraclavicular and tangential beams affect the divergence of tangential fields. Therefore, opposite tangential field can be parallel either in posterior border or beam central axis. The aim of this study is to compare the dosimetric parameters of three plans for tangential beams arrangement and select the optimal one. Materials and Methods: In this study, we selected 6 patients with breast cancer that underwent breast conserving surgery and considered for radiotherapy. CT simulation of patients were done based on standard protocols and imported to Isogray treatment planning system. Contouring of target volume and organs at risk (OARs) was done by radiotherapist. The tangential fields were considered in three different geometries of parallel in the posterior border with divergence in back jaws, parallel in central axis with divergence in back jaws and Parallel in posterior border without divergence of back jaws (half beam). Dosimetric parameters of each plan for OARs and target volumes extracted from DVHs data and compared statistically using ANOVA one-way repeated measurement test. Results: There was no statistical difference between dosimetric parameters (D95, V95, Dmax, and Dmean) of the target volume in three mentioned plans (P-value = 0.93). Although, there was no statistical difference between mean dose of the ipsilateral lung, the difference of V10 and V20 parameters for this organ is significant (P=0.01). Furthermore, there was no statistical difference in dosimetric parameters of OARs such as contralateral breast, lung, heart, and spinal cord. Conclusion: This study showed that back jaw divergence and arrangement of parallel opposite field can affect the ipsilateral lung dose. The V20 and V10 of ipsilateral lung are two dose constraints parameters in quantitative treatment planning evaluation of breast treatment. Quantitative variations of these parameters with changing the tangential field’s arrangement was significant which depends on the isocenter position and back jaw divergence. The values of these parameters were the highest when tangential fields were arranged as parallel in posterior border with divergence in the back jaw.

A meta-analysis comparing Dosimetric between volumetric-modulated arc therapy and intensity-modulated radiotherapy for left sided breast cancer after breast-conserving surgery

Objective To compare the dosimetric parameters of target volumes and organs at risk between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for left sided breast cancer after breast-conserving surgery by a meta-analysis. Methods Literature search was performed to include related studies to analyze the dosimetric parameters of target volumes and organs at risk. Results A total of 11 studies involving 154 patients were included in meta-analysis. There were no significant differences in Dmean, HI of PTV-Whole breast and PTV-Boost. Comparing to IMRT, VMAT increased the conformity index (CI) of PTV-Whole breast (P=0.000) and PTV-Boost (P=0.002). When the mean volume of target volumes was≤634 cm3, there were no significant differences in Dmean, V5, V20 of the heart and left sided lung, V30 of the heart, Dmean of the right sided lung and breast between VMAT and IMRT.When the mean volume of target volumes was>634 cm3, the Dmean(P=0.037), V5(P=0.005) and V20(P=0.030) of the heart in IMRT was lower than VMAT, but the V30(P=0.001) of heart in VMAT was lower than IMRT.IMRT showed significantly lower Dmean(P=0.013), V5(P=0.000), V20(P=0.000) of the left sided lung, and Dmean(P=0.001) of the right sided lung than VMAT.There were no significant differences in Dmean of the right sided breast. Conclusions There were no significant differences in dosimetric parameters of target volumes between VMAT and IMRT.When the mean volume of target volumes was≤634 cm3, there were no significant differences in dosimetric parameters of organs at risk. When the mean volume of target volumes was>634 cm3, IMRT has some advantages in protection of the heart and lung. Key words: Breast neoplasms/breast-conserving surgery; Breast neoplasms/volumetric-modulated arc therapy; Breast neoplasms/intensity-modulated radiotherapy; Meta-analysis

Quantifying the performance of two different types of commercial software programs for 3D patient dose reconstruction for prostate cancer patients: Machine log files vs. machine log files with EPID images

We clarified the reconstructed 3D dose difference between two different commercial software programs (Mobius3D v2.0 and PerFRACTION v1.6.4).Five prostate cancer patients treated with IMRT (74 Gy/37 Fr) were studied. Log files and cine EPID images were acquired for each fraction. 3D patient dose was reconstructed using log files (Mobius3D) or log files with EPID imaging (PerFRACTION). The treatment planning dose was re-calculated on homogeneous and heterogeneous phantoms, and log files and cine EPID images were acquired. Measured doses were compared with the reconstructed point doses in the phantom. Next, we compared dosimetric metrics (mean dose for PTV, rectum, and bladder) calculated by Mobius3D and PerFRACTION for all fractions from five patients.Dose difference at isocenter between measurement and reconstructed dose for two software programs was within 3.0% in both homogeneous and heterogeneous phantoms. Moreover, the dose difference was larger using skip arc plan than that using full arc plan, especially for PerFRACTION (e.g., dose difference at isocenter for PerFRACTION: 0.34% for full arc plan vs. −4.50% for skip arc plan in patient 1).For patients, differences in dosimetric parameters were within 1% for almost all fractions. PerFRACTION had wider range of dose difference between first fraction and the other fractions than Mobius3D (e.g., maximum difference: 0.50% for Mobius3D vs. 1.85% for PerFRACTION), possibly because EPID may detect some types of MLC positioning errors such as miscalibration errors or mechanical backlash which cannot be detected by log files, or that EPID data might include image acquisition failure and image noise.

Influence of CT value division on dose calculation in treatment planning

Objective To divide computed tomography (CT) values into different ranges and investigate the influence of CT value division on dose calculation, and to propose a method to combine magnetic resonance imaging (MRI) with assigned CT values. Methods Ten CT images each were collected from patients with head and neck, chest, and pelvic tumors. Random sampling was performed for the CT values of main tissues or organs at the three parts, and then the mean CT value of each tissue or organ was calculated to divide the CT values into different ranges. A virtual phantom was built in the Varian Eclipse treatment planning system, and for the prescribed dose of 100 cGy, the machine output was recorded at different CT values. The influence of different CT value ranges on dose calculation was analyzed. The treatment plans of intensity-modulated radiotherapy were selected from 5 cervical cancer patients, and new CT values were assigned to the planning target volume (PTV) and organs at risk to obtain new CT images. The plans were transferred to the new CT images and compared with the results on the original CT images in terms of dosimetric parameters. Results After dividing the CT values into different ranges and verifying the results in dose calculation, the CT values corresponding to different human tissues or organs were -100 to 100 HU. The influence of CT value variation on dose calculation was within 3%. In the same treatment plan, there were small differences in dosimetric parameters between new CT images and original CT images. Dmax, Dmean, D98%, D95%, D5%, and D2% of PTV were all below 3%, and Dmax and Dmean of the bladder, rectum, small intestine, femoral head, and bone marrow were below 2%. Conclusions The influence of CT value division on dose calculation in the treatment planning for pelvic tumors is acceptable, so it can be used in combination with MRI. Key words: Tomograpy, X-ray computed; Dose calculation; Treatment planning system; Magnetic resonance image

Relationship of Th17/Treg Cells and Radiation Pneumonia in Locally Advanced Esophageal Carcinoma.

Radiation pneumonia is a main side-effect that has limited the clinical usage of radiotherapy in locally advanced esophageal carcinoma. T helper cells 17 (Th 17) and T regulatory cells (Tregs) play an important role in inflammatory diseases. The balance between Treg and Th17 cells is a key factor in the progression of many inflammatory and autoimmune diseases. Whether Tregs and Th17 cells are predictive factors of radiation pneumonia has not yet been reported. In this study, we investigated the relationships of Treg/Th17 cells and radiation pneumonia in patients with locally advanced esophageal cancer who received radiotherapy. One hundred and forty-eight patients with locally advanced esophageal cancer who received radical and palliative radiotherapy were enrolled. The levels of Th17 and Treg cells in the blood of patients were detected using flow cytometry at the time point of pre-radiotherapy, 1st, 2nd, 3rd, 4th, 5th and 6th week from the start of radiation and 4 weeks after completion of radiotherapy. Radiation pneumonia was evaluated according to Radiation Therapy Oncology Group's acute radiation pneumonia standards, with the endpoint being grade 2 or above radiation pneumonia. There were 24 cases of radiation pneumonia in 148 cases of locally advanced esophageal cancer patients who underwent radiotherapy. Th17 cells increased and, in contrast, Treg cells decreased in the radiation pneumonia group. The change in the ratio of Th17/Treg was more pronounced and the difference was statistically significant from the 5th week after irradiation compared to patients with no radiation pneumonia (p<0.05). There was no significant difference in dosimetric parameters, including V5, V20, V30 and mean lung dose (MLD) and clinical factors, such as gender, age, smoking history, history of surgery and chemotherapy. The ratio of Th17/Treg cells may be an effective predictive factor of radiation pneumonia.

Immediate tissue expander or implant-based breast reconstruction does not compromise the oncologic delivery of post-mastectomy radiotherapy (PMRT).

Increasingly, women are choosing immediate breast reconstruction (IBR) following mastectomy. Reports have indicated IBR may compromise post-mastectomy radiotherapy (PMRT). We investigated the impact of IBR on timing of PMRT, target coverage, and doses to organs at risk in a modern radiotherapy practice using advanced planning techniques. Between 2013 and 2015, PMRT was delivered to 116 patients (66 mastectomy alone, 50 IBR). PMRT was delivered with a median dose of 50Gy in 25 fractions. Left-sided patients were treated in breath-hold under image guidance. Differences in dosimetric parameters and time to the initiation of PMRT were assessed between patients with and without reconstruction. Reconstructed patients were younger and had lower clinical stage disease. Reconstruction did not significantly increase the mean time to PMRT initiation (51days reconstructed vs. 45days non-reconstructed, p=0.14) or the number of patients who initiated PMRT within 12weeks of the last therapeutic intervention (48/50 [96.0] vs. 61/66 [92.4%], p=0.41). There was no significant difference in the percentage of patients in whom the internal mammary lymph nodes (IMNs) were targeted (72 vs. 80%, p=0.29) or in IMN target coverage (mean IMN V40.5Gy 92.6 vs. 94.1%, p=0.62). Reconstruction did not significantly affect the mean ipsilateral lung V20 (25.4 vs. 26.4%, p=0.37) or the mean heart dose (2.2 vs. 2.1Gy, p=0.63). In a specialized breast multidisciplinary practice, immediate breast reconstruction did not significantly delay PMRT, compromise target coverage, or increase dose to organs at risk.

Dosimetric comparison between automatic three-dimensional conformal radiotherapy, inverse three-dimensional conformal radiotherapy, and inverse intensity-modulated radiotherapy

Objective To compare dosimetric parameters between automatic three-dimensional conformal radiotherapy (a3DCRT), inverse three-dimensional conformal radiotherapy (i3DRT), inverse intensity-modulated radiotherapy (iIMRT). Methods Ten lung cancer patients with a single target and 10 intracranial tumor patients also with a single target, who were treated in our radiotherapy center from 2014 to 2015, were included in the study. Their image data were transferred to RayStation 4.5 via network, and then the treatment plans for a3DCRT, i3DCRT, and iIMRT were designed for the 20 patients. The dosimetric parameters for planning target volume (PTV) and organs at risk (OAR) were compared between the three plans using multiple dependent variables and two dependent variables. Results For lung cancer patients, iIMRT achieved better results in D98%, D50%, D2%, conformity index (CI), and homogeneity index (HI) than i3DCRT and a3DCRT (P=0.007, 0.001, 0.002, 0.000, and 0.000), and the CI of a3DCRT was superior to that of i3DCRT (P=0.000); there were no significant differences in heart D33, spinal cord Dmax and D1 cm3, and both lungs between the three plans (P=0.702, 0.237, 0.163, 0.739, 0.908, 0.832, 0.886, 0.722, 0.429, 0.840, and 0.702). For intracranial tumor patients, there were no significant differences in dosimetric parameters between the three plans, except that the CI of iIMRT and a3DCRT was superior to that of i3DCRT (P=0.648, 0.783, 0.256, 0.931, 0.002, and 0.034); there were no significant differences in whole brain irradiation dose between the three plans (P=0.446, 0.755, 0.772, 0.0266, 0.440, 0.290, and 0.939). Conclusions For the single target in patients with lung cancer and intracranial tumors, a3DCRT can improve the CI of PTV compared with i3DCRT, and shows no significant dosimetric disadvantage for OARs compared with iIMRT. Considering the simplicity and low cost of 3DCRT, a3DCRT holds promise as a novel radiotherapy technique. Key words: Beamset’s orientation auto-optimization; Inverse three-dementional conformal radiotherapy; Automatic three-dementional conformal radiotherapy; Inverse intensity-modulated radiotherapy

Comparison of dosimetric and radiobiological parameters on plans for prostate stereotactic body radiotherapy using an endorectal balloon for different dose-calculation algorithms and delivery-beam modes

The purpose of this study was to evaluate the impact of dosimetric and radiobiological parameters on treatment plans by using different dose-calculation algorithms and delivery-beam modes for prostate stereotactic body radiation therapy using an endorectal balloon. For 20 patients with prostate cancer, stereotactic body radiation therapy (SBRT) plans were generated by using a 10-MV photon beam with flattening filter (FF) and flattening-filter-free (FFF) modes. The total treatment dose prescribed was 42.7 Gy in 7 fractions to cover at least 95% of the planning target volume (PTV) with 95% of the prescribed dose. The dose computation was initially performed using an anisotropic analytical algorithm (AAA) in the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA) and was then re-calculated using Acuros XB (AXB V. 11.0.34) with the same monitor units and multileaf collimator files. The dosimetric and the radiobiological parameters for the PTV and organs at risk (OARs) were analyzed from the dose-volume histogram. An obvious difference in dosimetric parameters between the AAA and the AXB plans was observed in the PTV and rectum. Doses to the PTV, excluding the maximum dose, were always higher in the AAA plans than in the AXB plans. However, doses to the other OARs were similar in both algorithm plans. In addition, no difference was observed in the dosimetric parameters for different delivery-beam modes when using the same algorithm to generate plans. As a result of the dosimetric parameters, the radiobiological parameters for the two algorithm plans presented an apparent difference in the PTV and the rectum. The average tumor control probability of the AAA plans was higher than that of the AXB plans. The average normal tissue complication probability (NTCP) to rectum was lower in the AXB plans than in the AAA plans. The AAA and the AXB plans yielded very similar NTCPs for the other OARs. In plans using the same algorithms, the NTCPs for delivery-beam modes showed no differences. This study demonstrated that the dosimetric and the radiobiological parameters for the PTV and the rectum affected the dose-calculation algorithms for prostate SBRT using an endorectal balloon. However, the dosimetric and the radiobiological parameters in the AAA and the AXB plans for other OARs were similar. Furthermore, difference between the dosimetric and the radiobiological parameters for different delivery-beam modes were not found when the same algorithm was used to generate the treatment plan.