A comparative analysis of Acuros XB and the analytical anisotropic algorithm for volumetric modulation arc therapy

BackgroundThis study aimed to verify the dosimetric impact of Acuros XB (AXB) (AXB, Varian Medical Systems Palo Alto CA, USA), a two model-based algorithm, in comparison with Anisotropic Analytical Algorithm (AAA ) calculations for prostate, head and neck and lung cancer treatment by volumetric modulated arc therapy (VMAT ), without primary modification to AA. At present, the well-known and validated AA algorithm is clinically used in our department for VMAT treatments of different pathologies. AXB could replace it without extra measurements. The treatment result and accuracy of the dose delivered depend on the dose calculation algorithm.Materials and methodNinety-five complex VMAT plans for different pathologies were generated using the Eclipse version 15.0.4 treatment planning system (TPS). The dose distributions were calculated using AA and AXB (dose-to-water, AXB_w and dose-to-medium, AXB_m), with the same plan parameters for all VMAT plans. The dosimetric parameters were calculated for each planning target volume (PTV) and involved organs at risk (OA R). The patient specific quality assurance of all VMAT plans has been verified by Octavius^®-4D phantom for different algorithms.ResultsThe relative differences among AA, AXB_w and AXB_m, with respect to prostate, head and neck were less than 1% for PTV D_95%. However, PTV D_95% calculated by AA tended to be overestimated, with a relative dose difference of 3.23% in the case of lung treatment. The absolute mean values of the relative differences were 1.1 ± 1.2% and 2.0 ± 1.2%, when comparing between AXB_w and AA, AXB_m and AA, respectively. The gamma pass rate was observed to exceed 97.4% and 99.4% for the measured and calculated doses in most cases of the volumetric 3D analysis for AA and AXB_m, respectively.ConclusionThis study suggests that the dose calculated to medium using AXB_m algorithm is better than AAA and it could be used clinically. Switching the dose calculation algorithm from AA to AXB does not require extra measurements.     

Treatment planning and dosimetric comparison study on two different volumetric modulated arc therapy delivery techniques

Aim

To compare and evaluate the performance of two different volumetric modulated arc therapy delivery techniques.

Background

Volumetric modulated arc therapy is a novel technique that has recently been made available for clinical use. Planning and dosimetric comparison study was done for Elekta VMAT and Varian RapidArc for different treatment sites.

Materials and methods

Ten patients were selected for the planning comparison study. This includes 2 head and neck, 2 oesophagus, 1 bladder, 3 cervix and 2 rectum cases. Total dose of 50 Gy was given for all the plans. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. All plans were generated with 6 MV X-rays for both RapidArc and Elekta VMAT. Plans were evaluated based on the ability to meet the dose volume histogram, dose homogeneity index, radiation conformity index, estimated radiation delivery time, integral dose and monitor units needed to deliver the prescribed dose.

Results

RapidArc plans achieved the best conformity (CI_95% = 1.08 ± 0.07) while Elekta VMAT plans were slightly inferior (CI_95% = 1.10 ± 0.05). The in-homogeneity in the PTV was highest with Elekta VMAT with HI equal to 0.12 ± 0.02 Gy when compared to RapidArc with 0.08 ± 0.03. Significant changes were observed between the RapidArc and Elekta VMAT plans in terms of the healthy tissue mean dose and integral dose. Elekta VMAT plans show a reduction in the healthy tissue mean dose (6.92 ± 2.90) Gy when compared to RapidArc (7.83 ± 3.31) Gy. The integral dose is found to be inferior with Elekta VMAT (11.50 ± 6.49) × 10⁴ Gy cm³ when compared to RapidArc (13.11 ± 7.52) × 10⁴ Gy cm³. Both Varian RapidArc and Elekta VMAT respected the planning objective for all organs at risk. Gamma analysis result for the pre-treatment quality assurance shows good agreement between the planned and delivered fluence for 3 mm DTA, 3% DD for all the evaluated points inside the PTV, for both VMAT and RapidArc techniques.

Conclusion

The study concludes that a variable gantry speed with variable dose rate is important for efficient arc therapy delivery. RapidArc presents a slight improvement in the OAR sparing with better target coverage when compared to Elekta VMAT. Trivial differences were noted in all the plans for organ at risk but the two techniques provided satisfactory conformal avoidance and conformation.     

A comparative study evaluating the dose volume parameters in 3D conformal radiation of left sided whole breast irradiation including regional lymphnodes — a need of resource constrained countries

BackgroundThe purpose of this study was to compare four 3D conformal radiation techniques in treatment of left breast cancer patients.Materials and methodsRadiation was planned for 20 patients to the left breast and regional lymph nodes using four techniques: partially wide tangents, photon-photon mix, photon-electron mix and 30/70 photon-electron mix. All plans were evaluated for internal mammary nodes (IMN) coverage, hotspot and normal tissue constraints.ResultThe 85% of planning target volume (PTV) coverage was lesser for upper IMN than the lower IMN (below the lower border of the clavicular head) for all four techniques. The lower IMN coverage was better for partially wide tangent (80.46%) and photon-photon mix (88.88%). The lowest value of hotspot was seen in the partially wide tangent technique (112.69% ± 1.92). Hotspot is unacceptably high in both photon-electron mix and 30/70 photon-electron mix (> 120%). Left lung mean dose for all techniques on a pair-wise comparison showed no statistical difference. Left lung V20 values for partially wide tangent was 37.56% ± 8.17 and for photon-photon mix it was 40.49% ± 3.36. The mean heart dose with partially wide tangent was 9.43 ± 3.15 Gy and with photon-photon mix it was 10.10 ± 2.70 Gy. The mean heart dose for photon-electron mix was 7.56 ± 1.95 Gy and for 30/70 photon-electron mix it was 7.98 ± 2.16 Gy.ConclusionNo single technique satisfies all the criteria. The decision should be made on a case-by-case basis, considering the anatomy of the patient, availability of electron facilities and setup accuracy and reproducibility.     

Dosimetric comparison of normal breathing and deep inspiration breath hold technique for synchronous bilateral breast cancer using 6MV flattened beam and flattening filter free beam

BackgroundThe present study was to investigate the usefulness of deep inspiration breath hold (DIBH) in bilateral breast patients using 6MV flattened beam (FB) and flattening filter free beam (FFFB).Materials and methodsTwenty bilateral breast cancer patients were simulated, using left breast patients treated with DIBH technique. CT scans were performed in the normal breathing (NB) and DIBH method. Three-dimensional conformal radiotherapy (3DCRT) and volumetric arc therapy (VMAT) plans were generated.ResultsIn our study the best organ at risk (OAR) sparing is achieved in the 3DCRT DIBH plan with adequate PTV coverage (V₉₅ ≥ 47.5 Gy) as compared to 6MV FB and FFFB VMAT DIBH plans. The DIBH scan plan reduces the heart mean dose significantly at the rate of 49% in 3DCRT (p = 0.00) and 22% in VMAT (p = 0.010). Similarly, the DIBH scan plan produces lesser common lung mean dose of 18% in 3DCRT (p = 0.011) and 8% in VMAT (0.007) as compared to the NB scan. The conformity index is much better in VMAT FB (1.04 ± 0.04 vs. 1.04 ± 0.05), p =1.00 and VMAT FFFB (1.04 ± 0.05 vs. 1 ± 0.24, p = 0.345) plans as compared to 3DCRT (1.63 ± 0.2 vs. 1.47 ± 0.28, p = 0.002). The homogeneity index of all the plans is less than 0.15. The global dmax is more in VMAT FFFB DIBH plan (113.7%). The maximum MU noted in the NB scan plan (478 vs. 477MU, 1366 vs. 1299 MU and 1853 vs. 1788 MU for 3DCRT, VMAT FB and VMAT FFFB technique as compared to DIBH scan.ConclusionWe recommend that the use of DIBH techniques for bilateral breast cancer patients significantly reduces the radiation doses to OARs in both 3DCRT and VMAT plans.     

Comparison of pre-treatment and in-vivo dosimetry for advanced radiotherapy of prostate cancer

BackgroundThe usage of advanced radiotherapy techniques requires validation of a previously calculated dose with the precise delivery with a linear accelerator. This study aimed to review and evaluate new verification methods of dose distribution. Moreover, our purpose was to define an internal protocol of acceptance for in-vivo measurements of dose distribution.Materials and methodsThis study included 43 treatment plans of prostate cancer calculated using the Monte Carlo algorithm. All plans were delivered using the Volumetric Modulated Arc Therapy (VMAT) technique of advanced radiotherapy by the linear accelerator Elekta VersaHD. The dose distribution was verified using: MatriXX, iViewDose, and in-vivo measurements. The verification also included recalculation of fluence maps of quality assurance plans in another independent algorithm.ResultsThe acceptance criterion of 95% points of dose in agreement was found for pre-treatment verification using MatriXX; the average γ value was 99.09 ± 0.93 (SD) and 99.64 ± 0.35 (SD) for recalculation in the Collapse Cone algorithm. Moreover, using the second algorithm in the verification process showed a positive correlation ρ = 0.58, p < 0.001. However, verification using iViewDose in a phantom and in-vivo did not meet this γ-pass rate.ConclusionsEvaluation of gamma values for in-vivo measurements utilizing iViewDose software was helpful to establish an internal dosimetry protocol for prostate cancer treatments. We assumed value at a minimum of 50% points of the dose in agreement with the 3%/3 mm criterion as an acceptable compliance level. The recalculated dose distribution of QA plans in regard to the Collapse Cone algorithm in the other treatment planning system can be used as a pre-treatment verification method used by a medical physicist in their daily work. The effectiveness of use in iViewDose software, as a pre-treatment tool, is still debatable, unlike the MatriXX device.     

Volumetric modulated arc therapy for prostate cancer patients with hip prosthesis

Aim

To study the use of RapidArc techniques in the treatment of prostate cancer patients with hip prosthesis.

Background

An important aspect of treatment planning is to achieve dose homogeneity inside the planning target volume (PTV). Especially for those patients presenting with hip prosthesis, it becomes a challenging task to achieve dose uniformity inside the PTV.

Materials and methods

Five prostate patients presenting with hip prosthesis who had undergone radical radiotherapy were selected for this study. Depending on the composition of prosthesis, a predefined set of Hounsfield values were assigned to each study set. RapidArc plans were generated on an Eclipse treatment planning system. Two arcs that include clockwise and counter-clockwise arcs were used in all these cases. To avoid beams passing through the prosthesis, a simple structure was defined around it with 1 cm margin and a strict dose constraint applied to the block during VMAT optimization.

Results

The mean D2/D98 ratio of PTV for all the patients was 1.06 ± 0.01. The mean percentage rectum volume receiving 50 Gy, 60 Gy, 70 Gy and 75 Gy for all the patients were 33.1 ± 5.9, 21.7 ± 5.5, 13.8 ± 4.4 and 9.5 ± 3.0, respectively.

Conclusions

This study shows that using a double arc RapidArc technique is a simple and effective treatment method of treating prostate cancer in patients presenting with a hip prosthesis. The definition of a beam avoidance structure encompassing the prosthesis and applying strict dose constraints to it reduces the beam contribution to the prosthesis     

Quality assurance-based optimization (QAO): Towards improving patient-specific quality assurance in volumetric modulated arc therapy plans using machine learning

IntroductionPrevious literature has shown general trade-offs between plan complexity and resulting quality assurance (QA) outcomes. However, existing solutions for controlling this trade-off do not guarantee corresponding improvements in deliverability. Therefore, this work explored the feasibility of an optimization framework for directly maximizing predicted QA outcomes of plans without compromising the dosimetric quality of plans designed with an established knowledge-based planning (KBP) technique.Materials and MethodsA support vector machine (SVM) was developed – using a database of 500 previous VMAT plans – to predict gamma passing rates (GPRs; 3%/3mm percent dose-difference/distance-to-agreement with local normalization) based on selected complexity features. A heuristic, QA-based optimization (QAO) framework was devised by utilizing the SVM model to iteratively modify mechanical treatment features most commonly associated with suboptimal GPRs. Specifically, leaf gaps (LGs) <50 mm were widened by random amounts, which impacts all aperture-based complexity features. 13 prostate KBP-guided VMAT plans were optimized via QAO using user-specified maximum LG displacements before corresponding changes in predicted GPRs and dose were assessed.ResultsPredicted GPRs increased by an average of 1.14 ± 1.25% (p = 0.006) with QAO using a 3 mm maximum random LG displacement. There were small differences in dose, resulting in similarly small changes in tumor control probability (maximum increase = 0.05%) and normal tissue complication probabilities in the bladder, rectum, and femoral heads (maximum decrease = 0.2% in the rectum).ConclusionThis study explored the feasibility of QAO and warrants future investigations of further incorporating QA endpoints into plan optimization.     

Comparative performance analysis of 2D and 3D gamma metrics for patient specific QA in VMAT using Octavius 4D with 2D-Array 1500

IntroductionGamma pass percentage (GPP) is the predominant metric used for Patient Specific Quality Assurance (PSQA) in radiation therapy. The dimensionality of the measurement geometry in PSQA has evolved from 2D planar to 3D planar, and presently to state-of-the-art 3D volumetric geometry. We aim to critically examine the performance of the three-dimensional gammas vis-à-vis the older gamma metrics of lower dimensionality to determine their mutual fungibility in PSQA, using clinically approved Volumetric Arc Therapy (VMAT) plans.Methods and materialsGamma pass percentages derived from PSQA for VMAT plans using Octavius 4D phantom with 2D-Array 1500 and its proprietary software were recorded. 2D planar, 3D planar, and 3D volumetric gamma pass percentages were retrospectively extracted for multiple treatment plans at three sites, using three acceptance limits, and for two modes of normalization. The differences in mean pass percentages, and the pairwise correlation between geometries were calculated within limits of statistical significance.ResultsA significant increase in mean pass rates was observed from 2D planar to 3D planar geometries. The difference was less pronounced from 3D planar to 3D volumetric. 2D planar v/s 3D planar showed a significant degree of correlation among themselves, which was not seen against most of the 3D volumetric pass rates.ConclusionThe mean gamma pass rates show conclusive evidence of the benefits of shifting from 2D planar to higher dimensions measurement geometries, but the benefits of using 3D volumetric compared to 3D planar is not always unequivocal. The correlations show mixed results regarding the interdependence of pass percentages at different geometries.     

Analysis of the planned,delivered dose distributions and quality assurance for helical tomotherapy and volumetric modulated arc therapy in locally advanced non-small cell lung cancer

BackgroundWith full access to both helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT), we compared locally advanced non-small cell lung cancer (LA-NSCLC) treatment plans and verified the plans using patient-specific pretreatment quality assurance (PSQA).Materials and methodsFor each of the seventeen patients included in the study, two treatment plans (i.e. HT and VMAT) were created. Optimized plans were evaluated following the ICRU 83 criteria. Planned quality indexes and dosimetric parameters were compared. Lastly, all plans were subjected to PSQA assessment by determining the gamma passing rate (GPR).ResultsAll dosimetry results obtained from the planning target volume passed the ICRU 83 criteria. With regard to similar homogeneity indices, VMAT produced better conformity number values than HT (0.78 vs. 0.64), but differences in the values were insignificant. Furthermore, VMAT was associated with a significantly shorter mean treatment time (1.91 minutes vs. 6.66 minutes). For PSQA assessment, both techniques resulted in adequate GPR values (> 90% at the 3%/3 mm criteria).ConclusionBoth HT and VMAT techniques led to the generation of clinically satisfactory and reliable radiotherapy plans. However, the VMAT plan was associated with a non-significantly better degree of conformity and a significantly shorter treatment time. Thus, VMAT was determined to be a better choice for LA-NSCLC.     

Vitamin D? Supplementation in Batswana Children and Adults with HIV: A Pilot Double Blind Randomized Controlled Trial

ObjectivesSince vitamin D insufficiency is common worldwide in people with HIV, we explored safety and efficacy of high dose cholecalciferol (D₃) in Botswana, and evaluated potential modifiers of serum 25 hydroxy vitamin D change (Δ25D).DesignProspective randomized double-blind 12-week pilot trial of subjects ages 5.0–50.9 years.MethodsSixty subjects randomized within five age groups to either 4000 or 7000IU per day of D₃ and evaluated for vitamin D, parathyroid hormone, HIV, safety and growth status. Efficacy was defined as serum 25 hydroxy vitamin D (25D) ≥32ng/mL, and safety as no simultaneous elevation of serum calcium and 25D. Also assessed were HIV plasma viral RNA viral load (VL), CD4%, anti-retroviral therapy (ART) regime, and height-adjusted (HAZ), weight-adjusted (WAZ) and Body Mass Index (BMIZ) Z scores.ResultsSubjects were 50% male, age (mean±SD) 19.5±11.8 years, CD4% 31.8±10.4, with baseline VL log₁₀ range of <1.4 to 3.8 and VL detectable (>1.4) in 22%. From baseline to 12 weeks, 25D increased from 36±9ng/ml to 56±18ng/ml (p<0.0001) and 68% and 90% had 25D ≥32ng/ml, respectively (p = 0.02). Δ25D was similar by dose. No subjects had simultaneously increased serum calcium and 25D. WAZ and BMIZ improved by 12 weeks (p<0.04). HAZ and CD4% increased and VL decreased in the 7000IU/d group (p<0.04). Younger (5–13y) and older (30–50y) subjects had greater Δ25D than those 14–29y (26±17 and 28±12 vs. 11±11ng/ml, respectively, p≤0.001). Δ25D was higher with efavirenz or nevirapine compared to protease inhibitor based treatment (22±12, 27±17, vs. 13±10, respectively, p≤0.03).ConclusionsIn a pilot study in Botswana, 12-week high dose D₃ supplementation was safe and improved vitamin D, growth and HIV status; age and ART regimen were significant effect modifiers.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT02189902","term_id":"NCT02189902"}}NCT02189902     

The Use of Biologically Related Model (Eclipse) for the Intensity-Modulated Radiation Therapy Planning of Nasopharyngeal Carcinomas

Purpose

Intensity-modulated radiation therapy (IMRT) is the most common treatment technique for nasopharyngeal carcinoma (NPC). Physical quantities such as dose/dose-volume parameters are used conventionally for IMRT optimization. The use of biological related models has been proposed and can be a new trend. This work was to assess the performance of the biologically based IMRT optimization model installed in a popular commercial treatment planning system (Eclipse) as compared to its dose/dose volume optimization model when employed in the clinical environment for NPC cases.

Methods

Ten patients of early stage NPC and ten of advanced stage NPC were selected for this study. IMRT plans optimized using biological related approach (BBTP) were compared to their corresponding plans optimized using the dose/dose volume based approach (DVTP). Plan evaluation was performed using both biological indices and physical dose indices such as tumor control probability (TCP), normal tissue complication probability (NTCP), target coverage, conformity, dose homogeneity and doses to organs at risk. The comparison results of the more complex advanced stage cases were reported separately from those of the simpler early stage cases.

Results

The target coverage and conformity were comparable between the two approaches, with BBTP plans producing more hot spots. For the primary targets, BBTP plans produced comparable TCP for the early stage cases and higher TCP for the advanced stage cases. BBTP plans reduced the volume of parotid glands receiving doses of above 40 Gy compared to DVTP plans. The NTCP of parotid glands produced by BBTP were 8.0±5.8 and 7.9±8.7 for early and advanced stage cases, respectively, while those of DVTP were 21.3±8.3 and 24.4±12.8, respectively. There were no significant differences in the NTCP values between the two approaches for the serial organs.

Conclusions

Our results showed that the BBTP approach could be a potential alternative approach to the DVTP approach for NPC.     

Influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy

Aim

To study the influence of segment width on plan quality for volumetric modulated arc based stereotactic body radiotherapy.

Background

The redundancy of modulation for regularly shaped small volume tumors results in creation of many small segments and an increase of monitor units, with a consequent prolongation of treatment and uncertainty in treatment delivery.

Materials and methods

Six cases each in lung, abdomen and liver were taken for the study. For each case, three VMAT SBRT plans were generated with different penalties on minimum segment width of 0.5, 1.0 and 1.5 cm. A comparison was made on the metrics of dose volume histogram, dosimetric indices, monitor units (MUs) and delivery accuracy.

Results

The mean reduction of total MUs when compared with 0.5 cm plan was observed as 12.7 ± 6.0% and 17.5 ± 7.2% for 1.0 cm and 1.5 cm of minimum segment width, respectively. The p value showed a significant degradation in dosimetric indices for 1.5 cm plans when compared with 0.5 cm and 1.0 cm plans. The average deviation of measured dose with TPS calculated was 3.0 ± 1.1%, 2.1 ± 0.84% and 1.8 ± 0.9% for 0.5, 1.0 and 1.5 cm, respectively. The calculated gamma index with pass criteria of 2% dose difference and 2 mm distance to agreement was 95.9 ± 2.8%, 96.5 ± 2.6% and 97.8 ± 1.6% as calculated for 0.5, 1.0 and 1.5 cm of penalties, respectively. In view of the trade off between delivery efficiency and plan quality, 1 cm minimum segment width plans showed an improvement.

Conclusions

VMAT SBRT plans with increased optimal value of minimum segment width showed better plan quality and delivery efficiency for stereotactic body radiotherapy.     

Evaluation of volumetric modulated arc therapy (VMAT) — based total body irradiation (TBI) in pediatric patients

BackgroundThe dosimetric characterization of volumetric modulated arc therapy (VMAT)-based total-body irradiation (TBI) in pediatric patients is evaluated.Materials and methodsTwenty-two patients between the ages of 2 and 12 years were enrolled for VMAT-based TBI from 2018 to 2020. Three isocenters were irradiated over three overlapping arcs. While prescribing 90% of the TBI dose to the planning treatment volume (PTV), two fractions (2 Gy each) were delivered each day; hence 12 Gy was delivered in six fractions. During treatment optimization, the mean lung and kidney doses were set not to exceed 7 Gy and 7.5 Gy, respectively. The maximum lens dose was also set to less than 4 Gy. Patient quality assurance was carried out by comparing treatment planning system doses to the 3-dimensional measured doses by the ArcCHECK^® detector. The electronic portal imaging device (EPID) gamma indices were also obtained.ResultsThe average mean lung dose was 7.75 ± 0.18 Gy, mean kidney dose 7.63 ± 0.26 Gy, maximum lens dose 4.41 ± 0.39 Gy, and the mean PTV dose 12.69 ± 0.16 Gy. The average PTV heterogeneity index was 1.15 ± 0.03. Average differences in mean kidney dose, mean lung dose, and mean target dose were 2.79% ± 0.88, 0.84% ± 0.45 and 0.93% ± 0.47, respectively; when comparing planned and ArcCHECK^® measured doses. Only grade 1–2 radiation toxicities were recorded, based on CTCAE v5.0 scoring criteria.ConclusionsVMAT-TBI was characterized with good PTV coverage, homogeneous dose distribution, planned and measured dose agreement, and low toxicity.     

Comparison of dosimetric variation between prostate IMRT and VMAT due to patient's weight loss: Patient and phantom study

Aim

This study compared the dosimetric impact between prostate IMRT and VMAT due to patient''s weight loss.

Background

Dosimetric variation due to change of patient''s body contour is difficult to predict in prostate IMRT and VMAT, since a large number of small and irregular segmental fields is used in the delivery.

Materials and methods

Five patients with prostate volumes ranging from 32.0 to 86.5 cm³ and a heterogeneous pelvis phantom were used for prostate IMRT and VMAT plans using the same set of dose–volume constraints. Doses in IMRT and VMAT plans were recalculated with the patient''s and phantom''s body contour reduced by 0.5–2 cm to mimic size reduction. Dose coverage/criteria of the PTV and CTV and critical organs (rectum, bladder and femoral heads) were compared between IMRT and VMAT.

Results

In IMRT plans, increases of the D99% for the PTV and CTV were equal to 4.0 ± 0.1% per cm of reduced depth, which were higher than those in VMAT plans (2.7 ± 0.24% per cm). Moreover, increases of the D30% of the rectum and bladder per reduced depth in IMRT plans (4.0 ± 0.2% per cm and 3.5 ± 0.5% per cm) were higher than those of VMAT (2.2 ± 0.2% per cm and 2.0 ± 0.6% per cm). This was also true for the increase of the D5% for the right femoral head in a patient or phantom with size reduction due to weight loss.

Conclusions

VMAT would be preferred to IMRT in prostate radiotherapy, when a patient has potential to suffer from weight loss during the treatment.     

Intermediate Megavoltage Photon Beams for Improved Lung Cancer Treatments

The goal of this study is to evaluate the effects of intermediate megavoltage (3-MV) photon beams on SBRT lung cancer treatments. To start with, a 3-MV virtual beam was commissioned on a commercial treatment planning system based on Monte Carlo simulations. Three optimized plans (6-MV, 3-MV and dual energy of 3- and 6-MV) were generated for 31 lung cancer patients with identical beam configuration and optimization constraints for each patient. Dosimetric metrics were evaluated and compared among the three plans. Overall, planned dose conformity was comparable among three plans for all 31 patients. For 21 thin patients with average short effective path length (< 10 cm), the 3-MV plans showed better target coverage and homogeneity with dose spillage index R_50% = 4.68±0.83 and homogeneity index = 1.26±0.06, as compared to 4.95±1.01 and 1.31±0.08 in the 6-MV plans (p < 0.001). Correspondingly, the average/maximum reductions of lung volumes receiving 20 Gy (V_20Gy), 5 Gy (V_5Gy), and mean lung dose (MLD) were 7%/20%, 9%/30% and 5%/10%, respectively in the 3-MV plans (p < 0.05). The doses to 5% volumes of the cord, esophagus, trachea and heart were reduced by 9.0%, 10.6%, 11.4% and 7.4%, respectively (p < 0.05). For 10 thick patients, dual energy plans can bring dosimetric benefits with comparable target coverage, integral dose and reduced dose to the critical structures, as compared to the 6-MV plans. In conclusion, our study indicated that 3-MV photon beams have potential dosimetric benefits in treating lung tumors in terms of improved tumor coverage and reduced doses to the adjacent critical structures, in comparison to 6-MV photon beams. Intermediate megavoltage photon beams (< 6-MV) may be considered and added into current treatment approaches to reduce the adjacent normal tissue doses while maintaining sufficient tumor dose coverage in lung cancer radiotherapy.     

Race/Ethnicity-Specific Association of Vitamin D and Global DNA Methylation: Cross-Sectional and Interventional Findings

ObjectivesUnderstanding of the influence of vitamin D deficiency on epigenome will provide novel insights into the chronic disease risk. We tested our hypotheses that 1) vitamin D deficiency is associated with global hypomethylation and this association may be race/ethnicity dependent; and 2) vitamin D supplementation will increase global DNA methylation level.MethodsA two-stage design, cross-sectional observation followed by a 16 week randomized, double- blinded, placebo-controlled trial (RCT) of vitamin D3 supplementation, was undertaken. Global DNA methylation level (percentage of 5-methylcytosine, %5-mC) was quantified using leukocyte DNA with the MethylFlash^TM Methylated DNA Quantification kit (Epigentek). Global methylation data was obtained from 454 Caucasians and African Americans (42%) in the observation cohort and 58 African Americans with vitamin D deficiency in the dose responsive RCT.ResultsIn the cross-sectional study, African Americans had lower %5-mC than Caucasians (P = 0.04). A significant interaction was detected between plasma 25(OH)D and race on %5-mC (P = 0.05), as a positive association was observed between plasma 25(OH)D and %5-mC in African Americans (β = 0.20, p<0.01), but not in Caucasians (β = 0.03, p = 0.62). In the 16-week RCT, a dose-response benefit of vitamin D₃ supplementation was observed for %5-mC, as indicated by a significant linear upward trend (-0.01 ± 0.01%, placebo; 0.11 ± 0.01%, ~600 IU/day; 0.30 ± 0.01%, ~2,000 IU/day; and 0.65 ± 0.01%, ~4,000 IU/day group; P-trend = 0.04).ConclusionsVitamin D deficiency is associated with global hypomethylation in African Americans. Vitamin D3 supplementation increases global DNA methylation in a dose-response manner in African Americans with vitamin D deficiency.     

Comparison of dosimetric data of bone marrow between standard IMRT and bone marrow sparing IMRT in carcinoma cervix

BackgroundThe aim of the study was to assess the dosimetric comparison of bone marrow between standard IMRT(SD-IMRT) and bone marrow sparing IMRT (BMS-IMRT) among carcinoma cervix patients who underwent radical or adjuvant chemoradiation in a tertiary cancer center.Materials and methodsForty eligible patients of histo-pathologically proven carcinoma cervix were enrolled in the study that was randomized on a 1:1 basis between SD-IMRT and BMS-IMRT from July 2018 to October 2019. The whole pelvis, bilateral femoral heads, and upper 1/3^rd femur were contoured using the whole bone technique as a surrogate marker for the bone marrow. In both arms, V10, V20, and V40, bone marrow was noted along with mean, maximum, minimum dose, and total volume. DVH for the bone marrow in both arms was compared using the unpaired student t-test.ResultsWe found no significant difference in the mean of various parameters in SD-IMRT arm vs. BMS IMRT arm — for the bone marrow: V10 (89 ± 4.3% vs. 86.7 ± 3.7%), V20 (73.2 ± 5.3% vs. 73.1 ± 4.5%), V40 (23.9 ± 5.4% vs. 26.6 ± 7.4%) and, similarly, for mean dose (28.1 ± 3.5% vs. 28.1 ± 1.8%), maximum dose (53.4 ± 0.58% vs. 53.2 ± 0.58%), minimum dose (0.33 ± 0.18% vs. 0.38 ± 0.38%), total volume (961 ± 110 cc vs. 901 ± 152 cc).ConclusionThis study shows no statistically significant difference in dosimetry between the two groups, which suggests that SD-IMRT spares the bone marrow adequately. Therefore, the need for BMS-IMRT using the present contouring technique does not give any added advantage over SD-IMRT. However, large sample size, other novel contouring technique, and multivariate analysis are needed to reach a definite conclusion.