Static Intensity-modulated Radiotherapy Research Articles

Comparison of Doses to Parotid, Temporomandibular Joint, and Pharyngeal Constrictor Muscles Using Different Techniques in Radiotherapy for Oropharyngeal Cancer.

The purpose of this research was to compare two treatment techniques for oropharyngeal cancers: conventional linac-based static intensity-modulated radiotherapy (sIMRT) and helical tomotherapy (HT). The study examined several parameters, including target coverage, organs at risk, integral dose, and beam on time. Additionally, the study evaluated the doses to the parotid, temporomandibular joint, and pharyngeal constrictor muscles, which are important for swallowing. The present study retrospectively analyzed the data of 13 patients with oropharyngeal cancer who underwent radiotherapy between 2019 and 2021. The treatment plans for each patient were regenerated using both sIMRT and HT treatment planning systems with the sequential boost method. The techniques were evaluated and compared based on dose-volume histogram, homogeneity index, and conformity index parameters. The target coverage and organs at risk were statistically compared for two techniques. Additionally, the doses received by the healthy tissue volume were obtained for integral dose evaluation. The beam on time for each technique was assessed. When considering planning target volume evaluation, there was no difference in Dmeans between the two techniques and sIMRT demonstrated higher D2% values compared to the HT. The HT technique had better results for all organs at risk, such as the parotid, temporomandibular joint, and pharyngeal constrictor muscle. As for integral dose, it has been shown that the sIMRT technique provides better protection compared to HT. In addition, the beam on time was also longer with the HT technique. Both techniques may provide optimal target coverage for patients with oropharyngeal cancer. HT conferred notable advantages, especially with regard to critical structures implicated in swallowing, such as the parotid, temporomandibular joint, and pharyngeal constrictor muscle, in comparison to sIMRT.

Ten-Year Outcomes of Hypofractionated (45 Gy in 9 Fractions) Intensity Modulated Radiotherapy for Localized Prostate Cancer.

We reported 10-year outcomes of localized prostate cancers treated with hypofractionated intensity-modulated radiotherapy of 45 Gy in 9 consecutive fractions. From October 2011 to April 2017, thirty patients with localized prostate cancer were enrolled in this prospective trial. The median age of the patients was 72.5 years. According to NCCN recurrence risk criteria, eight patients were at low-risk group, 17 at intermediate risk group, 5 at high-risk group. All patients were treated with hypofractionated intensity-modulated radiotherapy (IMRT) of 45 Gy in 9 consecutive fractions to their prostate with or without seminal vesicles. Before radiotherapy, three gold fiducials were implanted into the prostate. In order to reduce the rectal high dose irradiation volume, an inflated rectal balloon was placed in the rectum at simulation and every treatment and patients were treated with comfortable full bladder. Static Intensity-modulated radiotherapy (SIMRT) was applied in 1 patient, Volumetric Modulated Arc Therapy (VMAT) in 27 patients, and tomotherapy in 2 patients. Image guided radiotherapy (IGRT) with gold fiducial registration was adopted. Twenty-six patients also received androgen deprivation therapy (ADT). The median time of ADT was 6 months. Progression⁃free survival (PFS) and overall survival (OS) were analyzed using Kaplan-Meier analysis. All grade ≥1 genitourinary (GU) and gastrointestinal (GI) toxicities were recorded using Common Terminology Criteria for Adverse Event version 5.0 (CTCAE 5.0) and Radiation Therapy Oncology Group (RTOG) late morbidity criteria, and GU and GI toxicities were cumulatively calculated. After a median follow-up of 102 months (65∼131 months), the 10-year OS was 90.0% (95% confidence interval, 83.3%-96.7%), and the 10-year PFS was 86.5% (95% confidence interval, 79.1%-93.9%). According to CTCAE 5.0, grade 1 acute gastrointestinal (GI) toxicity developed in 12 patients, grade 2 in 2 patients, grade 3 in 2 patients, and grade 1 acute genitourinary (GU) toxicity developed in 12 patients, grade 2 in 2 patients, and no grade 3 or higher toxicity occurred. According to RTOG late morbidity criteria, late (≥3 months after radiotherapy) grade 1 GI toxicity developed in 4 patients (13.3%), grade 2 in 1 (3.3%), grade 3 in 1 (3.3%), and late grade 1 GU toxicity occurred in 1 patient (3.3%), grade 2 in 1 (3.3%), grade 3 in 1 (3.3%). No grade 4 or higher GI and GU toxicities developed. Only one grade 3 GI and one grade 2 GU toxicities were observed for the maximum toxicity at the last follow-up. The potency was not evaluated. The 10-year oncologic outcomes of this shortened hypofractionated IMRT regimen for mainly low/intermediate risk prostate cancer patients is favorable with acceptable acute and late toxicities.

Clinical evaluation of 4D dynamic dose for thoracic tumor stereotactic body radiation therapy with variable parameters

ObjectiveTo evaluate the dose uncertainty in stereotactic body radiation therapy induced by respiratory motion using a 4D dynamic dose (4DDD) reconstruction method. MethodsA retrospective analysis was conducted on five lung cancer patients who received static intensity-modulated radiation therapy. The 4DDD was constructed using beam delivery log files, four-dimensional computed tomography (4DCT) scans, and treatment plans. To evaluate the impact of respiratory motion, 4DDD calculations were performed with 10 starting phases for each field. A total of 270 field doses were simulated and calculated. The differences between the cumulative volume histogram in whole-course treatment and the field doses' gamma passing rate (GPR) were compared. The correlations between plan complexity metrics and the dose deviation caused by respiratory motion were evaluated independently. The phase distributions of 398 subfields were calculated and evaluated for the influence of dose rate and breathing frequency. ResultsThe GPRs of all fields were different among various starting phases, with the highest range from 62.20% to 76.87% for 2 mm/3% GPR. The deviation of mean point dose was (5.42 ​± ​5.21) %, and the deviation in the mean dose and D98% within the internal gross tumor volume were (0.97 ​± ​0.71) % and (0.77 ​± ​0.53) %, respectively. There was a significant correlation between the beam aperture-to-volume (BA2V) ratio and the average 2 mm/2% GPR (R ​= 0.601, P ​< ​0.01). Lower dose rates led to a more homogeneous distribution of phases among subfields (t ​= ​44.100, P ​< ​0.001). ConclusionsDifferent beam starting phases had a limited impact on the overall treatment evaluation. However, the respiratory motion could be observed to induce dose deviations using the 4DDD reconstruction model, particularly for fields with small BA2V.

Ten-year outcomes of hypofractionated (45 Gy in 9 fractions) intensity-modulated radiotherapy for localized prostate cancer.

e17100 Background: We reported 10-year outcomes of localized prostate cancers treated with hypofractionated intensity-modulated radiotherapy of 45 Gy in 9 consecutive fractions. Methods: From October 2011 to April 2017, thirty patients with localized prostate cancer were enrolled in this prospective trial. The median age of the patients was 72.5 years. According to NCCN recurrence risk criteria, eight patients were at low risk group, 17 at intermediate risk group, 5 at high risk group. All patients were treated with hypofractionated intensity-modulated radiotherapy (IMRT) of 45 Gy in 9 consecutive fractions to their prostate with or without seminal vesicles. Before radiotherapy, three gold fiducials were implanted into the prostate. In order to reduce the rectal high dose irradiation volume , an inflated rectal balloon was placed in the rectum at simulation and every treatment and patients were treated with comfortable full bladder. Static Intensity-modulated radiotherapy (SIMRT) was applied in 1 patient, Volumetric Modulated Arc Therapy (VMAT) in 27 patients, and tomotherapy in 2 patients. Image guided radiotherapy (IGRT) with gold fiducial registration was adopted. Twenty-six patients also received androgen deprivation therapy (ADT). The median time of ADT was 6 months. Progression⁃free survival(PFS) and overall survival(OS) were analyzed using Kaplan-Meier analysis. All grade ≥1 genitourinary (GU) and gastrointestinal (GI) toxicities were recorded using Common Terminology Criteria for Adverse Event version 5.0 (CTCAE 5.0) and Radiation Therapy Oncology Group (RTOG) late morbidity criteria , and GU and GI toxicities were cumulatively calculated. Results: After a median follow-up of 102 months (65~131 months), the 10-year OS was 90.0%(95% confidence interval, 83.3%-96.7%), and the 10-year PFS was 86.5% (95% confidence interval, 79.1%-93.9%). According to CTCAE 5.0, grade 1 acute gastrointestinal (GI) toxicity developed in 12 patients, grade 2 in 2 patients, grade 3 in 2 patients, and grade 1 acute genitourinary (GU) toxicity developed in 12 patients, grade 2 in 2 patients, and no grade 3 or higher toxicity occurred. According to RTOG late morbidity criteria, late (≥3 months after radiotherapy) grade 1 GI toxicity developed in 4 patients (13.3%), grade 2 in 1 (3.3%), grade 3 in 1 (3.3%), and late grade 1 GU toxicity occurred in 1 patient (3.3%), grade 2 in 1 (3.3%), grade 3 in 1 (3.3%). No grade 4 or higher GI and GU toxicities developed. Only one grade 3 GI and one grade 2 GU toxicities were observed for the maximum toxicity at the last follow-up. The potency was not evaluated. Conclusions: The 10-year oncologic outcomes of this shortened hypofractionated IMRT regimen for mainly low/intermediate risk prostate cancer patients is favorable with acceptable acute and late toxicities.

Effective optimization strategy for large optimization volume object, remaining volume at risk (RVR): α-value selection and usage from generalized equivalent uniform dose (gEUD) curve deviation perspective

Objective. A large optimization volume for intensity-modulated radiation therapy (IMRT), such as the remaining volume at risk (RVR), is traditionally unsuitable for dose-volume constraint control and requires planner-specific empirical considerations owing to the patient-specific shape. To enable less empirical optimization, the generalized equivalent uniform dose (gEUD) optimization is effective; however, the utilization of parameter a-values remains elusive. Our study clarifies the a-value characteristics for optimization and to enable effective a-value use. Approach. The gEUD can be obtained as a function of its a-value, which is the weighted generalized mean; its curve has a continuous, differentiable, and sigmoid shape, deforming in its optimization state with retained curve characteristics. Using differential geometry, the gEUD curve changes in optimization is considered a geodesic deviation intervened by the forces between deforming and retaining the curve. The curvature and gradient of the curve are radically related to optimization. The vertex point (a = a k ) was set and the a-value roles were classified into the following three parts of the curve with respect to the a-value: (i) high gradient and middle curvature, (ii) middle gradient and high curvature, and (iii) low gradient and low curvature. Then, a strategy for multiple a-values was then identified using RVR optimization. Main results. Eleven head and neck patients who underwent static seven-field IMRT were used to verify the a-value characteristics and curvature effect for optimization. The lower a-value (i) (a = 1–3) optimization was effective for the whole dose-volume range; in contrast, the effect of higher a-value (iii) (a = 12–20) optimization addressed strongly the high-dose range of the dose volume. The middle a-value (ii) (around a = a k ) showed intermediate but effective high-to-low dose reduction. These a-value characteristics were observed as superimpositions in the optimization. Thus, multiple gEUD-based optimization was significantly superior to the exponential constraints normally applied to the RVR that surrounds the PTV, normal tissue objective (NTO), resulting in up to 25.9% and 8.1% improvement in dose-volume indices D2% and V10Gy, respectively. Significance. This study revealed an appropriate a-value for gEUD optimization, leading to favorable dose-volume optimization for the RVR region using fixed multiple a-value conditions, despite the very large and patient-specific shape of the region.

Dosimetric Study of the Effect of Calypso-Compatible Couch Top for Spine Stereotactic Body Radiation Therapy

Purpose: To study the effect of the Qfix kVue Calypso-compatible couch top on the dosimetry of Spine Stereotactic Body Radiation Therapy (SBRT). Methods and Materials: The computed tomography (CT) data set for Qfix kVue Calypso-compatible couch top with rails were imported into the treatment planning system (TPS). Nine patients who underwent spine SBRT were selected for this study. The inclusion criteria included patients who were treated on a stereotactic linear accelerator with 5 fractions or less from 2016 to 2017 without the couch model. Seven patients were treated with static intensity-modulated radiation therapy (IMRT) fields and two patients were treated using volumetric modulated arc therapy (VMAT) technique. The dose was recalculated for 1) couch top and rails setup (CR) 2) couch-top no rails setup (CNR), and then compared to 3) no couch no-rails setup (NCNR). Dose to 100% of the target volume (D100%), Dose to cover 99% of the target volume (D99%), Dose to cover 95% of the target volume (D95%), Dose to cover 90% of the target volume (D90%), volume receiving 100% of the prescription dose (V100%), conformity index (CI), dose gradient index (DGI), and spinal cord threshold and maximum dose were compared to the plan with NCNR. Results: The average D100% was 77.89% ± 11.78%, 74.51% ± 12.24%, and 75.83 ± 12.67% for NCNR, CR, CNR (р = 0.84), respectively. The average D99% was 91.64% ± 9.57%, 89.93% ± 9.48%, and 91.15% ± 9.55% for NCNR, CR, CNR (р = 0.98), respectively. The average D95% was 99.14% ± 9.96%, 95.23% ± 9.76, and 96.78% ± 9.84% for NCNR, CR, CNR (р = 0.047), respectively. The average D90% was 101.3% ± 0.65%, 97.11% ± 2.48%, and 98.75% ± 2.12% for NCNR, CR, CNR (р = 0.0004), respectively. The maximum dose to the spinal cord was 1750.79 ± 41.84, 1672.90 ± 40.90, and 1709.91 ± 41.35 (cGy) for NCNR, CR, CNR (р = 0.97), respectively. In all cases, the spinal cord threshold dose was far below the tolerances and the differences were insignificant. Average CI was 1.18 ± 0.16, 0.53 ± 0.39, and 0.86 ± 0.24 for NCNR, CR, CNR (р = 0.0002), respectively. Conclusions: The study investigated the dosimetric impact of Qfix kVue Calypso-compatible couch top on the quality of the spinal SBRT treatment using static IMRT or VMAT techniques. IMRT plans showed more sensitivity to the couch being in the plan than the VMAT plans.

Correlation of Left Anterior Descending Coronary Artery Radiation Dose with Major Adverse Cardiac Events and Feasibility of Coronary Artery Sparing Treatment Planning in Lung Cancer

<h3>Purpose/Objective(s)</h3> Radiation dose to the left anterior descending (LAD) coronary artery is associated with major adverse cardiac events (MACE) in patients with locally advanced non-small cell lung cancer (LA-NSCLC). However, the newly identified LAD metric (percent volume receiving 15 Gy [LAD V15Gy]) has not been independently validated and the extent to which modern radiotherapy (RT) planning techniques can reduce LAD V15Gy without exceeding dose tolerances to other critical organs at risk (OAR) remains uncertain. <h3>Materials/Methods</h3> This is a single institution retrospective study of 98 patients with LA-NSCLC treated with RT between 2005-2020. The LAD was manually delineated for each patient. MACE (unstable angina, myocardial infarction, heart failure, coronary revascularization, and cardiac death) cumulative incidence was estimated and Fine and Gray regressions were performed, adjusting for non-cardiac death as a competing risk. Patients who received LAD V15Gy ≥10% and experienced MACE were re-planned with volumetric-modulated arc therapy (VMAT) to optimize reduction of LAD V15Gy while maintaining target coverage and meeting standard OAR constraints. <h3>Results</h3> The median follow up was 23.2 months. The median age was 69 years, 30.6% of patients had pre-existing coronary heart disease (CHD) or a CHD risk-equivalent. The mean LAD V15Gy was 32% (standard deviation [SD] 27.8%). Ten patients developed at least one MACE, with a 2-year cumulative incidence of 10.2% (95% CI: 3.1-17.0%). Adjusting for pre-existing CHD there was an increased risk of MACE with LAD V15Gy (subdistribution hazard ratio 1.03; 95% CI 1.00-1.06; p=.034), with a significant interaction between LAD V15Gy and CHD (p=.005). Among the 10 patients who developed a MACE, 6 (60%) had an LAD V15Gy ≥ 10% (mean 52%, range 10-100%). The original planning techniques included: 3-dimensional conformal RT (3D-CRT; n=2), static intensity-modulated RT (IMRT; n=2), and VMAT (n=2). In 4 of these plans (n=2 IMRT, n=1 3D-CRT, n=1 VMAT), the re-planned LAD V15Gy was reduced to <10%, however all 6/6 plans achieved some degree of LAD V15Gy reduction (range, 9-100%). Specifically, optimization with LAD-sparing VMAT achieved a mean absolute decrease of 35.1% for LAD V15Gy (SD 32.4%) and 6.2 Gy mean heart dose (SD 10.9 Gy), with a concomitant mean increase of 0.8 Gy mean lung dose (SD 1.8 Gy), and mean lung V20Gy of 0.2% (SD 4.1%). All re-plans achieved similar target coverage and remained within national guideline OAR constraints. <h3>Conclusion</h3> LAD V15Gy is associated with an increased risk of MACE in this independent retrospective cohort. VMAT-based LAD-sparing RT plan optimization is feasible and can achieve meaningful reductions in LAD V15Gy with potentially clinically acceptable tradeoffs in lung dose. Together, these findings underscore the need for more aggressive LAD-sparing RT planning approaches.

The impact of the radiotherapy technique in sparing the heart substructures in central tumor irradiation in lung cancer

Abstract Introduction: In thoracic radiotherapy (RT), heart sparing is very essential, as the high cardiac dose is associated with poor survival in patients with locally advanced non-small-cell lung cancer (NSCLC). The study aims to determine the doses exposed to heart substructures and coronary arteries by different RT techniques in central tumor irradiation in lung cancer. Methods: Twenty patients with NSCLC, irradiated between January 2018 and December 2020 in our department, were included in this study. Patients whose primary tumor was centrally located in the left lung were selected. The heart substructures [left atrium, right atrium (RA), left ventricle, and right ventricle] and coronary arteries (left main, left anterior descending, circumflex, and right coronary arteries) were delineated by the same physician. The doses of 60 Gy external RT were prescribed in 30 fractions using three-dimensional conformal radiotherapy (3D-CRT), static intensity-modulated radiotherapy (s-IMRT), and dynamic intensity-modulated radiotherapy (d-IMRT) techniques in all patients. The obtaining plans using three different techniques were compared. Results: The d-IMRT plans were statistically the best optimal plan for planning target volume (PTV) [Dmean (p = 0 04), Dmax (p &lt; 0 0001), V95 (p &lt; 0 0001), V107 (p &lt; 0 0001), CI (p &lt; 0 0001) and HI (p &lt; 0 0001)]. The s-IMRT plans were significantly superior to 3D-CRT plans for PTV. RA Dmax and V45 were not different between the three techniques [Dmax (p = 0 148) and V45 (p = 0 12)]. The d-IMRT technique was significantly better in other heart substructures and coronary arteries. Conclusions: Compared to 3D-CRT and s-IMRT techniques, the d-IMRT technique provided the best protection in all heart substructures except for a few parameters (RA Dmax and V45 doses).

Dosimetric investigation of non-coplanar field technology in static intensity-modulated radiation therapy for gastric carcinoma

Objective To compare the dosimetric characteristics of non-coplanar and coplanar field technology in static intensity-modulated radiotherapy of gastric cancer patients, so as to provide a reference for clinical radiotherapy plan selection. Methods Thirty-six patients with gastric cancer were selected to receive intensity-modulated radiotherapy in Huanggang Central Hospital, which was designed plan A and B. Group A used 7-field coplanar technology, while Group B used 7-fleld non-coplanar technology. We compared the differences of the optimized monitor unit, the dosimetry of organs at risk and target areas between group A and group B. Results Both group A and B could meet the requirements of doctors. The homogeneity index (0.14 ± 0.02), the conformity index (0.98 ± 0.01), D min (4 315.21 ± 16.74) cGy, D mean (4 679.28 ± 28.39) cGy and D max (4 952.30 ± 33.26) cGy of target areas in group B were better than those of group A. Moreover, the monitor unit of group B was much lower than that of group A, and the difference was statistically significant ( P < 0.05). The D max, D mean, V 15, V 20 and V 30 of the left and right kidneys in group B were lower than those of group A. The D max (3 408.57 ± 46.03) cGy, D mean (1 250.32 ± 14.27) cGy and V 20 (44.91% ± 6.67%) of spinal cord and the D max (3 408.57 ± 46.03) cGy, D mean (1 720.55 ± 17.42) cGy, V 20 (25.31% ± 7.78%) and V 30 (18.52% ± 1.56%) of small intestine were also lower than those of group A. The differences were statistically significant ( P < 0.05). Conclusion The non-coplanar field radiation plan has more advantages in terms of target dose distribution and protection of organs so that it can be more considerably used in the process of planning and design. 摘要： 目的 通过比较非共面射野与共面射野计划在胃癌静态调强中的剂量学特点, 为临床放疗计划选择提供依 据。 方法 选取黄冈市中心医院接受调强放射治疗的胃癌患者 36 例, 每名患者均设计A、B 2 组计划, A 组采用 7 野 共面技术, B 组采用 7 野非共面技术, 比较 A 组和 B 组优化后机器跳数、危及器官和靶区的剂量学差异。 结果 A、B 两组计划均能满足医生要求, B 组靶区均匀性指数 HI (0.14 ± 0.02)和适形度指数 CI (0.98 ± 0.01), 靶区 D min (4 315.21 ± 16.74) cGy, D mean (4 679.28 ± 28.39) cGy 和 D max (4 952.30 ± 33.26) cGy 均优于 A 组, 且 B 组机器跳数更 少, 差异有统计学意义 ( P < 0.05)。B 组左右侧肾脏 D max、 D mean、 V 15、 V 20 和 V 30均低于A组, 脊髓的 D max (3 408.57 ± 46.03) cGy、 D mean (1 250.32 ± 14.27) cGy 和 V 20 (44.91% ± 6.67%)以及小肠的 D max (3 408.57 ± 46.03) cGy、 D mean (1 720.55 ± 17.42) cGy、 V 20 (25.31% ± 7.78%) 和 V 30 18.52% ± 1.56%)也均低于 A 组, 差异有统计学意义 ( P < 0.05)。 结论 非共面射野计划在靶区剂量分布和危及器官保护上更优, 计划设计过程中可以更多的考虑非共面布野技术。

Volumetric-Modulated Arc Radiotherapy with Daily Image-Guidance Carries Better Toxicity Profile for Higher Risk Prostate Cancer.

Purpose:To compare radiotherapy-induced toxicity for localized prostate-cancer (PCa) treated with versus without daily image-guidance. Patients and Methods:We identified consecutive intermediate and high-risk localized PCa patients treated with definitive radiotherapy using intensity-modulated radiotherapy (IMRT) with variable duration of androgen-deprivation therapy (ADT) within 2015-2016 (Arm-A) and 2005-2007 (Arm-B). Arm-A cases received daily online imaging guidance (IGRT) using cone-beam computed tomography (CBCT) unlike Arm-B candidates with no daily IGRT. After reporting demographic, clinico-pathological features and treatment details, we compared acute (within 3 months post-therapy) and late RT-induced toxicities between study groups graded by RTOG/CTCAE criteria. Uni/multivariate analyses (UVA/MVA) were performed to identify independent predictors for RT-related side-effects. Results:We were able to identify 257 cases who met our inclusion criteria. Overall, median age was 73 years (48-85), 67% had intermediate-risk and 47% received ADT. Arm-A included 72 patients who received IMRT delivered using volumetric-modulated arc therapy (VMAT), whereas, Arm-B was formed of 185 cases who utilized step-and-shoot static IMRT. Clinico-pathological features and treatment details were non-different across study arms except that Arm-A had more Grade Group 3, higher median total dose (79.2 vs. 74 Gy) and more pelvic lymph-nodes RT (P<0.05). Although acute toxicity was similar across groups, Arm-B encountered higher late toxicity score, more intense late genitourinary side-effects (P=0.008), with non-different late lower-gastrointestinal toxicities. On MVA, lack of daily CBCT, African-American race and higher comorbidities were independently predictive for late toxicities. Conclusion:IMRT with daily CBCT permitted safe delivery of dose-escalated IMRT with improved toxicity profile for higher-risk prostate cancer.

Proton beam therapy can achieve lower vertebral bone marrow dose than photon beam therapy during chemoradiation therapy of esophageal cancer.

Chemoradiation therapy plays an important role in both the neoadjuvant and definitive management of esophageal cancer (EC). Prior studies have suggested that advanced planning techniques can better spare organs at risk including the heart. Although multiple toxicities can result from esophageal radiotherapy, one less studied acute toxicity is that of myelosuppression, which can result, in part, from the combination of chemotherapy and incidental radiotherapy administration to the vertebral bodies (VBs), which abut the posterior aspect of the esophagus, especially in the lower thoracic esophagus. Traditionally, VB bone marrow doses are not accounted during EC radiation therapy planning. We sought to compare the doses to VBs between proton and photon radiation therapy as part of chemoradiation therapy for EC treatment. By reducing doses to the vertebrae, radiation therapy can decrease treatment-related myelosuppression, which can avoid delays or chemotherapy dose reductions in therapy, which likely affect long-term patient survival. Dose constraints are not routinely employed for bone marrow in radiation treatment planning. In our previous work, we identified thresholds to avoid grade ≥3 leukopenia, including VB V10Gy, VB V20Gy, and a mean VB dose (MVD) of 18.8 Gy. Herein we perform a retrospective dosimetric planning study comparing passive- or double-scattering proton beam therapy (PS-PBT), volumetric-modulated arc therapy (VMAT) (photon-based), and intensity-modulated radiation therapy (IMRT) (photon-based) in 25 patients with locally advanced EC who were treated originally with photon RT at our institution between 2011 and 2016. The aforementioned dose constraints were included in the retrospective planning process for PS-PBT, VMAT, and IMRT to determine the feasibility of achieving these VB constraints while maintaining reasonable target coverage and planned, consistent constraints to other organs at risk including lungs, spinal cord, and stomach. PS-PBT plans were found to achieve lower doses for VB V10Gy, V20Gy, and MVD than VMAT and static IMRT plans while achieving the same target coverage. PS-PBT resulted in lower organs at risk dosimetric parameters than the photon plans, with p < 0.0001. Student's paired t-test p-values in favor of proton therapy's ability to spare organs were as follows: for PS-PBT vs VMAT and PS-PBT vs IMRT in mean doses for lung, liver, and VB and VB V10Gy and VB V20Gy were all <0.001 (Bonferroni corrected α=0.017). One-way ANOVA found that VB doses (VB V10Gy, VB V20Gy, and MVD) were significantly lower for proton therapy (p < 0.006) among the 3 planning techniques.

Dosimetric comparison of three-dimensional conformal radiotherapy and static and dynamic intensity-modulated radiotherapy for the treatment of early-stage glottic cancer

The aim of this study was to compare dosimetric variations using the three-dimensional conformal radiotherapy (3DCRT), dynamic intensity-modulated radiation therapy (D-IMRT), and static intensity-modulated radiation therapy (S-IMRT) techniques for glottic cancer. Ten patients with early-stage glottic cancer were retrospectively selected and evaluated. The 3DCRT and IMRT treatment plans were performed using the solution commercialized by Varian with the Eclipse treatment planning system (TPS). For each patient, five different treatment plans were created and compared with respect to the doses received by the organs at risk (OARs) including the carotid arteries, thyroid gland, and spinal cord; the dose homogeneity index (DHI); conformity indexes (CI); and total monitor unit (MU) counts required for the treatment. The Mann-Whitney U test was used for statistical analyses. Statistically significant differences for the 3DCRT, D-IMRT, and S-IMRT techniques were observed for the planning target volume (PTV) mean and maximum doses. The results of this study indicated an increase in DHI for 3DCRT compared with D-IMRT and S-IMRT. Furthermore, the S-IMRT technique led to the superior decreased dose to the OAR. The 3DCRT plans performed better at the Dmax of the spinal cord and MU counts. The D-IMRT and S-IMRT techniques allowed more homogeneous dose distributions in PTV. Considering the dose to OAR, S-IMRT was more appropriate rather than 3DCRT and D-IMRT.

Dosimetric Comparison of Static Intensity Modulated Radiotherapy, Dynamic Intensity Modulated Radiotherapy and Volumetric Modulated Arc Therapy for Thoracic Esophageal Cancer: A Single Institutional Experience

The aim of this study was to evaluate the dosimetric variations of static intensity-modulated radiotherapy (sIMRT), dynamic intensity-modulated radiotherapy (dIMRT) and volumetric modulated arc therapy (VMAT) for thoracic esophageal cancer (EC). Ten patients with pathologically-confirmed EC were randomly selected. The Monaco 5.11 treatment planning system was used to design six radiotherapy plans, namely sIMRT with 5 fixedfields (S5) and 7 fixed-fields (S7), dIMRT with 5 fixed-fields (D5) and 7 fixed-fields (D7) and VMAT plan with single arc (VMAT1) and double arc (VMAT2), respectively. The dosimetric parameters were compared among six different plans. The dose to target volumes met the clinical prescription requirements in all six plans. The D5 plan had the lowest dose exposed to the whole lungs, except for V5, which was only 1.7% higher than that in the D7 plan. The low dose to lungs (V5 and V10) in VMAT plans (VMAT1 and VMAT2) were higher than in IMRT plans, but the statistical differences were significant (P &lt; 0.05) only in comparison with dynamic IMRT plans (D5 and D7). The V20 and V30 of lungs in VMAT2 plan were also higher than that in other plans, but the statistical differences were significant (P &lt; 0.05) only in comparison with D5 plan. The doses delivered to the spinal cord and heart showed no statistical significance (P &gt; 0.05). The monitor units (MUs) and treatment time (TT) significantly increased with the increasing number of fields in the same kind of fixed-fields IMRT plans (S5 vs. S7; D5 vs. D7). The MUs in VMAT plans, especially in VMAT2, increased significantly (P &lt; 0.05) when compared with sIMRT and 5-fields dIMRT plans, respectively. VMAT1 plan had the shortest TT and the highest delivery efficiency. For thoracic esophageal cancer, the D5 plan can shorten the TT and improve the delivery efficiency while meeting the dosimetric requirements and sparing the lungs. VMAT can significantly reduce the TT, but at the expense of increasing the dose to lower-dose regions of lungs, which means VMAT plan may not shows obvious dose advantage for thoracic esophageal cancer.

Changing Practice Patterns in the Radiation Treatment Delivery for Locally Advanced Lung Cancer: Results from a Statewide Consortium

In 2014, the RTOG 0617 trial defined the standard radiation therapy (RT) dose as 60 Gy with concurrent chemotherapy in locally advanced non-small cell lung cancer (LA-NSCLC) patients. Further analyses of the study showed a decrease in grade 3 pneumonitis with static intensity modulated radiation therapy (sIMRT). Radiation treatment techniques used in routine clinical practice have evolved from 3D conformal radiation therapy (3DCRT) to sIMRT and more recently to rotational IMRT (rIMRT). However, the uptake of lower lung tumor RT dose recommendations and RT treatment techniques used in the “real world” setting is not known. The purpose of this study was to evaluate patterns of practice of both radiation dose and type of radiation technique used in a statewide radiation oncology consortium. From 2012 to 2018, 2741 patients with lung cancer treated with curative intent RT at 24 institutions participating in a statewide Radiation Oncology Quality Consortium were enrolled. Patients with small cell lung cancer, previous surgical resection, and patients who did not complete treatment were excluded. Furthermore, for RT dose analyses, outliers of RT doses (<45 Gy and >100 Gy) were excluded. Patients lacking DICOM information regarding treatment plans were excluded for the RT technique analyses. Changes in prescription doses and treatment techniques over time were evaluated. Trends over time in academic (n=4) vs. non-academic centers (n=20) were also analyzed. Academic centers were defined as those with a medical residency training program. Sample t-tests were used to compare means. 1134 patients were analyzed for RT dose analysis, while 1087 patients were evaluated for the RT treatment technique. The mean prescription RT dose delivered to tumor decreased from 63 Gy to 60 Gy (p<0.001) over the 6-year time period. In the earlier years of the data collection (2012-2013), >50% of the cases were treated with 3DCRT and rIMRT was used in ≤5%. However, by 2018, the rate of rIMRT increased to 56.9% (p<0.0001). See Table below. Similar practice patterns were seen in academic and non-academic centers for both RT dose and treatment technique analyses. In this large prospective “real world” study from a statewide consortium of practicing radiation oncologists, prescription mean RT dose used to treat LA-NSCLC has decreased to 60 Gy as per evidence-based guidelines. The primary treatment technique of delivering RT in LA-NSCLC has also changed in this interval. More than half of LA-NSCLC patients are now receiving rIMRT. The clinical implications of potential increases in low dose volumes (e.g., Lung and Heart V5) resulting from rIMRT will have to be evaluated going forward, especially in the changing systemic therapy paradigm that includes immunotherapy.Abstract 3120; Table 1Year3DCRTsIMRTrIMRT201263.5%34.6%1.9%201355.1%40.4%4.5%201444.8%38.1%17.2%201540.2%33.1%26.7%201619.0%31.4%49.6%201721.9%25.1%53%201821.8%21.3%56.9% Open table in a new tab

Dosimetric comparison of static intensity-modulated radiation therapy and volumetric modulated arc therapy in lymphoma patients received mediastinal radiation

Objective To compare target dosimetric distribution and normal tissue radiation between different static intensity-modulated radiation therapy (IMRT) plans and volumetric modulated arc therapy (VMAT), and to identify the best IMRT plan for lymphoma patients needed mediastinal radiation. Methods A total of 11 patients with lymphoma who received first course radiotherapy in the mediastinal region after che-motherapy in Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College from March 2017 to January 2019 were included in the study. There were 8 males and 3 females, 2 patients were in Ann Arbor stage Ⅰ-Ⅱ, and 9 cases in Ⅲ-Ⅳ stage. There were 6 patients with Hodgkin lymphoma (HL) and 5 patients with non-Hodgkin lymphoma (NHL). Patients with HL and NHL were given prescript doses of 36 Gy and 50 Gy, respectively. Three plans were designed for each patient: static 5F-IMRT, 7F-IMRT and VMAT plan. The target dosimetric distribution, normal tissue radiation dose, and efficiency of each plan were evaluated. Results The mean conformity index (CI) and homogeneity index (HI) values of plan target volume (PTV) in 5F-IMRT, 7F-IMRT, VMAT plan were 0.64±0.06, 0.67±0.05, 0.76±0.04 (F=17.045, P<0.001) and 1.07±0.01, 1.07±0.01, 1.09±0.01 (F=9.258, P=0.001), respectively. VMAT showed significantly better CI than two static IMRT plans (both P<0.001), but worse HI (both P<0.001). The lungs low dose irradiation volume (V5) and high dose irradiation volume (V30) in 5F-IMRT, 7F-IMRT, VMAT plan were (43.98±7.77)%, (42.71±4.98)%, (55.92±8.16)% (F=8.281, P=0.001) and (8.19±2.97)%, (8.25±2.87)%, (7.53±3.16)% (F=0.140, P=0.870), respectively. The volume of low dose irradiation in lungs of VMAT plan was significantly higher than 5F-IMRT and 7F-IMRT plans (both P<0.001), while high dose volume was no significant difference. The left and right breast low dose irradiation volume (V4) in 5F-IMRT, 7F-IMRT and VMAT plan were (24.29±8.14)%, (23.87±7.70)%, (80.17±22.92)% (F=14.505, P=0.005) and (22.12±13.28)%, (21.13±13.01)%, (81.77±20.76)% (F=13.938, P=0.006), respectively. VMAT showed significantly higher breast low dose irradiation volume than static IMRT plan (both P<0.05). The number of monitor units and treatment time in 5F-IMRT, 7F-IMRT, VMAT plan were (1 622±281) MU, (1 729±286) MU, (411±75) MU (F=105.277, P<0.001) and (6.79±0.93) min, (7.42±0.95) min, (4.98±0.00) min (F=29.545, P<0.001), respectively. VMAT showed significantly less monitor units than static IMRT (both P<0.001) and shorter treatment time (both P<0.001). Conclusion For lymphoma patients who have the indication of mediastinal radiotherapy, VMAT is highly efficient and has no definite dose advantage, the static 5F-IMRT or 7F-IMRT plan has good conformal and uniform target area, and some organs at risk exposure is even lower. Key words: Lymphoma; Radiotherapy planning, computer-assisted; Radiotherapy plan comparison

Dosimetric Comparison Between Jaw Tracking and No Jaw Tracking in Intensity-Modulated Radiation Therapy.

Purpose:This article compares the dosimetric differences between jaw tracking and no jaw tracking technique in static intensity-modulated radiation therapy plans of large and small tumors.Methods:Eight plans with large tumor (nasopharyngeal carcinoma, volume range: 510.9 to 768.0 cm3) and 8 plans with small tumor (single brain metastasis, volume range: 5.3 to 9.9 cm3) treated with jaw tracking on Varian EDGE LINAC were chosen and recalculated with no jaw tracking to study the dosimetric differences. We compared the differences of organ-at-risk doses (Dmax, Dmean), monitor units, and γ passing rate of plan verification (3mm/3%, threshold 10%; 2mm/2%, threshold 10%) between the 2 techniques.Results:The organ-at-risk doses of nasopharyngeal carcinoma cases having jaw tracking are all less than those with no jaw tracking. The Dmax and Dmean of organ-at-risks reduced 0.61% to 17.65% and 2.17% to 19.32%, P < .05, respectively. In cases with single brain metastasis, the organ-at-risk doses with jaw tracking were also lower than no jaw tracking. The Dmax and Dmean of organ-at-risk doses reduced 0.84% to 1.52% and 0.90% to 1.86%, P < .05, respectively. The monitor units for the large tumor and small tumor were increased by 2.41% and 1.1%, respectively. The γ passing rates (3mm/3%, th10%; 2mm/2%, th10%) of nasopharyngeal carcinoma plans are 99.89% ± 0.06% (jaw tracking) versus 99.56% ± 0.19% (no jaw tracking; P = .127); 97.15% ± 0.98% (jaw tracking) versus 91.90% ± 1.40% (no jaw tracking; P = .000), and the γ passing rates (3mm/3%, th10%; 2mm/2%, th10%) of brain metastasis plans are 99.97% ± 0.05% (jaw tracking) versus 99.44% ± 1.24% (no jaw tracking; P = .251), 98.65% ± 1.27% (jaw tracking) versus 93.35% ± 2.72% (no jaw tracking; P = .000).Conclusion:Jaw tracking can reduce the dose of organ-at-risks compared to no jaw tracking, and the effect is more significant for plans with large tumor. The γ passing rate of plans with jaw tracking is also higher than the plans with no jaw tracking. Although the monitor units in plans of jaw tracking will increase slightly, it is recommended to use jaw tracking in static intensity-modulated radiation therapy both in large and in small tumors.

High-Dose Static and Dynamic Intensity-Modulated Radiotherapy Combined with Chemotherapy for Patients with Locally Advanced Nasopharyngeal Carcinoma Improves Survival and Reduces Brainstem Toxicity.

BackgroundIntensity-modulated radiotherapy (IMRT) is the standard treatment for patients with nasopharyngeal cancer (NPC). However, the dose-volume criteria for adjacent anatomically normal organs at risk (OARs) remain controversial. The aim of this study was to evaluate the effects of higher than conventional doses of static and dynamic IMRT on the locoregional control of NPC, patient survival, and brainstem radiation toxicity.Material/MethodsPatients (n=186) with stage III and stage IVa NPC underwent high-dose static and dynamic IMRT treatment (68–76.96 Gy) with or without chemotherapy for 34–57 days. Overall survival (OS), the presence of distant metastases, and brainstem toxicity were assessed. One-year, three-year, and five-year follow-up was performed.ResultsHigh-dose IMRT alone or in combination with chemotherapy resulted in a 100% objective response rate and significantly improved OS rates, with one-year, three-year, and five-year OS rates of 94.1%, 89.8%, and 88.2%, respectively. The local recurrence rate (17.6%), and distant metastasis to the lung, liver, and bone (17.2%), and mortality (n=22) were reduced. Chemotherapy was the only factor that was significantly correlated with patient survival. Brainstem toxicity was reduced in patients treated with static IMRT (0.07%) and dynamic IMRT (0.08%). There were 26 additional factors that were not found to significantly affect brainstem toxicity.ConclusionsHigh-dose static or dynamic IMRT combined with chemotherapy improved survival and reduces distal metastasis with a very low occurrence of brainstem toxicity in patients with locally advanced NPC. These findings might provide therapeutic guidance for clinicians when planning optimal dose-volume IMRT parameters.

Analysis of a volumetric-modulated arc therapy (VMAT) single phase prostate template as a class solution.

To assess a class solution template for volumetric-modulated arc therapy (VMAT) for prostate cancer using plan analysis software. VMAT is a development of intensity-modulated radiotherapy (IMRT) with potential advantages for the delivery of radiotherapy (RT) in prostate cancer. Class solutions are increasingly used for facilitating RT planning. Plan analysis software provides an objective tool for evaluating class solutions. The class solution for VMAT was based on the current static field IMRT template. The plans of 77 prostate cancer patients were evaluated using a set of in-house plan quality metrics (scores) (PlanIQ™, Sun Nuclear Corporation). The metrics compared the class solution for VMAT planning with the IMRT template and the delivered clinical plan (CP). Eight metrics were associated with target coverage and ten with organs-at-risk (OAR). Individual metrics were summed and the combined scores were subjected to non-parametric analysis. The low-dose wash for both static IMRT and VMAT plans were evaluated using 40Gy and 25Gy isodose volumes. VMAT plans were of equal or better quality than the IMRT template and CP for target coverage (combined score) and OAR combined score. The 40Gy isodose volume was marginally higher with VMAT than IMRT (4.9%) but lower than CP (-6.6%)(P=0.0074). The 25Gy volume was significantly lower with VMAT than both IMRT (-32.7%) and CP (-34.4%)(P<0.00001). Automated VMAT planning for prostate cancer is feasible and the plans are equal to or better than the current IMRT class solution and the delivered clinical plan.

Locoregional irradiation including internal mammary nodal region for left-sided breast cancer after breast conserving surgery: Dosimetric evaluation of 4 techniques

The present study aimed to compare 4 techniques in the planning of locoregional irradiation including internal mammary nodal region for left-sided breast cancer. Ten patients with left-sided breast cancer undergoing breast conservation surgery were enrolled. For each patient, 4 treatment plans were performed: a helical tomotherapy (HT) plan, a volumetric modulated arc therapy (VMAT) plan, a static intensity modulated radiation therapy (IMRT) plan, and a hybrid IMRT plan, designed to encompass the whole breast, internal mammary, and supraclavicular nodal regions. The prescribed dose of radiation was 50 Gy in 25 fractions. The dosimetric parameters of the target and organs at risk, as well as the dose delivery time, were evaluated and compared using an independent-samples t-test. The HT and VMAT plans had the best conformity and homogeneity. For the HT, VMAT, IMRT, and hybrid IMRT plans, the mean conformity index (CI) and homogeneity index (HI) were 0.83, 0.82, 0.8, and 0.77 (p < 0.001); and 1.07, 1.11, 1.14, and 1.14 (p < 0.001), respectively. The corresponding V55 values were 0.3%, 11.4%, 27.02%, and 23.29% (p < 0.001). The Dmean and V20 of the left lung obtained using the HT plan were significantly lower than those of VMAT, IMRT, and hybrid IMRT plans (p = 0.002, p = 0.004). There were no significant differences in D max of LAD descending coronary artery, or the Dmean of the heart among the 4 types of plans. The HT and VMAT plans had a lower dose to other organ at risk (OARs) compared with the IMRT and hybrid IMRT plans. The mean delivery times were 1042 ± 33 seconds, 136 ± 12 seconds, 450 ± 65 seconds, and 451 ± 70 seconds for the HT, VMAT, IMRT, and hybrid IMRT plans, respectively (p < 0.001). For whole breast plus supraclavicular and internal mammary nodal irradiation in left-sided breast cancer, the VMAT technique is recommended considering both the dose distribution and the delivery time. Under circumstances in which dose distribution is a priority, the HT technique is a valid option.

4πVMAT: A Novel Method to Efficiently Deliver Non-Coplanar Treatment

Existing Volumetric Modulated Arc Therapy (VMAT) optimization using one or more arcs, each being coplanar by itself, is a highly efficient way to deliver intensity modulated radiation therapy (IMRT). Static beam IMRT utilizing optimized non-coplanar beam orientation has resulted in superior dosimetry to VMAT but is substantially less efficient. In this study, we developed a novel optimization framework for non-coplanar VMAT, incorporating simultaneous couch and gantry rotation during the arc motion, to maximally utilize the 4π solid angle (4πVMAT) with high efficiency. The 4πVMAT optimization framework includes a Direct Aperture Optimization (DAO) module and a beam trajectory selection (BTS) module. DAO was achieved by adding to the dose fidelity objective a total variation term for regulating the fluence smoothness, a single segment term for forming deliverable fluence map, and a group sparsity term for selecting beam angles. The BTS was formulated as a travelling salesman problem on a hierarchical graph, where the edge and node costs were determined by the maximal gantry rotation speed and the estimated fluence map at the current iteration, respectively. Continuous gantry/couch angle trajectories were selected on the graph using the Dijkstra's algorithm. Candidate beams in the couch-gantry-patient collision space, evaluated on actual machine geometry and a human subject 3D surface, were excluded in both the DAO and BTS modules. The optimization framework was solved by alternating between the DAO module and the BTS. Efficacy of 4πVMAT using one full-arc or two full arcs was tested on a brain, a lung and a prostate cancer patient. The plan was compared against a coplanar VMAT (2πVMAT) plan using more arcs with collimator rotation. The 4πVMAT consisted of two efficient arcs, each taking 160 seconds in estimate to deliver. In the first arc, the couch rotated in either the clockwise or counterclockwise direction, and then reversed the rotation in the second arc. The gantry rotations were coordinated with the couch rotation for optimal dose distribution while avoiding couch-gantry-patient collision. With the same target coverage, 4πVMAT remarkably reduced the max and mean organs-at-risk (OARs) doses compared to 2πVMAT, as shown in Table 1. The dose compactness measured using R50 was reduced by 19.7%. By optimizing feasible and efficient non-coplanar arc trajectories, the novel 4πVMAT optimization framework simultaneously achieves the desirable dosimetric quality of 4π therapy and the delivery efficiency of coplanar 2πVMAT.Abstract TU_35_3241: Table 1OAR dose: 2πVMAT - 4πVMAT (% of the prescription dose)patientDmaxDmeanLargestAverageLargestAveragebrain12.847.529.324.68lung32.6012.7810.583.62prostate10.502.764.300.35OAR mean and maximum dose differences between πVMAT and 2πVMAT for all patients. “Largest” and “Average” represent the largest and average values among all OARs. Open table in a new tab