Dynamic Intensity Modulated Radiation Therapy Research Articles

Effects of minimum monitor unit per dynamic control point on intensity‐modulated radiotherapy planning for nasopharyngeal carcinoma: A retrospective study

The present study aimed to improve the dose distribution of radiotherapy planning for nasopharyngeal carcinoma (NPC) by comparing the effects of various minimum monitor units (MUs) per dynamic control point (MMCP) values on the quality and execution efficiency of dynamic intensity-modulated radiotherapy (IMRT) planning. Thirty-four clinically implemented dynamic IMRT plans for patients with NPC were retrospectively selected. In total, 170 plans were obtained by modifying only the MMCP values (set as 1, 3, 5, 7, and 9) in the treatment planning system's (TPS) optimization parameters. These plans were divided into 5 groups. Analyzing the effects of MMCP on the target and organ dose at risk (OAR), also the execution efficiency of the treatment plan in each group and using a quality score system, we conducted an objective quantitative study of the dose distribution and execution efficiency. The target dose evaluation indicators (target coverage (TC), homogeneity index (HI), and conformity index (CI)) of all IMRT plans showed a trend of variation with an increase in MMCP values, and the difference was statistically significant when MMCP values were 5, 7, 9, and 1 (p < 0.05). With an increase in MMCP, the dose to OAR slightly increased, but the difference was not statistically significant (p > 0.05). With an increase in MMCP, the average number of MUs per segment significantly increased (p < 0.01). The groups based on MMCP values of 1, 3, 5, 7, and 9 received quality score system of 1.188, 1.180, 1.171, 0.987, and 1.184, respectively, with the MMCP7 group achieving the lowest score, indicating that this plan had the highest overall quality. The MMCP value for dynamic IMRT planning in the Monaco TPS for patients with NPC should be set to 7 to achieve fewer segments, the best execution efficiency without significantly deteriorating the target and OAR dose.

Evaluation of Dynamic Multi-Leaf Collimator (MLC) versus Fixed MLC for Intensity Modulated Radiotherapy (IMRT) Using the Agility 160-Leaf Collimator.

This study aimed to evaluate the efficacy of static or step-and-shoot intensity-modulated radiotherapy (ssIMRT) and dynamic intensity-modulated radiotherapy (dIMRT) delivery techniques for various treatment sites. The treatment planning system (TPS) was utilized to develop optimal treatment plans for twenty-seven patients selected for this comparative study, including nine with head and neck cancer, nine with prostate cancer, and nine with cervical cancer. The prescribed doses were 7000cGy/33fr, 7425cGy/33fr, and 5000cGy/25fr for the nasopharynx, prostate, and cervix cases, respectively, in both ssIMRT and dIMRT delivery techniques. Plans were generated using the Monaco treatment planning system with a 6MV photon beam and nine equidistant fields. Plan evaluation criteria included dose-volume histogram analysis, dose homogeneity index, conformity index, radiation delivery time, and monitor unit requirements. All plans were optimized to ensure that 98% of the planning target volume (PTV) received at least 95% of the prescribed dose, while meeting the planning objectives for organs at risk. dIMRT plans exhibited superior conformity (CI = 0.85 ± 0.05) compared to ssIMRT plans (CI = 0.79 ± 0.08), with statistically significant differences (P < 0.01). Inhomogeneity within the PTV was significantly higher in ssIMRT plans (HI = 0.10 ± 0.02) compared to dIMRT plans (HI = 0.09 ± 0.01), with a significant difference (P < 0.01). Delivery time per fraction was significantly lower in dIMRT compared to ssIMRT (P < 0.01). Furthermore, dIMRT plans required a higher mean monitor unit value (1335.4 ± 172.2) compared to ssIMRT plans (974.4 ± 133.6) with a significant difference (P < 0.001). The findings of this study indicate that dIMRT provides improved target coverage, homogeneity, and conformity while reducing treatment delivery time compared to ssIMRT.

Optimizing Treatment Quality in Head and Neck Cancer Therapy: Impact of Adaptive Intensity-Modulated Radiotherapy on Plan Quality and Tumor Volume Changes

Objective: This research analyses whether volumetric changes and PTV shifting affect adaptive intensity-modulated radiotherapy (IMRT) plan quality and head and neck cancer therapy. Methods: The research was carried out at the Sohag Cancer Centre in Egypt, including a sample of 36 individuals diagnosed with head and neck squamous cell carcinoma (HNSCC). Patients were chosen on the basis of the following criteria: locally progressed and node-positive malignancy, oropharyngeal cancer, oral cavity cancer, and unknown primary. The research used dynamic intensity-modulated radiation therapy (D-IMRT) to establish treatment plans and Siemens SOMATOM DEFINITION CT scanners to acquire 3D anatomical images. A range of 1.64 to 2.12 Gy was observed for the median dosage per fraction. Using the conformance index (CI) and the homogeneity index, the quality of the plan was assessed (HI). The threshold for statistical significance was set at 0.05. Results: The study analysed patients with unilateral and bilateral HNSCC tumors, with a majority having bilateral tumors. The findings demonstrated that the tumor PTV was significantly reduced as a consequence of the suggested adaptive radiation techniques. Both the homogeneity index and the conformity index were used to evaluate the plan's quality (HI). The maximal homogeneity index (HI) was reached after 7 and 14 fractions, respectively. The positive correlation between PTV reduction and CI after 7 fractions, while a negative correlation found after fractions 14 and 21. It was also shown that HI is positively correlated with PTV changes after 7 and 14. Conclusion: The use of adaptive radiotherapy in intensity-modulated radiation therapy (IMRT) treatment planning improves plan quality and decreases error rates due to tumor margin movement. Following radiation fractions, PTV shifting affects the homogeneity index (HI).

Quantify the Effect of Air Gap Errors on Skin Dose for Breast Cancer Radiotherapy.

Purpose: Determining the impact of air gap errors on the skin dose in postoperative breast cancer radiotherapy under dynamic intensity-modulated radiation therapy (IMRT) techniques. Methods: This was a retrospective study that involved 55 patients who underwent postoperative radiotherapy following modified radical mastectomy. All plans employed tangential IMRT, with a prescription dose of 50 Gy, and bolus added solely to the chest wall. Simulated air gap depth errors of 2 mm, 3 mm, and 5 mm were introduced at depression or inframammary fold areas on the skin, resulting in the creation of air gaps named Air2, Air3, and Air5. Utilizing a multivariable GEE, the average dose (Dmean) of the local skin was determined to evaluate its relationship with air gap volume and the lateral beam's average angle (AALB). Additionally, an analysis was conducted on the impact of gaps on local skin. Results: When simulating an air gap depth error of 2 mm, the average Dmean in plan2 increased by 0.46 Gy compared to the initial plan (planO) (p < .001). For the 3-mm air gap, the average Dmean of plan3 was 0.51 Gy higher than that of planO (p < .001). When simulating the air gap as 5 mm, the average Dmean of plan5 significantly increased by 0.59 Gy compared to planO (p < .001). The TCP results showed a similar trend to those of Dmean. As the depth of air gap error increases, NTCP values also gradually rise. The linear regression of the multivariable GEE equation indicates that the volume of air gaps and the AALB are strong predictors of Dmean. Conclusion: With small irregular air gap errors simulated in 55 patients, the values of skin's Dmean, TCP, and NTCP increased. A multivariable linear GEE regression model may effectively explain the impact of air gap volume and AALB on the local skin.

Ninety-degree angled collimator: a dosimetric study related to dynamic intensity-modulated radiotherapy in patients with endometrial carcinoma

BackgroundOur purpose was to ensure that the dose constraints of the organs at risk (OARs) were not exceeded while increasing the prescription dose to the planning target volume (PTV) from 45 to 50.4 Gray (Gy) with the dynamic intensity-modulated radiotherapy (IMRT) technique. While trying for this purpose, a new dynamic IMRT technique named 90° angled collimated dynamic IMRT (A-IMRT) planning was developed by us.MethodsThis study was based on the computed tomography data sets of 20 patients with postoperatively diagnosed International Federation of Gynecology and Obstetrics stage 2 endometrial carcinoma. For each patient, conventional dynamic IMRT (C-IMRT, collimator angle of 0° at all gantry angles), A-IMRT (collimator angle of 90° at gantry angles of 110°, 180°, 215°, and 285°), and volumetric modulated arc therapy (VMAT) were planned. Planning techniques were compared with parameters used to evaluate PTV and OARs via dose-volume-histogram analysis using the paired two-tailed Wilcoxon’s signed-rank test; p < 0.05 was considered indicative of statistical significance.ResultsAll plans achieved adequate dose coverage for PTV. Although the technique with the lowest mean conformality index was A-IMRT (0.76 ± 0.05) compared to both C-IMRT (0.79 ± 0.04, p = 0.000) and VMAT (0.83 ± 0.03, p = 0.000), it protected the OARs especially the bladder (V45 = 32.84 ± 2.03 vs. 44.21 ± 6.67, p = 0.000), rectum (V30 = 56.18 ± 2.05 vs. 73.80 ± 4.75, p = 0.000) and both femoral heads (V30 for right = 12.19 ± 1.34 vs. 21.42 ± 4.03, p = 0.000 and V30 for left = 12.58 ± 1.48 vs. 21.35 ± 4.16, p = 0.000) better than C-IMRT. While the dose constraints of the bladder, rectum and bilateral femoral heads were not exceeded in any patient with A-IMRT or VMAT, they were exceeded in 19 (95%), 20 (100%) and 20 (100%) patients with C-IMRT, respectively.ConclusionsOARs are better protected when external beam radiotherapy is applied to the pelvis at a dose of 50.4 Gy by turning the collimator angle to 90° at some gantry angles with the dynamic IMRT technique in the absence of VMAT.

The effect of breath-hold technique on conformal and intensity modulated radiotherapy techniques at right breast cancer radiotherapy including internal mammarian field

Background/Aim: Significantly lower heart doses can be achieved by breath-hold technique at left-sided breast cancer radiotherapy (RT). We see high doses at organs at risk such as lung, heart, and contralateral breast during right-sided breast cancer RT planning especially in the presence of RT indication for mammaria interna (MI) lymph nodes. This study compared RT-planning methods that are conformal with intensity-modulated RT (IMRT) with breath holding and free breathing for right-sided breast cancer RT including full axillary and MI lymph node fields. Methods: Computed tomography (CT) simulations were performed using free-breath (FB) and breath-hold (BH) methods in 10 patients with right-sided breast cancer. A total of 40 RT treatment plans were calculated. Right-sided breast, level 1-2-3 axillary regions, and MI regions served for the target-planning volume. Left-sided breast, heart, as well as right-sided and left lungs were contoured as critical organs according to the atlas of the "Radiation Therapy Oncology Group." We used a Varian Eclipse v.13 for treatment planning. Conformal “FieldinField” RT (FinFRT) and dynamic IMRT (dIMRT) planning were performed separately for each patient over breath-hold and free-breath images. For PTV, 50 Gy was prescribed in 25 fractions and optimized such that the planned target volume (PTV) remained between 95% and 110% of the dose. The mean and maximum doses of the heart, V5 and V20 of the lungs, as well as V95 doses for MI were recorded. Statistical analyses were performed with SPSS version 22, and a paired t-test was used for comparison. Results: Four treatment plans (FB FinFRT, BH FinFRT, FB dIMRT, BH dIMRT) were made separately for 10 patients. For comparison, common FB FinFRT plans were accepted as the baseline plan. As expected, there were no significant differences in PTV coverage. The mean dose received by 95% of the MI volume was between 42.27 Gy and 42.4 Gy. For the maximum heart dose, the breath hold technique had no significant effect on plans. The lowest average maximum heart dose was seen in the BH FinFRT group. Mean heart doses are between 1.28 Gy – 4.85 Gy. There was no significance between BH FinFRT and FB FinFRT plan (P=0.504), and there was a significant difference for heart mean dose versus dIMRT plans (P=0.001). The mean V20 of the lungs ranged from 11.9 to 17.8. There was a significant decrease in V20 with BH or FB dIMRT plans (P=0.001). There was no difference between BH FinFRT (P=0.138). On the contrary, lung V5 values were significantly higher in dIMRT plans, and the lowest mean V5 value was seen in BH FinFRT plan. Conclusion: With the BH method, lower doses (but not significantly lower doses) were obtained in critical organ doses. There was a significant decrease with FinFRT plans in terms of heart mean and maximum dose and lung V5 percentages. The dIMRT plans were significant only in lung V20 percentages. When planning RT, we recommend evaluating all treatment techniques individually for right-sided breast cancer patients to obtain lower doses in critical organs.

Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

BackgroundStereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.MethodsEligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.ResultsEighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.ConclusionLINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium.

In Radiotherapy, computation of dose is important since in a small field with heterogeneity, dose is usually computed with discrepancies. The present study was aimed to evaluate the dosimetry of treatment planning algorithms in lung equivalent heterogeneous medium for Volumetric Modulated Arc Therapy (VMAT) with step and shoot Intensity-Modulated Radiation Therapy (ss-IMRT), and dynamic Intensity-Modulated Radiation Therapy (d-IMRT). In this experimental study, Computerized Imaging Reference System (CIRS) phantom was used with an inhomogeneous Racemosa wood cylinder for two types of tumors, namely, Left Lung Central Tumor (LCT) and Left Lung Peripheral Tumor (LPT) in the CIRS left lung cavity. The computed tomography (CT) datasets were employed with the generation of VMAT, d-IMRT and ss-IMRT plans for the LCT and LPT irradiated with 6 MV photon beams. In this study, the accuracy and efficacy of two algorithms: Monte Carlo (MC) and the Pencil Beam (PB), from the Monaco treatment planning system (TPS), were tested by using Gafchromic EBT3 films and CIRS thorax phantom. Regardless of treatment techniques, both algorithms exhibited higher divergence in LPT than LCT. In both LCT and LPT, the highest deviation was near the tumor-lung junction. However, the deviation was higher in the PB algorithm than MC algorithm, with a minimally acceptable variation of -0.8%. The MC algorithm shows more consistency for EBT3 measured dose in lung equivalent heterogeneous medium. However, accurate dose predictions are complicated due to electronic disequilibrium within and at the interface of inhomogeneity. These constraints may cause variations from the anticipated outcomes of the treatments.

Influence of beamlet width on dynamic IMRT plan quality in nasopharyngeal carcinoma.

ObjectiveThis study aimed to identify the effects of beamlet width on dynamic intensity-modulated radiation therapy (IMRT) for nasopharyngeal carcinoma (NPC) and determine the optimal parameters for the most effective radiotherapy plan.MethodsThis study evaluated 20 patients with NPC were selected for dynamic IMRT. Only the beamlet width in the optimization parameters was changed (set to 2, 4, 6, 8, and 10 mm that were named BL02, BL04, BL06, BL08, and BL10, respectively) to optimize the results of the five groups of plans. Using the plan quality scoring system, the dose results of the planning target volumes (PTVs) and organs at risks (OARs) were analyzed objectively and comprehensively. The lower the quality score, the better the quality of the plan. The efficiency and accuracy of plan execution were evaluated using monitor units (MUs) and plan delivery time (PDT).ResultsThe BL04 mm group had the lowest quality score for the targets and OARs (0.087), while the BL10 mm group had the highest total score (1.249). The BL04 mm group had the highest MUs (837 MUs) and longest PDT (358 s). However, the MUs range of each group plan was below 100 MUs, and the PDT range was within 30 s. In the BL02, BL04, BL06, BL08, and BL10 plans, <5 MUs segments accounted for 33%, 16%, 24%, 33%, and 40% of total segments, respectively, with which the lowest was in the BL04 mm group.ConclusionSmaller beamlet widths have not only reduced OARs dose while maintaining high dose coverage to the PTVs, but also lead to more MUs that would produce greater PDT. Considering the quality and efficiency of dynamic IMRT, the beamlet width value of the Monaco treatment planning system set to 4 mm would be optimal for NPC.

Dosimetric Comparison of Three-Dimensional Conformal Radiotherapy, Dynamic Intensity Modulated Radiation Therapy, and Hybrid Planning for Treatment of Locally Advanced Lung Cancer

Dosimetric Comparison of Three-Dimensional Conformal Radiotherapy, Dynamic Intensity Modulated Radiation Therapy, and Hybrid Planning for Treatment of Locally Advanced Lung Cancer

Does CyberKnife improve dose distribution versus IMRT and VMAT on a linear accelerator in low-risk prostate cancer?

BackgroundHypofractionated stereotactic body radiation therapy (SBRT) for prostate cancer (PCa) can be delivered with the robot-assisted CyberKnife (CK) system or on a linear accelerator using dynamic intensity-modulated radiotherapy (IMRT) or volumetric arc radiotherapy (VMAT). This retrospective study was performed to determine whether CK offers better dose distribution than IMRT and/or VMAT.Materials and methodsTreatment plans for three techniques were prepared using the same treatment parameters (36.35 Gy, 7.25 Gy/fr). We evaluated target coverage, conformity index (CI), homogeneity index (HI), gamma index (GI), and organs at risk (OAR) constraints.ResultsThe mean planning target volume (PTV) dose for CK (39.58 Gy) was significantly greater than VMAT or IMRT (both 36.25 Gy). However, CK resulted in a wider dose range (31.48 to 45.89 Gy) vs. VMAT and IMRT (34.6–38.76 Gy). The mean dose to the rectum (V36Gy, mm3) was significantly lower (p < 0.001) in the CK plans (219.78 vs. 519.59 and 422.62, respectively). The mean bladder dose (V37Gy, mm3) was significantly greater for CK (3256 vs. 1090.75 for VMAT and 4.5 for IMRT (p < 0.001). CK yielded significantly better CI (1.07 vs. 1.17 and 1.25 for VMAT and IMRT, respectively; p < 0.01) and HI values (1.27 vs. 1.07 and 1.04; p < 0.01). GI values for the δd = 3mm, δ% = 3% criteria were 99.86 (VMAT), 99.07 (IMRT) and 99.99 (CK). For δd = 2mm, δ% = 2%, the corresponding values were 98.3, 93.35, and 97.12, respectively.ConclusionsFor most variables, CK was superior to both VMAT and IMRT. However, dynamic IMRT techniques, especially VMAT, do not differ significantly from CK plans and are therefore acceptable alternatives to CyberKnife.

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).

Performance evaluation of a Monte Carlo-based treatment planning system in out-of-field dose estimation during dynamic IMRT with different dose rates

AimThe present study aimed to investigate the effect of dose rate variations in the out-of-field regions on the dose calculation accuracy of an algorithm based on the Monte Carlo (MC) method implemented in Monaco (V.5.11.03) Treatment Planning System (TPS). Materials and methodsNine fields of the IMRT plan for the CShape structure were created in the CIRS IMRT Thorax phantom, and the related doses were calculated using the MC-based algorithm of the Monaco TPS. Afterward, the CIRS IMRT Thorax phantom was irradiated by an Elekta Synergy linear accelerator and the 160-leaf MLC Agility 6 MV photon beams using the Dynamic Intensity Modulated Radiation Therapy (D-IMRT) technique. To this end, 3 ion chambers were inserted in 3 cavities, which were equivalent to water, bone, and lung, and were located in the out-of-field regions within the phantom. Finally, the dose measurements were performed, and the values were compared with the doses calculated by the Monaco TPS. ResultsFindings revealed that the Monaco TPS underestimated the dose by an average of 40% for most of the out-of-field measurement distances. Moreover, at distant positions of the out-of-field edge, out-of-field doses were significantly underestimated for all media and dose rates. Finally, the percentage of the TPS error and out-of-field dose values were different for each dose rate. ConclusionsResults in the present research showed remarkable differences between the measured and calculated doses. Thus, it was concluded that the dose calculation accuracy of the Monaco TPS was not reliable for out-of-field regions at different dose rates, and the application of the current commercial treatment planning systems in these regions could lead to underestimating the risk of secondary cancer development.

Comparison of dosimetric parameters and three-dimensional dosimetric verification of three intensity-modulated radiotherapy plans for thymoma based on the dose-volume histogram and ArcCHECK-3DVH system

Objective: To compare the dosimetric parameters of step-shoot intensity-modulated radiotherapy (sIMRT), dynamic intensity-modulated radiotherapy (dIMRT), and volume-modulated arc therapy (VMAT) in thymoma and to study the feasibility of the ArcCHECK-3DVH system in three intensity-modulated radiotherapy plans to choose a more appropriate intensity-modulated radiotherapy for thymoma. Materials and Methods: Seventeen patients with thymoma were enrolled in this study. Treatment plans of sIMRT, dIMRT, and VMAT for each patient were based on the Monaco treatment planning system (TPS). Dosimetric verification was performed via the ArcCHECK-3DVH system. We compared and analyzed the 3D γ pass rates of the TPS dose calculation and ArcCHECK-3DVH system dose reconstruction with the three gamma criteria (3 mm/3%, 2 mm/2%, and 1 mm/1%) with a threshold of 10%. Dose-volume histogram analysis was used to compare the dose parameters for target volumes, and organs at risk (OARs), such as D98%, D50%, D2%, Dmax, V20, and V5. Monitor units (MUs) and delivery time were also compared. Results: There were significant differences in the three intensity-modulated radiotherapy plans. For target volume, VMAT showed the highest planning target volume (PTV) D98% and the lowest PTV D50% compared with sIMRT or dIMRT. The PTV D2% of VMAT was lower than that of sIMRT and higher than that of dIMRT, and VAMT demonstrated the highest conformity index and MU, lowest homogeneity index, and shortest treatment delivery time. For the OARs, VMAT is not inferior to sIMRT and dIMRT in OARs protection. For the dosimetric verification, the entire area, PTV, lungs, heart, and spinal cord of VMAT showed the highest γ pass rates than the other two techniques under the gamma 3 mm/3% criteria, which was even more pronounced when the stricter gamma criteria of 2 mm/2% and 1 mm/1% were applied. Conclusion: VMAT can be applied to radiotherapy of thymoma, and the accuracy of treatment plan execution can be guaranteed through the ArcCHECK-3DVH system.

Evaluating the Effects of Dose Rate on Dynamic Intensity-Modulated Radiation Therapy Quality Assurance

Evaluating the Effects of Dose Rate on Dynamic Intensity-Modulated Radiation Therapy Quality Assurance

Quality of Automated Stereotactic Radiosurgery Plans in Patients with 4 to 10 Brain Metastases.

Simple SummaryStereotactic radiosurgery (SRS) and hypofractionated stereotactic radiotherapy (SRT) are promising treatment options for patients with multiple brain metastases in the current era of personalized medicine. Recent international guidelines propose SRS also in patients with more than three brain metastases with low-volume disease. Optimal treatment quality with sparing of healthy brain tissue is essential to avoid SRS/SRT complications such as brain necrosis. The aim of this study was to compare linac (linear accelerator)-based SRS/SRT plan quality of automated planning, intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT) and manually planned dynamic conformal arc (DCA) plans as well as single- and multiple-isocenter techniques. We found that automated planning with DCA or IMRT can make linac-based SRS/SRT plan quality with single isocenter comparable with a manually planned DCA plan with a separate isocenter for each metastasis.The purpose was to compare linac-based stereotactic radiosurgery and hypofractionated radiotherapy plan quality of automated planning, intensity modulated radiotherapy (IMRT) and manual dynamic conformal arc (DCA) plans as well as single- and multiple-isocenter techniques for multiple brain metastases (BM). For twelve patients with four to ten BM, seven non-coplanar linac-based plans were created: a manually planned DCA plan with a separate isocenter for each metastasis, a single-isocenter dynamic IMRT plan, an automatically generated single-isocenter volumetric modulated arc radiotherapy (VMAT) plan, four automatically generated single-isocenter DCA plans with three or five couch angles, with high or low sparing of normal tissue. Paddick conformity index, gradient index (GI), mean dose, total V12Gy and V5Gy of uninvolved brain, number of monitor units (MUs), irradiation time and pass rate were compared. The GI was significantly higher for VMAT than for separate-isocenter, IMRT, and all automatically generated plans. The number of MUs was lowest for VMAT, followed by automatically generated DCA and IMRT plans and highest for manual DCA plans. Irradiation time was the shortest for automatically planned DCA plans. Automatically generated linac-based single-isocenter plans for multiple BM reduce the number of MUs and irradiation time with at least comparable GI and V5Gy relative to the reference separate-isocenter DCA plans.

Premature Ovarian Insufficiency (POI) Induced by Dynamic Intensity Modulated Radiation Therapy via P13K-AKT-FOXO3a in Rat Models.

This study is aimed to investigate the mechanisms of radiation-induced mouse models of premature ovarian insufficiency (POI). Wistar female rats were grouped into the control, 3.2 Gy, 4.0 Gy, and 4.8 Gy groups. Overall ovarian functions were assessed with the H&E staining and ELISA. Proinflammatory cytokine secretion was analyzed ELISA, and the reactive oxygen species (ROS) levels were analyzed with immunohistochemistry. Protein expressions were analyzed by Western blot analysis. The 4.0 Gy and 4.8 Gy groups had significantly lower ovarian weight coefficients than the control and 3.2 Gy groups (after only one irradiation therapy). The 3.2 Gy radiation group induced periodic disturbance and hormone change at 4 weeks after radiation. In the 4.0 Gy and 4.8 Gy groups, the preantral follicles and antral follicles were decreased, while Atresia follicles were increased. E2 was decreased, while FSH and LH secretions were increased. The ovaries in the 4.0 Gy group were not completely atrophied, and some preantral follicles remained. Ovarian atrophy and follicular Atresia were found in the 4.8 Gy group. Inflammatory and oxidative markers were upregulated. PI3K and AKT were downregulated in the 4.0 Gy and 4.8 Gy groups, while FOXO3a was upregulated. Ovarian injuries may lead to oxidative damages and inflammatory injuries, downregulate the expression of P13k and Akt, upregulate the expression of FOXO3a, and lead to follicular atresia in the ovary.

Estimation of monitor unit through analytical method for dynamic IMRT using control points as an effective parameter

AbstractIntroduction:The control points (CP) play a significant role in the delivery of segmented based Intensity-Modulated Radiation Therapy (IMRT) delivery, particularly in dynamic mode. The number of segments is determined by control points and these segments will transfer from one to the other either during beam ON called dynamic delivery or during beam OFF called static delivery or step and shoot. This study was aimed at indirect estimation of the total monitor units (MU) to be delivered per field by exploiting the control points and also to find the MUs at any nth segment.Materials and methods:This study was performed in the Eclipse treatment planning software version 13.8.0. The details of control points, metre set weight per segment, leaf positions for each segment, field size, etc. were taken into consideration.Results:TPS calculated MU value and analytically estimated MU value were compared and the percentage of difference was estimated. The overall mean percentage of deviation was 1·03% between the TPS calculated method and the analytical method. The paired sample t-test was performed and, p-value &lt;0·05, no significant difference was found. The analytical relationship determined to estimate the total number of MU delivered for any nth control point was also evaluated.Conclusion:The control points are a potential parameter in the conventional IMRT delivery. Through this study, we have addressed the indirect method to estimate the monitor units delivered per segment.

Comparing treatment plans for stomach cancer: three-dimensional conformal radiotherapy (3D-CRT), physical wedge-based conformal RT (WB-CRT) and intensity-modulated radiotherapy (IMRT)

AbstractObjective:The aim of this study was to find the optimal radiotherapy (RT) method using three-dimensional (3D) conformal RT (CRT), physical wedge-based CRT (WB-CRT) and dynamic intensity-modulated RT (D-IMRT) techniques for stomach cancer.Methods:Ten patients with gastric cancer were selected for this study. For each patient, three different treatment plans were generated. 3D-CRT, WB-CRT and IMRT plans were evaluated in terms of dosimetry. Treatment plans were compared with respect to the planning target volume and organs at risk (OARs) volumes including right and left kidney doses (V13, V20 and V28), heart mean and maximum doses, spinal cord maximum doses, dose homogeneity index, conformity index (CI), delivery time and the monitor unit counts for the treatment. Statistical analysis was performed using the SPSS (Statistical Package for the Social Sciences) v25.1 software (IBM Inc., Chicago, IL, USA).Results:In stomach plans, IMRT showed a significantly lower dose for the left and right kidneys than that of WB-CRT or 3D-CRT (p &lt; 0·05). Compared with WB-CRT or 3D-CRT, IMRT reduced the V28, V20, V13 and mean dose to bilateral kidneys (p &lt; 0·05). IMRT plans indicated better dosimetry for at the Dmean of the liver and heart. Concerning the calculated CI, values for IMRT plans gave significant results than other plans (p &lt; 0·05).Conclusions:IMRT plans provided better protection for the kidneys, liver, heart and spinal cord. For the treatment of stomach cancer, considering the dose to the OARs, IMRT appears to be the most superior technique.

The structural similarity index for IMRT quality assurance: radiomics‐based error classification

The implementation of radiomics and machine learning (ML) techniques on analyzing two-dimensional gamma maps has been demonstrated superior to the conventional gamma analysis for error identification in intensity modulated radiotherapy (IMRT) quality assurance (QA). Recently, the Structural SIMilarity (SSIM) sub-index maps were shown to be able to reveal the error types of the dose distributions. In this study, we aimed to apply radiomics analysis on SSIM sub-index maps and develop ML models to classify delivery errors in patient-specific dynamic IMRT QA. Twenty-one sliding-window IMRT plans of 180 beams for three treatment sites were involved in this study. Four types of machine-related errors of various magnitudes were simulated for each beam at each control point, including the monitor unit (MU) variations, same-directional and opposite-directional shifts of the multileaf collimators (MLCs) and random mispositioning of the MLCs. In the QA process, a total of 1620 portal dose (PD) images were acquired for the beams with and without errors. The predicted PD images of the original beams were set as references. To quantify the agreement between a measured PD image and the corresponding predicted PD image, four difference maps including three SSIM sub-index maps, and one dose difference-derived map were calculated. Then, radiomic features were extracted from the four difference maps of each measured PD image. We tested four typical classifiers including linear discriminant classifier (LDC), two supporting vector machine (SVM) classifiers, and random forest (RF) for this multiclass classification task. A nested cross-validation scheme was used for model evaluations, where the SVM recursive feature elimination method was applied for feature selection. Finally, the performance of the ML model on identifying the error-free and the erroneous cases was compared to that of the conventional gamma analysis. The statistics of the selected features showed that all of the difference maps and the feature categories made balanced contributions to solve this classification task. Best performance was achieved by the Linear-SVM model with average overall classification accuracy of 0.86. Specifically, the average classification accuracies of the shift, opening, and the random errors were around 0.9. Moreover, ~80% of error-free and MU errors were correctly classified. Using gamma analysis, the 3mm/3% criterion was found insensitive to errors (sensitivity was only 0.33). Although the sensitivity to errors with the 2mm/2% criterion increased to 0.79, still 8% worse than that of the ML model. We proposed an ML-based method for machine-related error identification in patient-specific dynamic IMRT QA, where radiomic analysis on SSIM sub-index maps were used for feature extraction. With extensive validation to select the best features and classifiers, high accuracies in error classification were achieved. Compared with the conventional gamma threshold method, this approach has great potential in error identification for the patient-specific IMRT QA process.