Dosimetric evaluation study of IMRT and VMAT techniques for prostate cancer based on different multileaf collimator designs

Purpose: To compare volumetric modulated arc radiotherapy (VMAT) technique with fixed-gantry intensity-modulated radiotherapy (IMRT) technique for locally recurrent nasopharyngeal carcinoma. Methods: CT datasets of eleven nasopharyngeal-carcinoma patients were included. Dual-arc VMAT and seven-field IMRT plans were created for each case, and were then compared in terms of conformity index (CI), homogeneity index (HI) of the planning target volume (PTV), organ-at-risk (OAR) sparing, monitor unit (MU) and delivery time. Results: The D98% (near-minimal dose) of PTV in the VMAT plans was slightly lower than that of the IMRT plans (P 0.05). Compared with the IMRT plans, the VMAT plans demonstrated lower Dmean (mean dose) of the bilateral temporal lobes and the whole surrounding normal tissue (P 0.05). The MUs of the VMAT plans (672 ± 112) was significantly lower than that of the IMRT plans (917 ± 206), by 25 ± 13% (P < 0.05). The average delivery time of the VMAT plans (2.3 ± 0.1 min) was less than that of the IMRT plans (5.1 ± 0.4 min), by 54 ± 3%. Conclusion: For locally recurrent nasopharyngeal carcinoma, the VMAT technique could achieve equivalent or superior dose distribution of the target and better protect the bilateral temporal lobes, compared with the IMRT technique. Moreover, it could reduce the MU and delivery time effectively.

Background:Since 2009, the use of IMRT for the treatment of breast cancer with lymph node involvement has been considerably growing at our institution. Helical Tomotherapy (HT) was chosen as main technique using field width of 2.5 cm (HT_FW_2.5). Alternatively HT using field width of 5 cm (HT_FW_5), Volumetric Modulated Arc Therapy (VMAT), or Proton Therapy with Pencil Beam Scanning (PT-PBS) were used to reduce treatment duration or optimize organs at risk (OAR) sparing. Purpose: the aim of this study is to compare the 4 modalities of treatment available at our site. Patients and methods: We studied 10 patients treated for breast cancer with lymph node involvement. The prescribed dose was 51.8 Gy to breast with simultaneous integrated boost till 63 Gy, 50.4 Gy to the lymph nodes in 28 fractions for all studied patients. The CTV (clinical target volume) were delineated using ESTRO Guidelines. Dosimetric plan used in routine clinical practice was done using HT_FW_2.5. Clinical plan approved was compared to the plan using the 3 others IMRT techniques. Dosimetric parameters were noted down. For Planning Target Volume (PTV) coverage, dosimetric goals were D95% ≥ 95% and D2% ≤ 107% of the prescribed dose. Regarding OAR, mean dose were noted for heart, contralateral/ipsilateral lung and contralateral breast. Maximum dose in the spinal cord was also recorded. Dosimetric score was made to evaluate plan quality. For both PTV score (PTVs) and OAR score (OARs), 1 was the best and 4 the worst achievable score. Results:HT_FW_5 and VMAT plans ensure an equivalent or even better PTV coverage than the initial clinically approved plan (PTVs = 2.3 and 2.0 VS 2.5) but at the cost of a deterioration of OAR sparing (OARs = 3.3 and 3.2 VS 2.3). PT_PBS plans show that an excellent PTV coverage can be maintained with significantly lower doses to OAR (PTVs = 2.0; OARs = 1.1) Conclusion:HT_FW_5 and VMAT plans allow significantly reducing treatment duration and can be good alternative to HT_FW_2.5 for specified population which has already a good OAR sparing and needs to reduce treatment duration. HT_FW_2.5 could be chosen for patient with higher risk of side effect. In addition PT_PBS treatment should be considered in the near future as it showed great potential benefit to lower the risk of side effects without deteriorating PTV coverage. Dosimetric Scores of different IMRT techniquesHT_FW_2,5HT_FW_5VMATPT_PBSD95% (Gy)PTV Breast49.449.950.149.7PTV Tumor Bed60.160.160.361.1PTV Lymph Nodes47.748.148.548.3PTV Score2.52.32.02.0Dmean (Gy)Heart7.28.47.31.0Contralateral Lung4.35.16.40.4Ipsilateral Lung13.513.714.59.3Contralateral Breast3.53.64.30.0OAR Score2.33.33.21.1 Citation Format: Wassim El Amine, Laurent Bartolucci, Camille Adrien, Marie Lejars, Alain Fourquet, Marion Vaillant, Magalie Robilliard, Emilie Costa, Alejandro Mazal, Farid Goudjil, Youlia Kirova. Intensity modulated radiotherapy (IMRT) for breast and lymph node irradiation [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-32.

Introduction: During intensity modulated radiation therapy (IMRT) technique, theoretically, presence of flattening filter (FF) across the beamline of clinical linear accelerator (linac) is not essential to obtain uniform lateral profiles due to intensity modulation of photon beams by multileaf collimators (MLCs). The aim of this study was to investigate the dosimetrical properties of 18 MV photon Beam-Varian linac with and without FF. Materials and Methods: All dose measurements were performed on 18 MV, FF Mode-Varian 2100C/D linac. The FF and flattening filter free (FFF) modes of linac were modeled by MCNPX 2.4. code. The photon and contaminant electrons spectra, dose rate, present depth doses (PDD), lateral dose profiles, total and collimator scatter factors and out of field doses were calculated and compared with and without FF. Results: Removing the FF increased the photon and contaminant electron fluences by factors of 5.48 and 3.94 for a 5 × 5 cm2 field size, respectively. The surface dose increased up to 155%. The flatness of dose profile was disturbed and deteriorated with increase of field size. Despite the dependence of the total scattering factor on field size, the variation of collimator scattering factors was neglected. The out-of-field dose decreased about 81.5 % for a 5 × 5 cm2 field size. Conclusion: Removing FF from the linac’s head increases the dose rate and decreases the out-of-field dose, but the increased skin dose and deteriorated flatness of lateral dose profile are the main

The average lifetime risk of secondary cancer after irradiating glioblastoma radiation therapy to healthy organs shows that the technique of volumetric modulated arc therapy (VMAT) has a smaller risk of developing secondary cancer compared to intensity modulated radiation therapy (IMRT) and three-dimensional radiation therapy (3DCRT). Parameters of dose distribution, namely the target volume and dose received by the organs at risk (OAR), are used to compare these three techniques. The distribution of doses from TPS results in the form of DVH and isodose in the 3D CRT, IMRT, and VMAT techniques shows that the distribution of doses to healthy organs around the glioblastoma irradiation area is in the safe category and is still within tolerance limits. With VMAT, the PTV and CTV dose results were more optimal compared to the 3D CRT and IMRT techniques. 3D CRT showed a PTV dose value of 5551.8 cGy and a CTV of 5515.3 cGy. IMRT shows a PTV dose value of 6035.0 cGy and a CTV of 6018.8 cGy. VMAT shows PTV dose values of 6101.8 cGy and CTV of 6044.7 cGy. It can be seen that the distribution of doses to healthy organs in general in the VMAT technique is more optimal than the IMRT and 3D CRT techniques in protecting OAR.

Volumetric Modulated Arc Therapy vs. IMRT for the Treatment of Distal Esophageal Cancer

The build‐up dose in the megavoltage photon beams can be a limiting factor in intensity‐modulated radiation therapy (IMRT) treatments. Excessive surface dose can cause patient discomfort and treatment interruptions, while underdosing may lead to tumor repopulation and local failure. Dose in the build‐up region was investigated for IMRT delivery with solid brass compensator technique (compensator‐based IMRT) and compared with that of multileaf collimator (MLC)‐based IMRT. A Varian Trilogy linear accelerator equipped with an MLC was used for beam delivery. A special solid brass step‐wise compensator was designed and built for testing purposes. Two step‐and‐shoot MLC fields were programmed to produce a similar modulated step‐wise dose profile. The MLC and compensator dose profiles were measured and adjusted to match at the isocenter depth of 10 cm. Build‐up dose in the 1–5 mm depth range was measured with an ultrathin window, fixed volume parallel plate ionization chamber. Monte Carlo simulations were used to model the brass compensator and step‐and‐shoot MLC fields. The measured and simulated profiles for the two IMRT techniques were matched at the isocenter depth of 10 cm. Different component contributions to the shallow dose, including the MLC scatter, were quantified. Mean spectral energies for the open and filtered beams were calculated. The compensator and MLC profiles at 10 cm depth were matched better than ±1.5%. The build‐up dose was up to 7% lower for compensator IMRT compared to MLC IMRT due to beam hardening in the brass. Low‐energy electrons contribute 22% and 15% dose at 1 mm depth for compensator and MLC modalities, respectively. Compensator‐based IMRT delivers less dose in the build‐up region than MLC‐based IMRT does, even though a compensator is closer to the skin than the MLC.PACS number: 87.55.dk, 87.56.ng

BackgroundThe advent of volumetric modulated arc therapy (VMAT) in radiotherapy has made it one of the most commonly used techniques in clinical practice. VMAT is the delivery of intensity modulated radiation therapy (IMRT) while the gantry is in motion, and existing literature has shown it has decreased treatment delivery times and the number of monitor units without sacrificing coverage. It has previously been shown that for IMRT, multi‐leaf collimators (MLC) with narrower leaf widths produce demonstrably higher treatment plan quality. However, as VMAT is rapidly becoming the global standard, this needs to be re‐evaluated, especially in a global context. This study assesses the impact of MLC leaf width on VMAT treatment plans and asks whether reducing the number of leaves‐ and thus increasing leaf width‐ provides clinically acceptable treatment plans using VMAT delivery.Material & methodsUsing Varian Eclipse, 51 anonymised patients with prostate, lung, liver, colorectal, or cervical cancer had VMAT treatment plans generated. Treatment plans were generated for MLC leaf widths of 2.5, 5 and 10 mm. Plans were compared using D2[%], D50[%], and D98[%], homogeneity index (HI), conformity index (CI), average leaf pair opening (ALPO), modulation factor (MF) and Estimated Treatment Delivery Time.ResultsThe dose to the target structures showed little difference between 2.5 and 5 mm MLC leaves, however 10 mm MLC provided 5% more median dose than the narrower leaf widths for D2[%] (p < 0.05) and D50[%] (p < 0.05). The average HI per leaf width was 0.0777 for 2.5 mm, 0.0752 for 5 mm, and 0.0890 for 10 mm. Organs At Risk (OAR) sparing was consistent between all leaf widths except at low dose percentages, where 10 mm MLC delivered an extra dose to the bladder (p < 0.05) and the heart (p < 0.05). The average ALPO was 38.0 mm for 2.5 mm, 34.1 mm for 5 mm, and 32.7 mm for 10 mm leaf width. 10 mm MLC leaves traveled a shorter distance from the center (p < 0.05). The median MF was 336 MU/Gy for 2.5 mm, 344 MU/Gy for 5 mm, and 384 MU/Gy for 10 mm. There were no differences in estimated treatment delivery time between MLC leaf width.ConclusionThere is little difference in treatment quality between any of the investigated MLC leaf widths. This work demonstrates that for VMAT treatments, wider MLC leaf widths can still deliver acceptable treatment plans. This finding has potential implications for radiotherapy in low‐ and middle‐income countries and low socio‐economic or rural areas where a focus on MLC robustness and LINAC up‐time is paramount.

Inverse and forward optimization of one- and two-dimensional intensity-modulated radiation therapy-based treatment of concave-shaped planning target volumes: the case of prostate cancer.

This study aims to compare the dosimetric coverage of the Planning Target Volume (PTV) and the dose to main organs at risk (OARs) between two different algorithms fast superposition (FSUP), superposition (SUP) using intensity-modulated radiotherapy (IMRT) techniques for prostate cancer. Ten patients with prostate cancer were selected for this study. For each patient, IMRT plans were created with 6 MV photon beam quality using CMS XiO treatment planning system. The delivery of IMRT was carried out using the step and shoot techniques. The dose coverage for each patient was designated to an ICRU report 62 reference point in the PTV, medium coverage of the planned target volume to be 95% of the prescribed dose while the maximum dose in the target volume to be not greater than 107% of the prescribed dose. A hypofractionated prescription dose of 70 Gy/28# at 2.5 Gy per fraction was used. Besides we compared the number of MUs and OARs dose to D15%, D25%, D35%, D50% on both algorithm planning sets. For target, this evaluation was made with comparing the conformity index (CI) and homogeneity index (HI). In our study, the results show the OARs got less dose from the SUP algorithm compared to FSUP algorithms. Statistically not significant difference was observed in V107% of PTV, MU/CC, conformity Index (p = 0.057, p = 0.215, p = 0.370) and 95% PTV Volume received prescription dose from both Plans. But Homogeneity Index for both algorithms was statistically significant (p = 0.000, p = 0.001). For prostate cancer, the superposition algorithm showed better results in the IMRT plan compared to the fast superposition algorithm.

Objectives: To compare treatment plans of intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT), and helical tomotherapy (HT) with simultaneous integrated boost (SIB) technique for esophageal cancer (EC) of different locations using dosimetry and radiobiology.Methods: Forty EC patients were planned for IMRT, VMAT, and HT plans, including 10 cases located in the cervix, upper, middle, and lower thorax, respectively. Dose-volume metrics, conformity index (CI), homogeneity index (HI), tumor control probability (TCP), and normal tissue complication probability (NTCP) were analyzed to evaluate treatment plans.Results: HT showed significant improvement over IMRT and VMAT in terms of CI (p = 0.007), HI (p < 0.001), and TCP (p < 0.001) in cervical EC. IMRT yielded more superior CI, HI and TCP compared with VMAT and HT in upper and middle thoracic EC (all p < 0.05). Additionally, V30 (27.72 ± 8.67%), mean dose (1801.47 ± 989.58cGy), and NTCP (Niemierko model: 0.44 ± 0.55%; Lyman-Kutcher-Burman model: 0.61 ± 0.59%) of heart in IMRT were sharply reduced than VMAT and HT in middle thoracic EC. For lower thoracic EC, the three techniques offered similar CI and HI (all p > 0.05). But VMAT dramatically lowered liver V30 (9.97 ± 2.84%), and reduced NTCP of lungs (Niemierko model: 0.47 ± 0.48%; Lyman-Kutcher-Burman model: 1.41 ± 1.07%) and liver (Niemierko model: 0.10 ± 0.08%; Lyman-Kutcher-Burman model: 0.17 ± 0.17%).Conclusions: HT was a good option for cervical EC with complex target coverage but little lungs and heart involvement as it achieved superior dose conformity and uniformity. Due to potentially improving tumor control and reducing heart dose with acceptable lungs sparing, IMRT was a preferred choice for upper and middle thoracic EC with large lungs involvement. VMAT could ameliorate therapeutic ratio and lower lungs and liver toxicity, which was beneficial for lower thoracic EC with little thoracic involvement but being closer to heart and liver. Individually choosing optimal technique for EC in different location will be warranted.

The aim of the present study was to compare the techniques of dynamic intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiotherapy (3DCRT) in patients with gastric cancer. Implementation of the IMRT technique does not significantly affect the minimum and maximum dose levels in the planning target volume (PTV), but more effectively protects the critical organs. The study group consisted of 25 patients. The results of the analysis of the conformity index (CI) and the homogeneity index (HI) showed that the doses in the PTV regions were at a comparable level. The CI for the PTV was 0.95 for the 2-field technique, 0.95 for the 3-field technique, 0.96 for the 4-field technique and 0.94 for the IMRT technique. The CIs for these techniques for the clinical target volume (CTV) were 0.96, 0.96, 0.97 and 0.96, respectively, and the CIs for the gross tumor volume (GTV) were 0.99, 0.99, 0.99 and 0.98, respectively. The HI values for the PTV were 1.12 for the 2-field technique, 1.12 for the 3-field technique, 1.09 for the 4-field technique and 1.09 for the IMRT technique, and the HI values for the CTV were 1.12, 1.12, 1.09 and 1.08 for the same techniques, respectively. The HI values for the GTV were 1.09, 1.09, 1.07 and 1.06, respectively, which indicated significantly superior performance in the regions of healthy tissue. Statistical study was based on Friedman's rank analysis of variance to determine the level of reliability of the tested groups of variables (P<0.001). The present study demonstrated that the IMRT technique in the pre-operative radiotherapy of gastric cancer patients results in superior treatment tolerance and reduces the risk of damage to healthy tissue that is in close proximity to the irradiated area.

&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;The purpose of this study is to analyze and compare the dosimetric parameters of three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) in selected non-small cell lung cancer (NSCLC) cases. &lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Ten patients with inoperable NSCLC were selected for this study. The 3DCRT and IMRT plans were generated for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. Generated plans were then compared on the basis of planning target volume (PTV) coverage, dose delivered to organs at risk, homogeneity index (HI), and conformity index (CI) for the prescribed dose (PD) of 50 Gy in 25 fractions.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;The mean D&lt;sub&gt;95 &lt;/sub&gt;and D&lt;sub&gt;99 &lt;/sub&gt;(dose to the 95% and 99% volume) for the PTV were found better in the 3DCRT plans compared to the ones in the IMRT plans. On an average, the volume receiving 20 Gy (V&lt;sub&gt;20&lt;/sub&gt;) of contralateral lung was 2.91% and 3.03% in the 3DCRT and IMRT plans, respectively. The D&lt;sub&gt;mean&lt;/sub&gt; of contralateral lung was 3.17 Gy (3DCRT) versus 4.2 Gy (IMRT), whereas the D&lt;sub&gt;mean&lt;/sub&gt; of ipsilateral lung was 12.69 Gy (3DCRT) and 13.82 Gy (IMRT). The V&lt;sub&gt;20&lt;/sub&gt; of ipsilateral lung was found to be slightly lower in the 3DCRT (25.67%) when compared to the IMRT (30.50%). The dose to the heart was comparable in the 3DCRT and IMRT plans (mean dose: 4.42 Gy versus 4.48 Gy; D&lt;sub&gt;33&lt;/sub&gt;: 3.77 Gy versus and 4.02 Gy). For the spinal cord, the D&lt;sub&gt;max &lt;/sub&gt;was found to be lower in the 3DCRT plans (18.40 Gy) when compared to the IMRT plans (25.49 Gy). The HI was 1.08 versus 1.41 in the 3DCRT and IMRT plans, respectively. The CI was identical (1.67) in both sets of plans.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;Based on the results of this study, the PTV coverage was found to be slightly better in the 3DCRT plans when compared to the one in the IMRT plans. On average, the dose to the organs at risk were found to be comparable.&lt;/p&gt;

A multileaf collimator phantom for the quality assurance of radiation therapy planning systems and CT simulators

This study aimed to conduct a thorough dosimetric comparison between two advanced radiotherapy techniques, Intensity-Modulated Radiation Therapy (IMRT) and Volumetric-Modulated Arc Therapy (VMAT), to ascertain the superior modality in terms of dose distribution and organ-at-risk sparing for rectal cancer patients. Thirty-three patients with ECOG performance status 1, aged between 18 to 60 years, diagnosed with Stage II to III rectal cancer, were included in this prospective study. Each patient underwent treatment planning with IMRT and VMAT techniques using Varian system simulation computed tomography scans. The dosimetric analysis encompassed the evaluation of target volume dose homogeneity, conformity, and doses to at-risk organs. The dosimetric comparison was conducted utilizing seven-field IMRT and dual arc VMAT plans. Statistical analysis was performed using paired t-tests and SPSS 20 software. Treatment plan constraints adhered to the RTOG 9406 guidelines, ensuring adequate planning target volume (PTV) coverage, homogeneity index, conformity index, and dose limits for organs at risk, including small bowel V20 (&lt;200cc), bladder V45 (&lt;21Gy), and femoral head V50 (≤30 Gy). Volumetric arc therapy plans demonstrated superior dose homogeneity to fixed-field intensity-modulated plans (p-value = 0.04), particularly in femoral head dose-limiting toxicity (p-value = 0.00). However, intensity-modulated therapy exhibited equivalent or superior performance in other evaluated parameters. Our findings suggest that while VMAT offers advantages in PTV coverage homogeneity and femoral head dose-limiting toxicity, IMRT remains competitive and potentially preferable in certain dosimetric aspects. The choice between IMRT and VMAT should be carefully considered based on individual patient characteristics and treatment goals. This comprehensive dosimetric comparison contributes valuable insights into optimizing radiotherapy planning for rectal cancer patients, potentially guiding clinical decision-making and improving treatment outcomes.

Purpose Because of the poor prognosis for high-grade glioma (HGG) patients, it is important to increase the dose of the tumor to improve the efficacy while minimizing the dose of organs at risk (OARs). Thus, we evaluated the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for high-grade glioma (HGG). Methods A total of 42 HGG patients were retrospectively selected who had undergone helical tomotherapy; then, IMRT and VMAT plans were generated and optimized for comparison after contouring crucial neuronal structures for neurogenesis and neurocognitive function. IMRT and VMAT were optimized with the Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60 Gy to planning target volume (PTV) 1 and 50-54 Gy to PTV2. We also analyzed the homogeneity index (HI) and conformity index (CI) of PTVs and organ at risk (OAR) sparing. Results There was no significant difference in the PTV coverage among IMRT, VMAT, or HT. As for the HI, HT plans (PTV1 HI: 0.09 ± 0.03, PTV2 HI: 0.17 ± 0.05) had the best homogeneity when compared to IMRT plans (PTV1 HI: 0.10 ± 0.04, PTV2 HI: 0.18 ± 0.04) and VMAT plans (PTV1 HI: 0.11 ± 0.03, PTV2 HI: 0.20 ± 0.03). The CI value of HT (PTV1 CI: 0.98 ± 0.03, PTV2: 0.98 ± 0.05) was closest to the optimal value. Except for the IMRT and VMAT groups, there were statistically significant differences between the other two groups of the CI values in both PTV1 and PTV2. The other comparison values were statistically significant except for the optic nerve, and VMAT had the best sparing of the optic chiasm. The mean and max doses of OARs declined significantly in HT. Conclusions For high-grade glioma patients, HT had superior outcomes in terms of PTV coverage and OAR sparing as compared with IMRT/VMAT.