Volumetric Modulated Arc Therapy Treatment Plans Research Articles

Advancing Precision in Post-mastectomy Chest Wall Radiotherapy: A Comparative Dosimetric Analysis of Volumetric-Modulated Arc Therapy (VMAT) and Intensity-Modulated Radiotherapy (IMRT) Based on Institutional Experience.

Post-mastectomy radiation therapy (PMRT) is an important component in the management of breast cancer patients who have undergone mastectomy. Intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) are two popular methods of delivering PMRT. With IMRT, high radiation doses are directed at the tumor, while exposure to healthy tissue is kept to a minimum. VMAT, on the other hand, is a more advanced version of IMRT that allows for faster radiation dose delivery while maintaining precision. The complexity of the VMAT treatment planning and delivery process, on the other hand, may increase the risk of technical errors, which can reduce treatment effectiveness. Studies have compared VMAT and IMRT in PMRT for breast cancer patients, but most have found no significant differences in treatment outcomes between the two methods. Individual patient factors such as treatment goals, available resources, and other characteristics may influence the choice between the two techniques. This prospective observational study aimed to compare the dosimetry of two cutting-edge modern radiotherapy techniques for post-mastectomy breast cancer patients receiving hypofractionated doses. For 58 patients with breast cancer, 116 plans for radiotherapy treatment were generated by both VMAT and IMRT. To maintain the uniformity of contouring, every CT image was contoured by the same physician, and Radiotherapy Oncology Group (RTOG) contouring guidelines were strictly followed during contouring. Both techniques had comparable target volume coverage, but VMAT produced a significantly better conformity index than IMRT for both the left (0.71 vs. 0.65) and right (0.72 vs. 0.66) breasts (p-value < 0.05). VMAT plans had significantly higher low-dose spillage to the ipsilateral lung (V5Gy and V10Gy) but significantly lower high-dose spillage (V20Gy, V30Gy, and V40Gy) than IMRT plans (p-value < 0.05). Dmax and Dmean for the ipsilateral lung were comparable for both techniques. When compared to alternative treatment approaches, IMRT treatment plans were found to be more effective in minimizing radiation exposure to the heart for all patients with right-sided breast cancer, resulting in considerably lower levels of Dmean, V5Gy, V10Gy, V20Gy, and V35Gy. Plans for VMAT treatment were found to be significantly superior to left-side chest wall radiotherapy in terms of lower exposure to the heart for higher doses. IMRT plans, on the other hand, were successful in dramatically lowering the levels of Dmax that reached the spinal cord for both right- and left-sided breast cancers. Apart from similar planning target volume (PTV) coverage to IMRT plans, VMAT produced significantly better conformity. VMAT plans have more low-dose spillage to normal tissues, while IMRT plans spare various organs at risk significantly better at lower doses in both right and left-sided breast cancer. VMAT was found to be better at sparing the heart (in left-sided breast cancer only) and ipsilateral lung at a high dose range. The best radiotherapy approach for breast cancer should be established on an individual basis, taking into account tumor laterality and the risk-benefit ratio.

Application of a linear interpolation algorithm in radiation therapy dosimetry for 3D dose point acquisition

Air-vented ion chambers are generally used in radiation therapy dosimetry to determine the absorbed radiation dose with superior precision. However, in ion chamber detector arrays, the number of array elements and their spacing do not provide sufficient spatial sampling, which can be overcome by interpolating measured data. Herein, we investigated the potential principle of the linear interpolation algorithm in volumetric dose reconstruction based on computed tomography images in the volumetric modulated arc therapy (VMAT) technique and evaluated how the ion chamber spacing and anatomical mass density affect the accuracy of interpolating new data points. Plane measurement doses on 83 VMAT treatment plans at different anatomical sites were acquired using Octavius 729, Octavius1500, and MatriXX ion chamber detector arrays, followed by the linear interpolation to reconstruct volumetric doses. Dosimetric differences in planning target volumes (PTVs) and organs at risk (OARs) between treatment planning system and reconstruction were evaluated by dose volume histogram metrics. The average percentage dose deviations in the mean dose (Dmean) of PTVs reconstructed by 729 and 1500 arrays ranged from 4.7 to 7.3% and from 1.5 to 2.3%, while the maximum dose (Dmax) counterparts ranged from 2.3 to 5.5% and from 1.6 to 7.6%, respectively. The average percentage dose/volume deviations of mixed PTVs and OARs in the abdomen/gastric and pelvic sites were 7.6%, 3.5%, and 7.2%, while mediastinum and lung plans showed slightly larger values of 8.7%, 5.1%, and 8.9% for 729, 1500, and MatriXX detector arrays, respectively. Our findings indicated that the smaller the spacing between neighbouring detectors and the more ion chambers present, the smaller the error in interpolating new data points. Anatomical regions with small local mass density inhomogeneity were associated with superior dose reconstruction. Given a large mass density difference in the various human anatomical structures and the characteristics of the linear interpolation algorithm, we suggest that an alternative data interpolation method should be used in radiotherapy dosimetry.

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.

Robust VMAT treatment planning for extremity soft tissue sarcomas.

Volumetric modulated arc therapy (VMAT) is a frequently employed and guideline-recommended radiotherapy (RT) modality for extremity soft tissue sarcomas (eSTS). Prior studies have demonstrated that significant tumor volume changes during treatment result in loss of target volume coverage with highly conformal techniques such as VMAT, but few solutions exist to these issues aside from adaptive replanning. Here, we describe a related but novel phenomenon in which relatively minor changes in surface volume contour (whether due to daily setup uncertainty, edema of peritumoral tissue, or progression or pseudo-progression of tumor volume itself) can result in unexpected subcutaneous hotspots. This phenomenon is of significant clinical concern given the known association between skin dose and major wound complications during preoperative RT for eSTS. By evaluating daily cone-beam CT (CBCT) images from thirteen eSTS patients treated with VMAT RT, we identify daily surface contour changes (range: 2 mm-15 mm, median: 8 mm) which are frequently below conventional adaptive replanning thresholds. When applied under experimental conditions, these external contour changes did not have major impacts on target volume coverage (range: 30.2%-91.2%, mean: 72.5%) but did result in unexpected hotspots of 125.8% on average (range: 110.0%-142.2%) in the subcutaneous tissues. To mitigate this issue, we develop a methodology for VMAT treatment planning using flash PTV and virtual bolus (VB) to produce robust treatment plans that are more resistant to target volume changes, surface contour changes, and setup uncertainties than conventional planning methods. With this methodology, robust plans were equivalent to standard plans at baseline, but, after incorporation of surface volume changes, both maintained target volume coverage (p < 0.001) and prevented development of subcutaneous hotspots (p < 0.001) better than standard plans. As such, this treatment planning methodology may facilitate development of robust VMAT treatment plans that minimize development of subcutaneous hotspots and preserve target volume coverage in the context of routine volumetric changes during preoperative RT.

Hippocampal-sparing whole-brain radiotherapy under coplanar or noncoplanar VMAT.

Whole-brain radiotherapy (WBRT) can alleviate symptoms in patients with brain metastases. However, WBRT may damage the hippocampus. Volumetric modulated arc therapy (VMAT) can achieve a suitable coverage of the target region and a more conforming dose distribution whereas decreasing the dose to organs-at-risk (OARs). Herein, we aimed to compare the differences between treatment plans utilizing coplanar VMAT and noncoplanar VMAT in hippocampal-sparing WBRT (HS-WBRT). Ten patients were included in this study. For each patient, the Eclipse A10 treatment planning system was used to generate 1 coplanar VMAT (C-VMAT) and 2 noncoplanar VMAT treatment plans with various beam angles (noncoplanar VMAT A [NC-A] and noncoplanar VMAT B [NC-B]) for HS-WBRT. The prescribed dose was 30 Gy in 12 fractions. Treatment plans were established based on the OAR dose constraints of the Radiation Therapy Oncology Group 0933 (RTOG 0933). Parameters such as the global maximum dose, dose conformity, dose homogeneity of plans, and OAR doses were evaluated. The maximum biologically equivalent doses in 2-Gy fractions (EQD2) of OARs in C-VMAT were 9.17 ± 0.61, 42.79 ± 2.00, and 42.84 ± 3.52 Gy in the hippocampus, brain stem, and optic chiasm, respectively, which were the lowest among the 3 treatment plans. There was no significant difference in dose conformity among the 3 treatment plans. However, NC-A had a slightly better conformity than C-VMAT and NC-B. NC-A had the best homogeneity, and NC-B had the worst homogeneity (p = 0.042). NC-A and NC-B had the lowest and highest global dose maximum, respectively. Therefore, NC-A, which had an intermediate performance in terms of OAR doses, had the best quality parameters. We used the quality score table based on the p-value to evaluate the significant difference between each treatment technique from the multiparameter results. In terms of treatment plan parameters, only NC-A received a score of 2; for OAR doses, C-VMAT, NC-A, and NC-B received a score of 6, 3, and 5, respectively. For the overall evaluation, C-VMAT, NC-A, and NC-B received a total score of 6, 5, and 5, respectively. Rather than noncoplanar VMAT, 3 full-arc C-VMATs should be utilized in HS-WBRT. C-VMAT can simultaneously maintain treatment plan quality and decrease patient alignment time and total treatment time.

Dosimetric evaluation of VMAT treatment plans for patients with stage IIB or III non-small cell lung carcinomas

Abstract Introduction: Volumetric-modulated arc therapy (VMAT) has emerged as a promising radiation treatment technique. One of the challenges in VMAT planning for lung carcinoma is the lack of consistency among different institutions with respect to what is considered an acceptable treatment plan in terms of target coverage and doses to the organs at risk (OAR). Additionally, the accuracy of dose calculations in the presence of heterogeneous medium (i.e. air) is another challenge in lung VMAT planning. Our objective is to develop an institutional criteria for non-stereotactic body radiotherapy (non-SBRT) lung treatment plans by evaluating the dosimetric impact of plan normalisation and dose calculation algorithms, including the Anisotropic Analytical Algorithm (AAA), AcurosXB (AXB) and Monte Carlo (MC) simulation, on VMAT plans for non-small cell lung cancer (NSCLC). Methods: The CT dataset of 20 patients with NSCLC was randomly selected to ensure a spectrum of target sizes and locations. All treatment planning was accomplished with 2–3 VMAT arcs and a prescription of 60 Gy in 30 fractions. Two plan normalisation methods were employed: (i) planning target volume (PTV) V100% = 95% and (ii) PTV V95% = 95%. Results: All three dose calculation algorithms revealed heterogeneous and conformal plans irrespective of plan normalisations. The PTV and OARs dose–volume constraints were met using both normalisation methods. However, we observed that AAA overestimated the minimum PTV doses by 2–5% regardless of plan normalisation. The mean PTV-V100% was lower for AAA in comparison with AXB and MC algorithms. Conclusions: VMAT is an effective radiotherapy technique for achieving greater target dose conformity, heterogeneity and dose fall-off from the PTV for the treatment of NSCLC. The results of this study can provide the basis for the development of local plan acceptability criteria for NSCLC VMAT plans, and the clinical implementation can be achieved with minimal or no imposition on resources and time constraints. Occasionally, plan normalisation of PTV-V95% = 95% may be required to ensure that the OAR dose tolerances are not exceeded.

Knowledge-Based Treatment Planning Model Improves Organ-at-Risk Sparing and Plan Consistency across Clinics for Prostate Radiation Therapy

<h3>Purpose/Objective(s)</h3> The quality of volumetric modulated arc therapy (VMAT) plans highly depends on the planner's preference and experience. A commercially available knowledge-based planning (KBP) module has been widely implemented to estimate the patient-specific optimal dose-volume histogram and enable semi-automatic treatment planning. The purpose of this study was to investigate whether the KBP clinical implementations have improved organ-at-risk (OAR) sparing and plan quality consistency across clinics within our institution for prostate cancer VMAT treatments. <h3>Materials/Methods</h3> A cohort of 1,484 prostate cancer VMAT treatment plans delivered across three different clinics within our institution from January 2016 to January 2022 were retrospectively identified. The prescription (Rx) schemes of 45 Gy and 70 Gy were selected for statistical investigations since these were the only Rx schemes containing more than 50 VMAT plans created with KBP models. Dosimetric parameters of the bladder, rectum, left/right femoral heads, penile bulb, and volume ratio of 50% isodose line to PTV (R50) were extracted. <h3>Results</h3> Since its first adoption in the last quarter of 2018, KBP planning remained at a low application rate from 0% to 20.0% in each quarter. After publishing KBP models clinically at the beginning of 2021, the application rate of prostate KBP models raised to levels from 53.5% to 71.0% in each quarter. For the 70 Gy Rx scheme, parameters of R50 (w/ KBP: 3.67±4.35 vs w/o KBP: 4.17±6.25, <i>p</i>=0.009), bladder (V_40Gy: 25.49%±13.02% vs 30.50%±16.52%, <i>p</i>=0.002; D_mean: 26.47±9.17 Gy vs 30.51±10.11 Gy, <i>p</i>=0.003) and rectum (V_45Gy: 17.45%±9.25% vs 25.23%±10.40%, <i>p</i><0.001; D_mean: 25.41±5.97 Gy vs 30.59±6.77 Gy, <i>p</i><0.001) were all statistically significantly improved with KBP planning. For the 45 Gy Rx scheme, the results were consistent with the 70 Gy Rx scheme. Across the three different clinics, the investigated parameters became more consistent after the adoption of KBP planning (e.g., bladder D_mean in Gy, w/ KBP: 27.52±10.21, 26.47±9.15 and 31.10±9.83 for clinic 1, 2 and 3, respectively, <i>p</i>₁₂=0.646, <i>p</i>₁₃=0.276, <i>p</i>₂₃=0.453; w/o KBP: 28.03±12.52, 27.02±13.97 and 39.85±23.27 for clinic 1, 2 and 3, respectively, <i>p</i>₁₂=0.425, <i>p</i>₁₃<0.001, <i>p</i>₂₃<0.001). This indicates that, with KBP implementations, we have achieved improved OAR-sparing across the institution as well as increased levels of plan quality standardization. <h3>Conclusion</h3> This study demonstrated that KBP models could improve OAR sparing and plan quality consistency across clinics for prostate VMAT radiation therapy. Clinical adoptions of KBP could potentially reduce inter-planner variations and facilitate the standardization of VMAT treatment planning.

The effect of using virtual bolus on VMAT plan quality for left-sided breast cancer patients

In breast cancer radiotherapy treatment with Volumetric Modulated Arc Therapy (VMAT), the respiratory motion may lead to underdosing of the target and overdosing of critical organs such as the heart and lungs. This study aims to investigate the effect of using Virtual Bolus with different thicknesses on VMAT plan quality for patients with 20 advanced left-sided breast cancers. The result of the study showed that using Virtual Bolus for VMAT treatment planning is a viable method to avoid any missing target coverage.

Treatment plan comparison of volumetric-modulated arc therapy to intensity-modulated radiotherapy in lung stereotactic body radiotherapy using either 6- or 10-MV photon energies.

PurposeThe aim of this study was to dosimetrically compare volumetric‐modulated arc therapy (VMAT) with intensity‐modulated radiotherapy (IMRT) techniques using either 6‐ or 10‐MV photon beam energies in lung stereotactic body radiation therapy (SBRT) plans.MethodsThirty patients with primary or metastatic lung tumors eligible for SBRT were randomly selected. VMAT and IMRT treatment plans using either 6‐ or 10‐MV photon energies were generated through automatic SBRT planning software in the RayStation treatment planning system.ResultsFor planning target volume, there was no difference in D 95% for all plans, whereas D 2% and D 50% were significantly increased by 5.22%–5.98% and 2.47%–2.59%, respectively, using VMAT6/10‐MV plans compared to IMRT6/10‐MV plans. When comparing the D max of organs at risk (OARs), VMAT6/10‐MV was 18.32%–47.95% lower than IMRT6/10‐MV for almost all OARs. VMAT6/10‐MV obviously decreased D mean, V 5Gy, V 10Gy, and V 20Gy of whole lung by 9.68%–20.92% than IMRT6/10‐MV. Similar results were found when comparing VMAT6‐MV with IMRT10‐MV or VMAT10‐MV with IMRT6‐MV. The differences in the D 2%, heterogeneity index, and conformity index between 6‐ and 10‐MV plans are not statistically significant. Plans using 6‐MV performed 4.68%–8.91% lower levels of D max of spinal cord, esophagus, great vessels, and trachea and proximal bronchial tree than those using 10‐MV plans. Similarly, D mean, V 5Gy, V 10Gy, and V 20Gy of whole lung were also reduced by 2.79%–5.25% using 6‐MV. For dose fall‐off analysis, the D 2cm and R 50% of VMAT6/10‐MV were lower than those of IMRT6/10‐MV. Dose fall‐off curve based on 10 rings was steeper for VMAT plans than IMRT plans regardless of the energy used.ConclusionsFor lung SBRT plans, VMAT‐based plans significantly reduced OARs dose and steepened dose fall‐off curves compared to IMRT‐based plans. A 6‐MV energy level was a better choice than 10‐MV for lung SBRT. In addition, the dose differences between different techniques were more obvious than those between different energy levels.

Validation of RapidPlan Knowledge-Based Model for Volumetric-Modulated Arc Therapy in Prostate Cancer.

This study aims to investigate the viability of using RapidPlan (RP) knowledge-based (KB) treatment plans to initiate the new prostate volumetric-modulated arc therapy (VMAT) plans. The planning data for 120 prostate VMAT treatment plans were entered into the RP system's database. The database of previous VMAT plans was divided into four model groups for training in the RP system. The models were based on the numbers of 20, 60, and 120 prostate VMAT plans. The model of 120 plans used automated priority and manual priority for the optimization process. The models of 20 and 60 plans used only manual priority for optimization. Each model was validated on 15 cases of new prostate cancer patients by comparing RP model plans against manual clinical plans optimized according to the clinical dose constraints. The RP models can estimate the dose comparable target volume to the manual clinical plan, which evaluated values of Dmax, D95%, D98%, HI, and CI and showed comparable results. For the normal organ doses of the bladder, rectum, penile bulb, and femoral head, all RP models exhibited a comparable or better dose than the manual clinical plan, except for the RP models using the automated priority for the optimization process, which cannot control the rectum dose below the dose constraints. The Varian RP KB planning can produce comparable doses or better doses with the clinical manual in a single optimization, although the RP model uses a minimum requirement of the planning number for the model training. The RP models can enhance the efficacy and quality of plans, which depend on the number of VMAT plans used in RP model training for prostate cancer.

Implementation of TG-218 for patient-specific quality assurance tolerance and action limits determination: Gamma passing rate evaluation using 3DVH software.

To determine the tolerance limit (TL) and action limit (AL) of gamma passing rates (%GP) for volumetric-modulated arc therapy (VMAT) patient-specific quality assurance (PSQA) according to the American Association of Physicists in Medicine (AAPM) Task Group (TG)-218 recommendations, and to comparatively evaluate the clinical relevance of 2D %GP and 3D %GP. PSQA was performed for 100 head and neck (H&N) and 73 prostate cancer VMAT treatment plans. Measurements were acquired using a cylindrical water equivalent phantom, hollow in the center, allowing measurements with homogeneous or heterogeneous inserts. The LINAC-delivered dose distributions were compared to those calculated from the treatment planning system through the gamma index. TL and AL were determined through the computation of two-dimensional (2D) %GP using the recommended acceptance criteria. Dose-volume histograms were reconstructed from the measurements using a commercially available software to detect the dosimetric errors (%DE) between the compared dose distributions. Utilizing the estimated dose on the patient anatomy, structure-specific %GP (3D %GP) were calculated. The 3D %GP were compared to the 2D %GP ones based on their correlation with the %DE. Each metric's sensitivity was determined through receiver operator characteristic analysis. TL and AL were in concordance with the universal ones, regarding the prostate cancer cases, but were lower for the H&N cases. Evaluation of %DE did not deem the plans unacceptable. The 2D %GP and the 3D %GP did not differ significantly regarding their correlation with %DE. For prostate plans, %GP sensitivity was higher than for H&N cases. Determination of institutional-specific TL and AL allows the monitoring of the PSQA procedure, yet for plans close to the limits, clinically relevant metrics should be used before they are deemed unacceptable for the process to be of higher sensitivity and efficiency.

Dosimetric advantages of volumetric modulated arc therapy (VMAT) with deep inspiration breath hold (DIBH) technique in Halcyon Linac for left breast cancer treatment.

To evaluate the dosimetric advantages of incorporating the deep inspiration breath hold (DIBH) technique into left breast cancer volumetric modulated arc therapy (VMAT) treatment under Halcyon Linac and to investigate the correlation between mean heart dose (MHD) and distance from the heart to target volumes in left breast cancer VMAT treatment. Fifteen Post-lumpectomy, left-sided breast patients treated between January 2017 and October 2020 were selected. Two plans were generated for each patient using Eclipse treatment planning system (TPS) with the prescription of 50.4 Gy to planning target volume (PTV) breast and 58.8 Gy to PTV boost in 28 fractions. For each patient, DIBH and free breathing (FB) VMAT treatment plans under Halcyon Linac were generated. Dosimetric parameters, monitor unit and beam-on time of both DIBH and FB groups were compared. Three-dimensional distances from heart surface to each target volume were measured on computed tomography images using the TPS contouring tool and their correlation with MHD was evaluated by Pearson's correlation coefficient (r). Comparable target coverage was shown in both groups. Mean dose to heart, left anterior descending artery, and left ventricle in Halcyon-DIBH-VMAT group were significantly reduced by 0.49 Gy, 1.19 Gy, and 0.57 Gy, respectively, compared to Halcyon-FB-VMAT (p < 0.001). A significant lung dose reduction was also achieved in Halcyon-DIBH-VMAT group. There was also a strong negative correlation between MHD and distance from heart surface to PTV boost in both FB and DIBH group (r = -0.741, p < 0.001), but not observed for distance from heart surface to PTV breast. Incorporating DIBH into left breast cancer VMAT treatment under Halcyon Linac demonstrated significant cardiac and lung dose reduction. It was also demonstrated that MHD had a strong negative correlation with distance from heart surface to PTV boost but relatively independent of distance from heart surface to PTV breast. Recognizing the distance from the heart surface to PTV boost as the main factor in affecting MHD could potentially facilitate clinical treatment planning workflow and decision.

Assessment of HDR brachytherapy-replicating prostate radiotherapy planning for tomotherapy, cyberknife and VMAT.

A dosimetric study was undertaken to assess the ability of Cyberknife (CK), Volumetric Modulated Arc Therapy (VMAT), and TomoTherapy (Tomo) to generate treatment plans that mimic the dosimetry of high dose-rate brachytherapy (HDR BT) for prostate cancer. The project aimed to assess the potential of using stereotactic body radiotherapy (SBRT) for boost treatment of high-risk prostate cancer patients where HDR BT in combination with conformal external beam radiotherapy (EBRT) is the standard of care. The datasets of 6 prostate patients previously treated with HDR BT were collated. VMAT, CK, and TomoTherapy treatment plans were generated for each dataset using the target and organ-at-risk structures as defined by the Radiation Oncologist during the HDR BT treatment process. The HDR BT plan isodoses were also converted into planning structures to assist the other modalities to achieve a HDR BT-like dose distribution. CK plans were created using both the iris collimator (IC) and a multileaf collimator (MLC). Comparison of the techniques was made based on dose-volume indices. Each plan was created at centres experienced using the respective treatment planning systems (TPS). Planning target volume (PTV V100%), i.e., the volume of the planning target volume (PTV) receiving 100% of the relative dose, in VMAT and TomoTherapy SBRT plans was higher than HDR BT plans. PTV V150% and V200%, i.e., volume of the PTV receiving 150% and 200% of the relative dose, were approached on all the CK MLC and TomoTherapy SBRT plans. However, it is not presently achievable for "virtual brachytherapy" SBRT to replicate the same high intraprostatic doses as HDR BT while meeting the constraints on the organs-at-risk (OARs). Half of the CK IC plans achieved PTV V150% but this was at the expense of high rectal dose. TomoTherapy and CK MLC plans achieved PTV V150% and V200% but the bladder dose was higher compared to CK IC plans. VMAT exhibited excellent PTV coverage based on V100 and OAR sparing, but without any ability to achieve the high intra-prostatic doses of HDR (V150% and V200%). SBRT techniques can be used to deliver hypofractionated radiotherapy to the PTV V100%. Based on the comparison of "physical" dose distributions, SBRT cannot presently achieve the same high intraprostatic doses as HDR BT while respecting the OAR constraints. SBRT still remains an attractive treatment option for delivering hypofractionated treatments for prostate cancer compared to HDR BT, in particular as it is less invasive and less resource intensive. Long-term outcomes of clinical trials comparing HDR BT and SBRT "prostate boosts" may show whether the high intraprostatic doses are clinically significant and correlate with outcomes.

Retrospective analysis of portal dosimetry pre-treatment quality assurance of intracranial SRS/SRT VMAT treatment plans

AbstractBackground:The complexity associated with the treatment planning and delivery of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) volumetric modulated arc therapy (VMAT) plans which employs continuous dynamic modulation of dose rate, field aperture and gantry speed necessitates diligent pre-treatment patient-specific quality assurance (QA). Numerous techniques for pre-treatment VMAT treatment plans QA are currently available with the aid of several different devices including the electronic portal imager (EPID). Although several studies have provided recommendations for gamma criteria for VMAT pre-treatment QA, there are no specifics for SRS/SRT VMAT QA. Thus, we conducted a study to evaluate intracranial SRS/SRT VMAT QA to determine clinical action levels for gamma criteria based on the institutional estimated means and standard deviations.Materials and methods:We conducted a retrospective analysis of 118 EPID patient-specific pre-treatment QA dosimetric measurements of 47 brain SRS/SRT VMAT treatment plans using the integrated Varian solution (RapidArcTM planning, EPID and Portal dosimetry system) for planning, delivery and EPID QA analysis. We evaluated the maximum gamma (γmax), average gamma (γave) and percentage gamma passing rate (%GP) for different distance-to-agreement/dose difference (DTA/DD) criteria and low-dose thresholds.Results:The gamma index analysis shows that for patient-specific SRS/SRT VMAT QA with the portal dosimetry, the mean %GP is ≥98% for 2–3 mm/1–3% and Field+0%, +5% and +10% low-dose thresholds. When applying stricter spatial criteria of 1 mm, the mean %GP is &gt;90% for DD of 2–3% and ≥88% for DD of 1%. The mean γmax ranges: 1·32 ± 1·33–2·63 ± 2·35 for 3 mm/1–3%, 1·57 ± 1·36–2·87 ± 2·29 for 2 mm/1–3% and 2·36 ± 1·83–3·58 ± 2·23 for 1 mm/1–3%. Similarly the mean γave ranges: 0·16 ± 0·06–0·19 ± 0·07 for 3 mm/1–3%, 0·21 ± 0·08–0·27 ± 0·10 for 2 mm/1–3% and 0·34 ± 0·14–0·49 ± 0·17 for 1 mm/1–3%. The mean γmax and mean γave increase with increased DTA and increased DD for all low-dose thresholds.Conclusions:The establishment of gamma criteria local action levels for SRS/SRT VMAT pre-treatment QA based on institutional resources is imperative as a useful tool for standardising the evaluation of EPID-based patient-specific SRS/SRT VMAT QA. Our data suggest that for intracranial SRS/SRT VMAT QA measured with the EPID, a stricter gamma criterion of 1 mm/2% or 1 mm/3% with ≥90% %GP could be used while still maintaining an in-control QA process with no extra burden on resources and time constraints.

A dosimetric and radiobiological evaluation of VMAT following mastectomy for patients with left-sided breast cancer

BackgroundTo compare the dosimetric, normal tissue complication probability (NTCP), secondary cancer complication probabilities (SCCP), and excess absolute risk (EAR) differences of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for left-sided breast cancer after mastectomy.Methods and materialsThirty patients with left-sided breast cancer treated with post-mastectomy radiation therapy (PMRT) were randomly enrolled in this study. Both IMRT and VMAT treatment plans were created for each patient. Planning target volume (PTV) doses for the chest wall and internal mammary nodes, PTV1, and PTV of the supraclavicular nodes, PTV2, of 50 Gy were prescribed in 25 fractions. The plans were evaluated based on PTV1 and PTV2 coverage, homogeneity index (HI), conformity index, conformity number (CN), dose to organs at risk, NTCP, SCCP, EAR, number of monitors units, and beam delivery time.ResultsVMAT resulted in more homogeneous chest wall coverage than did IMRT. The percent volume of PTV1 that received the prescribed dose of VMRT and IMRT was 95.9 ± 1.2% and 94.5 ± 1.6%, respectively (p < 0.001). The HI was 0.11 ± 0.01 for VMAT and 0.12 ± 0.02 for IMRT, respectively (p = 0.001). The VMAT plan had better conformity (CN: 0.84 ± 0.02 vs. 0.78 ± 0.04, p < 0.001) in PTV compared with IMRT. As opposed to IMRT plans, VMAT delivered a lower mean dose to the ipsilateral lung (11.5 Gy vs 12.6 Gy) and heart (5.2 Gy vs 6.0 Gy) and significantly reduced the V5, V10, V20, V30, and V40 of the ipsilateral lung and heart; only the differences in V5 of the ipsilateral lung did not reach statistical significance (p = 0.409). Although the volume of the ipsilateral lung and heart encompassed by the 2.5 Gy isodose line (V2.5) was increased by 6.7% and 7.7% (p < 0.001, p = 0.002), the NTCP was decreased by 0.8% and 0.6%, and SCCP and EAR were decreased by 1.9% and 0.1% for the ipsilateral lung. No significant differences were observed in the contralateral lung/breast V2.5, V5, V10, V20, mean dose, SCCP, and EAR. Finally, VMAT reduced the number of monitor units by 31.5% and the treatment time by 71.4%, as compared with IMRT.ConclusionsCompared with IMRT, VMAT is the optimal technique for PMRT patients with left-sided breast cancer due to better target coverage, a lower dose delivered, NTCP, SCCP, and EAR to the ipsilateral lung and heart, similar doses delivered to the contralateral lung and breast, fewer monitor units and a shorter delivery time.

Dosimetric comparison of MR-linac-based IMRT and conventional VMAT treatment plans for prostate cancer

BackgroundThe aim of this study was to evaluate and compare the performance of intensity modulated radiation therapy (IMRT) plans, planned for low-field strength magnetic resonance (MR) guided linear accelerator (linac) delivery (labelled IMRT MRL plans), and clinical conventional volumetric modulated arc therapy (VMAT) plans, for the treatment of prostate cancer (PCa). Both plans used the original planning target volume (PTV) margins. Additionally, the potential dosimetric benefits of MR-guidance were estimated, by creating IMRT MRL plans using smaller PTV margins.Materials and methods20 PCa patients previously treated with conventional VMAT were considered. For each patient, two different IMRT MRL plans using the low-field MR-linac treatment planning system were created: one with original (orig.) PTV margins and the other with reduced (red.) PTV margins. Dose indices related to target coverage, as well as dose-volume histogram (DVH) parameters for the target and organs at risk (OAR) were compared. Additionally, the estimated treatment delivery times and the number of monitor units (MU) of each plan were evaluated.ResultsThe dose distribution in the high dose region and the target volume DVH parameters (D98%, D50%, D2% and V95%) were similar for all three types of treatment plans, with deviations below 1% in most cases. Both IMRT MRL plans (orig. and red. PTV margins) showed similar homogeneity indices (HI), however worse values for the conformity index (CI) were also found when compared to VMAT. The IMRT MRL plans showed similar OAR sparing when the orig. PTV margins were used but a significantly better sparing was feasible when red. PTV margins were applied. Higher number of MU and longer predicted treatment delivery times were seen for both IMRT MRL plans.ConclusionsA comparable plan quality between VMAT and IMRT MRL plans was achieved, when applying the same PTV margin. However, online MR-guided adaptive radiotherapy allows for a reduction of PTV margins. With a red. PTV margin, better sparing of the surrounding tissues can be achieved, while maintaining adequate target coverage. Nonetheless, longer treatment delivery times, characteristic for the IMRT technique, have to be expected.

Implementation of a Knowledge-Based Treatment Planning Model for Cardiac-Sparing Lung Radiation Therapy

PurposeHigh radiation doses to the heart have been correlated with poor overall survival in patients receiving radiation therapy for stage III non-small cell lung cancer (NSCLC). We built a knowledge-based planning (KBP) tool to limit the dose to the heart during creation of volumetric modulated arc therapy (VMAT) treatment plans for patients being treated to 60 Gy in 30 fractions for stage III NSCLC. Methods and MaterialsA previous study at our institution retrospectively delineated intracardiac volumes and optimized VMAT treatment plans to reduce dose to these substructures and to the whole heart. Two RapidPlan (RP) KBP models were built from this cohort, 1 model using the clinical plans and a separate model using the cardiac-optimized plans. Using target volumes and 6 organs at risk (OARs), models were trained to generate treatment plans in a semiautomated process. The cardiac-sparing KBP model was tested in the same cohort used for training, and both models were tested on an external validation cohort of 30 patients. ResultsBoth RP models produced clinically acceptable plans in terms of target coverage, dose uniformity, and dose to OARs. Compared with the previously created cardiac-optimized plans, cardiac-sparing RPs showed significant reductions in the mean dose to the esophagus and lungs while performing similarly or better in all evaluated heart dose metrics. When comparing the 2 models, the cardiac-sparing RP showed reduced (P < .05) heart mean and maximum doses as well as volumes receiving 60 Gy, 50 Gy, and 30 Gy. ConclusionsBy using a set of cardiac-optimized treatment plans for training, the proposed KBP model provided a means to reduce the dose to the heart and its substructures without the need to explicitly delineate cardiac substructures. This tool may offer reduced planning time and improved plan quality and might be used to improve patient outcomes.

Dosimetric evaluation of IMRT (SS / SW) and VMAT treatment plans for nasopharyngeal cancer

Introduction: Radiotherapy of the sphere ORL is still difficult by the presence of complex geometries and very sensitive organs around the target volume.This weapon has benefited from the advances of the VMAT (Volumetric Modulated Arc Therapy) technique, introduced in 2009, it combines the advantages of dynamic arc therapy techniques with the advantages of conformational radiotherapy techniques with intensity modulation (RCMI) by stationary beams.Materials and Methods: The treatment plans of the 4 patients were compared and treated with SS, SW, and VMAT (6MV X-ray beam). The target volumes were three: PTV 70, PTV 63, and PTV56. The organs at risk delineated were the spinal cord, the brainstem, the parotid gland .The dose was delivered once a day, five days a week and in 35 sessions in Integrated Boost (Simultaneaous Integrated Boost (SIB)), aiming to deliver the prescribed dose to the tumor volume while respecting the dose constraints in the organs at risk and minimizing their degree of toxicity.Results: Similar results were found for target volume coverage (Dmax). The SS technique allowed better parotid sparing, which explains its contribution to limiting late complications such as xerostomia. The VMAT technique allows better protection of the brainstem by reducing about 6 Gy, for the spinal cord the doses received were almost equal. Finally, there is no statistically significant difference between the different techniques.Conclusion: All these results conform the conformational capacities of these innovative techniques from a dosimetric and above all clinical point of view. Their ability to cover the target volumes while largely respecting the constraints on organs at risk.

Cardiac substructure exposure in breast radiotherapy: a comparison between intensity modulated proton therapy and volumetric modulated arc therapy

Introduction Proton therapy for breast cancer treatment reduces cardiac radiation exposure. Left-sided breast cancer patients with indication for internal mammary chain (IMC) irradiation are most at risk of radiation-induced cardiotoxicity. This study aims to evaluate in this situation the potential dosimetric benefit of intensity modulated proton therapy (IMPT) over volumetric modulated arc therapy (VMAT) at the cardiac substructure level. Materials and methods Cardiac substructures were retrospectively delineated according to ESTRO guidelines on the simulation CT scans of fourteen left-sided breast cancer patients having undergone conserving surgery and adjuvant locoregional free-breathing (FB-) or deep inspiration breath-hold (DIBH-) VMAT with internal mammary chain irradiation. IMPT treatment was re-planned on the simulation CT scans. Mean doses to cardiac substructures were retrieved and compared between VMAT treatment plans and IMPT simulation plans. Pearson correlation coefficients were calculated between mean doses delivered to cardiac substructures using these two techniques. Results Mean doses to all cardiac substructures were significantly lower with IMPT than with VMAT. Regardless of the irradiation technique, the most exposed cardiac substructure was the mid segment of the left anterior descending coronary artery (LADCA). Pearson correlation coefficients between mean doses to cardiac substructures were usually weak and statistically non-significant for IMPT; mean heart dose (MHD) only correlated with mean doses delivered to the right ventricle, to the mid segment of the right coronary artery (RCA) and, to a lesser extent, to the LADCA. Conclusion The dosimetric benefit of IMPT over conformal photon therapy was consistently observed for all cardiac substructures. MHD may not be a reliable dosimetric parameter for precise cardiac exposure evaluation when planning IMPT.

Evaluation of dosimetric implications of Pareto and constrained mode of optimization for Monaco TPS generated VMAT plans in post operated carcinoma of the left breast

AbstractIntensity-modulated radiotherapy (IMRT) is being practiced for the last several years with a special approach for radiation therapy in post-mastectomy breast cancer patients. Meeting the cardiac dose constraints has always been a challenge during radiotherapy planning by both IMRT and VMAT (volumetric modulated arc therapy) of post-mastectomy left breast patients. With the advancement in IMRT planning techniques, it has been modified to VMAT with more degrees of freedom for modulation and is being utilised more frequently. This helps in obtaining a suitable plan for achieving both the dose homogeneity in target volume and dose constraints to Organ at Risk (OAR). 10 Patients with carcinoma of the left breast (post-mastectomy) were selected for this study. VMAT treatment plans for these patients were generated for 6 MV photons on the Monaco treatment planning system (TPS) using two types of optimization modes i.e. Pareto and Constrained mode available in Monaco TPS. For comparative dosimetric evaluation of the efficacy of these two types of optimization modes similar calculation algorithms, calculation grids, arcs, and beam sequencing parameters were used for generating treatment plans. The dosimetric quantities such as volume receiving more than 95% of the prescribed dose (V95), volume receiving more than 107% of the prescribed dose (V107) and Maximum dose (Dmax) for target volume, mean dose (Dmean) for heart, volume receiving more than 30 Gy (V30) volume receiving more than 20 Gy (V20) volume receiving more than 5 Gy (V5) for ipsilateral lung and total monitor units delivered were analysed for both optimization modes. A judicious mix of multiple planning parameters and variables using these two modes of optimization was applied and recorded. Both optimization modes yielded similar outcomes. However, Pareto mode has shown better coverage for planning target volume (PTV) with comparable doses to OARs.