The robustness of dual isocenter VMAT radiation therapy for bilateral lymph node positive breast cancer

Single isocenter versus dual isocenter treatment using flattening filter-free and jaw-tracking volumetrically modulated arc therapy for boot-shaped lung cancer: Evaluation of dosimetric and feasibility

BACKGROUND

To determine whether a dual-isocenter volumetrically modulated arc therapy (VMAT) technique results in lower normal pulmonary dosage compared to a traditional single isocenter technique for boot-shaped lung cancer.

METHODS

A cohort of 15 patients with advanced peripheral or central lung cancer who had metastases in the mediastinum and supraclavicular lymph nodes was randomly selected for this retrospective study. VMAT plans were generated for each patient using two different beam alignment techniques with the 6-MV flattening filter-free (FFF) photon beam: single-isocenter jaw-tracking VMAT based on the Varian TrueBeam linear accelerator (S-TV), and dual-isocenter VMAT based on both TrueBeam (D-TV) and Halcyon linear accelerator (D-HV). For all 45 treatment plans, planning target volume (PTV) dose coverage, conformity/homogeneity index (CI/HI), mean heart dose (MHD), mean lung dose (MLD) and the total lung tissue receiving 5, 20, 30 Gy (V5, V20, V30) were evaluated. The monitor units (MUs), delivery time, and plan quality assurance (QA) results were recorded.

RESULTS

The quality of the objectives of the three plans was comparable to each other. In comparison with S-TV, D-TV and D-HV improved the CI and HI of the PTV (p < 0.05). The MLD was 13.84 ± 1.44 Gy (mean ± SD) for D-TV, 14.22 ± 1.30 Gy and 14.16 ± 1.42 Gy for S-TV and D-HV, respectively. Lungs-V5Gy was 50.78 ± 6.24%, 52.00 ± 7.32% and 53.36 ± 8.48%, Lungs-V20Gy was 23.72 ± 2.27%, 26.18 ± 2.86% and 24.96 ± 3.09%, Lungs-V30Gy was 15.69 ± 1.76%, 17.20 ± 1.72% and 16.52 ± 2.07%. Compared to S-TV, D-TV provided statistically significant better protection for the total lung, with the exception of the lungs-V5. All plans passed QA according the gamma criteria of 3%/3 mm.

CONCLUSIONS

Taking into account the dosimetric results and published clinical data on radiation-induced pulmonary injury, dual-isocenter jaw-tracking VMAT may be the optimal choice for treating boot-shaped lung cancer.

Feasibility of using a dual isocentre technique for treating cervical cancer on the 1.5 T MR-Linac

Objective.Patients treated for cervical cancer exhibit large inter and intra-fraction anatomical changes. The Unity MR-Linac (MRL) can image these patients with MR prior to and during treatment which enables daily plan adaptation. However, the MRL has a limited treatment field in the sup/inf direction of 22 cm which can restrict the treatment of patients who require longer treatment fields. Here we explore potential adaptive workflows in combination with a dual isocentre approach, to widen the range of cervix patients that can benefit from this treatment.Approach.Ten cervical cancer patients were retrospectively planned with a dual isocentre technique to deliver 45 Gy in 25 fractions. 5 node-negative and 5 node-positive patients were planned using the EMBRACE II protocol. A 2 cm overlap region between the two isocentres was positioned entirely in the nodal region. A treatment workflow was simulated to account for inter-fraction anatomical change. Isocentre shifts of 3 and 6 mm were applied to investigate the effect of intra-fraction motion.Main results.Dual isocentre adapted plans ensured significantly better coverage than non-adapted (recalculated) plans with a larger benefit seen for the node-negative cases. The difference to the reference plan for the V4275 cGy to the ITV was -0.8 cGy and -8.2 cGy for the adapted and recalculated plans respectively. Movements superiorly did not affect the coverage of the ITV by more than 1%, but shifting it inferiorly caused the ITV coverage on the plan to reduce by ∼2.4% per mm.Significance.A dual isocentre technique for cervical cancer treatments and adaptive workflows have been demonstrated to recover the required plan quality for inter-fraction changes. This illustrates the feasibility of a dual isocentre technique for the MRL.

Dosimetric Comparison of Postmastectomy Radiotherapy Plans for Synchronous Bilateral Breast Cancer, Including Regional Lymph Node Irradiation

BACKGROUND

To investigate the optimal radiotherapy plans for synchronous bilateral breast cancer (SBBC) patients receiving postmastectomy radiotherapy (PMRT), including regional lymph node irradiation (RNI).

METHODS

For 10 SBBC patients who underwent bilateral mastectomy and received bilateral PMRT with RNI, 3 integrally optimized plans with a single isocenter were designed for each patient in this retrospective study: intensity-modulated radiation therapy (IMRT) with 9 fixed beams (9F-IMRT), volumetric-modulated arc therapy (VMAT) with 2 pairs of half arcs (2F-VMAT), VMAT with 2 pairs of outer tangential arcs and 1 pair of 200-degree arcs (3F-VMAT). The paired t-test (in the case of normal variables) and Friedman's test (in the case of nonnormal variables) were applied to compare the planning target volumes (PTVs) and organs at risk (OARs) values of the 3 techniques.

RESULTS

The 3 techniques provided adequate target dose coverage and comparable results for PTVs. For OARs, 3F-VMAT yielded the lowest mean or median values of the left lung (15.02 ± 1.57 Gy) and right lung (14.91 ± 1.14 Gy), heart (6.19 (1.96) Gy), coronary artery (15.96 ± 5.76 Gy) and liver (8.10 ± 2.70 Gy) which were significantly different from those of 9F-IMRT and 2F-VMAT. The percentages of volume at various doses (V5, V10, V20, and V30) of 3F-VMAT plans were also lower than or comparable with those of 9F-IMRT and 2F-VMAT. The monitor units (MUs) of 3F-VMAT were 31% higher than those of 9F-IMRT and comparable with those of 2F-VMAT; however, there were time savings and halved beam-on times (BOTs) compared to 9F-IMRT.

CONCLUSIONS

The 3F-VMAT plan yielded comparable target coverage compared with 9F-IMRT and 2F-VMAT, was superior in dose sparing of normal tissues and enabled shorter BOTs, improving treatment efficiency. In our research, 3F-VMAT was the optimal radiotherapy technique for SBBC patients receiving PMRT including RNI.

Synchronous bilateral chest wall irradiation with regional nodal irradiation: A literature review of techniques and a case study

The optimal radiotherapy technique for patients requiring both breasts or chest walls simultaneous irradiation with or without regional nodal irradiation is currently under investigation. In the last decade several publications present case reports and case series of patients treated with adjuvant radiotherapy in both breasts or chest walls for synchronous bilateral breast cancer (SBBC) with modern radiotherapy techniques. This article presents a systematic review of relevant literature as well as a case report of a SBBC patient who received bilateral chest wall radiotherapy with regional nodal irradiation at our institution with Truebeam - Edge Linear Accelerator. Solid evidence is provided that the practice of avoiding adjuvant radiotherapy in SBBC out of fear of toxicity with older radiotherapy techniques is outdated. Modern techniques can safely and effectively deliver treatment to patients requiring both sides irradiation and even in mastectomy patients in need of regional nodal irradiation.

Evaluation of the dosimetric and radiobiological parameters in four radiotherapy regimens for synchronous bilateral breast cancer

This study is to investigate the optimal treatment option for synchronous bilateral breast cancer (SBBC) by comparing dosimetric and radiobiological parameters of intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans using single and dual isocenters.

Twenty patients with SBBC without lymph node involvement were selected retrospectively. Four treatment plans were generated for each patient using the Eclipse treatment planning system (Varian Medical System, Palo Alto, CA, USA) following two delivery techniques with two isocenter conditions—IMRT using a single isocenter (IMRT_Iso1), VMAT using a single isocenter (VMAT_Iso1), IMRT using dual isocenters (IMRT_Iso2), and VMAT using dual isocenters (VMAT_Iso2). A dose of 42.56 Gy in 16 fractions was prescribed for the planning target volume (PTV). All plans were calculated using the Acuros XB algorithm and a photon optimizer for a 6‐MV beam of a Vital Beam linear accelerator. PTV‐related dosimetric parameters were analyzed. Further, the homogeneity index, conformity index, and conformation number were computed to evaluate plan quality. Dosimetric parameters were also measured for the organs at risk (OARs). In addition, the equivalent uniform dose corresponding to an equivalent dose related to a reference of 2 Gy per fraction, the tumor control probability, and the normal tissue complication probability were calculated based on the dose–volume histogram to investigate the radiobiological impact on PTV and OARs.

IMRT_Iso1 exhibited similar target coverage and a certain degree of dosimetric improvement in OAR sparing compared to the other techniques. It also exhibited some radiobiological improvement, albeit insignificant. Although IMRT_Iso1 significantly increased monitor unit compared to VMAT_Iso1, which is the best option in terms of delivery efficiency, there was only a 22% increase in delivery time. Therefore, in conclusion, IMRT_Iso1, the complete treatment of which can be completed using a single setup, is the most effective method for treating SBBC.

Quantitative and dosimetric analysis for treating synchronous bilateral breast cancer using two radiotherapy planning techniques

Objective: We compared mono-isocenter and dual-isocenter plans in synchronous bilateral breast cancer (SBBC), which is defined as tumours occurring simultaneously in both breasts, and evaluated the effects of these differences in plans on organs-at-risk (OARs).

Materials and methods: We evaluated 10 women with early stage, nod negative (Tis-2N0M0) SBBC. The treatment dose was determined to be 50 Gy. We used mean dose and VXGy to evaluate the OARs. To evaluate the effectiveness of treatment plans, Homogeneity index (HI), conformity index (CI) and sigma index (SI) and monitor units (MU) of monoisocenter (MIT) and dual-isocenter (DIT) plans were compared. During bilateral breast planning, for the single-centre plan, the isocenter was placed at the center of both breasts at a depth of 3-4 cm. For the two-center plan, dual-isocenters were placed on the right and left breasts.

Results: No significant difference between the techniques in terms of the scope of the target volume was observed. Statistically significant results were not achieved in MIT and DIT plans for OARs. Upon comparing MIT and DIT, the right-side monitor unit (MU) value in DIT (p = 0.011) was statistically significantly lower than that in MIT. Upon comparing right-left side MIT and DIT, the MU value (p = 0.028) was significantly lower in DIT than MIT.

Conclusion: SBBC irradiation is more complex than unilateral breast radiotherapy. No significant difference between both techniques and OARs was observed. However, we recommend MIT as a priority technique due to the ability to protect OARs, ease of administration during treatment, and the fact that the patient stays in the treatment unit for a shorter period of time.

VMAT-like plans for magnetic resonance guided radiotherapy: Addressing unmet needs

PURPOSE

VMAT delivery technique is currently not applicable to Magnetic Resonance-guided radiotherapy (MRgRT) hybrid systems. Aim of this study is to evaluate an innovative VMAT-like (VML) delivery technique.

MATERIAL AND METHODS

First, planning and dosimetric evaluation of the MRgRT VML treatment have been performed on 10 different disease sites and the results have been compared with the corresponding IMRT plans. Then, in the second phase, 10 of the most dosimetrically challenging locally advanced pancreas treatment plans have been retrospectively re-planned using the VML approach to explore the potentiality of this new delivery technique. Finally, VML robustness was evaluated and compared with the IMRT plans, considering a lateral positioning error of ± 5 mm.

RESULTS

In phase one, all VML plans were within constraint for all OARs. When PTV coverage is considered, in the 50% of the cases VML PTV coverage is equal or higher than in IMRT plan. In the remaining 50%, the highest target under coverage difference in comparison with IMRT plan is -1.71%. The mean and maximum treatment time differences (VML-IMRT) is 0.2 min and 3.1 min respectively. In phase two, the treatment time variation (VML-IMRT), shows a mean, maximum and minimum variations of 1.3, 4.6 and -0.6 min respectively. All VML plans have a better target coverage if compared with IMRT plans, keeping in any case the OARs constraints within tolerance. VML doesn't increase plan robustness.

CONCLUSION

VMAT-like treatment approach appeared to be an efficient planning solution and it was decided to clinically implement it in daily practice, especially in the frame of hypo fractionated treatments.

Dosimetric accuracy of dual isocenter irradiation in low magnetic field resonance guided radiotherapy system for extended abdominal tumours

PURPOSE

Due to limited field size of Magnetic Resonance Linear Accelerators (MR-Linac), some treatments could require a dual-isocenter planning approach to achieve a complete target coverage and thus exploit the benefits of the online adaptation. This study evaluates the dosimetric accuracy of the dual-isocenter intensity modulated radiation therapy (IMRT) delivery technique for MR-Linac.

MATERIAL AND METHODS

Dual-isocenter multi leaf collimator (MLC) and couch accuracy tests have been performed to evaluate the delivery accuracy of the system. A mono-isocenter plan delivered in clinical practice has then been retrospectively re-planned with dual-isocenter technique. The dual-isocenter plan has been re-calculated and delivered on a 3-dimensional (3D) ArcCHECK phantom and 2-dimensional (2D) films to assess its dosimetric accuracy in terms of gamma analysis. Clinical and planning target volume (CTV and PTV respectively) coverage robustness was then investigated after the introduction of ± 2 mm and ± 5 mm positioning errors by shifting the couch.

RESULTS

MLC and couch accuracy tests confirmed the system accuracy in delivering a dual-isocenter irradiation. 2D/3D gamma analysis results occurred always to be above 95% if considered a gamma criteria 1%/2 mm and 1%/1 mm respectively for the 2D and 3D analysis. The mean variations for CTV D98% and PTV V95% were 0.2% and 1.1% respectively when positioning error was introduced separately in each direction, while the maximum observed variations were 0.9% (CTV) and 3.7% (PTV).

CONCLUSION

The dosimetric accuracy of dual-isocenter irradiation has been verified for MR-Linac, achieving accurate and robust treatment strategy and improving dose conformality also in presence of targets whose extension exceeds the nominal maximum field size.

Treatment planning comparison of volumetric modulated arc therapy with the trilogy and the Halcyon for bilateral breast cancer

Background

The Halcyon is a new machine from the Varian company. The purpose of this study was to evaluate the dosimetry of the Halcyon in treatment of bilateral breast cancer with volumetric modulated arc therapy.

Methods

On CT images of 10 patients with bilateral breast cancer, four Halcyon plans with different setup fields were generated, and dosimetric comparisons using Bonferroni’s multiple comparisons test were conducted among the four plans. Whole and partial arc plans on the Trilogy and the Halcyon, referred to as T-4arc, T-8arc, H-4arc and H-8arc, were designed. The prescription dose was 50 Gy in 2-Gy fractions. All plans were designed with the Eclipse version 15.5 treatment planning system. The dosimetric differences between whole and partial arc plans in the same accelerator were compared using the Mann–Whitney U test. The better Halcyon plan was selected for the further dosimetric comparison of the plan quality and delivery efficiency between the Trilogy and the Halcyon.

Results

Halcyon plans with high‐quality megavoltage cone beam CT setup fields increased the D_mean, D₂ and V₁₀₇ of the planning target volume (PTV) and the V₅ and D_mean of the heart, left ventricle (LV) and lungs compared with other Halcyon setup plans. The mean dose and low dose volume of the heart, lungs and liver were significantly decreased in T-8arc plans compared to T-4arc plans. In terms of the V₅, V₂₀, V₃₀, V₄₀ and D_mean of the heart, the V₂₀, V₃₀, V₄₀ and D_mean of the LV, the V₃₀, V₄₀, D_max and D_mean of the left anterior descending artery (LAD), and the V₅ and V₄₀ of lungs, H-8arc was significantly higher than H-4arc (p < 0.05). Compared with the Trilogy’s plans, the Halcyon’s plans reduced the high-dose volume of the heart and LV but increased the mean dose of the heart. For the dose of the LAD and the V₂₀ and V₃₀ of lungs, there was no significant difference between the two accelerators. Compared with the Trilogy, plans on the Halcyon significantly increased the skin dose but also significantly reduced the delivery time.

Conclusion

For the Halcyon, the whole-arc plans have more dosimetric advantages than partial-arc plans in bilateral breast cancer radiotherapy. Although the mean dose of the heart and the skin dose are increased, the doses of the cardiac substructure and other OARs are comparable to the Trilogy, and the delivery time is significantly reduced.

Heart and Cardiac Substructure Dose Sparing in Synchronous Bilateral Breast Radiotherapy: A Dosimetric Study of Proton and Photon Radiation Therapy

Background: Synchronous bilateral breast cancer (SBBC) is rare. The purpose of this study was to compare the dosimetric differences in intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), helical tomotherapy (HT), and intensity-modulated proton therapy (IMPT) to find an optimal radiotherapy technique for bilateral breast cancer radiotherapy. Methods: For 11 patients who received synchronous bilateral whole-breast irradiation without local lymph nodal regions, six plans were designed for each patient: IMRT with a single isocenter (IMRT-ISO1), IMRT with two isocenters (IMRT-ISO2), VMAT with a single isocenter (VMAT-ISO1), VMAT with two isocenters (VMAT-ISO2), HT, and IMPT. The differences between the single- and dual-isocentric plans for IMRT and VMAT were compared, and the plan with the better quality was selected for further dosimetric comparisons with IMPT and HT. The plan aimed for a target coverage of at least 95% with the prescription dose of 50 Gy [relative biological effectiveness (RBE)] while minimizing the dose of organs at risk (OARs). Results: IMRT-ISO1 and VMAT-ISO2 plans were adopted for further dosimetric comparisons because of the reduced dose of the heart and/or lungs compared to IMRT-ISO2 and VMAT-ISO1 plans. The dose coverage of the planning target volume (PTV) was significantly higher in IMPT plans than that in all other plans. VMAT and IMPT plans showed the best conformity, whereas IMRT plans showed the worst conformity. Compared to IMRT and VMAT plans, IMPT and HT plans achieved significantly higher dose homogeneity. IMPT plans reduced the mean dose and low dose volume (V₅, V₁₀, and V₂₀) of the heart, left anterior descending artery (LAD), and left ventricle (LV). In high-dose volumes of the heart and cardiac substructures, the IMPT, VMAT, and HT techniques showed similar advantages, and IMRT plans increased the values more than other techniques. IMPT plans had the maximal lung and normal tissue sparing but increased the skin dose compared to IMRT and VMAT plans. Conclusions: IMPT plans improve both the target coverage and the OARs sparing, especially for the heart, cardiac substructures (LAD and LV), lungs and normal tissue, in synchronous bilateral breast radiotherapy. VMAT and HT could be selected as suboptimal techniques for SBBC patients.

Evaluation of optimal treatment planning for radiotherapy of synchronous bilateral breast cancer including regional lymph node irradiation

Background

We evaluated the optimal radiotherapy (RT) plan for synchronous bilateral breast cancer (SBBC), especially treatment plans including the regional lymph node (LN) area.

Methods

This study was conducted using 15 patients with SBBC (5 with small breasts, 5 with large breasts, and 5 who underwent a left total mastectomy). The clinical target volume (CTV) was defined as the volume enveloping the bilateral whole breasts/chest wall and left regional LN area. We established the following plans: 1) volumetric-modulated arc therapy (VMAT)-the only plan using two pairs of partial arcs for the whole target volume, 2) VMAT using one partial arc for the left CTV followed by a 3D tangential technique for the right breast (primary hybrid plan), and 3) VMAT for the left CTV followed by a tangential technique using an automatically calculated prescription dose for the right breast, considering the background dose from the left breast VMAT plan (modified hybrid plan). The Tukey test and one-way analysis of variance were used to compare the target coverage and doses to organs at risk (OARs) of the three techniques.

Results

For target coverage, the VMAT-only and modified hybrid plans showed comparable target coverage in terms of D_mean (50.33 Gy vs. 50.53 Gy, p = 0.106). The primary hybrid plan showed the largest distribution of the high-dose volume, with V_105% of 25.69% and V_110% of 6.37% for the planning target volume (PTV) (p < 0.001). For OARs including the lungs, heart, and left anterior descending artery, the percentages of volume at various doses (V_5Gy, V_10Gy, V_20Gy, V_30Gy) and D_mean were significantly lower in both the primary and modified hybrid plans compared to those of the VMAT-only plan. These results were consistent in subgroup analyses of breast size and morphological variation.

Conclusions

The modified hybrid plan, using an automatically calculated prescription dose for the right breast and taking into consideration the background dose from the left breast VMAT plan, showed comparable target coverage to that of the VMAT-only plan, and was superior for saving OARs. However, considering that VMAT can be adjusted according to the physician’s intention, further evaluation is needed for developing a better plan.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1257-5) contains supplementary material, which is available to authorized users.

Volumetric modulated arc therapy with robust optimization for larynx cancer

PURPOSE

The aim of this study was to perform a comparison between robust optimization and planning target volume (PTV)-based optimization plans using volumetric modulated arc-therapy (VMAT) by evaluating perturbed doses induced by localization offsets for setup uncertainties in larynx cancer radiation therapy.

METHODS

Ten patients with early-stage (T1-2N0) glottis carcinoma were selected. The clinical target volume (CTV), carotid arteries, and spinal cord were contoured by a radiation oncologist. PTV-based and robust optimization plans were normalized at D_50% to the PTV and D_98% to the CTV, respectively. Both optimization plans were evaluated using perturbed doses by specifying user defined shifted values from the isocenter. CTV dose (D_98%, D_50%, and D_2%), homogeneity index (HI) and conformity index (CI_95%, CI_80%, and CI_50%), as well as doses to the carotid arteries and spinal cord were compared between PTV-based and robust optimization plans.

RESULTS

The robust optimization plans exhibited superior CTV coverage and a reduced dose to the carotid arteries compared to the PTV-based optimization plans (p < 0.05). HI, CI_95% and the dose to the spinal cord did not significantly differ between the PTV-based and robust optimization plans (p > 0.05). The robust optimization plans showed better CI_80% and CI_50% compared to the PTV-based optimization plans (p < 0.05). Plan perturbed evaluations showed that the robust optimization plan has small variations in the doses to the CTV, carotid arteries, and spinal cord compared to the PTV-based optimization plan.

CONCLUSIONS

The robust optimization plan may be a suitable treatment method in radiotherapy for larynx cancer patient.