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

Comparison of skin dose in IMRT and VMAT with TrueBeam and Halcyon linear accelerator for whole breast irradiation

With the increasing use of flattening filter free (FFF) beams, it is important to evaluate the impact on the skin dose and target coverage of breast cancer treatments. This study aimed to compare skin doses of treatments using FFF and flattening filter (FF) beams for breast cancer. The study established treatment plans for left breast of an anthropomorphic phantom using Halcyon's 6-MV FFF beam and TrueBeam's 6-MV FF beam. Volumetric modulated arc therapy (VMAT) with varying numbers of arcs and intensity modulated radiation therapy (IMRT) were employed, and skin doses were measured at five points using Gafchromic EBT3 film. Each measurement was repeated three times, and averaged to reduce uncertainty. All plans were compared in terms of plan quality to ensure homogeneous target coverage. The study found that when using VMAT with two, four, and six arcs, in-field doses were 19%, 15%, and 6% higher, respectively, when using Halcyon compared to TrueBeam. Additionally, when using two arcs for VMAT, in-field doses were 10% and 15% higher compared to four and six arcs when using Halcyon. Finally, in-field dose from Halcyon using IMRT was about 1% higher than when using TrueBeam. Our research confirmed that when treating breast cancer with FFF beams, skin dose is higher than with traditional FF beams. Moreover, number of arcs used in VMAT treatment with FFF beams affects skin dose to the patient. To maintain a skin dose similar to that of FF beams when using Halcyon, it may be worth considering increasing the number of arcs.

Benchmarking halcyon ring delivery system for hypofractionated breast radiotherapy: Validation and clinical implementation of the fast-forward trial

PURPOSE

The aim of this study was to demonstrate the feasibility and efficacy of an iterative CBCT-guided breast radiotherapy with Fast-Forward trial of 26 Gy in five fractions on a Halcyon Linac. This study quantifies Halcyon plan quality, treatment delivery accuracy and efficacy by comparison with those of clinical TrueBeam plans.

MATERIALS AND METHODS

Ten accelerated partial breast irradiation (APBI) patients (four right, six left) who underwent Fast-Forward trial at our institute on TrueBeam (6MV beam) were re-planned on Halcyon (6MV-FFF). Three site-specific partial coplanar VMAT arcs and an Acuros-based dose engine were used. For benchmarking, PTV coverage, organs-at-risk (OAR) doses, beam-on time, and quality assurance (QA) results were compared for both plans.

RESULTS

The average PTV was 806 cc. Compared to TrueBeam plans, Halcyon provided highly conformal and homogeneous plans with similar mean PTVD95 (25.72  vs. 25.73 Gy), both global maximum hotspot < 110% (p = 0.954) and similar mean GTV dose (27.04  vs. 26.80 Gy, p = 0.093). Halcyon provided lower volume of ipsilateral lung receiving 8 Gy (6.34% vs. 8.18%, p = 0.021), similar heart V1.5 Gy (16.75% vs. 16.92%, p = 0.872), V7Gy (0% vs. 0%), mean heart dose (0.96  vs. 0.9 Gy, p = 0.228), lower maximum dose to contralateral breast (3.2  vs. 3.6 Gy, p = 0.174), and nipple (19.6  vs. 20.1 Gy, p = 0.363). Compared to TrueBeam, Halcyon plans provided similar patient-specific QA pass rates and independent in-house Monte Carlo second check results of 99.6% vs. 97.9% (3%/2 mm gamma criteria) and 98.6% versus 99.2%, respectively, suggesting similar treatment delivery accuracy. Halcyon provided shorter beam-on time (1.49  vs. 1.68 min, p = 0.036).

CONCLUSION

Compared to the SBRT-dedicated TrueBeam, Halcyon VMAT plans provided similar plan quality and treatment delivery accuracy, yet potentially faster treatment via one-step patient setup and verification with no patient collision issues. Rapid delivery of daily APBI on Fast-Forward trial on Halcyon with door-to-door patient time < 10 min, could reduce intrafraction motion errors, and improve patient comfort and compliance. We have started treating APBI on Halcyon. Clinical follow-up results are warranted. We recommend Halcyon users consider implementing the protocol to remote and underserved APBI patients in Halcyon-only clinics.

Sensitivity and specificity of Varian Halcyon's portal dosimetry for plan-specific pre-treatment QA

PURPOSE

Developed as a plan-specific pre-treatment QA tool, Varian portal dosimetry promises a fast, high-resolution, and integrated QA solution. In this study, the agreement between predicted fluence and measured cumulative portal dose was determined for the first 140 patient plans at our Halcyon linear accelerator. Furthermore, the capability of portal dosimetry to detect incorrect plan delivery was compared to that of a common QA phantom. Finally, tolerance criteria for verification of VMAT plan delivery with Varian portal dosimetry were derived.

METHODS

All patient plans and the corresponding verification plans were generated within the Eclipse treatment planning system. Four representative plans of different treatment sites (prostate, prostate with lymphatic drainage, rectum, and head & neck) were intentionally altered to model incorrect plan delivery. Investigated errors included both systematic and random errors. Gamma analysis was conducted on both portal dose (criteria γ2%/2 mm , γ2%/1 mm , and γ1%/1 mm ) and ArcCHECK measurements (criteria γ3%/3 mm , γ3%/2 mm , and γ2%/2 mm ) with a 10% low-dose threshold. Performance assessment of various acceptance criteria for plan-specific treatment QA utilized receiver operating characteristic (ROC) analysis.

RESULTS

Predicted and acquired portal dosimetry fluences demonstrated a high agreement evident by average gamma passing rates for the clinical patient plans of 99.90%, 96.64%, and 91.87% for γ2%/2 mm , γ2%/1 mm , and γ1%/1 mm , respectively. The ROC analysis demonstrated a very high capability of detecting erroneous plan delivery for portal dosimetry (area under curve (AUC) > 0.98) and in this regard outperforms QA with the ArcCHECK phantom (AUC ≈ 0.82). With the suggested optimum decision thresholds excellent sensitivity and specificity is simultaneously possible.

CONCLUSIONS

Owing to the high achievable spatial resolution, portal dosimetry at the Halcyon can reliably be deployed as plan-specific pre-treatment QA tool to screen for errors. It is recommended to support the fluence integrated portal dosimetry QA by independent phantom-based measurements of a random sample survey of treatment plans.

Volumetric modulated arc therapy for hippocampal-sparing prophylactic cranial irradiation: Planning comparison of Halcyon and C-arm accelerators

Background

The purpose of the study was to evaluate the dosimetry of the Halcyon in prophylactic cranial irradiation (PCI) with volumetric modulated arc therapy (VMAT) and hippocampal-sparing for small cell lung cancer (SCLC).

Methods

Five VMAT plans were designed on CT images of 15 patients diagnosed with SCLC and received PCI. Three plans with two full arcs were generated on the Trilogy and the TrueBeam accelerators, and flattening filter (FF) and flattening filter free (FFF) modes were used on TrueBeam. Two Halcyon plans with two and three full arcs were generated, referred to as H-2A and H-3A, respectively. The prescription dose was 25 Gy in 2.5-Gy fractions. The dose limit for hippocampus were D₁₀₀ ≤ 9Gy and D_max ≤ 16Gy. The Wilcoxon matched-paired signed-rank test was used to evaluate the significance of the observed differences between the five plans.

Results

H-2A plans significantly increased the D₂ of PTV, and H-3A plans showed comparable or even better target dosimetry (better conformity) compared to the three plans on C-arm accelerators. Compared to T and TB plans, the two Halcyon plans significantly reduced the D₁₀₀ and mean doses of bilateral hippocampus, the mean doses of eyeballs, and the maximum doses of lenses. D₁₀₀ of hippocampus was reduced in TrueBeam plans comparing to Trilogy plans. The FFF plans on TrueBeam also represented advantages in D_mean and D₁₀₀ of hippocampas, D_mean and D_max of eyeballs, and the D_max of lenses compared to FF plans. Halcyon plans and TrueBeam plans with FFF mode increased the MUs compared to FF plans. Comparing to H-2A, the H-3A plans exhibited additional dosimetric advantages, including D₂, CI and HI of PTV, as well as the maximum and mean doses of hippocampus and eyeballs, and the maximum doses of optic nerves and brainstem. The two Halcyon plans significantly reduced the delivery time and showed the higher gamma passing rate than the three plans of C-arm accelerators.

Conclusions

Compared with the C-arm accelerators, the dose of hippocampus and the delivery times on Halcyon are relatively significantly reduced for hippocampal-sparing PCI. Three arcs are recommended for VMAT plans with the Halcyon in hippocampal-sparing PCI.

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.

Effect of the simulated half leaf width of a multileaf collimator on volumetric modulated arc therapy plan quality in hippocampal avoidance whole-brain radiotherapy

Purpose

Whole‐brain radiotherapy (WBRT) is commonly used in patients with multiple brain metastases. Compared with conventional WBRT, hippocampal avoidance WBRT (HA‐WBRT) more favorably preserves cognitive function and the quality of life. The hippocampal volume is considerably small (approximately 3.3 cm³). Therefore, downsizing the leaf width of a multileaf collimator (MLC) may provide higher spatial resolution and better plan quality. Volumetric modulated arc therapy (VMAT) could simulate the half MLC leaf width through couch shifting between arcs. This study investigated changes in VMAT quality for HA‐WBRT with a simulated fine MLC leaf width.

Methods

We included 18 patients with brain metastasis. All target and avoidance structures were contoured by an experienced radiation oncologist. The prescribed dose was 30 Gy in 10 fractions. For each patient, three different treatment plans were generated for comparison: VMAT with couch‐shift, VMAT without couch‐shift, and TomoTherapy. All treatment plans fulfilled Radiation Therapy Oncology Group (RTOG) 0933 criteria for HA‐WBRT. The Wilcoxon paired signed‐rank test was used to compare different treatment plans.

Results

VMAT with couch‐shift had the better average conformity index (0.823) with statistically significant difference compared to VMAT without couch‐shift (0.810). VMAT with couch‐shift (0.219) had a more favorable average homogeneity index (HI) than did VMAT without couch‐shift (0.230), although the difference was not significant. TomoTherapy had an optimal average HI of 0.070. In terms of the hippocampus, all three treatment plans met the RTOG 0933 criteria. VMAT with couch‐shift had a lower average D_max (15.2 Gy) than did VMAT without couch‐shift (15.3 Gy, p = 0.071) and TomoTherapy (15.5 Gy, p = 0.133). The average D_100% of hippocampus was the same for both VMAT with and without couch‐shift (8.5 Gy); however, TomoTherapy had a lower average D_100% value of 7.9 Gy. The treatment delivery time was similar between VMAT with and without couch‐shift (average, 375.0 and 369.6 s, respectively). TomoTherapy required a long average delivery time of 1489.9 s.

Conclusion

The plan quality of VMAT for HA‐WBRT was improved by using the couch‐shift technique to simulate the half MLC leaf width. However, the improvement was not statistically significant except conformity index. The downsizing effect decreased with the use of the sophisticated grade of VMAT. TomoTherapy offered superior plan quality but required the longest delivery time.

Plan Quality Comparison Between Hippocampus-Sparing Whole-Brain Radiotherapy Treated With Halcyon and Tomotherapy Intensity-Modulated Radiotherapy

Objective: Hippocampus-sparing whole-brain radiotherapy using Halcyon, an instrument dedicated to volumetric modulated arc therapy, has not been studied till date; hence, we aimed to examine whether it can meet the RTOG0933 criteria. Based on this, we compared Halcyon to Tomotherapy, which also uses an O-ring-type linear accelerator. Methods: This exploratory, experimental, and retrospective study used 5 sets of computed tomography images in the head area to investigate the planning target volume, hippocampal doses, and irradiation time. Calculations were performed from 1 to 4 arcs to determine the optimal number of arcs in the Halcyon plan, which were compared to those of Tomotherapy. Results: The Radiation Therapy Oncology Group 0933 criteria could not be satisfied in Halcyon with 1 arc. With 2 arcs, the condition D_max<16 Gy was not satisfied for 1 case in the hippocampus. Since there were no significant differences between 3 and 4 arcs, including the irradiation time, 3 arcs were considered the best. We compared Halcyon at 3 arcs with tomotherapy and found that tomotherapy was inferior to Halcyon at D_98%; however, it was superior to Halcyon in other dose parameters. In contrast, the irradiation time in Halcyon was overwhelmingly superior, with the irradiation time for Halcyon being 1/ninth the time for Tomotherapy. Conclusion: Halcyon was effective in handling hippocampus-sparing whole-brain radiotherapy. We believe that 3-arc radiation is best suited for this procedure. Although Halcyon was inferior to Tomotherapy in terms of dose distribution excluding D_98%, it was overwhelmingly superior in terms of irradiation time.

Dosimetric comparison of VitalBeam® and HalcyonTM 2.0 for hypofractionated VMAT with simultaneous integrated boost treatment of early-stage left-sided breast cancer

Purpose

This study compared the quality of treatment plans for early‐stage, left‐sided breast cancer, as planned for and delivered by the Halcyon^TM and VitalBeam^®.

Materials and methods

Fifteen patients diagnosed with early‐stage left‐sided breast cancer, who had received VMAT with hypofractionated SIB, were recruited. All cases were planned using Halcyon^TM comprising a dual‐layer MLC (DL‐MLC) and VitalBeam^® with a Millennium 120 MLC (VB‐MLC). For the PTVs, the quality of coverage (QC), conformity index (CI), and homogeneity index (HI) were calculated for each plan. The dosimetric differences between the two treatment plans were statistically compared using the Wilcoxon signed‐rank test (p < 0.05). To evaluate delivery efficiency, the average delivery time for each patient's treatment plan was recorded and compared.

Results

For the PTVs, the two plans (DL‐MLC and VB‐MLC) were comparable in terms of the QC, CI, and HI. However, V_30Gy and D_mean for the heart in the DL‐MLC plan were significantly reduced by 0.49% and 14.6%, respectively, compared with those in the VB‐MLC plan (p < 0.05). The D_mean value for the ipsilateral lung in the DL‐MLC plan significantly decreased by 5.5%, compared with that in the VB‐MLC plan (p < 0.05). In addition, the delivery times for the DL‐MLC and VB‐MLC plans were 79 ± 10 and 101 ± 11 s, respectively.

Conclusions

DL‐MLC plans were found to improve OAR sparing. In particular, when treating left‐sided breast cancer via DL‐MLC plans, the risk of heart toxicity is expected to be reduced.

Comparison of treatment plans for hypofractionated high-dose prostate cancer radiotherapy using the Varian Halcyon and the Elekta Synergy platforms

Purpose

To compare radiotherapy plans between an O‐ring and a conventional C‐arm linac for hypofractionated high‐dose prostate radiotherapy in terms of plan quality, dose distribution, and quality assurance in a multi‐vendor environment.

Methods

Twenty prostate cancer treatment plans were irradiated on the O‐ring Varian Halcyon linac and were re‐optimized for the C‐arm Elekta Synergy Agility linac. Dose‐volume histogram metrics for target coverage and organ at risk dose, quality assurance, and monitor units were retrospectively compared. Patient‐specific quality assurance with ion chamber measurements, gamma index analysis, and portal dosimetry was performed using the Varian Portal Dosimetry system and the ArcCHECK^® phantom (Sun Nuclear Corporation). Prostate‐only radiotherapy was delivered with simultaneous integrated boost (SIB) volumetric modulated arc therapy (VMAT) in 20 fractions of 2.5/3.0 Gy each.

Results

For both linacs, target coverage was excellent and plan quality comparable. Homogeneity in PTV_Boost was high for Synergy as well as Halcyon with a mean homogeneity index of 0.07 ± 0.01 and 0.05 ± 0.01, respectively. Mean dose for the organs at risk rectum and bladder differed not significantly between the linacs but were higher for the femoral heads and penile bulb for Halcyon. Quality assurance showed no significant differences in terms of ArcCHECK gamma pass rates. Median pass rate for 3%/2 mm was 99.3% (96.7 to 99.8%) for Synergy and 99.8% (95.6 to 100%) for Halcyon. Agreement between calculated and measured dose was high with a median deviation of −0.6% (−1.7 to 0.8%) for Synergy and 0.2% (−0.6 to 2.3%) for Halcyon. Monitor units were higher for the Halcyon by approximately 20% (p < 0.001).

Conclusion

Hypofractionated high‐dose prostate cancer SIB VMAT on the Halcyon system is feasible with comparable plan quality in reference to a standard C‐arm Elekta Synergy linac.