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

Dosimetric and radiobiological comparison of IMRT, VMAT, and helical tomotherapy planning techniques in hippocampal sparing whole brain radiotherapy with simultaneous integrated boost for multiple brain metastases

To compare treatment planning and dosimetric outcomes for hippocampal sparing whole brain radiotherapy (WBRT) with the simultaneous integrated boost (SIB) in brain metastasis (BM) patients using tumour control probability (TCP) and normal tissue complication probability (NTCP) formalism between IMRT, VMAT, and HT techniques. In this retrospective study, the treatment data of 20 BM patients who typically received whole brain radiation with SIB treatment were used. Prescription doses of 30 Gy and 36 Gy was delivered in 10 fractions for WBRT and SIB, respectively. Niemierko and LKB models were applied for calculating TCP and NTCP. All the plans were evaluated for the RTOG 0933 protocol criteria and found acceptable. Additionally, the homogeneity of the PTV boost is 0.07 ± 0.01, 0.1 ± 0.04, and 0.08 ± 0.02 for IMRT, VMAT, and HT, respectively (P < 0.05). The percentage of TCP for the PTV boost was 99.99 ± 0.003, 99.98 ± 0.004, and 99.99 ± 0.002 of IMRT, VMAT, and HT, respectively, (P < 0.005). The NTCP value of the lenses was higher with the VMAT plan as compared to IMRT and HT Plans. The hippocampal NTCP values are equal in all three planning proficiencies. The techniques like IMRT, VMAT, and HT can reduce the dose received by hippocampus to the dosimetric threshold during the delivery of WBRT with hippocampal sparing and can simultaneously boost multiple metastases. Overall, the high-quality dose distribution, TCP, and NTCP comparison between all three planning techniques show that the HT technique has better results when compared to the VMAT and IMRT techniques.

Comparative Evaluation of Dosimetric Quality and Treatment Efficiency for Halcyon, TrueBeam, and TomoTherapy in Cervical-Thoracic Esophageal Cancer Radiotherapy

INTRODUCTION

This study primarily aims to investigate the suitability of Halcyon in the context of cervical-thoracic esophageal cancer by exploring the dosimetric quality and delivery efficiency of Halcyon plans with different arc configurations. Additionally, it compares these findings with the dosimetric indices and delivery efficiency of TrueBeam and TomoTherapy accelerators, focusing on their capability to optimize protection for organs at risk (OARs) while maintaining efficient treatment delivery strategies.

METHODS

This retrospective study involved 26 patients diagnosed with cervical-thoracic esophageal cancer, and new radiotherapy plans were created using Halcyon, TrueBeam, and TomoTherapy. Dose volume histogram (DVH) metrics and delivery efficiency for plans involving different arc numbers on Halcyon (2, 3, and 4 arcs) were compared with those from TrueBeam and TomoTherapy. T-tests were employed to evaluate differences in organ protection among the accelerators.

RESULTS

The Halcyon plans, especially those with 4 arcs, provided superior protection for organs at risk, including the heart, lungs, and spinal cord, while maintaining excellent delivery efficiency. Compared to TrueBeam 2arc plans and TomoTherapy helical plans, Halcyon plans with 3 arcs also showed slight advantages. Although TomoTherapy offered better uniformity in dose distribution, it did not demonstrate a clear advantage over the other accelerators in terms of OAR protection or treatment efficiency. Furthermore, despite the lack of clear advantages in TrueBeam 2arc plans with flattening filter (FF), TrueBeam with flattening filter free (FFF) plans may hold potential in the treatment.

CONCLUSION

Halcyon, particularly with 4 arcs, offers an optimal balance between reducing toxicity to organs at risk and maintaining treatment efficiency, making it a preferred choice in cervical thoracic esophageal cancer radiotherapy. The findings highlight the need for careful selection of radiotherapy accelerators based on specific clinical goals, with Halcyon showing potential advantages in scenarios where both treatment efficiency and OAR protection are paramount.

Comparison of Different Head Tilt Angles in Tomotherapy and Volumetric Modulated Arc Therapy for Hippocampal-Avoidance Whole-Brain Radiotherapy

PURPOSE

Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) planning can present challenges. This study examines the influence of head tilt angles on the dosimetric characteristics of target and organs at risk (OARs), aiming to identify the optimal tilt angle that yields optimal dosimetric outcomes using tomotherapy (TOMO).

METHODS

Eight patients diagnosed with brain metastases underwent CT scans at five tilt angles: [0°, 10°), [10°, 20°), [20°, 30°), [30°, 40°), and [40°, 45°]. Treatment plans were generated using TOMO and volumetric modulated arc therapy (VMAT). Dosimetric parameters including conformity index (CI), homogeneity index (HI), D2cc, D98%, and Dmean of PTV, as well as Dmax, and Dmean of OARs were analyzed. Furthermore, a comparison was made between the dosimetric parameters of TOMO and VMAT plans. Finally, delivery efficiency of TOMO plans were assessed.

RESULTS

For the PTV, [40°, 45°] tilt angle demonstrated significantly better conformity, homogeneity, lower D2cc, and lower Dmean for the PTV. Regarding the OARs, the [40°, 45°] head tilt angle demonstrated significantly lower Dmax and Dmean in hippocampus, eyes, optic chiasm, and optic nerves. The [40°, 45°] tilt angle also showed significantly lower Dmax for brainstem and cochleas, as well as a lower Dmean for lens. In the [40°,45°] tilt angle for HA-WBRT, TOMO showed superior performance over VMAT for the PTV. TOMO achieved lower Dmax for brainstem, cochleas, optic nerves, and optic chiasm, as well as a lower Dmean for hippocampus. Furthermore, a significant correlation was found between delivery time and the PTV projection length in the sagittal plane.

CONCLUSION

The TOMO plan utilizing a tilt angle range of [40°, 45°] demonstrated superior PTV conformity and uniformity, along with enhanced OARs sparing. Furthermore, it exhibited a dosimetric advantage over VMAT for PTV and most OARs at the same angle range.

Dosimetric comparison of helical tomotherapy and volumetric modulated arc therapy in hippocampal avoidance whole-brain radiotherapy

OBJECTIVE

This study aimed to discuss the dosimetric advantages of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) technology in hippocampal avoidance whole-brain radiotherapy and provide references for clinical selection of ideal radiotherapy technology.

METHODS

A total of 20 patients with hippocampal avoidance whole-brain radiotherapy were chosen randomly. Computed tomography (CT) and MRI scanning images were input into the treatment planning system (TPS). After the CT and enhanced magnetic resonance T1 weighted images were fused and registered, the same radiation therapy physician was invited to outline the tumor target volume. PTV-HS refers to the whole brain subtracted by 5 mm outward expansion of the hippocampus (HP). The prescribed dose was 30 Gy/10 fractions. HT and VMAT plans were designed for each patient in accordance with PTV. Under the premise that the 95% isodose curve covers the PTV, dose-volume histogram was applied to evaluate the PTV, conformal index (CI), heterogeneity index (HI), maximum dose (Dmax), mean dose (Dmean), minimum dose (Dmin) and absorbed doses of organs at risk (OARs) in HT and VMAT plans. Paired t-test was performed to compare the differences between two radiation therapy plans, and p  <  0.05 was considered statistically significant.

RESULTS

These two plans had no significant difference in PTV-HS (max, min, and mean). However, the HI and CI of the HT plan were significantly better than those of the VMAT plan, showing statistically significant difference (p < 0.05). The HT plan was significantly superior to the VMAT plan in terms of the Dmax, Dmin, and Dmean of HP, left and right eye lens, left and right eye, and spinal cord, showing statistically significant difference (p < 0.05). The HT plan was also better than the VMAT plan in terms of the Dmax of the left optic nerve. However, the two plans showed no obvious differences in terms of the absorbed doses of the right optic nerve and brainstem, without statistical significance.

CONCLUSIONS

Compared with the VMAT plan of hippocampal avoidance, HT technology has significant dosimetric advantages. HT plans significantly decreased the radiation dose and radiation volume of OARs surrounding the target area (e.g., surrounding eye lens and eye, especially hippocampal avoidance area) while increasing the CI and HI of PTV dose in whole brain radiotherapy (WBRT) greatly, thus enabling the decrease in the incidence rate of radioactive nerve function impairment.

Whole-brain radiotherapy with hippocampus sparing and simultaneous integrated boost to metastases: A plan quality comparison study between Ethos, HyperArc, VMAT and Tomotherapy

This study provides a concise and structured overview of a dosimetric comparison study conducted to assess the feasibility and effectiveness of 4 advanced radiotherapy techniques in treating brain metastases with hippocampus sparing and simultaneous integrated boost (HS-WBRT+SIB). Eleven patients with brain metastases previously treated with radiotherapy were included in the study. Planning CT scans with 2 mm slice thickness and MR imaging were used for contouring and dose prescription. The bilateral hippocampus and other organs at risk (OARs) were automatically contoured, and hippocampal avoidance regions (HAR) were defined as a 7 mm 3D expansion around the hippocampus. Gross tumor volume for each metastasis (GTVmet) and planning target volume for metastases (PTVmet) were delineated. The whole-brain CTV (CTVWB) and planning target volume for whole brain (PTVWB) were defined accordingly. Treatment planning and optimization were conducted using state-of-the-art radiotherapy techniques: Ethos, HyperArc, VMAT, and Tomotherapy. Tomotherapy achieved the highest D98% for PTVmet, indicating the best metastasis coverage. HyperArc plans showed the highest D98% for PTVWB, suggesting superior whole-brain coverage. Tomotherapy demonstrated significantly lower D98%, D2%, and Dmean values for the hippocampus, indicating its superiority in sparing the hippocampus. VMAT resulted in the lowest D2% values for the eyes, optic nerves, brainstem, and hypophysis, showing the best sparing of these critical structures. Tomotherapy consistently achieved lower Dmean values for parotids, oral cavity, and lips compared to the other techniques. The dosimetric comparison revealed distinct strengths and weaknesses for each radiotherapy technique. Tomotherapy excelled in sparing the hippocampus, while VMAT showed promise in sparing OARs. HyperArc plans demonstrated the best overall whole-brain coverage. These findings should guide clinicians in selecting the most suitable technique based on patient characteristics and institutional resources.

Dosimetric performance evaluation of the Halcyon treatment platform for stereotactic radiotherapy: A pooled study

With the advancement of radiotherapy equipment, stereotactic radiotherapy (SRT) has been increasingly used. Among the many radiotherapy devices, Halcyon shows promising applications. This article reviews the dosimetric performance such as plan quality, plan complexity, and gamma passing rates of SRT plans with Halcyon to determine the effectiveness and safety of Halcyon SRT plans. This article retrieved the last 5 years of PubMed studies on the effectiveness and safety of the Halcyon SRT plans. Two authors independently reviewed the titles and abstracts to decide whether to include the studies. A search was conducted to identify publications relevant to evaluating the dosimetric performance of SRT plans on Halcyon using the key strings Halcyon, stereotactic radiosurgery, SRT, stereotactic body radiotherapy, and stereotactic ablative radiotherapy. A total of 18 eligible publications were retrieved. Compared to SRT plans on the TrueBeam, the Halcyon has advantages in terms of plan quality, plan complexity, and gamma passing rates. The high treatment speed of SRT plans on the Halcyon is impressive, while the results of its plan evaluation are also encouraging. As a result, Halcyon offers a new option for busy radiotherapy units while significantly improving patient comfort in treatment. For more accurate results, additional relevant publications will need to be followed up in subsequent studies.

Tomotherapy: Comparison of Hi-ART, Tomo-HD, and Radixact

Aim In this study, we compared three generations of tomotherapy (Hi-ART, Tomo-HD, and Radixact). This is to study the difference among tomotherapy systems in terms of dose distribution to planning target volume and organs at risk, and irradiation time.  Materials and methods The treatment planning CT and contour information used were seven cases of rectum cancer pre-operative irradiation. The contour information used was the planning target volume, and the organs at risk were set as the bladder and body. Optimization was conducted at each planning station using the parameters that were actually used in a clinical setting. The prescribed radiation dose was 25 Gy in five fractions and normalized at the isodose line, covering 95% of the planning target volume. Results There were no significant differences in planning target volume among the three models. Meanwhile, Hi-ART had a significantly higher dose than Tomo-HD and Radixact at body D_50%. Radixact shortened the irradiation time by approximately 15% compared to Hi-ART/Tomo-HD. Conclusion Planning target volume dose distribution of tomotherapy devices was not different. Radixact required a significantly shorter time than Hi-ART and Tomo-HD.