Dosimetric evaluation of intensity-modulated radiotherapy, volumetric modulated arc therapy, and helical tomotherapy for hippocampal-avoidance whole brain radiotherapy

Modulated Arc Therapy for hippocampal-avoidance whole brain radiation therapy: planning comparison with intensity modulated Radiation Therapy

This study aimed to evaluate the modulated arc therapy (mARC) technique as a planning and treatment option for hippocampal sparing whole brain radiotherapy (HS-WBRT) following the Radiation Therapy Oncology Group (RTOG) 0933 dosimetric criteria. Computed tomography (CT) and magnetic resonance imaging (MRI) were selected retrospectively for 15 patients. Two types of plans were created for each patient, namely an intensity-modulated radiation therapy (IMRT) and a mARC plan. IMRT and mARC plans were compared in terms of plan quality indices, absorbed dose to organs at risk (OARs), number of monitor units (MUs), and treatment time. All plans in both techniques were considered clinically acceptable for treatment. However, IMRT plans presented a higher conformity (p = 0.01) as well as a higher homogeneity as compared to mARC plans, but this difference was not statistically significant (p > 0.05). In terms of the preservation of the hippocampus, it was observed that the IMRT plans achieved significantly lower doses for both 100% of its volume and for its maximum dose (p < 0.001). The evaluation of the remaining OARs showed that the IMRT technique resulted in lower doses, and significant differences were observed for the following organs: left cochlea (p < 0.001), left eye (p < 0.001), right eye (p = 0.03), both lenses of the eye (p < 0.001), and right optic nerve (p = 0.02). Despite these differences, the absolute differences in all dosimetric parameters were low enough to bear any clinical relevance. A drastic (close to 65%) and significant (p < 0.001) decrease was observed in the number of MUs for the mARC plans. This resulted in a substantial decrease in treatment time (60.45%, p < 0.001). It is concluded that the mARC technique is a feasible planning and treatment solution for HS-WBRT that meets the RTOG 0933 criteria. The main advantage of using mARC over IMRT for HS-WBRT is the considerable reduction in MUs and treatment time.

Current dilemma and future directions over prophylactic cranial irradiation in SCLC: a systematic review in MRI and immunotherapy era

Small cell lung cancer (SCLC) is the most malignant pathological type of lung cancer with the highest mortality, and the incidence of brain metastasis (BM) is in high frequency. So far, prophylactic cranial irradiation (PCI) has been suggested as an effective treatment for preventing brain metastasis of SCLC. PCI has long been applied to limited-stage SCLC (LS-SCLC) patients who have achieved complete remission after radiotherapy and chemotherapy as a standard treatment. However, the neurocognitive decline is a major concern surrounding PCI. New therapeutic approaches targeting PCI-induced neurotoxicity, including hippocampal protection or memantine, have been increasingly incorporated into the therapeutic interventions of PCI. Helical tomotherapy, RapidArc, and Volumetric-modulated arc therapy (VMAT) with a head-tilting baseplate are recommended for hippocampal protection. Besides, in the MRI and immunotherapy era, the significance of PCI in SCLC patients is controversial. SCLC patients with PCI should be recruited in clinical trials since this is the only way to improve the existing standard of care. This review summarizes the current therapeutic strategy and dilemma over PCI for SCLC, providing a theoretical basis for clinical decision-making and suggestions for PCI practice in clinical.

Safety and Feasibility of Hippocampal Sparing Cranial Radiation in Pediatric and Adolescent Acute Lymphoblastic Leukemia Patients: A Prospective Study

Introduction Acute lymphoblastic leukemia (ALL) constitutes a significant portion of pediatric malignancies, with central nervous system (CNS) relapse posing a considerable threat to patient outcomes. While cranial radiation therapy (CRT) has been utilized to mitigate CNS relapse, it is associated with neurocognitive (NC) side effects. This study explores the feasibility and safety of using volumetric arc therapy (VMAT) with hippocampal sparing (HS) during cranial radiation therapy for ALL patients, aiming to reduce these side effects. Methodology This prospective observational study included pediatric and young adult patients with ALL who were in remission. HS was achieved using VMAT, and NC assessments were performed at baseline, six months, one year, and, to a limited extent, four years posttreatment. Results VMAT enabled precise hippocampal-sparing CRT with minimal dose to the hippocampus. Dosimetric analysis revealed that patients receiving 18 Gy had mean doses to planning target volume (PTV) and bilateral hippocampus of 18.9 and 9 Gy, respectively. Those receiving 12 Gy had corresponding doses of 13.3 and 7 Gy, respectively. Conformity and homogeneity indices were 0.9 and 0.1, and no brain relapses were observed among the patients in this study. NC assessments demonstrated no decline in intelligence quotient (IQ) scores over time, while only a subset of patients could be assessed at the four-year mark; telephone interviews suggested no significant cognitive decline. Conclusions This study highlights the potential of VMAT with HS as a promising approach to CRT for ALL patients in reducing the risk of NC side effects. The absence of brain relapses and preservation of NC function are encouraging findings, though larger studies are necessary to establish conclusive evidence.

Hippocampal region avoidance in whole brain radiotherapy in brain metastases: For all or for some? A real-world feasibility report

PURPOSE

Hippocampal sparing whole-brain radiotherapy (HS-WBRT) showed significantly lower long-term side effects compared to standard WBRT. Aim of this study is to describe a HS-WBRT real-world monoinstitutional experience within a retrospective cohort.

METHODS

Patients who completed HS-WBRT course, with Karnofsky Performance Status ⩾ 60 and radiological diagnosis of brain metastases (BMs) were enrolled. Treatment was performed using helical Tomotherapy scheduled in 30 Gy in 10 or 12 fractions or 25 Gy in 10 fractions. Oncological outcomes were clinically and radiologically assessed every three months. Toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events 4.3.

RESULTS

One hundred and nineteen patients from 2016 to 2020 met inclusion criteria; after a median follow-up of 18 months, 29 patients were alive; 6- and 12-months overall survival rates were 66% and 41%, respectively. HS-WBRT response was assessed for 72 patients. Median time to any progression and intracranial failure (IF) was 4.5 and 13.7 months, respectively. The 6- and 12-month IF rates were 85% and 57%. Among 40 patients (34%) who experienced IF, 17 (42%) were oligometastatic, 23 (58%) polymetastatic and 15/40 developed IF within the hippocampi avoidance zone. No grade (G) ⩾ 2 acute toxicities were reported and one G2 (dizziness) late toxicity was described.

CONCLUSIONS

HS-WBRT is well tolerated, and despite the hippocampal sparing region, the oncological control is satisfying. Further investigation is warranted to find patients who could most benefit from a HS-WBRT approach.

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.

Dosimetric comparison of coplanar and noncoplanar volumetric modulated arc therapy for hippocampal-sparing whole-brain radiation therapy

Whole brain radiation therapy with hippocampal-sparing (HS-WBRT) is a novel treatment of brain metastases, which can relieve symptoms reduce recurrence in the central nervous system, and spare the hippocampus without compromising target coverage. This study aims to find out the superior combination of the treatment planning system and linear accelerator between Eclipse (version 15.6) with TrueBeam and uRT-TPOIS (vision R001.4) with uRT-linac 506c in HS-WBRT. The coplanar and noncoplanar volumetric modulated arc therapy (VMAT) for HS-WBRT plans were evaluated and compared on both combinations, respectively. Twenty patients for HS-WBRT were retrospectively selected at Peking Union Medical College Hospital (PUMCH) from 2021 to 2022. The coplanar and noncoplanar HS-WBRT treatment plans were designed by Eclipse and uRT-TPOIS referring to RTOG 0933 dose criteria, and their dosimetry parameters were compared. In addition, the plan complexity, monitor units, and beam-on time were recorded for Eclipse plans delivered on TrueBeam and uRT-TPOIS plans delivered on uRT-linac 506c. The results demonstrated that the dosimetric criteria of 4 types of HS-WBRT plans could meet the requirements of RTOG 0933. In terms of target coverage, dosimetric indexes of Eclipse plans and uRT-TPOIS plans were comparable, and the former is slightly better. As for metrics of organs-at-risk protection, coplanar and noncoplanar plans conducted by uRT-TPOIS were greatly superior to those by Eclipse. For coplanar and noncoplanar plans designed by the same treatment planning system, most of the dosimetric indexes had no significant difference. The monitor units of uRT-TPOIS plans was higher than that of Eclipse plans, but the modulation complexity of them were close, and uRT-TPOIS with uRT-linac 506c significantly reduced beam-on-time consumption by 9% on average for coplanar plans and 26% for noncoplanar plans compared to Eclipse with TrueBeam. This study firstly compared the coplanar and noncoplanar HS-WBRT treatment plans between Eclipse with TrueBeam and uRT-TPOIS with uRT-linac 506c in terms of dosimetry indexes, modulation complexity, and time consumption. It is shown that the radiation treatment solution of uRT-TPOIS with uRT-linac 506c is comparable with Eclipse with TrueBeam in terms of planning design, and significantly reduced the delivery time, which can be applied in clinical practice and promoted as a treatment format.

Helical tomotherapy and two types of volumetric modulated arc therapy: dosimetric and clinical comparison for several cancer sites

Radiotherapy accelerators have undergone continuous technological developments. We investigated the differences between Radixact™ and VMAT treatment plans. Sixty patients were included in this study. Dosimetric comparison between the Radixact™ and VMAT plans was performed for six cancer sites: whole-brain, head and neck, lymphoma, lung, prostate, and rectum. The VMAT plans were generated with two Elekta linear accelerators (Synergy^® and Versa HD™). The planning target volume (PTV) coverage, organs-at-risk dose constraints, and four dosimetric indexes were considered. The deliverability of the plans was assessed using quality assurance (gamma index evaluation) measurements; clinical judgment was included in the assessment. The mean AAPM TG218 (3%-2 mm, global normalization) gamma index values were 99.4%, 97.8%, and 96.6% for Radixact™, Versa HD™, and Synergy®, respectively. Radixact™ performed better than Versa HD™ in terms of dosimetric indexes, hippocampi D_100%, spinal cord D_max, rectum V_{38.4  Gy}, bladder V_{30 Gy}, and V_{40 Gy}. Versa HD™ saved more of the (lungs-PTV) V_{5 Gy} and (lungs-PTV) D_mean, heart D_mean, breasts V_{4 Gy}, and bowel V_{45 Gy}. Regarding Synergy^®, the head and neck Radixact™ plan saved more of the parotid gland, oral cavity, and supraglottic larynx. From a clinical point of view, for the head and neck, prostate, and rectal sites, the Radixact™ and Versa HD™ plans were similar; Radixact™ plans were preferable for the head and neck and rectum to Synergy^® plans. The quality of linac plans has improved, and differences with tomotherapy have decreased. However, tomotherapy continues to be an essential add-on in multi-machine departments.

A simplified non-coplanar volumetric modulated arc therapy for the whole brain radiotherapy with hippocampus avoidance

Purpose

To evaluate the feasibility of using a simplified non-coplanar volumetric modulated arc therapy (NC-VMAT) and investigate its dosimetric advantages compared with intensity modulated radiation therapy (IMRT) and coplanar volumetric modulated arc therapy (C-VMAT) for hippocampal-avoidance whole brain radiation therapy (HA-WBRT).

Methods

Ten patients with brain metastase (BM) were included for HA-WBRT. Three treatment plans were generated for each case using IMRT, C-VMAT, and NC-VMAT, respectively.

Results

The dosimetric results of the three techniques complied roughly with the RTOG 0933 criteria. After dose normalization, the V_30Gy of whole brain planned target volume (WB-PTV) in all the plans was controlled at 95%. Homogeneity index (HI) of WB-PTV was significantly reduced in NC-VMAT (0.249 ± 0.017) over IMRT (0.265 ± 0.020, p=0.005) and C-VMAT (0.261 ± 0.014, p=0.020). In terms of conformity index (CI), NC-VMAT could provide a value of 0.821 ± 0.010, which was significantly superior to IMRT (0.788 ± 0.019, p<0.001). According to D_2% of WB-PTV, NC-VMAT could provide a value of 35.62 ± 0.37Gy, significantly superior to IMRT (36.43 ± 0.65Gy, p<0.001). According to D_50% of WB-PTV, NC-VMAT can achieve the lowest value of 33.18 ± 0.29Gy, significantly different from IMRT (33.47 ± 0.43, p=0.034) and C-VMAT (33.58 ± 0.37, p=0.006). Regarding D_2%, D_98%, and D_mean of hippocampus, NC-VMAT could control them at 15.57 ± 0.18Gy, 8.37 ± 0.26Gy and 11.71 ± 0.48Gy, respectively. D_2% and D_mean of hippocampus for NC-VMAT was significantly lower than IMRT (D_2%: 16.07 ± 0.29Gy, p=0.001 D_mean: 12.18 ± 0.33Gy, p<0.001) and C-VMAT (D_2%: 15.92 ± 0.37Gy, p=0.009 D_mean: 12.21 ± 0.54Gy, p<0.001). For other organs-at-risk (OARs), according to D_2% of the right optic nerves and the right lenses, NC-VMAT had the lowest values of 31.86 ± 1.11Gy and 7.15 ± 0.31Gy, respectively, which were statistically different from the other two techniques. For other organs including eyes and optic chiasm, NC-VMAT could achieve the lowest doses, different from IMRT statistically.

Conclusion

The dosimetry of the three techniques for HA-WBRT could roughly comply with the proposals from RTOG 0933. After dose normalization (D_95%=30Gy), NC-VMAT could significantly improve dose homogeneity and reduce the D_50% in the brain. Besides, it can reduce the D_2% of the hippocampus, optic nerves, and lens. With this approach, an efficient and straightforward plan was accomplished.

Actual, Personalized Approaches to Preserve Cognitive Functions in Brain Metastases Breast Cancer Patients

Breast cancer (BC) is the most often diagnosed cancer among women worldwide and second most common cause of brain metastases (BMs) among solid malignancies being responsible for 10-16% of all BMs in oncological patients. Moreover, BMs are associated with worse prognosis than systemic metastases. The quality of life (QoL) among brain metastases breast cancer (BMBC) patients is significantly influenced by cognitive functions. Cancer-related cognitive deficits and the underlying neural deficits in BMBC patients can be caused via BMs per se, chemotherapy administration, brain irradiation, postmenopausal status, or comorbidities. Brain RT often leads to cognitive function impairment by damage of neural progenitor cells of the hippocampus and hence decreased QoL. Sparing the hippocampal region of the brain during RT provides protective covering of the centrally located hippocampi according to the patient's clinical requirements. This article discusses the personalized strategies for treatment options to protect cognitive functions in BMBC patients, with special emphasis on the innovative techniques of radiation therapy.

Perihippocampal failure after hippocampal-avoidance whole-brain radiotherapy in cancer patients with brain metastases: Results of a retrospective analysis

Perihippocampal failure is a rare clinical scenario in brain metastatic cancer patients following hippocampal-avoidance (HA) whole-brain radiotherapy (HA-WBRT). The clinical features have not been fully identified because clinical data on intracranial failure after HA-WBRT are limited. It is thus necessary to accumulate clinical data.We retrospectively analyzed cancer patients with brain metastases who were diagnosed between January 2014 and September 2020 at a regional referral hospital. The medical records of patients who underwent HA-WBRT were reviewed. The clinical features of intracranial recurrence were described. Dosimetry parameters were compared in terms of deviation from the recommended protocol of the Radiation Therapy Oncology Report 0933.Twenty-four eligible patients with brain metastases who underwent HA-WBRT were identified; 13 (54%) were male. Seventeen patients (71%) had lung cancer, 6 (25%) had breast cancer, and 1 (4%) had liver cancer. The median overall survival was 12 months. Three patients developed intracranial failure during clinical follow-up, and 2 relapsed with intracranial failure in the perihippocampal region at 13 and 22 months, respectively. The perihippocampal failure rate was about 8%. One patient with small cell lung cancer received HA-prophylactic cranial irradiation; the minimum and maximum doses to the hippocampi were 6.8 and 10.7 Gy, respectively. Another patient with brain metastases from lung adenocarcinoma received HA-WBRT; the minimum and maximum doses to the hippocampi were 5.4 and 10.6 Gy, respectively.We reported unusual cases of intracranial failure in the perihippocampal region following HA-WBRT. Perihippocampal failure could be attributed to an under-dose of radiation partially or be resulted from aggressiveness of cancer per se. Further research on this topic is encouraged.

Dosimetric feasibility of hippocampal avoidance whole brain radiotherapy with an MRI-guided linear accelerator

Purpose/Objective(s)

Whole brain radiotherapy with hippocampal avoidance (HA‐WBRT) is a technique utilized to treat metastatic brain disease while preserving memory and neurocognitive function. We hypothesized that the treatment planning and delivery of HA‐WBRT plans is feasible with an MRI‐guided linear accelerator (linac) and compared plan results with clinical non‐MRI‐guided C‐Arm linac plans.

Materials/Methods

Twelve HA‐WBRT patients treated on a non‐MRI‐guided C‐Arm linac were selected for retrospective analysis. Treatment plans were developed using a 0.35T MRI‐guided linac system for comparison to clinical plans. Treatment planning goals were defined as provided in the Phase II Trial NRG CC001. MRI‐guided radiotherapy (MRgRT) treatment plans were developed by a dosimetrist and compared with clinical plans. quality assurance (QA) plans were generated and delivered on the MRI‐guided linac to a cylindrical diode detector array. Planning target volume (PTV) coverage was normalized to ∼95% to provide a control point for comparison of dose to the organs at risk.

Results

MRgRT plans were deliverable and met all clinical goals. Mean values demonstrated that the clinical plans were less heterogeneous than MRgRT plans with mean PTV V37.5 Gy of 0.00% and 0.03% (p = 0.013), respectively. Average hippocampi maximum doses were 14.19 ± 1.29 Gy and 15.00 ± 1.51 Gy, respectively. The gamma analysis comparing planned and measured doses resulted in a mean of 99.9% ± 0.12% of passing points (3%/2mm criteria). MRgRT plans had an average of 38.33 beams with average total delivery time and beam‐on time of 13.7 (11.2–17.5) min and 4.1 (3.2–5.4) min, respectively. Clinical plan delivery times ranged from 3 to 7 min depending on the number of noncoplanar arcs. Planning time between the clinical and MRgRT plans was comparable.

Conclusion

This study demonstrates that HA‐WBRT can be treated using an MRI‐guided linear accelerator with comparable treatment plan quality and delivery accuracy.

Parotid gland dose reduction in the hippocampus avoidance whole-brain radiotherapy using helical tomotherapy

The present study aimed to reduce the parotid gland dose in the hippocampus avoidance with whole-brain radiotherapy (HA-WBRT) using the helical tomotherapy (HT). Ten patients who had previously undergone WBRT were randomly selected and enrolled in this study. During the treatment planning, two different techniques to the jaw were applied for each patient, namely, 1.0 cm fixed jaw and 2.5 cm dynamic jaw. To efficiently reduce the dose in the bilateral parotid glands, directional block (DB) mode was set. The DB is a function of a treatment planning system for the dose reduction in organs at risk. The standard HA-WBRT plan which did not reduce the parotid gland dose was also designed to compare the plan quality. Compared with the standard HA-WBRT plan, the parotid gland dose could be reduced by approximately 70% without extending the delivery time by adding the parotid gland on the DB mode to the dose constraint. In addition, the differences in dosimetric parameters observed between the plans employing the 1.0 cm fixed jaw and 2.5 cm dynamic jaw were almost negligible. Moreover, delivery time in the 2.5 cm dynamic jaw could be greatly reduced by 60% compared with that in the 1.0 cm fixed jaw.

Influence of Modulation Factor on Treatment Plan Quality and Irradiation Time in Hippocampus-Sparing Whole-Brain Radiotherapy Using Tomotherapy

Objectives: Hippocampus-sparing whole-brain radiotherapy (HS-WBRT) using tomotherapy is known to provide a better dose distribution than volumetric-modulated arc therapy but requires an extended irradiation time. The present study aimed to investigate whether irradiation time can be shortened by reducing the modulation factor (MF) without losing the target dose distribution. Methods: Using six tilted computed tomography images in the head area, the planning target volume (PTV) and hippocampal doses, and the irradiation time was investigated with a jaw width of 1 cm, a pitch of 0.200, and the MF changed from 3.0 to 2.6, 2.2, 1.8, and 1.4. Results: No significant changes in the PTV or hippocampus were found with MF in the range from 3.0 to 1.8, but marked deterioration was found with that of 1.4. The irradiation time showed a linear relationship with the MF within the range from 3.0 to 1.8, with 1334, 1158, 986, and 817 s at modulation factors of 3.0, 2.6, 2.2, and 1.8, respectively. However, when the MF was 1.4, the irradiation time was 808 s. Conclusions: When HS-WBRT is performed with a tilted body position and a jaw width of 1 cm, with a MF of 1.8, a favorable balance between dose parameters and irradiation time is achieved, whereas with a MF of 1.4, the quality of the radiotherapy plan deteriorates, and the irradiation time is approximately the same as that with a MF of 1.8.

Fully automated planning and delivery of hippocampal-sparing whole brain irradiation

The goal of this study is to fully automate the treatment planning and delivery process of hippocampal-sparing whole brain irradiation (HS-WBRT) by combining a RapidPlan (RP) knowledge-based planning model and HyperArc (HA) technology. Additionally, this study compares the dosimetric performance of RapidPlan-HyperArc (RP-HA) treatment plans with RP plans and volumetric modulated arc therapy (VMAT) plans. Ten patients previously treated with HS-WBRT using conventional VMAT were re-planned using RP-HA technique and RP model for HS-WBRT. Treatment plans were generated for 30Gy in 3Gy fractions using 6MV photon beam on a TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA) equipped with high definition multileaf collimator (HDMLC). Target coverage, homogeneity index (HI), Paddick Conformity index (CI), dose to organs-at-risk (OARs) provided by the 3 planning modalities were compared, and a paired t-test was performed. Total number of monitor units (MU), effective planning time and beam-on-time time were reported and evaluated for each plan. RP-HA plans achieved on average a 4% increase in D_98% of PTV, a 26% improvement in HI, a 2.3% increase in CI, when compared to RP plans. Furthermore, RP-HA plans provided on average 11% decrease in D_100% of hippocampi when compared to VMAT plans. All RP-HA plans were generated in less than 30 minutes while RP plans took 40 minutes and VMAT plans required on average 9 hours to complete. Regarding beam-on-time time, it was estimated that RP-HA plans take on average 5 minutes to deliver while RP and VMAT plans require 6.5 and 10 minutes, respectively. RP-HA method provides fully automated planning and delivery for HS-WBRT. The auto-generated plans together with automated treatment delivery allow standardization of plan quality, increased efficiency and ultimately improved patient care.

Treatment planning of volumetric modulated arc therapy and positioning optimization for hippocampal-avoidance prophylactic cranial irradiation

BACKGROUND

Hippocampal-avoidance prophylactic cranial irradiation (HA-PCI) offers potential neurocognitive benefits but raises technical challenges to treatment planning. This study aims to improve the conventional planning method using volumetric modulated arc therapy (VMAT) technique and investigate a better patient's head positioning to achieve a high quality of HA-PCI treatment plans.

METHODS

The improved planning method set a wide expansion of hippocampus as a special region for dose decline. The whole brain target was divided into two parts according to whether the slice included hippocampus and their optimization objectives were set separately. Four coplanar full arcs with partial field sizes were employed to deliver radiation dose to different parts of the target. The collimator angle for all arcs was 90°. Tilting patient's head was achieved by rotating CT images. The improved planning method and tilted head positioning were verified using datasets from 16 patients previously treated with HA-PCI using helical tomotherapy (HT).

RESULTS

For the improved VMAT plans, the max and mean doses to hippocampus were 7.88 Gy and 6.32 Gy, respectively, significantly lower than those for the conventional VMAT plans (P < 0.001). Meanwhile, the improved planning method significantly improved the plan quality. Compared to the HT plans, the improved VMAT plans result in similar mean dose to hippocampus (P > 0.1) but lower max dose (P < 0.02). Besides, the target coverage was the highest for the improved VMAT plans. The tilted head positioning further reduced the max and mean doses to hippocampus (P < 0.05), significantly decreased the max dose to lens (P < 0.001) and resulted in higher plan quality as compared to nontilted head positioning.

CONCLUSIONS

The improved planning method enables the VMAT plans to meet the clinical requirements of HA-PCI treatment with high plan quality and convenience. The tilted head positioning provides superior dosimetric advantages over the nontilted head positioning, which is recommended for clinical application.

The Capabilities and Characteristics of Helical Tomotherapy and Co-Planar Dual Arcs Volumetric-Modulated arc Therapy Associated with Hippocampal Sparing During Prophylactic Cranial Irradiation

Objective: To investigate the features of helical tomotherapy and co-planar dual Arcs volumetric-modulated arc therapy during prophylactic cranial irradiation associated with bilateral hippocampal tissue sparing. Materials and methods: Helical tomotherapy and co-planar dual arcs volumetric-modulated arc therapy treatment plans were generated with a dose of 30 Gy/10 fractions in 16 patients treated with prophylactic cranial irradiation. The dose to the bilateral hippocampal tissues, organs at risk, and planning target volume were determined when the average dose of bilateral hippocampal tissues was reduced by approximately 4 Gy as an observation point. Changes in dosimetry when sparing the bilateral hippocampal tissues were determined for both modalities. Results: When bilateral hippocampal tissues were restricted to 8 Gy, D40%mean-bilateral hippocampal tissues = 7.64 ± 0.41 Gy in helical tomotherapy, while D40%mean-bilateral hippocampal tissues = 10.96 ± 0.38 Gy in co-planar dual arcs volumetric-modulated arc therapy volumetric-modulated arc therapy. Helical tomotherapy was associated with significantly lower doses to organs at risk, including Dmean-bilateral hippocampal tissues (P = .03), D98%-bilateral hippocampal tissues (P = .01), D2%-bilateral hippocampal tissues (P = .01), Dmean-inner ear (P = .02), Dmean-parotid glands (P = .02), Dmax-lens (P = .02), and Dmax-brainstem (P = .02), but not Dmax-optic nerves (P = .87). Helical tomotherapy provided better target coverage, with lower average D2%-PTV (P = .02), higher average D98%-PTV (P = .02), and better conformal index (0.87 vs 0.84, P = .02) and homogeneity index (0.15 vs 0.21, P = .05). With smaller bilateral hippocampal tissues doses, the planning target volume dose changed across 3 dosimetry regions for both modalities; the plateau region (>20.0 Gy for helical tomotherapy versus >16.0 Gy for co-planar dual arcs volumetric-modulated arc therapy), gradient region (20.0-12.0 Gy vs 16.0-11.0 Gy), and falling region (<12.0 Gy vs <11.0 Gy). The average delivery duration of helical tomotherapy was almost 7.7 times longer than that of co-planar dual arcs volumetric-modulated arc therapy. Conclusions: Helical tomotherapy was better at sparing the bilateral hippocampal tissues and organs at risk and had better target coverage but a significantly longer treatment duration than co-planar dual arcs volumetric-modulated arc therapy. Further dose decreases in the bilateral hippocampal tissues would yield worse target dose coverage.

Sparing the hippocampus and the hypothalamic- pituitary region during whole brain radiotherapy: a volumetric modulated arc therapy planning study

BACKGROUND

Feasibility testing of a simultaneous sparing approach of hippocampus, hypothalamus and pituitary gland in patients undergoing whole-brain radiotherapy (WBRT) with and without a concomitant boost to metastatic sites.

INTRODUCTION

Cognitive impairment and hormonal dysfunction are common side effects of cranial radiotherapy. A reduced dose application to the patho-physiologically involved functional brain areas, i.e. hippocampus, hypothalamus and pituitary gland, could reduce these common side effects. While hippocampal sparing is already a common practice to improve cognitive outcome, technical experience of additional combined sparing of the hypothalamus/pituitary gland (HT-P) is insufficient.

METHODS

Twenty patients were included in the planning study. In 11 patients, a total dose of 36 Gy of WBRT (2 Gy per fraction) plus a simultaneous integrated boost (SIB) of 9 Gy (0.5 Gy per fraction, total dose: 45 Gy) to the brain metastases was applied. In 9 patients, prophylactic cranial irradiation (PCI) was simulated with a total dose of 30 Gy (2 Gy per fraction). In both patient cohorts, a sparing approach of the hippocampus and the HT-P area was simulated during WBRT. For all treatment plans, volumetric modulated arc therapy (VMAT) was used. Quality assurance included assessment of homogeneity, conformality and target coverage.

RESULTS

The mean dose to the hippocampus and HT-P region was limited to less than 50% of the prescribed dose to the planning target volume (PTV) in all treatment plans. Dose homogeneity (HI) of the target volume was satisfying (median HI = 0.16 for WBRT+SIB and 0.1 for PCI) and target coverage (conformation number, CN) was not compromised (median CN = 0.82 for SIB and 0.86 for PCI).

CONCLUSION

Simultaneous dose reduction to the hippocampus and the HT-P area did not compromise the PTV coverage in patients undergoing WBRT+SIB or PCI using VMAT. While the feasibility of the presented approach is promising, prospective neurologic, endocrine outcome and safety studies are required.

Comparison of Dosimetric Gains Provided by Intensity-Modulated Radiotherapy, Volume-Modulated Arc Therapy, and Helical Tomotherapy for High-Grade Glioma

PURPOSE

Because of the poor prognosis for high-grade glioma (HGG) patients, it is important to increase the dose of the tumor to improve the efficacy while minimizing the dose of organs at risk (OARs). Thus, we evaluated the potential dosimetric gains of helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT) or volume-modulated arc therapy (VMAT) for high-grade glioma (HGG).

METHODS

A total of 42 HGG patients were retrospectively selected who had undergone helical tomotherapy; then, IMRT and VMAT plans were generated and optimized for comparison after contouring crucial neuronal structures for neurogenesis and neurocognitive function. IMRT and VMAT were optimized with the Eclipse treatment planning system (TPS) (Version 11.0.31) and HT using TomoTherapy Hi-Art Software (Version 2.0.7) (Accuray, Madison, WI, USA). All three techniques were optimized for simultaneously delivering 60 Gy to planning target volume (PTV) 1 and 50-54 Gy to PTV2. We also analyzed the homogeneity index (HI) and conformity index (CI) of PTVs and organ at risk (OAR) sparing.

RESULTS

There was no significant difference in the PTV coverage among IMRT, VMAT, or HT. As for the HI, HT plans (PTV1 HI: 0.09 ± 0.03, PTV2 HI: 0.17 ± 0.05) had the best homogeneity when compared to IMRT plans (PTV1 HI: 0.10 ± 0.04, PTV2 HI: 0.18 ± 0.04) and VMAT plans (PTV1 HI: 0.11 ± 0.03, PTV2 HI: 0.20 ± 0.03). The CI value of HT (PTV1 CI: 0.98 ± 0.03, PTV2: 0.98 ± 0.05) was closest to the optimal value. Except for the IMRT and VMAT groups, there were statistically significant differences between the other two groups of the CI values in both PTV1 and PTV2. The other comparison values were statistically significant except for the optic nerve, and VMAT had the best sparing of the optic chiasm. The mean and max doses of OARs declined significantly in HT.

CONCLUSIONS

For high-grade glioma patients, HT had superior outcomes in terms of PTV coverage and OAR sparing as compared with IMRT/VMAT.

Helical tomotherapy: Comparison of Hi-ART and Radixact clinical patient treatments at the Technical University of Munich

The helical tomotherapy (HT) Hi-ART system was installed at our department in April 2007. In July 2018 the first Radixact system in Germany has been launched for clinical use. We present differences, advantages and disadvantages and show future perspectives in patient treatment using two HT devices. We investigate patient characteristics, image quality, radiotherapy treatment specifications and analyze the time effort for treatments with the Hi-ART system from April 2010 until May 2017 and compare it to the data acquired in the first nine months of usage of the Radixact system. Comparing the Hi-ART and Radixact system, the unique option of integrated MVCT image acquisition has experienced distinct improvement in image quality. Time effort for irradiation treatment could be improved resulting in a mean beam on time for craniospinal axis treatment of 636.2 s for the Radixact system compared to 915.9 s for the Hi-ART system. The beneficial use of tomotherapy for complex target volumes is demonstrated by a head and neck tumor case and craniospinal axis treatment. With the Radixact system MVCT image quality has been improved allowing for fast and precise interfraction dose adaptation. The improved time effort for patient treatment could increase the accessibility for clinical usage.

Volumetric modulated arc therapy (VMAT) for hippocampal-avoidance whole brain radiation therapy: planning comparison with Dual-arc and Split-arc partial-field techniques

BACKGROUND

Although whole brain radiation therapy (WBRT) provides palliation and prophylaxis, reduces local recurrence probability and improves overall survival, it is evident that WBRT is associated with neurocognitive deficits due to radiation induced damage of the hippocampus. Therefore, minimizing hippocampal dose to the least possible level is of high clinical relevance. In dual-arc conventional volumetric modulated arc therapy (dac-VMAT), the large irradiation field for whole brain planned target volume (PTV) requires a wide jaw opening in which substantial low dose volume to the hippocampus may be produced due to suboptimal multi-leaf collimator (MLC) movements. The present study investigates the potential of a radiation therapy technique with split-arc and reduced field size, namely split-arc partial-field volumetric modulated arc therapy (sapf-VMAT) to spare the hippocampus during WBRT.

METHODS

Computed tomography and magnetic resonance images of 20 patients with brain metastases were retrieved in this retrospective planning study. The hippocampus was manually delineated by single radiation oncologist strictly following the RTOG 0933 atlas definition. Plans delivering 30 Gy in 10 fractions were generated for each patient using dac-VMAT and sapf-VMAT. Dosimetric parameters from both techniques were compared by paired t-test.

RESULTS

The results demonstrated that radiation dose to the hippocampus was significantly reduced using sapf-VMAT relative to dac-VMAT plans. sapf-VMAT (7.86Gy, p = 0.001) had significantly lowered average D_100% compared to dac-VMAT (9.23 Gy). Decrease in hippocampus D_max using sapf-VMAT (13.23 Gy, p = 0.001) was statistically significant when compared to dac-VMAT (16.33 Gy). The resulting mean dose to the hippocampus was 9.16 Gy for the for sapf-VMAT. Mean dose of sapf-VMAT was significantly lower than dac-VMAT (10.85 Gy, p < 0.05). In both eyes, sapf-VMAT demonstrated significantly lower D_mean compared to dac-VMAT (p < 0.05). Whole brain PTV coverage was not compromised in both techniques.

CONCLUSION

sapf-VMAT has demonstrated significant dose reduction to the hippocampus and both eyes compared to dac-VMAT.

Dosimetric evaluation of four whole brain radiation therapy approaches with hippocampus and inner ear avoidance and simultaneous integrated boost for limited brain metastases

AIMS

To perform a dosimetric evaluation of four different simultaneous integrated boost whole brain radiotherapy modalities with hippocampus and inner ear avoidance in the treatment of limited brain metastases.

METHODS

Computed tomography/magnetic resonance imaging data of 10 patients with limited (1-5) brain metastases were used to replan step-and-shoot intensity-modulated radiotherapy (sIMRT), dynamic intensity-modulated radiation therapy (dIMRT), volumetric-modulated arc therapy (VMAT), and helical tomotherapy (Tomo). The prescribed doses of 40-50 Gy in 10 fractions and 30 Gy in 10 fractions were simultaneously delivered to the metastatic lesions and the whole-brain volume, respectively. The hippocampal dose met the RTOG 0933 criteria for hippocampal avoidance (Dmax ≤17 Gy, D100% ≤10 Gy). The inner ear dose was restrained to Dmean ≤15 Gy. Target coverage (TC), homogeneity index (HI), conformity index (CI), maximum dose (Dmax), minimum dose (Dmin) and dose to organs at risk (OARs) were compared.

RESULTS

All plans met the indicated dose restrictions. The mean percentage of planning target volume of metastases (PTVmets) coverage ranged from 97.1 to 99.4%. For planning target volume of brain (PTVbrain), Tomo provided the lowest average D2% (37.5 ± 2.8 Gy), the highest average D98% (25.2 ± 2.0 Gy), and the best TC (92.6% ± 2.1%) and CI (0.79 ± 0.06). The two fixed gantry IMRT modalities (step and shot, dynamic) provided similar PTVbrain dose homogeneity (both 0.76). Significant differences across the four approaches were observed for the maximum and minimum doses to the hippocampus and the maximum doses to the eyes, lens and optic nerves.

CONCLUSION

All four radiotherapy modalities produced acceptable treatment plans with good avoidance of the hippocampus and inner ear. Tomo obtained satisfactory PTVbrain coverage and the best homogeneity index.

TRIAL REGISTRATION

Clinicaltrials.gov, NCT03414944 . Registered 29 January 2018.

Dosimetric Comparison of Four Volumetric-Modulated Arc Therapy Beam Arrangements Utilized for Hippocampal-Sparing Whole-Brain Radiation Therapy

PURPOSE

In the present study, the performance of four VMAT beam arrangements used for hippocampal-sparing whole-brain radiation therapy is addressed.

MATERIAL AND METHODS

Data corresponding to 20 patients were utilized so as to generate plans for every beam configuration. A preliminary study was conducted to assess the optimal distance between optimization structures (PTVx) and hippocampi. V25, V30, D50%, D2%, D98%, homogeneity index (HI) and Paddick conformity factor (CF) were evaluated for PTV. D100% and Dmax were considered for hippocampi. All plans were required to perform at least as recommended in RTOG 0933 trial regarding organs at risk (OAR) sparing and PTV objectives.

RESULTS

Considerable hippocampi sparing alongside with a reasonably low decrease in PTV coverage was achieved using a 7 mm distance between hippocampi and PTV optimization structure. Beam setup 3 (comprised of two full arcs with 0° couch angle and two half arcs with 90° couch angle) achieved the best PTV coverage, HI and CF, while it performed the second-best sparing in hippocampi and lenses. Moreover, beam setup 3 was the second-fastest treatment, although it resulted in the highest number of delivered MU among all beam setups. Beam setup 1 (comprised of two full arcs with no couch angles) was the fastest and it delivered a significantly less amount of monitor units compared with the other beam setups evaluated. Furthermore, a higher robustness was obtained by using no couch angles. Although beam setup 1 was the least optimal considering OAR sparing, it still performed better than required in the RTOG 0933 trial.

CONCLUSIONS

Overall, beam setup 3 was considered to be the best. It is worth mentioning that, apart from our results, the election of one of these beam arrangements might be dependent on the amount of patient workload at a specific institution.

Dosimetric and radiobiological comparison in different dose calculation grid sizes between Acuros XB and anisotropic analytical algorithm for prostate VMAT

To investigate feasible treatment planning parameters, we aimed to evaluate the dosimetric and radiobiological impact of the dose calculation algorithm and grid size in the volumetric modulated arc therapy (VMAT) plan for prostate cancer. Twenty patients were selected, and the treatment plans were initially generated with anisotropic analytical algorithm (AAA) and recalculated with Acuros XB (AXB) algorithm. Various dose grids were used for AXB (1, 2, and 3 mm) and AAA (1, 3, and 5 mm) plan. Dosimetric parameters such as homogeneity index (HI) and conformity index (CI), and radiobiological parameters such as tumor control probability (TCP) and normal tissue complication probability (NTCP) were calculated. Significant differences were observed in the planning target volume (PTV) coverage between both algorithms, and the V95%, HI, and CI of AAA were significantly affected by grid (p < 0.01). On 1 mm grid, the mean rectal dose difference between both algorithms was 2.87% of the prescription dose (p < 0.01), which was the highest among the critical organs. The TCP and NTCP of the AAA were higher than those of AXB (p < 0.01). Compared to AXB with 1 mm grid, the 2 mm grid showed comparable dose calculation accuracy with short calculation time. This study found that the PTV and rectum show significant differences according to dose calculation algorithm and grid. Considering the dose calculation performance for heterogeneous area, we recommend AXB with 2 mm grid for improving treatment efficiency of prostate VMAT.

Comparison of four techniques for spine stereotactic body radiotherapy: Dosimetric and efficiency analysis

PURPOSE

The aim of this study is to compare the dosimetric differences between four techniques for spine stereotactic body radiotherapy (SBRT): CyberKnife (CK), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) with dynamic jaws (HT-D) and fixed jaws (HT-F).

MATERIALS/METHODS

Data from 10 patients were utilized. All patients were planned for 24 Gy in two fractions, with the primary objectives being: (a) restricting the maximum dose to the cord to ≤ 17 Gy and/or cauda equina to ≤ 20 Gy, and (b) to maximize the clinical target volume (CTV) to receive the prescribed dose. Treatment plans were generated by separate dosimetrists and then compared using velocity AI. Parameters of comparison include target volume coverage, conformity index (CI), gradient index (GI), homogeneity index (HI), treatment time (TT) per fraction, and monitor units (MU) per fraction.

RESULTS

PTV D2 and D5 were significantly higher for CK compared to VMAT, HT-F, and HT-D (P < 0.001). The average volume of CTV receiving the prescription dose (CTV D95) was significantly less for VMAT compared to CK, HT-F and HT-D (P = 0.036). CI improved for CK (0.69), HT-F (0.66), and HT-D (0.67) compared to VMAT (0.52) (P = 0.013). CK (41.86) had the largest HI compared to VMAT (26.99), HT-F (20.69), and HT-D (21.17) (P < 0.001). GI was significantly less for CK (3.96) compared to VMAT (6.76) (P = 0.001). Likewise, CK (62.4 min, 14059 MU) had the longest treatment time and MU per fraction compared to VMAT (8.5 min, 9764 MU), HT-F (13 min, 10822 MU), and HT-D (13.5 min, 11418 MU) (P < 0.001).

CONCLUSION

Both CK and HT plans achieved conformal target coverage while respecting cord tolerance. Dose heterogeneity was significantly larger in CK. VMAT required the least treatment time and MU output, but had the least steep GI, CI, and target coverage.

Assessment of multi-criteria optimization (MCO) for volumetric modulated arc therapy (VMAT) in hippocampal avoidance whole brain radiation therapy (HA-WBRT)

This study compared the dosimetric performance of (a) volumetric modulated arc therapy (VMAT) with standard optimization (STD) and (b) multi‐criteria optimization (MCO) to (c) intensity modulated radiation therapy (IMRT) with MCO for hippocampal avoidance whole brain radiation therapy (HA‐WBRT) in RayStation treatment planning system (TPS). Ten HA‐WBRT patients previously treated with MCO‐IMRT or MCO‐VMAT on an Elekta Infinity accelerator with Agility multileaf collimators (5‐mm leaves) were re‐planned for the other two modalities. All patients received 30 Gy in 15 fractions to the planning target volume (PTV), namely, PTV30 expanded with a 2‐mm margin from the whole brain excluding hippocampus with margin. The patients all had metastatic lesions (up to 12) of variable sizes and proximity to the hippocampus, treated with an additional 7.5 Gy from a simultaneous integrated boost (SIB) to PTV37.5. The IMRT plans used eight to eleven non‐coplanar fields, whereas the VMAT plans used two coplanar full arcs and a vertex half arc. The averaged target coverage, dose to organs‐at‐risk (OARs) and monitor unit provided by the three modalities were compared, and a Wilcoxon signed‐rank test was performed. MCO‐VMAT provided statistically significant reduction of D100 of hippocampus compared to STD‐VMAT, and Dmax of cochleas compared to MCO‐IMRT. With statistical significance, MCO‐VMAT improved V30 of PTV30 by 14.2% and 4.8%, respectively, compared to MCO‐IMRT and STD‐VMAT. It also raised D95 of PTV37.5 by 0.4 Gy compared to both MCO‐IMRT and STD‐VMAT. Improved plan quality parameters such as a decrease in overall plan Dmax and total monitor units (MU) were also observed for MCO‐VMAT. MCO‐VMAT is found to be the optimal modality for HA‐WBRT in terms of PTV coverage, OAR sparing and delivery efficiency, compared to MCO‐IMRT or STD‐VMAT.

Converting Treatment Plans From Helical Tomotherapy to L-Shape Linac: Clinical Workflow and Dosimetric Evaluation

This work evaluated a commercial fallback planning workflow designed to provide cross-platform treatment planning and delivery. A total of 27 helical tomotherapy intensity-modulated radiotherapy plans covering 4 anatomical sites were selected, including 7 brain, 5 unilateral head and neck, 5 bilateral head and neck, 5 pelvis, and 5 prostate cases. All helical tomotherapy plans were converted to 7-field/9-field intensity-modulated radiotherapy and volumetric-modulated radiotherapy plans through fallback dose-mimicking algorithm using a 6-MV beam model. The planning target volume (PTV) coverage ( D₁, D₉₉, and homogeneity index) and organs at risk dose constraints were evaluated and compared. Overall, all 3 techniques resulted in relatively inferior target dose coverage compared to helical tomotherapy plans, with higher homogeneity index and maximum dose. The organs at risk dose ratio of fallback to helical tomotherapy plans covered a wide spectrum, from 0.87 to 1.11 on average for all sites, with fallback plans being superior for brain, pelvis, and prostate sites. The quality of fallback plans depends on the delivery technique, field numbers, and angles, as well as user selection of structures for organs at risk. In actual clinical scenario, fallback plans would typically be needed for 1 to 5 fractions of a treatment course in the event of machine breakdown. Our results suggested that <1% dose variance can be introduced in target coverage and/or organs at risk from fallback plans. The presented clinical workflow showed that the fallback plan generation typically takes 10 to 20 minutes per case. Fallback planning provides an expeditious and effective strategy for transferring patients cross platforms, and minimizing the untold risk of a patient missing treatment(s).

Comparison of Volumetric Modulated Arc Therapy and Intensity Modulated Radiation Therapy for Whole Brain Hippocampal Sparing Treatment Plans Based on Radiobiological Modeling

INTRODUCTION

In this article, we report the results of our investigation on comparison of radiobiological aspects of treatment plans with linear accelerator-based intensity-modulated radiation therapy and volumetric-modulated arc therapy for patients having hippocampal avoidance whole-brain radiation therapy.

MATERIALS AND METHODS

In this retrospective study using the dose-volume histogram, we calculated and compared biophysical indices of equivalent uniform dose, tumor control probability, and normal tissue complication probability (NTCP) for 15 whole-brain radiotherapy patients.

RESULTS AND DISCUSSIONS

Dose-response models for tumors and critical structures were separated into two groups: mechanistic and empirical. Mechanistic models formulate mathematically with describable relationships while empirical models fit data through empirical observations to appropriately determine parameters giving results agreeable to those given by mechanistic models.

CONCLUSIONS

Techniques applied in this manuscript could be applied to any other organs or types of cancer to evaluate treatment plans based on radiobiological modeling.

Radiological distribution of brain metastases and its implication for the hippocampus avoidance in whole brain radiotherapy approach

OBJECTIVE

Hippocampus avoidance in whole brain radiotherapy (HA-WBRT) offers the feasibility of less-impaired cognitive function than conventional WBRT. The study aims to assess the radiological distribution of brain metastases (BMs) with relation to the hippocampus and peri-hippocampus region as defined by the RTOG 0933 for better understanding of margin definition in HA-WBRT treatment planning.

METHODS

Consecutive patients with diagnosis of BM from enhanced MRI between March 2011 and July 2016 were analysed. The pre-treatment T₁ weighted, T₂ weighted, T₂ flair, three-dimensional spoiled gradient axial and contrast-enhanced axial cranial MR images of 226 patients are examined. The closest distances between the edge of hippocampus and the margin of tumours on different planes were measured.

RESULTS

A total of 226 patients with 1080 visible metastatic sites were reviewed. The origin of the primary tumors was in 72.6% lung (n = 164), in 45 cases (19.9%) breast cancer and in 7.5% other malignancies (n = 17). There were 758 (70.2%) lesions situated beyond the tentorium. The median size of single lesion was 13.9 ± 14.7 mm. Impossible, it seems that more of the patients are with only one lesion, to verify. The hippocampus involvement was found in 3.1% (n = 7, 95% CI 0.01-0.05) within 5 mm, 5.7% (n = 13, 95% CI 0.03-0.09) within 10mm and 8.4% (n = 19, 95% CI 0.05-0.12) within 20 mm. In multivariate analysis, the number 6 BM or higher was found to be an independent risk factor for hippocampal involvement (HI) (OR: 5.2, 5.38 and 3.84 in 5, 10 and 20 mm).

CONCLUSION

This radiological study found that the incidence of hippocampus involvement is low in patients with BM. HA-WBRT can be delivered under the context of complete radiological diagnosis after careful delineation, proper margin definition and individual planning optimization. Advances in knowledge: The incidence of HI in patients with initial diagnosis of BM from solid tumours impacts the radiotherapeutic decision. Our radiological data analysed the incidence of HI not only to the conventional 5 mm margin definition, but also expanded to wider margins as 10 and 20 mm from hippocampus, which will help the treatment planning optimization with different technique.

Perihippocampal metastasis following hippocampus-avoiding prophylactic cranial irradiation for small cell lung cancer: a case report

Prophylactic cranial irradiation (PCI) lowers the risk of brain metastasis (BM) and increases survival in small cell lung cancer (SCLC) patients, but it also entails a risk of neurocognitive dysfunction (NCD). One strategy to mitigate this neurotoxicity is hippocampus-avoiding (HA) whole-brain radiation therapy, as the hippocampus is mainly responsible for radiation-related NCD and hippocampal or perihippocampal metastases are rare. A few prospective clinical trials have demonstrated a reduction in NCD following HA whole-brain radiation therapy. The 59-year-old male patient described in this report had limited-stage SCLC and a complete response to thoracic chemoradiotherapy. Seven months after receiving HA-PCI of 25 Gy in 10 fractions using intensity-modulated radiation therapy, a 36 mm solitary metastasis was detected in the right perihippocampal region. The mass was surgically removed but the patient died 2 months later. The development of a solitary HA region metastasis is uncommon, considering that metastasis in this area usually occurs in patients with high numbers of BMs. Our case demonstrates the need for further validation of HA-PCI for SCLC patients in terms of both neurocognitive protection and the absence of compromise in terms of BM prevention.

Clinical features of brain metastases in breast cancer: an implication for hippocampal-sparing whole-brain radiation therapy

Objective

The objectives of this study were to describe the distribution of brain metastases (BM) in breast cancer patients and investigate the risk factors for perihippocampal metastases (PHM).

Patients and methods

Retrospective analysis of the clinicopathological characteristics and patterns of BM was performed. Associations between clinicopathological characteristics and PHM (the hippocampus plus 5 mm margin) were evaluated using logistic regression analyses.

Results

A total of 1,356 brain metastatic lesions were identified in 192 patients. Patients with 1–3 BM, 4–9 BM, and ≥10 BM accounted for 63.0%, 18.8%, and 18.2%, respectively. There were only 7 (3.6%) patients with hippocampal metastases (HM) and 14 (7.3%) patients with PHM. On logistic regression, the number of BM was an independent risk factor for PHM. Patients with ≥10 BM had a significantly higher risk of PHM compared with those with <10 BM. Breast cancer subtype (BCS) was not associated with PHM. The number of BM was significantly correlated with various BCSs. Patients with hormone receptor (HR)+/human epidermal growth factor receptor 2 (HER2)+, HR−/HER2+, and HR−/HER2− subtypes had a higher probability of ≥10 BM, relative to patients with an HR+/HER2− subtype.

Conclusion

Our study suggests that a low incidence of PHM may be acceptable to perform hippocampal-sparing whole-brain radiation therapy for breast cancer patients. Patients with extensive diffuse metastases (≥10 BM) were associated with higher odds of PHM.

Distribution of metastatic disease in the brain in relation to the hippocampus: a retrospective single-center analysis of 6064 metastases in 632 patients

This study aimed to investigate the patterns of brain metastasis and to explore the risk factors affecting hippocampus metastasis (HM). We retrospectively analyzed the clinical information of patients with metastatic disease in the brain. The associations between clinicopathologic variables with HM and peri-hippocampal metastasis (PHM) were evaluated in univariate and multivariate regression analyses. A total of 632 patients with 6064 metastatic lesions were recruited into the present study. Of these, 4.1% (26/632) of patients developed HM, and 5.5% (35/632) of patients developed PHM. Only 0.5% (31/6064) of metastatic lesions were located in the hippocampus and 0.6% (37/6064) were in the PHM. Age ≤60 years was an independent risk factor for HM (odds ratio [OR]: 2.602, 95% confidence interval [CI]: 1.115–6.076, P = 0.027) and PHM (OR: 2.555, 95%CI: 1.229–5.310, P = 0.012) in univariate and multivariate analyses. The hippocampus is a rare site of brain metastasis. Younger patients (age ≤60 years) had increased risk of developing HM and PHM. The current study provides the opportunity to investigate the clinical feasibility of hippocampal sparing whole brain radiation therapy, especially in older patients.

Hippocampal-Sparing Whole-Brain Radiotherapy for Lung Cancer

Brain metastases occur in 20% to 40% of lung cancer patients. Whole-brain radiotherapy (WBRT) has long been considered the treatment of choice for many patients with lung cancer, because of its wide availability, ease of delivery, and effectiveness in prolonging survival. However, WBRT is also associated with several side effects, such as decline in memory and other cognitive functions. There exists significant preclinical and clinical evidence that radiation-induced injury to the hippocampus correlates with neurocognitive decline of patients who receive WBRT. Technological advances in treatment planning and delivery facilitate the use of hippocampal-sparing (HS) WBRT as prophylactic cranial irradiation or the primary treatment modality for lung cancer patients with brain metastases. In this review, we provide a detailed and comprehensive discussion of the safety profile, techniques for hippocampus-sparing, and the clinical evidence of HS-WBRT for lung cancer patients.

Improvement of dose homogeneity with irregular surface compensator in whole brain radiotherapy

Purpose

The aim of this study was to evaluate the dosimetric aspects of whole brain radiotherapy (WBRT) using an irregular surface compensator (ISC) in contrast to conventional radiotherapy techniques.

Methods

Treatment plans were devised for 20 patients. The Eclipse treatment planning system (Varian Medical Systems) was used for dose calculation. For the ISC, a fluence editor application was used to extend the range of optimal fluence. The treatment plan with the ISC was compared with the conventional technique in terms of doses in the planning target volume (PTV), dose homogeneity index (DHI), three-dimensional (3D) maximum dose, eye and lens doses and monitor unit (MU) counts required for treatment.

Results

Compared with conventional WBRT, the ISC significantly reduced the DHI, 3D maximum dose and volumes receiving 105% of the prescription dose, in addition to reducing both eye and lens doses (p<0·05 for all comparisons). In contrast, MU counts were higher for the ISC technique than for conventional WBRT (828 versus 328, p<0·01).

Conclusion

The ISC technique for WBRT considerably improved the dose homogeneity in the PTV. As patients who receive WBRT have improved survival, the long-term side effects of radiotherapy are highly important.

Monitoring cancer stem cells: insights into clinical oncology

Cancer stem cells (CSCs) are a small, characteristically distinctive subset of tumor cells responsible for tumor initiation and progression. Several treatment modalities, such as surgery, glycolytic inhibition, driving CSC proliferation, immunotherapy, and hypofractionated radiotherapy, may have the potential to eradicate CSCs. We propose that monitoring CSCs is important in clinical oncology as CSC populations may reflect true treatment response and assist with managing treatment strategies, such as defining optimal chemotherapy cycles, permitting pretreatment cancer surveillance, conducting a comprehensive treatment plan, modifying radiation treatment, and deploying rechallenge chemotherapy. Then, we describe methods for monitoring CSCs.

A prospective study on neurocognitive effects after primary radiotherapy in high-grade glioma patients

BACKGROUND

Neurocognition is a very important aspect of a brain tumor patient's quality of life following radiotherapy. The aim of the present study was to assess neurocognitive functions of patients diagnosed with high-grade gliomas undergoing radiotherapy by using the NeuroCogFx(®) test and to examine relevant dose/volume parameters as well as patient characteristics potentially influencing the neurological baseline status and subsequent outcome.

METHODS

The cohort consisted of 44 astrocytoma World Health Organization grade III/IV patients. The NeuroCogFx(®) test was carried out on patients during (N = 44) and after (N = 21) irradiation. The test examines verbal/figural/short-term/working memory, psychomotorical speed, selective attention and verbal speed. The results were compared with regular patient and treatment data with an emphasis on the dose applied to the hippocampus.

RESULTS

Overall there were only slight changes in the median test results when comparing the baseline to the follow-up tests. In the 'verbal memory test' lower percentile ranks were achieved in left-sided tumors compared to right-sided tumors (p = 0.034). Dexamethasone intake during radiotherapy was significantly correlated with the difference between the two test batteries. Concerning figural memory, a correlation was detected between decreased figural recognition and the radiation dose to the left hippocampus (p = 0.045).

CONCLUSION

We conclude that tumor infiltration of the hippocampus has an impact on neurocognitive function. However, treatment with radiotherapy seems to have less influence on cognitive outcome than expected.