Stereotactic radiosurgery versus stereotactic radiotherapy for patients with vestibular schwannoma: a Leksell Gamma Knife Society 2000 debate

Executive summary from American Radium Society's appropriate use criteria on neurocognition after stereotactic radiosurgery for multiple brain metastases

BACKGROUND

The American Radium Society (ARS) Appropriate Use Criteria brain malignancies panel systematically reviewed (PRISMA [Preferred Reporting Items for Systematic Reviews and Meta-Analyses]) published literature on neurocognitive outcomes after stereotactic radiosurgery (SRS) for patients with multiple brain metastases (BM) to generate consensus guidelines.

METHODS

The panel developed 4 key questions (KQs) to guide systematic review. From 11 614 original articles, 12 were selected. The panel developed model cases addressing KQs and potentially controversial scenarios not addressed in the systematic review (which might inform future ARS projects). Based upon quality of evidence, the panel confidentially voted on treatment options using a 9-point scale of appropriateness.

RESULTS

The panel agreed that SRS alone is usually appropriate for those with good performance status and 2-10 asymptomatic BM, and usually not appropriate for >20 BM. For 11-15 and 16-20 BM there was (between 2 case variants) agreement that SRS alone may be appropriate or disagreement on the appropriateness of SRS alone. There was no scenario (among 6 case variants) in which conventional whole-brain radiotherapy (WBRT) was considered usually appropriate by most panelists. There were several areas of disagreement, including: hippocampal sparing WBRT for 2-4 asymptomatic BM; WBRT for resected BM amenable to SRS; fractionated versus single-fraction SRS for resected BM, larger targets, and/or brainstem metastases; optimal treatment (WBRT, hippocampal sparing WBRT, SRS alone to all or select lesions) for patients with progressive extracranial disease, poor performance status, and no systemic options.

CONCLUSIONS

For patients with 2-10 BM, SRS alone is an appropriate treatment option for well-selected patients with good performance status. Future study is needed for those scenarios in which there was disagreement among panelists.

Study on the Appropriate Timing of Postoperative Adaptive Radiotherapy for High-Grade Glioma

PURPOSE

To investigate the appropriate timing of adaptive radiotherapy (ART) for high-grade glioma.

METHODS

Ten patients with high-grade gliomas were selected and underwent CT/MRI (CT1/MRI1, CT2/MRI2, CT3/MRI3, and CT4/MRI4) scans before RT and during 10-, 20- and 30-fraction RT, and the corresponding RT plans (plan1, plan2, plan3 and plan4) were made. The dose of the initial plan (plan1) was projected to CT2 and CT3 using the image registration technique to obtain the projection plans (plan1-2 and plan1-3) and by superimposing the doses to obtain the ART plans (plan10+20 and plan20+10), respectively. The dosimetric differences in the target volume and organs at risk (OARs) were compared between the projection and adaptive plans. The tumor control probability (TCP) for the planning target volume (PTV) and normal tissue complication probability (NTCP) for the OARs were compared between the two adaptive plans.

RESULTS

Compared with the projection plan, the D2 to the PTV of ART decreased, the conformity index (CI) to the PTV increased, and the D2/Dmean to the brainstem, optic chiasm and pituitary, as well as the V20, V30, V40 and V50 to the normal brain decreased. The D2 to the pituitary and optic chiasm as well as the V20, V30, V40 and V50 to the normal brain in plan10+20 were lower than those in plan20+10, while the CI to the PTV was higher than that in plan20+10. The TCP of the PTV in plan10+20 was higher than that in plan20+10.

CONCLUSION

ART can improve the precision of target volume irradiation and reduce the irradiation dose to the OARs in high-grade glioma. The time point after 10 fractions of RT is appropriate for ART.

Single isocenter treatment planning techniques for stereotactic radiosurgery of multiple cranial metastases

•

DCA in most cases is superior to VMAT for multi metastases single isocenter SRS.

•

Normal brain V_12Gy was significantly reduced with DCA, predicting for lower S-NEC.

•

Maximum doses to critical organs-at-risk were significantly lower with DCA.

•

Conformity was comparable between VMAT and DCA.

Background and purpose

Whole brain radiation therapy use has decreased in favor of stereotactic radiosurgery (SRS) for the treatment of multiple brain metastases due to reduced neurotoxicity. Here we compare two single isocenter radiosurgery planning techniques, volumetric modulated arc therapy (VMAT) and dynamic conformal arcs (DCA) in terms of their dosimetric and delivery performance.

Materials and methods

Sixteen patients with 2– 18 brain metastases (total 103; median 4) previously treated with single fraction SRS were replanned for multiple lesion single isocenter treatments using VMAT and DCA using different treatment planning systems for each and three different plan geometries for DCA. Plans were evaluated using the Paddick conformity index, normal tissue V_12Gy, the probability for symptomatic brain necrosis (S-NEC), maximum organ-at-risk (OAR) point doses, and total number of monitor units (MU).

Results

Conformity was not significantly different between VMAT and DCA plans. VMAT plans showed a trend towards higher MU with a median difference between 18% and 24% (p ≤ 0.09). Median V_12Gy differences were 7.0 cm³–8.6 cm³ favoring DCA plans (p < 0.01). VMAT plans had median excess absolute and relative S-NEC risks compared to DCA plans of 8%–10% and 25%–31%, respectively (p < 0.01). Moreover for VMAT compared to DCA, maximum OAR doses were significantly higher for the brainstem (1.9 Gy; p < 0.01), chiasm (0.5 Gy; p ≤ 0.02), and optic nerves (0.5 Gy; p ≤ 0.04).

Conclusions

In most cases DCA plans were found to be dosimetrically superior to VMAT plans with reduced V_12Gy and associated risk for S-NEC. Maximum doses to important OARs showed significant improvement, increasing the ability for subsequent salvage treatments involving radiation.

Iatrogenic Ocular Surface Diseases Occurring during and/or after Different Treatments for Ocular Tumours

Simple Summary

The ocular surface represents a finely regulated system that allows the protection of the eye. It can be affected by therapies used for the treatment of various intraocular tumours, particularly conjunctival cancers and uveal melanoma. In these conditions, treatments are chosen according to the characteristics of the lesion, and include a combination of selective surgery, anticancer eye drops, and/or radiotherapy delivered through different mechanisms. Possible side effects affecting the ocular surface range from transient dry eye or keratitis up to more severe complications such as corneal melting and perforation. These complications deserve careful evaluation for the risk of permanent sight-threatening sequelae. Physicians involved in the management of patients affected by ocular tumours should be aware of this risk in order to reach an early diagnosis and promptly set up an adequate treatment. The present review summarizes acute and chronic complications affecting the ocular surface following different therapies for the treatment of conjunctival cancers and uveal melanoma, and also reports clinical cases of representative patients who experienced these complications.

Abstract

The ocular surface represents a finely regulated system that allows the protection of the eye. It is particularly susceptible to different treatments for intraocular tumours, such as uveal melanoma and conjunctival cancers. Traditionally, the management of ocular tumours depends on the characteristics of the lesion, and is based on a combination of selective surgery, topical chemotherapy, and/or radiotherapy delivered through different mechanisms (e.g., charged-particle radiotherapy or brachytherapy). Possible complications involving the ocular surface range from transient dry eye disease or keratitis up to corneal melting and perforation, which in any case deserve careful evaluation for the risk of permanent sigh-threatening complications. Clinicians involved in the management of these patients must be aware of this risk, in order to reach an early diagnosis and promptly set up an adequate treatment. The present review of the literature will summarize acute and chronic complications affecting the ocular surface following different therapies for the treatment of ocular tumours.

Repeat stereotactic radiosurgery for progressive vestibular schwannomas after previous radiosurgery: a systematic review and meta-analysis

Vestibular schwannomas (VS) are slow-growing intracranial extraaxial benign tumors, developing from the vestibular part of the eight cranial nerves. Stereotactic radiosurgery (SRS) has now a long-term scientific track record as first intention treatment for small- to medium-sized VS. Though its success rate is very high, SRS for VS might fail to control tumor growth in some cases. However, the literature on repeat SRS after previously failed SRS remains scarce and reported in a low number of series with a limited number of cases. Here, we aimed at performing a systematic review and meta-analysis of the literature on repeat SRS for VS. Using PRISMA guidelines, we reviewed manuscripts published between January 1990 and October 2020 and referenced in PubMed. Tumor control and cranial nerve outcomes were evaluated with separate meta-analyses. Eight studies comprising 194 patients were included. The overall rate of patients treated in repeat SRS series as per overall series with first SRS was 2.2% (range 1.2–3.2%, p < 0.001). The mean time between first and second SRS was 50.7 months (median 51, range 44–64). The median marginal dose prescribed at first SRS was 12 Gy (range 8–24) and at second SRS was 12 Gy (range 9.8–19). After repeat SRS, tumor stability was reported in 61/194 patients, i.e., a rate of 29.6% (range 20.2–39%, I² = 49.1%, p < 0.001). Tumor decrease was reported in 83/194 patients, i.e., a rate of 54.4% (range 33.7–75.1%, I² = 89.1%, p < 0.001). Tumor progression was reported in 50/188 patients, i.e., a rate of 16.1% (range 2.5–29.7%, I² = 87.1%, p = 0.02), rarely managed surgically. New trigeminal numbness was reported in 27/170 patients, i.e., a rate of 9.9% (range 1.4–18.3%, p < 0.02). New facial nerve palsy of worsened of previous was reported in 8/183 patients, i.e., a rate of 4.3% (range 1.4–7.2%, p = 0.004). Hearing loss was reported in 12/22 patients, i.e., a rate of 54.3% (range 24.8–83.8%, I² = 70.7%, p < 0.001). Repeat SRS after previously failed SRS for VS is associated with high tumor control rates. Cranial nerve outcomes remain favorable, particularly for facial nerve. The rate of hearing loss appears similar to the one related to first SRS.

The long-term outcome of CyberKnife-based stereotactic radiotherapy for central skull base meningiomas: a single-center experience

Few reports exist demonstrating the effects of stereotactic radiotherapy (SRT) on the central skull base meningiomas (CSMs). A retrospective analysis of 113 patients was performed. The median age was 62 (IQR 50-72) years old, and 78 patients (69%) were female. Upfront SRT was performed in 41 (36%), where 17 (15%) patients were asymptomatic. The other SRT was for postoperative adjuvant therapy in 32 (28%), and for the recurrent or relapsed tumors in 40 (35%) patients. Previous operation was done in 74 patients (66%). Among the available pathology in 46 patients, 37 (80%) were WHO grade I, 8 (17%) were grade II, and 1 (2%) was grade III. The median prescribed dose covered 95% of the planning target volume was 25 (IQR 21-25) Gy, and the median target volume was 9.5 (IQR 3.9-16.9) cm³. The median progression-free survival (PFS) was 48 (IQR 23-73) months and 84% and 78% were free of tumor progression at 5 and 10 years respectively. The median follow-up was 49 (IQR 28-83) months. PFS was better in grade I than grade II (p = 0.02). No other baseline factors including the history of previous operation were associated with PD or PFS. Adverse events of radiation therapy were radiation-induced optic neuropathy (0.9%), and cerebral edema (4.4%). Asymptomatic cavernous carotid stenosis was found in three (2.7%), five (4.4%) underwent ventriculoperitoneal shunt placement for normal pressure hydrocephalus, and five (4.4%) died. SRT is useful for the management of CSMs with a low rate of adverse events.

Dosimetric comparison of volumetric modulated arc therapy (VMAT) and high-dose-rate brachytherapy (HDR-BT) for superficial skin irradiation with significant curvature in one or more planes

PURPOSE

This study compares the plan quality of high-dose-rate brachytherapy (HDR-BT) and volumetric modulated arc therapy (VMAT) for superficial irradiation of large areas of skin with significant curvature in one or more planes.

METHODS

A total of 14 patients from two centres previously treated with either HDR-BT or VMAT were retrospectively replanned using the alternative technique. Sites included scalp and lower limbs. Identical computed tomography (CT) scans, clinical target volume (CTV) and organs at risk (OARs) and prescription were used for both techniques. Conformity, skin surface dose and OAR doses were compared.

RESULTS

Conformity index was consistently better with VMAT than HDR-BT (p < 0.01). Maximum skin surface dose (D0.1cc) had a higher mean of 49.6 Gy with HDR-BT compared to 31.4 Gy for VMAT (p < 0.01). Significantly smaller volumes of healthy tissue were irradiated with VMAT than with HDR-BT. This can be seen in brain volumes receiving 10, 20 and 30 Gy EQD2 and in extremities receiving 5 and 10 Gy. When close to the volume, the lens received significantly lower doses with VMAT (p < 0.01).

CONCLUSION

In this small sample, VMAT gives equal coverage with lower OAR and skin surface doses than HDR-BT for both scalp and extremities. VMAT is a useful technique for treating large, superficial volumes with significant curvature in one or more planes.

Radiosurgery-Based AVM Scale Is Proposed for Combined Embolization and Gamma Knife Surgery for Brain Arteriovenous Malformations

Background and purpose: To evaluate whether a radiosurgery-based arteriovenous malformation (AVM) scale (RBAS) could be used to predict obliteration of brain arteriovenous malformations (bAVMs) supposed for combined endovascular embolization (EMB) and gamma knife surgery (GKS) treatment. Methods: bAVM patients who underwent GKS with or without previous EMB from January 2011 to December 2016 at our institution were retrospectively reviewed. The patients were categorized into a combined treatment group and a GKS group. A 1:1 propensity score matching (PSM) was used to match the two groups. Pre-EMB and pre-GKS RBAS were assessed for every patient. Multivariate analysis was performed to find factors associated with complete obliteration in the combined treatment group. Survival analysis based on sub-groups according to RBAS was performed to compare obliteration rate and find cutoffs for appropriate treatment modalities. Results: A total of 96 patients were involved, and each group comprised 48 patients. There was no difference between the two groups in terms of obliteration rate (75.0 vs. 83.3%, p = 0.174). Pre-EMB RBAS (p = 0.010) and the number of feeding arteries (p = 0.014) were independent factors associated with obliteration rate in the combined treatment group. For the combined treatment patients, sub-group analysis according to pre-EMB RBAS (score <1.0, 1.0-1.5, and >1.5) showed statistical difference in obliteration rate (p = 0.002). Sub-group analysis according to RBAS between the two groups showed that the obliteration rate of the GKS group is significantly higher than the combined group when RBAS >1.5 (47.4 vs. 66.7%, p = 0.036). Conclusions: The RBAS is proposed to be efficient in predicting obliteration of bAVMs supposed to receive combined EMB and GKS treatment. Patients with RBAS >1.5 are inclined to be more suitable for GKS instead of the combined treatment.

Long-term disease control and treatment outcomes of stereotactic radiosurgery in cavernous sinus meningiomas

BACKGROUND

Most of the current knowledge on the clinical effects of stereotactic radiosurgery (SRS) on the treatment of cavernous sinus meningiomas (CSM) is based on series with limited follow-up. However, determining the role of radiation in a tumor with slow disease progression such as CSM necessitates long term follow up.

OBJECTIVE

To review and pool metadata in the literature to determine the long-term outcomes of SRS with respect to clinical and radiographic tumor control of CSM.

METHODS

A systematic search was conducted following MOOSE guidelines. Results were screened against predefined criteria, which excluded studies with a median follow-up less than 5 years. The incidences of each outcome were calculated using random-effects metanalysis of proportions.

RESULTS

Seven studies met the inclusion criteria, comprising 645 patients. The median follow-up was 74 months (range 62-87). Progression-free-survival at 5, 10, and 15 years was 93.4% (95% CI 89.1-96.7%), 84.9% (95% CI 77-91.4%), and 81.3% (95% CI 74-87.7%), respectively. Clinical response to SRS at last follow-up defined as improvement of cranial nerve deficits was found in in 36.4% (95% CI 26.3-47.1%) of patients, while worsening or onset of new cranial nerve deficits was found in 11.5% (95% CI 7.9-15.7%). Radiological regression was found in 57.8% (95% CI 43-71.8%), while tumor progression was found in 8.5% (95% CI 5.2-12.6%).

CONCLUSION

SRS achieves excellent disease control and radiographic response in CSM. Although the risk of long-term cranial neuropathies is minimal, it is relatively higher to what has been previously reported in early series with limited follow-up.

Commissioning cranial single-isocenter multi-target radiosurgery for the Versa HD

PURPOSE

Brainlab's Elements Multiple Brain Mets SRS (MBMS) is a dedicated treatment planning system for single-isocenter multi-target (SIMT) cranial stereotactic radiosurgery (SRS) treatments. The purpose of this study is to present the commissioning experience of MBMS on an Elekta Versa HD.

METHODS

MBMS was commissioned for 6 X, 6 FFF, and 10 FFF. Beam data collected included: output factors, percent depth doses (PDDs), diagonal profiles, collimator transmission, and penumbra. Beam data were processed by Brainlab and resulting parameters were entered into the planning system to generate the beam model. Beam model accuracy was verified for simple fields. MBMS plans were created on previously treated cranial SRS patient data sets. Plans were evaluated using Paddick inverse conformity (ICI), gradient indices (GI), and cumulative volume of brain receiving 12 Gy. Dosimetric accuracy of the MBMS plans was verified using microDiamond, Gafchromic film, and SRS Mapcheck measurements of absolute dose and dose profiles for individual targets. Finally, an end-to-end (E2E) test was performed with a MR-CT compatible phantom to validate the accuracy of the simulation-to-delivery process.

RESULTS

For square fields, calculated scatter factors were within 1.0% of measured, PDDs were within 0.5% past dmax, and diagonal profiles were within 0.5% for clinically relevant off-axis distances (<10 cm). MBMS produced plans with ICIs < 1.5 and GIs < 5.0 for targets > 10 mm. Average point doses of the MBMS plans, measured by microDiamond, were within 0.31% of calculated (max 2.84%). Average per-field planar pass rates were 98.0% (95.5% minimum) using a 2%/1 mm/10% threshold relative gamma analysis. E2E point dose measurements were within 1.5% of calculated and Gafchromic film pass rates were 99.6% using a 5%/1 mm/10% threshold gamma analysis.

CONCLUSION

The experience presented can be used to aid the commissioning of the Versa HD in the Brainlab MBMS treatment planning system, to produce safe and accurate SIMT cranial SRS treatments.

Knowledge Models as Teaching Aid for Training Intensity Modulated Radiation Therapy Planning: A Lung Cancer Case Study

Purpose: Artificial intelligence (AI) employs knowledge models that often behave as a black-box to the majority of users and are not designed to improve the skill level of users. In this study, we aim to demonstrate the feasibility that AI can serve as an effective teaching aid to train individuals to develop optimal intensity modulated radiation therapy (IMRT) plans.

Methods and Materials: The training program is composed of a host of training cases and a tutoring system that consists of a front-end visualization module powered by knowledge models and a scoring system. The current tutoring system includes a beam angle prediction model and a dose-volume histogram (DVH) prediction model. The scoring system consists of physician chosen criteria for clinical plan evaluation as well as specially designed criteria for learning guidance. The training program includes six lung/mediastinum IMRT patients: one benchmark case and five training cases. A plan for the benchmark case is completed by each trainee entirely independently pre- and post-training. Five training cases cover a wide spectrum of complexity from easy (2), intermediate (1) to hard (2). Five trainees completed the training program with the help of one trainer. Plans designed by the trainees were evaluated by both the scoring system and a radiation oncologist to quantify planning quality.

Results: For the benchmark case, trainees scored an average of 21.6% of the total max points pre-training and improved to an average of 51.8% post-training. In comparison, the benchmark case's clinical plans score an average of 54.1% of the total max points. Two of the five trainees' post-training plans on the benchmark case were rated as comparable to the clinically delivered plans by the physician and all five were noticeably improved by the physician's standards. The total training time for each trainee ranged between 9 and 12 h.

Conclusion: This first attempt at a knowledge model based training program brought unexperienced planners to a level close to experienced planners in fewer than 2 days. The proposed tutoring system can serve as an important component in an AI ecosystem that will enable clinical practitioners to effectively and confidently use KBP.

Successful management of an intraluminal superior sagittal sinus meningioma causing elevated intracranial pressure using gamma knife radiosurgery in subacute setting: A case report

Background:

Gamma Knife stereotactic radiosurgery (GKRS) facilitates precisely focused radiation to an intracranial target while minimizing substantial off-target radiation in the surrounding normal tissue. Meningiomas attached to or invading the superior sagittal sinus may result in sinus occlusion and are often impossible to completely resect safely. The authors describe successful management of a patient with a meningioma located completely inside the posterior aspect of the superior sagittal sinus.

Case Description:

A 46-year-old woman presented to the emergency department with progressive generalized headaches accompanied by worsening vision. The patient underwent a diagnostic brain magnetic resonance imaging which showed a solitary a 7 × 6 × 10 mm homogeneously contrast-enhancing lesion within the lumen of the posterior aspect of superior sagittal sinus without ventricular enlargement or peritumoral edema. The lesion was thought to be a meningioma radiographically. To evaluate the suspected increased intracranial pressure, a lumbar puncture was subsequently performed and demonstrated an opening pressure of 30 cm H2O. After drainage of 40 cc of CSF, the spinal closing pressure was 9 cm H2O. After failure of conservative management with acetazolamide, and determination of surgical inoperability due to the critical intraluminal location of the mass lesion, the patient underwent Gamma Knife radiosurgery. The 0.36 cc tumor was treated as an outpatient in the Perfexion® model Gamma Knife with a highly conformal and selective plan that enclosed the 3D geometry of the tumor with a minimal margin tumor dose of 14 gy at the 50% isodose. Three months after GKRS, the patient reported continued reduction in the frequency and severity of both her headaches and her visual disturbance. Ophthalmological consultation noted progressive resolution of her optic disc edema confirmed by formal optical coherence tomography. The patient is now 3 years out from GKRS with complete resolution of headache symptoms along with persistent reduction in tumor size (3 × 1 × 4 mm) on serial period imaging and resolution of papilledema.

Conclusion:

Tumors located in such critical anatomic regions, as in our patient, should be considered for primary GKRS when the risks of biopsy or removal are too high. GKRS was able to provide great radiographic and clinical result in an intricately located meningioma.

Dosimetric study between a single isocenter dynamic conformal arc therapy technique and Gamma Knife radiosurgery for multiple brain metastases treatment: impact of target volume geometrical characteristics

Purpose

To compare linac-based mono-isocentric radiosurgery with Brainlab Elements Multiple Brain Mets (MBM) SRS and the Gamma Knife using a specific statistical method and to analyze the dosimetric impact of the target volume geometric characteristics. A dose fall-off analysis allowed to evaluate the Gradient Index relevancy for the dose spillage characterization.

Material and methods

Treatments were planned on twenty patients with three to nine brain metastases with MBM 2.0 and GammaPlan 11.0. Ninety-five metastases ranging from 0.02 to 9.61 cc were included. Paddick Index (PI), Gradient Index (GI), dose fall-off, volume of healthy brain receiving more than 12 Gy (V_12Gy) and DVH were used for the plan comparison according to target volume, major axis diameter and Sphericity Index (SI). The multivariate regression approach allowed to analyze the impact of each geometric characteristic keeping all the others unchanged. A parallel study was led to evaluate the impact of the isodose line (IDL) prescription on the MBM plan quality.

Results

For mono-isocentric linac-based radiosurgery, the IDL around 70–75% was the best compromise found. For both techniques, the GI and the dose fall-off decreased with the target volume. In comparison, PI was slightly improved with MBM for targets < 1 cc or SI > 0.78. GI was improved with GP for targets < 2.5 cc. The V_12Gy was higher with MBM for lesions > 0.4 cc or SI < 0.84 and exceeded 10 cc for targets > 5 cc against 6.5 cc with GP. The presence of OAR close to the PTV had no impact on the dose fall off values. The dose fall-off was higher for volumes < 3.8 cc with GP which had the sharpest dose fall-off in the infero-superior direction up to 30%/mm. The mean beam-on time was 94 min with GP against 13 min with MBM.

Conclusions

The dose fall-off and the V_12Gy were more relevant indicators than the GI for the low dose spillage assessment. Both evaluated techniques have comparable plan qualities with a slightly improved selectivity with MBM for smaller lesions but with a healthy tissues sparing slightly favorable to GP at the expense of a considerably longer irradiation time. However, a higher healthy tissue exposure must be considered for large volumes in MBM plans.

Optimizing Adjuvant Stereotactic Radiotherapy of Motor-Eloquent Brain Metastases: Sparing the nTMS-Defined Motor Cortex and the Hippocampus

Brain metastases can effectively be treated with surgical resection and adjuvant stereotactic radiotherapy (SRT). Navigated transcranial magnetic stimulation (nTMS) has been used to non-invasively map the motor cortex prior to surgery of motor eloquent brain lesions. To date, few studies have reported the integration of such motor maps into radiotherapy planning. The hippocampus has been identified as an additional critical structure of radiation-induced deficits. The aim of this study is to assess the feasibility of selective dose reduction to both the nTMS-based motor cortex and the hippocampi in SRT of motor-eloquent brain metastases. Patients with motor-eloquent brain metastases undergoing surgical resection and adjuvant SRT between 07/2014 and 12/2018 were retrospectively analyzed. The radiotherapy treatment plans were retrieved from the treatment planning system (“original” plan). For each case, two intensity-modulated treatment plans were created: the “motor” plan aimed to reduce the dose to the motor cortex, the “motor & hipp” plan additionally reduce the dose to the hippocampus. The optimized plans were compared with the “original” plan regarding plan quality, planning target volume (PTV) coverage, and sparing of organs at risk (OAR). 69 plans were analyzed, all of which were clinically acceptable with no significant differences for PTV coverage. All OAR were protected according to standard protocols. Sparing of the nTMS motor map was feasible: mean dose 9.66 ± 5.97 Gy (original) to 6.32 ± 3.60 Gy (motor) and 6.49 ± 3.78 Gy (motor & hipp), p<0.001. In the “motor & hipp” plan, dose to the ipsilateral hippocampi could be significantly reduced (max 1.78 ± 1.44 Gy vs 2.49 ± 1.87 Gy in “original”, p = 0.003; mean 1.01 ± 0.92 Gy vs. 1.32 ± 1.07 Gy in “original”, p = 0.007). The study confirms the results from previous studies that inclusion of nTMS motor information into radiotherapy treatment planning is possible with a relatively straightforward workflow and can achieve reduced doses to the nTMS-defined motor area without compromising PTV coverage. Furthermore, we demonstrate the feasibility of selective dose reduction to the hippocampus at the same time. The clinical significance of these optimized plans yet remains to be determined. However, with no apparent disadvantages these optimized plans call for further and broader exploration.

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

Background

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

Methods

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

Results

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

Conclusion

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

Accuracy of dose-volume metric calculation for small-volume radiosurgery targets

PURPOSE

For stereotactic radiosurgery (SRS), accurate evaluation of dose-volume metrics for small structures is necessary. The purpose of this study was to compare the DVH metric capabilities of five commercially available SRS DVH analysis tools (Eclipse, Elements, Raystation, MIM, and Velocity).

METHODS

DICOM RTdose and RTstructure set files created using MATLAB were imported and evaluated in each of the tools. Each structure set consisted of 50 randomly placed spherical targets. The dose distributions were created on a 1-mm grid using an analytic model such that the dose-volume metrics of the spheres were known. Structure sets were created for 3, 5, 7, 10, 15, and 20 mm diameter spheres. The reported structure volume, V100% [cc], and V50% [cc], and the RTOG conformity index and Paddick Gradient Index, were compared with the analytical values.

RESULTS

The average difference and range across all evaluated target sizes for the reported structure volume was - 4.73%[-33.2,0.2], 0.11%[-10.9, 9.5], -0.39%[-12.1, 7.0], -2.24%[-21.0, 1.3], and 1.15%[-15.1,0.8], for TPS-A through TPS-E, respectively. The average difference and range for the V100%[cc] (V20Gy[cc]) was - 0.4[-24.5,9.8], -2.73[-23.6, 1.1], -3.01[-23.6, 0.6], -3.79[-27.3, 1.3], and 0.26[-6.1,2.6] for TPS-A through TPS-E, respectively. For V50%[cc](V10Gy[cc]) in TPS-A through TPS-E the average and ranger were - 0.05[-0.8,0.4], -0.18[-1.2, 0.5], -0.44[-1.4, 0.3], -0.26[-1.8, 2.6], and 0.09[-1.4,2.7].

CONCLUSION

This study expanded on the previously published literature to quantitatively compare the DVH analysis capabilities of software commonly used for SRS plan evaluation and provides freely available and downloadable analytically derived set of ground truth DICOM dose and structure files for the use of radiotherapy clinics. The differences between systems highlight the need for standardization and/or transparency between systems, especially when evaluating plan quality for multi-institutional clinical trials.

Feasibility of a mini-pig model of radiation-induced brain injury to one cerebral hemisphere

BACKGROUND

Radiation-induced brain injury is a common concern for survivors of adult and pediatric brain cancer. Pre-clinically, rodent models are the standard approach to evaluate mechanisms of injury and test new therapeutics for this condition. However, these rodent models fail to recapitulate the radiological and histological characteristics of the clinical disease.

METHODS

Here we describe a hemispheric mini-pig model of radiation-induced brain injury generated with a clinical 6 MV photon irradiator and evaluated with a clinical 3T MRI. Two pairs of Yucatan mini-pigs each received either 15 Gy or 25 Gy to the left brain hemisphere. Quality of intensity modulated radiation therapy treatment plans was evaluated retrospectively with parameters reported according to ICRU guidelines. The pigs were observed weekly to check for any outright signs of neurological impairment. The pigs underwent anatomical MRI examination before irradiation and up to 6 months post-irradiation. Immediately after the last imaging time point, the pigs were euthanized and their brains were collected for histopathological assessment.

RESULTS

Analysis of the dose volume histograms showed that 93% of the prescribed dose was delivered to at least 93% of the target volume in the left hemisphere. Organs at risk excluded from the target volume received doses below clinical safety thresholds. For the pigs that received a 25 Gy dose, progressive neurological impairment was observed starting at 2 months post-irradiation leading to the need for euthanasia by 3-4 months. On MRI, these two animals presented with diffuse white matter pathology consistent with the human disease that progressed to outright radiation necrosis and severe brain swelling. Histology was consistent with the final MRI evaluation. The pigs that received a 15 Gy dose appeared normal all the way to 6 months post-irradiation with no obvious neurological impairment or lesions on MRI or histopathology.

CONCLUSION

Based on our results, a mini-pig model of radiation-induced brain injury is feasible though some optimization is still needed. The mini-pig model produced lesions on MRI that are consistent with the human disease and which are not seen in rodent models. Our data shows that the ideal radiation dose for this model likely lies between 15 and 25 Gy.

Factors affecting long-lasting pain relief after Gamma Knife radiosurgery for trigeminal neuralgia: a single institutional analysis and literature review

Gamma Knife radiosurgery (GKRS) is a well-established safe and effective treatment for trigeminal neuralgia (TN) with high initial success rate (80-90%). Why the pain relief is progressively decreased with time is a matter of considerable debate. To investigate factors related to long-lasting pain relief, the authors conducted a retrospective analysis focusing on anatomical and radiosurgical related parameters, chosen according to literature review. One hundred and twelve patients with classical trigeminal neuralgia and follow-up longer than 12 months were selected from our institutional consecutive series of patients treated by GKRS. Patients were followed for a mean period of 61.5 ± 3.5 months (range, 12-126 months) to evaluate, as endpoints, long-term pain relief and hypoesthesia onset. The median maximum radiation dose was 80 Gy (range 70-90 Gy). Factors related to poor long-term pain relief were prescription dose < 80 Gy (p = 0.038), calibration dose rate < 2.5 Gy/min (p = 0.018), and distance between isocenter and trigeminal nerve emergence > 8 mm (p < 0.001). When analyzing patients who received 80 Gy as maximum dose without any sector blocking, we notice that ID₅₀ < 2.7 mJ was predictive for longer period of pain control (p = 0.043). It was experienced also among patients in which a small volume of the nerve (< 35%) received more than 80% of the maximal dose, compared to those in which a larger volume of the nerve was irradiated with maximal dose (p 0.034). This last result was significant if the shot was 8 mm or less from the pons. Several single-patient anatomical and radiosurgical parameters should be considered to improve GKRS effectiveness.

Dose-escalated simultaneously integrated boost photon or proton therapy in pancreatic cancer in an in-silico study: Gastrointestinal organs remain critical

•

Robustly optimized proton plans (rMFO-IMPT) with simultaneously integrated boost (SIB) were clinically applicable.

•

Gastrointestinal organs reached critical dose values in rMFO-IMPT, VMAT and Tomotherapy techniques.

•

rMFO-IMPT significantly reduced the low and intermediate dose to organs at risk.

•

No clinically significant differences on results depending on tumor location or surgical status were observed.

Purpose

To compare the dosimetric results of an in-silico study among intensity-modulated photon (IMRT) and robustly optimized intensity-modulated proton (IMPT) treatment techniques using a dose-escalated simultaneously integrated boost (SIB) approach in locally recurrent or advanced pancreatic cancer patients.

Material and methods

For each of 15 locally advanced pancreatic cancer patients, a volumetric-modulated arc therapy (VMAT), a Tomotherapy (TOMO), and an IMPT treatment plan was optimized on free-breathing treatment planning computed tomography (CT) images. For the photon treatment plans, doses of 66 Gy and 51 Gy, both as SIB in 30 fractions, were prescribed to the gross tumor volume (GTV) and to the planning target volume (PTV), respectively. For the proton plans, a dose prescription of 66 Gy(RBE) to the GTV and of 51 Gy(RBE) to the clinical target volume (CTV) was planned. For each SIB-treatment plan, doses to the targets and OARs were evaluated and statistically compared.

Results

All treatment techniques reached the prescribed doses to the GTV and CTV or PTV. The stomach and the bowel, in particular the duodenum and the small bowel, were found to be frequently exposed to doses exceeding 50 Gy, irrespective of the treatment technique. For doses below 50 Gy, the IMPT technique was statistically significant superior to both IMRT techniques regarding decreasing dose to the OARs, e.g. volume of the bowel receiving 15 Gy (V_15Gy) was reduced for IMPT compared to VMAT (p = 0.003) and TOMO (p < 0.001).

Conclusion

With all photon and proton techniques investigated, the radiation dose to gastrointestinal OARs remained critical when treating patients with unresectable locally recurrent or advanced pancreatic cancer using a dose-escalated SIB approach.

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.

Dosimetric Comparison of Robotic and Linear Accelerator Multi-Leaf Collimator-Based Stereotactic Radiosurgery for Arteriovenous Malformation

PURPOSE

To investigate the dosimetric comparison of different collimators which are used in robotic radiosurgery (cyberknife-CK) and linear accelerator (LINAC) for stereotactic radiosurgery (SRS) in arteriovenous malformation (AVM).

MATERIALS AND METHODS

Twenty-five AVM patients were planned in CK using FIXED cone, IRIS collimator, and multi-leaf collimator (MLC) based in LINAC. Dosimetric comparison was performed using Paddick conformity index (CIPaddick) and International Commission on Radiation Units and measurements (ICRU) homogeneity index (HIICRU), gradient score (GS), normal brain dose received by 10cc (D10cc) and critical structure (brain stem, optic chiasma, optic nerves) doses. Paired sample t-test was used for statistical analysis.

RESULTS

Mean treatment volume was 3.16cc (standard deviation ± 4.91cc). No significant deviation (P =0.45, 0.237 for FIXED vs. IRIS and FIXED vs. MLC, respectively) was found in target coverage. For CIPaddick, the mean difference (MD) between FIXED- and MLC-based plans was 0.16(P = 0.001); For HIICRU, difference between FIXED and IRIS was insignificant (0.5, P = 0.823); but, when FIXED versus MLC, the deviation was 7.99% (P = 0.002). In FIXED- and MLC-based plans, significant difference was found in GS70 and GS40 (P < 0.041 and 0.005, respectively). MD between FIXED- and MLC-based plans for normal brain for 5Gy, 10Gy, 12Gy, and 20Gy were 36.08cc (P = 0.009), 7.12cc (P = 0.000), 5.84cc (P = 0.000) and 1.56cc (P = 0.000), respectively. AVM volume <0.7cc should be treated with CK FIXED and >0.7cc were treated by using FIXED or IRIS collimators. AVM volume > 1.4cc can be treated by either LINAC MLC-based SRS or CK.

CONCLUSION

Our study shows CK collimator (IRIS and FIXED) could be able to treat brain AVMs in any size. Linac MLC-based SRS has some limitations in terms of conformity and low-dose spillage, and advantages like reduced treatment time and MU.

A Special Report on 2019 International Planning Competition and a Comprehensive Analysis of Its Results

Purpose

The aim of this work is to introduce the 2019 International Planning Competition and to analyze its results.

Methods and materials

A locally advanced non-small cell lung cancer (LA-NSCLC) case using the simultaneous integrated boost approach was selected. The plan quality was evaluated by using a ranking system in accordance with practice guidelines. Planners used their clinical Treatment Planning System (TPS) to generate the best possible plan along with a survey, designed to obtain medical physics aspects information. We investigated the quality of the large population of plans designed by worldwide planners using different planning and delivery systems. The correlations of plan quality with relevant planner characteristics (work experience, department scale, and competition experience) and with technological parameters (TPS and modality) were examined.

Results

The number of the qualified plans was 287 with a wide range of scores (38.61–97.99). The scores showed statistically significant differences by the following factors: 1) department scale: the mean score (89.76 ± 8.36) for planners from the departments treating >2,000 patients annually was the highest of all; 2) competition experience: the mean score for the 107 planners with previous competition experience was 88.92 ± 9.59, statistically significantly from first-time participants (p = .001); 3) techniques: the mean scores for planners using VMAT (89.18 ± 6.43) and TOMO (90.62 ± 7.60) were higher than those using IMRT (82.28 ± 12.47), with statistical differences (p <.001). The plan scores were negligibly correlated with the planner’s years of work experience or the type of TPS used. Regression analysis demonstrated that plan score was associated with dosimetric objectives that were difficult to achieve, which is generally consistent with a clinical practice evaluation. However, 51.2% of the planners abandoned the difficult component of total lung receiving a dose of 5 Gy in their plan design to achieve the optimal plan.

Conclusion

The 2019 international planning competition was carried out successfully, and its results were analyzed. Plan quality was not correlated with work experiences or the TPS used, but it was correlated with department scale, modality, and competition experience. These findings differed from those reported in previous studies.

Moderately Hypofractionated Radiation for Benign Meningiomas and Schwannomas: A Report of 70 Patients Treated Between 2008 and 2018

Purpose

Radiosurgery and fractionated intensity modulated radiation therapy (IMRT) are effective treatment modalities for meningiomas and schwannomas. Although fractionated IMRT yields favorable tumor control, daily treatments for 5 to 6 weeks can be burdensome for patients and health care systems. Thus, hypofractionated radiation may be a reasonable alternative. The purpose of this study was to review the results of patients with benign meningiomas or schwannomas treated at our institution with moderately hypofractionated IMRT.

Methods and Materials

After institutional review board approval, patients treated at a single academic institution between 2008 and 2018 with a primary diagnosis of either meningioma or schwannoma and who received 30 Gy at 3 Gy per fraction were identified. Patient and tumor characteristics, as well as follow-up documentation, were reviewed. Tumor progression was determined by reviewing patient imaging and provider notations.

Results

From 2008 to 2018, 70 patients with either meningioma or schwannoma were treated to 30 Gy. The median patient age was 73 years (range, 43-92 years). At the median follow up of 3.2 years, the local control was 92.9%. Two patients (2.9%) had disease progression, which occurred at 9.6 and 6.6 years after treatment. One patient developed asymptomatic radiographic changes consistent with radiation necrosis, which resolved without intervention. All patients completed the prescribed course without interruption. The mean tumor volume was 18.9 cm³, median volume was 36.6 cm³ (range, 3.4-245.5 cm³), and tumor volume was not associated with recurrence risk. Both tumors with progression were schwannomas.

Conclusions

Hypofractionated radiation with 30 Gy at 3 Gy per fraction is an effective, convenient, and well-tolerated alternative for patients with benign meningiomas or schwannomas. Modest hypofractionation provided durable control for a wide range of tumor volumes and should be considered for patients with a limited life expectancy or those unable to receive a more extended fractionated radiation therapy course.

Frameless radiosurgical third ventriculostomy: Technical report

Background:

We describe the technical report and results of the first image-guided, linear accelerator, frameless radiosurgical third ventriculostomy.

Methods:

We report a 20 years old man, with diplopia, balance disturbances, and limitation for gaze supraversion. Magnetic resonance imaging resonance imaging of the brain and cranial computed tomography showed showed a left thalamic-midbrain lesion that caused partial compression of the Silvio aqueduct and mild ventricular dilatation. The biopsy revealed the diagnosis of pleomorphic xanthoastrocytoma. Before radical treatment of the tumor with fractionated stereotactic radiotherapy, the patient underwent to frameless radiosurgical third ventriculostomy, on the TrueBeam STX® platform with the ExacTrac localization system. The target used was the one defined on the floor of the third ventricle, at the midpoint between the mammillary bodies and the infundibular recess. The prescription dose was 120 Gy, given using a monoisocentric technique of multiple noncoplanar circular arches. The geometric arrangement of the plan consisted of 15 arches, with a 4 mm cone, distributed over a 110° table.

Results:

There was symptomatic and image improvement two days after radiosurgery. On CT, a reduction in ventricular dilation was observed with a reduction in the Evans index from 0.39 (initial CT) to 0.29 (CT at 15 days). In 3.0T magnetic resonance image at 3 months, we showed the third ventriculostomy. There have been no treatment failures or complications.

Conclusion:

It is possible to effectively perform the frameless radiosurgical third ventriculostomy without associated morbidity in the short term.

Does the Diffuseness of the Nidus Affect the Outcome of Stereotactic Radiosurgery in Patients with Unruptured Cerebral Arteriovenous Malformations?

BACKGROUND

We proposed an algorithm to automate the components within the identification of components within the nidus of cerebral arteriovenous malformations (AVMs) which may be used to analyze the relationship between its diffuseness and treatment outcomes following stereotactic radiosurgery (SRS).

OBJECTIVES

to determine the impact of the diffuseness of the AVM nidus on SRS outcomes.

METHODS

This study conducted regular follow-ups of 209 patients with unruptured AVMs who underwent SRS. The diffuseness of the AVM nidus was estimated by quantifying the proportions of vascular nidal component, brain parenchyma, and cerebrospinal fluid in T2-weighted MRIs. We used Cox regression analysis to characterize the association between nidal diffuseness and treatment outcomes in terms of obliteration rate and radiation-induced change (RICs) rate following SRS.

RESULTS

The median AVM volume was 20.7 cm3. The median duration of imaging follow-up was 51 months after SRS. The overall AVM obliteration rate was 68.4%. RICs were identified in 156 of the 209 patients (74.6%). The median proportions of the nidus of AVM and brain parenchyma components within the prescription isodose range were 30.2 and 52.2%, respectively. Cox regression multivariate analysis revealed that the only factor associated with AVM obliteration rate after SRS was AVM volume. However, a larger AVM volume (>20 mL) and a larger proportion of brain parenchyma (>50%) within the prescription isodose range were both correlated with a higher RIC rate following SRS.

CONCLUSIONS

The diffuseness of the nidus indeed appears to affect the RIC rate following SRS in patients with unruptured AVMs.

Image-Guided Multisession Radiosurgery of Skull Base Meningiomas

Simple Summary

Stereotactic radiosurgery has changed the landscape of treatment for skull base meningiomas. Lesions encasing or compressing radiosensitive structures are considered not suitable for single session stereotactic radiosurgery because of the high risk of side effects. Multisession stereotactic radiosurgery can reduce these risks, allowing for normal tissue repair between fractions, while delivering a high dose per fraction. The aim of this study is to validate the role of multi-session stereotactic radiosurgery in the treatment of skull base meningiomas, through a retrospective analysis of 156 patients affected by skull base meningioma, treated at the University of Messina between 2008 and 2018. Our study suggests that multisession stereotactic radiosurgery represents a safe and effective profile in the treatment of skull base meningioma, providing a satisfactory local control and a low toxicity rate, together with patient comfort from a frameless procedure.

Abstract

Background: The efficacy of single-session stereotactic radiosurgery (sSRS) for the treatment of intracranial meningioma is widely recognized. However, sSRS is not always feasible in cases of large tumors and those lying close to critically radiation-sensitive structures. When surgery is not recommended, multi-session stereotactic radiosurgery (mSRS) can be applied. Even so, the efficacy and best treatment schedule of mSRS are not yet established. The aim of this study is to validate the role of mSRS in the treatment of skull base meningiomas. Methods: A retrospective analysis of patients with skull base meningiomas treated with mSRS (two to five fractions) at the University of Messina, Italy, from 2008 to 2018, was conducted. Results: 156 patients met the inclusion criteria. The median follow-up period was 36.2 ± 29.3 months. Progression-free survival at 2-, 5-, and 10- years was 95%, 90%, and 80.8%, respectively. There were no new visual or motor deficits, nor cranial nerves impairments, excluding trigeminal neuralgia, which was reported by 5.7% of patients. One patient reported carotid occlusion and one developed brain edema. Conclusion: Multisession radiosurgery is an effective approach for skull base meningiomas. The long-term control is comparable to that obtained with conventionally-fractionated radiotherapy, while the toxicity rate is very limited.

Initial Gamma Knife Radiosurgery for Large or Documented Growth Asymptomatic Meningiomas: Long-Term Results From a 27-Year Experience

Objective

The aims of this study were to investigate the long-term outcomes of initial Gamma Knife radiosurgery (GKRS) for large (≥20 mm) or documented growth asymptomatic meningiomas.

Design and Methods

This was a single-center retrospective study. Fifty-nine patients with large (≥20 mm) or documented growth asymptomatic meningiomas undergoing initial GKRS were enrolled. The median age was 56 (range, 27–83) years. The median time of follow-up was 66.8 (range, 24.6–245.6) months, and the median tumor margin dose was 13.0 Gy (range, 11.6–22.0 Gy).

Results

Tumors shrunk in 35 patients (59.3%) and remained stable in 23 (39.0%). One patient (1.7%) experienced radiological progression at 54 months after GKRS. The PFS was 100%, 97%, and 97% at 3, 5, and 10 years, respectively. Nine patients (15.3%) occurred new neurological symptoms or signs at a median time of 8.1 (range, 3.0–81.6) months. The symptom PFS was 90% and 78% at 5 and 10 years, respectively. Fifteen patients (25.4%) occurred peritumoral edema (PTE) at a median time of 7.2 (range, 2.0–81.6) months. One patient underwent surgical resection for severe PTE. In univariate and multivariate analysis, Only tumor size (≥25 mm) and maximum dose (≥34 Gy) were significantly associated with PTE [hazard ratio (HR)= 3.461, 95% confidence interval (CI)=1.157-10.356, p=0.026 and HR=3.067, 95% CI=1.068-8.809, P=0.037, respectively].

Conclusions

In this study, initial GKRS can provide a high tumor control rate as well as an acceptable rate of complications in large or documented growth asymptomatic meningiomas. GKRS may be an alternative initial treatment for asymptomatic meningiomas.

Prostate Stereotactic Body Radiation Therapy With Halcyon 2.0: Treatment Plans Comparison Based on RTOG 0938 Protocol

Purpose

The aim of this study is to investigate the feasibility of prostate stereotactic body radiation therapy treatment with a newly developed Varian Halcyon^TM 2.0 machine by comparing radiotherapy plans with previously delivered CyberKnife G4 plans created with the previous version of CyberKnife Treatment Planning System Multiplan 4.6.1.

Methods

Fifteen previously treated prostate stereotactic body radiation therapy treatment CyberKnife plans were re-planned retrospectively according to the Radiation Therapy Oncology Group 0938 protocol on a Halcyon^TM 2.0 machine with a prescription of 3625 cGy in five fractions.

Results

All re-plans on a Halcyon^TM 2.0 were able to meet the Radiation Therapy Oncology Group 0938 protocol goals and constraints. The re-plans decreased the maximum dose to skin and urethra, mean doses to the bladder and rectum, and also improve the conformity index and the Planning Target Volume coverage. However, D1cc to the rectum, D1cc and D10% to the bladder increased with no statistically significant differences (p > 0.05) with the re-plans.

Conclusion

The Halcyon^TM 2.0 can generate stereotactic body radiation therapy treatment prostate plans created based on the Radiation Therapy Oncology Group 0938 protocol by delivering adequate coverage to the target while sparing healthy tissues.

Tomotherapy as an Alternative Irradiative Treatment for Complicated Keloids

The aim of this study was to investigate the treatment of complicated keloids with helical tomotherapy (HT) and electron beam radiotherapy. From July 2018 to September 2018, 11 patients with 23 keloid lesions treated with HT were enrolled. Additionally, 11 patients with 20 lesions treated with electron beam radiotherapy in the same period were enrolled. Patients in both groups were treated within 24 h after surgical excision of the keloid lesion with 13.5 Gy in three consecutive daily fractions. The median follow-up period was 15 months. The local control rate was 91.3% and 80% in the HT group and the electron beam group, respectively. No acute adverse effects were observed in either group, but most patients exhibited pigmentation. No radiation-induced cancer occurred in these patients up to the time of this report. Pain and pruritus improved for all patients and more obviously for three patients with complicated keloids treated with HT. The measured surface dose was 103.7–112.5% and 92.8–97.6% of the prescribed dose in the HT group and the electron beam group, respectively. HT can be considered an alternative in cases where it is not feasible to use multiple electron fields, due to encouraging clinical outcomes.

Radiation-induced cavernous malformation after stereotactic radiosurgery for cavernous sinus meningioma: a case report

Background

Radiation-induced cavernous malformation (RICM) is a rare sequela of stereotactic radiosurgery (SRS) treatment of intracranial tumors. To date, no study reported on RICM after SRS for meningiomas originating from the skull base. The relationship between locus of initial meningioma and RICM has not been studied.

Case presentation

A 57-year-old woman presented with persistent headaches and blepharoptosis at initial episode. MRI disclosed a right parasellar lesion, diagnosed as a cavernous sinus meningioma (CSM). After receiving a single-fractionated SRS, headache relieved, but blepharoptosis did not significantly improve. Three years and three months later, she returned with headaches and dizziness. MRI showed an enlarged CSM. Moreover, a new mass-like lesion, suspected hemangioma, appeared in the nearby right temporal lobe. After surgical removal of the new lesion and the CSM, the patient’s neurological symptoms significantly improved. Pathology confirmed CSM and temporal RICM.

Conclusions

We report the first rare case of RICM occurring after SRS for CSM. The RICM may be in the same region as the initial tumor. Surgical intervention was preferred for symptomatic RICM and initial meningioma. We recommend long-term regular followup MRIs for patients with meningioma after SRS treatment.

Recommended dose voxel size and statistical uncertainty parameters for precision of Monte Carlo dose calculation in stereotactic radiotherapy

Monte Carlo (MC)‐based treatment planning requires a choice of dose voxel size (DVS) and statistical uncertainty (SU). These parameters effect both the precision of displayed dose distribution and time taken to complete a calculation. For efficient, accurate, and precise treatment planning in a clinical setting, optimal values should be selected. In this investigation, 30 volumetric modulated arc therapy (VMAT) stereotactic radiotherapy (SRT) treatment plans, 10 brain, 10 lung, and 10 spine were calculated in the Monaco 5.11.02 treatment planning system (TPS). Each plan was calculated with a DVS of 0.1 and 0.2 cm using SU values of 0.50%, 0.75%, 1.00%, 1.50%, and 2.00%, along with a ground truth calculation using a DVS of 0.1 cm and SU of 0.15%. The variance at each relative dose level was calculated for all SU settings to assess their relationship. The variation from the ground truth calculation for each DVS and SU combination was determined for a range of DVH metrics and plan quality indices along with the time taken to complete the calculations. Finally, the effect of defining the maximum dose using a volume of 0.035 cc was compared to 0.100 cc when considering DVS and SU settings. Changes in the DVS produced greater variations from the ground truth calculation than changes in SU across the values tested. Plan quality metrics and mean dose values showed less sensitivity to changes in SU than DVH metrics. From this study, it was concluded that while maintaining an average calculation time of <10 min, 75% of plans could be calculated with variations of <2.0% from their ground truth values when using an SU setting of 1.50% and a DVS of 0.1 cm in the case of brain or spine plans, and a 0.2 cm DVS in the case of lung plans.

Volume-Staged Radiosurgery for Large Arteriovenous Malformation

Large arteriovenous malformations (AVMs) are challenges in management because of outcomes and adverse affects. Volume-staged radiosurgery has been an appropriate approach when removal resection and embolization are not recommended. A 53-year-old gentleman was diagnosed with a large intracranial AVM with persistent headache and short-term seizure. Brain magnetic resonance and angiograph showed a bulky volume of AVM nidus. Removal resection and embolization were not recommended because of high risk of adverse affects. The patient was treated by volume-staged radiosurgery. One year post-treatment, obliteration for right internal carotid artery was completed. Volume-staged radiosurgery is a potential treatment option for large AVM with controlled and obliteration efficacy, especially to AVMs which are not appropriate for removal surgery and embolization.

A Retrospective Dosimetric Analysis of the New ESTRO-ACROP Target Volume Delineation Guidelines for Postmastectomy Volumetric Modulated Arc Therapy After Implant-Based Immediate Breast Reconstruction

Purpose: The European Society of Radiation & Oncology and Advisory Committee on Radiation Oncology Practice (ESTRO-ACROP) presented new guidelines for clinical target volume (CTV) delineation in post-mastectomy radiation therapy (PMRT) after implant-based immediate breast reconstruction (IBR-i). This study evaluated the dosimetric characteristics, dosimetric accuracy, and delivery accuracy of these guidelines in volumetric modulated arc therapy (VMAT). Methods and Materials: This retrospective study included 15 patients with left breast cancer who underwent mastectomy with tissue expander placement followed by PMRT. An experienced radiation oncologist delineated the CTV twice on the same image datasets based on the ESTRO-ACROP (EA-TVD) and conventional target volume delineation (C-TVD) guidelines. All VMAT plans, which used a double partial arc, were generated using six MV photons. Clinically relevant dose-volume parameters for organs at risk were compared. Dosimetric accuracy of the treatment plans and delivery accuracy were assessed. Results: Target volume of EA-TVD was significantly smaller than that of C-TVD. Although no statistically significant difference was noted in the target coverage between the two VMAT plans, EA-TVD VMAT significantly reduced the mean heart dose (3.99 ± 1.02 vs. 5.84 ± 1.78 Gy, p = 0.000), the maximum left anterior descending coronary artery (LAD) dose (9.43 ± 3.04 vs. 13.97 ± 6.04 Gy, p = 0.026), and the mean LAD dose (4.52 ± 1.31 vs. 6.35 ± 2.79 Gy, p = 0.028) compared with C-TVD VMAT. No significant difference was observed with respect to the total monitor units, plan complexity, and delivery quality assurance. Conclusions: This is the first study to show significant dose reduction for the normal heart and LAD tissue offered by the EA-TVD, while maintaining dosimetric and delivery accuracy, in PMRT after IBR-i in VMAT for left-sided breast cancer patients.

Surgical Treatment of Parkinson's Disease: Devices and Lesion Approaches

Surgical treatments have transformed the management of Parkinson's disease (PD). Therapeutic options available for the management of PD motor complications include deep brain stimulation (DBS), ablative or lesioning procedures (pallidotomy, thalamotomy, subthalamotomy), and dopaminergic medication infusion devices. The decision to pursue these advanced treatment options is typically done by a multidisciplinary team by considering factors such as the patient's clinical characteristics, efficacy, ease of use, and risks of therapy with a goal to improve PD symptoms and quality of life. DBS has become the most widely used surgical therapy, although there is a re-emergence of interest in ablative procedures with the introduction of MR-guided focused ultrasound. In this article, we review DBS and lesioning procedures for PD, including indications, selection process, and management strategies.

Managing Essential Tremor

Essential tremor is one of the most common tremor syndromes. According to the recent tremor classification, tremor as a symptom is defined as an involuntary, rhythmic, oscillatory movement of a body part and is classified along two axes: axis 1-defining syndromes based on the clinical features such as historical features, tremor characteristics, associated signs, and laboratory tests; and axis 2-classifying the etiology (Bhatia et al., Mov Disord 33:75-87, 2018). The management of this condition has two major approaches. The first is to exclude treatable etiologies, as particularly during the onset of this condition the presentation of a variety of etiologies can be with monosymptomatic tremor. Once the few etiologies with causal treatments are excluded, all further treatment is symptomatic. Shared decision-making with enabling the patient to knowledgeably choose treatment options is needed to customize the management. Mild to moderate tremor severity can sometimes be controlled with occupational treatment, speech therapy of psychotherapy, or adaptation of coping strategy. First-line pharmacological treatments include symptomatic treatment with propranolol, primidone, and topiramate. Botulinum toxin is for selected cases. Invasive treatments for essential tremor should be considered for severe tremors. They are generally accepted as the most powerful interventions and provide not only improvement of tremor but also a significant improvement of life quality. The current standard is deep brain stimulation (DBS) of the thalamic and subthalamic region. Focused ultrasound thalamotomy is a new therapy attracting increasing interest. Radiofrequency lesioning is only rarely done if DBS or focused ultrasound is not possible. Radiosurgery is not well established. We present our treatment algorithm.

Evaluation of Automatic Segmentation Model With Dosimetric Metrics for Radiotherapy of Esophageal Cancer

Background and Purpose: Automatic segmentation model is proven to be efficient in delineation of organs at risk (OARs) in radiotherapy; its performance is usually evaluated with geometric differences between automatic and manual delineations. However, dosimetric differences attract more interests than geometric differences in the clinic. Therefore, this study aimed to evaluate the performance of automatic segmentation with dosimetric metrics for volumetric modulated arc therapy of esophageal cancer patients.

Methods: Nineteen esophageal cancer cases were included in this study. Clinicians manually delineated the target volumes and the OARs for each case. Another set of OARs was automatically generated using convolutional neural network models. The radiotherapy plans were optimized with the manually delineated targets and the automatically delineated OARs separately. Segmentation accuracy was evaluated by Dice similarity coefficient (DSC) and mean distance to agreement (MDA). Dosimetric metrics of manually and automatically delineated OARs were obtained and compared. The clinically acceptable dose difference and volume difference of OARs between manual and automatic delineations are supposed to be within 1 Gy and 1%, respectively.

Results: Average DSC values were greater than 0.92 except for the spinal cord (0.82), and average MDA values were <0.90 mm except for the heart (1.74 mm). Eleven of the 20 dosimetric metrics of the OARs were not significant (P > 0.05). Although there were significant differences (P < 0.05) for the spinal cord (D2%), left lung (V10, V20, V30, and mean dose), and bilateral lung (V10, V20, V30, and mean dose), their absolute differences were small and acceptable for the clinic. The maximum dosimetric metrics differences of OARs between manual and automatic delineations were ΔD2% = 0.35 Gy for the spinal cord and ΔV30 = 0.4% for the bilateral lung, which were within the clinical criteria in this study.

Conclusion: Dosimetric metrics were proposed to evaluate the automatic delineation in radiotherapy planning of esophageal cancer. Consequently, the automatic delineation could substitute the manual delineation for esophageal cancer radiotherapy planning based on the dosimetric evaluation in this study.

Validation of the clinical applicability of knowledge-based planning models in single-isocenter volumetric-modulated arc therapy for multiple brain metastases

PURPOSE

To validate the clinical applicability of knowledge-based (KB) planning in single-isocenter volumetric-modulated arc therapy (VMAT) for multiple brain metastases using the k-fold cross-validation (CV) method.

METHODS

This study comprised 60 consecutive patients with multiple brain metastases treated with single-isocenter VMAT (28 Gy in five fractions). The patients were divided randomly into five groups (Groups 1-5). The data of Groups 1-4 were used as the training and validation dataset and those of Group 5 were used as the testing dataset. Four KB models were created from three of the training and validation datasets and then applied to the remaining Groups as the fourfold CV phase. As the testing phase, the final KB model was applied to Group 5 and the dose distributions were calculated with a single optimization process. The dose-volume indices (DVIs), modified Ian Paddick Conformity Index (mIPCI), modulation complexity scores for VMAT plans (MCSv), and the total number of monitor units (MUs) of the final KB plan were compared to those of the clinical plan (CL) using a paired Wilcoxon signed-rank test.

RESULTS

In the fourfold CV phase, no significant differences were observed in the DVIs among the four KB plans (KBPs). In the testing phase, the final KB plan was statistically equivalent to the CL, except for planning target volumes (PTVs) D_2% and D_50% . The differences between the CL and KBP in terms of the PTV D_99.5% , normal brain, and D_max to all organs at risk (OARs) were not significant. The KBP achieved a lower total number of MUs and higher MCSv than the CL with no significant difference.

CONCLUSIONS

We demonstrated that a KB model in a single-isocenter VMAT for multiple brain metastases was equivalent in dose distribution, MCSv, and total number of MUs to a CL with a single optimization.

Development of a Tongue Immobilization Device Using a 3D Printer for Intensity Modulated Radiation Therapy of Nasopharyngeal Cancer Patients

Purpose

This study aimed to reduce radiation doses to the tongue, a patient-specific semi-customized tongue immobilization device (SCTID) was developed using a 3D printer for helical tomotherapy (HT) of nasopharyngeal cancer (NPCa). Dosimetric characteristics and setup stability of the SCTID were compared with those of a standard mouthpiece (SMP).

Materials and Methods

For displacement and robust immobilization of the tongue, the SCTID consists of four parts: upper and lower tooth stoppers, tongue guider, tongue-tip position guide bar, and connectors. With the SCTID and SMP, two sets of planning computed tomography and HT plans were obtained for 10 NPCa patients. Dosimetric and geometric characteristics were compared. Position reproducibility of the tongue with SCTID was evaluated by comparing with planned dose and adaptive accumulated dose of the tongue and base of the tongue based on daily setup mega-voltage computed tomography.

Results

Using the SCTID, the tongue was effectively displaced from the planning target volume compared to the SMP. The median mucosa of the tongue (M-tongue) dose was significantly reduced (20.7 Gy vs. 27.8 Gy). The volumes of the M-tongue receiving a dose of 15 Gy, 30 Gy, and 45 Gy and the volumes of the mucosa of oral cavity and oropharynx (M-OC/OP) receiving a dose of 45 Gy and 60 Gy were significantly lower than using the SMP. No significant differences was observed between the planned dose and the accumulated adaptive dose in any dosimetric characteristics of the tongue and base of tongue.

Conclusion

SCTID can not only reduce the dose to the M-tongue and M-OC/OP dramatically, when compared to SMP, but also provide excellent reproducibility and easy visual verification.

Long-term outcomes of brainstem arteriovenous malformations after different management modalities: a single-centre experience

OBJECTIVE

The aims of this study are to clarify the long-term outcomes of brainstem arteriovenous malformations (AVMs) after different management modalities.

METHODS

The authors retrospectively reviewed 61 brainstem AVMs in their institution between 2011 and 2017. The rupture risk was represented by annualised haemorrhagic rate. Patients were divided into five groups: conservation, microsurgery, embolisation, stereotactic radiosurgery (SRS) and embolisation+SRS. Neurofunctional outcomes were evaluated by the modified Rankin Scale (mRS). Subgroup analysis was conducted between different management modalities to compare the long-term outcomes in rupture or unruptured cohorts.

RESULTS

All of 61 brainstem AVMs (12 unruptured and 49 ruptured) were followed up for an average of 4.5 years. The natural annualised rupture risk was 7.3%, and the natural annualised reruptured risk in the ruptured cohort was 8.9%. 13 cases were conservative managed and 48 cases underwent intervention (including 6 microsurgery, 12 embolisation, 21 SRS and 9 embolisation+SRS). In the selection of interventional indication, diffuse nidus were often suggested conservative management (p=0.004) and nidus involving the midbrain were more likely to be recommended for intervention (p=0.034). The risk of subsequent haemorrhage was significantly increased in partial occlusion compared with complete occlusion and conservative management (p<0.001, p=0.036, respectively). In the subgroup analysis, the follow-up mRS scores of different management modalities were similar whether in the rupture cohort (p=0.064) or the unruptured cohort (p=0.391), as well as the haemorrhage-free survival (p=0.145). In the adjusted Bonferroni correction analysis of the ruptured cohort, microsurgery and SRS could significantly improve the obliteration rate compared with conservation (p<0.001, p=0.001, respectively) and SRS may have positive effect on avoiding new-onset neurofunctional deficit compared with microsurgery and embolisation (p=0.003, p=0.003, respectively).

CONCLUSIONS

Intervention has similar neurofunctional outcomes as conservation in these brainstem AVM cohorts. If intervention is adopted, partial obliteration should be avoided because of the high subsequent rupture risk.

TRIAL REGISTRATION NUMBER

NCT04136860.

Comparison of VMAT complexity-reduction strategies for single-target cranial radiosurgery with the Eclipse treatment planning system

Complexity in MLC‐based radiosurgery treatment delivery can be characterized by the efficiency of monitor unit (MU) utilization and the average MLC leaf separation distance for a treatment plan. A reduction in plan complexity may be desirable if plan quality is not impacted. In this study, a number of strategies are explored to determine how plan quality is affected by efforts to reduce plan complexity. Ten radiosurgery cases of varying complexity are retrospectively planned using six optimization strategies: an unconstrained volumetric modulated arc therapy (VMAT) technique, a MU‐constrained VMAT technique, three techniques using various strengths of the aperture shape controller (ASC), and a hybrid technique consisting of a final‐stage VMAT optimization applied to a dynamic conformal arc leaf sequence (ODCA). The plans are compared in terms of MU efficiency, MLC leaf‐separation, conformity index (CI), gradient index (GI), and QA measurement results. The five VMAT techniques exhibited only minor differences in CI and GI values, though the ASC and MU‐constrained techniques did require 6–20% fewer MU and had mean field apertures 5–19% larger. On average, the ODCA technique had CI values 3.5% lower and GI values 1.0–2.5% higher than the VMAT techniques, but also had a mean field aperture 24–47% larger and required 16–32% fewer MU. The QA measurement results showed a 0.61% variation in mean per‐field 2%/1 mm gamma passing rates across all techniques (range 96.81%–97.42%), with no observed correlation between passing rate and technique. For simple targets, the ODCA technique achieved CI results that were equivalent to the unconstrained VMAT technique with an average 30% reduction in required MU, an average 50% increase in mean leaf separation distance, and brain V12_Gy values within 0.38 cc of the VMAT technique for targets up to approximately 2 cm diameter. For MLC‐based single‐target radiosurgery, plan complexity can often be significantly reduced without an equivalent reduction in plan quality.

Associating dose-volume characteristics with theoretical radiobiological metrics for rapid Gamma Knife stereotactic radiosurgery plan evaluation

Purpose

To examine general dose–volume characteristics in Gamma Knife (GK) plans which may be associated with higher tumor control probability (TCP) and equivalent uniform dose (EUD) using characteristic curve sets.

Methods

Two sets of dose–volume histograms (DVHs) were exported alongside an analytical purpose‐generated DVH: (a) single‐shot large collimator (8 or 16 mm) emulated with multiple shots of 4 mm collimator. (b) shot‐within‐shot (SWS) technique with isodose lines (IDLs) of 40–75%. TCP, average dose, EUD in single‐fraction (EUD_T) and 2 Gy fractionated regimens (EUD_R) were examined for trends with cumulative DVH (cDVH) shape as calculated using a linear‐quadratic cell survival model (α/β = 10.0 Gy, N₀ = 1 × 10⁶) with both α = 0.20 Gy⁻¹ and α = 0.23 Gy⁻¹.

Results

Using α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), plans in the analytical set with higher shoulder regions had TCP, EUD_T, EUD_R increased by 180%, 5.9%, 10.7% (11.2%, 6.3%, 10.0%), respectively. With α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), plans with higher heels had TCP, EUD_T, EUD_R increased by 4.0%, <1%, <1% (0.6%, <1%, <1%), respectively. In emulating a 16 (8) mm collimator, 64 (12) shots of the small collimators were used. Plans based on small collimators had higher shoulder regions and, with α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), TCP, EUD_T, EUD_R was increased up to 351.4%, 5.0%, 8.8% (270.4%, 5.0%, 6.8%) compared with the single‐shot large collimator. Delivery times ranged from 10.2 to 130.3 min. The SWS technique used 16:8 mm collimator weightings ranging from 1:2 to 9.2:1 for 40–75% IDL. With α = 0.20 Gy⁻¹ (α = 0.23 Gy⁻¹), the 40% IDL plan had the highest shoulder with increased TCP, EUD_T, EUD_R by 130.7%, 9.6%, 17.1% (12.9%, 9.1%, 16.4%) over the 75% IDL plan. Delivery times ranged 6.9–13.8 min.

Conclusions

The magnitude of the shoulder region characteristic to GK cDVHs may be used to rapidly identify superior plan among candidates. Practical issues such as delivery time may require further consideration.

Using deep learning to predict beam-tunable Pareto optimal dose distribution for intensity-modulated radiation therapy

PURPOSE

Many researchers have developed deep learning models for predicting clinical dose distributions and Pareto optimal dose distributions. Models for predicting Pareto optimal dose distributions have generated optimal plans in real time using anatomical structures and static beam orientations. However, Pareto optimal dose prediction for intensity-modulated radiation therapy (IMRT) prostate planning with variable beam numbers and orientations has not yet been investigated. We propose to develop a deep learning model that can predict Pareto optimal dose distributions by using any given set of beam angles, along with patient anatomy, as input to train the deep neural networks. We implement and compare two deep learning networks that predict with two different beam configuration modalities.

METHODS

We generated Pareto optimal plans for 70 patients with prostate cancer. We used fluence map optimization to generate 500 IMRT plans that sampled the Pareto surface for each patient, for a total of 35 000 plans. We studied and compared two different models, Models I and II. Although they both used the same anatomical structures - including the planning target volume (PTV), organs at risk (OARs), and body - these models were designed with two different methods for representing beam angles. Model I directly uses beam angles as a second input to the network as a binary vector. Model II converts the beam angles into beam doses that are conformal to the PTV. We divided the 70 patients into 54 training, 6 validation, and 10 testing patients, thus yielding 27 000 training, 3000 validation, and 5000 testing plans. Mean square loss (MSE) was taken as the loss function. We used the Adam optimizer with a default learning rate of 0.01 to optimize the network's performance. We evaluated the models' performance by comparing their predicted dose distributions with the ground truth (Pareto optimal) dose distribution, in terms of dose volume histogram (DVH) plots and evaluation metrics such as PTV D98 , D95 , D50 , D2 , Dmax , Dmean , Paddick Conformation Number, R50, and Homogeneity index.

RESULTS

Our deep learning models predicted voxel-level dose distributions that precisely matched the ground truth dose distributions. The DVHs generated also precisely matched the ground truth. Evaluation metrics such as PTV statistics, dose conformity, dose spillage (R50), and homogeneity index also confirmed the accuracy of PTV curves on the DVH. Quantitatively, Model I's prediction error of 0.043 (confirmation), 0.043 (homogeneity), 0.327 (R50), 2.80% (D95), 3.90% (D98), 0.6% (D50), and 1.10% (D2) was lower than that of Model II, which obtained 0.076 (confirmation), 0.058 (homogeneity), 0.626 (R50), 7.10% (D95), 6.50% (D98), 8.40% (D50), and 6.30% (D2). Model I also outperformed Model II in terms of the mean dose error and the max dose error on the PTV, bladder, rectum, left femoral head, and right femoral head.

CONCLUSIONS

Treatment planners who use our models will be able to use deep learning to control the trade-offs between the PTV and OAR weights, as well as the beam number and configurations in real time. Our dose prediction methods provide a stepping stone to building automatic IMRT treatment planning.

Ten-year follow-up after Gamma Knife radiosurgery of meningioma and review of the literature

Objectives

With regard to the generally slow growth of meningioma, it is essential to analyse clinical treatment results in a long-term perspective. The purpose of the present analysis is to provide clinical data after Gamma Knife radiosurgery of meningioma in a 10-year perspective together with a review of the current literature.

Methods

The current study is a retrospective analysis of 86 consecutive Swedish patients with meningiomas treated using Gamma Knife radiosurgery at the Karolinska Hospital Stockholm between March 1991 and May 2001. A total of 130 tumours were treated in 115 treatment sessions. The median radiological follow-up was 10 years (1.8–16.5 years), and the median clinical follow-up was 9.4 years (2.1–17.4 years).

Results

After a median follow-up period of 10 years, local tumour control was achieved in 87.8% of meningiomas (108/123 tumours). The median latency between initial treatment and local (in-field) recurrence (n = 15) was 5.8 years (1.9–11.5). Recurrences adjacent but outside the initial radiation field occurred in 15.1% of patients (13/86) at a median of 7.5 years (1.3–15.7). New meningiomas were seen in 10.5% after a median of 5.4 years (0.9–10.8). In 72% of patients, no further treatment was required, 17.4% (15/86) underwent a second Gamma Knife treatment, 4.7% (4/86) required later open surgery and 5.8% (5/86) required both secondary treatments. Eighty-six percent of patients were neurologically unchanged or improved. A significantly lower rate of local (in-field) recurrences was seen in meningiomas treated with a prescription dose of > 13.4 Gy (7.1% vs. 24%, p = 0.02).

Conclusions

The current retrospective analysis provides a 10-year follow-up and comprises one of the longest available follow-up studies of radiosurgically treated meningiomas. The current series documents a persistent high local tumour control after Gamma Knife treatment, while providing an estimation of a necessary minimum dose for long-term tumour control in meningiomas. The study confirms the validity of previous short-term data in a long-term perspective.

Dosimetric and Radiobiological Comparison of Five Techniques for Postmastectomy Radiotherapy with Simultaneous Integrated Boost

Purpose

To compare five techniques for the postmastectomy radiotherapy (PMRT) with simultaneous integrated boost (SIB).

Materials and Methods

Twenty patients with left-sided breast cancer were retrospectively selected. Five treatment plans were created for each patient: TomoDirect (TD), unblocked helical TomoTherapy (unb-HT), blocked HT (b-HT), hybrid intensity-modulated radiotherapy (hy-IMRT), and fixed-field IMRT (ff-IMRT). A dose of 50.4 Gy in 28 fractions to PTV_total and 60.2 Gy in 28 fractions to PTV_boost were prescribed. The dosimetric parameters for targets and organs at risk (OARs), the normal tissue complication probability (NTCP), the second cancer complication probability (SCCP) for OARs, and the treatment efficiency were assessed and compared.

Results

TD plans and hy-IMRT plans had similar good dose coverage and homogeneity for both PTV_boost and PTV_total and superior dose sparing for the lungs and heart. The ff-IMRT plans had similar dosimetric results for the target volumes compared with the TD and hy-IMRT plans, but gave a relatively higher NTCP and SCCP for the lungs. The unb-HT plans exhibited the highest OAR mean dose, highest NTCP for the lungs (0.97 ± 1.25‰) and heart (4.58 ± 3.62%), and highest SCCP for the lungs (3.57 ± 0.05%) and contralateral breast (2.75 ± 0.29%) among all techniques. The b-HT plans significantly outperformed unb-HT plans with respect to the sparing of the lungs and heart. This technique also showed the best conformity index (0.73 ± 0.08) for PTV_boost and the optimal NTCP for the lungs (0.03 ± 0.03‰) and heart (0.61 ± 0.73%). Concerning the delivery efficiency, the hy-IMRT and ff-IMRT achieved much higher delivery efficiency compared with TomoTherapy plans.

Conclusion

Of the five techniques studied, TD and hy-IMRT are considered the preferable options for PMRT with SIB for left-sided breast cancer treatment and can be routinely applied in clinical practice.

Efficiency of a novel non-monotonic segmented leaf sequence delivery of Varian MLC for non-split IMRT fields

Aim

Development of bidirectional non-monotonic segmented leaf sequence (NSLS) MLC delivery technique compatible with Varian MLC for non-split IMRT fields reducing total monitor units (TotalMU) and the number of segments (NS) simultaneously and assessment of its efficiency using a plan scoring index (PSI).

Materials and methods

The optimal fluence of IMRT plans of ten patients of lung carcinoma, calculated using Eclipse TPS version 11.0 (Varian Medical Systems, Palo Alto, CA, USA), was used to generate the segmented MLC fields using our newly developed equally spaced (ES) reducing level and NSLS algorithms in MATLAB® version 2011b for 6-10 intensity levels. These MLC fields were imported into the plans with the same field setup and the final dose was recalculated. The results were compared with those of commercially available multiple static segments (MSS) leaf motion calculation (LMC) algorithm and few previously published algorithms. Plan scoring index (PSI) and degree of modulation (DoM) was calculated to compare the quality of different plans for the same patient.

Results

The average differences in TotalMU and NS with respect to MSS algorithm are -3.80% and -14.28% for the NSLS algorithm, respectively. The calculated average PSI and DoM is 0.75, 2.51 and 0.91, 2.41 for the MSS and NSLS algorithms, respectively.

Conclusions

IMRT plans generated using the NSLS algorithm resulted in the best PSI, DoM values among all the leaf sequencing algorithms. Our proposed NSLS algorithm allows bidirectional delivery in Varian medical linear accelerator which is not commercially available. NSLS algorithm is efficient in reducing the TotalMU and NS with equivalent plan quality as that of MSS.

IntuitivePlan inverse planning performance evaluation for Gamma Knife radiosurgery of AVMs

Purpose

To compare planning indices achieved using manual and inverse planning approaches for Gamma Knife radiosurgery of arterio‐venous malformations (AVMs).

Methods and materials

For a series of consecutive AVM patients, treatment plans were manually created by expert planners using Leksell GammaPlan (LGP). Patients were re‐planned using a new commercially released inverse planning system, IntuitivePlan. Plan quality metrics were calculated for both groups of plans and compared.

Results

Overall, IntuitivePlan created treatment plans of similar quality to expert planners. For some plan quality metrics statistically significant higher scores were achieved for the inversely generated plans (Coverage 96.8% vs 96.3%, P = 0.027; PCI 0.855 vs 0.824, P = 0.042), but others did not show statistically significant differences (Selectivity 0.884 vs 0.856, P = 0.071; GI 2.85 vs 2.76, P = 0.096; Efficiency Index 47.0% vs 48.1%, P = 0.242; Normal Brain V₁₂(cc) 5.81 vs 5.79, P = 0.497). Automatic inverse planning demonstrated significantly shorter planning times over manual planning (3.79 vs 11.58 min, P < 10⁻⁶) and greater numbers of isocentres (40.4 vs 10.8, P < 10⁻⁶), with an associated cost of longer treatment times (57.97 vs 49.52 min, P = 0.009). When planning and treatment time were combined, there was no significant difference in the overall time between the two methods (61.76 vs 61.10, P = 0.433).

Conclusions

IntuitivePlan can offer savings on the labor of treatment planning. In many cases, it achieves higher quality indices than those achieved by an “expert planner”.

Conventionally fractionated large volume head and neck re-irradiation using multileaf collimator-based robotic technique: A feasibility study

Purpose

To report on the feasibility and performance of conventionally fractionated multileaf collimator (MLC)-based robotic stereotactic body re-irradiation of the head and neck region using MLC-based Cyberknife (CK) technology.

Methods

Patients treated for recurrent or second primary head and neck cancer (HNC) with curative proton therapy to a target volume > 30 cm³ between 2011 and 2015 were included. MLC-based CK plans were generated using the CK M6 InCise2 MLC system. Dose statistics from MLC-based CK plans were compared to proton beam therapy (PBT) plans according to the following metrics: target coverage, target homogeneity index, gradient index, Paddick conformity index (CI), prescription isodose volume (PIV), treatment time (tTime) for one fraction as well as doses to organs at risk (OAR). Wilcoxon signed-rank test was used to compare dose metrics.

Results

Eight patients were included; the tumor sites included: salivary glands, pharynx (oropharynx, hypopharynx and retropharynx) and sinonasal cavities. Five of 8 patients were treated with multifield optimisation intensity modulated proton therapy, 3 were treated with passive scattering proton therapy. Median dose was 67 Gy (range 60-70) in 32 fractions (range 30-35). The median high-dose planning target volume (PTV) was 45.4 cm³ (range 2.4 - 130.2 cm³) and the median elective PTV was 91.9 cm³ (range 61.2 - 269.7 cm³). Overall, the mean target coverage (mean 98.3% vs. 96.2% for CK vs. PBT, respectively), maximum dose to PTV (mean 111% vs. 111%, p = 0.2) and mean dose to PTV (mean 104% vs. 104%) were similar across modalities. Highly conformal plans were achieved with both modalities, but mean CI was better with PBT (0.5 vs. 0.6 for CK vs. PBT, p = 0.04). Homogeneity and gradient indexes were similar between the 2 modalities; mean tTime with PBT and CK was 17 vs. 18 min, respectively (p = 0.7). Case-based study revealed that CK and PBT plans allowed for excellent sparing of OAR, with some clinical scenarios associated with better performance of CK while others with better performance of PBT.

Conclusion

Our study has demonstrated the dosimetric performance of large volume head and neck re-irradiation using MLC-based CK in various clinical scenarios. While conformity was generally better achieved with PBT, MLC-based CK allowed for high dose gradient leading to rapid dose drop-off and sparing of OAR. Conventionally fractionated MLC-based CK could be a competitive alternative in large volume head and neck re-irradiation that deserves further investigation in the clinical setting.

Manual segmentation versus semi-automated segmentation for quantifying vestibular schwannoma volume on MRI

Purpose

Management of vestibular schwannoma (VS) is based on tumour size as observed on T1 MRI scans with contrast agent injection. The current clinical practice is to measure the diameter of the tumour in its largest dimension. It has been shown that volumetric measurement is more accurate and more reliable as a measure of VS size. The reference approach to achieve such volumetry is to manually segment the tumour, which is a time intensive task. We suggest that semi-automated segmentation may be a clinically applicable solution to this problem and that it could replace linear measurements as the clinical standard.

Methods

Using high-quality software available for academic purposes, we ran a comparative study of manual versus semi-automated segmentation of VS on MRI with 5 clinicians and scientists. We gathered both quantitative and qualitative data to compare the two approaches; including segmentation time, segmentation effort and segmentation accuracy.

Results

We found that the selected semi-automated segmentation approach is significantly faster (167 s vs 479 s, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$p<0.001$$\end{document}p<0.001), less temporally and physically demanding and has approximately equal performance when compared with manual segmentation, with some improvements in accuracy. There were some limitations, including algorithmic unpredictability and error, which produced more frustration and increased mental effort in comparison with manual segmentation.

Conclusion

We suggest that semi-automated segmentation could be applied clinically for volumetric measurement of VS on MRI. In future, the generic software could be refined for use specifically for VS segmentation, thereby improving accuracy.

Electronic supplementary material

The online version of this article (10.1007/s11548-020-02222-y) contains supplementary material, which is available to authorized users.