Potential Morbidity Reduction for Lung Stereotactic Body Radiation Therapy Using Respiratory Gating

We investigated the potential of respiratory gating to mitigate the motion-caused misdosage in lung stereotactic body radiotherapy (SBRT). For fourteen patients with lung tumors, we investigated treatment plans for a gating window (GW) including three breathing phases around the maximum exhalation phase, GW40-60. For a subset of six patients, we also assessed a preceding three-phase GW20-40 and six-phase GW20-70. We analyzed the target volume, lung, esophagus, and heart doses. Using normal tissue complication probability (NTCP) models, we estimated radiation pneumonitis and esophagitis risks . Compared to plans without gating, GW40-60 significantly reduced doses to organs at risk without impairing the tumor doses. On average, the mean lung dose decreased by 0.6 Gy (p < 0.001), treated lung V20Gy by 2.4% (p = 0.003), esophageal dose to 5cc by 2.0 Gy (p = 0.003), and maximum heart dose by 3.2 Gy (p = 0.009). The model-estimated mean risks of 11% for pneumonitis and 12% for esophagitis without gating decreased upon GW40-60 to 7% and 9%, respectively. For the highest-risk patient, gating reduced the pneumonitis risk from 43% to 32%. Gating is most beneficial for patients with high-toxicity risks. Pre-treatment toxicity risk assessment may help optimize patient selection for gating, as well as GW selection for individual patients.

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Dosimetric Comparison of Upfront Boosting With Stereotactic Radiosurgery Versus Intraoperative Radiotherapy for Glioblastoma

Frontiers in Oncology ◽

10.3389/fonc.2021.759873 ◽

2021 ◽

Vol 11 ◽

Author(s):

Gustavo R. Sarria ◽

Zuzanna Smalec ◽

Thomas Muedder ◽

Jasmin A. Holz ◽

Davide Scafa ◽

...

Keyword(s):

Stereotactic Radiosurgery ◽

Organs At Risk ◽

External Beam Radiotherapy ◽

Intraoperative Radiotherapy ◽

Target Volume ◽

Maximum Diameter ◽

Target Definition ◽

Treatment Plans ◽

Previously Treated Patients ◽

The Mean

PurposeTo simulate and analyze the dosimetric differences of intraoperative radiotherapy (IORT) or pre-operative single-fraction stereotactic radiosurgery (SRS) in addition to post-operative external beam radiotherapy (EBRT) in Glioblastoma (GB).MethodsImaging series of previously treated patients with adjuvant radiochemotherapy were analyzed. For SRS target definition, pre-operative MRIs were co-registered to planning CT scans and a pre-operative T1-weighted gross target volume (GTV) plus a 2-mm planning target volume (PTV) were created. For IORT, a modified (m)GTV was expanded from the pre-operative volume, in order to mimic a round cavity as during IORT. Dose prescription was 20 Gy, homogeneously planned for SRS and calculated at the surface for IORT, to cover 99% and 90% of the volumes, respectively. For tumors > 2cm in maximum diameter, a 15 Gy dose was prescribed. Plan assessment was performed after calculating the 2-Gy equivalent doses (EQD2) for both boost modalities and including them into the EBRT plan. Main points of interest encompass differences in target coverage, brain volume receiving 12 Gy or more (V12), and doses to various organs-at-risk (OARs).ResultsSeventeen pre-delivered treatment plans were included in the study. The mean GTV was 21.72 cm3 (SD ± 19.36) and mGTV 29.64 cm3 (SD ± 25.64). The mean EBRT and SRS PTV were 254.09 (SD ± 80.0) and 36.20 cm3 (SD ± 31.48), respectively. Eight SRS plans were calculated to 15 Gy according to larger tumor sizes, while all IORT plans to 20 Gy. The mean EBRT D95 was 97.13% (SD ± 3.48) the SRS D99 99.91% (SD ± 0.35) and IORT D90 83.59% (SD ± 3.55). Accounting for only-boost approaches, the brain V12 was 49.68 cm3 (SD ± 26.70) and 16.94 cm3 (SD ± 13.33) (p<0.001) for SRS and IORT, respectively. After adding EBRT results respectively to SRS and IORT doses, significant lower doses were found in the latter for mean Dmax of chiasma (p=0.01), left optic nerve (p=0.023), right (p=0.008) and left retina (p<0.001). No significant differences were obtained for brainstem and cochleae.ConclusionDose escalation for Glioblastoma using IORT results in lower OAR exposure as conventional SRS.

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Can volumetric modulated arc radiation therapy reduce organ at risk dose in stage 4 sinonasal tumors in dogs treated with boost irradiation?

PLoS ONE ◽

10.1371/journal.pone.0259112 ◽

2021 ◽

Vol 16 (10) ◽

pp. e0259112

Author(s):

Valeria Meier ◽

Felicitas Czichon ◽

Linda Walsh ◽

Carla Rohrer Bley

Keyword(s):

At Risk ◽

Radiation Therapy ◽

Degrees Of Freedom ◽

Organs At Risk ◽

Volumetric Modulated Arc Therapy ◽

Intensity Modulated Radiation Therapy ◽

Target Volume ◽

Normal Tissue Complication Probability ◽

Lacrimal Glands ◽

Stage 4

Intensity modulated radiation therapy (IMRT) introduced marked changes to cancer treatment in animals by reducing dose to organs at risk (OAR). As the next technological step, volumetric modulated arc therapy (VMAT) has advantages (increased degrees-of-freedom, faster delivery) compared to fixed-field IMRT. Our objective was to investigate a possible advantage of VMAT over IMRT in terms of lower OAR doses in advanced-disease sinonasal tumors in dogs treated with simultaneously-integrated boost radiotherapy. A retrospective, analytical, observational study design was applied using 10 pre-existing computed tomography datasets on dogs with stage 4 sinonasal tumors. Each dataset was planned with both, 5-field IMRT and 2 arc VMAT with 10x4.83 Gy to the gross tumor volume and 10x4.2 Gy to the planning target volume. Adequate target dose coverage and normal tissue complication probability of brain ≤5% was required. Dose constraints aspired to were D60 <15 Gy for eyes, D2 <35.4 Gy for corneae, and Dmean <20 Gy for lacrimal glands. OAR dose was statistically significantly higher in IMRT plans than in VMAT plans. Median eye D60% was 18.5 Gy (interquartile range (IQR) 17.5) versus 16.1 Gy (IQR 7.4) (p = 0.007), median lacrimal gland dose 21.8 Gy (IQR 20.5) versus 18.6 Gy (IQR 7.0) (p = 0.013), and median cornea D2% 45.5 Gy (IQR 6.8) versus 39.9 Gy (IQR 10.0) (p<0.005) for IMRT versus VMAT plans, respectively. Constraints were met in 21/40 eyes, 7/40 corneae, and 24/40 lacrimal glands. Median delivery time was significantly longer for IMRT plans than for VMAT plans (p<0.01). Based on these results, VMAT plans were found to be superior in sparing doses to eyes, lacrimal glands, corneae. However, not all ocular OAR constraints could be met while ensuring adequate dose coverage and restricting brain toxicity risk for both planning techniques.

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Clinical Validation and Treatment Plan Evaluation Based on Auto-Delineation of the Clinical Target Volume for Prostate Cancer Radiotherapy

10.21203/rs.3.rs-1226468/v1 ◽

2022 ◽

Author(s):

Jing Shen ◽

Yinjie TAO ◽

Hui GUAN ◽

Hongnan ZHEN ◽

Lei HE ◽

...

Keyword(s):

Prostate Cancer ◽

At Risk ◽

Organs At Risk ◽

Treatment Plan ◽

Statistical Significance ◽

Locally Advanced ◽

Target Volume ◽

Ct Scans ◽

Dice Similarity Coefficient ◽

Treatment Plans

Abstract Purpose Clinical target volumes (CTV) and organs at risk (OAR) could be auto-contoured to save workload. The goal of this study was to assess a convolutional neural network (CNN) for totally automatic and accurate CTV and OAR in prostate cancer, while also comparing anticipated treatment plans based on auto-contouring CTV to clinical plans. Methods From January 2013 to January 2019, 217 computed tomography (CT) scans of patients with locally advanced prostate cancer treated at our hospital were collected and analyzed. CTV and OAR were delineated with a deep learning based method, which named CUNet. The performance of this strategy was evaluated using the mean Dice similarity coefficient (DSC), 95th percentile Hausdorff distance (95HD), and subjective evaluation. Treatment plans were graded using predetermined evaluation criteria, and % errors for clinical doses to the planned target volume (PTV) and organs at risk(OARs) were calculated. Results The defined CTVs had mean DSC and 95HD values of 0.84 and 5.04 mm, respectively. For one patient's CT scans, the average delineation time was less than 15 seconds. When CTV outlines from CUNetwere blindly chosen and compared to GT, the overall positive rate in clinicians A and B was 53.15% vs 46.85%, and 54.05% vs 45.95%, respectively (P>0.05), demonstrating that our deep machine learning model performed as good as or better than human demarcation Furthermore, 8 testing patients were chosen at random to design the predicted plan based on the auto-courtoring CTV and OAR, demonstrating acceptable agreement with the clinical plan: average absolute dose differences of D2, D50, D98, Dmean for PTV are within 0.74%, and average absolute volume differences of V45, V50 for OARs are within 3.4%. Without statistical significance (p>0.05), the projected findings are comparable to clinical truth. Conclusion The experimental results show that the CTV and OARs defined by CUNet for prostate cancer were quite close to the ground reality.CUNet has the potential to cut radiation oncologists' contouring time in half. When compared to clinical plans, the differences between estimated doses to CTV and OAR based on auto-courtoring were small, with no statistical significance, indicating that treatment planning for prostate cancer based on auto-courtoring has potential.

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PS1 - 189 A Universal Predictive Model for Dose Fall-Off in MLC-Based Stereotactic Brain Radiosurgery

Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques ◽

10.1017/cjn.2016.350 ◽

2016 ◽

Vol 43 (S4) ◽

pp. S8-S8

Author(s):

M. Ruschin ◽

A. Sahgal ◽

H. Soliman ◽

B. Chugh ◽

S. Myrehaug ◽

...

Keyword(s):

Clinical Decision Making ◽

Treatment Plan ◽

Clinical Decision ◽

Target Volume ◽

Adjustment Factor ◽

Ongoing Work ◽

Toxicity Risk ◽

Treatment Plans ◽

Prescription Dose ◽

Prediction Band

Predictive modeling of dose fall-off in radiosurgery could assist in clinical decision-making when prescribing a treatment plan with minimized toxicity risk. The purpose of this study is to develop a predictive dose fall-off model. Materials/Methods: We retrospectively reviewed treatment plans from 257 patients (365 lesions) with total doses ranging from 20 to 35Gy in 5 fractions. For each plan, we measured both total volume of the external contour (EXT) and BrainMinusPTV (BMP) receiving P=20% to P=80% of the prescription dose. The model has form y=Fa(PTV)b+/-delta. y=volume of EXT or BMP (cc’s); a and b are curve-fitting coefficients; PTV=total planning target volume (cc’s); F is an adjustment factor (>1) to account for number of targets; delta is the 95% prediction band. F, a, b, and delta were modeled such that dose-fall can be forecast for any PTV and dose level. Results: The model coefficients were as follows: Coefficient EXT BMP a 19927(100×P)exp(-2) 17122(100×P)exp(-2) b 0.42(100×P)exp(0.17) 0.63 F -0.0156×(100×P)+2.5517 delta 384467×(100×P)exp(-2.3159) The table can be used to determine the model for any P from 20% to 80%. Example: the EXT receiving 50%, P=0.5, a=8.0, b=0.82, F=1.8, delta=45. Thus, EXT-50=8(PTV0.82) or 1.8×8(PTV0.82) for 1-3 or >3 targets, respectively,+/-45cc’s. The model was verified against published values of dose fall-off from linacs. Conclusion: A predictive dose fall-off model was generated for linac-based radiosurgery. The model can be used for quality assurance or for inter-institutional comparisons. Ongoing work is being conducted to extend the model to a SRS cones system.

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MR guided high intensity focused ultrasound (MRgHIFU) for treating recurrent gynaecological tumours: a pilot feasibility study

British Journal of Radiology ◽

10.1259/bjr.20181037 ◽

2019 ◽

pp. 20181037 ◽

Cited By ~ 1

Author(s):

Sharon L Giles ◽

Georgios Imseeh ◽

Ian Rivens ◽

Gail R ter Haar ◽

Alexandra Taylor ◽

...

Keyword(s):

High Intensity ◽

Focused Ultrasound ◽

Organs At Risk ◽

Symptom Relief ◽

Tumour Volume ◽

Target Volume ◽

High Intensity Focused Ultrasound ◽

Limiting Factors ◽

Treatment Plans ◽

Gynaecological Tumours

Objective: To assess the feasibility of targeting recurrent gynaecological tumours with MR guided high intensity focused ultrasound (MRgHIFU). Methods: 20 patients with recurrent gynaecological tumours were prospectively scanned on a Philips/Profound 3 T Achieva MR/ Sonalleve HIFU system. Gross tumour volume (GTV) and planning target volume (PTV) were delineated on T 2W and diffusion-weighted imaging (DWI). Achievable treatment volumes that (i) assumed bowel and/or urogenital tract preparation could be used to reduce risk of damage to organs-at-risk (TVoptimal), or (ii) assumed no preparations were possible (TVno-prep) were compared with PTV on virtual treatment plans. Patients were considered treatable if TVoptimal ≥ 50 % PTV. Results: 11/20 patients (55%) were treatable if preparation strategies were used: nine had central pelvic recurrences, two had tumours in metastatic locations. Treatable volume ranged from 3.4 to 90.3 ml, representing 70 ± 17 % of PTVs. Without preparation, 6/20 (30%) patients were treatable (four central recurrences, two metastatic lesions). Limiting factors were disease beyond reach of the HIFU transducer, and bone obstructing tumour access. DWI assisted tumour outlining, but differences from T 2W imaging in GTV size (16.9 ± 23.0%) and PTV location (3.8 ± 2.8 mm in phase-encode direction) limited its use for treatment planning. Conclusions: Despite variation in size and location within the pelvis, ≥ 50 % of tumour volumes were considered targetable in 55 % patients while avoiding adjacent critical structures. A prospective treatment study will assess safety and symptom relief in a second patient cohort. Advances in knowledge: Target size, location and access make MRgHIFU a viable treatment modality for treating symptomatic recurrent gynaecological tumours within the pelvis.

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Evaluation of the radiobiological gamma index with motion interplay in tangential IMRT breast treatment

Journal of Radiation Research ◽

10.1093/jrr/rrw073 ◽

2016 ◽

Vol 57 (6) ◽

pp. 691-701 ◽

Cited By ~ 3

Author(s):

Iori Sumida ◽

Hajime Yamaguchi ◽

Indra J. Das ◽

Hisao Kizaki ◽

Keiko Aboshi ◽

...

Keyword(s):

Early Stage ◽

Organs At Risk ◽

Intensity Modulated Radiation Therapy ◽

Target Volume ◽

Normal Tissue Complication Probability ◽

Tumor Control ◽

Tumor Control Probability ◽

Equivalent Uniform Dose ◽

Gamma Index ◽

The Impact

Abstract The purpose of this study was to evaluate the impact of the motion interplay effect in early-stage left-sided breast cancer intensity-modulated radiation therapy (IMRT), incorporating the radiobiological gamma index (RGI). The IMRT dosimetry for various breathing amplitudes and cycles was investigated in 10 patients. The predicted dose was calculated using the convolution of segmented measured doses. The physical gamma index (PGI) of the planning target volume (PTV) and the organs at risk (OAR) was calculated by comparing the original with the predicted dose distributions. The RGI was calculated from the PGI using the tumor control probability (TCP) and the normal tissue complication probability (NTCP). The predicted mean dose and the generalized equivalent uniform dose (gEUD) to the target with various breathing amplitudes were lower than the original dose (P < 0.01). The predicted mean dose and gEUD to the OARs with motion were higher than for the original dose to the OARs (P < 0.01). However, the predicted data did not differ significantly between the various breathing cycles for either the PTV or the OARs. The mean RGI gamma passing rate for the PTV was higher than that for the PGI (P < 0.01), and for OARs, the RGI values were higher than those for the PGI (P < 0.01). The gamma passing rates of the RGI for the target and the OARs other than the contralateral lung differed significantly from those of the PGI under organ motion. Provided an NTCP value <0.05 is considered acceptable, it may be possible, by taking breathing motion into consideration, to escalate the dose to achieve the PTV coverage without compromising the TCP.

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Dosimetric evaluation of SBRT treatment plans of non-central lung tumours: clinical experience

Journal of Radiotherapy in Practice ◽

10.1017/s146039692000103x ◽

2020 ◽

pp. 1-21

Author(s):

Ernest Osei ◽

Johnson Darko ◽

Steph Swanson ◽

Katrina Fleming ◽

Ronald Snelgrove ◽

...

Keyword(s):

Lung Cancer ◽

Radiation Therapy ◽

Early Stage ◽

Organs At Risk ◽

Volumetric Modulated Arc Therapy ◽

Target Volume ◽

Conformal Radiation Therapy ◽

Lung Sbrt ◽

Treatment Plans ◽

The Mean

Abstract Objectives: Lung cancer is the most commonly diagnosed cancer in Canada and the leading cause of cancer-related mortality in both men and women in North America. Surgery is usually the primary treatment option for early-stage non-small cell lung cancer (NSCLC). However, for patients who may not be suitable candidates for surgery, stereotactic body radiation therapy (SBRT) is an alternative method of treatment. SBRT has proven to be an effective technique for treating NSCLC patients by focally administering high radiation dose to the tumour with acceptable risk of toxicity to surrounding healthy tissues. The goal of this comprehensive retrospective dosimetric study is to compare the dosimetric parameters between three-dimensional conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT) lung SBRT treatment plans for two prescription doses. Methods: We retrospectively analysed and compared lung SBRT treatment plans of 263 patients treated with either a 3DCRT non-coplanar or with 2–3 VMAT arcs technique at 48 Gy in 4 fractions (48 Gy/4) or 50 Gy in 5 fractions (50 Gy/5) prescribed to the planning target volume (PTV), typically encompassing the 80% isodose volume. All patients were treated on either a Varian 21EX or TrueBeam linear accelerator using 6-MV or 10-MV photon beams. Results: The mean PTV V95% and V100% for treatment plans at 48 Gy/4 are 99·4 ± 0·6% and 96·0 ± 1·0%, respectively, for 3DCRT and 99·7 ± 0·4% and 96·4 ± 3·4%, respectively, for VMAT. The corresponding mean PTV V95% and V100% at 50 Gy/5 are 99·0 ± 1·4% and 95·5 ± 2·5% for 3DCRT and 99·5 ± 0·8% and 96·1 ± 1·6% for VMAT. The CIRI and HI5/95 for the PTV at 48 Gy/4 are 1·1 ± 0·1 and 1·2 ± 0·0 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The corresponding CIRI and HI5/95 at 50 Gy/5 are 1·1 ± 0·1 and 1·3 ± 0·1 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The mean R50% and D2cm at 48 Gy/4 are 5·0 ± 0·8 and 61·2 ± 7·0% for 3DCRT and 4·9 ± 0·8 and 57·8 ± 7·9% for VMAT. The corresponding R50% and D2cm at 50 Gy/5 are 4·7 ± 0·5 and 65·5 ± 9·4% for 3DCRT and 4·7 ± 0·7 and 60·0 ± 7·2% for VMAT. Conclusion: The use of 3DCRT or VMAT technique for lung SBRT is an efficient and reliable method for achieving dose conformity, rapid dose fall-off and minimising doses to the organs at risk. The VMAT technique resulted in improved dose conformity, rapid dose fall-off from the PTV compared to 3DCRT, although the magnitude may not be clinically significant.

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Benefit of replanning in MR-guided online adaptive radiation therapy in the treatment of liver metastasis

Radiation Oncology ◽

10.1186/s13014-021-01813-6 ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Michael Mayinger ◽

Roman Ludwig ◽

Sebastian M. Christ ◽

Riccardo Dal Bello ◽

Alex Ryu ◽

...

Keyword(s):

Radiation Therapy ◽

Liver Metastases ◽

Organs At Risk ◽

Treatment Plan ◽

Target Volume ◽

Target Coverage ◽

Adaptive Replanning ◽

Pre Treatment ◽

Grade 3 ◽

Dosimetric Analysis

Abstract Purpose To assess the effects of daily adaptive MR-guided replanning in stereotactic body radiation therapy (SBRT) of liver metastases based on a patient individual longitudinal dosimetric analysis. Methods Fifteen patients assigned to SBRT for oligometastatic liver metastases underwent daily MR-guided target localization and on-table treatment plan re-optimization. Gross tumor volume (GTV) and organs at risk (OARs) were adapted to the anatomy-of-the-day. A reoptimized plan (RP) and a rigidly shifted baseline plan (sBP) without re-optimization were generated for each fraction. After extraction of DVH parameters for GTV, planning target volume (PTV), and OARs (stomach, duodenum, bowel, liver, heart) plans were compared on a per-patient basis. Results Median pre-treatment GTV and PTV were 14.9 cc (interquartile range (IQR): 7.7–32.9) and 62.7 cc (IQR: 42.4–105.5) respectively. SBRT with RP improved PTV coverage (V100%) for 47/75 of the fractions and reduced doses to the most proximal OARs (D1cc, Dmean) in 33/75 fractions compared to sBP. RP significantly improved PTV coverage (V100%) for metastases within close proximity to an OAR by 4.0% (≤ 0.2 cm distance from the edge of the PTV to the edge of the OAR; n = 7; p = 0.01), but only by 0.2% for metastases farther away from OAR (> 2 cm distance; n = 7; p = 0.37). No acute grade 3 treatment-related toxicities were observed. Conclusions MR-guided online replanning SBRT improved target coverage and OAR sparing for liver metastases with a distance from the edge of the PTV to the nearest luminal OAR < 2 cm. Only marginal improvements in target coverage were observed for target distant to critical OARs, indicating that these patients do not benefit from daily adaptive replanning.

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Using FFF beams to improve the therapeutic ratio of lung SBRT

Journal of Radiotherapy in Practice ◽

10.1017/s1460396920000576 ◽

2020 ◽

pp. 1-7

Author(s):

Oleg N. Vassiliev ◽

Christine B. Peterson ◽

Joe Y. Chang ◽

Radhe Mohan

Keyword(s):

At Risk ◽

Early Stage ◽

Organs At Risk ◽

Normal Tissue Complication Probability ◽

Planning System ◽

Treatment Planning System ◽

Early Stage Lung Cancer ◽

Therapeutic Ratio ◽

Treatment Plans ◽

Flattening Filter

Abstract Aim: The aim of this study was to investigate the extent to which lung stereotactic body radiotherapy (SBRT) treatment plans can be improved by replacing conventional flattening filter (FF) beams with flattening filter-free (FFF) beams. Materials and methods: We selected 15 patients who had received SBRT with conventional 6-MV photon beams for early-stage lung cancer. We imported the patients’ treatment plans into the Eclipse 13·6 treatment planning system, in which we configured the AAA dose calculation model using representative beam data for a TrueBeam accelerator operated in 6-MV FFF mode. We then created new treatment plans by replacing the conventional FF beams in the original plans with FFF beams. Results: The FFF plans had better target coverage than the original FF plans did. For the planning target volume, FFF plans significantly improved the D98, D95, D90, homogeneity index and uncomplicated tumour control probability. In most cases, the doses to organs at risk were lower in FFF plans. FFF plans significantly reduced the mean lung dose, V10, V20, V30, and normal tissue complication probability for the total lung and improved the dosimetric indices for the ipsilateral lung. For most patients, FFF beams achieved lower maximum doses to the oesophagus, heart and the spinal cord, and a lower chest wall V30. Conclusions: Compared with FF beams, FFF beams achieved lower doses to organs at risk, especially the lung, without compromising tumour coverage; in fact, FFF beams improved coverage in most cases. Thus, replacing FF beams with FFF beams can achieve a better therapeutic ratio.

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Automatic Radiotherapy Planning for Glioblastoma Radiotherapy With Sparing of the Hippocampus and nTMS-Defined Motor Cortex

Frontiers in Neurology ◽

10.3389/fneur.2021.787140 ◽

2022 ◽

Vol 12 ◽

Author(s):

Michaela Schuermann ◽

Yvonne Dzierma ◽

Frank Nuesken ◽

Joachim Oertel ◽

Christian Rübe ◽

...

Keyword(s):

Motor Cortex ◽

Maximum Dose ◽

Organs At Risk ◽

Target Volume ◽

Brain Regions ◽

Additional Treatment ◽

Radiotherapy Planning ◽

Plan Quality ◽

Planning Algorithm ◽

Treatment Plans

BackgroundNavigated transcranial magnetic stimulation (nTMS) of the motor cortex has been successfully implemented into radiotherapy planning by a number of studies. Furthermore, the hippocampus has been identified as a radiation-sensitive structure meriting particular sparing in radiotherapy. This study assesses the joint protection of these two eloquent brain regions for the treatment of glioblastoma (GBM), with particular emphasis on the use of automatic planning.Patients and MethodsPatients with motor-eloquent brain glioblastoma who underwent surgical resection after nTMS mapping of the motor cortex and adjuvant radiotherapy were retrospectively evaluated. The radiotherapy treatment plans were retrieved, and the nTMS-defined motor cortex and hippocampus contours were added. Four additional treatment plans were created for each patient: two manual plans aimed to reduce the dose to the motor cortex and hippocampus by manual inverse planning. The second pair of re-optimized plans was created by the Auto-Planning algorithm. The optimized plans were compared with the “Original” plan regarding plan quality, planning target volume (PTV) coverage, and sparing of organs at risk (OAR).ResultsA total of 50 plans were analyzed. All plans were clinically acceptable with no differences in the PTV coverage and plan quality metrics. The OARs were preserved in all plans; however, overall the sparing was significantly improved by Auto-Planning. Motor cortex protection was feasible and significant, amounting to a reduction in the mean dose by >6 Gy. The dose to the motor cortex outside the PTV was reduced by >12 Gy (mean dose) and >5 Gy (maximum dose). The hippocampi were significantly improved (reduction in mean dose: ipsilateral >6 Gy, contralateral >4.6 Gy; reduction in maximum dose: ipsilateral >5 Gy, contralateral >5 Gy). While the dose reduction using Auto-Planning was generally better than by manual optimization, the radiated total monitor units were significantly increased.ConclusionConsiderable dose sparing of the nTMS-motor cortex and hippocampus could be achieved with no disadvantages in plan quality. Auto-Planning could further contribute to better protection of OAR. Whether the improved dosimetric protection of functional areas can translate into improved quality of life and motor or cognitive performance of the patients can only be decided by future studies.

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