Is it still necessary to perform measured based pre-treatment patient-specific QA for SRS HyperArc treatments?

PURPOSE: The Mobius3D system was validated as a modern secondary check dosimetry system. In particular, our objective has been to assess the suitability of the M3D as pre-treatment patient-specific Quality Assurance (QA) tool for Stereotactic Radiosurgery (SRS) HyperArc (HA) treatments. We aimed to determine whether Mobius3D could safely replace the measurements-based patient-specific QA for this type of treatment. METHODS: 30 SRS HA treatment plans for brain were selected. The dose distributions, calculated by Mobius and our routinely used algorithm (AcurosXB v.15.6), were compared using gamma analysis index and DVH parameters based on the patient's CT dataset. All 30 plans were then delivered across the ionization chamber in a homogeneous phantom and the measured dose was compared with both M3D and TPS calculated one. The plans were delivered and verified in terms of PSQA using the electronic portal imaging device (EPID) with Portal Dosimetry (PD) and myQA SRS (IBA Dosimetry) detector. Plans that achieved a global gamma passing rate (GPR) ≥ 97% based on 2%/2 mm criteria, with both Mobius3D and the conventional methods were evaluated acceptable. Finally, we assessed the capability of the M3D system to detect errors related to the position of the Multi-Leaf Collimator (MLC) in comparison to the analyzed measurement-based systems. RESULTS: No relevant differences were observed in the comparison between the dose calculated on the CT-dataset by M3D and the TPS. Observed discrepancies are imputable to different used algorithms, but no discrepancies related to goodness of plans have been found. Average differences between calculated (M3D and TPS) vs measured dose with ionization chamber were 2.5% (from 0.41% to 3.2%) and 1.81% (from 0.66% to 2.65%), for M3D and TPS, respectively. All plans passed with a gamma passing rate > 97% using conventional PSQA methods with a gamma criterion of 2% dose difference and 2 mm distance-to-agreement. The average gamma passing rate for the M3D system was determined to be 99.4% (from 97.3% to 100%). Results from this study also demonstrated Mobius has better error detectability than conventional measurement-based systems. CONCLUSION: Our study shows Mobius3D could be a suitable alternative to conventional measured based QA methods for SRS HyperArc treatments.

Impact of inter-observer variability on first axillary level dosimetry in breast cancer radiotherapy: An AIRO multi-institutional study.

This study quantified the incidental dose to the first axillary level (L1) in locoregional treatment plan for breast cancer. Eighteen radiotherapy centres contoured L1-L4 on three different patients (P1,2,3), created the L2-L4 planning target volume (single centre planning target volume, SC-PTV) and elaborated a locoregional treatment plan. The L2-L4 gold standard clinical target volume (CTV) along with the gold standard L1 contour (GS-L1) were created by an expert consensus. The SC-PTV was then replaced by the GS-PTV and the incidental dose to GS-L1 was measured. Dosimetric data were analysed with Kruskal-Wallis test. Plans were intensity modulated radiotherapy (IMRT)-based. P3 with 90° arm setup had statistically significant higher L1 dose across the board than P1 and P2, with the mean dose (Dmean) reaching clinical significance. Dmean of P1 and P2 was consistent with the literature (77.4% and 74.7%, respectively). The incidental dose depended mostly on L1 proportion included in the breast fields, underlining the importance of the setup, even in case of IMRT.

Organ dose in CT: Comparison between measurements and computational methods.

PURPOSE: This study aims to compare two methods for the organ dose evaluation in computed tomography (CT) in the head- and thorax regions: an experimental method, using radiochromic films, and a computational one, using a commercial software. METHODS: Gafchromic® XR-QA2 and EBT-3 were characterized in terms of energetic, angular, and irradiation configurations dependence. Two free-in-air irradiation calibration configurations were employed using a CT scanner: with the sensitive surface of the film orthogonal (OC) and parallel (PC) to the beam axis. Different dose-response curves were obtained by varying the irradiation configurations and the beam quality (BQ). Subsequently, films were irradiated within an anthropomorphic phantom using CT-thorax and -head protocols, and the organ dose values obtained were compared with those provided by the commercial software. RESULTS: At different configurations, an unchanged dose response was achieved with EBT-3, while a dose response of 15% was obtained with XR-QA2. By varying BQ, XR-QA2 showed a different response below 10%, while EBT-3 showed a variation below 5% for dose values >20 mGy. For films irradiation angle equal to 90°, the normalized to 0° relative response was 41% for the XR-QA2 model and 83% for the EBT-3 one. Organ dose values obtained with EBT-3 for both configurations and with XR-QA2 for OC were in agreement with the DW values, showing percentage discrepancies of less than 25%. CONCLUSIONS: The obtained results showed the potential of EBT-3 in CT patient dosimetry since the lower angular dependence, compared to XR-QA2, compensates for low sensitivity in the diagnostic dose range.

HyperArcTM Dosimetric Validation for Multiple Targets Using Ionization Chamber and RT-100 Polymer Gel.

Multiple brain metastases single-isocenter stereotactic radiosurgery (SRS) treatment is increasingly employed in radiotherapy department. Before its use in clinical routine, it is recommended to perform end-to-end tests. In this work, we report the results of five HyperArcTM treatment plans obtained by both ionization chamber (IC) and polymer gel. The end-to-end tests were performed using a water equivalent Mobius Verification PhantomTM (MVP) and a 3D-printed anthropomorphic head phantom PseudoPatient® (PP) (RTsafe P.C., Athens, Greece); 2D and 3D dose distributions were evaluated on the PP phantom using polymer gel (RTsafe). Gels were read by 1.5T magnetic resonance imaging (MRI). Comparison between calculated and measured distributions was performed using gamma index passing rate evaluation by different criteria (5% 2 mm, 3% 2 mm, 5% 1 mm). Mean point dose differences of 1.01% [min −0.77%−max 2.89%] and 0.23% [min 0.01%−max 2.81%] were found in MVP and PP phantoms, respectively. For each target volume, the obtained results in terms of gamma index passing rate show an agreement >95% with 5% 2 mm and 3% 2 mm criteria for both 2D and 3D distributions. The obtained results confirmed that the use of a single isocenter for multiple lesions reduces the treatment time without compromising accuracy, even in the case of target volumes that are quite distant from the isocenter.

Ex Vivo Irradiation of Lung Cancer Stem Cells Identifies the Lowest Therapeutic Dose Needed for Tumor Growth Arrest and Mass Reduction In Vivo.

Radiotherapy represents a first-line treatment for many inoperable lung tumors. New technologies offer novel opportunities for the treatment of lung cancer with the administration of higher doses of radiation in smaller volumes. Because both therapeutic and toxic treatment effects are dose-dependent, it is important to identify a minimal dose protocol for each individual patient that maintains efficacy while decreasing toxicity. Cancer stem cells sustain tumor growth, promote metastatic dissemination, and may give rise to secondary resistance. The identification of effective protocols targeting these cells may improve disease-free survival of treated patients. In this work, we evaluated the existence of individual profiles of sensitivity to radiotherapy in patient-derived cancer stem cells (CSCs) using both in vitro and in vivo models. Both CSCs in vitro and mice implanted with CSCs were treated with radiotherapy at different dose intensities and rates. CSC response to different radiation doses greatly varied among patients. In vitro radiation sensitivity of CSCs corresponded to the therapeutic outcome in the corresponding mouse tumor model. On the other side, the dose administration rate did not affect the response. These findings suggest that in vitro evaluation of CSCs may potentially predict patients' response, thus guiding clinical decision.

SBRT/SRS patient-specific QA using GAFchromicTM EBT3 and FilmQATM Pro software.

The aim of this work is to verify the potential use of GAFchromicTM EBT3 and FILMQATM pro software for patient specific quality assurance (QA) for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatment plans in clinical routine use. In particular, encephalic, pulmonary and lymph node treatments plans were selected for this study. The agreement between the calculated and measured dose distributions were evaluated in terms of ɣ index with 3%3mm, 2%2mm, 1.5%1.5mm and 3%1.5mm criteria. The obtained results were then compared to the routine pre-treatment verification method which uses electronic portal imaging device (EPID) and EPIQA analysis software. EBT3-FilmQA method results show a mean ɣ index passing rate >95% with 2%1.5mm analysis criteria and an improvement of about 7% compared with EPID-EPIQA method results.

Whole Brain Irradiation or Stereotactic RadioSurgery for five or more brain metastases (WHOBI-STER): A prospective comparative study of neurocognitive outcomes, level of autonomy in daily activities and quality of life.

AIMS: To evaluate neurocognitive performance, daily activity and quality of life (QoL), other than usual oncologic outcomes, among patients with brain metastasis ≥5 (MBM) from solid tumors treated with Stereotactic Brain Irradiation (SBI) or Whole Brain Irradiation (WBI). METHODS: This multicentric randomized controlled trial will involve the enrollment of 100 patients (50 for each arm) with MBM ≥ 5, age ≥ 18 years, Karnofsky Performance Status (KPS) ≥ 70, life expectancy > 3 months, known primary tumor, with controlled or controllable extracranial disease, baseline Montreal Cognitive Assessment (MoCA) score ≥ 20/30, Barthel Activities of Daily Living score ≥ 90/100, to be submitted to SBI by LINAC with monoisocentric technique and non-coplanar arcs (experimental arm) or to WBI (control arm). The primary endpoints are neurocognitive performance, QoL and autonomy in daily-life activities variations, the first one assessed by MoCa Score and Hopkins Verbal Learning Test-Revised, the second one through the EORTC QLQ-C15-PAL and QLQ-BN-20 questionnaires, the third one through the Barthel Index, respectively. The secondary endpoints are time to intracranial failure, overall survival, retreatment rate, acute and late toxicities, changing of KPS. It will be considered significant a statistical difference of at least 30% between the two arms (statistical power of 80% with a significance level of 95%). DISCUSSION: Several studies debate what is the decisive factor accountable for the development of neurocognitive decay among patients undergoing brain irradiation for MBM: radiation effect on clinically healthy brain tissue or intracranial tumor burden? The answer to this question may come from the recent technological advancement that allows, in a context of a significant time saving, improved patient comfort and minimizing radiation dose to off-target brain, a selective treatment of MBM simultaneously, otherwise attackable only by WBI. The achievement of a local control rate comparable to that obtained with WBI remains the fundamental prerequisite. TRIAL REGISTRATION: NCT number: NCT04891471.

Volumetric Modulated Arc Therapy Capabilities for Treating Lower-Extremity Skin Affected by Several Merkel Cell Carcinoma Nodules: When Technological Advances Effectively Achieve the Palliative Therapeutic Goal while Minimising the Risk of Potential Toxicities.

The peculiar and rare clinical condition below clearly requires a customized care approach in the context of personalized medicine. An 80-year-old female patient who was subjected in 2018 to surgical removal of a cutaneous Merkel cell carcinoma (MCC) nodule located on the posterior surface of the left thigh and to three subsequent palliative radiotherapy treatments developed a fourth relapse in October 2020, with fifteen nodular metastases located in the left thigh and leg. Since the overall macroscopic disease was still exclusively regionally located and microscopic spread was likely extended also to clinically negative skin of the thigh and leg, we performed an irradiation of the whole left lower extremity. For this purpose the total target (65.5 cm) was divided into three sub-volumes. Dose prescription was 30 Gy in 15 daily fractions. A sequential boost of 10 Gy in 5 daily fractions was planned for macroscopic nodules. Plans were calculated by means of volumetric modulated arc therapy (VMAT) with the field overlap technique. Thanks to this, we obtained a homogeneous dose distribution in the field junction region; avoidance structures were delineated in the central part of the thigh and leg with the aim of achieving an optimal superficial dose painting and to reduce bone exposure to radiation. This case study demonstrates that VMAT allows for a good dose coverage for circumferential cutaneous targets while sparing deeper organs at risk. A reproducible image-guided set-up is fundamental for an accurate and safe dose delivery. However, local treatments such as radiotherapy for very advanced MCC of the lower extremities might have limited impact due to the high probability of systemic progression, as illustrated in this case. Radiation is confirmed as being effective in preventing MCC nodule progression toward skin wounding.

The influence of basic plan parameters on calculated small field output factors - A multicenter study.

PURPOSE: The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study. METHODS AND MATERIALS: Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3 mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm2 field sizes (FSs) (normalized to 10x10 cm2 FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3 mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs. RESULTS: A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p < 0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic Algorithms, presented a dependence on GR (p < 0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible. CONCLUSIONS: Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.

Geometric contour variation in clinical target volume of axillary lymph nodes in breast cancer radiotherapy: an AIRO multi-institutional study.

OBJECTIVES: To determine interobserver variability in axillary nodal contouring in breast cancer (BC) radiotherapy (RT) by comparing the clinical target volume of participating single centres (SC-CTV) with a gold-standard CTV (GS-CTV). METHODS: The GS-CTV of three patients (P1, P2, P3) with increasing complexity was created in DICOM format from the median contour of axillary CTVs drawn by BC experts, validated using the simultaneous truth and performance-level estimation and peer-reviewed. GS-CTVs were compared with the correspondent SC-CTVs drawn by radiation oncologists, using validated metrics and a total score (TS) integrating all of them. RESULTS: Eighteen RT centres participated in the study. Comparative analyses revealed that, on average, the SC-CTVs were smaller than GS-CTV for P1 and P2 (by -29.25% and -27.83%, respectively) and larger for P3 (by +12.53%). The mean Jaccard index was greater for P1 and P2 compared to P3, but the overlap extent value was around 0.50 or less. Regarding nodal levels, L4 showed the highest concordance with the GS. In the intra-patient comparison, L2 and L3 achieved lower TS than L4. Nodal levels showed discrepancy with GS, which was not statistically significant for P1, and negligible for P2, while P3 had the worst agreement. DICE similarity coefficient did not exceed the minimum threshold for agreement of 0.70 in all the measurements. CONCLUSIONS: Substantial differences were observed between SC- and GS-CTV, especially for P3 with altered arm setup. L2 and L3 were the most critical levels. The study highlighted these key points to address. ADVANCES IN KNOWLEDGE: The present study compares, by means of validated geometric indexes, manual segmentations of axillary lymph nodes in breast cancer from different observers and different institutions made on radiotherapy planning CT images. Assessing such variability is of paramount importance, as geometric uncertainties might lead to incorrect dosimetry and compromise oncological outcome.

How Much Daily Image-guided Volumetric Modulated Arc Therapy Is Useful for Proctitis Prevention With Respect to Static Intensity Modulated Radiotherapy Supported by Topical Medications Among Localized Prostate Cancer Patients?

BACKGROUND/AIM: To evaluate if topical support therapy during static-intensity modulated radiotherapy (sIMRT) course is able to equal the characteristic minimum risk for radiation proctitis of Image-guided volumetric modulated arc therapy (IG-VMAT) treatment among localized prostate cancer patients. PATIENTS AND METHODS: Rectal toxicity data of the above patients were retrospectively collected throughout three different clinical periods at our Radiotherapy Deparment: from October 2011 to December 2012, prostate cancer patients were treated with sIMRT and in advance supported by means of daily topical corticosteroids; from January 2013 to November 2016, topical corticosteroids were replaced by daily hyaluronic acid enemas; from December 2016 to May 2018 eligible patients were treated with newly introduced IG-VMAT supported by only on-demand topical corticosteroids. RESULTS: Among 359 eligible patients, IG-VMAT was proven generally more effective than sIMRT supported by topical medications in terms of proctitis reduction, although without clinical and practical relevance. CONCLUSION: Topical medications might have a role in radiation proctitis prevention.

Anatomical Predictors of Dosimetric Advantages for Deep-inspiration-breath-hold 3D-conformal Radiotherapy Among Women With Left Breast Cancer.

BACKGROUND/AIM: This study aimed to analyze the dosimetric gain of the deep-inspiration-breath-hold (DIBH) technique over the free-breathing (FB) one in left breast cancer (LBC) 3D-conformal-radiotherapy (3D-CRT), and simultaneously investigate the anatomical parameters related to heart RT-exposure. PATIENTS AND METHODS: Treatment plans were generated in both DIBH and FB scenarios for 116 LBC patients monitored by the Varian RPM™ respiratory gating system for delivery of conventional or moderately hypofractionated schedules (±sequential boost). For comparison, we considered cardiac and ipsilateral lung doses and volumes. RESULTS: A significant reduction of cardiac and pulmonary doses using DIBH technique was achieved compared to FB plans. Larger clinical target volumes generally need longer distance between medial and lateral entrances of tangent fields at body surface, thus conditioning a worse heart RT-exposure. CONCLUSION: The DIBH technique reduces cardiac and pulmonary doses for LBC patients. Through easily detectable anatomical parameters, it is possible to predict which patients benefit most from DIBH-RT.

Radiosensitivity of Cancer Stem Cells Has Potential Predictive Value for Individual Responses to Radiotherapy in Locally Advanced Rectal Cancer.

Neo-adjuvant radiotherapy is frequently employed in the therapeutic management of locally advanced rectal cancer (LARC). Radiotherapy can both reduce local recurrence and improve the success of surgical procedures by reducing tumor mass size. However, some patients show a poor response to treatment, which results in primary resistance or relapse after apparent curative surgery. In this work, we report in vitro and in vivo models based on patient-derived cancer stem cells (CSCs); these models are able to predict individual responses to radiotherapy in LARC. CSCs isolated from colorectal cancer biopsies were subjected to in vitro irradiation with the same clinical protocol used for LARC patients. Animal models, generated by CSC xenotransplantation, were also obtained and treated with the same radiotherapy protocol. The results indicate that CSCs isolated from rectal cancer needle biopsies possess an intrinsic grade of sensitivity to treatment, which is also maintained in the animal model. Notably, the specific CSCs' in vitro and in vivo sensitivity values correspond to patients' responses to radiotherapy. This evidence suggests that an in vitro radiotherapy response predictivity assay could support clinical decisions for the management of LARC patients, thus avoiding radiation toxicity to resistant patients and reducing the treatment costs.

Lung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies.

PURPOSE: A large-scale multi-institutional planning comparison on lung cancer SABR is presented with the aim of investigating possible criticism in carrying out retrospective multicentre data analysis from a dosimetric perspective. METHODS: Five CT series were sent to the participants. The dose prescription to PTV was 54Gy in 3 fractions of 18Gy. The plans were compared in terms of PTV-gEUD2 (generalized Equivalent Uniform Dose equivalent to 2Gy), mean dose to PTV, Homogeneity Index (PTV-HI), Conformity Index (PTV-CI) and Gradient Index (PTV-GI). We calculated the maximum dose for each OAR (organ at risk) considered as well as the MLD2 (mean lung dose equivalent to 2Gy). The data were stratified according to expertise and technology. RESULTS: Twenty-six centers equipped with Linacs, 3DCRT (4% - 1 center), static IMRT (8% - 2 centers), VMAT (76% - 20 centers), CyberKnife (4% - 1 center), and Tomotherapy (8% - 2 centers) collaborated. Significant PTV-gEUD2 differences were observed (range: 105-161Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively, 56.8±3.4Gy, 14.2±10.1%, 0.70±0.15, and 4.9±1.9. Significant correlations for PTV-gEUD2 versus PTV-HI, and MLD2 versus PTV-GI, were observed. CONCLUSIONS: The differences in terms of PTV-gEUD2 may suggest the inclusion of PTV-gEUD2 calculation for retrospective data inter-comparison.