Is it beneficial to use apertures in proton radiosurgery with a scanning beam? A dosimetric comparison in neurinoma and meningioma patients.

PURPOSE: To assess the dosimetric advantages of apertures in intracranial single fraction proton radiosurgery. MATERIALS AND METHODS: Six neuroma and 10 meningioma patients were investigated. For each patient, six plans were computed, with two spot spacing and three aperture settings (no apertures, 5 and 8 mm margin between aperture and clinical target volume [CTV]). All plans were optimized on the CTV with the same beam arrangement and the same single-field robust optimization (2 mm setup errors, 3.5% range uncertainties). Robustness analysis was performed with 0.5 and 1.0 mm systematic setup errors and 3.5% range uncertainties. CTV coverage in the perturbed scenarios and healthy brain tissue sparing in the surrounding of the CTV were compared. RESULTS: Meningiomas were larger and at a shallow depth than neuromas. In neuromas, spot spacing did not affect OAR doses or the robustness of CTV coverage and the apertures reduced brain dose without any significant impact on CTV robustness. In meningiomas, smaller spot spacing produced a reduction in brain V5Gy and improved robustness of CTV coverage; in addition, an 8 mm margin aperture reduced low and medium brain tissue doses without affecting robustness in the 0.5 mm perturbed scenario. A 5 mm margin aperture caused a reduction of plan robustness. CONCLUSION: The optimal use of apertures is a trade-off between sparing of low and medium dose to the healthy brain and robustness of target coverage, also depending on size and depth of the lesion.

Potential skin morbidity reduction with intensity-modulated proton therapy for breast cancer with nodal involvement.

Background: Different modern radiation therapy treatment solutions for breast cancer (BC) and regional nodal irradiation (RNI) have been proposed. In this study, we evaluate the potential reduction in radiation-induced skin morbidity obtained by intensity modulated proton therapy (IMPT) compared with intensity modulated photon therapy (IMXT) for left-side BC and RNI. Material and Methods: Using CT scans from 10 left-side BC patients, treatment plans were generated using IMXT and IMPT techniques. A dose of 50 Gy (or Gy [RBE] for IMPT) was prescribed to the target volume (involved breast, the internal mammary, supraclavicular, and infraclavicular nodes). Two single filed optimization IMPT (IMPT1 and IMPT2) plans were calculated without and with skin optimization. For each technique, skin dose-metrics were extracted and normal tissue complication probability (NTCP) models from the literature were employed to estimate the risk of radiation-induced skin morbidity. NTCPs for relevant organs-at-risk (OARs) were also considered for reference. The non-parametric Anova (Friedman matched-pairs signed-rank test) was used for comparative analyses. Results: IMPT improved target coverage and dose homogeneity even if the skin was included into optimization strategy (HIIMPT2 = 0.11 vs. HIIMXT = 0.22 and CIIMPT2 = 0.96 vs. CIIMXT = 0.82, p < .05). A significant relative skin risk reduction (RR = NTCPIMPT/NTCPIMXT) was obtained with IMPT2 including the skin in the optimization with a RR reduction ranging from 0.3 to 0.9 depending on the analyzed skin toxicity endpoint/model. Both IMPT plans attained significant OARs dose sparing compared with IMXT. As expected, the heart and lung doses were significantly reduced using IMPT. Accordingly, IMPT always provided lower NTCP values. Conclusions: IMPT guarantees optimal target coverage, OARs sparing, and simultaneously minimizes the risk of skin morbidity. The applied model-based approach supports the potential clinical relevance of IMPT for left-side BC and RNI and might be relevant for the setup of cost-effectiveness evaluation strategies based on NTCP predictions, as well as for establishing patient selection criteria.

Universal field matching in craniospinal irradiation by a background-dose gradient-optimized method.

PURPOSE: The gradient-optimized methods are overcoming the traditional feathering methods to plan field junctions in craniospinal irradiation. In this note, a new gradient-optimized technique, based on the use of a background dose, is described. METHODS: Treatment planning was performed by RayStation (RaySearch Laboratories, Stockholm, Sweden) on the CT scans of a pediatric patient. Both proton (by pencil beam scanning) and photon (by volumetric modulated arc therapy) treatments were planned with three isocenters. An 'in silico' ideal background dose was created first to cover the upper-spinal target and to produce a perfect dose gradient along the upper and lower junction regions. Using it as background, the cranial and the lower-spinal beams were planned by inverse optimization to obtain dose coverage of their relevant targets and of the junction volumes. Finally, the upper-spinal beam was inversely planned after removal of the background dose and with the previously optimized beams switched on. RESULTS: In both proton and photon plans, the optimized cranial and the lower-spinal beams produced a perfect linear gradient in the junction regions, complementary to that produced by the optimized upper-spinal beam. The final dose distributions showed a homogeneous coverage of the targets. DISCUSSION: Our simple technique allowed to obtain high-quality gradients in the junction region. Such technique universally works for photons as well as protons and could be applicable to the TPSs that allow to manage a background dose.

Occupational burnout among radiation therapy technologists in Italy before and during COVID-19 pandemic.

INTRODUCTION: Radiation therapy technologists (RTTs) are exposed to high stress levels which may lead to burnout, which could be further increased by the current pandemic. The aim of our study was to assess burnout and stress among Italian RTTs before and during the pandemic. METHODS: The Italian Association of Radiation Therapy and Medical Physics Technologists (AITRO) and the Italian Federation of Scientific Radiographers Societies (FASTeR) proposed a national online survey, including the Maslach Burnout Inventory assessing emotional exhaustion (EE), depersonalisation (DP), and personal accomplishment (PA) to RTTs before and during the pandemic. Multivariate regression analyses and χ2 tests were used for data analysis. RESULTS: We obtained 367 answers, 246 before and 121 during the pandemic. RTTs before and during the pandemic showed high EE and DP, intermediate PA. Median EE was 37 (interquartile range [IQR] 31-46] before and 37 (IQR 30-43) during the pandemic, median DP was 16 (IQR 13-21) and 15 (IQR 12-20), respectively. PA was 31 (IQR 28-34) and 32 (IQR 28-34), respectively. Through multivariate analysis, being female and having children led to higher EE scores before and during the pandemic (p≤0.026). Only the presence of workplace stress management courses was related to lower DP before and being female was related to higher DP during the pandemic (p<0.001). Being female, having children, and working with paediatric patients were related to lower PA before and during the pandemic (p≤0.015). CONCLUSION: Our study highlighted high burnout levels for RTTs regardless of the pandemic. Future interventions aimed at preventing burnout should be implemented in their work environment, independently of the impact of exceptional events.

Rosette-Forming Glioneuronal Tumor of the Fourth Ventricle: A Case of Relapse Treated with Proton Beam Therapy.

Rosette-forming glioneuronal tumors (RGNTs) are rare, grade I, central nervous system (CNS) tumors typically localized to the fourth ventricle. We describe a 9-year-old girl with dizziness and occipital headache. A magnetic resonance imaging (MRI) revealed a large hypodense posterior fossa mass lesion in relation to the vermis, with cystic component. Surgical resection of the tumor was performed. A RGNT diagnosis was made at the histopathological examination. During follow-up, the patient experienced a first relapse, which was again surgically removed. Eight months after, MRI documented a second recurrence at the local level. She was a candidate for the proton beam therapy (PBT) program. Three years after the end of PBT, the patient had no evidence of disease recurrence. This report underlines that, although RGNTs are commonly associated with an indolent course, they may have the potential for aggressive behavior, suggesting the need for treatment in addition to surgery. Controversy exists in the literature regarding effective management of RGNTs. Chemotherapy and radiation are used as adjuvant therapy, but their efficacy management has not been adequately described in the literature. This is the first case report published in which PBT was proposed for adjuvant therapy in place of chemotherapy in RGNT relapse.

The role of radiation therapy technologist in interventional radiotherapy (brachytherapy) in Italy: Italian Association of Radiotherapy and Clinical Oncology (AIRO) and Italian Association of Radiation Therapy and Medical Physics Technologists (AITRO) joint project.

PURPOSE: Interventional radiotherapy (IRT, brachytherapy and intra-operative radiotherapy) is a complex treatment approach that requires a multi-professional approach. The aim of this work was to assess the role of radiation therapy technologist (RTT) in IRT team, with a special focus on brachytherapy as well as to define more appropriate ways to improve skills and training to promote cooperation of multi-professional team. MATERIAL AND METHODS: A nationwide survey consisting of 16 questions was proposed between April and May 2020, with collaboration between the Italian Association of Radiation Therapy and Medical Physics Technologists (AITRO) and the Interventional Radiotherapy Study Group of Italian Association of Radiotherapy and Clinical Oncology (AIRO). The survey was sent through the AITRO contact list to RTTs' contacts from all Italian radiotherapy (RT) departments. RESULTS: A total of 37 answered questionnaires returned (36% of all contacts reached), each from different center. 23 centers (62%) presented with dedicated team for IRT treatments, while 15 centers (41%) had dedicated RTT staff. The majority of RTT (86%) did not consider undergraduate training adequate to acquire the skills required to work in IRT departments or units. CONCLUSIONS: This survey underlines the need of additional education and training for RTTs that should focus on treatment management optimization in development of an IRT multi-professional team. Specific updates could be the key to develop further collaboration and to improve cancer patient care.

Clinical validation of a GPU-based Monte Carlo dose engine of a commercial treatment planning system for pencil beam scanning proton therapy.

PURPOSE: To perform the validation of the GPU-based (Graphical Processing Unit based) proton Monte Carlo (MC) dose engine implemented in a commercial TPS (RayStation 10B) and to report final dose calculation times for clinical cases. MATERIALS AND METHODS: 440 patients treated at the Proton Therapy Center of Trento, Italy, between 2018 and 2019 were selected for this study. 636 approved plans with 3361 beams computed with the clinically implemented CPU-MC dose engine (version 4.2 and 4.5), were used for the validation of the new algorithm. For each beam, the dose was recalculated using the new GPU-MC dose engine with the initial CPU computation settings and compared to the original CPU-MC dose. Beam dose difference distributions were studied to ensure that the two dose distributions were equal within the expected fluctuations of the MC statistical uncertainty (s) of each computation. Plan dose distributions were compared with respect to the dosimetric indices D98, D50 and D1 of all ROIs defined as targets. A complete assessment of the computation time as a function of s and dose grid voxel size was done. RESULTS: The median over all mean beam dose differences between CPU- and GPU-MC was -0.01% and the median of the corresponding standard deviations was close to (√2s) both for simulations with an s of 0.5% and 1.0% per beam. This shows that the two dose distributions can be considered equal. All the DVH indices showed an average difference below 0.04%. About half of the plans were computed with 1.0% statistical uncertainty on a 2 mm dose calculation grid, for which the median computation time was 5.2 s. The median computational speed for all plans in the study was 8.4 million protons/second. CONCLUSION: A validation of a clinical MC algorithm running on GPU was performed on a large pool of patients treated with pencil beam scanning proton therapy. We demonstrated that the differences with the previous CPU-based MC were only due to the intrinsic statistical fluctuations of the MC method, which translated to insignificant differences on plan dose level. The significant increase in dose calculation speed is expected to facilitate new clinical workflows.

An avoidance method to minimize dose perturbation effects in proton pencil beam scanning treatment of patients with small high-Z implants.

To implement a multi-field-optimization (MFO) technique for treating patients with high-Z implants in pencil beam scanning proton-therapy and generate treatment plans that avoids small implants. Two main issues were addressed: (i) the assessment of the optimal CT acquisition and segmentation technique to define the dimension of the implant and (ii) the distance of pencil beams from the implant (avoidance margin) to assure that it does not affect dose distribution. Different CT reconstruction protocols (by O-MAR or standard reconstruction and by 12 bit or 16 bit dynamic range) followed by thresholding segmentation were tested on a phantom with lead spheres of different sizes. The proper avoidance margin was assessed on a dedicated phantoms of different materials (copper/tantalum and lead), shape (square slabs and spheres) and detectors (two-dimensional array chamber and radio-chromic films). The method was then demonstrated on a head-and-neck carcinoma patient, who underwent carotid artery embolization with a platinum coil close to the target. Regardless the application of O-MAR reconstruction, the CT protocol with a full 16 bit dynamic range allowed better estimation of the sphere volumes, with maximal error around -5% in the greater sphere only. Except the configuration with a shallow target (which required a pre-absorber), particularly with a retracted snout, an avoidance margin of around 0.9-1.3 cm allowed to keep the difference between planned and measured dose below 5-10%. The patient plan analysis showed adequate plan quality and confirmed effective implant avoidance. Potential target under-dosage can be produced by patient misalignment, which could be minimized by daily alignment on the implant, identifiable on orthogonal kilovolt images. By implant avoidance MFO it was possible to minimize potential dose perturbation effects produced by small high-Z implants. An advantage of such approach lies in its potential applicability for any type of implant, regardless the precise knowledge of its composition.

Modelling the risk of radiation induced alopecia in brain tumor patients treated with scanned proton beams.

PURPOSE: To develop normal tissue complication probability (NTCP) models for radiation-induced alopecia (RIA) in brain tumor patients treated with proton therapy (PT). METHODS AND MATERIALS: We analyzed 116 brain tumor adult patients undergoing scanning beam PT (median dose 54 GyRBE; range 36-72) for CTCAE v.4 grade 2 (G2) acute (≤90 days), late (>90 days) and permanent (>12 months) RIA. The relative dose-surface histogram (DSH) of the scalp was extracted and used for Lyman-Kutcher-Burman (LKB) modelling. Moreover, DSH metrics (Sx: the surface receiving ≥ X Gy, D2%: near maximum dose, Dmean: mean dose) and non-dosimetric variables were included in a multivariable logistic regression NTCP model. Model performances were evaluated by the cross-validated area under the receiver operator curve (ROC-AUC). RESULTS: Acute, late and permanent G2-RIA was observed in 52%, 35% and 19% of the patients, respectively. The LKB models showed a weak dose-surface effect (0.09 ≤ n ≤ 0.19) with relative steepness 0.29 ≤ m ≤ 0.56, and increasing tolerance dose values when moving from acute and late (22 and 24 GyRBE) to permanent RIA (44 GyRBE). Multivariable modelling selected S21Gy for acute and S25Gy, for late G2-RIA as the most predictive DSH factors. Younger age was selected as risk factor for acute G2-RIA while surgery as risk factor for late G2-RIA. D2% was the only variable selected for permanent G2-RIA. Both LKB and logistic models exhibited high predictive performances (ROC-AUCs range 0.86-0.90). CONCLUSION: We derived NTCP models to predict G2-RIA after PT, providing a comprehensive modelling framework for acute, late and permanent occurrences that, once externally validated, could be exploited for individualized scalp sparing treatment planning strategies in brain tumor patients.

An advanced junction concept in pediatric craniospinal irradiation by proton pencil beam scanning.

PURPOSE: To present an advanced junction concept in craniospinal irradiation (CSI) by proton pencil beam scanning (PBS). MATERIALS AND METHODS: In PBS CSI, whole brain irradiation (WBI) is commonly delivered by opposed lateral-beams, whereas spine irradiation is delivered by posterior entrances. Since lateral-beams would cross a large portion of the patient at the shoulder level, the junction between WBI and spine irradiation cannot extend below that level, thus the size of the lateral-beams needs to be limited and the number of required isocenters can increase. To overcome such limitation, a pseudo-junction was introduced below the posterior fossa, to turn in this region the WBI beam arrangement to a single posterior beam pointed at the same isocenter, that was matched to the posterior spinal beam more caudally, below shoulder level, in the true-junction. After assessing robustness of the technique to range and setup uncertainties, twenty-three treated patients were reviewed to estimate the percentage that might benefit of being treated by two instead of three isocenters. RESULTS: Target coverage at the junction levels resulted robust, with D95% > 95% on pseudo-junction and D95% > 90% on the true-junction. By the advanced junction concept, 91% of patients might by treated with only two isocenters, whereas, by the conventional method, 83% of patients required three isocenters. CONCLUSION: With the presented junction concept the number of isocenters can be reduced, with a consequent relevant reduction of treatment time, which is particularly valuable in the management of pediatric patients under anesthesia.

A pre-absorber optimization technique for pencil beam scanning proton therapy treatments.

PURPOSE: To implement a new proton therapy planning method for the treatment of shallow lesions with PBS and to compare it to the standard method. METHODS AND MATERIALS: In order to treat shallow lesions, a pre-absorber, usually called range-shifter (RS), is needed: it is used to degrade the beam energy and treat tumors shallower than the minimum range available. Its use is associated to dose calculation uncertainties and plan quality degradation which should be minimized. We studied five tumor localizations requiring RS and created three plans for each case: a) standard method with the RS close to the patient surface, b) with the RS used only for the shallow part of the tumor (when strictly needed) and completely retracted and c) as the b) approach but with the RS close to the patient. We called these two approaches 'Range Shifter Optimization' (RSO) techniques. We compared those plans in terms of dose distribution quality, delivery time and patient-specific-QA results. RESULTS: In most cases a good dose reduction to OARs with no significant loss in terms of target coverage was obtained when the RSO techniques were used. Patient-specific-QA gave very good results in terms of γ-Passing-Rate (PR) (3%, 3 mm) for both RSO techniques (mean 98.09%), while the standard had some very low PR (minimum 81.09%). The delivery time increased (5.0 min on average per treatment) but was still acceptable in terms of patient compliance. CONCLUSION: We developed a new planning technique for shallow lesions and we demonstrated its superiority in terms of both plan quality and patient-specific-QA results with respect to the standard method. This technique is routinely used to treat patients in our center.

Radiation-Induced Moyamoya Syndrome After Proton Therapy in Child with Clival Chordoma: Natural History and Surgical Treatment.

BACKGROUND: Proton therapy has proven to be effective and safe in the treatment of radioresistant skull base tumors such as chordomas. Thanks to the peculiar physical properties of the proton beam, radiation energy is delivered in a narrow space called the Bragg peak and the surrounding normal tissues receive a minimal amount of the radiation dose. This is important to lower the risk of radiation-induced damage, especially in children. However, local adverse effects in proximity to the target volume may occur. In particular, the development of moyamoya syndrome (MMS) has been rarely reported in children receiving proton beam therapy for brain tumors. CASE DESCRIPTION: We report on a child who developed rapidly progressive MMS after proton beam therapy for a clivus chordoma. A combined indirect revascularization procedure by encephalo-duro-arterio-synangiosis and encephalo-myo-synangiosis was performed with good neuroradiologic and clinical outcome. CONCLUSIONS: Regardless of the presence of known risk factors for MMS, strict neuroimaging surveillance is indicated in all patients treated with radiotherapy including those receiving proton beam therapy. We suggest that an early revascularization procedure should be considered in patients with worsening symptoms and/or sign of neuroradiologic progression of cerebral vasculopathy. This management of MMS could lower the risk of permanent neurologic deficits and improve patients' quality of life.

Impact of dose engine algorithm in pencil beam scanning proton therapy for breast cancer.

PURPOSE: Proton therapy for the treatment of breast cancer is acquiring increasing interest, due to the potential reduction of radiation-induced side effects such as cardiac and pulmonary toxicity. While several in silico studies demonstrated the gain in plan quality offered by pencil beam scanning (PBS) compared to passive scattering techniques, the related dosimetric uncertainties have been poorly investigated so far. METHODS: Five breast cancer patients were planned with Raystation 6 analytical pencil beam (APB) and Monte Carlo (MC) dose calculation algorithms. Plans were optimized with APB and then MC was used to recalculate dose distribution. Movable snout and beam splitting techniques (i.e. using two sub-fields for the same beam entrance, one with and the other without the use of a range shifter) were considered. PTV dose statistics were recorded. The same planning configurations were adopted for the experimental benchmark. Dose distributions were measured with a 2D array of ionization chambers and compared to APB and MC calculated ones by means of a γ analysis (agreement criteria 3%, 3 mm). RESULTS: Our results indicate that, when using proton PBS for breast cancer treatment, the Raystation 6 APB algorithm does not allow obtaining sufficient accuracy, especially with large air gaps. On the contrary, the MC algorithm resulted into much higher accuracy in all beam configurations tested and has to be recommended. CONCLUSIONS: Centers where a MC algorithm is not yet available should consider a careful use of APB, possibly combined with a movable snout system or in any case with strategies aimed at minimizing air gaps.

Water equivalent thickness of immobilization devices in proton therapy planning - Modelling at treatment planning and validation by measurements with a multi-layer ionization chamber.

PURPOSE: To investigate the range errors made in treatment planning due to the presence of the immobilization devices along the proton beam path. METHODS: The measured water equivalent thickness (WET) of selected devices was measured by a high-energy spot and a multi-layer ionization chamber and compared with that predicted by treatment planning system (TPS). Two treatment couches, two thermoplastic masks (both un-stretched and stretched) and one headrest were selected. At TPS, every immobilization device was modelled as being part of the patient. The following parameters were assessed: CT acquisition protocol, dose-calculation grid-sizes (1.5 and 3.0mm) and beam-entrance with respect to the devices (coplanar and non-coplanar). Finally, the potential errors produced by a wrong manual separation between treatment couch and the CT table (not present during treatment) were investigated. RESULTS: In the thermoplastic mask, there was a clear effect due to beam entrance, a moderate effect due to the CT protocols and almost no effect due to TPS grid-size, with 1mm errors observed only when thick un-stretched portions were crossed by non-coplanar beams. In the treatment couches the WET errors were negligible (<0.3mm) regardless of the grid-size and CT protocol. The potential range errors produced in the manual separation between treatment couch and CT table were small with 1.5mm grid-size, but could be >0.5mm with a 3.0mm grid-size. In the headrest, WET errors were negligible (0.2mm). CONCLUSIONS: With only one exception (un-stretched mask, non-coplanar beams), the WET of all the immobilization devices was properly modelled by the TPS.

Supine craniospinal irradiation in pediatric patients by proton pencil beam scanning.

BACKGROUND AND PURPOSE: Proton therapy is the emerging treatment modality for craniospinal irradiation (CSI) in pediatric patients. Herein, special methods adopted for CSI at proton Therapy Center of Trento by pencil beam scanning (PBS) are comprehensively described. MATERIALS AND METHODS: Twelve pediatric patients were treated by proton PBS using two/three isocenters. Special methods refer to: (i) patient positioning in supine position on immobilization devices crossed by the beams; (ii) planning field-junctions via the ancillary-beam technique; (iii) achieving lens-sparing by three-beams whole-brain-irradiation; (iv) applying a movable-snout and beam-splitting technique to reduce the lateral penumbra. Patient-specific quality assurance (QA) program was performed using two-dimensional ion chamber array and γ-analysis. Daily kilovoltage alignment was performed. RESULTS: PBS allowed to obtain optimal target coverage (mean D98%>98%) with reduced dose to organs-at-risk. Lens sparing was obtained (mean D1∼730cGyE). Reducing lateral penumbra decreased the dose to the kidneys (mean Dmean<600cGyE). After kilovoltage alignment, potential dose deviations in the upper and lower junctions were small (average 0.8% and 1.2% respectively). Due to imperfect modeling of range shifter, QA showed better agreements between measurements and calculations at depths >4cm (mean γ>95%) than at depths<4cm. CONCLUSIONS: The reported methods allowed to effectively perform proton PBS CSI.

Nasal cavity reirradiation: a challenging case for comparison between proton therapy and volumetric modulated arc therapy.

BACKGROUND: The aim of this case report is to report on a dosimetric comparison between volumetric modulated arc therapy (RapidArc technique and active scanning proton therapy (single-field (SFO) and multifield (MFO) techniques) in a case of nasal cavity cancer recurrence. CASE REPORT: A 72-year-old man, who received adjuvant radiotherapy for a carcinoma of the nasal cavity, experienced an unresectable local recurrence in the previous surgical bed. Hence, the patient was evaluated for reirradiation by comparing different modalities, with a total prescribed dose of 50 Gy in standard fractionation. RA plan was revealed to be equivalent to the MFO plan in terms of target dose coverage and conformity index. SFO plan was not able to respect a maximum dose of 9 Gy to nervous structures, in contrast to RA and MFO plans. CONCLUSIONS: In this challenging scenario, although a clear preference would be given to the MFO proton plan, the RA plan was revealed to be adequate for the clinical goal of target coverage and sparing of organs at risk.

Helical tomotherapy and intensity modulated proton therapy in the treatment of dominant intraprostatic lesion: a treament planning comparison.

PURPOSE: To compare helical tomotherapy (HT) and intensity modulated proton therapy (IMPT) for prostate cancer irradiation while concomitantly boosting dominant intraprostatic lesions (DILs). METHODS AND MATERIALS: Treatment plans of seven patients were designed for HT and IMPT (pencil beam size: 3mm sigma). The prescribed median PTV/DIL doses were 71.4/100 Gy in 28 fractions, while satisfying "safe" dose constraints for organs at risks (OARs) including rectum, bladder, femoral heads, penile bulb and urethra. The planner could further reduce the dose to OARs if PTV/DIL constraints were reached. RESULTS: IMPT achieved better dose conformity (CI=1.11 vs 1.31, p<0.05) and coverage (V95%=97.3% vs 95.3%, p<0.05) in PTV. Concerning DIL volumes, both techniques delivered the prescribed dose (D median: HT=100 Gy, IMPT=102.1 Gy) with similar dose conformity (CI: HT=1.49, IMPT=1.44) and same dose homogeneity, D99%, D1%, while satisfying the OARs constraints. Excepting urethra, the sparing of OARs was significantly better with IMPT; in general, the lower the dose, the greater the benefit of IMPT. Normal tissue complication probabilities for the rectum were in favor of IMPT with an absolute reduction of 3-8%, depending on the NTCP model (p<0.05). CONCLUSIONS: Both techniques allowed delivering 100 Gy to DILs, while complying with the OARs constraints. IMPT was superior in sparing OARs for doses up to approximately 70 Gy, with larger benefit at lower doses.

Systematic evaluation of three different commercial software solutions for automatic segmentation for adaptive therapy in head-and-neck, prostate and pleural cancer.

PURPOSE: To validate, in the context of adaptive radiotherapy, three commercial software solutions for atlas-based segmentation. METHODS AND MATERIALS: Fifteen patients, five for each group, with cancer of the Head&Neck, pleura, and prostate were enrolled in the study. In addition to the treatment planning CT (pCT) images, one replanning CT (rCT) image set was acquired for each patient during the RT course. Three experienced physicians outlined on the pCT and rCT all the volumes of interest (VOIs). We used three software solutions (VelocityAI 2.6.2 (V), MIM 5.1.1 (M) by MIMVista and ABAS 2.0 (A) by CMS-Elekta) to generate the automatic contouring on the repeated CT. All the VOIs obtained with automatic contouring (AC) were successively corrected manually. We recorded the time needed for: 1) ex novo ROIs definition on rCT; 2) generation of AC by the three software solutions; 3) manual correction of AC.To compare the quality of the volumes obtained automatically by the software and manually corrected with those drawn from scratch on rCT, we used the following indexes: overlap coefficient (DICE), sensitivity, inclusiveness index, difference in volume, and displacement differences on three axes (x, y, z) from the isocenter. RESULTS: The time saved by the three software solutions for all the sites, compared to the manual contouring from scratch, is statistically significant and similar for all the three software solutions. The time saved for each site are as follows: about an hour for Head&Neck, about 40 minutes for prostate, and about 20 minutes for mesothelioma. The best DICE similarity coefficient index was obtained with the manual correction for: A (contours for prostate), A and M (contours for H&N), and M (contours for mesothelioma). CONCLUSIONS: From a clinical point of view, the automated contouring workflow was shown to be significantly shorter than the manual contouring process, even though manual correction of the VOIs is always needed.

In-gantry or remote patient positioning? Monte Carlo simulations for proton therapy centers of different sizes.

PURPOSE: We estimated the potential advantage of remote positioning (RP) vs. in-room positioning (IP) for a proton therapy facility in terms of patient throughput. MATERIALS AND METHODS: Monte Carlo simulations of facilities with one, two or three gantries were performed. A sensitivity analysis was applied by varying the imaging and setup correction system (ICS), the speed of transporters (for RP) and beam switching time. Possible advantages of using three couches (for RP) or of switching the beam between fields was also investigated. RESULTS: For a single gantry facility, an average of 20% more patients could be treated using RP: ranging from +45%, if a fast transporter and slow ICS were simulated, to -14% if a slow transporter and fast ICS was simulated. For two gantries, about 10% more patients could be treated with RP, ranging from +32% (fast transporter, slow ICS) to -12% (slow transporter, fast ICS). The ability to switch beam between fields did not substantially influence the throughput. In addition, the use of three transporters showed increased delays and therefore a slight reduction of the fractions executables. For three gantries, RP and IP showed similar results. CONCLUSIONS: The advantage of RP vs. IP strongly depends on ICS and the speed of the transporters. For RP to be advantageous, reduced transport times are required. The advantage of RP decreases with increasing number of gantries.