Francesco Fellin

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

PurposeTo validate, in the context of adaptive radiotherapy, three commercial software solutions for atlas-based segmentation.Methods and materialsFifteen 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.ResultsThe 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).ConclusionsFrom 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.

Helical tomotherapy and intensity modulated proton therapy in the treatment of early stage prostate cancer: A treatment planning comparison

PURPOSE To compare helical tomotherapy (HT) and intensity modulated proton therapy (IMPT) on early stage prostate cancer treatments delivered with simultaneous integrated boost (SIB) in moderate hypofractionation. MATERIAL/METHODS Eight patients treated with HT were replanned with two-field IMPT (2fIMPT) and five-field IMPT (5fIMPT), using a small pencil beam size (3 mm sigma). The prescribed dose was 74.3 Gy in 28 fractions on PTV1 (prostate) and PTV2 (proximal seminal vesicles), 65.5 Gy on PTV3 (distal seminal vesicles) and on the overlap between rectum and PTVs. RESULTS IMPT and HT achieved similar target coverage and dose homogeneity, with 5fIMPT providing the best results. The conformity indexes of IMPT were significantly lower for PTV1+2 and PTV3. Above 65 Gy, HT and IMPT were equivalent in the rectum, while IMPT spared the bladder and the penile bulb from 0 to 70 Gy. From 0 up to 60 Gy, IMPT dosimetric values were (much) lower for all OARs except the femur heads, where HT was better than 2fIMPT in the 25-35 Gy dose range. OARs mean doses were typically reduced by 30-50% by IMPT. NTCPs for the rectum were within 1% between the two techniques, except when the endpoint was stool frequency, where IMPT showed a small (though statistically significant) benefit. CONCLUSIONS HT and IMPT produce similar dose distributions in the target volume. The current knowledge on dose-effect relations does not allow to quantify the clinical impact of the large sparing of IMPT at medium-to-low doses.

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.

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.

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

Abstract 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.

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.

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.

Evaluation of different CT lung anatomies for proton therapy with pencil beam scanning delivery, using a validated non-rigid image registration method

Elisa Scalco, Marco Schwarz, Marina Sutto, Daniele Ravanelli, Francesco Fellin, Giovanni M. Cattaneo and Giovanna Rizzo Istituto di Bioimmagini e Fisiologia Molecolare (IBFM), CNR, Segrate (MI), Italy; Centro di Protonterapia, Azienda Provinciale per i Servizi Sanitari (APSS), Trento, Italy; Università degli studi di Trento, Trento, Italy; Dipartimento di fisica medica, Ospedale San Raffaele, Milano, Italy

OC-0342: Anatomical changes in mesothelioma patients: effect on proton dose distributions and benefits of early replanning

Results: Mean(standard deviation) V95 of the PTV of all plans was 98.6(4.3), and 94.7(5.8) in the recomputed plans on the localization CT (p=0.007). V95 for the GTV was 99.6(4.1) and 99.0(4.7) on the localization and the planning CT, respectively; this difference was not significant (p=0.0549). V98 for the GTV was 82.3(10.9) and 83.5(13.6) on the localization and the planning CT, respectively; this difference was again not significant (p=0.1483). Conclusions: The coverage of the PTV (5 mm margin) was significantly lower in the recomputation on the localization CT, whereas V95 and V98 of the GTV remained unchanged in this group of patients. The clinical relevance of these changes remains to be elucidated. Jet ventilation appears to be a feasible technique for irradiation of small peripheral tumors with proton therapy. The study of new planning strategies and margin concepts is warranted.