Stereotactic MR-guided adaptive radiotherapy (SMART) for primary rectal cancer: evaluation of early toxicity and pathological response

Background: The purpose of this study is to measure the effects of stereotactic MR-guided adaptive radiotherapy (SMART) for rectal cancer patients in terms of early toxicity and pathological response. Materials and methods: For this prospective pilot study, patients diagnosed with locally advanced rectal cancer (LARC) with positive lymph node clinical staging underwent SMART on rectal lesion and mesorectum using hybrid MR-Linac (MRIdian ViewRay). Dose prescription at 80% isodose for the rectal lesion and mesorectum was 40 Gy (8 Gy/fr) and 25 Gy (5 Gy/fr), respectively, delivered on 5 days (3 fr/week). Response assessment by MRI was performed 3 weeks after SMART, then patients fit for surgery underwent total mesorectal excision. Primary endpoint was evaluation of adverse effect of radiotherapy. Secondary endpoint was pathological complete response rate. Early toxicity was graded according to the Common Terminology Criteria for Adverse Events (CTCAE v5.0). Results: From October 2020 to January 2022, twenty patients underwent rectal SMART. No grade 3–5 toxicity was recorded. Twelve patients were eligible for total mesorectal excision (TME). Mean interval between the completion of SMART and surgery was 4 weeks. Pathological downstaging occurred in all patients; rate of pathological complete response (pCR) was 17%. pCR occurred with a prolonged time to surgery (> 7 weeks). Conclusion: To our knowledge, this is the first study to use stereotactic radiotherapy for primary rectal cancer. SMART for rectal cancer is well tolerated and effective in terms of tumor regression, especially if followed by delayed surgery.

Dose Volume Distribution in Digital Breast Tomosynthesis: A Phantom Study

Monte Carlo (MC) calculations for breast dosimetry in digital breast tomosynthesis (DBT) require experimental validations. We measured the 3-D dose distribution in breast phantoms, using XR-QA2 radiochromic films, compared to dose maps obtained with a previously validated MC code. Film sheets were positioned at the entrance surface, at the bottom surface as well as at four depths between adjacent slabs in the fiveslabs 50-mm-thick phantoms simulating a compressed breast. We employed a homogeneous PMMA phantom, for the method validation, and a heterogeneous (BR 50/50) phantom for a preliminary study in a complex breast phantom. Irradiations were made at 40 kV at ±25° and 0° in craniocaudal view. A continuous scan over 15° was carried out for the homogeneous phantom. In the direction of the beam axis the dose decreases down to 12% of the entrance value. In the transverse planes, the dose varies up to 17%; in the heterogeneous phantom, it decreases to 25% in the direction of the beam axis. In transverse planes the maximum dose variations are up to 18% at θ = 0°, whereas the dose varies up to 22% in angular views. The simulations agreed with the measured values within the measurement uncertainties

Rotational radiotherapy of breast cancer with polyenergetic kilovoltage X-ray beams: An experimental and Monte Carlo phantom study

Purpose We investigated the feasibility of kilovoltage rotational radiotherapy for breast cancer (kV-EBRT) via Monte Carlo simulations and measurements on phantoms. Methods We derived the dose distributions for X-ray beams at 150 kV, 300 kVp and 320 kV irradiating breast cylindrical phantoms of 14 cm diameter, mimicking the pendant breast. Simulations were based on the Geant4 toolkit. The point-like X-ray source was rotated either over a full circle or on a limited arc around the phantom. We studied the influence on the surface dose of the distance between the tumor lesion to the skin, of the irradiation protocol (full scan or partial scan) and of the X-ray tube current modulation. Results Rotational kV-EBRT permitted a periphery-to-center dose ratio from 13% to 9% in homogeneous breast phantoms. Dose distributions in phantoms with off-center simulated lesions, showed a skin-to-tumor dose ratio of 16% and 34% for lesions at 3.25 and 5.25 cm from cylinder axis, respectively. Simulation of the X-ray tube current modulation during the rotation, permits to reach a dose ratio of 20% for the lesion located at 5.25 cm from phantom axis. Conclusions We showed the possibility of using low-energy X-ray spectra for kV-EBRT with collimated beams, for obtaining a periphery-to-center dose ratio in the same order of conventional accelerator based megavoltage radiotherapy, when the irradiated area is localized in the center of the breast. For tumors localized near the breast border, we showed that the tube current modulation can be a good solution in order to reduce the skin-to-tumor dose ratio

In vivo comparison of micro-balloon interventions (MBI) advantage: a retrospective cohort study of DEB-TACE versus b-TACE and of SIRT versus b-SIRT

Purpose The purpose of this study was to evaluate in vivo the role of the micro-balloon by comparing trans-arterial chemoembolization (DEB-TACE) and selective internal radiotherapy (SIRT) procedures performed with and without balloon micro-catheter (b-DEB-TACE and DEBTACE/ SIRT and b-SIRT) for the treatment of hepatocellular carcinoma (HCC). Methods The impact of a balloon micro-catheter on transarterial loco-regional treatment was analyzed using nonenhanced post-procedural cone-beam CT (Ne-CBCT) by comparing the attenuation values in the embolized area and the surrounding liver tissue before and after DEB-TACEversus b-DEB-TACE and by comparing 2D/3D dosimetry in single-photon emission computed tomography after SIRT versus b-SIRT, and by comparing the histological count of the beads following orthotopic liver transplantation in the DEB-TACE versus b-DEB-TACE subgroup. Results We treated 84 HCC patients using trans-arterial loco-regional therapy. Fifty-three patients (26 DEB-TACE and 27 b-DEB-TACE) were analyzed in the TACE group. Contrast, signal-to-noise ratio, and contrast-to-noise ratio were all significantly higher in b-DEB-TACE subgroup than DEB-TACE (182.33 HU [CI95% 160.3–273.5] vs. 124 HU [CI95% 80.6–163.6]; 8.3 [CI95% 5.7–10.1] vs. 4.5 [CI95% 3.7–6.0]; 6.9 [CI95% 4.3–7.8] vs. 3.1 [CI95% 2.2–5.0] p.05). Thirty-one patients (24 SIRT and 7 b-SIRT) were analyzed in the SIRT group. 2D dosimetry profile evaluation showed an activity intensity peak significantly higher in the b-SIRT than in the SIRT subgroup (987.5 ± 393.8 vs. 567.7 ± 302.2, p = 0.005). Regarding 3D dose analysis, the mean dose administered to the treated lesions was significantly higher in the b-SIRT than in the SIRT group (151.6 Gy ± 53.2 vs. 100.1 Gy ± 43.4, p = 0.01). In histological explanted liver analysis, there was a trend for higher intra-tumoral localization of embolic microspheres for b-DEB-TACE in comparison with DEBTACE. Conclusions Due to the use of three different methods, the results of this study demonstrate in vivo, a better embolization profile of oncological intra-arterial interventions performed with balloon micro-catheter regardless of the embolic agent employed

Radiochromic film dosimetry in synchrotron radiation breast computed tomography: a phantom study

This study relates to the INFN project SYRMA-3D for in vivo phase-contrast breast computed tomography using the SYRMEP synchrotron radiation beamline at the ELETTRA facility in Trieste, Italy. This peculiar imaging technique uses a novel dosimetric approach with respect to the standard clinical procedure. In this study, optimization of the acquisition procedure was evaluated in terms of dose delivered to the breast. An offline dose monitoring method was also investigated using radiochromic film dosimetry. Various irradiation geometries have been investigated for scanning the prone patient's pendant breast, simulated by a 14 cm-diameter polymethylmethacrylate cylindrical phantom containing pieces of calibrated radiochromic film type XR-QA2. Films were inserted mid-plane in the phantom, as well as wrapped around its external surface, and irradiated at 38 keV, with an air kerma value that would produce an estimated mean glandular dose of 5 mGy for a 14 cm-diameter 50% glandular breast. Axial scans were performed over a full rotation or over 180°. The results point out that a scheme adopting a stepped rotation irradiation represents the best geometry to optimize the dose distribution to the breast. The feasibility of using a piece of calibrated radiochromic film wrapped around a suitable holder around the breast to monitor the scan dose offline is demonstrated

Modelling of the neutron production in a mixed beam DT neutron generator

Compact DT neutron generators based on accelerators are often built on the principle of a mixed beam operation, meaning that deuterium (D) and tritium (T) are both present in the ion beam and in the target. Moreover, the beam consists of a mixture of ions and ionized molecules (D, T ions, and ionized D-D, T-T and D-T molecules) so the relevant source components come from T(d, n), D(t, n), D(d, n) and T(t, 2n) reactions at different ion energies. The method for assessing the relative amplitudes of different source components (DD, DT, TT) is presented. The assessment relies on the measurement of the neutron spectrum of different DT components (T(d, n) and D(t, n) at different energies) using a high resolution neutron spectrometer, e.g. a diamond detector, fusion reaction cross-sections, and simulations of neutron generation in the target. Through this process a complete description of the neutron source properties of the mixed beam neutron generator can be made and a neutron source description card, in a format suitable for Monte Carlo code MCNP, produced