Juliana Fernandes Pavoni

Postmastectomy radiation therapy (PMRT) is an adjuvant treatment for breast cancer. Some mastectomized women undergoing PMRT can have breast reconstruction with expander implant reconstruction. However, the expander implant contains a magnetic metal port for its inflation, and in patients with a high risk of recurrence, the PMRT is performed before the expander replacement. The difficulties in radiation treatment near high-Z metals are mainly due to dose alterations around them. Therefore, this study proposes using a realistic breast phantom and gel dosimetry to investigate the effects of the metallic parts of the expandable prosthesis on the 3D delivery of the treatment. A conformal radiation treatment was planned and delivered to the gel phantom with the metal port. MAGIC-f gel was used with magnetic resonance imaging for dose assessment. The treatment plan dose distribution was compared to the measured dose distribution by gamma analysis (3%/3 mm/15% threshold). A significant gamma fail region was found near the metal port, corresponding to a dose reduction of approximately 5%. This underdose is within the tolerance threshold for dose heterogeneity established by the International Commission on Radiation Units (ICRU), but should be considered when treating these patients.

This study aims to investigate the relationship between the three-dimensional gamma index (3DGI) results and its clinical significance, proposing a correlation between changes in dose values in the dose-volume histogram (DVH) of the evaluated structures and 3DGI percentages of approval. In this study, we created 30 plans by including 1 mm displacement errors in the lateral, vertical, and longitudinal axes of each table, and compared them to a simulated, error-free treatment plan for prostate cancer. The plans were made in a commercial treatment planning system, using 6MV Varian 120-leaf multileaf collimators (MLC) linear accelerators and intensity modulated radiation therapy sliding window technique. We used a calculation algorithm-based MATLAB programming to evaluate the 3DGI analysis of fluence maps. The acceptance criteria were 3%/2 mm, 10% dose threshold, and 95% gamma passing rate. We compared 3DGI results with differences in structures DVH. DVH metrics versus 3DGI analysis showed a correlation between the percentage of point’s approval and planning target volume (PTV) coverage, presenting a degree of agreement of 0.85%, 0.96%, and 0.94% in the longitudinal, lateral, and vertical axes, respectively. In summary, it was possible to establish a linear relationship between the percentage of points approved in the 3DGI analysis and the PTV dose. A similar behavior was also observed in bladder and rectum DVH, but for these structures, the relationship was not the same in the three displaced axes.

Craniospinal irradiation (CSI) is a complex radiation technique employed to treat patients with primitive neuroectodermal tumors such as medulloblastoma or germinative brain tumors with the risk of leptomeningeal spread. In adults, this technique poses a technically challenging planning process because of the complex shape and length of the target volume. Thus, it requires multiple fields and different isocenters to guarantee the primary-tumor dose delivery. Recently, some authors have proposed the use IMRT technique for this planning with the possibility of overlapping adjacent fields. The high-dose delivery complexity demands three-dimensional dosimetry (3DD) to verify this irradiation procedure and motivated this study. We used an optical CT and a radiochromic Fricke-xylenol-orange gel with the addition of formaldehyde (FXO-f) to evaluate the doses delivered at the field junction region of this treatment. We found 96.91% as the mean passing rate using the gamma analysis with 3%/2 mm criteria at the junction region. However, the concentration of fail points in a determined region called attention to this evaluation, indicating the advantages of employing a 3DD technique in complex dose-distribution verifications.

This work intends to verify the influence on the dose distribution that the expansive prosthesis (SILIMED/470), containing a magnetic valve, generates in postoperative radiotherapy treatments of patients who underwent mastectomy. The presence of this metal during radiotherapy difficulties the treatment planning stage, due to the artifacts generated by the magnet in the acquisition of computed tomography. Radiochromic films (Gafchromic EBT2) were used for planar detection inside the prosthesis, around the metal in a plastic phantom that simulates breast geometry filled with water, an insert in the center allowed the placement of the magnet and 2.5 mm thick acrylic layers for film positioning above and below the metal at different depths. The phantom was irradiated with a 3D planning performed in XiO software (CMS RTP) with no heterogeneity correction, using beams of 6 MV and 15MV from the Oncor linear accelerator (Siemens) with a dose of 2Gy. The film calibration methodology was performed, and the optical densities of the films were measured using a CQ-01 digital densitometer (MRA). In the internal region of the prosthesis, for irradiation with 6MV, an unexpected dose increases of 7.6% was obtained for all films and, just above the magnet, an increase of 14.4% was noted. For the 15 MV beam, the films around the magnet had a dose increase of 10.4% considering the planning value and at 10mm away from the metal, a decrease of 1.28% of the expected dose was observed.

This study aims to verify the dose delivery of prostate radiotherapy treatments in an adult pelvic phantom with two metallic hip and femur prosthesis using a four‐field box technique. The prostate planned target volume (PTV) tridimensional (3D) dose distribution was evaluated using gel dosimetry, and thermoluminescent dosimeters (TLD) were used for point‐dose measurements outside it. Both results were compared to the treatment planning system (TPS) dose calculation without using heterogeneity corrections to evaluate the influence of the metal in the dose distribution. MAGIC‐f gel dosimeter (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper with Formaldehyde) associated with magnetic resonance imaging was used. TLD were positioned at several points at the bone metal interface and the sacrum region. The comparison of the gel measured and the TPS calculated dose distributions were done using gamma analysis (3%/3 mm), and a pass rate of 93% was achieved. The TLD dose values at the bone‐metal interface showed variations from the planned dose. However, at the sacrum region, where the beams did not intercept the prosthesis, there was a good agreement between TPS planning and TLD measurements. Our results show how the combination of 3D dosimetry and measurements at specific points in the phantom allowed a comprehensive view of the dose distribution and identified that care must also be paid to regions outside the PTV.

Purpose: Intensity‐modulated radiotherapy with simultaneous integrated boost (SIB) presents several attractive advantages to be employed in clinical practice. Its secure application demands a rigorous quality assurance (QA) procedure, ideal for three‐dimensional (3D) dose distribution measurements. Thus, a gel dosimetry methodology to evaluate the dose delivery of SIB treatments is presented and compared to conventional gamma evaluation.Methods: MAGIC‐f gel dosimeter with magnetic resonance images for dose reading were used following its standard procedures. Four SIB QA plans created in gel dosimeter phantoms were used. The gel measured and treatment planning system (TPS) calculated doses were compared using 3D gamma analyses (3%/3mm/15% threshold). Two structures were artificially on the TPS dose distribution expected on the phantom by converting the 1.7 and 2.0 Gy isodose levels into structures to represent the treatment. The gel and TPS dose‐volume histogram (DVH) were compared based on five dose points: D95%, D90%, D50%, D10%, and D5%.Results: Approvals of 93%, 96%, 98%, and 92% were achieved in the 3D gamma analyses for the plans QA 1, 2, 3, and 4. In the DVH analyses, QA plan 1 measured and expected curves showed a good agreement. QA plan 2 showed deviations in the highest doses for both structures with a maximum deviation (Δ_máx) of 8.0%. QA plans 3 and 4 showed the highest dose variation between the gel and TPS in the smaller doses of the DVH (Δ_máx of 7.2% and −8.9%, respectively). For QA plan 4, the curves of the 1.7 Gy structure presented a good agreement, but deviations in the smaller dose region of the DVH occurred for the 2 Gy structure (Δ_máx of 7.7%).Conclusions: A methodology for 3D dose evaluation of complex SIB treatments was proposed. It provided an important overview of the dose distributions. Their results significantly complemented the usual gamma analysis results.

This letter is a response to the letter to the editor written by Bevelacqua et al. regarding: ‘The risk of induced cancer and ischemic heart disease following low dose lung irradiation for COVID-19...