BACKGROUND: Radiotherapy plays an important role in cancer treatment today. Successful radiotherapy includes precise positioning and accurate dosimetry. OBJECTIVE: To use NIPAM gel dosimeter and concentric swing machine to simulate and evaluate the feasibility of lung or upper abdominal tumor dose distribution during breathing. METHODS: We used a concentric swing machine to simulate actual radiotherapy for lung or upper abdomen tumors. A 4 × 4 cm2 irradiation field area was set and MRI was performed. Next, readout analysis was performed using MATLAB and the 3 mm, 3% gamma passing rate > 95% was used as a basis for evaluation. RESULTS: The concentric dynamic dose curve for a simulated respiratory rate of 3 seconds/breath and 4 × 4 cm2 field was compared with 4 × 4, 3 × 3, and 2 × 2 cm2 treatment planning systems (TPS), and the 3 mm, 3% gamma passing rate was 42.87%, 54.96%, and 49.92%, respectively. Pre-simulation showed that the high-dose region dose curve was similar to the 2 × 2 cm2 TPS result. After appropriate selection and comparison, we found that the 3 mm, 3% gamma passing rate was 97.92% on comparing the > 60% dose curve with the 2 × 2 cm2 TPS. CONCLUSIONS: NIPAM gel dosimeter and concentric swing machine use is feasible to simulate dose distribution during breathing and results conforming to clinical evaluation standards.
Introduction: The use of a tissue expander in breast reconstruction is a popular option for patients undergo mastectomy. We applied Monte Carlo simulation to analyze the dose deposition from proton beams in the presence of a tissue expander containing a steel magnetic injection port. Methods:. A steel injection port for breast tissue expander (Mentor®) was studied with a single anterior (AP) proton beam. A general‐purpose Monte Carlo particle transport code FLUKA was applied for simulation. A 10×10 cm beam was delivered to a water phantom of 50×50×50 cm with the port positioned at the surface. Data on the proton fluence and dose deposited in phantom were collected for a range of initial proton energies forming the spread out Bragg peak (SOBP) of 100 to 200 MeV. Results: Our simulation shows that low energy proton fluence is disturbed significantly by the presence of the steel injection port. Impact of the port components varies at the crossbeam plane. The needle shielding plate edge decreases fluence in the beam direction by almost at 30%. The proton range shifts about 50 % for lower energies (100 MeV) and 15% for higher energies (200 MeV). Dose changes at distances close to metal‐phantom interface are between 5 and 10%; however, there are dramatic changes (up to 100%) in dose deposition at deep areas where the SOBP suppose to form. Combining multiple beams with various energies and weights into SOBP will cause multiple spots of significant over‐ and under dose. Conclusions: The dose perturbation by a steel injection port for breast tissue expanders is significant if the implant is in a proton field. The accuracy in treatment planning with conventional algorithms may be questionable in the presence of the inhomogeneity. Avoidance of such metallic components should be considered if adjuvant proton radiotherapy is considered.
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