Verification of lithium formate monohydrate in 3D-printed container for electron paramagnetic resonance dosimetry in radiotherapy.

The nondestructive dosimetry achieved with electron paramagnetic resonance (EPR) dosimetry facilitates repetitive recording by the same dosimeter to increase the reliability of data. In precedent studies, solid paraffin was needed as a binder material to make the lithium formate monohydrate (LFM) EPR dosimeter stable and nonfragile; however, its use complicates dosimetry. This study proposes a newly designed pure LFM EPR dosimeter created by inserting LFM into a 3D-printed container. Dosimetric characteristics of the LFM EPR dosimeter and container, such as reproducibility, linearity, energy dependence, and angular dependence, were evaluated and verified through a radiation therapy planning system (RTPS). The LFM EPR dosimeters were irradiated using a clinical linear accelerator. The EPR spectra of the dosimeters were acquired using a Bruker EMX EPR spectrometer. Through this study, it was confirmed that there is no tendency in the EPR response of the container based on irradiation dose or radiation energy. The results show that the LFM EPR dosimeters have a highly sensitive dose response with good linearity. The energy dependence across each photon and electron energy range seems to be negligible. Based on these results, LFM powder in a 3D-printed container is a suitable option for dosimetry of radiotherapy. Furthermore, the LFM EPR dosimeter has considerable potential for in vivo dosimetry and small-field dosimetry via additional experiments, owing to its small effective volume and highly sensitive dose response compared with a conventional dosimeter.

Image similarity evaluation of the bulk-density-assigned synthetic CT derived from MRI of intracranial regions for radiation treatment.

OBJECTIVE: Various methods for radiation-dose calculation have been investigated over previous decades, focusing on the use of magnetic resonance imaging (MRI) only. The bulk-density-assignment method based on manual segmentation has exhibited promising results compared to dose-calculation with computed tomography (CT). However, this method cannot be easily implemented in clinical practice due to its time-consuming nature. Therefore, we investigated an automatic anatomy segmentation method with the intention of providing the proper methodology to evaluate synthetic CT images for a radiation-dose calculation based on MR images. METHODS: CT images of 20 brain cancer patients were selected, and their MR images including T1-weighted, T2-weighted, and PETRA were retrospectively collected. Eight anatomies of the patients, such as the body, air, eyeball, lens, cavity, ventricle, brainstem, and bone, were segmented for bulk-density-assigned CT image (BCT) generation. In addition, water-equivalent CT images (WCT) with only two anatomies-body and air-were generated for a comparison with BCT. Histogram comparison and gamma analysis were performed by comparison with the original CT images, after the evaluation of automatic segmentation performance with the dice similarity coefficient (DSC), false negative dice (FND) coefficient, and false positive dice (FPD) coefficient. RESULTS: The highest DSC value was 99.34 for air segmentation, and the lowest DSC value was 73.50 for bone segmentation. For lens segmentation, relatively high FND and FPD values were measured. The cavity and bone were measured as over-segmented anatomies having higher FPD values than FND. The measured histogram comparison results of BCT were better than those of WCT in all cases. In gamma analysis, the averaged improvement of BCT compared to WCT was measured. All the measured results of BCT were better than those of WCT. Therefore, the results of this study show that the introduced methods, such as histogram comparison and gamma analysis, are valid for the evaluation of the synthetic CT generation from MR images. CONCLUSIONS: The image similarity results showed that BCT has superior results compared to WCT for all measurements performed in this study. Consequently, more accurate radiation treatment for the intracranial regions can be expected when the proper image similarity evaluation introduced in this study is performed.

The feasibility of a heart block with an electron compensation as an alternative whole breast radiotherapy technique in patients with underlying cardiac or pulmonary disease.

PURPOSE: We aimed to evaluate the feasibility of the heart block with electron compensation (HBE) technique, based on three-dimensional conformal radiotherapy (3D-CRT) in left-sided breast cancer patients with underlying cardiac or pulmonary disease. METHODS: Twenty patients with left-sided breast cancer who were treated with whole breast radiotherapy (WBRT) were included in this study. Intensity-modulated radiotherapy (IMRT), 3D-CRT, and HBE treatment plans were generated for each patient. Based on the 3D-CRT plan, the HBE plan included a heart block from the medial tangential field to shield the heart and added an electron beam to compensate for the loss in target volume coverage. The dosimetric parameters for the heart and lung and the target volume between the three treatment types were compared. RESULTS: Of the three plans, the HBE plan yielded the most significant reduction in the doses received by the heart and lung (heart Dmean: 5.1 Gy vs. 12.9 Gy vs. 4.0 Gy and lung Dmean: 11.4 Gy vs. 13.2 Gy vs. 10.5 Gy, for 3D-CRT, IMRT, and HBE, respectively). Target coverage with all three techniques was within the acceptable range (Dmean 51.0 Gy vs. 51.2 Gy vs. 50.6 Gy, for 3D-CRT, IMRT, and HBE, respectively). CONCLUSIONS: The HBE plan effectively reduced the amount of radiation exposure to the heart and lung. It could be beneficial for patients who are vulnerable to radiation-related cardiac or pulmonary toxicities.

Dosimetric comparison of simultaneous integrated boost with whole-breast irradiation for early breast cancer.

PURPOSE: The purpose of this study was to identify a more suitable boost plan for simultaneously integrated boost scheme in patients with breast cancer by comparing among 3 types of whole-breast irradiation plus tumor bed boost plans. METHODS: Twenty patients who received radiotherapy following breast-conserving surgery for early breast cancer were enrolled in this study. We performed 1 type of electron plan (E1P plan) and 2 types of 3-dimensional conformal plans using a photon (P3P and P5P plans). The dosimetric parameters for the heart, total lung and the target volume between the 3 treatment types were compared. RESULTS: For the tumor bed, the difference in the mean dose between the 3 plans was maximally 0.1 Gy. For normal breast parenchyma, the difference in the mean dose between the 3 plans was maximally 1.1 Gy. In the dose range over the prescribed dose of 51 Gy, V55 and V60 in the E1P plan were lower than those in the P3P and P5P plans, which indicated that the E1P plan was more suitable than the P3P and P5P plans. In case of the heart and total lung, the values of clinically important parameters were slightly higher in the E1P plan than in the P3P and P5P plans. However, these differences were less than 2%. CONCLUSION: We observed that a simple electron plan for tumor bed boost is preferable over multi-field photon plans in terms of the target volume coverage and normal tissue sparing.

Dosimetric evaluation of the skin-sparing effects of 3-dimensional conformal radiotherapy and intensity-modulated radiotherapy for left breast cancer.

The purpose of this study was to evaluate the skin-sparing effects of 3-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) in patients with early left-sided breast cancer. Twenty left breast cancer patients treated with whole breast radiotherapy following breast-conserving surgery were enrolled in this study, and the 3D-CRT and IMRT plans were generated for each patient. To evaluate the dose delivered to the skin, 2 mm thickness skin (2-mm skin) and 3 mm thickness skin (3-mm skin) were contoured and a dosimetric comparison between the 2 plans was performed. The target volume coverage was better in IMRT than in 3D-CRT. The mean dose was 50.8 Gy for 3D-CRT and 51.1 Gy for IMRT. V40Gy was 99.4% for 3D-CRT and 99.9% for IMRT. In the case of skin, the mean dose was higher in 3D-CRT than in IMRT (mean dose of 2-mm skin: 32.8 Gy and 24.2 Gy; mean dose of 3-mm skin: 37.2 Gy and 27.8 Gy, for 3D-CRT and IMRT, respectively). These results indicated that the skin-sparing effect is more prominent in IMRT compared to 3D-CRT without compromising the target volume coverage.

Dosimetric evaluation of incidental irradiation to the axilla during whole breast radiotherapy for patients with left-sided early breast cancer in the IMRT era.

The purpose of this study was to compare the dosimetric parameters for incidental irradiation to the axilla during whole breast radiotherapy (WBRT) with 3-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT). Twenty left breast cancer patients treated with WBRT after breast-conserving surgery (BCS) were enrolled in this study. Remnant breast tissue, 3 levels of the axilla, heart, and lung were delineated. We used 2 different radiotherapy methods: 3D-CRT with field-in-field technique and 7-field fixed-beam IMRT. The target coverage of IMRT was significantly better than that of 3D-CRT (Dmean: 49.72 ±â€Š0.64 Gy vs 50.24 ±â€Š0.66 Gy, P < 0.001; V45: 93.19 ±â€Š1.40% vs 98.59 ±â€Š0.30%, P < 0.001; V47.5: 86.43 ±â€Š2.72% vs 95.00 ±â€Š0.02%, P < 0.001, for 3D-CRT and IMRT, respectively). In the IMRT plan, a lower dose was delivered to a wider region of the heart and lung. Significantly lower axillary irradiation was shown throughout each level of axilla by IMRT compared to 3D-CRT (Dmean for level I: 42.58 ±â€Š5.31 Gy vs 14.49 ±â€Š6.91 Gy, P < 0.001; Dmean for level II: 26.25 ±â€Š10.43 Gy vs 3.41 ±â€Š3.11 Gy, P < 0.001; Dmean for level III: 6.26 ±â€Š4.69 Gy vs 1.16 ±â€Š0.51 Gy, P < 0.001; Dmean for total axilla: 33.9 ±â€Š6.89 Gy vs 9.96 ±â€Š5.21 Gy, P < 0.001, for 3D-CRT and IMRT, respectively). In conclusion, the incidental dose delivered to the axilla was significantly lower for IMRT compared to 3D-CRT. Therefore, IMRT, which only includes the breast parenchyma, should be cautiously used in patients with limited positive sentinel lymph nodes and who do not undergo complete axillary lymph node dissection.

A customized bolus produced using a 3-dimensional printer for radiotherapy.

OBJECTIVE: Boluses are used in high-energy radiotherapy in order to overcome the skin sparing effect. In practice though, commonly used flat boluses fail to make a perfect contact with the irregular surface of the patient's skin, resulting in air gaps. Hence, we fabricated a customized bolus using a 3-dimensional (3D) printer and evaluated its feasibility for radiotherapy. METHODS: We designed two kinds of bolus for production on a 3D printer, one of which was the 3D printed flat bolus for the Blue water phantom and the other was a 3D printed customized bolus for the RANDO phantom. The 3D printed flat bolus was fabricated to verify its physical quality. The resulting 3D printed flat bolus was evaluated by assessing dosimetric parameters such as D1.5 cm, D5 cm, and D10 cm. The 3D printed customized bolus was then fabricated, and its quality and clinical feasibility were evaluated by visual inspection and by assessing dosimetric parameters such as Dmax, Dmin, Dmean, D90%, and V90%. RESULTS: The dosimetric parameters of the resulting 3D printed flat bolus showed that it was a useful dose escalating material, equivalent to a commercially available flat bolus. Analysis of the dosimetric parameters of the 3D printed customized bolus demonstrated that it is provided good dose escalation and good contact with the irregular surface of the RANDO phantom. CONCLUSIONS: A customized bolus produced using a 3D printer could potentially replace commercially available flat boluses.