Comparison of Doses to Parotid, Temporomandibular Joint, and Pharyngeal Constrictor Muscles Using Different Techniques in Radiotherapy for Oropharyngeal Cancer.

OBJECTIVE: The purpose of this research was to compare two treatment techniques for oropharyngeal cancers: conventional linac-based static intensity-modulated radiotherapy (sIMRT) and helical tomotherapy (HT). The study examined several parameters, including target coverage, organs at risk, integral dose, and beam on time. Additionally, the study evaluated the doses to the parotid, temporomandibular joint, and pharyngeal constrictor muscles, which are important for swallowing. METHOD: The present study retrospectively analyzed the data of 13 patients with oropharyngeal cancer who underwent radiotherapy between 2019 and 2021. The treatment plans for each patient were regenerated using both sIMRT and HT treatment planning systems with the sequential boost method. The techniques were evaluated and compared based on dose-volume histogram, homogeneity index, and conformity index parameters. The target coverage and organs at risk were statistically compared for two techniques. Additionally, the doses received by the healthy tissue volume were obtained for integral dose evaluation. The beam on time for each technique was assessed. RESULTS: When considering planning target volume evaluation, there was no difference in Dmeans between the two techniques and sIMRT demonstrated higher D2% values compared to the HT. The HT technique had better results for all organs at risk, such as the parotid, temporomandibular joint, and pharyngeal constrictor muscle. As for integral dose, it has been shown that the sIMRT technique provides better protection compared to HT. In addition, the beam on time was also longer with the HT technique. CONCLUSION: Both techniques may provide optimal target coverage for patients with oropharyngeal cancer. HT conferred notable advantages, especially with regard to critical structures implicated in swallowing, such as the parotid, temporomandibular joint, and pharyngeal constrictor muscle, in comparison to sIMRT.

The feasibility of the pretreatment verification of 2D dose distributions in radiation therapy with small fields using the electronic portal imaging device.

BACKGROUND: The present study aims to evaluate the performance of an Electronic portal imaging device (EPID) for measuring dosimetric parameters and for verification of dose in small photon fields. MATERIAL AND METHODS: In this study, the beam profiles were obtained using the amorphous silicon (a-Si) EPID for field sizes ranging from 1 × 1 to 10 × 10 cm 2 at energies 6 and 18 mega-voltage (MV). For comparison, the dosimetric parameters, including penumbra widths and field sizes, were measured with the pinpoint, diode, and Semiflex dosimeters. Finally, Rando Phantom was used to compare the two-dimensional (2D) Dose distribution between EPID and Treatment Planning System (TPS). RESULTS: In both 5 cm and 10 cm depths, there were large differences between the measured doses obtained from TPS, Pinpoint detector, and Farmer detector in 1 × 1 field size. The differences become negligible as the field sizes increase and from 3 × 3 field size to 10 × 10 field size, the maximum observed differences are 2 cGy and 2.4 cGy for 5 cm and 10 cm depths, respectively. The results indicate that the penumbra widths are smaller in the Gantry-Target (GT) direction compared to the Right-Left (RL) direction. The maximum difference (47.6%) was observed for EPID in the 10 × 10 field size, and the minimum difference (16.6%) was observed for TPS in the 1 × 1 field size. Finally, 2D dose distributions obtained by EPID and TPS exhibit excellent agreement. CONCLUSION: EPID is an excellent tool for the measurement of dosimetry parameters such as dose profiles, penumbra widths, field sizes, and pretreatment verification of 2D dose distributions, especially in small fields.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer.

PURPOSE: The aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo-Helical (TH)/Tomo-Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC). METHODS: Twenty-five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed-rank test was used to analyze the difference in dosimetric parameters. p-Value < 0.05 was considered statistically significant. RESULTS: TH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001). CONCLUSION: Concurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.

Design and characterization of tissue-mimicking gel phantoms for diffusion kurtosis imaging.

PURPOSE: The aim of this work was to create tissue-mimicking gel phantoms appropriate for diffusion kurtosis imaging (DKI) for quality assurance, protocol optimization, and sequence development. METHODS: A range of agar, agarose, and polyvinyl alcohol phantoms with concentrations ranging from 1.0% to 3.5%, 0.5% to 3.0%, and 10% to 20%, respectively, and up to 3 g of glass microspheres per 100 ml were created. Diffusion coefficients, excess kurtosis values, and relaxation rates were experimentally determined. RESULTS: The kurtosis values for the plain gels ranged from 0.05 with 95% confidence interval (CI) of (0.029,0.071) to 0.216(0.185,0.246), well below the kurtosis values reported in the literature for various tissues. The addition of glass microspheres increased the kurtosis of the gels with values up to 0.523(0.465,0.581) observed for gels with the highest concentration of microspheres. Repeat scans of some of the gels after more than 6 months of storage at room temperature indicate changes in the diffusion parameters of less than 10%. The addition of the glass microspheres reduces the apparent diffusion coefficients (ADCs) and increases the longitudinal and transverse relaxation rates, but the values remain comparable to those for plain gels and tissue, with ADCs observed ranging from 818(585,1053) × 10-6  mm2 /s to 2257(2118,2296) × 10-6  mm2 /s, R1 values ranging from 0.34(0.32,0.35) 1/s to 0.51(0.50,0.52) 1/s, and R2 values ranging from 9.69(9.34,10.04) 1/s to 33.07(27.10, 39.04) 1/s. CONCLUSIONS: Glass microspheres can be used to effectively modify diffusion properties of gel phantoms and achieve a range of kurtosis values comparable to those reported for a variety of tissues.

Radiotherapy-induced decreases in substance P levels may potentiate melanoma growth.

Substance P, a member of the tachykinin family, is expressed in primary invasive malignant melanomas, metastatic melanomas, melanomas in situ, atypical naevi, and spindle and epithelioid cell naevi. The role of substance P in cancer development and progression is not clear. Radiotherapy, which is used extensively in the treatment of malignancies, alters substance P levels. It is, however, not known whether radiotherapy affects substance P levels in melanomas or in the tumor microenvironment. Given the fact that melanomas express substance P, possible radiation-induced changes in substance P content may underlie their radio-resistance. Hence, the aim of the present study was to determine the effects of radiotherapy on the growth of B16F10 melanomas as well as on the tumor and systemic expression of substance P. In vivo exposure of tumor-bearing C5BL/6 mice to ionizing radiation (45 Gy administered in three fractions) arrested tumor growth for three weeks and induced 3-fold increases in survival, as well as decreasing substance P levels in primary tumors and the surrounding skin. Although radiotherapy was applied locally (1 x 1 cm) at the mid-flank region of the animal, it also induced systemic changes in the levels of substance P. Specifically, radiotherapy decreased substance P levels in skin distant from the radiation field as well as in the lungs and adrenals. In order to understand the significance of this effect, B16F10 cells and cells made from metastatic lesions (B16LNAD cells) were treated with substance P. Substance P inhibited the growth of B16F10 and B16LNAD cells and further potentiated the inhibitory effects of radiotherapy. These findings demonstrate for the first time that substance P inhibits melanoma growth, and that radiotherapy-induced decreases in substance P levels may underlie the radio-resistance of melanomas.

Lycopene in the prevention of gastrointestinal toxicity of radiotherapy.

We conducted a study to investigate if lycopene could reduce gastrointestinal toxicity of abdominal and pelvic radiation in Wistar albino rats. Animals received either a control diet (Group 1), lycopene-supplemented diet (Group 2), control diet and radiation (Group 3), and lycopene-supplemented diet plus radiation (Group 4). In Groups 2 and 4, the rats received 5 mg/kg/day lycopene for 10 days. In Groups 3 and 4, the rats received single fraction 8 Gy abdominal and pelvic radiation (RT) on Day 10. Study endpoints included weight loss, diarrhea, duration of diarrhea, survival, and an oxidative stress marker, plasma level of thiobarbituric acid reactive substance (TBARS). The rats receiving RT only had significantly higher weight loss rate compared to the lycopene plus RT group (P = 0.001). Plasma TBARS levels after RT were also significantly higher in the RT only group compared to lycopene plus RT group (P = 0.001). In conclusion, lycopene supplementation significantly reduced the weight loss and prevented oxidative stress in rats treated with abdominopelvic radiation.

Assessment of setup accuracy in patients receiving postmastectomy radiotherapy using electronic portal imaging.

PURPOSE: The aim of this study was to investigate the setup accuracy for patients undergoing postmastectomy radiotherapy using electronic portal imaging. MATERIALS AND METHODS: Ten patients undergoing radiotherapy via tangent (TG), supraclavicular-axillary (SA), and internal mammary (IM) fields were included. To explore the setup accuracy, distances between chosen landmarks were taken as reference parameters (RPs). The difference between measured RPs on simulation films and electronic portal images (EPIs) was calculated as the setup error. RESULTS: A total of 30 simulation films and 120 EPIs were evaluated. In the SA field, calculated RPs were lung length (LL), clavicle-field center perpendicular distance, and clavicle-field center transverse distance. The mean of the standard deviations (SDs) of the random errors (sigma) for these parameters were 4.7, 7.3, and 7.6; and the SDs of the systematic errors (Sigma) were 6.8, 4.4, and 13.5, respectively. In the TG fields, the calculated RPs were the central lung distance (CLD), maximum lung distance (MLD), and central soft-tissue distance (CSTD). In the medial TG field, the sigma values for these parameters were 3.4, 3.6, and 4.1, respectively; and the sigma values were 6.6, 2.6, and 3.4, respectively. In the lateral TG field, Sigma values for the calculated RPs were 2.4, 3.2, and 3.3l, respectively; and the Sigma values were 5.6, 3.6, and 4.8, respectively. CONCLUSION: CLD, MLD, and CSTD in TG fields and LL in SA fields are easily identifiable and are helpful for detecting setup errors using EPIs in patients undergoing postmastectomy radiotherapy.

Geometric and dosimetric variations of ICRU bladder and rectum reference points in vaginal cuff brachytherapy using ovoids.

PURPOSE: To investigate the interfractional geometric and dose variations of rectal reference point (R) and bladder reference point (BL) doses in patients receiving vaginal cuff irradiation using high-dose-rate brachytherapy with 2 ovoids and the change in calculated radiobiologic-equivalent dose of R and BL. METHODS: ICRU-38 R and BL reference doses were calculated. The variation in positions of ovoids, R, and BL were determined. Whether the magnitude of displacement shows a time trend and has an effect on calculated R and BL doses was evaluated. The relation between the ovoid diameter and both the magnitude of displacement and changes in R and BL doses was studied. Changes in radiobiologic-equivalent dose of rectum and bladder were determined. RESULTS: The average magnitude of displacements was 3.2 and 12.1 mm, showed no time trend, and no tendency to displacement in a certain direction. Mean changes in BL and R doses were 64-75 cGy and 47-58 cGy, respectively. There was a relation between neither ovoid size and displacement nor R and BL dose change. Dose and geometric variation showed no correlation (p > 0.05). The differences in radiobiologic-equivalent dose of R and B were not significant. CONCLUSION: Although there were significant differences in R and B position and doses among the fractions, the magnitudes of dose changes were relatively small, and total calculated radiobiologic-equivalent doses of R and B did not change significantly. According to the results of this study, the benefit of treatment planning is limited to supporting treatment planning in each fraction.