Iranian Journal of Medical Physics
Volume:19 Issue: 2, Mar-Apr 2022

This work aimed to evaluate the accuracy of using parallel plane against thimble chambers in beam data commissioning of the high dose gradients region for versa HD linear accelerator performing clinical advanced modulated radiation treatment techniques. All clinical commissioning data were collected from Elekta Versa HD for energies of 6 MV, 10 MV, 6 MV FFF, and 10 MV FFF for different field sizes using thimble ionization chamber CC13, some from the pool of the measured data were rescanned using parallel plate chamber PPC05 and Gafchromic films and compared to those collected using the thimble ionization chamber. The skin doses differences measured by thimble chamber against reference films were (0.8%, 0.5%, 1.2% 4.7%) and for the parallel plane chamber against films were (8.4%, 9.7%, 9%, 12%) for 6 MV, 10 MV, 6 MV FFF, 10 MV FFF, respectively. The parried test-test showed a highly significant difference (p> 0.001) between the two chambers in measurements of penumbra regions taking over all the investigated field sizes and depths in both inline and crossline datasets. The parallel plate showed a wider and broader penumbra than the thimble chamber and films. Robust and consistent scans were obtained for the thimble chamber compared to the parallel plane chamber in the highest dose gradient of buildup and penumbra regions. Using a parallel plane chamber might bring dosimetric clinical uncertainties affecting the modeling of the gradient regions in the treatment planning system.

As a non-invasive method of tumor hyperthermia, high intensity focused ultrasound (HIFU) has been widely used in the treatment of various solid tumors in recent years. The purpose of this study was to investigate the effect of HIFU combined with ethanol on biological tissue lesions.
Firstly, 0.5ml 95% ethanol was injected into the porcine liver tissue in vitro, then HIFU was used to irradiate the porcine liver. The B-mode ultrasound and needle hydrophone were used to monitor the cavitation. A thermocouple was also used to measure the real-time focal temperature. The ultrasonic signal scattered at the focal point of HIFU irradiation was collected by the fiber hydrophone, and the attenuation coefficient was calculated. Finally, the attenuation coefficient was input into the Khokhlov-Zabolotskaya-Kuznetov (KZK) equation and combined with the Pennes equation. The thermal lesion of the porcine liver was simulated by MATLAB software.
The length of the long axis of the lesion area simulated by the attenuation coefficient of cavitation was closer to the length of the long axis of the actual measured lesion area with ethanol injection, but the length of the short axis of the simulated lesion area was smaller than that of the measured lesion area. However, the length of the long axis of the lesion area simulated by the attenuation coefficient of cavitation was larger than the length of the long axis of the lesion area simulated by the attenuation coefficient of liver at room temperature. The same results were obtained for the length of short axis.
HIFU combined with ethanol can produce larger lesions to biological tissues and improve the therapeutic effect.

Patient-specific quality assurance (PSQA) assumes a vital role in precise and accurate radiation delivery to cancer patients. Since the patient body comprises heterogeneous media, the present study aimed to fabricate a heterogeneous thoracic phantom for PSQA.

Heterogeneous thoracic (HT) phantom was fabricated using rib cage madeup of bone equivalent material, kailwood to mimic lungs and wax to mimic various body parts. Physical density of all these materials used in phantom fabrication was measured and compared with that of the corresponding part of actual human thorax. One beam was planned on the computed tomography (CT) images of phantom and actual patient thorax region. Dose distribution in both the plans was measured and analyzed.

The estimated densities of heart, lung, ribs, scapula, spine, and chest wall tissues were 0.804±0.007, 0.186±0.010, 1.796±0.061, 2.017±0.026, 2.106±0.029 and 0.739±0.028 respectively in case of HT phantom while 1.038±0.010, 0.199±0.031, 1.715±0.040, 2.006±0.019, 1.929±0.065 and 0.816±0.028 g/cc, respectively in case of actual human thorax region.The depths of isodose curves in HT phantom were also comparable to the isodose curve’s depths inreal patient. PSQA results were within ±3% for flat beam (FB) and flattening filtered free beam (FFFB) of 6 megavolts (MV) energy.

Density and dose distribution pattern in HT phantom were similar to that in actual human thorax region. Thus, fabricated HT phantom can be utilized for radiation dosimetry in thoracic cancer patients. The materials used to develop HT phantom are easily available in market at an affordable price and easy to craft.

Deep inspiration breath-hold (DIBH) technique is widely administered to left breast cancer (LBC) patients to reduce the cardiopulmonary radiation doses. The UK standardization of breast cancer radiotherapy (UK START) dose prescription was found comparable to the conventional schedule. The current study compared voluntary DIBH and free-breathing (FB) methods in the cardiopulmonary radiation doses of LBC patients with supraclavicular irradiation treated with the UK START trial.

Computed tomography (CT) scans were acquired for a group of 50 LBC patients in DIBH and FB and a radiotherapy plan was created on each scan. The dose-volume histogram parameters of the heart and lung were analyzed against their relevant first clinical acceptance criteria using one-sample t-test. Additionally, the correlation between the ipsilateral lung volume expansion and the cardiopulmonary dosimetric benefits was assessed.

The cardiopulmonary radiation doses were significantly reduced in DIBH compared with FB. For DIBH, the mean difference between the mean heart dose (MHD), Heart V16Gy, and Lung V16Gy and their first acceptance criteria was -62.6 cGy, -0.63%, and -2.18% (p < 0.001), respectively. In contrast, the first acceptance criteria of the cardiopulmonary dosimetric parameters were not accomplished with the FB method. In addition, the difference in MHD and heart V20Gy between DIBH and FB plans showed a moderate correlation with ipsilateral lung volume expansion (r = 0.51 and 0.5, respectively).

DIBH technique should be served to all locally advanced LBC patients, and the ipsilateral lung volume expansion could be a predictor for the cardiac-sparing radiotherapy in LBC.

This study aims to investigate the dosimetric impact of bladder volumetric changes during helical radiotherapy (RT) for rectal cancer (RC).

A total of 42 RC patients' helical RT treatment plans were analyzed. The bladder volumes were divided into 3 groups (Group1: V<100ml, Group2 100ml≤V≤200ml, and Group3V>200ml). Planning target volume (PTV), PTV boost, bladder, bowel, right, and left femoral head dose values were analyzed and compared between groups. Statistical analysis was done with a one-way ANOVA test in SPSS18.0 program. A value of p <0.05 was considered statistically significant.

The median age of the patients was 59 (range:22-87) and bladder volume ranged from 41.44ml-620.82ml. In the dosimetric data comparison of the patient groups with different bladder volumes, the D50 dose values of PTV and PTV boost volume was highest in Group 3 (p=0.039). No statistical significance was found between PTV and PTV boost’ doses of D98 and D2 ​​and groups. The optimum PTV dose value was in Group2. Bowel doses were highest in Group 1. As the bladder volume increased, the Dmax, Dmean, V15%, and V30% values of the bowel doses decreased. There was a statistically significant relationship between bladder Dmax doses and groups (p = 0.024). Femoral heads doses increased in proportion to increasing bladder volume groups and these results were statistically significant for V5% and V30% (p <0.05).

In our study, as the bladder volume increased, there was an inversely proportional decrease in the bowel doses and a directly proportional increase in the femoral head and bladder doses. Bladder volume values significantly affected values of the target and critical organs dose during helical RT for RC

This work aimed to investigate the use of megavoltage CT (MVCT) images for retrospective planning in high-dose and low-fractionation radiation techniques for Helical Tomotherapy and Linac. This work used pre-treatment MVCT images for retrospective planning in high-dose hypofractionation of eight hepatocellular carcinoma (HCC) patients using the stereotactic body radiation therapy (SBRT) technique. The dose per fraction was 5.5–8 Gy in 4–5 fractions. As the patients were scanned with Helical Tomotherapy (HT) MVCT before each treatment, the selected MVCT images were registered to kVCT for re-contouring, and then the images were exported to HT and Linac for planning. The kVCT scan images were also exported from HT to Linac for planning in Linac. The final plans were compared and analyzed using the following parameters: conformity index (CI), paddick conformity index (PCI), homogeneity index (HI), and organs at risk (OAR) constraints. The dose verification was performed by gamma passing rate (GPR) test using EBT3 films. CI values ​​were found in the range 0.7–1.00 ( : 0.95 ± 0.063), PCI values were found from 0.81 to 0.96 ( : 0.87 ± 0.04), and HI values were found from 0.02 to 0.53 ( : 0.16 ± 0.12). OAR constraints were clinically acceptable. Distance-to-agreement of 3mm and dose difference of 3% was used as GPR criteria for each plan modality. These results suggest that MVCT could be used as an alternative modality for high-dose re-planning in HT and Linac as well as being used for position verification.

Credible research shows that in many cases, infertility is caused by problems with men's sperm. Therefore, an accurate sperm analysis is a necessity to solve the problem of infertile couples. However, the first step in this analysis is to separate the sperm from the semen, which may not be accurate due to the poor contrast of the captured microscopy images. Curvelet transform has been introduced in recent years as an effective tool for object detection in the image processing domain. The most significant advantage of this transform is that it maps the raw image to a new space in which the features are sparser and parallelly more directional. Based on this fact, in this study, this approach is used to more effectively detect sperm in microscopic images. However, intelligent adjustment of the parameters of this mapping plays an important role in strengthening the weaker edges, and therefore in this article, a new method for optimizing the mapping parameters in order to achieve better separation of sperms from the background of the semen image is also proposed and examined. The comparison of the results obtained from examining the proposed method versus the results of the state of art methods was performed by using the two main criteria including sperm detection rate and false detection rate (i.e., false positives). This comparison clearly indicated the effectiveness of the proposed idea in distinguishing sperms from semen background. When the basis of performance evaluation is based on not detecting even a single false particle, it is observed that the correct sperm detection rate in the proposed method is between 4 and 17 percent higher than alternative methods. However, the false detection parameter itself shows an improvement of 33% to 3% in the proposed method compared to the weakest to the best among alternatives. Investigating the ROC curve which has been obtained from several examinations showed the effectiveness of the proposed idea over its alternatives either in correct detection of sperms or elimination of false objects. Therefore, the obtained results may lead us to the conclusion that the curvelet transform may be utilized as an effective solution for detecting sperms in low contrast microscopic images of human semen.

Considering the unwanted exposure to organs in the path of the beam, 4-field (4F) and subsequently, Intensity-modulated-radiation-therapy (IMRT), is known as the standard mode of treatment of carcinoma cervix. It is routine practice to inject intravenous contrast during simulation scan which elopes after that from the patient body. Therefore, the impact of contrast media should be investigated for radiation dose calculations.
An indigenously made phantom, named as ‘original contrast (OC)’, was used with dimensions 15 x 15 x 30 cm3. A sleeve was given to place the ionization chamber at the isocentre of the planning target volume (PTV) inside the cylindrical vial of iodinized contrast. Similarly, a virtual phantom was created with similar dimensions in the presence and absence of contrast media, called as ‘virtual contrast (VC)’ and ‘virtual without contrast (VWC)’ phantom. Plans were generated with photon energies (6MV/10MV/15MV/6FFF/10FFF) using 4F and IMRT technique. Plans were evaluated for PTV (D99%, D10%, Dmean) and Bladder & Rectum (V30Gy, V10Gy). Normal-tissue-integral-dose (NTID) and total-monitor-units (TMU) were also evaluated.
D99% of the PTV was comparable in VC and VWC phantoms but was decreased for OC phantom. Similarly, D10% was reportedly higher as 54.03 Gy (4F, 6 MV), 54.71 Gy (4F, 15 MV), 55.78 Gy (4F, 6 FFF) and 57.64 Gy (4F, 10 FFF) for OC phantom. D30% of the bladder and also the NTID was lesser for IMRT cases in all the selected phantoms. Additionally, 4F has shown lesser spillage with 6MV/15 MV photon beam energies in OC phantom. The ‘total monitor units (TMU)’ required for IMRT plans were significantly higher.
The contrast material under-estimates the planned dose yet has an insignificant influence on the dose calculation. Therefore, unnecessary exposure of dual scans should be avoided the use of 6MV and IMRT technique should be continued in the clinics.