|Ahead of print publication
To evaluate volume changes on computerized tomography scan and magnetic resonance imaging-based delineation during radiotherapy treatment planning in prostate cancer
Anil Sarolkar, Shashank N Singh, Priyusha Bagdare, Virendra Bhandari, Ashar Iqbal Lodi, Sarthak Moharir
Department of Radiation Oncology, Sri Aurobindo Medical College and PG Institute, Indore, Madhya Pradesh, India
|Date of Submission||10-Dec-2018|
|Date of Decision||23-May-2019|
|Date of Acceptance||09-Jun-2019|
|Date of Web Publication||31-Jan-2020|
Department of Radiation Oncology, Sri Aurobindo Medical College and PG Institute, Indore, Madhya Pradesh
Source of Support: None, Conflict of Interest: None
Aim: The aim of the present study was to evaluate the impact of magnetic resonance imaging (MRI) on radiotherapy target volume changes in prostate cancer.
Materials and Methods: Ten patients with localized prostate cancer receiving radical radiotherapy were included in the study. Computerized tomography (CT) simulation was done with adequate immobilization, and pelvic MRI was also done at the same time. The two were then registered on eclipse planning system and fused. Target delineation (gross tumor volume [GTV] and clinical target volume [CTV]) was done on both the image sets separately and their volumes were compared.
Results: In the current study, it has been found that the CT image-based contouring overestimated the GTV and CTV with 35.4% and 21.7%, respectively, as compared to that by MRI images. The difference observed was statistically significant in the case of GTV, whereas it was not statistically significant for CTV.
Conclusions: It can be concluded that MRI is found to be a better modality for GTV delineation, as it gives superior soft-tissue contrast.
Keywords: Gross tumor volume delineation, magnetic resonance imaging, prostate, tuscan
|How to cite this URL:|
Sarolkar A, Singh SN, Bagdare P, Bhandari V, Lodi AI, Moharir S. To evaluate volume changes on computerized tomography scan and magnetic resonance imaging-based delineation during radiotherapy treatment planning in prostate cancer. J Can Res Ther [Epub ahead of print] [cited 2020 Oct 31]. Available from: https://www.cancerjournal.net/preprintarticle.asp?id=277462
| > Introduction|| |
The prostate gland is a part of the male reproductive system. It is the largest accessory gland in the males and placed between the bladder and penis (around neck of bladder). It is comprised three distinct zones with different embryologic origins, such as peripheral zone, central zone, transition zone, which contains 70% glandular tissue and 30% fibromuscular or stromal tissue and provides ~30% of the volume of seminal fluid.
Risk factors include genetically inherited mutations such as BRCA1, BRCA2, Hereditary Non-Polyposis Colon Cancer Syndrome (HNPCC), obese men, smoking, inflammation of prostate, sexually transmitted diseases, older age, and African–American race/ethnicity. Selenium, Vitamin E, and lycopene have been linked to reduced risk. Patients of carcinoma prostate may present with the range of clinical symptoms ranging from being asymptomatic to having bone pain in case of metastasis. Most common presenting symptoms include increased frequency of maturation and dribbling of urine. Potential harms of screening include frequent false-positive results and psychological harms. Harms of prostate cancer treatment include erectile dysfunction, urinary incontinence, and bowel symptoms. Hence, periodic prostate specific antigen (PSA)-based screening includes discussion of the potential benefits and harms of screening with the clinician.
Surgical resections of the gland (either robotic or open) or radical radiation therapy are the treatment options. Androgen deprivation therapy and chemotherapy are the other modalities that can be used in combination with the above. With improvements in radiographic imaging and data processing capabilities, such as computerized tomography (CT), it is possible to treat carcinoma prostate with a high dose of localized radiation while sparing most of the surrounding normal tissues. Hence, it has been the treatment of choice in early prostate cancer. The primary goal for the treatment of prostate cancer by radiation is sparing of organs at risk (OAR), such as rectum, small intestine, and bladder, and at the same time achieving adequate dosage to the prostate, therefore, an accurate estimation of the size and location of rectum, bladder, gross tumor volume (GTV), and clinical target volume (CTV) is required. Magnetic resonance imaging (MRI) methods have proven to be superior to CT in terms of contrast resolution and accuracy of staging. Engelbrecht et al. computed sensitivity and specificity of 71% for overall tumor staging (cT2 vs. cT3 differentiation), 64% for finding of extracapsular extension, and 82% for recognition of seminal vesicle assault with MRI.
We undertook this study because major advancements in the anatomic and functional imaging technology continue to shape the radiation treatment planning process. This helped us in assessing changes in treatment volume and its impact on planning process. The objective of this study was to compare both prostate volume using CT and MRI imaging separately. MRI was used in carcinoma prostate for target delineation and compared with volumetric dimensions acquired from planning CT scan during treatment planning in patients of carcinoma prostate.
| > Materials And Methods|| |
A prospective observational study was carried out on ten localized prostate cancer patients that were advised radical radiotherapy from September 2016 to August 2018. All patients were asked to follow a strict bowel and bladder protocol. The patients were taken for planning CT scan with the immobilization cast. About 3-mm CT scan slices were taken, and then similar MR images were taken without the immobilization cast in the same position. The CT and MRI were then transferred to the eclipse treatment planning system version 13.7 from Varian. The two were fused together and then the GTV and CTV were delineated as per RTOG guidelines 0126 on CT scan [Figure 1]. GTV consisted of gross tumor tissue including the prostate gland and extraprostatic extension of tumor if seen. CTV included the prostate gland and seminal vesicles including the possibility of microscopic spread around the GTV. The apex is above the hourglass or slit shape that results from the inbowing of the levator ani just below and the penile bulb is best identified with MRI (bright T2, coronal section) or on CT when there is contrast in the urethra. On CT, the penile bulb will be posterior to the urethra and has a round shape. Lymph nodes to be treated were not included in CTV made for comparing the volumes. OAR such as the bladder, rectum, right and left femoral heads, and the small bowel is also delineated on the CT-scan. Similarly, target volume delineation (GTV, CTV) on the MRI image set was also done [Figure 2].
|Figure 1: Delineated prostate gland gross tumor volume (blue) and the clinical target volume (green) on computerized tomography image|
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|Figure 2: Delineated prostate gland gross tumor volume (cyan) and the clinical target volume (yellow) on magnetic resonance imaging image|
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| > Observations And Results|| |
Ten patients with mean age ranging between 51 and 70 years were included in this study. About 40% of patients receiving radiotherapy had stage T3N1M0 with a Gleason score of 3 + 3 = 6 and 4 + 4 = 8 in the same proportion. The mean GTV on MRI images was 43.5 cm3 (standard deviation [SD]: 24.2), whereas, on CT scan images, it was 66.8 cm3 (SD: 24.9) [Figure 3]. The mean CTV on CT scan was 139.0 cm3 (SD: 42.7), whereas, on MRI images, it was 108.9 cm3 (SD: 37.0). GTV defined by MRI was found to be 34.6% smaller (difference of 23.3 cm3) than that of defined by CT scan [Table 1]. The CT image-based GTV is significantly higher than that by MRI-based images with P = 0.0481 which is highly significant. CTV defined by MRI was found to be 21.7% smaller (difference of 30.1 cm3) than that of defined by CT scan. The two-tailed P value was 0.1099 which is statistically not significant.
|Figure 3: The mean of gross tumor volume and clinical target volume on computerized tomography scan and magnetic resonance imaging|
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|Table 1: Volumes (cm3) of gross tumor volume, clinical target volume as seen on computerized tomography, and magnetic resonance imaging image sets and their difference|
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| > Discussion|| |
In the current study including ten patients of prostate carcinoma taken up for radical radiotherapy where GTV and CTV were delineated on CT scan, and MRI showed that there was a significant change in volume of GTV in favor of MRI, but the changes in CTV volume were not statistically significant. Similar results have been seen in previous studies.
Kagawa et al. showed that localization of the prostate is more accurate on MRI than CT scan. Roach et al. also showed that there is a tendency to overestimate the prostate volume by noncontrast CT compared to MRI. Similarly, Sannazzari et al. also found that there was a mean overestimation of CTV by 34% with CT imaging compared to MRI image-based delineation of target volumes.
MRI scans are based on principles of using powerful magnetic, gradient fields, and radio frequency pulses to produce detailed pictures of internal body structures. Whereas, CT scan sees X-ray-based different levels of density of tissues inside a solid organ. Both the imaging modality works on different mechanisms and hence, there is different form of visualization of various internal structures with their own advantages and disadvantages.
The difference in volumes of GTV measured on MRI varies significantly as compared to CT, which justifies that MRI is undoubtedly the better imaging modality to identify the gross tumor tissue. The difference in volumes of CTV measured does show a difference, but it did not prove to be significant. Furthermore, Henderson et al. concluded that patient can be successfully planned without the need of MR fusion for prostate radiotherapy suggesting that the volume covering the microscopic extension of the disease does not show significant difference in volume compared on both the imaging modalities. Therefore, inference can be made that CT images are reliable imaging modality at least for the first phase of the treatment plan which includes the gross tumor and the elective nodal basin to be irradiated. However, while planning the second phase, i.e., planning boost to the actual gross tumor tissue, it is necessary for us to identify the same with accuracy. Hence, it is advisable to get better visualization of the gross tumor with the help of MRI. Alternative using MRI before the commencement of the treatment gives us the advantage of planning the boost and also evaluating the treatment response. Villeirs et al. concluded that in using CT and MRI as compared to CT alone, the mean CTV, prostate, and seminal vesicle volumes is significantly decreased, and Hentschel et al. studied the difference between prostate delineation in MRI and CT in three dimensions, and concluded that CT-MRI image fusion-based treatment planning allows more accurate prediction of the correct staging and more precise target volume identification in prostate cancer patients. Hence, the fusion of MRI with CT images together should be used as a routine procedure for radiotherapy treatment planning.
| > Conclusions|| |
MRI is found to be a better modality for GTV delineation, as it gives superior soft-tissue contrast. This fact can be used as an advantage, especially for radical prostatic radiotherapy or boost planning. Whereas, CT imaging can be efficiently used to cover microscopic tumor spread. The treatment planning systems commercially available for dose calculations are all CT based. Hence, the fusion of MRI with CT images together should be used as a routine procedure for radiotherapy treatment planning in carcinoma prostate.
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Conflicts of interest
There are no conflicts of interest.
| > References|| |
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[Figure 1], [Figure 2], [Figure 3]