Investigations and assessment for lung cancer radiotherapy treatments via daily cone beam CT Dose and radiomics physical parameters of phantom and patients’ studies
Creators: name: Albarakati, Hassan
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 320299
subject: Clinical sciences not elsewhere classified

description: Lung cancer is the fourth most commonly diagnosed invasive cancer in Australian men and women, and the leading cause of death, as reported by the Australian Institute of Health and Welfare. Lung cancer is usually treated with a combination of surgery, radiotherapy, chemotherapy, and immunotherapy. Among the various treatment options, radiotherapy is one of the most important. There is evidence that virtually all patients with lung cancer require radiotherapy despite the fact that radiotherapy is often underutilized. Across all stages of the disease, radiotherapy can be used as a cure or as a palliative treatment. Due to the advances in radiotherapy technology, tumours can be targeted more effectively, and incidental irradiation of healthy tissues is reduced. For successful treatment outcomes, precise patient positioning and beam placement are crucial and modern radiation therapy routinely employs cone-beam CT (CBCT) to compensate for positional errors and potential changes in tumour shape and volume. As the use of X-ray imaging for patient alignment in external beam radiation therapy has increased, especially with cone-beam computed tomography (CBCT), the additional dose patients receive is a concern. However, on the other hand the availability of multiple volumetric datasets opens an opportunity for monitoring the patient with radiomics seen as a promising tool adding value to the images already acquired. 

The thesis is divided into two main parts. The first part is dose assessment for daily cone-beam CT in lung radiotherapy patients and its combination with treatment planning, and the second part is radiomics physical parameters by using a phantom study and patient’s images. 

The first study is to assessment the imaging radiation dose delivered to lung cancer patients using the Monte Carlo (MC). With the increased use of X-ray imaging for patient alignment in external beam radiation therapy, particularly with cone-beam computed tomography (CBCT), the additional dose received by patients has become of greater consideration. In this study, we analysed the radiation dose from CBCT for clinical lung radiotherapy and assessed its relative contribution when combined with radiation treatment planning for a variety of lung radiotherapy techniques.

The Monte Carlo simulation program ImpactMC was used to calculate the 3D dose delivered by a Varian TrueBeam linear accelerator to patients undergoing thorax CBCT imaging. The concomitant dose was calculated by simulating the daily CBCT irradiation of 10 lung cancer patients. Each case was planned with a total dose of 50–60 Gy to the target lesion in 25–30 fractions using the 3DCRT or IMRT plan and retrospectively planned using VMAT. For each clinical case, the calculated CBCT dose was summed with the planned dose, and the dose to lungs, heart, and spinal cord were analysed according to conventional dose conformity metrics.

Our results indicate greater variations in dose to the heart, lungs, and spinal cord based on planning technique, (3DCRT, IMRT, VMAT) than from the inclusion of daily cone-beam imaging doses over 25-30 fractions. The average doses from CBCT imaging per fraction to the lungs, heart and spinal cord were 0.52 ± 0.10, 0.49 ± 0.15 and 0.39 ± 0.08 cGy, respectively. Lung dose variations were related to the patient’s size and body composition. Over a treatment course, this may result in an additional mean absorbed dose of 0.15–0.2 Gy. For lung V5, the imaging dose resulted in an average increase of ~0.6% of the total volume receiving 5 Gy. The increase in V20 was more dependent on the planning technique, with 3DCRT increasing by 0.11 ± 0.09% with imaging and IMRT and VMAT increasing by 0.17 ± 0.05% and 0.2 ± 0.06%, respectively. 

In this study, we assessed the concomitant dose for daily CBCT lung cancer patients undergoing radiotherapy. The additional radiation dose to the normal lungs from daily CBCT was found to range from 0.15–0.2 Gy when the patient was treated with 25-30 fractions. Consideration of potential variation in relative biological effectiveness between kilovoltage imaging and megavoltage treatment dose was outside the scope of this study. Regardless of this, our results show that the assessment of imaging dose can be incorporated into the treatment planning process and the relative effect on overall dose distribution was small compared to the difference among planning techniques. 

The second part of this thesis investigates the benefits of using daily CBCT for Radiomics. Radiotherapy has seen a steady rise in the digitisation of information created during clinical routines, similar to other fields of human activity in previous decades. As more medical data and images became accessible in digital form, newer and more powerful software to analyse it was created. Radiomics uses data-characterisation techniques to extract information from medical images. By identifying radiomics characteristics, we can identify tumoral patterns and characteristics which would otherwise not be apparent from the naked eye. A total of 107 radiomics features were calculated in the volume of interest. Radiomics features were extracted using pyradiomics code. 

Radiomics have shown promise for predicting outcomes in patients receiving radiotherapy for primary lung cancer. Often, however, patients are planned using motion-averaged or maximum-intensity projection reconstructions from 4D CT images and CBCT which help to characterise extent of tumour motion but may degrade the appearance of highly predictive radiomics features. In this study, we evaluate the stability of radiomics signal with 3D-printed inserts designed to mimic a variety of anatomically relevant tissue textures. CT images were acquired as static (3D) and in 4D with motion ranges from 1 to 30 millimetres. This study has shown that the variability in radiomics values calculated on CT images from different motion ranges from 1 to 30 millimetres can be comparable in motion to the variability found in lung patients CT images.

The last study explored the potential use of Delta-radiomics in sequential CBCT scans acquired over fractionated radiotherapy. Our goal is to characterise changes in CBCT-based radiomics features during treatment and quantify the association between CBCT-based delta-radiomics features and tumour shrinkage. This retrospective study includes other cohorts of 50 patients with daily CBCT. The prescription dose was 48 Gy, 54 Gy, delivered in 4 or 3 fractions respectively, with 25 patients in each fractionation group. As part of the study, CBCT delta radiomics stability was also evaluated in a subset of patients who had multiple CBCTs at the first and last fractions of treatment, under test-retest scenarios.

The results showed that of 107 features considered for evaluation, approximately half were found to reproduce the differences among patients with a moderate degree of stability, and 16 were found to be highly stable. As a cohort comparison, it is notable that few features were different between patients who received 48 Gy in four fractions as compared with those who received 54 Gy in three fractions. It is, however, indicated that 6 out of 25 patients treated with 48 Gy demonstrated more dramatic alterations in delta radiomics between the first CBCT and the last CBCT which would be worthwhile for investigating association with subsequent treatment outcome. Further, the delta radiomics signal was higher in the four-fraction group based on variance analysis across several features, suggesting that CBCT imaging may offer a more valid tool for assessing treatment progress over longer periods than hypofractionated radiation.