The impact of the radiotherapy technique in sparing the heart substructures in central tumor irradiation in lung cancer

Introduction: In thoracic radiotherapy (RT), heart sparing is very essential, as the high cardiac dose is associated with poor survival in patients with locally advanced non-small-cell lung cancer (NSCLC). The study aims to determine the doses exposed to heart substructures and coronary arteries by different RT techniques in central tumor irradiation in lung cancer. Methods: Twenty patients with NSCLC, irradiated between January 2018 and December 2020 in our department, were included in this study. Patients whose primary tumor was centrally located in the left lung were selected. The heart substructures [left atrium, right atrium (RA), left ventricle, and right ventricle] and coronary arteries (left main, left anterior descending, circumflex, and right coronary arteries) were delineated by the same physician. The doses of 60 Gy external RT were prescribed in 30 fractions using three-dimensional conformal radiotherapy (3D-CRT), static intensity-modulated radiotherapy (s-IMRT), and dynamic intensity-modulated radiotherapy (d-IMRT) techniques in all patients. The obtaining plans using three different techniques were compared. Results: The d-IMRT plans were statistically the best optimal plan for planning target volume (PTV) [Dmean (p = 0 04), Dmax (p < 0 0001), V95 (p < 0 0001), V107 (p < 0 0001), CI (p < 0 0001) and HI (p < 0 0001)]. The s-IMRT plans were significantly superior to 3D-CRT plans for PTV. RA Dmax and V45 were not different between the three techniques [Dmax (p = 0 148) and V45 (p = 0 12)]. The d-IMRT technique was significantly better in other heart substructures and coronary arteries. Conclusions: Compared to 3D-CRT and s-IMRT techniques, the d-IMRT technique provided the best protection in all heart substructures except for a few parameters (RA Dmax and V45 doses).

Comparison and Evaluation of Different Radiotherapy Techniques Using Biodosimetry Based on Cytogenetics

While rapid technological advances in radiotherapy techniques have led to a more precise delivery of radiation dose and to a decreased risk of side effects, there is still a need to evaluate the efficacy of the new techniques estimating the biological dose and to investigate the radiobiological impact of the protracted radiotherapy treatment duration. The aim of this study is to compare, at a cytogenetic level, advanced radiotherapy techniques VMAT and IMRT with the conventional 3D-CRT, using biological dosimetry. A dicentric biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used. For each patient blood sample and each subpopulation of the cultured cell line, three different irradiations were performed using the 3D-CRT, IMRT, and VMAT technique. The absorbed dose was estimated with the biodosimetry method based on the induced dicentric chromosomes. The results showed a statistically significant underestimation of the biological absorbed dose of ~6% for the IMRT and VMAT compared to 3D-CRT irradiations for peripheral blood lymphocytes, whereas IMRT and VMAT results were comparable without a statistically significant difference, although slightly lower values were observed for VMAT compared to IMRT irradiation. Similar results were obtained using the PC3 cell line. The observed biological dose underestimation could be associated with the relative decreased dose rate and increase irradiation time met in modulated techniques compared to the conventional 3D-CRT irradiations.

KẾT QUẢ XẠ TRỊ 3D-CRT VÀ VMAT TRONG HOÁ XẠ ĐỒNG THỜI UNG THƯ THỰC QUẢN TẠI BỆNH VIỆN K

Mục tiêu: Mô tả một số đặc điểm lâm sàng, cận lâm sàng và đánh giá kết quả xạ trị bằng kỹ thuật 3D-CRT và VMAT ở bệnh nhân hoá xạ đồng thời ung thư thực quản tại bệnh viện K. Đối tượng và phương pháp nghiên cứu: Nghiên cứu mô tả hồi cứu kết hợp tiến cứu trên 60 bệnh nhân điều trị hoá xạ đồng thời ung thư thực quản bằng kỹ thuật 3D-CRT và VMAT tại bệnh viện K từ tháng 5/2018 đến tháng 5/2021. Kết quả: Tuổi trung bình 54,4 ±7,0 (43-69). Tỷ lệ nam/nữ là 59/1. Tỷ lệ nuốt nghẹn 91,7%. Có 46 (76,7%) bệnh nhân giai đoạn T3, 14 (23,3%) bệnh nhân ở giai đoạn T4. Thể giải phẫu bệnh của các bệnh nhân là ung thư biểu mô vảy (100%). Các thông số bao phủ liều đến PTV (thể tích xạ kế hoạch – Planning target volume) của xạ trị VMAT so với 3D-CRT: V95: 98,4% - 94,35%, V110: 0,15% – 5,35%. Dmax tại tuỷ và da VMAT thấp hơn so với 3D-CRT. Liều tại phổi (V5,V20) và tại tim (V40) VMAT thấp hơn so với 3D-CRT.Tỷ lệ đáp ứng toàn bộ sau hóa xạ trị là 48,3%, tỷ lệ đáp ứng 1 phần là 41,7%, tỷ lệ bệnh không đổi là 10%. Độc tính trên hệ huyết học là hạ bạch cầu (6%), hạ tiểu cầu (1,7%). Độc tính viêm da do xạ trị (58,4%), viêm thực quản do xạ trị (18,3%), độc tính viêm phổi do xạ trị (3,3%), không ghi nhận độc tính trên hệ tim mạch. Kết luận: Xạ trị ung thư thực quản bằng kỹ thuật VMAT và 3D-CRT cho kết quả tốt và an toàn, kỹ thuật VMAT cho thấy tập trung liều xạ tốt hơn và ít độc tính hơn kỹ thuật 3D-CRT.

RADT-34. OLFACTORY PERCEPTION DURING PROTON RADIATION AND DIFFERENCES IN FREQUENCY OF OLFACTORY PERCEPTIONS BASED ON PROTON CRANIOSPINAL IRRADIATION TECHNIQUE FOR PEDIATRIC BRAIN TUMOR PATIENTS

BACKGROUND Unusual olfactory perception has been reported during brain radiation treatments but is infrequent and does not typically interfere with the ability to deliver treatment or cause notable distress. METHODS We performed a retrospective review of 127 pediatric patients treated with proton radiation therapy (PRT) for primary brain tumors in a single institution between 2016-2021. Patients received PRT to the brain as part of craniospinal irradiation (CSI) followed by a boost to the brain. Proton CSI was delivered with 3D-CRT protons (n=53) or pencil beam scanning technique (PBS) (n=74). Within the PBS group, treatment delivery to the CSI utilized a single PA field (n=24) or two posterior oblique fields (n=50). We collected data on abnormal olfactory sensations, nausea/vomiting, and the use of medical intervention for those symptoms. RESULTS Our cohort included 80 males and 47 females. The median age of patients was 10 years old (range, 3 – 21). Seventy-one patients received concurrent chemotherapy. Prior to PRT, 31 patients were nauseous. During the radiation course, 104 patients developed worsening nausea while 63 patients reported episodes of emesis. Four patients vomited while receiving radiation. Seventeen patients reported olfactory perceptions during CSI. We found a higher rate of olfactory perception in patients treated with PBS (n=16, 22%) than 3D-CRT (n=1, 2%) (p=0.001) and, within the PBS group, patients treated with a single PA field (n=11, 46%) than two oblique fields (n=5, 10%) (p=0.002). Seventy-eight patients required intervention including addition of anti-emetic or anti-anxiety medication. Two patients required sedation due to the malodorous smell during CSI. We did not find any significant difference in nausea/vomiting based on treatment technique. CONCLUSIONS PBS and PBS technique influence olfactory perceptions but not the occurrence of the rate of nausea/vomiting. Further studies should be performed to validate these findings and determine techniques to minimize unpleasant olfactory perceptions.

RADT-19. CLINICAL OUTCOMES OF RADIATION THERAPY FOR BRAIN STEM GLIOMA

PURPOSE/OBJECTIVES Brain stem gliomas are up to 20% of all brain tumor in children and unusual in adults. Radiotherapy is mainstay of treatment. Surgery for brain stem glioma is difficult because of anatomical location. This study was performed to evaluate the clinical outcomes of radiotherapy in brain stem glioma. METHODS Retrospective analysis of brain stem glioma patients treated with radiation therapy (54Gy/30 fractions of IMRT/ 3D CRT) with or without surgery or chemotherapy or other agents. RESULTS Twenty-four patients (median age 11.8 years) were treated between 2016 and 2020. Male to female ratio was 2:3. Surgical approach (biopsy and partial removal) was done in 16 patients. Histology revealed that anaplastic ependymoma in 2 patients, low grade astrocytoma in 2 patients, anaplastic astrocytoma in 8 patients, glioblastoma in 4 patients and remaining 8 patients had no histologic diagnosis. Radiotherapy (dose- 54Gy/ 30 fractions) was given with the technique of IMRT or 3D CRT. At the time of follow up, 8 patients had local recurrence, 10 patients died of due to disease and recurrence, 14 patients were alive. Among alive patients, 2 patients were treated with chemotherapy and 12 patients with temozolomide for 12 cycles. Patients who received temozolomide got improvement in performance status and reduced clinical symptoms; among them, 6 patients had more than 50% objective tumor response in radiological findings for follow-up 3-6 months after radiotherapy. The 2-years overall survival (OS) rate was 58.3% and 2-years Event-free Survival (EFS) rate was 50%. The median survival time was 14 months. There is no grade 3 or greater acute and late toxicities. CONCLUSION As the LMIC country with limited resources, our results of radiotherapy followed by temozolomide in brain stem glioma have optimal outcomes. However, prospective studies of this select group of patients with larger number and longer follow up is required.

Kết quả xạ trị điều biến liều theo thể tích hình cung (vmat) trong điều trị ung thư tuyến tiền liệt tại bệnh viện k Trung ương

Nghiên cứu nhằm mục tiêu đánh giá kết quả điều trị Ung thư tuyến tiền liệt bằng kỹ thuật xạ trị VMAT (Volumetric modulated Arc Therapy) tại Bệnh viện K trung ương. Nghiên cứu thực hiện trên 30 bệnh nhân ung thư tuyến tiền liệt được điều trị kỹ thuật VMAT tại Bệnh viện K trung ương từ tháng 9 năm 2017 đến tháng 3 năm 2021. Kết quả cho thấy tỷ lệ bệnh nhân ở các giai đoạn từ I - IV lần lượt là: 3.3%; 33.3%; 36.7%; 26.7%; 100% bệnh nhân sau điều trị đều có PSA < 4ng/ml. Độc tính cấp của hệ tiết niệu chủ yếu độ 1 gặp ở 73,3%. Độc tính trên tiêu hóa gặp ở độ 1 chiếm 26,7%. Độc tính muộn của hệ tiết niệu độ 1 chiếm tỷ lệ là 30%. Độc tính trên tiêu hóa gặp ở độ 1 có 6 bệnh nhân chiếm tỷ lệ 20%. Không gặp bệnh nhân nào có độc tính muộn trên da, và không bệnh nhân có biến chứng cổ xương đùi. Như vậy, VMAT giảm tác dụng phụ sớm và muộn so với 3D - CRT, rút ngắn thời gian xạ so với IMRT và giúp kéo dài thời gian sống thêm bệnh không tiến triển cho người bệnh.

A Dosimetric Analysis of Reduction Cardiac Dose with Lead Shielding in Breast Cancer Radiotherapy

Adjuvant radiotherapy is an important treatment modality after breast-conserving surgery. Due to its proximity, radiation therapy for the left breast can often lead to an escalated heart dose that can result in heart diseases. The purpose of this study was to evaluate the heart dose reduction by using lead shields surrounding the left breast. The doses of a 3D conformal radiotherapy (3D-CRT) plan, an intensity-modulated radiotherapy (IMRT) plan, and volumetric-modulated arc therapy (VMAT) to the left breast tumor in a CIRS ATOM anthropomorphic female adult phantom were measured by optically stimulated luminescence dosimeters (OSLDs). To protect critical organs, the skin around the target area was covered by lead shields of two different thicknesses (0.125 mm and 0.25 mm). The results showed that compared to IMRT and 3D-CRT, VMAT provided better planning target volume (PTV) coverage, a better conformity index (CI), and homogeneity index (HI). With the use of lead shields, the thyroid dose was reduced by 5.12–27.5% and 20.51–30%, respectively; the heart dose was reduced by 49.41–50.12% and 56.38–57.42%, respectively; and the lung dose was reduced by 1.23–45.22% and 0.98–57.83%, respectively. Although the clinical application of lead shields was rare, this study verified that it could effectively decrease the heart dose from 4.31 ± 0.09 Gy to 1.88–2.18 Gy, thereby potentially reducing the risk of associated heart diseases by 14.8%. Further works to implement this method into clinical practice are needed.

Estimated Risk of Radiation-Induced Cancer after Thymoma Treatments with Proton- or X-ray Beams

We compared the calculated risks of radiation-induced secondary malignant neoplasms (SMNs) for patients treated for thymic tumors with 3D-CRT, IMRT, or single-field uniform dose (SFUD) proton beam therapy (PBT) using the pencil beam scanning (PBS) technique. A cancer-induction model based on the organ equivalent dose (OED) concept was used. For twelve patients, treated with 3D-CRT for thymic tumors, alternative IMRT and SFUD plans were retrospectively prepared. The resulting DVHs for organs at risk (OARs) were extracted and used to estimate the risk of SMNs. The OED was calculated using a mechanistic model for carcinoma induction. Two limit cases were considered; the linear-exponential model, in which the repopulation/repair of the cells is neglected, and the plateau model, in which full repopulation/repair of the irradiated cells is assumed. The calculated risks for SMNs for the different radiation modalities and dose-relation models were used to calculate relative risks, which were compared pairwise. The risks for developing SMNs were reduced for all OARs, and for both dose-relation models, if SFUD was used, compared to 3D-CRT and IMRT. In conclusion, PBS shows a potential benefit to reduce the risk of SMNs compared to 3D-CRT and IMRT in the treatment of thymic tumors.