Critical Factors of Dose Distribution in Breast Cancer Tomotherapy With Metallic Port Breast Tissue Expander: Image Correction, Delivery Mode, and Volume Impact

Hsing-Yi Lee; Yu-Hsiu Yen; Yu-Lun Tsai; Pei-Chih Tu; Chi-Ming Pu; Chia-Hong Lin; Louis Tak Lui; Suzun Shaw; Ching-Jung Wu; Hsin-Hua Nien

doi:10.1177/15330338221093148

Critical Factors of Dose Distribution in Breast Cancer Tomotherapy With Metallic Port Breast Tissue Expander: Image Correction, Delivery Mode, and Volume Impact

Technol Cancer Res Treat. 2022 Jan-Dec:21:15330338221093148. doi: 10.1177/15330338221093148.

Authors

Hsing-Yi Lee¹, Yu-Hsiu Yen^{2

3}, Yu-Lun Tsai^{4

5}, Pei-Chih Tu¹, Chi-Ming Pu^{2

3}, Chia-Hong Lin¹, Louis Tak Lui^{1

4}, Suzun Shaw^{1

4}, Ching-Jung Wu^{1

4

6

7}, Hsin-Hua Nien^{3

4

8}

Affiliations

¹ Department of Radiation Oncology, Oncology Treatment Center, 124851Sijhih Cathay General Hospital, New Taipei City, Taiwan.
² Division of Plastic Surgery, Department of Surgery, 60616Cathay General Hospital, Taipei, Taiwan.
³ School of Medicine, 34903Fu Jen Catholic University, New Taipei City, Taiwan.
⁴ Department of Radiation Oncology, 60616Cathay General Hospital, Taipei, Taiwan.
⁵ Institute of Epidemiology and Preventive Medicine, College of Public Health, 33561National Taiwan University, Taipei, Taiwan.
⁶ Department of Radiation Oncology, National Defense Medical Center, Taipei, Taiwan.
⁷ Department of Biomedical Engineering, I-Shou University, Kaohsiung, Taiwan.
⁸ Institute of Biomedical Engineering, College of Electrical and Computer Engineering, 34914National Yang Ming Chiao Tung University, Hsinchu, Taiwan.

Abstract

Objectives: Breast reconstruction helps patients enhance their body image after mastectomy. Metallic ports in tissue expanders lead to dose attenuation during radiotherapy. Tissue expander volume shifts the metallic port position, possibly causing various dose alterations. This study aimed to evaluate the impact of the MAGNA-SITE^TM tissue expander volume on tomotherapy. Methods: Boluses and MAGNA-SITE^TM were placed on a Rando phantom to simulate the tissue expander under the pectoralis major. Computed tomography simulation images were transformed through replacing the electron density of (a) metallic artifact region only (Image metallic port) and (b) metallic port and artifact regions (Image Homo). Planning was calculated using fixed-beam and helical-mode techniques. Radiation was delivered with different volumes of the tissue expander. Results: Integrated 997 dose points were calculated. Planning with Image metallic port provided a calculated dose significantly closer to a realistic dose. The percentage of doses achieving the prescribed dose was significantly higher in the helical mode. In layer 2, the 100-mL tissue expander had a significantly lower measurement dose than all other volumes. Volume 150 mL had the highest increase in the measured dose difference from the plan dose at layer 2. Volume 250 mL had the highest percentage of measurement doses passing the 5% dose difference from plan dose. The coldest dose areas were noted in layers 1 and 2, especially in the metallic port-direct image mode. The average dose reduction of the measured cold areas was 6.03 ± 1.94%. Conclusion: Dose distribution was affected by the volume of the metallic port tissue expander. Tomotherapy with proper image heterogeneity correction and helical mode can reduce the attenuation from the metallic port. A tissue expander volume of 150 to 250 mL is suitable. Patients with high risk at the chest wall should be evaluated carefully to avoid underdosing. Radiation oncologists should closely cooperate with plastic surgeons to optimize treatment for each patient.

Keywords: helical; heterogeneity correction; radiotherapy; tissue expander; tomotherapy.

MeSH terms

Breast Neoplasms* / radiotherapy
Breast Neoplasms* / surgery
Female
Humans
Mastectomy / methods
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Tissue Expansion Devices*