Authors: Tetsukazu Kiriyama, RT^∗, Akira Fukui, MD^∗, Hirohumi Ishikawa, MD^∗, Misako Doi, RT^∗, Yuki Nishimoto, RT^∗, Kenta Cyosei, RT^∗, Koji Kishimoto, RT^∗, Tanabe Yoshinori, Ph.D.^†,1

^∗ Department of Radiology, Uwajima City Hospital, Ehime 798-8510 Japan
^† Department of Radiological Technology, Graduate School of Health Sciences, Okayama University, Okayama, 700-8558, Japan

One major adverse effect of prostate radiotherapy is associated with the rectum. The SpaceOAR system has been developed to address this problem, as it enables treatment planning with a reduced dose to the rectum. This study aimed to evaluate and compare the treatment plans between three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT) for prostate cancer using the SpaceOAR system. Thirty-?ve patients treated with prostate cancer radiation using the SpaceOAR system received a total radiation dose of 60 Gy/20 fractions. The dose constraints and robustness of the plan for VMAT and 3D-CRT were compared. For 3D-CRT, 6-?eld conformal method and 2-arc conformal method were created and compared in 3 treatment plans together with VMAT. The dose-constraint evaluation was performed using the planning target volume (PTV), rectum (mean dose), bladder (mean dose), and femoral head (mean dose).

One issue associated with prostate radiotherapy is the physiological movement of the target prostate gland, which reduces the accuracy of irradiation. The prostate moves several millimeters during irradiation due to physiological movements, and there are reports of a decrease in the PTV index due to this effect. This has a signi?cant impact on the cure rate of prostate cancer. A comparative study of the 3 irradiation methods was conducted to investigate this issue. Each study item was analyzed using the Friedman test to determine the signi?cance of the 3 irradiation methods.

Our analysis showed that the dose constraint was statistically signi?cant for VMAT, but 3D-CRT was also su?cient in achieving dose constraints. The hydrogel spacer reduced the rectal dose and improved the dose-constrained ful?llment rate in VMAT and 3D-CRT.

In a study of prostate motion during irradiation, 3D-CRT, a robust plan, was superior in the PTV mean evaluation over VMAT, where the multileaf collimator moved in ?ne increments.

VMAT is currently the standard treatment for prostate cancer; however, with the introduction of the SpaceOAR system using hydrogel spacers, 3D-CRT may also be a viable option for prostate cancer treatment.

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