eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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abstract:
Original paper

A new approach to assess transit dose impact in gynecological and prostate brachytherapy with effective transit time

Masato Nishitani
1, 2
,
Hiroyuki Okamoto
2
,
Satoshi Nakamura
2
,
Kotaro Iijima
2, 3
,
Takahito Chiba
2
,
Hiroki Nakayama
2
,
Tetsu Nakaichi
2
,
Mihiro Takemori
2
,
Yuka Urago
4
,
Weishan Chang
1
,
Hiroshi Igaki
5

  1. Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa-ku, Tokyo, Japan
  2. Division of Radiation Safety and Quality Assurance, National Cancer Center Hospital, Chuo-ku, Tokyo, Japan
  3. Department of Radiation Oncology, Juntendo University Graduate School of Medicine, Bunkyo-ku, Tokyo, Japan
  4. National Institute of Advanced Industrial Science and Technology (AIST), National Metrology Institute of Japan, Tsukuba, Ibaraki, Japan
  5. Department of Radiation Oncology, National Cancer Center Hospital, Chuo-ku, Tokyo, Japan
J Contemp Brachytherapy 2024
DOI: https://doi.org/10.5114/jcb.2024.146826
Online publish date: 2025/01/17
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Purpose:
The aim of this study was to evaluate the dosimetric impacts of transit doses in various brachytherapy techniques, e.g., intra-cavitary, interstitial, and hybrid brachytherapy, on prostate and gynecological cancers using commercially available treatment planning system (TPS).

Material and methods:
For the evaluation, 36 gynecological cancer and 12 prostate cancer treatment plans were investigated, and transit doses were calculated using effective transit time to the middle of dwell positions in TPS. Effective transit times varied with step size, and movements were determined with a high-speed camera. The increment of Δ in dose-volume histogram parameters for clinical target volume (CTV) V100% and CTV D90%, rectum D2cc and D1cc, and bladder D2cc and D1cc were evaluated, after which dwell time distribution for each technique was analyzed to examine relationships between dosimetric change in CTV D90% and dwell time.

Results:
The median Δ for interstitial technique in prostate cancer was larger than those in other techniques: that of CTV V100% was 0.7%, and those of bladder and rectum D2cc and D1cc were over 1.0%. In CTV D90%, the median Δ values for interstitial technique in gynecological and prostate cancers were 1.0% and 1.6%, respectively. The interstitial techniques displayed a positive correlation between Δ of CTV D90% and the percentage of dwell times of < 2 s of the total dwell times.

Conclusions:
In this study, the dosimetric impacts of transit doses in various brachytherapy techniques were comprehensively clarified. A relatively large impact was observed in interstitial techniques, and the percentage of dwell times of less than 2 s could be a rough indicator of the necessity of considering the transit dose.

keywords:

prostate cancer, brachytherapy, gynecological cancer, 192Ir, RALS, transit dose

  
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