Journal of Contemporary Brachytherapy

Abstract

5/2025 vol. 17
Original paper

Hybrid inverse treatment planning optimization in gynecologic brachytherapy: Comparison with conventional method

Hiroyuki Okamoto 1
,
Masato Nishitani 1, 2
,
Ayaka Nagao 3, 4
,
Naoya Murakami 5
,
Noriyuki Okonogi 5
,
Jun Takatsu 5
,
Kotaro Ijima 3, 5
,
Satoshi Nakamura 1
,
Takahito Chiba 1
,
Hiroki Nakayama 1
,
Tetsu Nakaichi 1
,
Takumi Sakamoto 1, 6
,
Kae Okuma 3
,
Hiroshi Igaki 3
,
Daisuke Ozaki 7
,
Ken Ando 8
,
Tatsuya Ohno 8
  1. Radiation Safety and Quality Assurance Division, National Cancer Center Hospital, Tokyo 104-0045, Japan
  2. Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo 116-8551, Japan
  3. Department of Radiation Oncology, National Cancer Center Hospital, Tokyo 104-0045, Japan
  4. Cancer Medicine, Cooperative Graduate School, Jikei University Graduate School of Medicine, Tokyo, 105-8461, Japan
  5. Department of Radiation Oncology, Juntendo University Graduate School of Medicine, Tokyo 113-8431, Japan
  6. Department of Radiological Sciences, Komazawa University, Tokyo 154-8525, Japan
  7. Department of Radiology, Gunma University Hospital, Gunma 371-8511, Japan
  8. Department of Radiation Oncology, Gunma University Graduate School of Medicine, Gunma 371-8511, Japan
J Contemp Brachytherapy 2025; 17, 5: 340–353
DOI: https://doi.org/10.5114/jcb.2025.156038
Online publish date: 2025/10/31
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Purpose

To investigate a semi-automatic hybrid inverse treatment planning optimization (HIPO) approach for gynecological brachytherapy that preserves the pear-shaped dose distribution without relying on dummy structures.

Material and methods

We retrospectively analyzed 29 patients with gynecological cancers, who underwent combined intracavitary and interstitial (IC/IS) brachytherapy. HIPO enables optimization of dwell times for specific applicators, while other applicators are fixed in Oncentra® Brachy. Clinical treatment plans (CPs) were compared based on manual adjustments using four HIPO methods: Hovoid, Hfree, HMS, and HMS*. Hovoid optimized tandem and IS needles with ovoid dwell time fixed; Hfree optimized all applicators with no fixation; HMS optimized IS needles with fixation using modified Manchester system, with safe organs at risks (OARs) doses generated in advance by graphical optimization. In HMS* plan, optimization parameters were adjusted to improve high-risk clinical target volume (HR-CTV) dose coverages based on comparisons between CPs and HMS.

Results

Hovoid, Hfree, HMS, and HMS* achieved clinically acceptable DVH parameters in terms of HR-CTV dose coverage and OARs sparing. However, considerable deviations from the conventional pear-shaped dose distributions were observed, particularly with Hfree, which exhibited zero dose contribution from ovoid applicators. Among all HIPO plans, HMS* with adjusted optimization parameters demonstrated the closest HR-CTV D90% to that of the CP, while maintaining a conventional pear-shaped dose distribution.

Conclusions

We recommend applying the modified Manchester system with safe OARs doses as the object of fixation, given its consistency with the conventional pear-shaped dose distribution. The proposed method demonstrated clinically acceptable dose distribution and DVH parameters.

Keywords

inverse planning, HIPO, gynecologic brachytherapy, IC/IS, Manchester system

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