Katsumaro Kubo1, Masahiro Kenjo2, Hideo Kawabata3, Koichi Wadasaki3, Mitsuru Kajiwara4, Yoshiko Doi2, Minoru Nakao2, Hideharu Miura2, Shuichi Ozawa2, Yasushi Nagata5,2. 1. Department of Radiation Oncology, Hiroshima University Hospital, 1-2-3 Kasumi Minami-ku Hiroshima-shi, Hiroshima, 734-8553, Japan. maro1987@hotmail.co.jp. 2. Hiroshima High-Precision Radiotherapy Cancer Center, 2-2 Futabanosato Higashi-ku Hiroshima-shi, Hiroshima, 732-0057, Japan. 3. Department of Radiation Oncology, Hiroshima Prefectural Hospital, 1-5-54 Ujinakanda Minami-ku Hiroshima-shi, Hiroshima, 734-0004, Japan. 4. Department of Urology, Hiroshima Prefectural Hospital, 1-5-54 Ujinakanda Minami-ku Hiroshima-shi, Hiroshima, 734-0004, Japan. 5. Department of Radiation Oncology, Hiroshima University Hospital, 1-2-3 Kasumi Minami-ku Hiroshima-shi, Hiroshima, 734-8553, Japan.
Abstract
BACKGROUND: Few studies have assessed hydrogel spacer shrinkage during external-beam radiation therapy following brachytherapy for localized high-risk prostate cancer. This case presentation evaluated the changes in hydrogel spacer appearance by magnetic resonance imaging during external-beam radiation therapy after brachytherapy for prostate cancer and analyzed the effect of this shrinkage on the dose distribution in four cases. CASE PRESENTATION: In all cases, we implanted 125I sources using a modified peripheral loading pattern for seed placement. The prescribed dose for each implant was 110 Gy. After delivering the sources, a hydrogel spacer was injected. All cases underwent external-beam radiation therapy approximately 1-2 months after brachytherapy. The prescribed dose of external-beam radiation therapy was 45 Gy in 1.8-Gy fractions. Magnetic resonance imaging was performed for evaluation on the day following seed implantation (baseline), at external-beam radiation therapy planning, and during external-beam radiation therapy. The median hydrogel spacer volume was 16.2 (range 10.9-17.7) cc at baseline, 14.4 (range, 9.4-16.1) cc at external-beam radiation therapy planning, and 7.1 (range, 2.0-11.4) cc during external-beam radiation therapy. The hydrogel spacer volume during external-beam radiation therapy was significantly lower than that at external-beam radiation therapy planning. The rectum V60-80 (rectal volume receiving at least 60-80% of the prescribed dose of external-beam radiation therapy) during external-beam radiation therapy was significantly higher than that at external-beam radiation therapy planning. CONCLUSIONS: The potential reduction in hydrogel spacer size during external-beam radiation therapy following brachytherapy can lead to unexpected irradiation to the rectum. This case presentation would be helpful for similar cases.
BACKGROUND: Few studies have assessed hydrogel spacer shrinkage during external-beam radiation therapy following brachytherapy for localized high-risk prostate cancer. This case presentation evaluated the changes in hydrogel spacer appearance by magnetic resonance imaging during external-beam radiation therapy after brachytherapy for prostate cancer and analyzed the effect of this shrinkage on the dose distribution in four cases. CASE PRESENTATION: In all cases, we implanted 125I sources using a modified peripheral loading pattern for seed placement. The prescribed dose for each implant was 110 Gy. After delivering the sources, a hydrogel spacer was injected. All cases underwent external-beam radiation therapy approximately 1-2 months after brachytherapy. The prescribed dose of external-beam radiation therapy was 45 Gy in 1.8-Gy fractions. Magnetic resonance imaging was performed for evaluation on the day following seed implantation (baseline), at external-beam radiation therapy planning, and during external-beam radiation therapy. The median hydrogel spacer volume was 16.2 (range 10.9-17.7) cc at baseline, 14.4 (range, 9.4-16.1) cc at external-beam radiation therapy planning, and 7.1 (range, 2.0-11.4) cc during external-beam radiation therapy. The hydrogel spacer volume during external-beam radiation therapy was significantly lower than that at external-beam radiation therapy planning. The rectum V60-80 (rectal volume receiving at least 60-80% of the prescribed dose of external-beam radiation therapy) during external-beam radiation therapy was significantly higher than that at external-beam radiation therapy planning. CONCLUSIONS: The potential reduction in hydrogel spacer size during external-beam radiation therapy following brachytherapy can lead to unexpected irradiation to the rectum. This case presentation would be helpful for similar cases.
Entities:
Keywords:
Brachytherapy; Case report; External-beam radiation therapy; Hydrogel spacer; Prostate cancer