A nomogram to determine required seed air kerma strength in planar 131Cesium permanent seed implant brachytherapy

Feasibility of collagen matrix tiles with cesium-131 brachytherapy for use in the treatment of head and neck cancer

BACKGROUND

Locoregional failure is a unique and challenging problem in head and neck cancer with controversy surrounding the use of re-irradiation in the treatment. We aimed to evaluate the dosimetry and technical parameters in utilizing a collagen matrix with embedded Cesium-131 (Cs-131) radioactive isotope seeds as it relates to dose distribution and dose to carotid artery.

METHODS AND MATERIALS

Cadaveric feasibility study randomizing Cs-131 strands alone or Cs-131 with collagen matrix to be placed into neck dissection defects. For the dose computation, physicists employed the TG-43 dosimetry calculation algorithm with a point source assumption to compute the dose. Carotid arteries were contoured in MIM-Symphony software and the carotid artery maximum and mean doses were calculated in accordance with TG-43 specifications. Ease of use of collagen matrix tiles on a 7-point Likert scale and mean radiation dose to the carotid artery.

RESULTS

Ease of use score was higher in collagen matrix compared to stranded seeds with a mean score of 6.3 +/- 1.2 compared to 4.5 +/- 0.87. Time of implantation was statistically significantly, p = 0.031, lower in the collagen matrix group (M = 5.17 min, SD = 4.62) compared to stranded seeds (M = 15.83 min, SD = 3.24). Mean radiation dose to the carotid artery was 62.8 Gy +/- 9.46 in the collagen matrix group compared to 108.2 Gy +/- 55.6 in the traditional Cs-131 seeds group.

CONCLUSIONS

We present a feasibility and concept cadaveric study using a collagen matrix with Cesium-131 demonstrating preliminary evidence to support its ease of use, decreased time to implantation, and decreased dose delivered to the carotid artery.

Single institution implementation of permanent 131Cs interstitial brachytherapy for previously irradiated patients with resectable recurrent head and neck carcinoma

Purpose

Permanent interstitial brachytherapy is an appealing treatment modality for patients with locoregional recurrent, resectable head and neck carcinoma (HNC), having previously received radiation. Cesium-131 (¹³¹Cs) is a permanent implant brachytherapy isotope, with a low average photon energy of 30 keV and a short half-life of 9.7 days. Exposure to medical staff and family members is low; patient isolation and patient room shielding are not required. This work presents a single institution’s implementation process of utilizing an intraoperative, permanent ¹³¹Cs implant for patients with completely resected recurrent HNC.

Material and methods

Fifteen patients receiving ¹³¹Cs permanent seed brachytherapy were included in this analysis. The process of pre-planning, selecting the dose prescription, seed ordering, intraoperative procedures, post-implant planning, and radiation safety protocols are described.

Results

Tumor volumes were contoured on the available preoperative PET/CT scans and a pre-implant treatment plan was created using uniform source strength and uniform 1 cm seed spacing. Implants were performed intraoperatively, following tumor resection. In five of the fifteen cases, intraoperative findings necessitated a change from the planned number of seeds and recalculation of the pre-implant plan. The average prescription dose was 56.1 ±6.6 Gy (range, 40-60 Gy). The average seed strength used was 2.2 ±0.2 U (3.5 ±0.3 mCi). Patients returned to a recovery room on a standard surgical floor and remained inpatients, without radiation safety restrictions, based on standard surgical recovery protocols. A post-implant treatment plan was generated based on immediate post-operative CT imaging to verify the seed distribution and confirm delivery of the prescription dose. Patients were provided educational information regarding radiation safety recommendations.

Conclusions

Cesium-131 interstitial brachytherapy is feasible and does not pose major radiation safety concerns; it should be considered as a treatment option for previously irradiated patients with recurrent, resectable HNC.

Carotid dosimetry after re-irradiation with 131Cs permanent implant brachytherapy in recurrent, resected head and neck cancer

PURPOSE

Permanent seed implant cesium-131 (131Cs) brachytherapy provides highly localized radiation for patients with recurrent head and neck cancer (HNC), who may be ineligible for external beam radiation therapy due to a high-risk of toxicity. As carotid blowout is a concern in the setting of re-irradiation, a dose to the carotid artery was examined for 131Cs brachytherapy implants.

MATERIAL AND METHODS

Eleven patients were implanted with 131Cs adjacent to carotid at the time of resection for recurrent HNC. Vascularized tissue flaps were used in some patients. The carotid artery was contoured on the post-implant brachytherapy treatment plan, and the maximum carotid point dose and minimum carotid-seed distances are reported. The incidence of carotid blowout in the follow-up period was also measured.

RESULTS

The maximum carotid dose was 77 ±52 Gy (range, 3-158 Gy). The closest seed to the carotid artery was 0.8 ±0.8 cm (range, 0.2-2.6 cm). One patient without a flap experienced carotid blowout, which was attributed to a non-healing wound rather than to high radiation doses.

CONCLUSIONS

Carotid artery doses from 131Cs are reported. Vascularized tissue flaps should be considered when planning 131Cs brachytherapy.