Brachytherapy for primary and recurrent nasopharyngeal carcinoma: treatment techniques and results

Evaluation of PC-ISO for customized, 3D Printed, gynecologic 192-Ir HDR brachytherapy applicators

The purpose of this study was to evaluate the radiation attenuation properties of PC-ISO, a commercially available, biocompatible, sterilizable 3D printing material, and its suitability for customized, single-use gynecologic (GYN) brachytherapy applicators that have the potential for accurate guiding of seeds through linear and curved internal channels. A custom radiochromic film dosimetry apparatus was 3D-printed in PC-ISO with a single catheter channel and a slit to hold a film segment. The apparatus was designed specifically to test geometry pertinent for use of this material in a clinical setting. A brachytherapy dose plan was computed to deliver a cylindrical dose distribution to the film. The dose plan used an 192Ir source and was normalized to 1500 cGy at 1 cm from the channel. The material was evaluated by comparing the film exposure to an identical test done in water. The Hounsfield unit (HU) distributions were computed from a CT scan of the apparatus and compared to the HU distribution of water and the HU distribution of a commercial GYN cylinder applicator. The dose depth curve of PC-ISO as measured by the radiochromic film was within 1% of water between 1 cm and 6 cm from the channel. The mean HU was -10 for PC-ISO and -1 for water. As expected, the honeycombed structure of the PC-ISO 3D printing process created a moderate spread of HU values, but the mean was comparable to water. PC-ISO is sufficiently water-equivalent to be compatible with our HDR brachytherapy planning system and clinical workflow and, therefore, it is suitable for creating custom GYN brachytherapy applicators. Our current clinical practice includes the use of custom GYN applicators made of commercially available PC-ISO when doing so can improve the patient's treatment. 

Recurrent nasopharyngeal carcinoma: current management approaches

OBJECTIVES

Providing the primary recurrence is localized, salvage treatment is possible for nasopharyngeal carcinoma (NPC). This is a review of the experience of retreatment of this malignancy highlighting the roles of surgery and repeat radiotherapy.

METHODS

The Tumor Registry of the Prince of Wales Cancer Centre was audited for patients with an initial diagnosis of squamous/nonsquamous cell NPC who had primary treatment with radiotherapy, and now presented for retreatment. Features relating to patient, disease and treatment factors were evaluated. The primary end point was subsequent local control, and secondary endpoints were overall and cancer-specific survival.

RESULTS

Over a 30-year period 39 patients were eligible, with 25 receiving both primary and retreatment at Prince of Wales Hospital. There were 25 males and 14 females with a median age of 50 years. Thirty-six patients had radiotherapy, 4 had stereotactic radiosurgery, 5 had brachytherapy, and the remainder had external treatment. Surgery was performed in 10 patients, of whom 3 had this as the only retreatment modality. Radiotherapy doses for retreatment ranged from 15 Gy (stereotactic radiosurgery) to 71.28 Gy (mean fractionated dose). Local control was achieved in 16 patients giving an overall rate of 41.0%, and the 5-year overall survival rate was 33.3%. Treatment modality was a significant prognostic factor for local control (P < 0.001) and cancer-specific survival (P < 0.05).

CONCLUSION

The presence of local recurrence after definitive treatment of NPC may still be salvageable. The best outcomes with reirradiation occur in the context of limited volume recurrence and a disease-free interval greater than 18 months.