Intraoperative high-dose rate of radioactive phosphorus 32 brachytherapy for diffuse recalcitrant conjunctival neoplasms: a retrospective case series and report of toxicity

Systematic review of intraoperative radiation therapy for head and neck cancer

Multidisciplinary treatments with surgery, radiation therapy, and chemotherapy are the cornerstones in the management of locally advanced head and neck malignancies. In most cases, radiation is delivered via external beam radiation therapy (EBRT). Intraoperative radiation therapy (IORT), on the other hand, is the delivery of precise doses of radiation to selected target volumes within the exposed surgical field while at the operating room. Most studies on its use on head and neck cancers are limited to single-institutional retrospective case series. We performed a systematic review to consolidate the existing literature on IORT for head and neck malignancies. Fifty-two studies representing a mixed population of 2,389 patients were included in this review. IORT via electrons (intraoperative electron radiation therapy), brachytherapy (intraoperative high dose-rate brachytherapy) or photons was administered in numerous settings, but most commonly as part of a reirradiation regimen following salvage surgery for recurrent tumours. Often, additional EBRT was also planned postoperatively. This review illustrates that IORT is a promising treatment modality in head and neck cancer. Multiple single-institutional studies spanning several decades have demonstrated benefit in terms of local control with reasonable toxicity. However, randomised trials comparing it with current standards of care are still needed.

Protocol for the measurement of the absorbed dose rate to water for a planar 32P beta emitting brachytherapy source: A multi-institutional validation

PURPOSE

This is a multi-institutional report on inter-observer and inter-instrument variation in the calibration of the absorbed dose rate for a planar ³²P beta emitting brachytherapy source. Measurement accuracy is essential since the dose profile is steep and the source is used for the treatment of tumors that are located in close proximity to healthy nervous system structures.

METHODS AND MATERIALS

An RIC-100 ³²P source was calibrated by three institutions using their own equipment and following their standard procedures. The first institution calibrated the source with an electron diode and EBT3 film. The second institution used an electron diode. The third institution used HD810 film. Additionally, each institution was asked to calibrate the source using an electron diode and procedure that was shared among all institutions and shipped along with the radiation source. The dose rate was reported in units of cGy*min^-1 at a water equivalent depth of 1 mm.

RESULTS

Close agreement was observed in the measurements from different users and equipment. The variation across all diode detectors and institutions had a standard deviation of 1.8% and maximum difference of 4.6%. The observed variation among two different diode systems used within the same institution had a mean difference of 1.6% and a maximum variation of 1.8%. The variations among film and diode systems used within the same institution had a mean difference of 2.9% and a maximum variation of 4.3% CONCLUSIONS: The absorbed dose rate measurement protocol of the planar beta-emitting ³²P source permits consistent dosimetry across three institutions and five different electron diode and radiochromic film systems. The methodologies presented herein should enable measurement consistency among other clinical users, which will help ensure high quality patient treatments and outcomes analysis.

Single-fraction low-energy electronic brachytherapy for conjunctival lymphoma

Purpose

Conjunctival lymphoma represents an uncommon tumor, accounting for 5-10% of total extranodal lymphomas. Although radiotherapy is a frequent treatment option, limited capacities and lack of specialized centers are common problems in Peru, forcing radiation oncologists to apply short courses of radiotherapy. Here, we report a case series of patients treated with a novel single-shot scheme. Additionally, we present a literature review of the current short-course irradiation strategies.

Cases presentation

Three cases of conjunctival marginal zone (B-cell) lymphoma (marginal zone lymphoma [MZL]/mucosa-associated lymphoid tissue [MALT]) of the fornix are presented. Following biopsy and sonographic assessment of the lesion thickness, we applied a focused single dose of 14 Gy kilovoltage brachytherapy (prescribed to the maximum thickness of the lesion). Follow-up was scheduled in quarterly intervals. After 28, 31, and 40 months of follow-up, none of the three patients treated exhibited acute or chronic toxicities and remained local or distant disease-free.

Conclusions

Single dose kilovoltage brachytherapy was effective and safe in this small cohort of patients. Based on the literature, there is an evidence that local treatment in short-course radiotherapy is effective and should be considered amongst therapeutic options for these patients; however, this novel approach should be evaluated prospectively in a larger cohort.

Investigation of Newly Prepared Biodegradable 32P-chromic Phosphate-polylactide-co-glycolide Seeds and Their Therapeutic Response Evaluation for Glioma Brachytherapy

³²P high-dose rate brachytherapy allows high-dose radiation delivery to target lesions with less damage to adjacent tissues. The early evaluation of its therapeutic effect on tumours is vital for the optimization of treatment regimes. The most commonly used ³²P-CP colloid tends to leak with blind therapeutic area after intratumour injection. We prepared ³²P-chromic phosphate-polylactide-co-glycolide (³²P-CP-PLGA) seeds with biodegradable PLGA as a framework and investigated their characteristics in vitro and in vivo. We also evaluated the therapeutic effect of ³²P-CP-PLGA brachytherapy for glioma with the integrin αvβ3-targeted radiotracer ⁶⁸Ga-3PRGD₂. ³²P-CP-PLGA seeds (seed group, SG, 185 MBq) and ³²P-CP colloid (colloid group, CG, 18.5 MBq) were implanted or injected into human glioma xenografts in nude mice. Scanning electron microscopy (SEM) of the seeds, micro-SPECT imaging, and biodistribution studies were performed at different time points. The tumour volume was measured using a caliper, and ⁶⁸Ga-3PRGD₂ micro-PET-CT imaging was performed to evaluate the therapeutic effect after ³²P intratumour administration. The delayed release of ³²P-CP was observed with biodegradation of vehicle PLGA. Intratumoural effective half-life of ³²P-CP in the SG (13.3 ± 0.3) d was longer than that in the CG (10.4 ± 0.3) d (P < 0.05), with liver appearance in the CG on SPECT. A radioactivity gradient developed inside the tumour in the SG, as confirmed by micro-SPECT and SEM. Tumour uptake of ⁶⁸Ga-3PRGD₂ displayed a significant increase on day 0.5 in the SG and decreased earlier (on day 2) than the volume reduction (on day 8). Thus, ³²P-CP-PLGA seeds, controlling the release of entrapped ³²P-CP particles, are promising for glioma brachytherapy, and ⁶⁸Ga-3PRGD₂ imaging shows potential for early response evaluation of ³²P-CP-PLGA seeds brachytherapy.

Advances in the management of conjunctival melanoma

Malignant melanoma of the conjunctiva is a rare but serious condition. Over the last several years, there have been important advances in the classification, diagnosis, and treatment of this condition. Recent cytogenetic and immunohistochemical studies are increasing understanding of its tumorigenesis. Diagnosis, although still made via histopathology, has been aided with imaging techniques such as ultrasound biomicroscopy and anterior segment optical coherence tomography. Primary treatment consists of surgical excision. But adjuvant treatments with cryotherapy, topical chemotherapy, and radiation therapy have shown increased success. Sentinel lymph node biopsy has shown early promise of detecting micro-metastasis. Long term follow-up of patients with conjunctival melanoma with systemic surveillance is necessary to detect recurrences and metastases.