phosphorus-radioisotopes and Central-Nervous-System-Cysts

Although microsurgery remains the first-line treatment, gross total resection of cystic craniopharyngeomas (CP) is associated with significant morbidity and mortality and the addition of external irradiation to subtotal resection proves to achieve similar tumor control. However, concern regarding long-term morbidity associated with external irradiation in children still remains. With this retrospective analysis, the authors emphasize intracavitary brachytherapy using phosphorus-32 (P-32) as a treatment option for children with cystic CP.. Between 1992 and 2009, 17 children (median age 15.4 years; range 7-18 years) with cystic CP underwent intracavitary brachytherapy using P-32. Eleven patients were treated for recurrent tumor cysts; 6 patients were treated primarily. MR imaging revealed solitary cysts in 7 patients; 10 patients had mixed solid-cystic lesions (median tumor volume 11.1 ml; range 0.5-78.9 ml). The median follow-up time was 61.9 months (range 16.9-196.6 months).. Local cyst control could be achieved in 14 patients (82 %). Three patients showed progression of the treated cystic formation (in-field progression) after a median time of 8.3 months (range 5.3-10.3 months), which led to subsequent interventions. The development of new, defined cysts and progression of solid tumor parts (out-of-field progression) occurred in 5 patients and led to additional interventions in 4 cases. There was neither surgery-related permanent morbidity nor mortality in this study. The overall progression-free survival was 75, 63, and 52 % after 1, 3, and 5 years, respectively.. Intracavitary brachytherapy using P-32 represents a safe and effective treatment option for children harboring cystic CP, even as primary treatment. However, P-32 does not clearly affect growth of solid tumor parts or the development of new cystic formations.

Topics: Adolescent; Brachytherapy; Central Nervous System Cysts; Child; Craniopharyngioma; Female; Humans; Male; Phosphorus Radioisotopes; Pituitary Neoplasms; Radiopharmaceuticals; Radiosurgery; Retrospective Studies; Treatment Outcome

Intracavity instillation of beta-emitting colloid pharmaceuticals is a common technique used to treat cystic brain tumors. Most of the dosimetric calculations that have been reported in the literature for this problem are based on empirical formulas derived by Loevinger. Concentration of P-32 radiolabeled solution for the delivery of a prescribed dose (200 Gy to the cyst wall) has been published previously using this formalism in what we refer to as a standard nomogram. The calculations using the Loevinger formulas for calculating the P-32 activity necessary to achieve 200 Gy at the cyst wall is re-evaluated and compared to numerically computed results based on full Monte Carlo simulations (EGSnrc) and the dose-point-kernel (DPK) integration method. For cyst diameters greater than 1 cm, the new calculations agree well with previously published results (the standard nomogram) to within a few percents. However, for cyst diameters of less than 1 cm, it is shown that the standard nomogram results underestimate the therapeutic activity by a factor of approximately 3 for very small diameters (approximately 0.2 cm). New tables based on our calculations are presented and the sources of discrepancies are identified. It is concluded that the new set of data based on our calculations should replace the standard nomogram to administer accurately the target dose to the cyst wall for the smaller diameter cysts (< 1 cm).

Topics: Beta Particles; Brain Neoplasms; Cell Wall; Central Nervous System Cysts; Colloids; Computer Simulation; Humans; Models, Biological; Models, Statistical; Monte Carlo Method; Phosphorus Radioisotopes; Radiometry; Radionuclide Imaging; Radiopharmaceuticals; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Relative Biological Effectiveness; Reproducibility of Results; Sensitivity and Specificity

The dosimetry for radiocolloid therapy of cystic craniopharyngiomas is investigated. Analytical calculations based on the Loevinger and the Berger formulas for electrons and photons, respectively, are compared with Monte Carlo simulations. The role of the material of which the colloid introduced inside the craniopharyngioma is made of as well as that forming the cyst wall is analyzed. It is found that the analytical approaches provide a very good description of the simulated data in the conditions where they can be applied (i.e., in the case of a uniform and infinite homogeneous medium). However, the consideration of the different materials and interfaces produces a strong reduction of the dose delivered to the cyst wall in relation to that predicted by the Loevinger and the Berger formulas.

Topics: Beta Particles; Brain Neoplasms; Cell Wall; Central Nervous System Cysts; Colloids; Computer Simulation; Craniopharyngioma; Humans; Models, Biological; Models, Statistical; Monte Carlo Method; Phosphorus Radioisotopes; Pituitary Neoplasms; Radioisotopes; Radiometry; Radiopharmaceuticals; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Relative Biological Effectiveness; Reproducibility of Results; Rhenium; Sensitivity and Specificity