3D dosimetry to assess potential side effects after an extravasation of 177Lu-DOTATATE

by Simon Lechien (1^st year PhD student)

Cancer is one of the deadliest diseases worldwide. Several therapies have been developed to treat patients, including radiotherapy. One type of radiotherapy is molecular radiotherapy (MRT) which consists in injecting a radiopharmaceutical to the patient. The radiopharmaceutical is made of a biological vector that targets cancer cells and a radioisotope that irradiates them. This approach allows for the local destruction of diffuse cancers. However, a vein may rupture, resulting in the irradiation of healthy tissue and side effects at the point of injection, including tissue necrosis. The standard method used to perform dosimetry in MRT is the MIRD formalism, which has limitations. For a better evaluation of potential toxicity, the use of Monte Carlo simulation for 3D dosimetry is a benefit. The standard threshold for necrosis according to Barré et al [1] for this modality is equal to 25 Gy. Because the main therapy is external beam radiotherapy, with more toxicity feedback, another necrosis threshold used in this modality can be evaluated. To do that, a biological model computing biological effect dose (BED) from the MIRD Pamphlet n°20 [2] is utilized. The BED enables the calculation of the dose, known as EQD2, that would lead to an equivalent biological effect in external beam radiotherapy. This talk will present a dosimetric assessment for an extravasation case occurred in CLCC François Baclesse and the limits of BED model for MRT as well as dose determination.

References:
[1] Barré, E., Nguyen, M.-L., Bruel, D., Fournel, C., Hosten, B., Lao, S., et al. (2013). Extravasation des médicaments radiopharmaceutiques : mesures préventives et prise en charge recommandées par la sofra. Annales Pharmaceutiques Françaises 71, 261–274. doi:10.1016/j.pharma.2013.05.001
[2] Medicine S of N. Errata. Journal of Nuclear Medicine. Society of Nuclear Medicine; 2011;52(9):1498–1498.