CME 13 Session - EANM'17

(3)
Dosimetry/Radionuclide Therapy/Radiation Protection: Treatment Planning for Radionuclide Therapy, How Simple Can it Be?

Educational Objectives:
  1. Learn the legal responsibilities for prospective treatment planning of radionuclide therapy
  2. Acknowledge the possible consequences of new regulations in radiation protection and radioactive waste disposal for the nuclear medicine practice
  3. Understand how the traditional way of fixed activity dosing schemes based on safe dose cohorts can be still considered to be part of a personalized treatment
  4. Comprehend the steps involved in a dosimetry guided treatment planning model that lead to a patient-specific therapy
Summary:
In all radiotherapy, including therapeutic application in nuclear medicine, patient exposuresshould be individually planned and appropriately verified taking into account that doses tonon-target volumes and tissues shall be as low as reasonably achievable and consistent withthe intended radiotherapeutic purpose of the exposure. This article from the revised BasisSafety Standards in EC directive 2013/59 will change the current clinical practice inradionuclide therapy considerably. These changes will have to be implemented very soon asthe national legislations in the EU are rewritten according to this directive and will be enforcedby February 6, 2018. The main change in the BSS is that the radiological protectionrecommendations are applied according to ICRP publication 103 (2007). This has severalconsequences for the definition of effective dose, but also operational limits like the eye lensdose limit is set at 20 mSv instead of the current 150 mSv.
The position of the EANM is bivalent; it is important to keep the current nuclear medicinetherapy practice alive and some guidance is needed to help initiating optimised patientspecificdosimetry. Radionuclide therapy treating patients with fixed activity possibly adjustedto weight does not lead to overt toxicity. Safe maximum tolerable activities have beendetermined in phase 1 trials for typical patient cohorts, or are based on decades of experience.This is comparable to the customary practice in cytotoxic chemotherapy, with the advantagethat patients can be selected by imaging with a theranostic companion drug and that thedelivery in most cases can be verified post-therapy.
Radionuclide therapies should be administered at the highest tolerance level. Dosimetry canhelp to define the thresholds at a patient-specific level, either by a pre-therapeutic assessmentor in between treatment cycles. Treating at a maximum tolerable threshold dose will maximisethe dose to the target, even when it is not observable like in most metastasized disease.Implementation of patient-specific treatment planning could be the next step to improveoutcome, although evidence by prospective clinical trials is needed. Simple dosimetry tominimally comply to the requirement of treatment planning or implementation of a fullcomprehensive patient-specific treatment planning protocol is the choice by which the burdenof another regulation can turn into an opportunity.

Key Words:
Dosimetry, patient-specific treatment planning, radionuclide therapy, EC directive 2013/59/Euratom, Basic Safety Standards, Medical Physics Expert, MIRD scheme
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