LETTER TO THE EDITOR

Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors: how important is internal dosimetry?

The South African Association of Physicists in Medicine and Biology (SAAPMB) and the associated South African Medical Physics Society (SAMPS) would like to congratulate the College of Nuclear Physicians on the publication of the practice guidelines on Peptide Receptor Radionuclide Therapy (PRRT) in Neuroendocrine Tumours.¹ Unfortunately these guidelines might create the impression that the associated internal dosimetry assessment is just an optional extra, with only a single short paragraph on post-therapy images that are obtained to confirm uptake of therapy agents in the tumour and for dosimetry assessment. This is in stark contrast to the joint IAEA, EANM and SNMMI guidance document,² which has a whole section on dosimetry. Radiation dosimetry of normal organs and malignant lesions allows the dose to the tumour to be maximised, while keeping the dose to normal tissues low enough to reduce the risk of delayed organ toxicity.

Prescriptions in radionuclide therapy are mostly based on a fixed amount of activity for all patients, sometimes tailored to patient weight or body surface area.³ There have been no randomised controlled trials to evaluate the merits of dosimetry-based versus fixed-activity-based approaches in PRRT,³ but there is increasing evidence that treatment outcome correlates with the absorbed doses delivered to tumours and healthy organs.⁴

The International Atomic Energy Agency (IAEA) published basic safety standards,⁵ in which it is clearly stated that "licensees shall ensure that dosimetry of patients is performed and documented by or under the supervision of a medical physicist..." and that medical exposures from therapeutic radiological procedures must be optimised, which also includes PRRT. Internal dosimetry offers one such optimisation avenue. Additionally, quality assurance, including the acceptance testing and commissioning of medical radiological equipment, must be done by or under supervision of the medical physicist.

In fact, an activity-based approach may lead to potential legal issues under South African regulations. The regulations relating to Group IV hazardous substances⁶ (i.e. radioactive substances) clearly state that an authority holder who applies for a Group IV hazardous substance for medical purposes must ensure that "a record is kept of the radio-therapeutic treatment given to patients, in which record is indicated of the parts of the body irradiated, the Group IV hazardous substance used for the treatment, the tumour dose and all relevant data on which the calculation of such dose is based."

We realise that doing internal dosimetry well can be quite challenging, but guidelines have been published on how to do this.^7,8 The European Association of Nuclear Medicine (EANM) also published a guidance document on good practice of clinical dosimetry reporting.⁹ We realise that the Medical Physics community is under-represented in most Nuclear Medicine practices in South Africa, but we maintain that internal radiation dosimetry should form part of any PRRT as part of good practice, and is mandatory under South African law.

Yours sincerely,

Christoph Trauernicht

(President of the SAAPMB - cjt@sun.ac.za)

and

Pieter du Toit

(Chairperson of SAMPS - dutoitpd@nuke.co.za)

Both authors have no conflict of interest.

REFERENCES

1. Lawal I, Louw L, Warwick J, et al. The College of Nuclear Physicians of South Africa Practice Guidelines on Peptide Receptor Radionuclide Therapy in Neuroendocrine Tumours. S Afr J Surg. 2018;56(3). Available from: http://dx.doi.org/10.17159/2078-5151/2018/v56n3a2775        [ Links ]

2. Zaknun JJ, Bodei L, Mueller-Brand J, et al. The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours. Eur J Nucl Med Mol Imaging. 2013;40:800. Available from: https://doi.org/10.1007/s00259-012-2330-6        [ Links ]

3. Flux GD, Sjogren Gleisner K, Chiesa C, et al. From fixed activities to personalized treatments in radionuclide therapy: lost in translation? Eur J Nucl Med Mol Imaging. 2018;45:152-4. Available from: https://doi.org/10.1007/s00259-017-3859-1        [ Links ]

4. Lassmann M, Eberlein U. The Relevance of Dosimetry in Precision Medicine. J Nucl Med. 2018;59:1494-9. doi: 10.2967/jnumed.117.206649        [ Links ]

5. IAEA Safety Standards for Protecting People and the Environment - Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards (General Safety Requirements Part 3) (ISBN 978-92-0-135310-8). 2014:7681.         [ Links ]

6. Regulation No. R. 247: Regulations relating to Group IV hazardous substances, Government Gazette, 26 Feb 1993.         [ Links ]

7. Dewaraja YK, Frey EC, Sgouros G, et al. MIRD Pamphlet No. 23: Quantitative SPECT for Patient-Specific 3-Dimensional Dosimetry in Internal Radionuclide. J Nucl Med. 2012; 53:1310-25. doi: 10.2967/jnumed.111.100123        [ Links ]

8. Ljungberg M, Celler A, Konijnenberg MW, et al. MIRD Pamphlet No. 26: Joint EANM/MIRD Guidelines for Quantitative 177Lu SPECT Applied for Dosimetry of Radiopharmaceutical Therapy. J Nucl Med. 2016;57:151-62. doi: 10.2967/jnumed.115.159012        [ Links ]

9. Lassmann M, Chiesa C, Flux G, Bardiès M. EANM Dosimetry Committee guidance document: good practice of clinical dosimetry reporting. Eur J Nucl Med Mol Imaging. Jan 2011;38(1):192-200. doi: 10.1007/s00259-010-1549-3        [ Links ]