Software-assisted dosimetry in peptide receptor radionuclide therapy with 177Lutetium-DOTATATE for various imaging scenarios

Abstract

In peptide receptor radionuclide therapy (PRRT) of patients with neuroendocrine neoplasias (NENs), intratherapeutic dosimetry is mandatory for organs at risk (e.g. kidneys) and tumours. We evaluated commercial dosimetry software (Dosimetry Toolkit) using varying imaging scenarios, based on planar and/or tomographic data, regarding the differences in calculated organ/tumour doses and the use for clinical routines. A total of 16 consecutive patients with NENs treated by PRRT with 177Lu-DOTATATE were retrospectively analysed. Single-photon emission computed tomography (SPECT)/low-dose computed tomography (CT) of the thorax and abdomen and whole body (WB) scintigraphy were acquired up to 7 days p.i. (at a maximum of five imaging time points). Different dosimetric scenarios were evaluated: (1) a multi-SPECT-CT scenario using SPECT/CT only; (2) a planar scenario using WB scintigraphy only; and (3) a hybrid scenario using WB scintigraphy in combination with a single SPECT/low-dose CT. Absorbed doses for the kidneys, liver, spleen, lungs, bladder wall and tumours were calculated and compared for the three different scenarios. The mean absorbed dose for the kidneys estimated by the multi-SPECT-CT, the planar and the hybrid scenario was 0.5 ± 0.2 Sv GBq-1, 0.8 ± 0.4 Sv GBq-1 and 0.6 ± 0.3 Sv GBq-1, respectively. The absorbed dose for the residual organs was estimated higher by the planar scenario compared to the multi-SPECT-CT or hybrid scenario. The mean absorbed tumour doses were 2.6 ± 1.5 Gy GBq-1 for the multi-SPECT-CT, 3.1 ± 2.2 Gy GBq-1 for the hybrid scenario and 5.3 ± 6.3 Gy GBq-1 for the planar scenario. SPECT-based dosimetry methods determined significantly lower kidney doses than the WB scintigraphy-based method. Dosimetry based completely on SPECT data is time-consuming and tedious. Approaches combining SPECT/CT and WB scintigraphy have the potential to ensure compromise between accuracy and user-friendliness.

A method for tumor dosimetry based on hybrid planar‐SPECT/CT images and semiautomatic segmentation

“…Mean and median values of the absorbed dose per administered activity calculated over groups of patients of between 2.6 Gy GBq and 9.7 Gy GBq have been reported . These were estimated using various methods involving planar images, SPECT/CT images, or a combination of planar and SPECT/CT images . In this work, the mean value obtained is 3.9 Gy GBq when estimated using the SPECT only method, and 3.6 Gy GBq when using the Max5 hybrid planar‐SPECT/CT method.…”

“…Published data on tumor absorbed doses in Lu‐DOTATATE PRRT reflect a wide range, as recently summarized by Eberlein et al. Mean and median values of the absorbed dose per administered activity calculated over groups of patients of between 2.6 Gy GBq and 9.7 Gy GBq have been reported . These were estimated using various methods involving planar images, SPECT/CT images, or a combination of planar and SPECT/CT images .…”

“…The reasons for the differences in reported absorbed‐dose values are difficult to elucidate and may be due to methodological differences or biological differences related to different primary tumor origins, the disease stage, the evaluated treatment cycle number, or the location of the tumors selected for evaluation. Most publications did not report the primary tumor origin; Garkavij et al included mainly small intestinal NET (13 of 21 pts), the remaining being pancreatic, thymic, rectal, and lung NET; Ilan et al only included pancreatic NET larger than 2.2 cm in diameter; and Del Prete et al mainly included small intestine (17 of 36 pts) and pancreatic NET (10 of 36 pts).…”

“…However, no trends of over‐ or underestimations can be discerned in their study. Kupitz et al evaluated Lu‐DOTATATE dosimetry with planar, hybrid, and pure SPECT methods for normal organs and tumors in patients. Higher absorbed doses were generally obtained with the hybrid method compared to pure SPECT.…”

“…Hybrid imaging techniques have been presented and applied earlier [16][17][18][19][20][21][22][23] and include methods of varying complexity, from separate analysis of planar and SPECT images 17 to more sophisticated methods where the SPECT/CT is used to correct for overlapping activity uptakes. 19,21 A few studies include evaluation of the dosimetric accuracy and uncertainty, 19,[23][24][25] mainly using phantom studies. Overall, the results show that hybrid methods perform better than methods based only on planar images and are generally comparable to purely SPECT-based methods, albeit with some losses of accuracy and precision that are dependent on which organ is analyzed and which radiopharmaceutical is used.…”