Screening?…OK!… Ma…quante radiazioni dannose si prendono per farlo?…
Da molti anni si dibatte sulla effettiva utilità dello screening per il cancro ai polmoni, argomento di scontro fra i molti medici sostenitori e gli altrettanto numerosi scettici. Solo recentemente, ed esattamente dalla seconda metà dello scorso anno, la controversia si avviata a soluzione grazie alla pubblicazione, sull’autorevolissimo New England Journal of Medicine, dei risultati del più ampio studio mai condotto sull’argomento (l’intera pubblicazione è liberamente visionabile on line alla pagina: http://www.nejm.org/doi/full/10.1056/NEJMoa1102873). Di questa imponente sperimentazione (chiamata in inglese “trial”) hanno moltissimo parlato i media, sia in Italia che nel mondo, e anche noi ne abbiamo dato conto all’interno di un articolo che riassume la posizione della Associazione Internazionale per lo Studio del Cancro del Polmone (IASLC): https://www.alcase.it/2011/07/screening-iaslc/ e in valutazioni critiche di esperti (https://www.alcase.it/2011/08/screening-opinione-di-prestigio/).
In buona sostanza, oggi si è pressoché tutti d’accordo che, nelle persone a rischio di cancro del polmone, la TAC del torace a basso dosaggio (o TAC spirale) è in grado di scoprire piccoli tumori asintomatici ancora asportabili chirurgicamente, riducendo notevolmente il rischio di morte (del 20% secondo il trial americano su citato).
Fatta questa premessa, vale la pena di domandarsi:
” TAC torace a basso dosaggio… OK. Ma… a quante radiazioni dannose ci si sottopone per farla?…”
A questa domanda rispondono gli stessi autori del trial già citato con uno nuovo studio di cui riportiamo l’abstract originale (con un successivo nostro breve riassunto e commento in italiano):
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Estimated Radiation Dose Associated With Low-Dose Chest CT of Average-Size Participants in the National Lung Screening Trial
(AJR November 2011 vol. 197 no. 5 1165-1169)
Author Affiliations:
- Department of Radiology, University of Colorado at Denver, 12401 E 17th Ave, Mail Stop L954, Rm 548, Aurora, CO 80045.
- Department of Radiology, Marshfield Clinic, Marshfield, WI.
- Department of Radiological Sciences, UCLA Medical Center, Los Angeles, CA.
- Department of Radiology, Henry Ford Health System, Detroit, MI.
- Department of Radiology, Thoracic Imaging Research Group, UCLA School of Medicine, Los Angeles, CA.
- Department of Radiology, University of Alabama at Birmingham, Birmingham, AL.
- Department of Radiology, Brigham & Women’s Hospital, Boston, MA.
- Department of Diagnostic Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, TX.
Abstract
OBJECTIVE. The objective of our study was to determine the distribution of effective dose associated with a single low-dose CT chest examination of average-size participants in the National Lung Screening Trial. Organ doses were also investigated.
MATERIALS AND METHODS. Thirty-three sites nationwide provided volume CT dose index (CTDIvol) data annually for the 97 MDCT scanners used to image 26,724 participants during the trial. The dose data were representative of the imaging protocols used by the sites for average-size participants. Effective doses were estimated first using the product of the dose-length product (CTDIvol × 35-cm scan length) and a published conversion factor, “k.” The commercial software product CT-Expo was then used to estimate organ doses to males and females from the average CTDIvol. Applying tissue-weighting factors from both publication 60 and the more recent publication 103 of the International Commission on Radiological Protection (ICRP) allowed comparisons of effective doses to males and to females.
RESULTS. The product of DLP and the k factor resulted in a mean effective dose of 1.4 mSv (SD = 0.5 mSv) for a low-dose chest examination across all scanners. The CT-Expo results based on ICRP 60 tissue-weighting factors yielded effective doses of 1.6 and 2.1 mSv for males and females, respectively, whereas CT-Expo results based on ICRP 103 tissue-weighting factors resulted in effective doses of 1.6 and 2.4 mSv, respectively.
CONCLUSION. Acceptable chest CT screening can be accomplished at an overall average effective dose of approximately 2 mSv as compared with an average effective dose of 7 mSv for a typical standard-dose chest CT examination.