Radiological Protection in Ion Beam Radiotherapy

Draft document: Radiological Protection in Ion Beam Radiotherapy
Submitted by Marie Claire Cantone, AIRP, Italian Association of Radiation Protection
Commenting on behalf of the organisation

Comments on Radiological Protection in Ion Beam Radiotherapy

by AIRP, the Italian Association of Radiation Protection

General Comments

The comments we have received about the document under consideration, show  positive judgments both  about the objective and the structure of document.

From the document it clearly emerges  the contribution given by the Radiological Protection in order to pursue “the goal” of ion beam radiotherapy, which is so important in relation to the complexity, fast progresses in the procedures and also the further  possibility of diffusion of this technique.

It has been appreciated the distribution of the chapters, starting with physical issues and radiobiological implications and then entering in the issues of exposures of patients due to the therapy and from imaging procedures, with additional and focused  attention to occupational exposure.

It has been also very much appreciated the focus given to  the training of the staff, to the  specific safety management and to the prospective approach in preventing accidental exposure, as already presented in ICRP 112.

Specific Comments

-lines 424, 425. Consider to change  'Second cancer - A term which  is used to describe either a new primary cancer or cancer that has spread from …'  with  'Second cancer - A term that is used to describe either a new primary cancer (of the same type as the original cancer ) or cancer that has spread from …'   or to use other words which help understanding the meaning of primary cancer

-lines 1100-1102. ‘Cataractogenesis is significantly spared by reducing dose-rate or by fractionation of the total dose for low LET photons (Belkacemi et al., 1996).’  The comment: Is it really correct this sentence in the light of what is expressed in ICRP 118? – (ICRP 118, pag. 15 : ‘Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. ‘)

-lines 1119-1128. Table 4.2. of this draft reproduces  table A.3.4 of ICRP 103 except for the time to develop effect and for the absorbed dose related to eye, which are taken from the data in table 4.4 (for morbidity) of ICRP 118.  The caption of the table, says ‘Reproduced from ICRP Publications 103 and 118.     Note that: 
i)  in table 4.5 (for mortality) of ICRP 118 in relation to lung, the same time to develop effect of 1-7 months as in ICRP 103 is indicated, but an absorbed dose of 7-8 Gy instead of 6 Gy.  In this draft it is indicated 6 Gy. Why not 7-8 Gy as in ICRP 118?
ii) in table 4.2. of this draft, the last column uses  the same formality  for indicating  the references (reported just at the end of the table) as in table A.3.4 of ICRP 103, except for (a) which  now refers not only to ICRP 1984 but also to ICRP 2012. It is a sort of copy and paste approach.   This approach does not seem correct, since,  while the part of the table on morbidity refers also to ICRP 2012 (and this info is already in the caption),  the part on mortality does not  refer at all to ICRP 2012, even if, in relation to bone marrow and small intestine , the data are also present  in ICRP 2012, which is the most recent publication on this issue.  The suggestion here is to not consider the references reported in ICRP 103 (dated 1984, 1988, 1996, 1989, 1993) and to just put in evidence the data already reported in ICRP 103 and ICRP 118. This same approach has been already used in ICRP 118 tables 4.4. and  4.5.

-lines 1131-1137. To consider the opportunity to : i) remember LNT is combined with a judged values of a dose and dose rate effectiveness factor, and provides a prudent basis for the practical purposes of radiological protection ; ii) change ‘For these diseases…’ with ‘For these effects…’

-lines 1154-1156. ‘However, the presence of rare genetically susceptible sub-populations will not distort the risk estimation in typical human populations (ICRP Publication 79, 1998a).’
By considering what expressed in ICRP 79 abstract  (‘Using the data cited, the likely contribution to radiation risk from familial cancer disorders is too low to generate an unacceptable distortion of current estimates of cancer risk in the vast majority of human populations.’), and  in ICRP 79 Conclusions (‘The principal conclusion by the Commission is that, on current knowledge, the presence of familial cancer disorders does not impose unacceptable distortions in the distribution of radiation cancer risk in typical human populations.’) on the issue, and moreover, by considering  what has been expressed in ICRP 103 (3.2.4. Genetic susceptibility to cancer, (90)  ‘On the basis of the data and judgments developed in Publication 79 and further information reviewed in the UNSCEAR (2000, 2001) and NAS/NRC (2006) reports, the Commission believes that strongly expressing, high penetrance, cancer genes are too rare to cause significant distortion of population-based estimates of low-dose radiation cancer risk. Although the Commission recognizes that variant cancer genes of low penetrance may, in principle, be sufficiently common to impact upon population-based estimates of radiation cancer risk, the information available is insufficient to provide a meaningful quantitative judgment on this issue.’)  the comment here concerns the wording used in this draft and in particular in the expression ‘will not distort’, which  should be revised with something in the sense of ‘is too low to generate an unacceptable distortion’;  ‘does not impose unacceptable distortion’;  ‘too rare to cause significant distortion’…..
Moreover, in addition to ICRP 79 as a reference in line 1156, consider to add also ICRP 103.

-lines 1161-1166. ‘Heritable effects. (70) Although there continues  to be no direct evidence in humans, there is evidence that radiation induces heritable effects in experimental animals. ICRP Publication 103 provides the estimated hereditary risk up to the second generation  of about 0.2% per Sv, which is much smaller than the estimated cancer risk of 5.5% per Sv.’  
To be taken into consideration that: i)- the estimate related to cancer risk should be better indicated in the previous part of the text, that relates to Cancers, since the title of this subparagraph is Heritable effects; ii)- according to ICRP 103 the risk up to the second generation is expressed per Gy, while the detriment-adjusted nominal risk in the whole population is estimated as 0.2% per Sv.

-lines 1167-1186 (71). Suggestions: i) in line 1169 it could be useful to indicate ICRP 90, 2003 as reference in addition to the NCRP, 2013. - ii) in line 1175 consider if useful to add ‘in humans’, thus to have : ‘Malformation in humans are mainly …’. - iii)  line 1178  suggests a threshold of 100 mGy for the decrease in IQ on the basis of ICRP 90, but ICRP 90 reports  non exactly the same concept:  in (46) ‘Other parameters such as variation in intelligence quotient (IQ) and school performance (Otake et al., 1988; Schull et al., 1988) or neurofunctional deficits (Yoshimaru et al., 1995) were indicative of linear dose responses, but the existence of thresholds remained obscure.’ and  in (440) ‘There is a suggestion of a threshold in that the mean score for the 10–90-mGy group was nominally higher than that of the zero-dose group; however, it is doubtful that a statistical test would have a narrow enough confidence bound to identify this as a threshold.’  Consider the opportunity to modify the wording in line 1178 of this draft.

-In table 4.3. the indication, in the last line, of the radiation weighting factor  for neutrons  as (2.5 -20) it seems extremely  simplified, and consider also that for 1 MeV this factor is even slightly larger than 20.

-line 1311.  The star of the footnote needs to be introduced also in the table in relation to Electrons

-Fig. 5.7. In the caption  ‘Equivalent dose as function of phantom age averaged over all fields’ consider to change it in  in ‘Equivalent dose as function of phantom age averaged over all fields  (i.e patients’s age)’.

-the title (line 1886) ‘5.2 Medical exposure of patients from imaging procedures’ maybe it does not fit to the paragraph (line 2081) ‘5.2.3 Exposure of comforters and carers’  which takes into consideration the person who stays  close to the patient after the ion beam radiotherapy.

-lines 2005-2011. The comparison between the mean organ dose in various examinations performed by using CBCT or by using only X-ray CT,    presented in these lines, needs a deeper discussion and a detailed relation with the data shown in table 5.1 and table 5.3 of this draft.

-lines 2262-2269. The text says ‘The Commission recommended the dose limits of occupational and public exposures in Publication 60 (ICRP, 1991). For occupational exposures, the dose limit in 5 years is 100 mSv (mean dose 20 mSv/y), and the maximum dose limit in a year is 50 mSv.  On the other hand, the dose limit for the public is 1 mSv in a year. The Commission published new recommendations in Publication 103 (ICRP, 2007b). Tsujii et al.  (2009) concluded from comparing estimated doses of radiological technologists  mentioned above with these dose limits of occupational exposure: the current  regulations for photon radiotherapy are also applicable to ion beam radiotherapy. ‘
The question is: Why so many details on the recommended dose limits indicated in ICRP 60 and no info on recommended limits indicated in ICRP 103 ?

-lines 2283-2285. In table 5.4 the part ‘Source to evaluation point distance’ is divided in two: ‘Effective dose’ and ‘Skin dose’. Consider to change in ‘ for effective dose evaluation’ and ‘for equivalent dose of skin evaluation’.

-line 2378.  ‘Radioactivity A1i (Bq) of a nuclide’ change in  ‘Radioactivity in air A1i (Bq) of a nuclide’

-line 2382. Consider the opportunity to give a definition for air cross section (cm-1)

-line  2380. Consider to check the consistency of the second part of the formula: the ratio V(cm3)D(Gy) x 10(-3) / E(MeV) x 1.6 x 10(-13) does not result in a number, as N is.

-line 2397. Consider to check the consistency of the units of the second member with the first member of the formula.  A(s-1)= lambda(s-1) sigma(cm-1) flux(cm-2 s-1) volume (cm3).

-line 2425. Consider to check the consistency of the units. Probably V,  as volume,  is missed in the denominator in the fraction at the second part.

-line 2387 and lines 2464-2467(table 6.1). Consider if it is really useful, for the scope of this document, to maintain Table 6.1 by reporting the list of (x,sp) reactions, the  cross section (mb) and air cross section (cm-1), or simply insert the main information in the text, as already done in page  61  (153), and page 67, lines 2400-2401 for other nuclides.

-lines 2526-2529. ‘…retrospective approaches are not sufficient in ion beam radiotherapy, and prospective approaches to identify potential risks should be carefully considered for comprehensive quality  assurance (QA) programme.’  It could be useful to remind, as an example, a recent paper on the application of the  prospective approach in proton radiotherapy which is focused on TPS (Cantone et al. Application of failure mode and effects analysis to treatment planning in scanned proton beam radiotherapy- (2013) Radiation Oncology, 8 (1) art. N. 127).

-lines 2688- 2693. The wording seems not fluent and incomplete in the presentation of the formula in line 2690, since m is not expressed. It is suggested to consider a sentence like: ‘For a sensitive volume containing a material of thermal capacity h, mass m, thermal defect d,  which  absorbs energy E, the temperature increase is given by:  FORMULA , where D is the average absorbed dose.  The thermal defect d is the fraction of E which   does not appear as heat, due to competing chemical reactions, if any.’  Moreover, note that D should indicate the average absorbed dose. 

-lines 2763-2769. LET, as defined in 2766, is better known as restricted LET.  In the glossary, it is explained as Linear Energy Transfer (LET) in terms of the average linear rate of energy loss, thus it could be useful to add in the glossary also the restricted LET.

-line 2770. In ‘Absorbed dose is given as the product of stopping power and fluence…’ consider to write as follows “Absorbed dose is given as the product of mass stopping power and fluence…’  or something similar in order to take into account all the terms of the formula in line 2772.

(A25) lines 2810-2811  say ‘The LQ model is usually considered to be valid for doses in the range of 1 to 10 Gy (for example, Brenner 2008)’.   The sentence could be expanded  to give more information.  Indeed the conclusions of the cited paper (Brenner, 2008) indicate :  ‘…It has been argued here, based both on experimental and theoretical considerations, that LQ is a reliable mechanistically plausible model for designing protocols in the dose per fraction range from 2 to 10 Gy.’


Errata Corrige

-Check the graphical format of the formulas in lines: 257, 258, 2640, 2666, 2766

-line 319, change Sievert in sievert

-line 369, change “The radio “  in  “ The ratio”

-lines 1052, 1053, sbb: single-strand break is indicated twice

-line 1869, correct the word : information

-line 1987, ‘fluoroscopic units with I.I.’ change in ‘fluoroscopic units with Image Intensifier’

-line 2006, ‘summarized in Table5.3. Table 5.1 and 5.3 showed’. Pay attention to the wording

-line2702 consider to write the title as “Termoluminescence Dosimeters” and not only “TLD”

-line 2730 consider to write the title  as “Radiophotoluminescence Glass Dosimeters” and not only “RGD”

-line 2830 consider to write the title as  “Microdosimetric kinetic model (MKM)”  and not only “MKM”

-In the text  is  used:  ‘sec’ for second,  ‘hr’ for hour , ‘yr’ for year, ‘min’ and ‘m’ for minute. It could be better to use the same modality and possible the symbols of SI units