Factors Affecting Implementation of Radiological Protection Aspects of Imaging in Radiotherapy

Round 1

Reviewer 1 Report

 

General comments

1     This paper describes the work of a task group set up by ICRP to develop the recommendations and guidelines on radiological protection of patient in X-ray image-guided radiotherapy.  Literally, the manuscript is nicely written and information well presented.

2     The information presented in the manuscript is basically based on a study that was published by the authors in 2021.  The main discussions presented in this manuscript are on management of patient dose due to X-ray imaging in IGRT, particularly in measurement, optimization and recording of imaging dose. However, no dose data have been presented and no definitive recommendations on dose measurement methodology have been provided in the paper, although a review on different kV dose measurement and estimation techniques have been presented.

3     An important aim of the study conducted by the authors and the ICRP task group is to raise the awareness of the radiotherapy community on protection and optimization of imaging radiation in IGRT and promote the implementation of appropriate QA measures to optimize image quality and dose in IGRT imaging systems. Routine implementation of such QA measures, particularly measurement and recording of imaging dose should be well justified by analysis and quantification of the potential reduction in risks involved in imaging during different scenarios of IGRT upon implementation of such measures. Appropriate studies should be conducted to obtain such information to support and justify the initiatives of the authors.

4     The value of this paper would be questionable if the above mentioned information is not presented since no relevant new scientific information are provided in the manuscript. 

Author Response

Responses to Reviewer 1

 General comments

1     This paper describes the work of a task group set up by ICRP to develop the recommendations and guidelines on radiological protection of patient in X-ray image-guided radiotherapy.  Literally, the manuscript is nicely written and information well presented.

 

2     The information presented in the manuscript is basically based on a study that was published by the authors in 2021.  The main discussions presented in this manuscript are on management of patient dose due to X-ray imaging in IGRT, particularly in measurement, optimization and recording of imaging dose. However, no dose data have been presented and no definitive recommendations on dose measurement methodology have been provided in the paper, although a review on different kV dose measurement and estimation techniques have been presented.

 

The aim of the paper is to start to raise awareness of methods that could be used for carrying out dose measurements at this stage. Since very few centres record dose data at the present time, inclusion of this information is not possible from our limited survey covering a number of different countries, almost all of whom record no imaging dose data at the present time. As mentioned in section 4 of the manuscript, the capability to record imaging dose is not available on current radiotherapy treatment platforms, and resources available at radiotherapy centers are adapted for measurements of high therapeutic doses rather than the low doses typically delivered with radiologic imaging. Some data is given, such as all the different frequencies of imaging used by centres for treatments of the head, which were not included in the previous paper because of lack of space. In addition, research efforts to find  appropriate imaging dose measurement methodologies for radiotherapy are being pursued by some of the authors.

3     An important aim of the study conducted by the authors and the ICRP task group is to raise the awareness of the radiotherapy community on protection and optimization of imaging radiation in IGRT and promote the implementation of appropriate QA measures to optimize image quality and dose in IGRT imaging systems. Routine implementation of such QA measures, particularly measurement and recording of imaging dose should be well justified by analysis and quantification of the potential reduction in risks involved in imaging during different scenarios of IGRT upon implementation of such measures. Appropriate studies should be conducted to obtain such information to support and justify the initiatives of the authors.

References have been included to previous studies in which doses from imaging in specific centres have been reported and risks have been evaluated.

More studies are starting to be carried out to provide more detailed information on imaging doses across larger numbers of centres, such as  UK initiative conducted through IPEM. These studies inevitably are taking a long time for the collection, analysis and interpretation of the data.

4     The value of this paper would be questionable if the above mentioned information is not presented since no relevant new scientific information are provided in the manuscript. 

We hope that the information provided on risks from other studies will fulfil the suggested requirements.

An aim of submitting a paper at this stage is to encourage further surveys of imaging doses by radiotherapy centres. Our project investigating measurements in different countries is taking time and in the meantime, it would be useful if other radiotherapy centres could employ similar methods for carrying out dose surveys to enable more comparisons to be made. We have therefore extended the conclusions to provide encouragement for others.

We have tried to bring out the aims of the paper more strongly by extending the conclusions section.

Reviewer 2 Report

In the discussion section it is recommended that non-ionizing surface-guided radiation therapy (SGRT) (AAPM task group report 302: Surface-guided radiotherapy (Med Phys. 2022;49:e82–e112)  as an approach of reducing X-ray imaging be discussed.  Perhaps in light of a countries wealth and does it make sense to incorporate in future surveys?

Author Response

Response to Reviewer 2

In the discussion section it is recommended that non-ionizing surface-guided radiation therapy (SGRT) (AAPM task group report 302: Surface-guided radiotherapy (Med Phys. 2022;49:e82–e112)  as an approach of reducing X-ray imaging be discussed.  Perhaps in light of a countries wealth and does it make sense to incorporate in future surveys?

This has been added to the discussion. Our data shows a weak correlation between HDI and the use of SGRT.

Reviewer 3 Report

The paper is very well written and provides useful information about the factors affecting implementation of radiological protection aspects of imaging in radiotherapy. The findings highlight the need to raise awareness of imaging doses and develop dose levels displayed on imaging equipment used in radiotherapy.

The research was conducted on a small number of countries, so it gives only limited information about the real situation, so it should be expanded in order to get a deeper insight. I suggest publishing the work and continuing the research in order to get a better insight into the issue.

Author Response

Responses to Reviewer 3

The paper is very well written and provides useful information about the factors affecting implementation of radiological protection aspects of imaging in radiotherapy. The findings highlight the need to raise awareness of imaging doses and develop dose levels displayed on imaging equipment used in radiotherapy.

The research was conducted on a small number of countries, so it gives only limited information about the real situation, so it should be expanded in order to get a deeper insight. I suggest publishing the work and continuing the research in order to get a better insight into the issue.

Thank you for your support. The aim in submitting the paper is try to highlight the need for more efforts in the area of measuring and recording doses from imaging. ICRP will be continuing with the project, but it is perhaps an area which ICRP should highlight for further study by other groups.

Reviewer 4 Report

In radiation therapy, radiation for normal tissues should be very limited, and optimization by diagnostic imaging is essential to achieve this. The survey of imaging practice has made clear that radiotherapy centres throughout the world, have little information on patient doses from imaging linked to radiation therapy treatments.  As radiotherapy has become a common cancer treatment method, the establishment of a database on patient doses is essential to eliminate regional differences in the quality of care, and I think this paper as an excellent contribution to this issue.

 

Author Response

Response to Reviewer 4

In radiation therapy, radiation for normal tissues should be very limited, and optimization by diagnostic imaging is essential to achieve this. The survey of imaging practice has made clear that radiotherapy centres throughout the world, have little information on patient doses from imaging linked to radiation therapy treatments.  As radiotherapy has become a common cancer treatment method, the establishment of a database on patient doses is essential to eliminate regional differences in the quality of care, and I think this paper as an excellent contribution to this issue.

Thank you for your support.

We have added statistical comparisons of practices with HDI level in the methods, and noted in the methods that a more detailed discussion of proposed methods for measuring CTDI and cumulative dose for CBCT is included in the section on the dosimetry project.

Reviewer 5 Report

The authors presented data from projects of the ICRP Task Group 116. I think that optimization of exposure dose in position alignment is a very important topic, but some questions arise. The impact of X-ray energy on diagnostics the same as that of MV X-ray? Can it simply be added to the prescribed dose for radiotherapy? If a second cancer occurs after radiotherapy, can we attribute it to CBCT? I think we should pay more attention to harmful side effects caused by exceeding the tolerable dose rather than secondary cancer.

 

Specific comments

Please clearly state the purpose of this research in the Introduction section.

 

Introduction (P3, L94-95), “However, increased imaging with x-rays exposes normal tissues surrounding a tumour to additional radiation that carries a risk of inducing second cancers.”. Please cite any reports that supports this mention.

 

Materials and Methods (P4, L140), What are “Several methods”?

 

Results (P5, L166-167), “The proportion of centres using these options in different countries declined with the HDI [8].”. Is this statistically correlated?

 

3.2 Imaging during the treatment cycle. Please discuss within what percentage the accuracy of positioning must be kept.

 

P7, L231-232. The term “stereotactic body radiotherapy” is not used for brain tumours, “stereotactic radiotherapy (SRT)” is correct.

 

4. Dosimetry methods for cone beam CT systems. Please describe the uncertainty of the exposure dose estimation by Monte Carlo calculations.

 

Is it justified to use a 0.6 cc chamber instead of the chamber for CTDI?

Author Response

Responses to Reviewer 5

The authors presented data from projects of the ICRP Task Group 116. I think that optimization of exposure dose in position alignment is a very important topic, but some questions arise. The impact of X-ray energy on diagnostics the same as that of MV X-ray?

The magnitude of imaging dose is at the level of the out-of-field scatter dose from MV beams used in radiotherapy. Regarding the effect of x-ray energy, imaging beam swill deposit most of their dose at the entrance organs (skin, lens of the eyes) while MV beams deposit their energy at depths > 1~2 cm. Also, kV beams have a larger cross-section for photoelectric interactions than MV beams, which leads to higher doses imparted to high density tissue like bone.

Can it simply be added to the prescribed dose for radiotherapy?

The summation of imaging dose to therapeutic dose is one of the goals of managing imaging dose for radiotherapy patients. It is a difficult task for several reasons. First, there is no commercial product that provide an accurate calculation of imaging dose encountered in radiotherapy and the only capability to calculate imaging dose on an individual patient basis requires Monte Carlo models of imaging sources. This can only be developed at academic institutions with appropriate resources and expertise. Another issue is that current treatment planning systems (TPS) that model RT beams are modelling the out of field scatter component with large uncertainty. Imaging dose is at the level of the scatter out-of-field MV dose and an accurate summation of imaging dose to therapeutic out-of-field dose will require an improvement of the beam models developed in clinical TPS.

If a second cancer occurs after radiotherapy, can we attribute it to CBCT? I think we should pay more attention to harmful side effects caused by exceeding the tolerable dose rather than secondary cancer.

The 2 issues raised in your question – increase stochastic risk and potential increase risk of developing acute tissue reactions - need to be addresses in parallel by health care providers. Since more and more cancer patients are cured by RT and tend to live longer, out-of-field dose and imaging dose received by healthy tissue surrounding tumors might increase the risk of developing secondary cancers years after RT. Given the high frequency of CBCT imaging revealed by our survey data, the magnitude of CBCT dose, can cumulatively reach and exceed that of a RT fraction dose and potentially increase the risk of developing acute tissue reactions for organs receiving close to their tolerance dose.

A sentence has been added to the introduction relating to organs at risk and the danger of exceeding the tolerance doses.

Specific comments

Please clearly state the purpose of this research in the Introduction section.

A paragraph has been inserted at the end of the introduction.

 Introduction (P3, L94-95), “However, increased imaging with x-rays exposes normal tissues surrounding a tumour to additional radiation that carries a risk of inducing second cancers.”. Please cite any reports that supports this mention.

Additional relevant references have been included.

 Materials and Methods (P4, L140), What are “Several methods”?

These are described in section 4 of the paper, leading into the description of the method that we are proposing. We have therefore added “which are described in section 4 of this paper” at this point.

 Results (P5, L166-167), “The proportion of centres using these options in different countries declined with the HDI [8].”. Is this statistically correlated?

The correlation between HDI and use of imaging modality by % centres was determined with the Pearson correlation coefficient with statistical significance at the 0.05 level (2-tailed test).

Additional correlations with HDI were analyzed:

• The proportion of centers using IGRT for >75% patients
• The proportion of centers using SGRT
• The proportion of centers using kVCBCT
• The proportion of centers using 4D CBCT
• The proportion of centers using vendors protocols for IGRT
• The proportion of centers performing IGRT QA monthly

Results were included in the manuscript.

3.2 Imaging during the treatment cycle. Please discuss within what percentage the accuracy of positioning must be kept.

The positioning accuracy depends on the treatment site, prescription (dose per fraction), technique and delivery (e.g. 3D conformal vs IMRT), type of immobilization used, etc… We have included a statement that provides the general range of clinical tolerances used with IGRT along with 2 references for readers who are interested in more details: the latest IGRT practice guideline from the American College of Radiology that provide recommendations and additional references on clinical tolerances for IGRT, and published results from a recent survey of clinical tolerances per sites used in radiotherapy centers in the USA.

P7, L231-232. The term “stereotactic body radiotherapy” is not used for brain tumours, “stereotactic radiotherapy (SRT)” is correct.

Deleted “body”

4. Dosimetry methods for cone beam CT systems. Please describe the uncertainty of the exposure dose estimation by Monte Carlo calculations.

Added

Is it justified to use a 0.6 cc chamber instead of the chamber for CTDI?

As explained in the text, the reason for using different chambers at this stage is that access to 100 mm chambers is limited in many radiotherapy centres, and use of a 0.6 cc chamber would be a viable alternative. We are finding that many RT centres in lower HDI countries do not have 100 mm chambers or the CTDI phantoms, while 0.6 cc chambers are part of the standard equipment used for the calibration of medical LINACS beams One approach might be to recommend purchase of such phantoms when a CBCT unit is purchase, which could then be used with a 0.6 cc chamber, which is used for RT dosimetry purposes. We have not added anything further to the text of the paper about this.

Round 2

Reviewer 1 Report

I have no further comments.

Reviewer 5 Report

 I thank the authors for addressing all my comments. The manuscript has been greatly improved and I recommend its publication.