Gated DIBH for Left Sided Breast Cancer Patients

Chapter III: Methodology

3.1 Research Objectives

The research project examines left-sided breast cancer patients receiving therapy with gated DIBH technique using the commercially available RPM system. The primary objective of this research is to evaluate whether left-sided breast cancer patients will benefit from gated DIBH. The interest in performing this research arises from having many left-sided breast cancer patients that have large volume of heart in the treatment field, and hence are at risk for cardiac toxicities in the future. The secondary objectives of this research is to look at patient’s comfort and understanding, and radiation therapist’s workload. This chapter will discuss the sample selection, ethical issues, instrumentation, data collection procedures, data analysis, limitations, expected results, budget and timeline.

3.2 Sample selection and description

The expected sample size was calculated using the formula (Chan, 2003) for paired samples as seen below,

Total sample size =

where c is 10.5 for 90% power,

δ is the standardised effect size, given by the formula (Chan, 2003):

where μ1 and μ2 are the means of the two treatment groups, and

σ is the common standard deviation.

The 90% power represents the probability of rejecting the null hypothesis when it is false (Chan, 2003). It is postulated that a good treatment difference (

) between the 2 groups is 0.2 units with an SD (σ) of 0.5 units (Chan, 2003). With these values, the expected sample size is 68.

Sixty-eight left-sided breast cancer patients will be selected for this research using a simple random sampling method. The patient population will be chosen at random to create a diverse group of patients with variable breast and heart volumes.

The criteria for this sample would be female patients with left-sided breast cancer below the age of 70. In addition, the patients must be able to hold their breath. These patients will be recruited after being screened by the oncologists. The oncologists will do a simple breath-hold test with patients to determine if they are able to hold their breath for at least 20 seconds. This is because patients will be required to hold their breath during the CT scan for a duration of 18 seconds.

This research will require 2 sets of computed-tomography (CT) scans from each patient of which one is at free breathing and the other at DIBH. Both sets will have identical patient setup. Patients will be lying supine with both arms above head on a posirest, having the visual goggles on (see Appendix M, image A) with a 6-reflective markers block on patient’s anterior abdominal surface (see Appendix H). With the goggles, they are able to view the screen, as seen in image B in Appendix M, in order to see their breathing patterns. For each patient, 2 treatment plans will be generated: one using the CT images at free breathing with photon electron match technique and the other using the CT images at DIBH with gated DIBH technique using RPM with 3-mm intervals.

3.3 Ethical Issues and Informed consent

Any research involving human subjects conducted in the hospital would require adherence to ethical standards. The procedure requires the collation of a list of investigators in the department that intends to conduct clinical trials (see Appendix N), and to apply and attend the Singapore Guideline for Good Clinical Practice (SGGCP) course. This Course ensures that the conduct of clinical trials follows internationally acceptable ethical and scientific standards (see Appendix O). The ethics review will be carried out by the National Healthcare Group domain specific review board which is an independent committee constituted of medical, scientific and non-scientific members, whose responsibility is to ensure the protection of the rights, safety and well-being of human subjects involved in a research study by reviewing, approving and providing continuing review of research studies, and of the methods and materials to be used in obtaining and documenting informed consent of the research subjects (National University Health System, 2010). When a principal investigator submits an application via the research online administration and management system, it is automatically routed to the department representative for endorsement, and subsequently the institution representative for endorsement, before it is delivered to the domain specific review board secretariat (National University Health System, 2010). All research studies submitted will be classified under one of the following review categories: exempt review, expedited review, full Board review (see Appendix P) (National University Health System, 2010). Based on the definitions in Appendix P, this study is classified as an expedited review.

Ethics approval for research is required for several reasons. Firstly, ethical norms promote the aims of research, such as knowledge, truth, and avoidance of error (Resnik, 2011).

Secondly, ethical standards promote the values that are essential to collaborative work, such as trust, accountability, mutual respect, and fairness (Resnik, 2011). For example, guidelines for authorship, copyright and patenting policies, data sharing policies, and confidentiality rules in peer review, are designed to protect intellectual property interests while encouraging collaboration (Poortmans, 2013).

Ethical norms in research also help to build public support for research as people are more likely to fund research project if they can trust the quality and integrity of research (Resnik, 2011).

Finally, many of the norms of research promote a variety of other important moral and social values, such as social responsibility, human rights, compliance with the law, and health and safety. This also protect the rights and welfare of participants and minimise the risk of physical and mental discomfort and harm from research procedures (Canterbury Christ Church University, 2006). Ethical lapses in research can significantly harm human subjects especially if the researcher fails to abide by the regulations and guidelines relating to radiation or biological safety (Resnik, 2011).

Informed consent is the process by which the patient voluntarily confirms her willingness to participate in this research, after being informed of all the aspects of the research that are relevant to her decision-making (National Healthcare Group, 2013). The informed consent is documented by means of written signatures, date informed consent form and the language used during the explanation to the patient by the oncologist. In the consent, there should be 3 signatures: the patient’s, the doctor’s and the witness’ signature. For patients who cannot read and speak English, a qualified translator will be around during the signing of the consent.

3.4 Research design and instrumentation

This research is a mixture of qualitative and quantitative research methods (see Appendix Q). Quantitative research corresponds to a deductive scientific method of research which uses data in the form of numbers and statistics to test hypotheses, using a large and randomly selected sample that is a representative of the population (Pearce, et al. 2013; Johnson & Christensen 2010).

This is in contrast to the qualitative approach which corresponds to an inductive method of research which uses words, pictures or objects to examine a phenomenon, requiring only a small and non-randomly selected sample (Pearce, et al. 2013; Johnson & Christensen 2010).

Patients will be scanned using Toshiba Aquilion Large Bore CT-simulator (Toshiba, 2014). The treatment plans will be generated using Varian Medical Eclipse™ Treatment Planning System and patients will be treated with DIBH technique using RPM from Varian Trilogy linear accelerator (Varian Medical System, 1999-2014).

3.5 Data collection procedures

The same radiation oncologist will perform all the delineation of the clinical target volume, the heart and LADCA for consistency purposes (see Appendix R). The delineation will be done according to radiation therapy oncology group (RTOG) breast contouring recommendations (Goksel, et al., 2013). Patient’s CT images at breath hold will be used to plan for DIBH technique while the one at free breathing will be planned for photon electron match technique. The treatments will be planned such that the clinical target volume’s coverage of the dose distribution is kept between 90% and 110% of the prescribed dose. For each plan, heart and LADCA volumes were calculated in cm3. Dose volumes to the heart and LADCA will be normalized by dividing with the total organ volume. Heart and LADCA volumes receiving 5Gy to 50Gy (V5-V50) will be generated for comparison of treatment techniques. Dose distributions can be presented as DVHs and representing the statistical dose distribution in a volume of interest. These statistical data will be recorded and presented in tables.

Patient education is a very important component in DIBH technique using RPM to reduce anxiety and increase their confidence about receiving radiation therapy (Halkett & Kristjanson, 2007). Patient education tools can be in many forms such as video or pamphlet (Halkett & Kristjanson, 2007). For this research, a pamphlet have been created to educate patients on DIBH technique using RPM (see Appendix S). A qualitative research method such as face-to-face interview is chosen to assess patient’s comfort and understanding at the middle of the treatment and on the last day of treatment as this only require the patients to speak the same language in which the questions are asked, and to have basic verbal and listening skills (Bowling, 2009). The primary objective of this standardised and open-ended interview (Valenzuela & Shrivastava, n.d.) is to determine the degree of understanding as well as patient’s comfort. The questions (see Appendix T) will be asked by the oncologist during the middle of the treatment and on the last day of treatment.

The advantages of face-to-face interviews are that reading and writing skills are not required, interviewers are able to probe fully for responses and clarify any ambiguities, they can ask more complicated and detailed questions, and patients are able to clarify if they do not understand the questions (Bowling, 2009). This would be a better technique than self-administered questionnaires because pre-coded response choices may not be sufficiently comprehensive and patients may be ‘forced’ to choose inappropriate pre-coded answers that might not fully represent their views (Bowling, 2009). This causes the data to be bias as the patient’s replies are influenced by the design of the pre-coded response choices. Self-administered questionnaires also assumed that the questions are worded in a way that is understood by the patients (Bowling, 2009). Patients may misinterpret the questions and reply based on their own interpretation and questionnaires may be a problem for patients who are unable to read or write (Bowling, 2009). Most importantly, one-to-one interviews with standardised questions appeared to have the highest reliability (University of Leicester, n.d.).

The radiation therapist’s workload will be measured in terms of training hours, and the comparison of treatment duration and manpower required for gated DIBH using RPM and photon electron match technique (see Appendix U) will be recorded and presented in charts.

3.6 Data analysis

Paired samples t-test will be used to determine whether there is a significant difference between the average dose to the heart and LADCA values made under photon electron match plan and gated DIBH using RPM plan (Norman & Streiner, 2008). This is used because the data are measured at the scale level and the data are related (Hawkins, 2009). The amount of radiation received by the heart can be recorded by comparing the DVHs of the photon electron match with gated DIBH using RPM. The statistical figures can be analysed using Statistical Package for Social Sciences (SPSS) (Yavas, et al., 2012). Paired samples t-test will be used to determine whether there is a significant difference between the average dose to the heart and LADCA values made under photon electron match plan and gated DIBH using RPM plan (Easton & McColl, 2014). A p-value of < 0.05 will be considered to be significant (Yavas, et al., 2012). Steps on a paired t-test can be seen in Appendix V.

Patient’s understanding and comfort

The questions (see Appendix T) from the standardised and open-ended interview were developed by a team of 2 radiation oncologists, a nurse and 2 radiation therapists. The areas of discussion were based on the group’s clinical experience with left-sided breast cancer patients and their extensive knowledge on DIBH using RPM. The interview aims to determine the patient’s level of comfort and understanding of the gated DIBH using RPM. The design of the questionnaire will determine the reliability and validity of the opened-ended interview to measure patient’s level of comfort and understanding.

Reliability is defined as the extent to which questionnaire will produce the same results on repeated trials (Miller, n.d.), and is measured by its equivalence and stability. Equivalence reliability assesses the consistency of the judgement of the patient’s answer by the interview (Miller, n.d.). It is improved by pre-empting a range of responses that might be given by the patients and give a pre-determined rating to each response so that the interviewers will have the same level of ‘judgement’ (Miller, n.d.). For example, _____________-

Stability reliability is correlated to the repeatability of the patient’s response under the same conditions after a period of time (Miller, n.d.). For this interview, the patients will be interviewed twice, once during mid-treatment and the other on the last day of their treatment. Their responses from both sessions will be compared to determine if there are any deviance. This assumes that the characteristics that is measured doesn’t change with time, and that the time period is long enough that the memories from the 1st interview will not influence the responses of the 2nd interview (Miller, n.d.).

The validity of the interview is the extent to which the interview questions measures what it purport to measure, and it generally takes the form of content validity (Miller, n.d.). Content validity is the degree to which the questions fully assess or measure the intention of the interview (Miller, n.d.). This was determined by letting the team review the individual questions for readability, clarity and comprehensiveness and come to some level of agreement as to which items should be included in the final interview questions. The interview questions (see Appendix T) were reviewed and accepted by the team prior to the conduct of the interview.

The treatment duration will be recorded as seen in Appendix U and a paired samples t-test similar to appendix V will be used to determine whether there is a significant difference, where the null hypothesis (H0) is there is no difference between the treatment time with photon electron match technique and DIBH using RPM technique.

The radiation therapist workload will be analysed based on the minimum number of manpower required for gated DIBH using RPM as compared to photon electron match technique and in terms of training hours. This will be discussed among the radiation therapists and presented in charts.

3.7 Limitation

This research can only sample from a small size due to constraint of resources where there is only 1 treatment unit that has the RPM equipment required for DIBH technique. The expected sample size calculated is only an estimate as the treatment difference and standard deviation are never known in advance (Norman & Streiner, 2008). As such, the actual sample size may be slightly smaller than 68.

3.8 Expected Results

The results from this research are expected to show optimal radiation exposure volumes and doses for the heart and LADCA when treated with gated DIBH using RPM compared to photon electron match technique at free breathing. These results are expected to be compatible with findings from previous studies (Pedersen, et al., 2004; Korreman, et al., 2005; Shim, et al., 2012; Mast, et al., 2013). As such, showing that patients with left sided breast cancer will benefit from gated DIBH using RPM. Treatment time duration for gated DIBH using RPM is expected to have a significant difference and be faster than photon electron match technique. As gated DIBH using RPM is new to the radiation therapists, the workload is expected to be heavier in the beginning.

3.9 Budget

There will be no additional cost for this research as the RPM equipment is already available together with the linear accelerator from Varian (Varian Medical System, 1999-2014). There will be no cost for training on the usage for RPM by Varian as it was included in the package when the linear accelerators were bought in 2013. Patients recruited for this research will be charged the same cost as photon electron match treatment technique.

3.10 Expected Timeline

This research aims to commence from January 2015 till December 2015. The work plan for both the principal investigator and research assistants can be seen in Appendix W.

Chapter IV: Conclusion

This research aims to review gated DIBH using RPM as a treatment technique for left-sided breast cancer patients as compared to photon electron match in terms of the radiation dose received by the heart and LADCA. Paired


test is chosen to measure the significant difference between the dose received by the heart in photon electron match technique and DIBH using RPM technique. Based on literatures that were review, the results are expected to be in favour of gated DIBH using RPM. Interviews will be conducted to assess patient’s comfort and understanding about gated DIBH using RPM. And data collection will be done gauge the workload of the radiation therapist. The results from interview and data collection will allow us to gauge further if it is really practical to implement gated DIBH using RPM in our department. If the results are clinically significant and positive, gated DIBH using RPM will be implemented into our department.

4.1 Recommendation

For future recommendation to try contrast-enhanced CT scan in left-sided breast patients so that the LADCA can be seen clearly in the scan and able to be delineated by the doctor effectively (Yu, et al., 2013). This is to increase the accuracy of the delineation of LADCA as well as the accurate amount of radiation dose received by it. After this research, another study can be done in the future on the reproducibility of patient’s breath holding level for every fraction using a cine acquisition mode (CAM) of a linear accelerator during treatment (Goksel, et al., 2013).

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