|Year : 2014 | Volume
| Issue : 2 | Page : 145-149
Can positron emission tomography be more than a diagnostic tool? A survey on clinical practice among radiation oncologists in India
HMT Thomas1, S Balukrishna2, D Devakumar3, P Muthuswamy4, EJJ Samuel1
1 Photonics, Nuclear and Medical Physics Division, School of Advanced Sciences, Vellore, Tamil Nadu, India
2 Department of Radiotherapy, Christian Medical College, Vellore, Tamil Nadu, India
3 Survey Research Centre, VIT University, Vellore, Tamil Nadu, India
4 Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India
|Date of Web Publication||7-Aug-2014|
Photonics, Nuclear and Medical Physics Division, School of Advanced Sciences, Vellore, Tamil Nadu
Source of Support: H M Thomas is supported by the CSIR Senior research fellowship., Conflict of Interest: None
Aim: The purpose of the survey was to understand the role of positron emission tomography (PET) in clinical radiotherapy practice among the radiation oncologists' in India. Settings and Design: An online questionnaire was developed to survey the oncologists on their use of PET, viewing protocols, contouring techniques practiced, the barriers on the use of PET and the need for training in use of PET in radiotherapy. The questionnaire was sent to about 500 oncologists and 76 completed responses were received. Results: The survey shows that radiation oncologists use PET largely to assess treatment response and staging but limitedly use it for radiotherapy treatment planning. Only manual contouring and fixed threshold based delineation techniques (e.g. 40% maximum standard uptake value [SUV max ] or SUV 2.5) are used. Cost is the major barrier in the wider use of PET, followed by limited availability of FDG radionuclide tracer. Limited or no training was available for the use of PET. Conclusions: Our survey revealed the vast difference between literature suggestions and actual clinical practice on the use of PET in radiotherapy. Additional training and standardization of protocols for use of PET in radiotherapy is essential for fully utilizing the capability of PET.
Keywords: Positron emission tomography, radiotherapy, radiation oncologists, survey
|How to cite this article:|
Thomas H, Balukrishna S, Devakumar D, Muthuswamy P, Samuel E. Can positron emission tomography be more than a diagnostic tool? A survey on clinical practice among radiation oncologists in India. Indian J Cancer 2014;51:145-9
|How to cite this URL:|
Thomas H, Balukrishna S, Devakumar D, Muthuswamy P, Samuel E. Can positron emission tomography be more than a diagnostic tool? A survey on clinical practice among radiation oncologists in India. Indian J Cancer [serial online] 2014 [cited 2019 Oct 20];51:145-9. Available from: http://www.indianjcancer.com/text.asp?2014/51/2/145/138247
| » Introduction|| |
The objective of this study was to survey the use of positron emission tomography (PET) in radiotherapy among radiation oncologists in India.
Globally, molecular imaging is increasingly recognized as an important tool for diagnosis, determination of prognosis, treatment planning and response monitoring in oncology. More than 5,000 combined PET/computed tomography (CT) have been installed world-wide and PET/CT is today considered one of the fastest-growing imaging modalities.  In India the first PET scanner was installed in 2004 in Tata Memorial Center. Now the numbers stand at about 70 functional PET/CT scanners; with sanctions approved for another 75 scanners ready to be installed by 2015. The sharp increase is due to the growing evidence supporting the usefulness of PET/CT in oncology.
In an article in 2009, Graham et al. and in 2011 Beyer et al. have reported in their survey that there is considerable variability in the way PET/CT scans are performed at academic institutions and other different centers, which makes it difficult to quantitatively compare studies. , Karantanis et al. said that the lack of standard guidelines for the appropriate use of PET/CT concerning clinical indications, imaging protocols and image interpretation have resulted in referring physicians expressing considerable uncertainty about the appropriate and best use of oncologic PET/CT.  Most of the studies have focused on establishing the diagnostic accuracy of PET while the clinical utility of PET on the decision making is poorly reported.  There have also been concerns about procedure costs ,,, and the quality of interpretation of PET across the oncology practicing community. ,,,
With the increase in the availability of PET/CT in the last few years, we focused on the impact of PET on tumor management and the use of PET as a complimentary imaging modality in radiation oncology in India. The study does not focus largely on oncologists organizational issues, but is expected to provide meaningful information to radiation oncologists to help in forming standardization protocols for the use of PET/CT in radiotherapy.
| » Subjects and Methods|| |
The 45-item questionnaire was developed using QuestionPro software (Seattle, USA) to assess the following aspects of PET in regular radiotherapy practice; the availability of PET/CT scanner, areas PET/CT scan finds use among the respondents routinely in the radiotherapy context, protocols followed for the display/viewing of PET, contouring techniques practiced for PET based planning, change in treatment outcomes with the use of PET, the barriers preventing the use of PET and the current training available. Demographic information included age, geographical location (state in India) from which they are practicing and the professional qualifications information included highest academic degrees and clinical experience of the respondents. Most questions required a single best response to be selected from multiple choices and the completion time required was approximately 10 min. Questions on the preferences for training and possible barriers that influence the wider use of PET allowed multiple items to be simultaneously selected.
Contact of potential respondents
Invitations to participate in the survey were sent as an email to all members of the Association of radiation oncologists of India. The email invitation had a brief introduction on the purpose of the survey and the link to the online survey questionnaire. To make the survey more viewable, the online survey link was also posted in the oncologists' community forum (isocentre.org). First reminder was sent to all the oncologists after 2 weeks and second reminder was sent after 4 weeks. After 6 weeks, the survey was closed. The completed surveys were received electronically and the data was analyzed using SAS® analytics software (SAS Institute Inc, Cary, NC, USA).
| » Results|| |
We collected an overall of 76 responses between February and April 2013, for an overall response rate of 15%. Anonymity was maintained during the analysis.
Almost half (53%) of the respondents were from tertiary care centers, the remaining were from exclusive cancer care centers. A majority (56%) had professional experience from three to around 10 years and 26% had more than 10 years with highest qualification reported was MD (radiotherapy) for about 79% and 12% holding a diploma in national board specialized in radiotherapy.
About half (51%) of the respondents were from South India, 27% were from north and central India, 16% from the western states, only 7% responded from the eastern states. No responses were recorded from the northeastern states, the Indian islands (Lakshadweep and Andaman and Nicobar) and Goa [Figure 1]. Majority (35%) reported to have PET/CT scanners installed by GE Healthcare, followed by Siemens Healthcare (27%) and Philips Healthcare (16%) systems and 21% reported they did not know the brand name of the PET/CT scanner. The waiting period for PET/CT appointments for majority (54%) was between 1 and 3 days; the rest reported <1 week.
|Figure 1: Survey response statistics and availability* of functional positron emission tomography scanners in India. (Obtained from internal sources)|
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Areas PET is used by radiation oncologists
[Figure 2] shows the responses for how radiation oncologists referred for a PET scan in routine practice. More than 74% of the respondents preferred to use PET often or more often for assessment to treatment response and 46% used it often or more often for follow-up after treatment. Nearly 65% use it either often or more often for staging of the disease; whereas 10% reported to have never used it for staging. Only 42% use it either often or more often for radiotherapy treatment planning.
|Figure 2: Areas positron emission tomography is commonly used for by radiation oncologists|
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Viewing/display protocols for PET
Respondents were asked if they knew of any method to optimally set the intensity while viewing their PET images. Only 60% reported to follow any protocol for intensity adjustments before viewing the PET. Of those who responded, majority reported that they either used a standard uptake value (SUV) cut-off of 2.5 or 40% of the maximum SUV (SUV max ) in the tumor for viewing. Mostly, all of the respondents (90%) preferred to view their PET images in pseudo-color scales available in their treatment planning system, only 18% were able to specify a valid name for the color scale used. The rest preferred to have their PET images displayed in grayscale.
PET in radiotherapy treatment planning
Most of the respondents, about 86% used the information from the PET for gross tumor volume delineation; with 80% being able to automatically register the PET/CT in their treatment planning systems. Nearly 42% could not or were not sure if PET/CT done at centers other than theirs could be registered in their treatment planning systems. This may be because the entire data may not be available and only few salient axial cuts showing the extent of the tumor may be available when presented.
When asked about the contouring techniques routinely used for tumor delineation while using PET information inclusive treatment planning, manual contouring was found to be the most preferred choice (47%) [Figure 3]. Some reported using percentage based technique (15%); fixed percentages of 30-40% of the SUV max in most patients and in very few patients 20-30% of SUV max was used. 2.5 SUV based method (6%) and automatic methods available in their planning system (4%) were the other methods reported. The rest 25% have not standardized any protocol for their contouring techniques while using PET in their radiotherapy treatment planning volume delineations.
|Figure 3: Tumor delineation techniques clinically used for positron emission tomography based treatment planning|
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The oncologists reported that they always (20%) or often (38%) include a larger margin for the gross tumor volume than what is seen on the PET. They preferred to use the outer boundary of the uptake region as their limiting boundary and more than two-third of them were never confident in limiting their margins if the gross tumor volume delineated based on the CT is larger than the PET SUV based gross tumor volume. Only half of them reported that the PET based tumor volumes were cross checked by nuclear medicine physicians.
Impact of PET imaging on patient outcomes
[Figure 4] shows the responses as reported in the survey on the impact that PET imaging has on patient outcomes. The inclusion of PET information for the radiotherapy decision making has changed the treatment strategy always (4%), often (32%) sometimes (50%) and rarely (8%) respectively.
|Figure 4: Impact of positron emission tomography imaging on patient outcomes in terms of treatment strategy, improved care and delineated tumor volumes|
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The rest (2%) were not sure of any such change and 4% said it was not applicable The respondents also report that PET imaging has helped to improve the care always (6%), often (28%), sometimes (48%) and rarely (4%) respectively. The rest were not sure of the outcome About 40% acknowledged that tumor volumes changed always or often and 45% said sometimes when PET was used for gross tumor volume delineation when compared to the tumor volumes obtained from using CT alone.
Barriers in using PET
[Figure 5] outlines the responses on the barriers as perceived by the radiation oncologists that limits the wider use of PET. Cost was ranked as the major barrier (37%), followed by the lack of PET availability (25%), the nearest cyclotron facility being too far (11%), lack of trained personnel (10%), limited or no training on the use PET (13%). Nearly 4% reported they were not fully convinced about the use of PET in clinical situations.
|Figure 5: Barriers preventing the use of positron emission tomography among radiation oncologists|
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Only about half of responding radiation oncologists had undertaken a contouring workshop for doing CT, magnetic resonance imaging (MRI) or PET based planning. [Figure 6] shows a good 72% have not undergone any hands-on training for use of PET in radiotherapy. They feel exclusive PET training workshops (52%) and PET workshops conducted during annual conferences (42%) might be helpful.
|Figure 6: Training available for the use of positron emission tomography in radiotherapy|
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| » Discussion|| |
The aim of this survey was to assess the PET/CT practice in clinical routine among Indian radiation oncologists. A total response rate of 15% was recorded which lies within the accepted response ranges for Web-based surveys. , The low response rate may reflect the confusion about the advantages of incorporating PET in regular radiotherapy practice. There were almost equal responses from government and private owned hospitals with 53% responding from tertiary care centers. The responses were roughly proportional to the availability of the PET/CT scanners across each state [Figure 1].
Only 53% of the respondents reported to have PET scanners attached to their hospitals, with less than half of them having a cyclotron attached to their facility. Majority, about 70% of respondents who reported not having PET scanners in their own hospitals referred their patients to have their PET scans done in diagnostic scanning centers or to nearby hospitals which did have the facility. We found out from our internal sources that all centers are concentrated in major cities and at present only 16 cyclotrons are available to cater to the national isotope requirement.
Overall, from our survey it is seen that there seems to be greater confidence in using PET for treatment response and staging. But, the use of PET for radiotherapy treatment planning is still in its nascent stage in India with about 56% respondents reported to have never incorporated PET information for radiotherapy treatment planning or used it less often (<5 cases/month).
Of the sites we surveyed the most frequent indications for PET/CT are lung cancers (51%), followed closely by the head and neck cancers (44%) and collectively for sarcomas, melanomas and lymphomas (40%). This trend is slightly different from recent studies from Germany  and an international survey  where breast cancer and colon cancers have a higher frequency of PET/CTs done than head and neck cancers.
Often, visual inspection of PET/CT images is the main tool for image interpretation and is usually adequate for interpreting PET findings as positive or negative for staging or assessing the response. Although, a more valid method is required for further quantification and tumor delineation techniques. Hence specific questions were asked about the intensity display settings used. The survey revealed that oncologists still advocate the use of a SUV max threshold of 2.5 or some arbitrary fixed threshold. Authors do not support this current practice of setting a top level of the intensity window at 2.5 SUV max or some arbitrary value of SUV max because when we worked with a large number of PET images for our studies it never produced consistent desirable results. This could also lead to erroneous results in identifying the presence or absence of tumor(s).
The survey indicates that oncologists mostly use manual contouring, although the use of auto segmentation techniques is strongly encouraged in literature to appropriately identify the functional uptake of interest and avoid the inclusion of non-tumor specific uptake. ,,,,, According to the survey, the only auto segmentation technique reported to be used was the fixed threshold (e.g. 40% or 50% of SUV max or SUV ma × 2.5); although the results of studies that used fixed threshold based segmentation have been reported to be highly questionable. , The 2.5 SUV max cut-off value largely marketed to differentiate benign and malignant tumors has largely been proven to be an oversimplification since several factors such as body weight, the time of measurement, dose extravasations, attenuation parameters, reconstruction parameters, partial volume effect and plasma glucose level in patient blood may independently or collectively affect the value of SUV ,,, and using it may lead to patient mismanagement. As Zaidi describes in,  the general clinical practice is to employ simplified techniques for PET based tumor delineation compared to advanced segmentation methods developed for research, which is no different in India. We assume that manual contouring may be widely used due to unavailability of in built segmentation algorithm in treatment planning systems. It appears that the difficulty in implementing some of the seemingly complex delineation techniques ,,, (gradient, clustering or region growing based techniques etc.) in clinical practice may be due to limited physics support to help with the implementation of these segmentation algorithms.  A fourth of the respondents also do not follow any standard protocol for their clinical tumor delineation practice while employing PET.
Questions on inclusion of margins for volumes segmented on PET, all respondents suggested that they include a larger margin for the gross tumor volume than what is seen on the PET; their reason being to account for unclear PET boundaries. This corresponds to the reports by Njeh  who felt that the interpretation of the extent of the microscopic disease by the radiation oncologists tends to be larger than other specialty physicians; speculated reason being the unconscious integration of geometric uncertainty. Some recommendations include more collaboration of oncologists with radiologists and nuclear medicine physicians while delineating the tumor since they are specialists trained to read and interpret images and oncologists to treat cancers. ,
According to our survey radiation oncologists acknowledge that often there have been situations when they have changed their treatment strategy (33%) or improved the care (29%) based on PET imaging information. In the last 5 years, many studies have reported the benefits of using PET/CT for practically all areas of tumor management including diagnosis, staging, treatment response and radiotherapy treatment planning. ,,, Differentiating between diseased and benign lymph nodes is reportedly better with PET/CT , and certain cases, patients being considered for radiotherapy were upstaged due to distant metastases findings on their FDG PET staging scans.  Since metabolic changes occur before most anatomical changes, PET also helps in early detection of preclinical relapse which would benefit if appropriate salvage therapy could be administered earlier, ultimately improving survival.  With its sensitivity and specificity being reported to be greater than 90% in various studies it also identifies non-responders early in the treatment so that further curative treatment, imaging, invasive interventions and surgeries can be easily avoided. ,, This way PET imaging can also indirectly serve to effectively use the scarce radiotherapy resources for patients for whom treatment would confer benefit. 
The survey points to procedural cost as the main barrier that affects the widespread use of PET in India. Since the medical care expenses in India are most often entirely borne by the patients, with very few having access to any form of insurance,  clinicians when assessing additional factors like family problems or inadequate funds often feel that they could rather do without the costly PET scan and use only the CT. Regulating the procedural cost of PET scans may have to be addressed at a national level.
The survey rates the unavailability of PET/CT scanners evenly across the country as the second largest barrier. It appears that the high operational costs and initial investments of these units could be the main reasons that restrict their penetration to smaller towns and cities. Establishing new scanners and operation of larger number of scans/day have also been reported in the survey to be limited due to the distance from the cyclotron facility. The short half-lives of the isotopes and the geography of the country's terrain together make it difficult to transport isotopes over large distances. However, establishing a cyclotron facility is much more complex than setting up other regular diagnostic centers since regulatory body has stringent rules on handling radioactive sources and nuclear medicine facilities. Baby cyclotron facilities might ease the burden and may be intrinsically financially more viable.
More than a fourth of the respondents felt that the lack of training for the effective use of PET for oncology is one of the deterrents to its frequent use. Only 50% reported to have undergone some training on contouring protocols for CT, MRI and PET with a majority 72% reporting to have had no hands-on experience with PET. With a large number of PET centers being opened, it may be imperative to provide adequate training and ensure uniformity in the use of PET for radiotherapy across the country. The suggestions by respondents were to include PET inclusive treatment planning in the radiotherapy curriculum and conduct regional continuing medical education programs regularly for all radiation oncologists, irrespective of them having PET scanners in their hospitals or not. Most of them expressed there should be clear national guidelines and training on the judicious use of PET for radiotherapy practice.
| » Conclusion|| |
This survey may serve as an audit of the existing clinical use of PET for radiotherapy in the country and may be repeated in a few years to assess the difference. Overall, theresults of the survey suggest that currently there is a wide variation in what the literature recommends and the routine oncology scenario presents. The survey shows that radiation oncologists use PET largely to assess treatment response and staging but limitedly use it for radiotherapy treatment planning. In clinical practice, only the simple fixed threshold based automatic segmentation method is used while majority still using manual contouring when integrating PET in radiotherapy tumor delineation process. Additional training and standardization of protocols for use of PET in radiotherapy is essential for fully utilizing the capability of PET.
| » Acknowledgment|| |
The authors would like to thank the members of the Association of radiation oncologists' of India and isocentre.org for their support in the conduct of this survey.
| » References|| |
|1.||Beyer T, Czernin J, Freudenberg LS. Variations in clinical PET/CT operations: Results of an international survey of active PET/CT users. J Nucl Med 2011;52:303-10. |
|2.||Graham MM, Badawi RD, Wahl RL. Variations in PET/CT methodology for oncologic imaging at U.S. academic medical centers: An imaging response assessment team survey. J Nucl Med 2011;52:311-7. |
|3.||Karantanis D, Kalkanis D, Allen-Auerbach M, Bogsrud TV, Subramaniam RM, Danielson A, et al. Oncologic 18F-FDG PET/CT: Referring physicians′ point of view. J Nucl Med 2012;53:1499-505. |
|4.||Langer A. A systematic review of PET and PET/CT in oncology: A way to personalize cancer treatment in a cost-effective manner? BMC Health Serv Res 2010;10:283. |
|5.||Saif MW, Tzannou I, Makrilia N, Syrigos K. Role and cost effectiveness of PET/CT in management of patients with cancer. Yale J Biol Med 2010;83:53-65. |
|6.||Buck AK, Herrmann K, Stargardt T, Dechow T, Krause BJ, Schreyögg J. Economic evaluation of PET and PET/CT in oncology: Evidence and methodologic approaches. J Nucl Med Technol 2010;38:6-17. |
|7.||Fletcher JW, Djulbegovic B, Soares HP, Siegel BA, Lowe VJ, Lyman GH, et al. Recommendations on the use of 18F-FDG PET in oncology. J Nucl Med 2008;49:480-508. |
|8.||Brambilla M, Matheoud R, Secco C, Sacchetti G, Comi S, Rudoni M, et al. Impact of target-to-background ratio, target size, emission scan duration, and activity on physical figures of merit for a 3D LSO-based whole body PET/CT scanner. Med Phys 2007;34:3854-65. |
|9.||Hatt M, Visvikis D, Le Rest CC. Autocontouring versus manual contouring. J Nucl Med 2011;52:658. |
|10.||Berson AM, Stein NF, Riegel AC, Destian S, Ng T, Tena LB, et al. Variability of gross tumor volume delineation in head-and-neck cancer using PET/CT fusion, Part II: The impact of a contouring protocol. Med Dosim 2009;34:30-5. |
|11.||Manfreda KL, Bosnjak M, Berzelak J, Haas I, Vehovar V, Berzelak N. Web surveys versus other survey modes: A meta-analysis comparing response rates. Int J Market Res 2008;50:79-104. |
|12.||Shih T, Fan X. Comparing response rates from web and mail surveys: A meta-analysis. Field Methods 2008;20:249-71. |
|13.||Kotzerke J, Oehme L, Lindner O, Hellwig D, Arbeitsausschuss PET der DGN. Positron emission tomography 2008 in Germany-Results of the query and current status. Nuklearmedizin 2010;49:58-64. |
|14.||Hollensen C, Jørgensen PS, Højgaard L, Specht L, Larsen R, Auto-Segmentation of head and neck cancer using textural features, Proc Eur Soc for Ther Radiol and Oncol (ESTRO), 2010. |
|15.||Toya R, Murakami R, Tashiro K, Yoshida M, Sakamoto F, Kawanaka K, et al. FDG-PET/CT-based gross tumor volume contouring for radiation therapy planning: An experimental phantom study. J Radiat Res 2012;53:338-41. |
|16.||Nelson AD, Werner-Wasik M, Choi W, Arai Y, Faulhaber PF, Ohri N, et al. PET tumor segmentation: Multi-observer validation of a gradient-based method using a NSCLC PET phantom. Int J Radiat Oncol Biol Phys 2009;75:627. |
|17.||Ford EC, Kinahan PE, Hanlon L, Alessio A, Rajendran J, Schwartz DL, et al. Tumor delineation using PET in head and neck cancers: Threshold contouring and lesion volumes. Med Phys 2006;33:4280-8. |
|18.||1 8. Werner-Wasik M, Nelson AD, Choi W, Arai Y, Faulhaber PF, Kang P, et al. What is the best way to contour lung tumors on PET scans? Multiobserver validation of a gradient-based method using a NSCLC digital PET phantom. Int J Radiat Oncol Biol Phys 2012;82:1164-71. |
|19.||Kirov A, Danford C, Schmidtlein C, Yorke E, Yahalom J, Kalaigian H, et al. SU-FF-J-83: Inaccuracy of fixed threshold segmentation for PET. Med Phys 2006;33:2039. |
|20.||Grégoire V, Haustermans K, Geets X, Roels S, Lonneux M. PET-based treatment planning in radiotherapy: A new standard? J Nucl Med 2007;48 Suppl 1:68S-77. |
|21.||Geets X, Lee JA, Bol A, Lonneux M, Grégoire V. A gradient-based method for segmenting FDG-PET images: Methodology and validation. Eur J Nucl Med Mol Imaging 2007;34:1427-38. |
|22.||Sutton MA, Bezdek JC and Cahoon TC. Image segmentation by fuzzy clustering: Methods and issues. In I.N. Bankman (Ed.), Handbook of Medical Imaging Processing and Analysis. San Diego, CA: Academic Press, Inc., 2000;87-106. |
|23.||Li H, Thorstad WL, Biehl KJ, Laforest R, Su Y, Shoghi KI, et al. A novel PET tumor delineation method based on adaptive region-growing and dual-front active contours. Med Phys 2008;35:3711-21. |
|24.||Dewalle-Vignion AS, Yeni N, Petyt G, Verscheure L, Huglo D, Béron A, et al. Evaluation of PET volume segmentation methods: Comparisons with expert manual delineations. Nucl Med Commun 2012;33:34-42. |
|25.||Zaidi H, El Naqa I. PET-guided delineation of radiation therapy treatment volumes: A survey of image segmentation techniques. Eur J Nucl Med Mol Imaging 2010;37:2165-87. |
|26.||Njeh CF. Tumor delineation: The weakest link in the search for accuracy in radiotherapy. J Med Phys 2008;33:136-40. |
|27.||Lee JA. Segmentation of positron emission tomography images: Some recommendations for target delineation in radiation oncology. Radiother Oncol 2010;96:302-7. |
|28.||Greco C, Rosenzweig K, Cascini GL, Tamburrini O. Current status of PET/CT for tumour volume definition in radiotherapy treatment planning for non-small cell lung cancer (NSCLC). Lung Cancer 2007;57:125-34. |
|29.||Ashamalla H, Rafla S, Parikh K, Mokhtar B, Goswami G, Kambam S, et al. The contribution of integrated PET/CT to the evolving definition of treatment volumes in radiation treatment planning in lung cancer. Int J Radiat Oncol Biol Phys 2005;63:1016-23. |
|30.||Griffeth LK. Use of PET/CT scanning in cancer patients: Technical and practical considerations. Proc (Bayl Univ Med Cent) 2005;18:321-30. |
|31.||MacManus M, Nestle U, Rosenzweig KE, Carrio I, Messa C, Belohlavek O, et al. Use of PET and PET/CT for radiation therapy planning: IAEA expert report 2006-2007. Radiother Oncol 2009;91:85-94. |
|32.||Martinuk SD. The use of positron emission tomography (PET) for cancer care across Canada. Time for a National Strategy. Class Print Serv. Ltd. Vanc.BC Can. Available from: http://www.aapsinc.com/wp-content/uploads/2012/05/TRIUMF-AAPS-Martinuk-PET-Across-Canada-REPORT.pdf. |
|33.||Balarajan Y, Selvaraj S, Subramanian SV. Health care and equity in India. Lancet 2011;377:505-15. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]