CT Gently can be used to estimate organ doses, as well as the associated cancer risks, delivered by CT and CBCT scans, based on individual anatomy and scan settings. The novel app also allows users to calculate optimized scanner settings and compare these with reference settings (pre-defined settings from a particular scan protocol or manufacturer, or a scan setting indicated by the user).

Deng, from Yale University School of Medicine and Yale New Haven Hospital (New Haven, CT), explained his motivation: "I am often approached by physicians, physicists or patients asking for an estimate of the dose from a CT or CBCT procedure. Usually I tell them 'give me some time and I'll give you some information', because I have Monte Carlo treatment planning available in-house that allows me to do that dose calculation."

Deng's research group at Yale has performed extensive research into the use of Monte Carlo algorithms for dose calculation, but Monte Carlo simulations are not routinely available in clinics and currently radiotherapy planning systems do not offer CT/CBCT dose calculation capability. "This made me think that maybe I should just combine all of my knowledge in this area and all of the publications, and create a very easy to use tool," he told medicalphysicsweb.

Working in collaboration with Komatsu Business Service in Tokyo, Japan, Deng started to develop the app back in October 2011. The prototype was uploaded into the Apple App Store in May of this year and final approval from Apple was granted in June 2013. Based on initial feedback from users, Deng and his collaborator have finished the first revision of the app, posting version 1.01 in the App Store on August 15 of this year.

Simple inputs

The CT Gently app, which is available in English, Chinese and Japanese, can be used in either CT or CBCT mode, and currently offers calculations for three anatomical sites: head, chest and abdomen. The user inputs the patient's gender, age, weight and circumference at the associated site, plus the tube voltage (kVp) and current-time (mAs) of the scanning system. These parameters are then used to estimate the organ dose and associated cancer risk associated with the particular scan and site.

Currently, the app calculates values for one organ per scan site: the brain for head scans, lung for the chest and red bone marrow for abdominal scans. Deng says that this functionality will be expanded in the future to cover more organs. He also hopes to develop Android and Windows-based apps at some point.

Scan optimization

CT Gently also provides users with the opportunity to optimize scan parameters for a particular patient. The app generates quantitative and graphical comparisons of organ dose and cancer risk between the optimized settings and the reference settings for a specific CT or CBCT scan. "We can probably lower the scan dose by providing an optimized set of mAs and kVp values based on our previous studies," said Deng.

The new tool is targeted for use by patients as well as clinicians. "We hope to provide the patient with all the information that they want, maybe even before they see the doctor," Deng explained. "This may give the clinician second thoughts on how to provide the most appropriate, lower dose imaging procedure to a specific patient. Patient A is different from patient B, you cannot just say all scans should use a particular energy."

Another unique feature of the app is its Q&A function. Here, if a patient wishes to find out more about the scanning procedure, they can access simple definitions of terms such as CT, CBCT, mAs, kVp and organ dose. "I get feedback from both sides," said Deng. "Both say that this is a very good tool and it's easy to use. The clinicians are going to use this to help train their residents."

• The CT Gently app is available to download free of charge from the Apple App Store.

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