AAPM 263 Standardized Naming for Radiation Therapy Structures

“The Late Spring Festival”!

In 2020, as the Mid-Autumn Festival coincided with National Day, each person’s feelings and reflections on the tumultuous past six months and the sense of loss and recovery are countless. As families reunite, let us together remember the past and cherish the present!

The National Day holiday is already halfway through. According to the website of the Ministry of Culture and Tourism, from October 1 to 4, the country received a total of 425 million tourists, generating tourism revenue of 312.02 billion yuan.

China has achieved decisive victory in the prevention and control of the COVID-19 pandemic! The main task now is to strictly prevent imported cases.However, the overseas COVID-19 situation remains grim, and it has been reported that the Trump couple has tested positive for the virus.

Will the pandemic resurface this winter? Wu Zunyou, chief epidemiologist at the Chinese Center for Disease Control and Prevention, responded that, in fact, the COVID-19 pandemic does not distinguish between winter and summer; if prevention and control measures are inadequate, it could resurface at any time. Of course, after more than half a year of practice, we are relatively optimistic and confident that we can control the pandemic. At the same time, China’s COVID-19 vaccine has been successfully developed, and the phase III clinical trials are progressing smoothly. The COVID-19 situation in China will not see a severe scenario like that of Wuhan at the beginning of the year.

Theme Content AAPM 263 Standardized Naming for Radiation Therapy Structures

The field of radiation oncology will benefit from standardized naming conventions for target areas, normal tissue structures, and treatment planning concepts and metrics. The AAPM 263 working group provides standardized naming guidelines for clinical trials, data aggregation, population studies, and routine clinical treatment in the field of radiation oncology.

The Significance of Standardized Naming for Radiation Oncology Structures:

1. Provides templates for initial subsets for clinical trial groups and user software platforms, offering naming patterns for other structures that may be included in the future;

2. Facilitates database development, automatic analysis of DVH metrics, and data exchange between institutions;

3. Promotes effective communication among all participants in clinical trials; common terminology can improve patient data exchange capabilities across multiple healthcare institutions;

4. Common terminology can provide a foundation for developing automated software tools and for automated extraction and analysis of data, submission, and data exchange; it can facilitate the implementation of automated QA processes;

5. Provides a framework for machine learning applications’ concepts and interrelationships;

1. Target Structure Naming Suggestions

The survey results of target structure naming members show that a very complex set of concepts is currently in use clinically: when several structures, doses, underlying structures, imaging modes, etc., exist, methods for classifying and enumerating the primary and lymph node target areas using ICRU and others emerge. Clinically, not all concepts are attempted to be represented; only some of the most important features are chosen for naming.

1/ The first group of characters must be one of the allowed target area types:

GTV

CTV

ITV

IGTV (Internal Tumor Volume – Consider Motion)

ICTV (Internal Clinical Target Volume – Consider Motion)

PTV

2/ When classifying target areas, place the target area classification symbol after the target area type, with no spaces. The target area classifications are as follows:

n: Lymph Node (e.g., PTVn)

p: Primary (e.g., GTVp)

sb: Surgical Tumor Bed (e.g., CTVsb)

par: Parenchyma (e.g., GTVpar)

v: Venous Thrombosis (e.g., CTVv)

vas: Vascular (e.g., CTVvas）

3/ When different target areas appear, add classification symbols at the end of the target area (e.g., PTV1, PTV2, GTVp1, GTVp2);

4/ For adaptive radiation therapy, when imaging modalities and sequences need to be recorded, follow the type/classification symbol/ enumeration style before the underscore, and then supplement with the imaging modality (CT, PT, MR, SP) and the number of images used in the sequence (e.g., PTVp1_CT1PT1, GTV_CT2);

5/ When using structural indicators, follow the type/classification symbol/enumeration style before the underscore and use its number to represent the reviewed structure naming list (e.g., CTV_A_Arota, CTV_A_Celiac GTV_Preop, PTV_Boost, PTV_Eval, PTV_MR2_Prostate);

6/ When indicating dose, the dose is placed at the end of the target area string with an underscore character. The working group strongly recommends using relative dose levels rather than absolute doses to specify physical doses;

High (PTV_High, CTV_High, GTV_High)

Low (PTV_Low, CTV_Low, GTV_Low)

Mid (PTV_Mid, CTV_Mid, GTV_Mid)

7/ If it is necessary to indicate the numerical value of physical dose, it is strongly recommended that these values must be in cGy (e.g., PTV_5040);

8/ If it is necessary to use numerical values of physical dose, these values must be in Gy, and Gy should be added to the dose value (e.g., PTV_50.4Gy). If this form is not allowed by the system, replace the decimal point with “p” (e.g., PTV_5050p4Gy);

9/ The dose must reflect the number of treatments required to achieve the total dose requirement, and the dose/treatment values must be expressed in cGy or Gy and followed by the dose unit. Additionally, use “x” to separate the number of treatments and dose/treatment, with the number of treatments appended after “x” (e.g., PTV_Liver_2000x3 or PTV_Liver_20Gyx3);

10/ When it is necessary to include the patient’s contour, place “-xx mm” at the end of the target area string. Its length follows the dose representation method and is expressed in xx mm style (e.g., PTV_Eval_7000-08, PTV-03, CTVp2-05);

11/ When using custom strings, they need to be appended after “^” (e.g., PTV^Physician1, GTV_Liver^ICG)

12/ If it is not possible to follow the above guidelines and maintain the 16-character limit, retain the relative order but require the removal of underscores, implementing this from left to right until the limit condition is met (e.g., PTVLiverR_2000x3);

2. Non-target Structure Naming Suggestions

1/ To be compatible with most VADE systems, all structure names are limited to 16 characters or less;

2/ To ensure that there are no duplicate definitions in case-insensitive format systems, all structure names must be unique and independent of case;

3/ Use plural forms to identify composite structures, i.e., add “s” or “I” to the root structure name (e.g., Lungs, Kidneys, Hippocampi, LNs (for all lymph nodes), Ribs_L), and capitalize the first character of each structure category (e.g., Furim_Head, Ears_External);

1) Do not use spaces

2) Use underscores to separate categories (e.g., Bower_Bag)

3) Characters representing spatial categories are placed at the end of the main name, separated by underscores (e.g., Lung_L, Lung_LUL, Lung_RLL, OpticNrv_PRV03_L)

L represents left side

R represents right side

A represents anterior side

P represents posterior side

I represents inferior side

S represents superior side

RUL, RLL, RML represent right upper lobe, right lower lobe, and right middle lobe respectively

LUL, LLL represent left upper lobe and left lower lobe respectively

NAdj represents non-adjacent

Dist represents distal, Prox represents proximal

4/ All substructures use a consistent root structure name (e.g., SeminalVes and SeminalVes_Dist have a consistent root structure name, while SeminalVesicle and SemVes_Dist do not);

5/ The standard categories of root structures span all structures in the body:

A represents artery (e.g., A_Aorta, A_Carotid)

V represents vein (e.g., V_Portal, V_Pulmonary)

LN represents lymph node (e.g., LN_Ax_L1, LN_IMN)

CN represents cranial nerve (e.g., CN_IX_L, CN_XII_R)

Glnd represents gland (e.g., Glnd_Submand)

Bone represents bone (e.g., Bone_Hyoid, Bone_Pelvic)

Musc represents muscle (e.g., Musc_Masseter, Musc_Sclmast_L)

Spc represents space (e.g., Spc_Bowel, Spc_Retrophar_L)

VB represents vertebra

Sinus represents sinus (e.g., Sinus_Frontal, Sinus_Maxillary)

6/ Use underscores to separate root structures and PVR to indicate planned organ at risk (PRV) (e.g., Brainstem_PRV); as an expanded form of this representation, use two digits to represent the length in millimeters formed on the root structure (e.g., SpinalCord_PRV05, Brainstem_PRV03), unless exceeding character limits, for example, OpticChaism_PRV03 17 characters, truncate it and represent it as OpticChaism_PRV3;

7/ Use a tilde character “~” appended to the root structure (e.g., Brain~, Lung~-L) to specify local structures. For example, if a CT scan is insufficient to include the entire lung, for the CT scan, Lungs~ only indicates that it is part of the lung structure;

8/ When using custom symbols to limit strings, place them after the character “^”

(e.g., Lungs^Ex);

9/ Establish a sequential name and a reverse name for each structure:

1) Sequential Name: From left to right, structure classification from general to specific. Thus, generate a list based on organ grouping in alphabetical order (e.g., Kidney_R, Kidney_Cortex_L, Kidney_Hilum_R);

2) Reverse Name: Reverse order. Some systems allow longer strings, but the default displayed number is less than 16 characters. Using this method can increase sufficient information to ensure safe and correct identification of structures. For example, if the system only allows the first 10 characters to be displayed, then R_Hilum_Kidney will display as R-Hilum-Ki. In the safe use of the main name constraints given by the vendor system, it is recommended to limit the use of reverse names;

10/ Only use double capital forms (composite words with each word capitalized, no spaces; e.g., CamelCase) when a structure can reflect two concepts, but this form does not serve as different categories (e.g., CaudaEquina instead of Cauda_Equina). There are not many objects represented in the form of CordaXXXXXX, and for this form, there is no difference between using sequential names and reverse names.

11/ Structures that do not require dose assessment (e.g., optimization structures, high and low dose areas) should be prefixed with “z” or “_” to alphabetically separate them from structures requiring dose assessment (e.g., zPTVopt). It is recommended to use “z” to indicate structures that require dose assessment.

3. Recommendations for Dose-Volume Histogram Standards

Input accurate parameters, dose, and volume units; all formats are parsed with regular expression operators to enhance the ability of computer algorithms to automatically calculate.

1/ Specify the unit or label of the measurement (output) at the end of the string, placing it in square brackets;

Dose: Gy or %, where percentage (%) indicates the dose on the PTV_High structure

Volume: cc or %, where percentage (%) indicates the reference volume of the structure

Equivalent 2 Gy: EQD2Gy

2/ Specify the measurement type at the beginning of the string, specifying the unit or label of the dose measurement on the (input) curve;

Vx: Sub-target area not lower than dose x, specify dose unit or label (e.g.: V20Gy[%], V95%[%], V20Gy[cc])

Dx: Minimum dose x of the hottest sub-target area, specify volume unit or label (e.g.: D0.1cc[Gy],

D95%[%])

CVx: Sub-target area not higher than dose x, specify dose unit or label (e.g.: CV10.5Gy[cc], CV95%[cc])

DCx Maximum dose x of the coldest sub-target area (e.g., DC0.1cc[Gy], DC1%[Gy])

3/ When using calculated parameters, insert them before the brackets containing physical doses or input parameters (e.g., V50EQD2Gy(2.5)[%]);

Reviewed by: Wang Lu Proofread by: Luo Ying Yang Siyao Editor: Guo Zhiwei Organized by: Jiang Shewei

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