PO-1006: Evaluation of an auto-segmentation software for definition of organs at risk in radiotherapy

15598 Background: In curative radiation treatment of prostate cancer,the advent of 3DCRT has made a reduction in the incidence of normal tissue toxicities while optimizing tumor control. To optimize 3DCRT, the ICRU has published standard definitions of target volumes and organs at risk such that the tumor can receive the optimal dose with as little as possible dose to the organs at risk. However, the definition of the rectum as an organ at risk in radiation treatment of the prostate varies widely among institutions and so does the report of toxicities. We studied the effect of varying rectal contouring on rectal dose obtained from DVHs in a homogenous group of prostate cancer patients treated with hypo fractionationed radiation. Methods: 71 patients with favorable risk prostate cancer treated with a total of 66Gy in 3Gy/day fractionation.18 MV photons in a 5-field technique was used. None of the patients received hormonal therapy. Their treatment plans were archived and the rectum was re-contoured by a single investigator. 4 different contours were drawn to compare the rectal dose: i) the whole rectum from the anal verge to the recto sigmoid junction (WR); ii) the rectum from 1cm below the PTV to 1cm above (RPTV); iii) the rectal wall (i.e. the inner and outer rectal wall) from the anal verge to the recto sigmoid junction (RW); iv) the rectal wall from 1cm below the PTV to 1cm above (RWPTV) Results: There were significant differences in the median volume, minimum, mean rectal doses and dose to 50% of the volume, (p=0.0001). The whole rectum (WR) is having the lowest and the rectal wall with 1cm above and below the PTV (RWPTV) having the highest in all the parameters. The only parameter not significantly different among the 4 contours is the maximum rectal dose. Conclusion: the varied rectal contouring across different institutions is a possible reason for the broadly different reports of rectal toxicity after prostate irradiation. Our results suggest significant differences in rectal doses with varied contouring. Contouring the rectal wall only and limiting the volume to 1cm above and below the PTV confers the highest mean rectal dose. Comparison of rectal toxicity between institutions can only be meaningful if a consensual volume definition of the organ at risk is agreed upon. No significant financial relationships to disclose.

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177 oral Integrating geometrical uncertainties in inverse treatment planning for IMRT to avoid a priori definition of planning margins for the tumor and the organs at risk

Radiotherapy and Oncology ◽

10.1016/s0167-8140(03)80196-2 ◽

2003 ◽

Vol 68 ◽

pp. S69-S70

Keyword(s):

At Risk ◽

Treatment Planning ◽

Organs At Risk ◽

A Priori ◽

Inverse Treatment Planning ◽

Inverse Treatment ◽

Definition Of

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Evaluation of an automatic segmentation algorithm for definition of head and neck organs at risk

Radiation Oncology ◽

10.1186/1748-717x-9-173 ◽

2014 ◽

Vol 9 (1) ◽

pp. 173 ◽

Cited By ~ 34

Author(s):

David Thomson ◽

Chris Boylan ◽

Tom Liptrot ◽

Adam Aitkenhead ◽

Lip Lee ◽

...

Keyword(s):

At Risk ◽

Head And Neck ◽

Organs At Risk ◽

Automatic Segmentation ◽

Segmentation Algorithm ◽

Definition Of

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TU-C-J-6B-01: From Morphological to Functional Definition of Organs at Risk: The Role of FMRI in Radiosurgery

Medical Physics ◽

10.1118/1.1998345 ◽

2005 ◽

Vol 32 (6Part15) ◽

pp. 2082-2082

Author(s):

J Stancanello ◽

C Cavedon ◽

P Francescon ◽

M Avanzo ◽

S Cora ◽

...

Keyword(s):

At Risk ◽

Organs At Risk ◽

Definition Of

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Dosimetric comparison of organs at risk using different contouring guidelines for definition of the clinical target volume in anal cancer

Strahlentherapie und Onkologie ◽

10.1007/s00066-020-01587-y ◽

2020 ◽

Vol 196 (4) ◽

pp. 368-375

Author(s):

Hendrik Dapper ◽

Markus Oechsner ◽

Stefan Münch ◽

Christian Diehl ◽

Jan C. Peeken ◽

...

Keyword(s):

At Risk ◽

Anal Cancer ◽

Clinical Target Volume ◽

Organs At Risk ◽

Target Volume ◽

Dosimetric Comparison ◽

Definition Of ◽

Contouring Guidelines

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Definitions and Concepts for Quantitative Rockfall Hazard and Risk Analysis

Geosciences ◽

10.3390/geosciences11040158 ◽

2021 ◽

Vol 11 (4) ◽

pp. 158

Author(s):

Didier Hantz ◽

Jordi Corominas ◽

Giovanni B. Crosta ◽

Michel Jaboyedoff

Keyword(s):

Risk Assessment ◽

At Risk ◽

Failure Probability ◽

Rockfall Hazard ◽

Process Failure ◽

Failure Propagation ◽

Element At Risk ◽

Hazard And Risk ◽

Hazard And Risk Assessment ◽

Definition Of

There is an increasing need for quantitative rockfall hazard and risk assessment that requires a precise definition of the terms and concepts used for this particular type of landslide. This paper suggests using terms that appear to be the most logic and explicit as possible and describes methods to derive some of the main hazards and risk descriptors. The terms and concepts presented concern the rockfall process (failure, propagation, fragmentation, modelling) and the hazard and risk descriptors, distinguishing the cases of localized and diffuse hazards. For a localized hazard, the failure probability of the considered rock compartment in a given period of time has to be assessed, and the probability for a given element at risk to be impacted with a given energy must be derived combining the failure probability, the reach probability, and the exposure of the element. For a diffuse hazard that is characterized by a failure frequency, the number of rockfalls reaching the element at risk per unit of time and with a given energy (passage frequency) can be derived. This frequency is relevant for risk assessment when the element at risk can be damaged several times. If it is not replaced, the probability that it is impacted by at least one rockfall is more relevant.

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