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Title: Effect of various methods for rectum delineation on relative and absolute dose-volume histograms for prostate IMRT treatment planning

Abstract

Several reports have dealt with correlations of late rectal toxicity with rectal dose-volume histograms (DVHs) for high dose levels. There are 2 techniques to assess rectal volume for reception of a specific dose: relative-DVH (R-DVH, %) that indicates relative volume for a vertical axis, and absolute-DVH (A-DVH, cc) with its vertical axis showing absolute volume of the rectum. The parameters of DVH vary depending on the rectum delineation method, but the literature does not present any standardization of such methods. The aim of the present study was to evaluate the effects of different delineation methods on rectal DVHs. The enrollment for this study comprised 28 patients with high-risk localized prostate cancer, who had undergone intensity-modulated radiation therapy (IMRT) with the prescription dose of 78 Gy. The rectum was contoured with 4 different methods using 2 lengths, short (Sh) and long (Lg), and 2 cross sections, rectum (Rec) and rectal wall (Rw). Sh means the length from 1 cm above the seminal vesicles to 1 cm below the prostate and Lg the length from the rectosigmoid junction to the anus. Rec represents the entire rectal volume including the rectal contents and Rw the rectal volume of the area with a wallmore » thickness of 4 mm. We compared dose-volume parameters by using 4 rectal contour methods for the same plan with the R-DVHs as well as the A-DVHs. For the high dose levels, the R-DVH parameters varied widely. The mean of V{sub 70} for Sh-Rw was the highest (19.4%) and nearly twice as high as that for Lg-Rec (10.4%). On the contrary, only small variations were observed in the A-DVH parameters (4.3, 4.3, 5.5, and 5.5 cc for Sh-Rw, Lg-Rw, Sh-Rec, and Lg-Rec, respectively). As for R-DVHs, the parameters of V{sub 70} varied depending on the rectal lengths (Sh-Rec vs Lg-Rec: R = 0.76; Sh-Rw vs Lg-Rw: R = 0.85) and cross sections (Sh-Rec vs Sh-Rw: R = 0.49; Lg-Rec vs Lg-Rw: R = 0.65). For A-DVHs, however, the parameters of Sh rectal A-DVHs hardly changed regardless of differences in rectal length at all dose levels. Moreover, at high dose levels (V{sub 70}), the parameters of A-DVHs showed less dependence on rectal cross sections (Sh-Rec vs Sh-Rw: R = 0.66; Lg-Rec vs Lg-Rw: R = 0.59). This study showed that A-DVHs were less dependent on the delineation methods than R-DVHs, especially for evaluating the rectal dose at higher dose levels. It can therefore be assumed that, in addition to R-DVHs, A-DVHs can be used for evaluating rectal toxicity.« less

Authors:
 [1];  [1];  [2];  [1];  [1];  [2];  [1];  [1]
  1. Department of Radiation Oncology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
22577874
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Dosimetry; Journal Volume: 41; Journal Issue: 2; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; 62 RADIOLOGY AND NUCLEAR MEDICINE; CROSS SECTIONS; HEALTH HAZARDS; NEOPLASMS; PATIENTS; PLANNING; PROSTATE; RADIATION DOSES; RADIOTHERAPY; RECTUM; STANDARDIZATION; THICKNESS; TOXICITY

Citation Formats

Kusumoto, Chiaki, Ohira, Shingo, Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Miyazaki, Masayoshi, Ueda, Yoshihiro, Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Suita, Isono, Masaru, and Teshima, Teruki, E-mail: teshima-te@mc.pref.osaka.jp. Effect of various methods for rectum delineation on relative and absolute dose-volume histograms for prostate IMRT treatment planning. United States: N. p., 2016. Web. doi:10.1016/J.MEDDOS.2015.11.001.
Kusumoto, Chiaki, Ohira, Shingo, Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Miyazaki, Masayoshi, Ueda, Yoshihiro, Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Suita, Isono, Masaru, & Teshima, Teruki, E-mail: teshima-te@mc.pref.osaka.jp. Effect of various methods for rectum delineation on relative and absolute dose-volume histograms for prostate IMRT treatment planning. United States. doi:10.1016/J.MEDDOS.2015.11.001.
Kusumoto, Chiaki, Ohira, Shingo, Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita, Miyazaki, Masayoshi, Ueda, Yoshihiro, Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Suita, Isono, Masaru, and Teshima, Teruki, E-mail: teshima-te@mc.pref.osaka.jp. 2016. "Effect of various methods for rectum delineation on relative and absolute dose-volume histograms for prostate IMRT treatment planning". United States. doi:10.1016/J.MEDDOS.2015.11.001.
@article{osti_22577874,
title = {Effect of various methods for rectum delineation on relative and absolute dose-volume histograms for prostate IMRT treatment planning},
author = {Kusumoto, Chiaki and Ohira, Shingo and Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, Suita and Miyazaki, Masayoshi and Ueda, Yoshihiro and Department of Radiation Oncology, Graduate School of Medicine, Osaka University, Suita and Isono, Masaru and Teshima, Teruki, E-mail: teshima-te@mc.pref.osaka.jp},
abstractNote = {Several reports have dealt with correlations of late rectal toxicity with rectal dose-volume histograms (DVHs) for high dose levels. There are 2 techniques to assess rectal volume for reception of a specific dose: relative-DVH (R-DVH, %) that indicates relative volume for a vertical axis, and absolute-DVH (A-DVH, cc) with its vertical axis showing absolute volume of the rectum. The parameters of DVH vary depending on the rectum delineation method, but the literature does not present any standardization of such methods. The aim of the present study was to evaluate the effects of different delineation methods on rectal DVHs. The enrollment for this study comprised 28 patients with high-risk localized prostate cancer, who had undergone intensity-modulated radiation therapy (IMRT) with the prescription dose of 78 Gy. The rectum was contoured with 4 different methods using 2 lengths, short (Sh) and long (Lg), and 2 cross sections, rectum (Rec) and rectal wall (Rw). Sh means the length from 1 cm above the seminal vesicles to 1 cm below the prostate and Lg the length from the rectosigmoid junction to the anus. Rec represents the entire rectal volume including the rectal contents and Rw the rectal volume of the area with a wall thickness of 4 mm. We compared dose-volume parameters by using 4 rectal contour methods for the same plan with the R-DVHs as well as the A-DVHs. For the high dose levels, the R-DVH parameters varied widely. The mean of V{sub 70} for Sh-Rw was the highest (19.4%) and nearly twice as high as that for Lg-Rec (10.4%). On the contrary, only small variations were observed in the A-DVH parameters (4.3, 4.3, 5.5, and 5.5 cc for Sh-Rw, Lg-Rw, Sh-Rec, and Lg-Rec, respectively). As for R-DVHs, the parameters of V{sub 70} varied depending on the rectal lengths (Sh-Rec vs Lg-Rec: R = 0.76; Sh-Rw vs Lg-Rw: R = 0.85) and cross sections (Sh-Rec vs Sh-Rw: R = 0.49; Lg-Rec vs Lg-Rw: R = 0.65). For A-DVHs, however, the parameters of Sh rectal A-DVHs hardly changed regardless of differences in rectal length at all dose levels. Moreover, at high dose levels (V{sub 70}), the parameters of A-DVHs showed less dependence on rectal cross sections (Sh-Rec vs Sh-Rw: R = 0.66; Lg-Rec vs Lg-Rw: R = 0.59). This study showed that A-DVHs were less dependent on the delineation methods than R-DVHs, especially for evaluating the rectal dose at higher dose levels. It can therefore be assumed that, in addition to R-DVHs, A-DVHs can be used for evaluating rectal toxicity.},
doi = {10.1016/J.MEDDOS.2015.11.001},
journal = {Medical Dosimetry},
number = 2,
volume = 41,
place = {United States},
year = 2016,
month = 7
}
  • Purpose: The purpose of this study was to analyze the relationship between prostate, bladder, and rectum volumes on treatment planning CT day and prostate shifts in the XYZ directions on treatment days. Methods: Prostate, seminal vesicles, bladder, and rectum were contoured on CT images obtained in supine position. Intensity modulated radiation therapy plans was prepared. Contours were exported to BAT-ultrasound imaging system. Patients were positioned on the couch using skin marks. An ultrasound probe was used to obtain ultrasound images of prostate, bladder, and rectum, which were aligned with CT images. Couch shifts in the XYZ directions as recommended bymore » BAT system were made and recorded. 4698 couch shifts for 42 patients were analyzed to study the correlations between interfraction prostate shifts vs bladder, rectum, and prostate volumes on planning CT. Results: Mean and range of volumes (cc): Bladder: 179 (42-582), rectum: 108 (28-223), and prostate: 55 (21-154). Mean systematic prostate shifts were (cm, {+-}SD) right and left lateral: -0.047{+-}0.16 (-0.361-0.251), anterior and posterior: 0.14{+-}0.3 (-0.466-0.669), and superior and inferior: 0.19{+-}0.26 (-0.342-0.633). Bladder volume was not correlated with lateral, anterior/posterior, and superior/inferior prostate shifts (P>0.2). Rectal volume was correlated with anterior/posterior (P<0.001) but not with lateral and superior/inferior prostate shifts (P>0.2). The smaller the rectal volume or cross sectional area, the larger was the prostate shift anteriorly and vice versa (P<0.001). Prostate volume was correlated with superior/inferior (P<0.05) but not with lateral and anterior/posterior prostate shifts (P>0.2). The smaller the prostate volume, the larger was prostate shift superiorly and vice versa (P<0.05). Conclusions: Prostate and rectal volumes, but not bladder volumes, on treatment planning CT influenced prostate position on treatment fractions. Daily image-guided adoptive radiotherapy would be required for patients with distended or empty rectum on planning CT to reduce rectal toxicity in the case of empty rectum and to minimize geometric miss of prostate.« less
  • Late rectal bleeding resulting from radiotherapy has been correlated with rectal dose-volume histograms (DVHs). The techniques of contouring the rectum have been inconsistent within the literature, making interpretations of DVHs difficult. This study was conducted to investigate the impact on rectal DVHs when using different ways of contouring. Ten prostate cancer patients were treated with a 4-field box-technique and received 70 Gy. Six different ways of contouring the rectum were implemented by using 3 different cross-sections and 2 different lengths. The 3 different cross sections were (1) anterior rectal wall (arw): only the anterior half of the rectal wall wasmore » contoured; (2) whole rectal wall (wrw): the entire rectal wall was contoured but excluding the rectal contents; and (3) the rectum (rec): including the rectal contents. Two different lengths were used for the above 3 volumes: (1) long (Lg): cranial border starting at where the rectum turned horizontally into the sigmoid and the caudal border 2 cm below the prostatic apex; (2) short (Sh): from 2 cm above to 2 cm below the prostate. Therefore, a total of 6 different volumes (Sh arw, Lg arw, Sh wrw, Lg wrw, Sh rec, and Lg rec) were generated. DVHs of all 6 volumes were compared with the y-axis being percentage volume as well as absolute volume (cc). When using percentage volume as the y-axis, Sh arw gave an impression that a large portion of rectum (median of 41.8%) received high dose (greater than 90% prescribed dose), while the Lg wrw and Lg rec revealed a smaller portion of rectum (median of 17.1% and 14.7%, respectively) received high dose. The other contours were somewhere in-between. When using absolute volume as the y-axis, the DVHs of the 4 rectal volumes, excluding the rectal content (Sh and Lg arw, Sh and Lg wrw), merged at doses greater than 80% to 85% prescription, therefore providing similar information within these high-dose regions. Configurations of rectal DVHs varied drastically with different techniques of contouring and may lead to different interpretations. By using absolute volume (cc) as the y-axis, the shape of the 4 rectal DVHs, excluding the rectal content, were similar in the high-dose region. Reporting rectal toxicities in relations to DVHs using absolute volume, as well as percentage volume, may eliminate inconsistencies secondary to different methods of contouring.« less
  • Purpose: The objective of this study was to evaluate and validate the use of the Geant4 application for emission tomography (GATE) Monte Carlo simulation platform for clinical intensity modulated radiotherapy (IMRT) dosimetry studies. Methods: The first step consisted of modeling a 6 MV photon beam linear accelerator (LINAC), with its corresponding validation carried out using percent depth dose evaluation, transverse profiles, tissue phantom ratio, and output factor on water phantom. The IMRT evaluation was performed by comparing simulation and measurements in terms of absolute and relative doses using IMRT dedicated quality assurance phantoms considering seven different patient datasets. Results: Concerningmore » the LINAC simulated model validation tissue phantom ratios at 20 and 10 cm in water TPR{sub 10}{sup 20} obtained from GATE and measurements were 0.672 {+-} 0.063 and 0.675, respectively. In terms of percent depth dose and transverse profiles, error ranges were, respectively: 1.472%{+-} 0.285% and 4.827%{+-} 1.323% for field size of 4 Multiplication-Sign 4, 5 Multiplication-Sign 5, 10 Multiplication-Sign 10, 15 Multiplication-Sign 15, 20 Multiplication-Sign 20, 25 Multiplication-Sign 25, 30 Multiplication-Sign 30, and 40 Multiplication-Sign 40 cm{sup 2}. Most errors were observed at the edge of radiation fields because of higher dose gradient in these areas. Output factors showed good agreement between simulation and measurements with a maximum error of 1.22%. Finally, for IMRT simulations considering seven patient datasets, GATE provided good results with a relative error of 0.43%{+-} 0.25% on absolute dose between simulated and measured beams (measurements at the isocenter, volume 0.125 cm{sup 3}). Planar dose comparisons were also performed using gamma-index analysis. For the whole set of beams considered the mean gamma-index value was 0.497 {+-} 0.152 and 90.8%{+-} 3.6% of the evaluated dose points satisfied the 5%/ 4 mm criterion. Conclusions: These results show that GATE allows reliable simulation of complex beams in radiotherapy after an accurate LINAC modeling is validated. A simple cross-calibration procedure proposed in this work allows obtaining absolute dose values even in complex fields.« less
  • Purpose: To assess whether a 4-field box technique (4FBT), along with its technical refinements, is an adequate approach in terms of rectal sparing and target coverage for patients with localized prostate cancer undergoing whole-pelvic radiotherapy followed by a prostate boost and whether or not intensity-modulated radiotherapy (IMRT) is needed. Methods and Materials: For 8 patients, 31 plans were generated, each of them differing in one or more features, including prescription (dose/volume) and/or technical factors. For the latter, several 'solutions' to try to reduce the amount of irradiated rectal volume were addressed, including modifications of the 4FBT and the use ofmore » sequential IMRT. We constructed a database with 248 plans that were tested for their ability to meet a series of rectal dose-volume constraints at V50, V60, V65, V70, V75, and V75.6. Multivariate logistic regression was used to identify factors independently associated with the end point. Successful solutions were also compared in terms of coverage of both pelvic node and prostate planning target volume (PTV) by isodose 95%. Results: At multivariate logistic regression, both rectal blocking and IMRT were independent predictors of the probability of meeting rectal dose-volume constraints during the pelvic and boost phases of treatment with close relative risks. However, on average, partial rectal blocking on lateral fields of 4FBT during whole-pelvic radiotherapy resulted in about 3% of pelvic node PTV being outside isodose 95%; only 2 of 8 patients had the pelvic nodal PTV covered similarly to what was achieved by whole-pelvis IMRT. Conversely, blocking the rectum during the last 3 fractions of the conformal boost showed a dosimetric coverage of prostate PTV similar to that achieved by IMRT boost. Interestingly, patient anatomic configuration was the strongest predictor of rectal sparing. Finally, the size of prostate margins to generate PTV was also independently associated with the probability of meeting rectal dose-volume constraints. Conclusion: In the dose range of 70-76 Gy to the prostate, IMRT and standard techniques are equally effective in meeting rectal dose-volume constraints. However, whole-pelvis IMRT might be preferable to standard techniques for its slightly superior PTV coverage.« less
  • Purpose: To develop a procedure for including dose constraints in convex programming-based approaches to treatment planning, and to support dynamic modification of such constraints during planning. Methods: We present a mathematical approach that allows mean dose, maximum dose, minimum dose and dose volume (i.e., percentile) constraints to be appended to any convex formulation of an inverse planning problem. The first three constraint types are convex and readily incorporated. Dose volume constraints are not convex, however, so we introduce a convex restriction that is related to CVaR-based approaches previously proposed in the literature. To compensate for the conservatism of this restriction,more » we propose a new two-pass algorithm that solves the restricted problem on a first pass and uses this solution to form exact constraints on a second pass. In another variant, we introduce slack variables for each dose constraint to prevent the problem from becoming infeasible when the user specifies an incompatible set of constraints. We implement the proposed methods in Python using the convex programming package cvxpy in conjunction with the open source convex solvers SCS and ECOS. Results: We show, for several cases taken from the clinic, that our proposed method meets specified constraints (often with margin) when they are feasible. Constraints are met exactly when we use the two-pass method, and infeasible constraints are replaced with the nearest feasible constraint when slacks are used. Finally, we introduce ConRad, a Python-embedded free software package for convex radiation therapy planning. ConRad implements the methods described above and offers a simple interface for specifying prescriptions and dose constraints. Conclusion: This work demonstrates the feasibility of using modifiable dose constraints in a convex formulation, making it practical to guide the treatment planning process with interactively specified dose constraints. This work was supported by the Stanford BioX Graduate Fellowship and NIH Grant 5R01CA176553.« less