EP-1839: Towards planning organ at risk volumes for rectum and bladder using cone beam CvT in prostate cancer

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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Influence of Organ at Risk Definition on Rectal Dose-Volume Histograms in Patients with Prostate Cancer Undergoing External-Beam Radiotherapy

Strahlentherapie und Onkologie ◽

10.1007/s00066-006-1462-7 ◽

2006 ◽

Vol 182 (5) ◽

pp. 277-282 ◽

Cited By ~ 17

Author(s):

Dirk Boehmer ◽

David Kuczer ◽

Harun Badakhshi ◽

Simone Stiefel ◽

Wolf Kuschke ◽

...

Keyword(s):

Prostate Cancer ◽

At Risk ◽

External Beam Radiotherapy ◽

External Beam ◽

Dose Volume Histograms ◽

Rectal Dose ◽

Dose Volume ◽

Risk Definition ◽

Organ At Risk

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Comparison of different contouring definitions of the rectum as organ at risk (OAR) and dose–volume parameters predicting rectal inflammation in radiotherapy of prostate cancer: which definition to use?

British Journal of Radiology ◽

10.1259/bjr.20160370 ◽

2017 ◽

Vol 90 (1070) ◽

pp. 20160370 ◽

Cited By ~ 1

Author(s):

Mirko Nitsche ◽

Werner Brannath ◽

Matthias Brückner ◽

Dirk Wagner ◽

Alexander Kaltenborn ◽

...

Keyword(s):

Prostate Cancer ◽

At Risk ◽

Dose Volume ◽

Organ At Risk

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OC-0555: Organ at risk dose parameters increased by daily anatomic changes in prostate cancer SBRT

Radiotherapy and Oncology ◽

10.1016/s0167-8140(16)31805-9 ◽

2016 ◽

Vol 119 ◽

pp. S266-S267

Author(s):

M. Faasse-de Hoog ◽

M.S. Hoogeman ◽

J.J.M.E. Nuyttens ◽

S. Aluwini

Keyword(s):

Prostate Cancer ◽

At Risk ◽

Organ At Risk

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Cone beam CT-based dose accumulation and analysis of delivered dose to the dominant intraprostatic lesion in primary radiotherapy of prostate cancer

Radiation Oncology ◽

10.1186/s13014-021-01933-z ◽

2021 ◽

Vol 16 (1) ◽

Author(s):

Jörg Tamihardja ◽

Sinan Cirsi ◽

Patrick Kessler ◽

Gary Razinskas ◽

Florian Exner ◽

...

Keyword(s):

Prostate Cancer ◽

At Risk ◽

Organs At Risk ◽

Peripheral Zone ◽

Planning System ◽

Treatment Planning System ◽

Cone Beam ◽

Target Coverage ◽

Dose Accumulation ◽

Delivered Dose

Abstract Background Evaluation of delivered dose to the dominant intraprostatic lesion (DIL) for moderately hypofractionated radiotherapy of prostate cancer by cone beam computed tomography (CBCT)-based dose accumulation and target coverage analysis. Methods Twenty-three patients with localized prostate cancer treated with moderately hypofractionated prostate radiotherapy with simultaneous integrated boost (SIB) between December 2016 and February 2020 were retrospectively analyzed. Included patients were required to have an identifiable DIL on bi-parametric planning magnetic resonance imaging (MRI). After import into the RayStation treatment planning system and application of a step-wise density override, the fractional doses were computed on each CBCT and were consecutively mapped onto the planning CT via a deformation vector field derived from deformable image registration. Fractional doses were accumulated for all CBCTs and interpolated for missing CBCTs, resulting in the delivered dose for PTVDIL, PTVBoost, PTV, and the organs at risk. The location of the index lesions was recorded according to the sector map of the Prostate Imaging Reporting and Data System (PIRADS) Version 2.1. Target coverage of the index lesions was evaluated and stratified for location. Results In total, 338 CBCTs were available for analysis. Dose accumulation target coverage of PTVDIL, PTVBoost, and PTV was excellent and no cases of underdosage in DMean, D95%, D02%, and D98% could be detected. Delivered rectum DMean did not significantly differ from the planned dose. Bladder mean DMean was higher than planned with 19.4 ± 7.4 Gy versus 18.8 ± 7.5 Gy, p < 0.001. The penile bulb showed a decreased delivered mean DMean with 29.1 ± 14.0 Gy versus 29.8 ± 14.4 Gy, p < 0.001. Dorsal DILs, defined as DILs in the posterior medial peripheral zone of the prostate, showed a significantly lower delivered dose with a mean DMean difference of 2.2 Gy (95% CI 1.3–3.1 Gy, p < 0.001) compared to ventral lesions. Conclusions CBCT-based dose accumulation showed an adequate delivered dose to the dominant intraprostatic lesion and organs at risk within planning limits. Cautious evaluation of the target coverage for index lesions adjacent to the rectum is warranted to avoid underdosage.

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Assessment of Knowledge-Based Planning for Prostate Intensity Modulated Proton Therapy

International Journal of Particle Therapy ◽

10.14338/ijpt-20-00088.1 ◽

2021 ◽

Author(s):

Yihang Xu ◽

Nellie Brovold ◽

Jonathan Cyriac ◽

Elizabeth Bossart ◽

Kyle Padgett ◽

...

Keyword(s):

Prostate Cancer ◽

At Risk ◽

Proton Therapy ◽

Volumetric Modulated Arc Therapy ◽

Model Quality ◽

Intensity Modulated Proton Therapy ◽

Intensity Modulated ◽

Knowledge Based ◽

Knowledge Based Planning ◽

Organ At Risk

Abstract Purpose To assess the performance of a proton-specific knowledge based planning (KBPP) model in creation of robustly optimized intensity-modulated proton therapy (IMPT) plans for treatment of patients with prostate cancer. Materials and Methods Forty-five patients with localized prostate cancer, who had previously been treated with volumetric modulated arc therapy, were selected and replanned with robustly optimized IMPT. A KBPP model was generated from the results of 30 of the patients, and the remaining 15 patient results were used for validation. The KBPP model quality and accuracy were evaluated with the model-provided organ-at-risk regression plots and metrics. The KBPP quality was also assessed through comparison of expert and KBPP-generated IMPT plans for target coverage and organ-at-risk sparing. Results The resulting R2 (mean ± SD, 0.87 ± 0.07) between dosimetric and geometric features, as well as the χ2 test (1.17 ± 0.07) between the original and estimated data, showed the model had good quality. All the KBPP plans were clinically acceptable. Compared with the expert plans, the KBPP plans had marginally higher dose-volume indices for the rectum V65Gy (0.8% ± 2.94%), but delivered a lower dose to the bladder (−1.06% ± 2.9% for bladder V65Gy). In addition, KBPP plans achieved lower hotspot (−0.67Gy ± 2.17Gy) and lower integral dose (−0.09Gy ± 0.3Gy) than the expert plans did. Moreover, the KBPP generated better plans that demonstrated slightly greater clinical target volume V95 (0.1% ± 0.68%) and lower homogeneity index (−1.13 ± 2.34). Conclusions The results demonstrated that robustly optimized IMPT plans created by the KBPP model are of high quality and are comparable to expert plans. Furthermore, the KBPP model can generate more-robust and more-homogenous plans compared with those of expert plans. More studies need to be done for the validation of the proton KBPP model at more-complicated treatment sites.

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