The benefit of using bladder sub-volume equivalent uniform dose constraints in prostate intensity-modulated radiotherapy planning

Abstract

BackgroundTo assess the benefits of bladder wall sub-volume equivalent uniform dose (EUD) constraints in prostate cancer intensity-modulated radiotherapy (IMRT) planning.MethodsTwo IMRT plans, with and without EUD constraints on the bladder wall, were generated using beams that deliver 80 Gy to the prostate and 46 Gy to the seminal vesicles and were compared in 53 prostate cancer patients. The bladder wall was defined as the volume between the external manually delineated wall and a contraction of 7 mm apart from it. The bladder wall was then separated into two parts: the internal-bladder wall (bla-in) represented by the portion of the bladder wall that intersected with the planning target volume (PTV) plus 5 mm extension; the external-bladder wall (bla-ex) represented by the remaining part of the bladder wall. In the IMRT plan with EUD constraints, the values of “a” parameter for the EUD models were 10.0 for bla-in and 2.3 for bla-ex. The plans with and without EUD constraints were compared in terms of dose–volume histograms, 5-year bladder and rectum normal tissue complication probability values, as well as tumor control probability (TCP) values.ResultsThe use of bladder sub-volume EUD constraints decreased both the doses to the bladder wall (V70: 22.76% vs 19.65%, Dmean: 39.82 Gy vs 35.45 Gy) and the 5-year bladder complication probabilities (≥LENT/SOMA Grade 2: 20.35% vs 17.96%; bladder bleeding: 10.63% vs 8.64%). The doses to the rectum wall and the rectum complication probabilities were also slightly decreased by the EUD constraints compared to physical constraints only. The minimal dose and the V76Gy of PTVprostate were, however, slightly decreased by EUD optimization, nevertheless without significant difference in TCP values between the two plans, and the PTV parameters finally respected the Groupe d’Etude des Tumeurs Uro-Génitales recommendations.ConclusionSeparating the bladder wall into two parts with appropriate EUD optimization may reduce bladder toxicity in prostate IMRT. Combining biological constraints with physical constraints in the organs at risk at the inverse planning step of IMRT may improve the dose distribution.

Dosimetric predictors and Lyman normal tissue complication probability model of hematological toxicity in cervical cancer patients with treated with pelvic irradiation

“…If HT is caused largely by damage to the marrow by a low dose on a large volume, parallel characteristics will be observed. Regarding this feature, Jian Zhu's investigation showed that an IMRT biological optimization scheme with two groups of different equivalent uniform dose parameters yielded improved organ protection 42 . In this study, analysis of the data of all patients showed that HT was sensitive to D mean , D max , V 16–53 , and NTCP, especially sensitive to V 16–18 , V 35,36,47 , and the NTCP.…”

“…Regarding this feature, Jian Zhu's investigation showed that an IMRT biological optimization scheme with two groups of different equivalent uniform dose parameters yielded improved organ protection. 42 In this study, analysis of the data of all patients showed that HT was sensitive to D mean , D max , V 16-53 , and NTCP, especially sensitive to V 16-18 , V 35,36,47 , and the NTCP. Given the level of PBM protection during cervical cancer radiotherapy, it has been suggested that both hot spots in the PTV overlapping with the PBM and large areas with low doses outside the PTV should be avoided to spare more of the PBM, which means that a "tight" dose distribution should also be considered during planning.…”

“…compared biological IMRT optimization strategies with physical IMRT optimization strategies using three TPSs and concluded that although biological IMRT spares normal organs better, it is easier to reach the target dose coverage standard with physical IMRT than with biological IMRT 46 . We proved previously that optimizing the objective function of IMRT under different biological constraints with various biological parameters may specifically reduce dosimetry‐related toxicities 42 . Therefore, based on the “serial‐parallel” behavior of the PBM during irradiation‐induced HT, biological IMRT with various specific parameters can be used.…”

Fitting NTCP models to bladder doses and acute urinary symptoms during post-prostatectomy radiotherapy

“…The model parameters based on the LENT/SOMA scoring system (≥ Grade 2) were D 50 = 69.56 Gy, γ = 1.7 and s = 0.35 for the RS model and D 50 = 78.68 Gy, m = 0.17 and n = 0.09 for the LKB model [ 39 , 40 ]. Regarding the symptoms of bladder contracture and volume loss, the parameters of the RS model are D 50 = 80.0 Gy, γ = 3.0 and s = 0.18, whereas those of the LKB model are D 50 = 80.0 Gy, m = 0.11 and n = 0.5 [ 41 – 43 ].…”

A Novel Definition of Equivalent Uniform Dose Based on Volume Dose Curve

“…This replacement needs an indicator for evaluation of the therapeutic effects, which is a great challenge for radiotherapy researchers [5], [6]. The equivalent uniform dose (EUD) is a kind of dose-based biomedical indicator [7], which is frequently used in the clinical system. Another kind of useful clinical evaluation system is the dose volume histogram (DVH) [8].Although the DVH can describe the clinical significance, it is not a bio-medical indicator, but physical dose indicator.…”