Histology-driven hypofractionated radiation therapy schemes for early-stage lung adenocarcinoma and squamous cell carcinoma

BACKGROUND AND PURPOSE

Histology was found to be an important prognostic factor for local tumor control probability (TCP) after stereotactic body radiotherapy (SBRT) of early-stage non-small-cell lung cancer (NSCLC). A histology-driven SBRT approach has not been explored in routine clinical practice and histology-dependent fractionation schemes remain unknown. Here, we analyzed pooled histologic TCP data as a function of biologically effective dose (BED) to determine histology-driven fractionation schemes for SBRT and hypofractionated radiotherapy of two predominant early-stage NSCLC histologic subtypes adenocarcinoma (ADC) and squamous cell carcinoma (SCC).

MATERIAL AND METHODS

The least-χ2 method was used to fit the collected histologic TCP data of 8510 early-stage NSCLC patients to determine parameters for a well-developed radiobiological model per the Hypofractionated Treatment Effects in the Clinic (HyTEC) initiative.

RESULTS

A fit to the histologic TCP data yielded independent radiobiological parameter sets for radiotherapy of early-stage lung ADC and SCC. TCP increases steeply with BED and reaches an asymptotic maximal plateau, allowing us to determine model-independent optimal fractionation schemes of least doses in 1-30 fractions to achieve maximal tumor control for early-stage lung ADC and SCC, e.g., 30, 44, 48, and 51 Gy for ADC, and 32, 48, 54, and 58 Gy for SCC in 1, 3, 4, and 5 fractions, respectively.

CONCLUSION

We presented the first determination of histology-dependent radiobiological parameters and model-independent histology-driven optimal SBRT and hypofractionated radiation therapy schemes for early-stage lung ADC and SCC. SCC requires substantially higher radiation doses to maximize tumor control than ADC, plausibly attributed to tumor genetic diversity and microenvironment. The determined optimal SBRT schemes agree well with clinical practice for early-stage lung ADC. These proposed optimal fractionation schemes provide first insights for histology-based personalized radiotherapy of two predominant early-stage NSCLC subtypes ADC and SCC, which require further validation with large-scale histologic TCP data.

ROE (Radiotherapy Outcomes Estimator): An open-source tool for optimizing radiotherapy prescriptions

BACKGROUND AND OBJECTIVES

Radiotherapy prescriptions currently derive from population-wide guidelines established through large clinical trials. We provide an open-source software tool for patient-specific prescription determination using personalized dose-response curves.

METHODS

We developed ROE, a plugin to the Computational Environment for Radiotherapy Research to visualize predicted tumor control and normal tissue complication simultaneously, as a function of prescription dose. ROE can be used natively with MATLAB and is additionally made accessible in GNU Octave and Python, eliminating the need for commercial licenses. It provides a curated library of published and validated predictive models and incorporates clinical restrictions on normal tissue outcomes. ROE additionally provides batch-mode tools to evaluate and select among different fractionation schemes and analyze radiotherapy outcomes across patient cohorts.

CONCLUSION

ROE is an open-source, GPL-copyrighted tool for interactive exploration of the dose-response relationship to aid in radiotherapy planning. We demonstrate its potential clinical relevance in (1) improving patient awareness by quantifying the risks and benefits of a given treatment protocol (2) assessing the potential for dose escalation across patient cohorts and (3) estimating accrual rates of new protocols.

Assessment of residual geometrical errors of clinical target volumes and their impact on dose accumulation for head and neck radiotherapy

PURPOSE

To assess the residual geometrical errors (dr) and their impact on the clinical target volumes (CTV) dose coverage for head and neck cancer (HNC) proton therapy patients.

METHODS

We analysed 28 HNC patients treated with 70 Gy (RBE) and 54.25 Gy (RBE) to the therapeutic CTV70 and prophylactic CTV54.25, respectively. Daily cone beam CTs were converted to high quality synthetic CTs (sCTs). The CTVs from the nominal CT were propagated to the corresponding sCTs using a hybrid deformable image registration (propagated CTVs) in RayStation 11B. For 11 patients, all propagated CTVs were reviewed by our HNC radiation oncologist (physician corrected CTVs). The residual geometrical error dr was quantified as a function of the daily CTVs volume overlap with the nominal plan CTV. The errors dr(propagated CTVs) and dr(physician corrected CTVs) and the difference in dice similarity coefficients (ΔDSC) were determined. Using clinical plans, dose coverage and the tumor control probability (TCP) for the nominal, accumulated and voxel-wise minimum scenarios were determined.

RESULTS

The difference in the residual geometrical error dr (propagated CTVs - physician corrected CTVs) and mean DSC (|ΔDSC|mean) were minor: Δdr(CTV70) = 0.16 mm, Δdr(CTV54.25) = 0.26 mm, |ΔDSC|mean < 0.9%. For all 28 patients, dr(CTV70) = 1.91 mm and dr(CTV54.25) = 1.90 mm. However, CTV54.25 above and below the cricoid cartilage differed substantially (1.00 mm c.f. 3.93 mm). The CTV54.25 coverage below the cricoid was then almost always lower, although the TCP of the accumulated dose was higher than the TCP of the voxel-wise minimum dose.

CONCLUSIONS

Setup uncertainty setting of 2 mm is possible. The feasibility of using propagated CTVs for error determination is demonstrated.

Evaluation of plan robustness on the dosimetry of volumetric arc radiotherapy (VMAT) with set-up uncertainty in Nasopharyngeal carcinoma (NPC) radiotherapy

Purpose

To evaluate the sensitivity to set up the uncertainty of VMAT plans in Nasopharyngeal carcinoma (NPC) treatment by proposing a plan robustness evaluation method.

Methods

10 patients were selected for this study. A 2-arc volumetric-modulated arc therapy (VMAT) plan was generated for each patient using Varian Eclipse (13.6 Version) treatment planning system (TPS). 5 uncertainty plans (U-plans) were recalculated based on the first 5 times set-up errors acquired from cone-beam computer tomography (CBCT). The dose differences of the original plan and perturbed plan corresponded to the plan robustness for the structure. Tumor control probability (TCP) and normal tissues complication probability (NTCP) were calculated for biological evaluation.

Results

The mean dose differences of D_98% and D_95% (ΔD_98% and ΔD_95%) of PTVp were respectively 3.30 Gy and 2.02 Gy. The ΔD_98% and ΔD_95% of CTVp were 1.12 Gy and 0.58 Gy. The ΔD_98% and ΔD_95% of CTVn were 1.39 Gy and 1.03 Gy, distinctively lower than those in PTVn (2.8 Gy and 2.0 Gy). The CTV-to-PTV margin increased the robustness of CTVs. The ΔD_98% and ΔD_95% of GTVp were 0.56 Gy and 0.33 Gy. GTVn exhibited strong robustness with little variation of D_98% (0.64 Gy) and D_95% (0.39 Gy). No marked mean dose variations of D_mean were seen. The mean reduction of TCP (ΔTCP) in GTVp and CTVp were respectively 0.4% and 0.3%. The mean ΔTCPs of GTVn and CTVn were 0.92% and 1.3% respectively. The CTV exhibited the largest ΔTCP (2.2%). In OARs, the brain stem exhibited weak robustness due to their locations in the vicinity of PTV. Bilateral parotid glands were sensitive to set-up uncertainty with a mean reduction of NTCP (ΔNTCP) of 6.17% (left) and 7.70% (right). The D_max of optical nerves and lens varied slightly.

Conclusion

VMAT plans had a strong sensitivity to set-up uncertainty in NPC radiotherapy, with increasing risk of underdose of tumor and overdose of vicinal OARs. We proposed an effective method to evaluate the plan robustness of VMAT plans. Plan robustness and complexity should be taken into account in photon radiotherapy.

A treatment planning study of urethra-sparing intensity-modulated proton therapy for localized prostate cancer

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US-IMPT can potentially reduce the risk of genitourinary toxicities.

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The urethral NTCP value in US-IMPT is significantly lower than in the clinical plan.

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TCP for CTV did not differ significantly between the clinical and US-IMPT plans.

Background and Purpose

Urethra-sparing radiation therapy for localized prostate cancer can reduce the risk of radiation-induced genitourinary toxicity by intentionally underdosing the periurethral transitional zone. We aimed to compare the clinical impact of a urethra-sparing intensity-modulated proton therapy (US-IMPT) plan with that of conventional clinical plans without urethral dose reduction.

Materials and Methods

This study included 13 patients who had undergone proton beam therapy. The prescribed dose was 63 GyE in 21 fractions for 99% of the clinical target volume. To compare the clinical impact of the US-IMPT plan with that of the conventional clinical plan, tumor control probability (TCP) and normal tissue complication probability (NTCP) were calculated with a generalized equivalent uniform dose-based Lyman–Kutcher model using dose volume histograms. The endpoints of these model parameters for the rectum, bladder, and urethra were fistula, contraction, and urethral stricture, respectively.

Results

The mean NTCP value for the urethra in US-IMPT was significantly lower than that in the conventional clinical plan (0.6% vs. 1.2%, p < 0.05). There were no statistically significant differences between the conventional and US-IMPT plans regarding the mean minimum dose for the urethra with a 3-mm margin, TCP value, and NTCP value for the rectum and bladder. Additionally, the target dose coverage of all plans in the robustness analysis was within the clinically acceptable range.

Conclusions

Compared with the conventional clinically applied plans, US-IMPT plans have potential clinical advantages and may reduce the risk of genitourinary toxicities, while maintaining the same TCP and NTCP in the rectum and bladder.

Tumour volume distribution can yield information on tumour growth and tumour control

BACKGROUND

It is shown that tumour volume distributions can yield information on two aspects of cancer research: tumour induction and tumour control.

MATERIALS AND METHODS

From the hypothesis that the intrinsic distribution of breast cancer volumes follows an exponential distribution, firstly the probability density function of tumour growth time was deduced via a mathematical transformation of the probability density functions of tumour volumes. In a second step, the distribution of tumour volumes was used to model the variation of the clonogenic cell number between patients in order to determine tumour control probabilities for radiotherapy patients.

RESULTS

Distribution of lag times, i.e. the time from the appearance of the first fully malignant cell until a clinically observable cancer, can be used to deduce the probability of tumour induction as a function of patient age. The integration of the volume variation with a Poisson-TCP model results in a logistic function which explains population-averaged survival data of radiotherapy patients.

CONCLUSIONS

The inclusion of tumour volume distributions into the TCP formalism enables a direct link to be deduced between a cohort TCP model (logistic) and a TCP model for individual patients (Poisson). The TCP model can be applied to non-uniform tumour dose distributions.

Development of generalized time-dependent TCP model and the investigation of the effect of repopulation and weekend breaks in fractionated external beam therapy

We developed a tumor control probability (TCP) model that incorporates variable time intervals between fractions and a kick-off time (T_k) for radiation-induced accelerated tumor proliferation. The resulting Lee-Rosen model, TCP_LR, was used to compute TCPs for treatment courses with and without weekend treatment for tumors with different proliferation rates - slow (prostate), moderate (breast), and rapid (head and neck). TCPs were computed using ideal uniform dose distributions and actual patient plans. The doses for the uniform plans were the mean doses for the prostate and breast cases and the minimum tumor dose for the head and neck case. The TCP_LR model predictions agreed with expectations that TCP increases with increasing T_k in all cases. For standard fractionation, as T_k increased from 0 to 4 weeks, TCP increased for the patient distributions by 74.7% for the head and neck cancer, by 6.2% for the breast cancer, and by 2.4% for the prostate cancers. For the uniform dose distributions, the increases were 79.2%, 5.7%, and 2.3%, respectively. TCP increased as the number of weekend breaks decreased. The effect of weekend breaks decreased as the tumor proliferation rate decreased. For the head and neck tumor, notable decreases in TCP of 6.0% (uniform dose distribution) and 6.8% (actual plan dose distribution) were observed with Friday starts compared to Monday starts for the standard 5 fx/wk schedule (T_k = 4 wk). The 7 fx/wk schedule produced increases in TCP of 17.0% and 20.5% for the uniform and patient dose distributions, respectively, compared to the standard schedule. For the breast cancer, starting the 5 fx/wk schedule on Friday decreased the TCP by 0.2% (T_k = 4 wk) compared to a Monday start. The 7 fx/wk schedule produced increases of 0.3% and 0.4% in TCP compared to the standard schedule for the uniform and patient dose distributions, respectively (T_k = 4 wk). For the prostate cancer, the change in TCP for 5 fx/wk schedules starting on different days was 0.1%. The 7 fx/wk schedule increased TCP by 0.8% compared to the standard schedule (T_k = 4 wk). TCP values for the uniform dose distributions for the standard schedule (T_k = 4 wk) agreed with the TCP values for the actual dose distributions within 4.5% for the head and neck tumor and within 0.2% for the breast and prostate tumors. This good agreement suggests that the doses chosen for the uniform dose distributions were good approximations to the clinical doses. The results for head and neck tumors support, in part, the current practice of hyperfractionated/accelerated radiotherapy. They also suggest that shortening the overall treatment time for conventional fractions by eliminating weekend breaks might be beneficial. The predicted effect on TCP of the various schedules studied was insignificant for prostate and breast tumors, suggesting that a weekend treatment might not be necessary for patients starting radiotherapy on a Friday. There is significant uncertainty in the values of the model parameters chosen for these calculations, and no consideration was given to the potential effects of these various schedules on normal tissues.

External Beam Radiation Therapy for Liver Metastases

Stereotactic ablative radiotherapy (SABR) commonly is used for small liver metastases. Modern conformal radiotherapy techniques, including 3-dimensional conformal radiotherapy and intensity-modulated radiation therapy, enable the safe delivery of SABR to small liver volumes. For larger tumors, the safe delivery of SABR can be challenging due to a more limited volume of healthy normal liver parenchyma and the proximity of the tumor to radiosensitive organs, such as the stomach, duodenum, and large intestine. Controlling respiratory motion, the use of image guidance, and increasing the number of radiation fractions sometimes are necessary for the safe delivery of SABR in these situations.

The impact of random microenvironmental fluctuations on tumor control probability

The tumor control probability (TCP) is a metric used to calculate the probability of controlling or eradicating tumors through radiotherapy. Cancer cells vary in their response to radiation, and although many factors are involved, the tumor microenvironment is a crucial one that determines radiation efficacy. The tumor microenvironment plays a significant role in cancer initiation and propagation, as well as in treatment outcome. We have developed stochastic formulations to study the impact of arbitrary microenvironmental fluctuations on TCP and extinction probability (EP), which is defined as the probability of cancer cells removal in the absence of treatment. Since the derivation of analytical solutions are not possible for complicated cases, we employ a modified Gillespie algorithm to analyze TCP and EP, considering the random variations in cellular proliferation and death rates. Our results show that increasing the standard deviation in kinetic rates initially enhances the probability of tumor eradication. However, if the EP does not reach a probability of 1, the increase in the standard deviation subsequently has a negative impact on probability of cancer cells removal, decreasing the EP over time. The greatest effect on EP has been observed when both birth and death rates are being randomly modified and are anticorrelated. In addition, similar results are observed for TCP, where radiotherapy is included, indicating that increasing the standard deviation in kinetic rates at first enhances the probability of tumor eradication. But, it has a negative impact on treatment effectiveness if the TCP does not reach a probability of 1.

Assessment of robustness of institutional applied clinical target volume (CTV) to planning target volume (PTV) margin in cervical cancer using biological models

The aim of this study is to investigate the robustness of our institutionally applied clinical target volume (CTV)-to-planning target volume (PTV) margins in cervical cancer patients in terms of an equivalent uniform dose (EUD) based on tumor control probability (TCP). We simulated target motion using 25 IMRT cervical cancer plans to demonstrate the effect of geometrical uncertainties on the EUD and TCP. The different components of the total geometrical uncertainties budget were estimated. The biological effects were compared by calculating the EUDs from the trial DVHs. The impact of geometric uncertainties was calculated as a percentage of the difference between 〖EUD〗_static and 〖EUD〗_motion, where the 〖EUD〗_static is the EUD calculated from the target DVHs and 〖EUD〗_motion is averaged, over a 1000 calculated EUDs for each of the analyzed IMRT treatment plans. The multivariate nonlinear regression was used to find the predicted difference between the static and motion EUD. The estimate of the systematic and random motion errors were Σ_(total(SI,LR,AP)) (mm)=(2.6; 2.5; 1.8) and σ_(total(SI,LR,AP)) (mm)=(3.4; 1.4; 3.4). For average 〈EUD〉_motion=44.3 Gy (over 25 patients) we have found a TCP decrease of about 1%, %(ΔTCP)≈1% for predefined PTV margin. According to the calculated EUD motion-distributions, for particular patients, the CTV does receive the prescribed EUD of 45 Gy. The predicted difference in EUD showed that our isotropic margin of 10 mm is large enough to absorb geometric uncertainties and ensure dose coverage of the moving CTV in the cervical cancer patients.

Clinical implication in the use of the AAA algorithm versus the AXB in nasopharyngeal carcinomas by comparison of TCP and NTCP values

Purpose

Retrospective analysis of volumetric modulated arc therapy treatment plans to investigate qualitative, possible, clinical consequences of the use of AAA versus AXB in nasopharyngeal cancer (NPC) cases.

Methods

The dose distribution of 26 treatment plans, produced using RapidArc technique and AAA algorithm, were recalculated using AXB and the same number of monitor units provided by AAA and clinically delivered to each patient. The potential clinical effect of dosimetric differences in the planning target volume (PTV) and in organs at risk (OAR) were evaluated by comparing TCP and NTCP values. The Wilcoxon Signed Rank test was used for statistical comparison of all results obtained from the use of the two algorithms.

Results

The poorer coverage of the PTV, with higher prescribed dose, was reflected in the TCP, which was significantly lower when AXB was used, the median value was 81.55% (range: 74.90, 88.60%) and 84.10% (range: 77.70, 89.90%) for AAA (p < 0.001). OAR mean dose was lower in the AXB recalculated plan than the AAA plan and the difference was statistically significant for all the structures. The NTCP for developing mandible necrosis showed the largest median percentage difference between AAA and AXB (56.6%), the NTCP of risk for larynx edema of Grade ≥ 2 followed with 12.2%.

Conclusions

Differences in dose distribution of NPC treatment plans recalculated with AXB are of clinical significance in those situations where the PTV and OAR involve air or bone, media in which AXB has been shown to more accurately represent the true dose distribution. The availability of AXB algorithm could improve patient dose estimation, increasing the data consistency of clinical trials.

Effect of hypofractionation on the incidental axilla dose during tangential field radiotherapy in breast cancer

Objective

Tangential field irradiation in breast cancer potentially treats residual tumor cells in the axilla after sentinel lymph node biopsy (SLNB). In recent years, hypofractionated radiotherapy has gained importance and currently represents the recommended standard in adjuvant breast cancer treatment for many patients. So far, the impact of hypofractionation on the effect of incidental lymph node irradiation has not be addressed.

Materials and methods

Biological effective dose (BED) and tumor control probability (TCP) were estimated for four different hypofractionated radiation schemes (42.50 Gy in 16 fractions [Fx]; 40.05 Gy in 15 Fx; 27 Gy in 5 Fx; and 26 in 5 Fx) and compared to conventional fractionation (50 Gy in 25 Fx). For calculation of BED and TCP, a previously published radiobiological model with an α/β ratio of 4 Gy was used. The theoretical BED and TCP for incidental irradiation between 0 and 100% of the prescribed dose were evaluated. Subsequently, we assessed BED and TCP in 431 axillary lymph node metastases.

Results

The extent of incidental lymph node irradiation and the fractionation scheme have a direct impact on BED and TCP. The estimated mean TCP in the axillary nodes ranged from 1.5 ± 6.4% to 57.5 ± 22.9%, depending on the patient’s anatomy and the fractionation scheme. Hypofractionation led to a significant reduction of mean TCP of lymph node metastases for all schedules.

Conclusion

Our data indicate that hypofractionation might affect the effectiveness of incidental radiotherapy in the axilla. This is particularly relevant for patients with positive sentinel lymph nodes who receive SLNB only.

Dose-effect response in image-guided adaptive brachytherapy for cervical cancer: A systematic review and meta-regression analysis

PURPOSE

This study aimed to integrate and update the dose-effect relationship between volumetric dose and local control for cervical cancer brachytherapy.

METHODS AND MATERIALS

We identified studies that reported high-risk clinical target volume (HR-CTV) D₉₀ and local control probability by searching PubMed, Web of Science, and the Cochrane Library databases through Oct 27, 2019. The regression analyses were performed using a probit model between HR-CTV D₉₀, D₁₀₀, intermediate-risk clinical target volume (IR-CTV) D₉₀, and dose to Point A vs. local control probability. Subgroup analyses were performed according to stratification: time of local control, income level of the country or region, stage of cancer, pathology, mean volume of HR-CTV, dose rate, image modality, concurrent chemoradiotherapy proportion, interstitial proportion, and mean overall treatment time.

RESULTS

Thirty-three studies encompassing 2893 patients were included. The probit model showed a significant relationship between the HR-CTV D₉₀ value and the local control probability, p < 0.0001. The D₉₀ corresponding to a probability of 90% local control was 83.7 Gy_EQD2,10 (80.6-87.8 Gy_EQD2,10). Of the 33 studies included in our analysis, eight studies, including 1172 patients, reported the IR-CTV D₉₀ value, ranging from 59.1 Gy_EQD2,10 to 72.3 Gy_EQD2,10. The probit model also showed a significant relationship between the IR-CTV D₉₀ value and the local control probability, p = 0.0464. The 60 Gy_EQD2,10 for IR-CTV D₉₀ corresponded to an 86.1% local control probability (82.0%-89.8%).

CONCLUSIONS

A significant dependence of local control on HR-CTV D₉₀ and IR-CTV D₉₀ was found. A tumor control probability of >90% can be expected at doses >84 Gy_EQD2,10 and 69 Gy_EQD2,10, respectively, based on an updated meta-regression analysis.

Clinical Impact of the Bolus in Intensity-Modulated Radiotherapy and Volumetric-Modulated Arc Therapy for Stage I-II Nasal Natural Killer/T-Cell Lymphoma

INTRODUCTION

To estimate the clinical impact of bolus in intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) for stage I-II nasal natural killer/T-cell lymphoma (NNKTCL), including target quality, organs at risk (OARs) sparing, and tumor control probability (TCP).

METHODS

Two different treatment plans were designed in IMRT and VMAT for 10 stage I-II NNKTCL patients. The clinical plans added bolus perfectly contacting the nose skin, similar to common clinical planning design practices. The edited bolus plans resulted from dose recalculation with the edited bolus, which simulated the actual shape of a commercial flat bolus during treatment. All the plans were with no beam passing through the couch avoiding beam attenuation caused by the couch. Differences between both types of plans in target quality, OARs sparing, and TCP were evaluated.

RESULTS

Compared with clinical plans, the D98%, D2%, Dmean, and TCP of edited bolus plans with IMRT slightly decreased (p = 0.002, 0.015, 0.000, and 0.000), the homogeneity index increased 8.33% (p = 0.024), and the doses to a small number of OARs slightly changed. Similar results were obtained for VMAT.

CONCLUSION

The bolus deformation in practical clinical treatment resulted clinically in tiny changes with respect to the target coverage, OARs sparing, and TCP in both IMRT and VMAT for stage I-II NNKTCL. This implied that the clinical impact of the boluscan be negligible when utilizing it to increase the dose to irregularly shaped tumors in the nasal area.

Dose response analysis program (DREAP): A user-friendly program for the analyses of radiation-induced biological responses utilizing established deterministic models at cell population and organ scales

PURPOSE

To develop a user-friendly program for biological modeling to analyze radiation-induced responses at the scales of the cell population and organ.

METHODS

The program offers five established cell population surviving fraction (SF) models to estimate the SF and the relative biological effectiveness (RBE) from clonogenic assay data, and two established models to calculate the normal tissue complication probability (NTCP) and tumor control probability (TCP) from radiation treatment plans. Users can also verify the results with multiple types of quantitative analyses and graphical representation tools.

RESULTS

Users can verify the estimated SF, model parameters, RBE, and the respective uncertainties in the calculations of the SF and RBE modes. The qualities of the treatment plans can also be compared with at most three rival plans in terms of the NTCP, TCP, uncomplicated TCP (UCP), and user-dependent weight-based UCP (UUCP), in the calculation of the NTCP and TCP modes. Based on the validation study on accuracy and speed, the averaged mean relative errors (MREs) of the estimated parameters for all tested cell lines were not higher than 0.3% in each of the studied SF models, and the averaged MREs of the calculated NTCP and TCP for all tested treatment plans were not higher than 0.1%. The computation times for SF, RBE, NTCP, and TCP were less than 1.5 s.

CONCLUSIONS

The dose response analysis program can provide a trustworthy and convenient environment for researchers to analyze radiation-induced biological effects.

RBE-weighted doses in target volumes of chordoma and chondrosarcoma patients treated with carbon ion radiotherapy: Comparison of local effect models I and IV

BACKGROUND AND PURPOSE

To compare the relative biological effectiveness (RBE)-weighted dose distributions in the target volume of chordoma and chondrosarcoma patients when using two different versions of the local effect model (LEM I vs. IV) under identical conditions.

MATERIALS AND METHODS

The patient collective included 59 patients treated with 20 fractions of carbon ion radiotherapy for chordoma and low-grade chondrosarcoma of the skull base at the Helmholtzzentrum für Schwerionenforschung (GSI) in 2002 and 2003. Prescribed doses to the planning target volume (PTV) were 60 (n = 49), 66 (n = 2) and 70 (n = 8) Gy (RBE). The original treatment plans that were initially biologically optimized with LEM I, were now recalculated using LEM IV based on the absorbed dose distributions. The resulting RBE-weighted dose distributions were quantitatively compared to assess the clinical impact of LEM IV relative to LEM I in the target volume.

RESULTS

LEM IV predicts 20-30 Gy (RBE) increased maximum doses as compared to LEM I, while minimum doses are decreased by 2-5 Gy (RBE). Population-based mean and median doses deviated by less than 2 Gy (RBE) between both models.

CONCLUSIONS

LEM I and LEM IV-based RBE-weighted doses in the target volume may be significantly different. Replacing the applied model in patient treatments may therefore lead to local over- or underdosages in the tumor. If LEM IV is to be tested clinically, comparisons of the RBE-weighted dose distributions of both models are required for the individual patients to assess whether the LEM IV-plan would also be acceptable and prescribed dose as well as clinical outcome data have to be carefully reassessed.

Estimation of the α/β ratio of non-small cell lung cancer treated with stereotactic body radiotherapy

BACKGROUND

High-dose hypofractionated radiotherapy should theoretically result in a deviation from the typical linear-quadratic shape of the cell survival curve beyond a certain threshold dose, yet no evidence for this hypothesis has so far been found in clinical data of stereotactic body radiotherapy treatment (SBRT) for early-stage non-small cell lung cancer (NSCLC). A pragmatic explanation is a larger α/β ratio than the conventionally assumed 10 Gy. We here attempted an estimation of the α/β ratio for NSCLC treated with SBRT using individual patient data.

MATERIALS AND METHODS

We combined two large retrospective datasets, yielding 1294 SBRTs (≤10 fractions) of early stage NSCLC. Cox proportional hazards regression, a logistic tumor control probability model and a biologically motivated Bayesian cure rate model were used to estimate the α/β ratio based on the observed number of local recurrences and accounting for tumor size.

RESULTS

A total of 109 local progressions were observed after a median of 17.7 months (range 0.6-76.3 months). Cox regression, logistic regression of 3 year tumor control probability and the cure rate model yielded best-fit estimates of α/β = 12.8 Gy, 14.9 Gy and 12-16 Gy (depending on the prior for α/β), respectively, although with large uncertainties that did not rule out the conventional α/β = 10 Gy.

CONCLUSIONS

Clinicians can continue to use the simple LQ formalism to compare different SBRT treatment schedules for NSCLC. While α/β = 10 Gy is not ruled out by our data, larger values in the range 12-16 Gy are more probable, consistent with recent meta-regression analyses.

Accurate outcome prediction after neo-adjuvant radio-chemotherapy for rectal cancer based on a TCP-based early regression index

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A TCP-based early regression index (ERI_TCP) was previously introduced.

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ERI_TCP was associated to improved survival after neo-adjuvant therapy for rectal cancer.

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Distant-metastasis-free survival was predicted by ERI_TCP and 5-FU dose.

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The resulting AUC (0.86) was significantly higher than models not including T ERI_TCP.

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ERI_TCP is a promising tool for therapy personalization.

Background and purpose

An early tumor regression index (ERI_TCP) was previously introduced and found to predict pathological response after neo-adjuvant radio-chemotherapy of rectal cancer. ERI_TCP was tested as a potential biomarker in predicting long-term disease-free survival.

Materials and methods

Data of 65 patients treated with an early regression-guided adaptive boosting technique (ART) were available. Overall, loco-regional relapse-free and distant metastasis-free survival (OS, LRFS, DMFS) were considered. Patients received 41.4 Gy in 18 fractions (2.3 Gy/fr), including ART concomitant boost on the residual GTV during the last 6 fractions (3 Gy/fr, D_mean: 45.6 Gy). Chemotherapy included oxaliplatin and 5-fluorouracil (5-FU). T2-weighted MRI taken before (MRI_pre) and at half therapy (MRI_half) were available and GTVs were contoured (V_pre, V_half). The parameter ERI_TCP = −ln[(1 − (V_half/V_pre))^Vpre] was calculated for all patients. Cox regression models were assessed considering several clinical and histological variables. Cox models not including/including ERI_TCP (CONV_model and REGR_model respectively) were assessed and their discriminative power compared.

Results

At a median follow-up of 47 months, OS, LRFS and DMFS were 94%, 95% and 78%. Due to too few events, multivariable analyses focused on DMFS: the resulting CONV_model included pathological complete remission or clinical complete remission followed by surgery refusal (HR: 0.15, p = 0.07) and 5-FU dose >90% (HR: 0.29, p = 0.03) as best predictors, with AUC = 0.75. REGR_model included ERI_TCP (HR: 1.019, p < 0.0001) and 5-FU dose >90% (HR: 0.18, p = 0.005); AUC was 0.86, significantly higher than CONV_model (p = 0.05). Stratifying patients according to the best cut-off value for ERI_TCP and to 5-FU dose (> vs <90%) resulted in 47-month DMFS equal to 100%/69%/0% for patients with two/one/zero positive factors respectively (p = 0.0002). ERI_TCP was also the only variable significantly associated to OS (p = 0.01) and LRFS (p = 0.03).

Conclusion

ERI_TCP predicts long-term DMFS after radio-chemotherapy for rectal cancer: an independent impact of the 5-FU dose was also found. This result represents a first step toward application of ERI_TCP in treatment personalization: additional confirmation on independent cohorts is warranted.

Comparison of hyper- and hypofractionated radiation schemes with IMRT technique in small cell lung cancer: Clinical outcomes and the introduction of extended LQ and TCP models

PURPOSE

To evaluate the outcomes of 45 Gy/15 fractions/once-daily and 45 Gy/30 fractions/twice-daily radiation schemes utilizing intensity-modulated radiation therapy (IMRT) in extensive stage small cell lung cancer (SCLC), and to build up a new radiobiological model for tumor control probability (TCP) considering multiple biological effects.

METHODS

Fifty-eight consecutive patients diagnosed with extensive stage SCLC, treated with chemotherapy and chest irradiation, were retrospectively reviewed. Thirty-seven received hyperfractionated IMRT (Hyper-IMRT, 45 Gy/30 fractions/twice-daily) and 21 received hypofractionated IMRT (Hypo-IMRT, 45 Gy/15 fractions/once-daily). Local progression-free survival (LPFS) and overall survival (OS) were calculated and compared. An extended linear-quadratic (LQ) model, LQRG, incorporating cell repair, redistribution, reoxygenation, regrowth and Gompertzian tumor growth was created based on the clinical data. The TCP model was reformulated to predict LPFS. The classical LQ and TCP models were compared with the new models. Akaike information criterion (AIC) was used to assess the quality of the models.

RESULTS

The 2-year LPFS (34.1% vs 27.9%, p = 0.44) and OS (76.9% vs 76.9%, p = 0.26) were similar between Hyper- and Hypo-IMRT patients. According to the LQRG model, the α/β calculated was 9.2 (95% confidence interval: 8.7-9.9) Gy after optimization. The average absolute and relative fitting errors for LPFS were 9.1% and 18.7% for Hyper-IMRT, and 8.8% and 16.2% for Hypo-IMRT of the new TCP model, compared with 29.1% and 62.3% for Hyper-IMRT, and 30.7% and 65.3% for Hypo-IMRT of the classical model.

CONCLUSIONS

Hypo- and Hyper-IMRT resulted in comparable local control in the chest irradiation of extensive stage SCLC. The LQRG model has better performance in predicting the TCP (or LPFS) of the two schemes.

The impact of local control on overall survival after stereotactic body radiotherapy for liver and lung metastases from colorectal cancer: a combined analysis of 388 patients with 500 metastases

BACKGROUND

The aim of this analysis was to model the effect of local control (LC) on overall survival (OS) in patients treated with stereotactic body radiotherapy (SBRT) for liver or lung metastases from colorectal cancer.

METHODS

The analysis is based on pooled data from two retrospective SBRT databases for pulmonary and hepatic metastases from 27 centers from Germany and Switzerland. Only patients with metastases from colorectal cancer were considered to avoid histology as a confounding factor. An illness-death model was employed to model the relationship between LC and OS.

RESULTS

Three hundred eighty-eight patients with 500 metastatic lesions (lung n = 209, liver n = 291) were included and analyzed. Median follow-up time for local recurrence assessment was 12.1 months. Ninety-nine patients with 112 lesions experienced local failure. Seventy-one of these patients died after local failure. Median survival time was 27.9 months in all patients and 25.4 months versus 30.6 months in patients with and without local failure after SBRT. The baseline risk of death after local failure exceeds the baseline risk of death without local failure at 10 months indicating better survival with LC.

CONCLUSION

In CRC patients with lung or liver metastases, our findings suggest improved long-term OS by achieving metastatic disease control using SBRT in patients with a projected OS estimate of > 12 months.

Image-guided radiotherapy reduces the risk of under-dosing high-risk prostate cancer extra-capsular disease and improves biochemical control

BACKGROUND

To determine if reduced dose delivery uncertainty is associated with daily image-guidance (IG) and Prostate Specific Antigen Relapse Free Survival (PRFS) in intensity-modulated radiotherapy (IMRT) of high-risk prostate cancer (PCa).

METHODS

Planning data for consecutive PCa patients treated with IMRT (n = 67) and IG-IMRT (n = 35) was retrieved. Using computer simulations of setup errors, we estimated the patient-specific uncertainty in accumulated treatment dose distributions for the prostate and for posterolateral aspects of the gland that are at highest risk for extra-capsular disease. Multivariate Cox regression for PRFS considering Gleason score, T-stage, pre-treatment PSA, number of elevated clinical risk factors (T2c+, GS7+ and PSA10+), nomogram-predicted risk of extra-capsular disease (ECD), and dose metrics was performed.

RESULTS

For IMRT vs. IG-IMRT, plan dosimetry values were similar, but simulations revealed uncertainty in delivered dose external to the prostate was significantly different, due to positioning uncertainties. A patient-specific interaction term of the risk of ECD and risk of low dose to the ECD (p = 0.005), and the number of elevated clinical risk factors (p = 0.008), correlate with reduced PRFS.

CONCLUSIONS

Improvements in PSA outcomes for high-risk PCa using IG-IMRT vs. IMRT without IG may be due to improved dosimetry for ECD.

An integrated strategy of biological and physical constraints in biological optimization for cervical carcinoma

Background

For cervical carcinoma cases, this study aimed to evaluate the quality of intensity-modulated radiation therapy (IMRT) plans optimized by biological constraints. Furthermore, a new integrated strategy in biological planning module was proposed and verified.

Methods

Twenty patients of advanced stage cervical carcinoma were enrolled in this study. For each patient, dose volume optimization (DVO), biological model optimization (BMO) and integrated strategy optimization (ISO) plans were created using same treatment parameters. Different biological models were also used for organ at risk (OAR) in BMO plans, which include the LKB and Poisson models. Next, BMO plans were compared with their corresponding DVO plans, in order to evaluate BMO plan quality. ISO plans were also compared with DVO and BMO plans, in order to verify the performance of the integrated strategy.

Results

BMO plans produced slightly inhomogeneity and less coverage of planning target volume (PTV) (V95=96.79, HI = 0.10: p < 0.01). However, the tumor control probability (TCP) value, both from DVO and BMO plans, were comparable. For the OARs, BMO plans produced lower normal tissue complication probability (NTCP) of rectum (NTCP = 0.11) and bladder (NTCP = 0.14) than in the corresponding DVO plans (NTCP = 0.19 and 0.18 for rectum and bladder; p < 0.01 for rectum and p = 0.03 for bladder). V95, D98, CI and HI values that were produced by ISO plans (V95 = 98.31, D98 = 54.18Gy, CI = 0.76, HI = 0.09) were greatly better than BMO plans (V95 = 96.79, D98 = 53.42Gy, CI = 0.71, HI = 0.10) with significant differences. Furthermore, ISO plans produced lower NTCP values of rectum (NTCP = 0.14) and bladder (NTCP = 0.16) than DVO plans (NTCP = 0.19 and 0.18 for rectum and bladder, respectively) with significant differences.

Conclusions

BMO plans produced lower NTCP values of OARs compared to DVO plans for cervical carcinoma cases, and resulted in slightly less target coverage and homogeneity. The integrated strategy, proposed in this study, could improve the coverage, conformity and homogeneity of PTV greater than the BMO plans, as well as reduce the NTCP values of OARs greater than the DVO plans.

Radiobiological parameters of liver and lung metastases derived from tumor control data of 3719 metastases

BACKGROUND AND PURPOSE

The radiobiological parameters for liver and lung metastases treated with stereotactic body radiation therapy (SBRT) are poorly defined. This project aimed at estimating these parameters from published tumor control probability (TCP) data, and separately for metastases with colorectal cancer (CRC) and non-CRC histology.

MATERIALS AND METHODS

A total of 62 studies with 89 different treatment prescriptions for a total of 3719 metastases were analyzed in a Bayesian framework using four different radiobiological models: The LQ, mLQ, LQ-L and the regrowth model which accounts for tumor regrowth after SBRT.

RESULTS

Depending on the particular model, α/β ratios in the range 13-23Gy for pulmonary metastases and 16-28Gy for hepatic metastases were estimated. For CRC metastases the estimated α/β ratio was 43.1±4.7Gy compared to 21.6±7.8Gy for non-CRC metastases. Typical isocenter dose prescriptions of 3×12Gy, 3×14.5Gy and 3×17Gy applied within 5days were predicted sufficient to control 90% of lung, liver and CRC metastases after 1yr, respectively.

CONCLUSIONS

α/β ratios for liver and lung metastases are higher than the usually assumed 10Gy. Differences between CRC and non-CRC histology were found. Future studies confirming these findings in individual patient data are needed.

Tumor dose-volume response in image-guided adaptive brachytherapy for cervical cancer: A meta-regression analysis

PURPOSE

Image-guided adaptive brachytherapy is a high precision technique that allows dose escalation and adaptation to tumor response. Two monocentric studies reported continuous dose-volume response relationships, however, burdened by large confidence intervals. The aim was to refine these estimations by performing a meta-regression analysis based on published series.

METHODS AND MATERIALS

Eligibility was limited to series reporting dosimetric parameters according to the Groupe Européen de Curiethérapie-European SocieTy for Radiation Oncology recommendations. The local control rates reported at 2-3 years were confronted to the mean D90 clinical target volume (CTV) in 2-Gy equivalent using the probit model. The impact of each series on the relationships was pondered according to the number of patients reported.

RESULTS

An exhaustive literature search retrieved 13 series reporting on 1299 patients. D90 high-risk CTV ranged from 70.9 to 93.1 Gy. The probit model showed a significant correlation between the D90 and the probability of achieving local control (p < 0.0001). The D90 associated to a 90% probability of achieving local control was 81.4 Gy (78.3-83.8 Gy). The planning aim of 90 Gy corresponded to a 95.0% probability (92.8-96.3%). For the intermediate-risk CTV, less data were available, with 873 patients from eight institutions. Reported mean D90 intermediate-risk CTV ranged from 61.7 to 69.1 Gy. A significant dose-volume effect was observed (p = 0.009). The D90 of 60 Gy was associated to a 79.4% (60.2-86.0%) local control probability.

CONCLUSION

Based on published data from a high number of patients, significant dose-volume effect relationships were confirmed and refined between the D90 of both CTV and the probability of achieving local control. Further studies based on individual data are required to develop nomograms including nondosimetric prognostic criteria.

Under conditions of large geometric miss, tumor control probability can be higher for static gantry intensity-modulated radiation therapy compared to volume-modulated arc therapy for prostate cancer

The purpose of this work was to compare static gantry intensity-modulated radiation therapy (IMRT) with volume-modulated arc therapy (VMAT) in terms of tumor control probability (TCP) under scenarios involving large geometric misses, i.e., those beyond what are accounted for when margin expansion is determined. Using a planning approach typical for these treatments, a linear-quadratic-based model for TCP was used to compare mean TCP values for a population of patients who experiences a geometric miss (i.e., systematic and random shifts of the clinical target volume within the planning target dose distribution). A Monte Carlo approach was used to account for the different biological sensitivities of a population of patients. Interestingly, for errors consisting of coplanar systematic target volume offsets and three-dimensional random offsets, static gantry IMRT appears to offer an advantage over VMAT in that larger shift errors are tolerated for the same mean TCP. For example, under the conditions simulated, erroneous systematic shifts of 15mm directly between or directly into static gantry IMRT fields result in mean TCP values between 96% and 98%, whereas the same errors on VMAT plans result in mean TCP values between 45% and 74%. Random geometric shifts of the target volume were characterized using normal distributions in each Cartesian dimension. When the standard deviations were doubled from those values assumed in the derivation of the treatment margins, our model showed a 7% drop in mean TCP for the static gantry IMRT plans but a 20% drop in TCP for the VMAT plans. Although adding a margin for error to a clinical target volume is perhaps the best approach to account for expected geometric misses, this work suggests that static gantry IMRT may offer a treatment that is more tolerant to geometric miss errors than VMAT.

Early toxicity of hypofractionated radiotherapy for prostate cancer

BACKGROUND

Hypofractionated accelerated radiotherapy (HART) is now a feasible option for prostate cancer treatment apropos toxicity, biochemical control and shortening of treatment. The aim of this study was to investigate hypofractionated schedules in the treatment of patients with localized prostate cancer.

PATIENTS AND METHODS

Between 2011-2014, 158 patients were treated using the RapidArc technique with IGRT. The target volume for low risk patients was the prostate alone with a prescribed dose of 20x3.0 Gy (EQD2=77 Gy). Targets volumes for intermediate and high risk patients were prostate and two thirds of the seminal vesicles with a prescribed dose 21-22x3.0/2.1 Gy (EQD2=81/45.4-84.9/47.5). Based on radiobiological modelling of early toxicity, we used four fractions per week in the low risk group and four fractions in odd weeks and three fractions in even weeks in intermediate and high risk groups. The RTOG/EORTC toxicity scale was used.

RESULTS

Early genitourinary (GU) toxicity was observed for grades 0, 1, 2, 3 and 4 in 73 (46%), 60 (38%), 22 (14%), 0 and 3 (2%), respectively; early gastrointestinal (GI) toxicity was recorded for grades 0, 1, 2 and 3 in 119 (75%), 37 (23%), and 2 (1%) patients, respectively.

CONCLUSION

A combination of moderate hypofractionation, number of fractions per week adapted to target volume and precise dose delivery technique with image guidance appears safe with low early toxicity. Longer follow up is needed to assess late toxicity and tumor control probability.

Local tumor control probability modeling of primary and secondary lung tumors in stereotactic body radiotherapy

BACKGROUND AND PURPOSE

To evaluate whether local tumor control probability (TCP) in stereotactic body radiotherapy (SBRT) varies between lung metastases of different primary cancer sites and between primary non-small cell lung cancer (NSCLC) and secondary lung tumors.

MATERIALS AND METHODS

A retrospective multi-institutional (n=22) database of 399 patients with stage I NSCLC and 397 patients with 525 lung metastases was analyzed. Irradiation doses were converted to biologically effective doses (BED). Logistic regression was used for local tumor control probability (TCP) modeling and the second-order bias corrected Akaike Information Criterion was used for model comparison.

RESULTS

After median follow-up of 19 months and 16 months (n.s.), local tumor control was observed in 87.7% and 86.7% of the primary and secondary lung tumors (n.s.), respectively. A strong dose-response relationship was observed in the primary NSCLC and metastatic cohort but dose-response relationships were not significantly different: the TCD90 (dose to achieve 90% TCP; BED of maximum planning target volume dose) estimates were 176 Gy (151-223) and 160 Gy (123-237) (n.s.), respectively. The dose-response relationship was not influenced by the primary cancer site within the metastatic cohort.

CONCLUSIONS

Dose-response relationships for local tumor control in SBRT were not different between lung metastases of various primary cancer sites and between primary NSCLC and lung metastases.

The effect of age in breast conserving therapy: a retrospective analysis on pathology and clinical outcome data

BACKGROUND AND PROPOSE

Age is an important prognostic marker of patient outcome after breast conserving therapy; however, it is not clear how age affects the outcome. This study aimed to explore the relationship between age with the cell quantity and the radiosensitivity of microscopic disease (MSD) in relation to treatment outcome.

MATERIALS AND METHODS

We employed a treatment simulation framework which contains mathematic models for describing the load and spread of MSD based on a retrospective cohort of breast pathology specimens, a surgery simulation model for estimating the remaining MSD quantity and a tumor control probability model for predicting the risk of local recurrence following radiotherapy.

RESULTS

The average MSD cell quantities around the primary tumor in younger (age⩽50years) and older patients were estimated at 1.9∗10(8)cells and 8.4∗10(7)cells, respectively (P<0.01). Following surgical simulation, these numbers decreased to 2.0∗10(7)cells and 1.3∗10(7)cells (P<0.01). Younger patients had smaller average surgical resection volume (118.9cm(3)) than older patients (162.9cm(3), P<0.01) but larger estimated radiosensitivity of MSD cells (0.111Gy(-1) versus 0.071Gy(-1), P<0.01).

CONCLUSION

The higher local recurrence rate in younger patients could be explained by larger clonogenic microscopic disease cell quantity, even though the microscopic disease cells were found to be more radiosensitive.

Impact of dose calculation algorithm on radiation therapy

The quality of radiation therapy depends on the ability to maximize the tumor control probability while minimize the normal tissue complication probability. Both of these two quantities are directly related to the accuracy of dose distributions calculated by treatment planning systems. The commonly used dose calculation algorithms in the treatment planning systems are reviewed in this work. The accuracy comparisons among these algorithms are illustrated by summarizing the highly cited research papers on this topic. Further, the correlation between the algorithms and tumor control probability/normal tissue complication probability values are manifested by several recent studies from different groups. All the cases demonstrate that dose calculation algorithms play a vital role in radiation therapy.

Radiobiological impact of planning techniques for prostate cancer in terms of tumor control probability and normal tissue complication probability

Background:

The radiobiological models describe the effects of the radiation treatment on cancer and healthy cells, and the radiobiological effects are generally characterized by the tumor control probability (TCP) and normal tissue complication probability (NTCP).

Aim:

The purpose of this study was to assess the radiobiological impact of RapidArc planning techniques for prostate cancer in terms of TCP and normal NTCP.

Subjects and Methods:

A computed tomography data set of ten cases involving low-risk prostate cancer was selected for this retrospective study. For each case, two RapidArc plans were created in Eclipse treatment planning system. The double arc (DA) plan was created using two full arcs and the single arc (SA) plan was created using one full arc. All treatment plans were calculated with anisotropic analytical algorithm. Radiobiological modeling response evaluation was performed by calculating Niemierko's equivalent uniform dose (EUD)-based Tumor TCP and NTCP values.

Results:

For prostate tumor, the average EUD in the SA plans was slightly higher than in the DA plans (78.10 Gy vs. 77.77 Gy; P = 0.01), but the average TCP was comparable (98.3% vs. 98.3%; P = 0.01). In comparison to the DA plans, the SA plans produced higher average EUD to bladder (40.71 Gy vs. 40.46 Gy; P = 0.03) and femoral heads (10.39 Gy vs. 9.40 Gy; P = 0.03), whereas both techniques produced NTCP well below 0.1% for bladder (P = 0.14) and femoral heads (P = 0.26). In contrast, the SA plans produced higher average NTCP compared to the DA plans (2.2% vs. 1.9%; P = 0.01). Furthermore, the EUD to rectum was slightly higher in the SA plans (62.88 Gy vs. 62.22 Gy; P = 0.01).

Conclusion:

The SA and DA techniques produced similar TCP for low-risk prostate cancer. The NTCP for femoral heads and bladder was comparable in the SA and DA plans; however, the SA technique resulted in higher NTCP for rectum in comparison with the DA technique.

A simulation framework for modeling tumor control probability in breast conserving therapy

BACKGROUND AND PURPOSE

Microscopic disease (MSD) left after tumorectomy is a major cause of local recurrence in breast conserving therapy (BCT). However, the effect of microscopic disease and RT dose on tumor control probability (TCP) was seldom studied quantitatively. A simulation framework was therefore constructed to explore the relationship between tumor load, radiation dose and TCP.

MATERIALS AND METHODS

First, we modeled total disease load and microscopic spread with a pathology dataset. Then we estimated the remaining disease load after tumorectomy through surgery simulation. The Webb-Nahum TCP model was extended by clonogenic cell fraction to model the risk of local recurrence. The model parameters were estimated by fitting the simulated results to the observations in two clinical trials.

RESULTS

Higher histopathology grade has a strong correlation with larger MSD cell quantity. On average 12.5% of the MSD cells remained in the patient's breast after surgery but varied considerably among patients (0-100%); illustrating the role of radiotherapy. A small clonogenic cell fraction was optimal in our model (one in every 2.7*10(6)cells). The mean radiosensitivity was estimated at 0.067Gy(-1) with standard deviation of 0.022Gy(-1).

CONCLUSION

A relationship between radiation dose and TCP was established in a newly designed simulation framework with detailed disease load, surgery and radiotherapy models.