Todd McNutt

Patient geometry-driven information retrieval for IMRT treatment plan quality control.

PURPOSEnIntensity modulated radiation therapy (IMRT) treatment plan quality depends on the planners level of experience and the amount of time the planner invests in developing the plan. Planners often unwittingly accept plans when further sparing of the organs at risk (OARs) is possible. The authors propose a method of IMRT treatment plan quality control that helps planners to evaluate the doses of the OARs upon completion of a new plan.nnnMETHODSnIt is achieved by comparing the geometric configurations of the OARs and targets of a new patient with those of prior patients, whose plans are maintained in a database. They introduce the concept of a shape relationship descriptor and, specifically, the overlap volume histogram (OVH) to describe the spatial configuration of an OAR with respect to a target. The OVH provides a way to infer the likely DVHs of the OARs by comparing the relative spatial configurations between patients. A database of prior patients is built to serve as an external reference. At the conclusion of a new plan, planners search through the database and identify related patients by comparing the OAR-target geometric relationships of the new patient with those of prior patients. The treatment plans of these related patients are retrieved from the database and guide planners in determining whether lower doses delivered to the OARs in the new plan are feasible.nnnRESULTSnPreliminary evaluation is promising. In this evaluation, they applied the analysis to the parotid DVHs of 32 prior head-and-neck patients, whose plans are maintained in a database. Each parotid was queried against the other 63 parotids to determine whether a lower dose was possible. The 17 parotids that promised the greatest reduction in D50 (DVH dose at 50% volume) were flagged. These 17 parotids came from 13 patients. The method also indicated that the doses of the other nine parotids of the 13 patients could not be reduced, so they were included in the replanning process as controls. Replanning with an effort to reduce D50 was conducted on these 26 parotids. After replanning, the average reductions for D50 of the 17 flagged parotids and nine unflagged parotids were 6.6 and 1.9 Gy, respectively. These results demonstrate that the quality control method has accurately identified not only the parotids that require dose reductions but also those for which dose reductions are marginal. Originally, 11 of out the 17 flagged parotids did not meet the Radiation Therapy Oncology Group sparing goal of V(30 Gy) < 50%. Replanning reduced them to three. Additionally, PTV coverage and OAR sparing of the original plans were compared to those of the replans by using pairwise Wilcoxon p test. The statistical comparisons show that replanning compromised neither PTV coverage nor OAR sparing.nnnCONCLUSIONSnThis method provides an effective quality control mechanism for evaluating the DVHs of the OARs. Adoption of such a method will advance the quality of current IMRT planning, providing better treatment plan consistency.

DATA-DRIVEN APPROACH TO GENERATING ACHIEVABLE DOSE-VOLUME HISTOGRAM OBJECTIVES IN INTENSITY-MODULATED RADIOTHERAPY PLANNING

PURPOSEnTo propose a method of intensity-modulated radiotherapy (IMRT) planning that generates achievable dose-volume histogram (DVH) objectives using a database containing geometric and dosimetric information of previous patients.nnnMETHODS AND MATERIALSnThe overlap volume histogram (OVH) is used to compare the spatial relationships between the organs at risk and targets of a new patient with those of previous patients in a database. From the OVH analysis, the DVH objectives of the new patient were generated from the database and used as the initial planning goals. In a retrospective OVH-assisted planning demonstration, 15 patients were randomly selected from a database containing clinical plans (CPs) of 91 previous head-and-neck patients treated by a three-level IMRT-simultaneous integrated boost technique. OVH-assisted plans (OPs) were planned in a leave-one-out manner by a planner who had no knowledge of CPs. Thus, DVH objectives of an OP were generated from a subdatabase containing the information of the other 90 patients. Those DVH objectives were then used as the initial planning goals in IMRT optimization. Planning efficiency was evaluated by the number of clicks of the Start Optimization button in the course of planning. Although the Pinnacle(3) treatment planning system allows planners to interactively adjust the DVH parameters during optimization, planners in our institution have never used this function in planning.nnnRESULTSnThe average clicks required for completing the CP and OP was 27.6 and 1.9, respectively (p <.00001); three OPs were finished within a single click. Ten more patients cord + 4 mm reached the sparing goal D(0.1cc) <44 Gy (pxa0<.0001), where D(0.1cc) represents the dose corresponding to 0.1 cc. For planning target volume uniformity, conformity, and other organ at risk sparing, the OPs were at least comparable with the CPs. Additionally, the averages of D(0.1cc) to the cord + 4 mm decreased by 6.9 Gy (p <.0001); averages of D(0.1cc) to the brainstem decreased by 7.7 Gy (p <.005). The averages of V(30 Gy) to the contralateral parotid decreased by 8.7% (p <.0001), where V(30 Gy) represents the percentage volume corresponding to 30 Gy.nnnCONCLUSIONnThe method heralds the possibility of automated IMRT planning.

Increased organ sparing using shape-based treatment plan optimization for intensity modulated radiation therapy of pancreatic adenocarcinoma

PURPOSEnTo develop a model to assess the quality of an IMRT treatment plan using data of prior patients with pancreatic adenocarcinoma.nnnMETHODSnThe dose to an organ at risk (OAR) depends in large part on its orientation and distance to the planning target volume (PTV). A database of 33 previously treated patients with pancreatic cancer was queried to find patients with less favorable PTV-OAR configuration than a new case. The minimal achieved dose among the selected patients should also be achievable for the OAR of the new case. This way the achievable doses to the OARs of 25 randomly selected pancreas cancer patients were predicted. The patients were replanned to verify if the predicted dose could be achieved. The new plans were compared to their original clinical plans.nnnRESULTSnThe predicted doses were achieved within 1 and 2 Gy for more than 82% and 94% of the patients, respectively, and were a good approximation of the minimal achievable doses. The improvement after replanning was 1.4 Gy (range 0-4.6 Gy) and 1.7 Gy (range 0-6.3 Gy) for the mean dose to the liver and the kidneys, respectively, without compromising target coverage or increasing radiation dose to the bowel, cord or stomach.nnnCONCLUSIONSnThe model could accurately predict the achievable doses, leading to a considerable decrease in dose to the OARs and an increase in treatment planning efficiency.

Fully Automated Simultaneous Integrated Boosted–Intensity Modulated Radiation Therapy Treatment Planning Is Feasible for Head-and-Neck Cancer: A Prospective Clinical Study

PURPOSEnTo prospectively determine whether overlap volume histogram (OVH)-driven, automated simultaneous integrated boosted (SIB)-intensity-modulated radiation therapy (IMRT) treatment planning for head-and-neck cancer can be implemented in clinics.nnnMETHODS AND MATERIALSnA prospective study was designed to compare fully automated plans (APs) created by an OVH-driven, automated planning application with clinical plans (CPs) created by dosimetrists in a 3-dose-level (70 Gy, 63 Gy, and 58.1 Gy), head-and-neck SIB-IMRT planning. Because primary organ sparing (cord, brain, brainstem, mandible, and optic nerve/chiasm) always received the highest priority in clinical planning, the study aimed to show the noninferiority of APs with respect to PTV coverage and secondary organ sparing (parotid, brachial plexus, esophagus, larynx, inner ear, and oral mucosa). The sample size was determined a priori by a superiority hypothesis test that had 85% power to detect a 4% dose decrease in secondary organ sparing with a 2-sided alpha level of 0.05. A generalized estimating equation (GEE) regression model was used for statistical comparison.nnnRESULTSnForty consecutive patients were accrued from July to December 2010. GEE analysis indicated that in APs, overall average dose to the secondary organs was reduced by 1.16 (95% CI = 0.09-2.33) with P=.04, overall average PTV coverage was increased by 0.26% (95% CI = 0.06-0.47) with P=.02 and overall average dose to the primary organs was reduced by 1.14 Gy (95% CI = 0.45-1.8) with P=.004. A physician determined that all APs could be delivered to patients, and APs were clinically superior in 27 of 40 cases.nnnCONCLUSIONSnThe application can be implemented in clinics as a fast, reliable, and consistent way of generating plans that need only minor adjustments to meet specific clinical needs.

Using overlap volume histogram and IMRT plan data to guide and automate VMAT planning: A head‐and‐neck case study

PURPOSEnTo investigate whether an overlap volume histogram (OVH)-driven planning application using an intensity-modulated radiation therapy (IMRT) database can guide and automate volumetric-modulated arc therapy (VMAT) planning for head-and-neck cancer.nnnMETHODSnBased on comparable head-and-neck dosimetric results between planner-generated VMAT and IMRT plans, an inhouse developed, OVH-driven automated planning application containing a database of prior clinical head-and-neck IMRT plans is built into Pinnacle(3) SmartArc for VMAT planning. Double-arc VMAT plans of four oropharynx, four nasopharynx, and four larynx patients are generated and compared with corresponding clinical IMRT plans.nnnRESULTSnEach VMAT plan is automatically generated in two optimization rounds, while the average number of optimization rounds in generating a clinical IMRT plan is 43. In VMAT plans, statistical superiority (p < 0.01) in sparing of the cord+4 mm, brainstem, brachial plexus, larynx, and inner ear is observed with a slight degradation in low-dose-level planning target volume (PTV) coverage. On average, D(0.1 cc) to the cord+4 mm, brainstem and brachial plexus is reduced by 3.7, 4.9, and 1.6 Gy, respectively; V(50 Gy) to the larynx is reduced by 5.3%; mean dose to the inner ear is reduced by 4.4 Gy; V(95) of low-dose-level PTV coverage is reduced by 0.3% with p = 0.25.nnnCONCLUSIONSnIMRT-data-driven VMAT planning offers a potential method for generating VMAT plans that are comparable to IMRT plans in terms of dosimetric quality.

An overlap-volume-histogram based method for rectal dose prediction and automated treatment planning in the external beam prostate radiotherapy following hydrogel injection

PURPOSEnHydrogel injected between the rectum and prostate prior to radiotherapy provides a possible means of increased dose sparing to the rectum. Here the authors evaluate the overlap volume histogram (OVH) metric as a means to predict the rectal dose following hydrogel injection. Whether OVH predicted dose can serve as the dose objective or constraint for automated treatment planning was also investigated.nnnMETHODSnTreatment planning was performed on 21 prostate cancer patients both pre- and posthydrogel injection, with five-field IMRT delivering 78 Gy to the planning target volume (PTV). The authors quantify the geometrical relationship between the rectum and the prostate PTV using an OVH metric which determines the fractional volume of the rectum that is within a specified distance of the PTV. For an OVH distance the authors selected, L(20), the PTV expansion distance at which 20% of the rectum overlaps. The authors calculated the rectal dose, D(20), received by 20% of the rectum volume on the dose volume histogram. Linear regression was used to examine the correlation between the L(20) and D(20), and between ΔL(20) and ΔD(20) (i.e., the change of L(20) and D(20) posthydrogel injection). Additionally, rectal dose D(15), D(25), D(35), D(50), and bladder dose D(15) were predicted from the OVH (L(15), L(25), L(35), L(50), for rectum and L(15) for bladder) by the L(x)-D(x) linear regression. The predicted doses were applied to the objectives for automated treatment planning of ten plans from five patients. Automatically generated plans were compared with plans manually generated on trial-and-error basis.nnnRESULTSnThe rectal L(20) was increased and dose D(20) decreased due to the enlarged separation of rectum caused by the hydrogel injection. Linear regression showed an inverse linear correlation between L(20) and D(20), and between ΔL(20) and ΔD(20) (r(2) = 0.77, 0.60, respectively; p < 0.0001). The increase in rectal sparing (ΔD(20)) is only weakly correlated with the volume of injected hydrogel (r(2) = 0.17; p = 0.07), indicating OVH is a more predictive indicator of rectal sparing than the volume of hydrogel itself. Application of the predicted rectum and bladder doses to automated planning produced acceptable treatment plans, with rectal dose reduced for eight of ten plans.nnnCONCLUSIONSnThe OVH metric can predict the rectal dose in the external beam prostate radiotherapy for patients with hydrogel injection. The predicted doses can be applied to the objectives of optimization in automated treatment planning to produce acceptable treatment plans.

Radiation dose to the floor of mouth muscles predicts swallowing complications following chemoradiation in oropharyngeal squamous cell carcinoma

OBJECTIVESnWhile radiation dose to the larynx and pharyngeal constrictors has been the focus of swallowing complications, the suprahyoid muscles, or floor of mouth (FoM) muscles, are critical for hyoid and laryngeal elevation and effective bolus diversion, preventing penetration and aspiration. We hypothesize that radiation dose to these muscles may be important in the development of dysphagia.nnnMATERIALS AND METHODSnWe studied 46 patients with OPSCC treated with CRT and who underwent baseline swallowing evaluations and post-treatment videofluoroscopic swallowing studies (VFSS) from 2007 to 2010. Patients with abnormal penetration aspiration scores (PAS>2) served as the study population and patients with normal PAS scores (≤ 2) served as the control cohort. Three suprahyoid muscles and two extrinsic tongue muscles were individually delineated and collectively referred to as the FoM muscles. Radiation dose-volume relationships for these muscles were calculated. Univariate logistic regression analysis was used to determine parameters of significance between patients with normal or abnormal PAS scores. A multivariate regression analysis was subsequently performed to isolate the most statistically critical structures associated with abnormal PAS.nnnRESULTSnUnivariate analysis resulted in significance/borderline significance of multiple structures associated with abnormal PAS following irradiation. However, when a multivariate model was applied, only the mean dose to the floor of mouth and minimum dose to the geniohyoid were associated with post-radiation abnormal PAS.nnnCONCLUSIONSnThe dose and volume delivered to the collective FoM muscles may be associated with an increased risk of laryngeal penetration/aspiration to a greater degree than previously recognized organs at risk.

Vision 20/20: Automation and advanced computing in clinical radiation oncology

This Vision 20/20 paper considers what computational advances are likely to be implemented in clinical radiation oncology in the coming years and how the adoption of these changes might alter the practice of radiotherapy. Four main areas of likely advancement are explored: cloud computing, aggregate data analyses, parallel computation, and automation. As these developments promise both new opportunities and new risks to clinicians and patients alike, the potential benefits are weighed against the hazards associated with each advance, with special considerations regarding patient safety under new computational platforms and methodologies. While the concerns of patient safety are legitimate, the authors contend that progress toward next-generation clinical informatics systems will bring about extremely valuable developments in quality improvement initiatives, clinical efficiency, outcomes analyses, data sharing, and adaptive radiotherapy.

Improved robotic stereotactic body radiation therapy plan quality and planning efficacy for organ-confined prostate cancer utilizing overlap-volume histogram-driven planning methodology.

BACKGROUND AND PURPOSEnThis study is to determine if the overlap-volume histogram (OVH)-driven planning methodology can be adapted to robotic SBRT (CyberKnife Robotic Radiosurgery System) to further minimize the bladder and rectal doses achieved in plans manually-created by clinical planners.nnnMETHODS AND MATERIALSnA database containing clinically-delivered, robotic SBRT plans (7.25 Gy/fraction in 36.25 Gy) of 425 patients with localized prostate cancer was used as a cohort to establish an organs distance-to-dose model. The OVH-driven planning methodology was refined by adding the PTV volume factor to counter the targets dose fall-off effect and incorporated into Multiplan to automate SBRT planning. For validation, automated plans (APs) for 12 new patients were generated, and their achieved dose/volume values were compared to the corresponding manually-created, clinically-delivered plans (CPs). A two-sided, Wilcoxon rank-sum test was used for statistical comparison with a significance level of p<0.05.nnnRESULTSnPTVs V(36.25 Gy) was comparable: 95.6% in CPs comparing to 95.1% in APs (p=0.2). On average, the refined approach lowered V(18.12 Gy) to the bladder and rectum by 8.2% (p<0.05) and 6.4% (p=0.14). A physician confirmed APs were clinically acceptable.nnnCONCLUSIONSnThe improvements in APs could further reduce toxicities observed in SBRT for organ-confined prostate cancer.

Effect of gabapentin on swallowing during and after chemoradiation for oropharyngeal squamous cell cancer

The aim of this study was to examine the impact of gabapentin (neurontin) on swallowing and feeding tube use during chemoradiation (CRT) for oropharyngeal squamous cell carcinoma (OPSCC), and physiologic swallowing outcomes following completion of treatment. A total of 23 patients treated for OPSCC with concurrent CRT and prophylactically treated for pain using gabapentin were assessed. Historical controls were matched for T stage and primary site of disease. Timing of PEG use and removal were recorded. Video fluoroscopic swallowing studies were completed post-treatment to assess physiologic outcomes as well as penetration–aspiration scores (PAS). Functional oral intake scale (FOIS) scores were determined at the time of swallowing evaluation to assess diet level. Patients treated with gabapentin began using their PEG tubes later (3.7 vs. 2.29xa0weeks; Pxa0=xa00.013) and had their PEG tubes removed earlier (7.29 vs. 32.56xa0weeks; Pxa0=xa00.039) than the historical controls. A number of physiologic parameters were found to be less impacted in the gabapentin group, including oral bolus control (Pxa0=xa00.01), epiglottic tilt (Pxa0=xa00.0007), laryngeal elevation (Pxa0=xa00.0017), and pharyngeal constriction (Pxa0=xa00.002). PAS scores were significantly lower in the group treated with gabapentin (1.89 vs. 4; Pxa0=xa00.0052). Patients receiving gabapentin had more advanced diet levels at the time of the initial swallowing study as evidenced by their FOIS scores (5.4 vs. 3.21; Pxa0=xa00.0003). We conclude that patients using gabapentin for pain management during CRT appears to do well maintaining swallow function during treatment and have favorable post-treatment physiologic swallowing outcomes. Prospective evaluation is warranted.