Evaluating dose coverage and conformity in stereotactic ablative body radiotherapy (SABR) plans.

PURPOSE: Accepted conformity metrics in stereotactic ablative body radiotherapy (SABR) have significant limitations. This work aimed to develop a spatial assessment methodology that improves and automates checks of dose prescription and dose gradient from planning target volume (PTV) edge. METHODS: A Python-based script was developed to determine linear distances from the PTV edge to specified isodose, every 15 degrees on all axial slices and along the central axis in the coronal plane. A new "Internal PTV contour" distance metric is introduced as a size and shape indicator. 134 previously treated SABR patients stratified by anatomical site and PTV volume were analysed to establish baselines and tolerances for automation acceptability. RESULTS: In the axial plane, median distance (MD) from PTV edge to the 100 % isodose was 0.13 mm (range: -0.67 to 0.53 mm), and for the 90 % isodose was 2.37 mm (1.36 to 3.40 mm). Lung and non-Lung dose gradient criteria was established by fitting a second order polynomial to the MD as a function of "Internal PTV contour". This resulted in acceptability criteria of MD + 1 mm for 80 % isodose and MD + 2 mm for the 50 % isodose. For the coronal plane, MD to the 100 % isodose was 0.49 mm (-1.24 to 2.14 mm) and for the 90 % was 1.73 mm (-0.49 to 4.13 mm). CONCLUSIONS: Our in-house script enables a high-quality spatial assessment of PTV dose coverage and gradient, with the new 'Internal PTV contour' distance metric correlating well with dose gradient.

A strategy to reduce fraction number in peripheral lung stereotactic ablative body radiotherapy.

Background and purpose: Hypo-fractionated lung Stereotactic Ablative Body Radiotherapy (SABR) has often been avoided when tumours are close to the chest wall. Our strategic objective was the reduction of fraction number, while maintaining target biological effective dose coverage without increasing chest wall toxicity (CWT) predictors. Materials and methods: Twenty previously treated lung SABR patients were stratified into four cohorts according to distance from PTV to the chest wall, <1 cm, <0.5 cm, overlapping up to 0.5 cm and 1.0 cm. For each patient, four plans were created; a chest wall optimised plan for 54 Gy in 3 fractions, the clinical plan re-prescribed for 55 Gy in 5, 48 Gy in 3 and 45 Gy in 3 fractions. Results: For a PTV distance of 0.5-0.0 cm, a reduction of the median (range) Dmax from 55.7 (57.5-54.1) Gy to 40.0 (37.1-42.0 Gy) Gy was observed for the chest wall optimised plans. The median V30Gy decreased from 18.9 (9.7-25.6) cm3 to 3.1 (1.8-4.5) cm3. For a PTV overlap of up to 0.5 cm, the Dmax reduced from 66.5 (64.1-70) Gy to 53.2 (50.6-55.1) Gy. The V30Gy decreased from 21.5 (16.5-29.5) cm3 to 14.9 (11.3-20.2) cm3. For the cohort with up to 1.0 cm overlap, there was a reduction in Dmax values of 9.9 Gy. The V30Gy for clinical plans, at 66.8 (18.7-188.8) cm3, decreased to 55.3 (15.5-149) cm3. Conclusion: When PTVs are within 0.5 cm of chest wall, lung SABR dose heterogeneity can be used to reduce fraction number without increasing CWT predictors.

The influence of Acuros XB on dose volume histogram metrics and tumour control probability modelling in locally advanced non-small cell lung cancer.

PURPOSE: Radiation therapy plans are assessed using dose volume metrics derived from clinical toxicity and outcome data. In this study, plans for patients with locally advanced non-small cell lung cancer (LA-NSCLC) are examined in the context of the implementation of the Acuros XB (AXB) dose calculation algorithm focussing on the impact on common metrics. METHODS: Volumetric modulated arc therapy (VMAT) plans were generated for twenty patients, using the Analytical Anisotropic Algorithm (AAA) and recalculated with AXB for both dose to water (Dw) and dose to medium (Dm). Standard dose volume histogram (DVH) metrics for both targets and organs-at-risk (OARs) were extracted, in addition to tumour control probability (TCP) for targets. RESULTS: Mean dose to the planning target volume (PTV) was not clinically different between the algorithms (within ±1.1 Gy) but differences were seen in the minimum dose, D99% and D98% as well as for conformity and homogeneity metrics. A difference in TCP was seen for AXBDm plans versus both AXBDw and AAA plans. No clinically relevant differences were seen in the lung metrics. For point doses to spinal cord and oesophagus, the AXBDm values were lower than AXBDw, by up to 1.0 Gy. CONCLUSION: Normalisation of plans to the mean/median dose to the target does not need to be adjusted when moving from AAA to AXB. OAR point doses may decrease by up to 1 Gy with AXBDm, which can be accounted for in clinical planning. Other OAR metrics do not need to be adjusted.

The potential for increased tumor control probability in non-small cell lung cancer with a hypofractionated integrated boost to the gross tumor volume.

Treatment outcomes in locally advanced non-small cell lung cancer (NSCLC) to date have been poor, with normal tissue toxicity often limiting the dose that can be delivered to the tumor. Treatment intensification in NSCLC via targeted dose escalation with modern delivery techniques may offer the potential for a significant increase in tumor control probability (TCP) without a clinically significant increase in organ-at-risk (OAR) toxicity. In this planning study, 20 patients were re-planned with a volumetric modulated arc therapy (VMAT) and an inhomogeneous dose distribution with iteratively escalated doses to the gross tumor volume (iGTV) (composite GTV across multiple 4-dimensional computed tomography [4DCT] phases) in a series of 20 fraction regimes. For each plan OAR doses, target coverage and predicted TCPs were collected and compared with homogenous 3-dimensional (3D) and VMAT plans, as well as with each other. In 70% of patients, it was possible to escalate to 75 Gy in 20 fractions within OAR tolerances, opening the possibility of treating these patients to a biological effective dose (BED) of 103.1 Gy10. This planning study forms the basis of a clinical trial INTENSE (Inhomogeneous Targeted Dose Escalation in Non-Small CEll Lung Cancer), CTRIAL 15-47.

Normal tissue considerations and dose-volume constraints in the moderately hypofractionated treatment of non-small cell lung cancer.

Hypofractionated radiation therapy (RT) regimes in non-small cell lung cancer (NSCLC) have become increasingly popular with a number of international trials currently underway. The majority of the dose-volume-constraints (DVCs) published in the literature refer to conventional 2Gy per fraction deliveries. Here relevant organs-at-risk (OARs) are identified and available dose-volume constraint data discussed and summarised for moderately hypofractionated NSCLC regimes. The OARs examined include lung, brachial plexus, heart, oesophagus, airway and spinal cord. Where available the toxicity rates are also reported with all data summarised tabulated to aid its use in the clinic.

A method for the prediction of late organ-at-risk toxicity after radiotherapy of the prostate using equivalent uniform dose.

PURPOSE: To evaluate the predictive value of equivalent uniform doses (EUD) for late bladder and rectal toxicity after high-dose three-dimensional conformal radiation therapy (3D-CRT) to the prostate. MATERIALS AND METHODS: Using the method developed by Kutcher et al., EUDs for whole bladder and rectum were calculated from the dose-volume histograms of 180 patients with localized prostate cancer treated to 70-74 Gy with 3D-CRT. Late complications were recorded using the Radiation Therapy Oncology Group scale, correlated against EUD and known physical predictive indicators. RESULTS: EUD is an independent prognostic factor for Grade 2+ long-term rectal and bladder toxicity after radiation treatment to the prostate. Patients receiving an EUD >63.1 Gy to the rectum have a statistically significant (10% vs. 30%; p = 0.002) higher risk of developing Grade 2+ late complications. Patients receiving an EUD >53.4 Gy to the bladder have a statistically significant (10% vs. 33%; p = 0.001) higher risk of developing Grade 2+ late complications. CONCLUSIONS: It has been demonstrated that EUD is a strong independent predictive factor for Grade 2+ late complications after 3D-CRT to the prostate. Threshold values have been demonstrated for both bladder and rectum, above which there is a clinically significant increased risk of complications.

Emergency first presentation of colorectal cancer predicts significantly poorer outcomes: a review of 356 consecutive Irish patients.

PURPOSE: Colorectal cancer commonly presents first as an emergency and is likely to be complicated by bowel obstruction/perforation requiring more difficult procedures, with poorer outcomes. Analysis of all of the procedures performed on patients diagnosed in Wexford General Hospital, Ireland, during the period 2000 to 2006 was carried out to validate this hypothesis in our western European population. METHODS: Retrospective analysis of a prospectively maintained database of patient demographics, diagnosis, procedures, and mode of presentation (elective, emergency) was undertaken. RESULTS: A total of 356 patients with colorectal cancer underwent 498 procedures during the years 2000 to 2006. Eighty-four emergency endoscopies and 100 emergency bowel resections were performed. Obstructive lesions were more likely to require emergency resection (P < 0.001). Median survival time for patients treated electively was 82 months vs. 59 months for patients treated on an emergency basis. CONCLUSIONS: Of all colonic resections, 34 percent were carried out as emergencies and were significantly more likely to be complicated by obstruction or perforation (P < 0.001). Emergency resections were associated with a significantly poorer perioperative mortality and five-year survival rate (P < 0.001). Forty-one percent of colorectal cancers diagnosed at endoscopy were first seen emergently. These data raise concerns regarding public awareness of colorectal cancer and resource allocation and reemphasize the need for a national colorectal screening program.