H. McNair

Radiotherapy treatment planning of prostate cancer using magnetic resonance imaging alone

PURPOSE Accurate anatomical delineation of the gross tumour volume (GTV) is crucial for effective radiotherapy (RT) treatment of prostate cancers. Although reference to pelvic magnetic resonance (MR) for improved delineation of the prostate is a regular practice in some clinics, MR has not replaced CT due to its geometrical distortions and lack of electron-density information. The possibility and practicality of using MR only for RT treatment planning were studied. MATERIALS AND METHODS The addition of electron-density information to MR images for conformal radiotherapy (CRT) planning of the prostate was quantified by comparing dose distributions created on the homogeneous density- and bulk-density assigned images to original CT for four patients. To quantify the MR geometrical distortions measurements of a phantom imaged in CT (Siemens Somatom Plus 4) and FLASH 3D T1-weighted MR (1.5 T whole body Siemens Magnetom Vision) were compared. Dose statistics from CRT treatment plans made on CT and MR for five patient data were compared to determine if MR-only treatment plans can be made. RESULTS The differences between dose-plans on bulk-density assigned images when compared to CT were less than 2% when water and bone values were assigned. Dose differences greater than 2% were observed when images of homogeneous-density assignment were compared to the CT. Phantom measurements showed that the distortions in the FLASH 3D T1-weighted MR averaged 2 mm in the volume of interest for prostate RT planning. For the CT and MR prostate planning study, doses delivered to the planning target volume (PTV) in CT and MR were always inside a 93-107% dose range normalised to the isocentre. Also, the doses to the organs-at-risk in the MR images were similar to the doses delivered to the volumes in the registered CT image when the organ volumes between the two images were similar. CONCLUSIONS Negligible differences were observed in dose distribution between CRT plans using bone+water CT number bulk-assigned image and original CT. Also, the MR distortions were reduced to negligible amounts using large bandwidth MR sequence for prostate CRT planning. MR treatment planning was demonstrated using a large bandwidth sequence and bulk-assigned images. The development of higher quality, low distortion MR sequence will allow regular practice of this technique.

The European Society of Therapeutic Radiology and Oncology-European Institute of Radiotherapy (ESTRO-EIR) report on 3D CT-based in-room image guidance systems: a practical and technical review and guide.

The past decade has provided many technological advances in radiotherapy. The European Institute of Radiotherapy (EIR) was established by the European Society of Therapeutic Radiology and Oncology (ESTRO) to provide current consensus statement with evidence-based and pragmatic guidelines on topics of practical relevance for radiation oncology. This report focuses primarily on 3D CT-based in-room image guidance (3DCT-IGRT) systems. It will provide an overview and current standing of 3DCT-IGRT systems addressing the rationale, objectives, principles, applications, and process pathways, both clinical and technical for treatment delivery and quality assurance. These are reviewed for four categories of solutions; kV CT and kV CBCT (cone-beam CT) as well as MV CT and MV CBCT. It will also provide a framework and checklist to consider the capability and functionality of these systems as well as the resources needed for implementation. Two different but typical clinical cases (tonsillar and prostate cancer) using 3DCT-IGRT are illustrated with workflow processes via feedback questionnaires from several large clinical centres currently utilizing these systems. The feedback from these clinical centres demonstrates a wide variability based on local practices. This report whilst comprehensive is not exhaustive as this area of development remains a very active field for research and development. However, it should serve as a practical guide and framework for all professional groups within the field, focussed on clinicians, physicists and radiation therapy technologists interested in IGRT.

WEEKLY VOLUME AND DOSIMETRIC CHANGES DURING CHEMORADIOTHERAPY WITH INTENSITY-MODULATED RADIATION THERAPY FOR HEAD AND NECK CANCER: A PROSPECTIVE OBSERVATIONAL STUDY

PURPOSE The aim of this study was to investigate prospectively the weekly volume changes in the target volumes and organs at risk and the resulting dosimetric changes during induction chemotherapy followed by chemoradiotherapy with intensity-modulated radiation therapy (C-IMRT) for head-and-neck cancer patients. METHODS AND MATERIALS Patients receiving C-IMRT for head-and-neck cancer had repeat CT scans at weeks 2, 3, 4, and 5 during radiotherapy. The volume changes of clinical target volume 1 (CTV1) and CTV2 and the resulting dosimetric changes to planning target volume 1 (PTV1) and PTV2 and the organs at risk were measured. RESULTS The most significant volume differences were seen at week 2 for CTV1 and CTV2. The reductions in the volumes of CTV1 and CTV2 at week 2 were 3.2% and 10%, respectively (p = 0.003 and p < 0.001). The volume changes resulted in a significant reduction in the minimum dose to PTV1 and PTV2 (2 Gy, p = 0.002, and 3.9 Gy, p = 0.03, respectively) and an increased dose range across PTV1 and PTV2 (2.5 Gy, p < 0.001, and 5.1 Gy, p = 0.008, respectively). There was a 15% reduction in the parotid volumes by week 2 (p < 0.001) and 31% by week 4 (p < 0.001). There was a statistically significant increase in the mean dose to the ipsilateral parotid only at week 4 (2.7 Gy, p = 0.006). The parotid glands shifted medially by an average of 2.3 mm (p < 0.001) by week 4. CONCLUSION The most significant volumetric changes and dosimetric alterations in the tumor volumes and organs at risk during a course of C-IMRT occur by week 2 of radiotherapy. Further adaptive radiotherapy with replanning, if appropriate, is recommended.

The UK HeartSpare Study: Randomised evaluation of voluntary deep-inspiratory breath-hold in women undergoing breast radiotherapy

PURPOSE To determine whether voluntary deep-inspiratory breath-hold (v_DIBH) and deep-inspiratory breath-hold with the active breathing coordinator™ (ABC_DIBH) in patients undergoing left breast radiotherapy are comparable in terms of normal-tissue sparing, positional reproducibility and feasibility of delivery. METHODS Following surgery for early breast cancer, patients underwent planning-CT scans in v_DIBH and ABC_DIBH. Patients were randomised to receive one technique for fractions 1-7 and the second technique for fractions 8-15 (40 Gy/15 fractions total). Daily electronic portal imaging (EPI) was performed and matched to digitally-reconstructed radiographs. Cone-beam CT (CBCT) images were acquired for 6/15 fractions and matched to planning-CT data. Population systematic (Σ) and random errors (σ) were estimated. Heart, left-anterior-descending coronary artery, and lung doses were calculated. Patient comfort, radiographer satisfaction and scanning/treatment times were recorded. Within-patient comparisons between the two techniques used the paired t-test or Wilcoxon signed-rank test. RESULTS Twenty-three patients were recruited. All completed treatment with both techniques. EPI-derived Σ were ≤ 1.8mm (v_DIBH) and ≤ 2.0mm (ABC_DIBH) and σ ≤ 2.5mm (v_DIBH) and ≤ 2.2mm (ABC_DIBH) (all p non-significant). CBCT-derived Σ were ≤ 3.9 mm (v_DIBH) and ≤ 4.9 mm (ABC_DIBH) and σ ≤ 4.1mm (v_DIBH) and ≤ 3.8mm (ABC_DIBH). There was no significant difference between techniques in terms of normal-tissue doses (all p non-significant). Patients and radiographers preferred v_DIBH (p=0.007, p=0.03, respectively). Scanning/treatment setup times were shorter for v_DIBH (p=0.02, p=0.04, respectively). CONCLUSIONS v_DIBH and ABC_DIBH are comparable in terms of positional reproducibility and normal tissue sparing. v_DIBH is preferred by patients and radiographers, takes less time to deliver, and is cheaper than ABC_DIBH.

Defining the margins in the radical radiotherapy of non-small cell lung cancer (NSCLC) with active breathing control (ABC) and the effect on physical lung parameters

BACKGROUND The effectiveness of ABC has been traditionally measured as the reduction in internal margin (IM) within the planning target volume (PTV). Not to overestimate the benefit of ABC, the effect of patient movement during treatment also needs to be taken into account. We determined the IM and set-up error with ABC and the effect on physical lung parameters compared to standard margins used with free breathing. We also assessed interfraction oesophageal movement to determine a planning organ at risk volume (PRV). MATERIALS AND METHODS Two sequential studies were performed using ABC in NSCLC patients suitable for radical radiotherapy (RT). Twelve out of 14 patients in Study 1 had tumours visible fluoroscopically and had intrafraction tumour movement assessed with and without ABC. Sixteen patients were recruited to Study 2 and had interfraction tumour movement measured using ABC in a moderate deep inspiration breath-hold, of these 7 patients also had interfraction oesophageal movement recorded. Interfraction movement was assessed by CT scan prior to and in the middle and final week of RT. Displacement of the tumour centre of mass and oesophageal borders relative to the first scan provided a measure of movement. Set-up error was measured in 9 patients treated with an in-house lung board adapted for the ABC device. Combining movement and set-up errors determined PTV and PRV margins with ABC. The effect of ABC on mean lung dose (MLD), lung V20 and V13 was calculated. RESULTS ABC in a moderate deep inspiration breath-hold was tolerated in 25 out of 30 patients (83%) in Study 1 and 2. The random contribution of periodic tumour motion was reduced by 90% in the y direction with ABC compared to free-breathing. The magnitude of motion reduction was less in the x and z direction. Combining the systematic and random set-up error in quadrature with the systematic and random intrafraction and interfraction tumour variations with ABC results in a PTV margin of 8.3mm in the x direction, 12.0mm in the y direction and 9.8mm in the z direction. There was a relative mean reduction in MLD, lung V20 and V13 of 25%, 21% and 18% with the ABC PTV compared to a free-breathing PTV. Oesophageal movement combined with set-up error resulted in an isotropic PRV of 4.7 mm. CONCLUSIONS The reduction in PTV size with ABC resulted in an 18-25% relative reduction in physical lung parameters. PTV margin reduction has the potential to spare normal lung and allow dose-escalation if coupled with image-guided RT. The oesophageal PRV needs to be considered when irradiating central disease and is of increasing importance with altered RT fractionation and concomitant chemoradiation schedules. Further reductions in PTV and PRV may be possible if patient set-up error was minimised, confirming that attention to patient immobilisation is as important as attempts to control tumour motion.

Treatment of lung cancer using volumetric modulated arc therapy and image guidance: A case study

Background. Volumetric modulated arc therapy (VMAT) is a radiotherapy technique in which the gantry rotates while the beam is on. Gantry speed, multileaf collimator (MLC) leaf position and dose rate vary continuously during the irradiation. For optimum results, this type of treatment should be subject to image guidance. The application of VMAT and image guidance to the treatment of a lung cancer patient is described. Material and methods. In-house software AutoBeam was developed to facilitate treatment planning for VMAT beams. The algorithm consisted of a fluence optimisation using the iterative least-squares technique, a segmentation and then a direct-aperture optimisation. A dose of 50 Gy in 25 fractions was planned, using a single arc with 35 control points at 10° intervals. The resulting plan was transferred to a commercial treatment planning system for final calculation. The plan was verified using a 0.6cm3 ionisation chamber and film in a rectangular phantom. The patient was treated supine on a customised lung board and imaged daily with cone-beam CT for the first three days then weekly thereafter. Results. The VMAT plan provided slightly improved coverage of the planning target volume (PTV) and slightly lower volume of lung irradiated to 20 Gy (V20) than a three-field conformal plan (PTV minimum dose 85.0 Gy vs. 81.8 Gy and lung V20 31.5% vs. 34.8%). The difference between the measured and planned dose was −1.1% (measured dose lower) and 97.6% of the film passed a gamma test of 3% and 3mm. The VMAT treatment required 90s for delivery of a single fraction of 2 Gy instead of 180s total treatment time for the conformal plan. Conclusion. VMAT provides a quality dose distribution with a short treatment time as shown in an example of a lung tumour. The technique should allow for more efficient delivery of high dose treatments, such as used for hypofractionated radiotherapy of small volume lung tumours, and the technique may also be used in conjunction with Active Breathing Control, where fewer breath holds will be required.

Feasibility of the use of the Active Breathing Co ordinator™ (ABC) in patients receiving radical radiotherapy for non-small cell lung cancer (NSCLC)

INTRODUCTION One method to overcome the problem of lung tumour movement in patients treated with radiotherapy is to restrict tumour motion with an active breathing control (ABC) device. This study evaluated the feasibility of using ABC in patients receiving radical radiotherapy for non-small cell lung cancer. METHODS Eighteen patients, median (range) age of 66 (44-82) years, consented to the study. A training session was conducted to establish the patients breath hold level and breath hold time. Three planning scans were acquired using the ABC device. Reproducibility of breath hold was assessed by comparing lung volumes measured from the planning scans and the volume recorded by ABC. Patients were treated with a 3-field coplanar beam arrangement and treatment time (patient on and off the bed) and number of breath holds recorded. The tolerability of the device was assessed by weekly questionnaire. Quality assurance was performed on the two ABC devices used. RESULTS 17/18 patients completed 32 fractions of radiotherapy using ABC. All patients tolerated a maximum breath hold time >15s. The mean (SD) patient training time was 13.8 (4.8)min and no patient found the ABC very uncomfortable. Six to thirteen breath holds of 10-14 s were required per session. The mean treatment time was 15.8 min (5.8 min). The breath hold volumes were reproducible during treatment and also between the two ABC devices. CONCLUSION The use of ABC in patients receiving radical radiotherapy for NSCLC is feasible. It was not possible to predict a patients ability to hold breath. A minimum tolerated breath hold time of 15 s is recommended prior to commencing treatment.

A randomised study of the use of a customised immobilisation system in the treatment of prostate cancer with conformal radiotherapy

PURPOSE To evaluate the impact of a customized immobilisation system on field placement accuracy, simulation and treatment delivery time, radiographer convenience and patient acceptability. PATIENTS AND METHODS Thirty men receiving radical radiotherapy for prostate cancer were randomised using a cross over trial design to have radiotherapy planning and treatment given either in a conventional treatment position (CTP) or using an immobilisation system (IMS). The randomisation was to have either the CTP or IMS for the initial 3 weeks of radiotherapy after which patients were replanned and changed to the alternative treatment set-up. Treatment accuracy was measured using an electronic portal imaging device. Radiographers and patients completed weekly questionnaires. RESULTS Median simulation time was 22.5 min (range 20-30 min) in the CTP and 25 min (range 15-40 min) for the IMS (P < 0.001). Median treatment time was 9 min for CTP (range 8-10 min), and 10 min (range 8.5-13.5 min) for IMS (P < 0.001). Median isocentre displacement for anterior fields was 1.7 mm from the simulated isocentre for the CTP compared to 2.0 mm for IMS (P = 0.07). For left lateral fields values were 1.8 and 1.8 mm (P = 0.98), and for right lateral fields 2.1 and 1.7 mm (P = 0.06), respectively. No clinically significant reduction in either systematic or random field placement errors was demonstrated. Radiographers reported that patients found the IMS more comfortable than CTP (P < 0.001), but when using the IMS, they noticed greater difficulty in patient positioning (P < 0.001), and alignment to skin tattoos (P < 0.001). CONCLUSIONS Although IMS may have been more comfortable, treatment accuracy was not improved compared to the CTP in our department. In addition, treatment took longer and patient set-up was more difficult.

Improvement in tumour control probability with active breathing control and dose escalation: A modelling study

INTRODUCTION The prognosis from non-small cell lung cancer remains poor, even in those patients suitable for radical radiotherapy. The ability of radiotherapy to achieve local control is hampered by the sensitivity of normal structures to irradiation at the high tumour doses needed. This study aimed to look at the potential gain in tumour control probability from dose escalation facilitated by moderate deep inspiration breath-hold. METHOD The data from 28 patients, recruited into two separate studies were used. These patients underwent planning with and without the use of moderate deep inspiration breath-hold with an active breathing control (ABC) device. Whilst maintaining the mean lung dose (MLD) at the level of the conventional plan, the ABC plan dose was theoretically escalated to a maximum of 84 Gy, constrained by usual normal tissue tolerances. Calculations were performed using data for both lungs and for the ipsilateral lung only. Resulting local progression-free survival at 30 months was calculated using a standard logistic model. RESULTS The prescription dose could be escalated from 64 Gy to a mean of 73.7+/-6.5 Gy without margin reduction, which represents a statistically significant increase in tumour control probability from 0.15+/-0.01 to 0.29+/-0.11 (p<0.0001). The results were not statistically different whether both lungs or just the ipsilateral lung was used for calculations. CONCLUSION A near-doubling of tumour control probability is possible with modest dose escalation, which can be achieved with no extra increase in lung dose if deep inspiration breath-hold techniques are used.

The use of the Active Breathing Coordinator throughout radical non-small-cell lung cancer (NSCLC) radiotherapy.

PURPOSE To assess feasibility and reproducibility of an Active Breathing Coordinator (ABC) used throughout radical radiotherapy for non-small-cell lung cancer, and compare lung dosimetric parameters between free-breathing and ABC plans. METHODS AND MATERIALS A total of 18 patients, recruited into an approved study, had free-breathing and ABC breath-hold treatment plans generated. Lung volume, the percentage volume of lung treated to a dose of ≥20 Gy (V(20)), and mean lung dose (MLD) were compared. Treatment (64 Gy in 32 fractions, 5 days/week) was delivered in breath-hold. Repeat breath-hold computed tomography scans were used to assess change in gross tumor volume (GTV) size and position. Setup error was also measured and potential GTV-planning target volume (PTV) margins calculated. RESULTS Seventeen of 18 patients completed radiotherapy using ABC daily. Intrafraction tumor position was consistent, but interfraction variation had mean (range) values of 5.1 (0-25), 3.6 (0-9.7), and 3.5 (0-16.6) mm in the superoinferior (SI), right-left (RL), and anteroposterior (AP) directions, respectively. Tumor moved partially outside the PTV in 5 patients. Mean reduction in GTV from planning to end of treatment was 25% (p = 0.003). Potentially required PTV margins were 18.1, 11.9, and 11.9 mm in SI, RL, and AP directions. ABC reduced V(20) by 13% (p = 0.0001), V(13) by 12% (p = 0.001), and MLD by 13% (p < 0.001) compared with free-breathing; lung volume increased by 41% (p < 0.001). CONCLUSIONS Clinically significant movements of GTV were seen during radiotherapy for non-small-cell lung cancer using ABC. Image guidance is recommended with ABC. The use of ABC can reduce dose volume parameters determining lung toxicity, and might allow for equitoxic radiotherapy dose escalation.