A dosimetric analysis of respiration-gated radiotherapy in patients with stage III lung cancer (original) (raw)
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Asia-Pacific Journal of Clinical Oncology, 2013
Aim: Despite advances in radiotherapy delivery, the prognosis of lung cancer remains poor. Higher doses of radiation have been associated with improved outcomes but may result in higher toxicities. Respiratory gated radiotherapy (RGRT) has the potential to reduce pulmonary toxicity but there are significant limitations and pitfalls to its use. The aim of this article is to (i) describe the RGRT technique currently employed at Nepean and Westmead Hospitals; (ii) discuss the practical issues of implementing such a program; (iii) present the results of our RGRT program and (iv) review the potential uncertainties in using this technique and the methods we have used to overcome these. Methods: A retrospective review of all patients who had a 4D-computed tomography (4D-CT) scan was undertaken. Records from treatment planning systems were used to assess the prospective gating program. Results: Between September 2007 and June 2011, 53 patients at Nepean and 26 patients at Westmead Hospital underwent a 4D-CT. Between April and August 2011, 26 patients at Westmead Hospital underwent a prospective 4D-CT scan as treatment verification. Two of the 26 patients (7.7%) were found to have incomplete coverage of the planning target volume. Both patients underwent respiratory re-coaching, alleviating the need for replanning. Conclusion: RGRT may reduce doses to organs at risk with the potential for dose escalation. However its implementation requires significant staff training, treatment time and resources. Treatment verification with image guided radiation therapy are essential for safe delivery.
The Effect of Respiratory on Dose Distributions in Radiotherapy of Lung Cancer: A Phantom Study
2016
Abstract: Internal organ motions are one of the most significant obstacles for radiotherapy, especially in the case of motions caused by respiratory during the lung irradiation. There is no any consensus about the margin limit given for the target volume (Clinical Target Volume-CTV, Planning Target Volume- PTV etc.), especially for tumors located moving organs such as lung. Besides, as far as we know, there is no any systematic phantom study showed the effects of respiratory motions on radiotherapy doses depending on PTV margins in the literature. In present study, our aim was to determine the success degree of enlarging the PTV margins on radiotherapy doses during the moving organ irradiations. The study was performed by using GaF-Chromic EBT films placed to a thorax phantom. A cylindrical part within the phantom can move on through craniocaudal direction with a range of 3 cm with 5 sec. period during the irradiation. From the profiles which were obtained from 3 cm moving situation...
Analysis of reproducibility of respiration-triggered gated radiotherapy for lung tumors
Radiotherapy and Oncology, 2008
Purpose: Respiration-gated radiotherapy (RGRT) can decrease the toxicity of chemo-radiotherapy (CT-RT) by allowing use of smaller treatment fields. RGRT requires a predictable relationship between tumor position and external surrogate, which must be verified during treatment. Time-integrated electronic portal imaging (TI-EPI) identifies mean intrafractional positions of moving structures, and was used to study reproducibility of anatomy during RGRT for lung tumors. Materials and methods: TI-EPIs were acquired using an amorphous silicon-based electronic portal imaging system (EPID, aS500) in continuous image acquisition mode in 11 patients treated with audio-coached RGRT at end-inspiration. The Varian Real-time Position Management (RPM) system was used for 4DCT imaging and RGRT delivery. All TI-EPI portals were co-registered to corresponding digitally reconstructed radiographs (DRR) of the planning 4DCT using the spinal column. Displacements in tumor position or that of an adjacent bronchus during RGRT was measured relative to the reference structure on the DRR. Results: Vertebra-matched portals revealed systematic (P) and random (r) errors of 1.8 and 1.3 mm in medial-lateral direction and 1.7 and 1.7 mm in cranial-caudal direction, indicating a reproducible tumor/bronchus position during the RPM-triggered gates. Conclusions: RGRT delivery at end-inspiration can achieve reproducible internal anatomy in 'gated' fields delivered with audio-coaching.
Radiotherapy and Oncology, 2010
Background: There is a great deal of excitement regarding respiratory gated radiotherapy (RGRT), however there remain potential errors and controversies surrounding its use. We aim to predict an improvement in the clinical outcome of RGRT in comparison with that of continuous (non-gated) irradiation by analysing toxicity parameters. Materials and methods: The 4DCT scans of 15 patients, with node-positive lung cancer and >5 mm of tumour movement, were used for this retrospective analysis. End-inspiration and end-expiration plans were created and the toxicity parameters were compared to continuous (non-gated) 4DCT plans. Results: Median reduction in V20 with inspiratory gating and expiratory gating, using a 10 mm set-up margin, was 2.0% (range 0.7% to 3.9%) and 0.6% (range À1.1% to 4.7%), respectively. The reduction in MLD was 2.1 Gy (range 0.6 to 3.9 Gy) and 1.6 Gy (range À1.0 to 3.9 Gy), respectively. Conclusions: Although there is a widespread excitement regarding this technique, this study demonstrates that there is limited reduction in toxicity parameters with the use of RGRT in comparison with continuous (non-gated) 4DCT irradiation. Due to the additional potential errors involved in RGRT, we feel that currently, it should only be performed if comparative planning of RGRT plans and continuous (nongated) 4DCT plans has been undertaken and a likely clinical benefit has been confirmed.
International Journal of Radiation Oncology*Biology*Physics, 2012
This study quantified the treatment field margins needed for various motion management strategies including 4DCT, respirationcorrelated image guidance, and beam gating, in the treatment of lung cancer. AAPM task group report 76, recommends that respiratory compensation should be considered during beam delivery for tumor motion above 5 mm. This study contests this recommended threshold, and presents Purpose: The purpose of this study was to quantify the effects of four-dimensional computed tomography (4DCT), 4D image guidance (4D-IG), and beam gating on calculated treatment field margins in a lung cancer patient population. Materials and Methods: Images were acquired from 46 lung cancer patients participating in four separate protocols at three institutions in Europe and the United States. Seven patients were imaged using fluoroscopy, and 39 patients were imaged using 4DCT.
Acta Oncologica, 2013
Background. the survival rates for patients with non-small cell lung cancer (NSCLC) may be improved by dose escalation; however, margin reduction may be required in order to keep the toxicity at an acceptable level. in this study we have investigated the dosimetric impact of tumor motion and anatomical changes during intensity-modulated radiotherapy (iMrt) of patients with NSCLC. Material and methods. Sixteen NSCLC patients received iMrt with concomitant chemotherapy. the tumor and lymph node targets were delineated in the mid-ventilation phase of a planning 4DCt scan (Ct1). typically 66 gy was delivered in 33 fractions using daily CBCt with bony anatomy match for patient setup. the daily baseline shifts of the mean tumor position relative to the spine were extracted from the CBCt scans. A second 4DCt scan (Ct2) was acquired halfway through the treatment course and the respiratory tumor motion was extracted. the plan was recalculated on Ct2 with and without inclusion of the respiratory tumor motion and baseline shifts in order to investigate the impact of tumor motion and anatomical changes on the tumor dose. Results. respiratory tumor motion was largest in the cranio-caudal (CC) direction (range 0-13.1 mm). tumor baseline shifts up to 18 mm (CC direction) and 24 mm (left-right and anterior-posterior) were observed. the average absolute difference in CtV mean dose to the primary tumor (CtV-t) between Ct1 and Ct2 was 1.28% (range 0.1-4.0%) without motion. respiratory motion and baseline shifts lead to average absolute CtV-t mean dose changes of 0.46% (0-1.9%) and 0.65% (0.0-2.1%), respectively. For most patients, the changes in the CtV-t dose were caused by anatomical changes rather than internal target motion. Conclusion. Anatomical changes had larger impact on the target dose distribution than internal target motion. Adaptive radiotherapy could be used to achieve better target coverage throughout the treatment course.
Acta Oncologica
Introduction: Minimizing the planning target volume (PTV) while ensuring sufficient target coverage during the entire respiratory cycle is essential for free-breathing radiotherapy of lung cancer. Different methods are used to incorporate the respiratory motion into the PTV. Material and methods: Fifteen patients were analyzed. Respiration can be included in the target delineation process creating a respiratory GTV, denoted iGTV. Alternatively, the respiratory amplitude (A) can be measured based on the 4D-CT and A can be incorporated in the margin expansion. The GTV expanded by A yielded GTV þ resp, which was compared to iGTV in terms of overlap. Three methods for PTV generation were compared. PTV del (delineated iGTV expanded to CTV plus PTV margin), PTV r (GTV expanded to CTV and A was included as a random uncertainty in the CTV to PTV margin) and PTV P (GTV expanded to CTV, succeeded by CTV linear expansion by A to CTV þ resp, which was finally expanded to PTV P). Results: Deformation of tumor and lymph nodes during respiration resulted in volume changes between the respiratory phases. The overlap between iGTV and GTV þ resp showed that on average 7% of iGTV was outside the GTV þ resp implying that GTV þ resp did not capture the tumor during the full deformable respiration cycle. A comparison of the PTV volumes showed that PTV r was smallest and PTV R largest for all patients. PTV r was in mean 14% (31 cm 3) smaller than PTV del , while PTV del was 7% (20 cm 3) smaller than PTV R. Conclusions: PTV r yields the smallest volumes but does not ensure coverage of tumor during the full respiratory motion due to tumor deformation. Incorporating the respiratory motion in the delineation (PTV del) takes into account the entire respiratory cycle including deformation, but at the cost, however, of larger treatment volumes. PTV R should not be used, since it incorporates the disadvantages of both PTV del and PTV r .