Bernt Louni Rekstad

Reirradiation of locally recurrent rectal cancer: A systematic review

BACKGROUND Many patients with rectal cancer receive radiotherapy as a component of primary multimodality treatment. Although local recurrence is infrequent, reirradiation may be needed to improve resectability and outcomes. This systematic review investigated the effects of reirradiation in terms of feasibility, toxicity, and long-term outcomes. METHODS A Medline, Embase and Cochrane search resulted in 353 titles/abstracts. Ten publications describing seven prospective or retrospective studies were included, presenting results of 375 patients reirradiated for rectal cancer. RESULTS Median initial radiation dose was 50.4Gy, median 8-30months before reirradiation. Reirradiation was mostly administered using hyperfractionated (1.2-1.5Gy twice-daily) or 1.8Gy once-daily chemoradiotherapy. Median total dose was 30-40Gy to the gross tumour volume with 2-4cm margins. Median survival was 39-60months in resected patients and 12-16months in palliative patients. Good symptomatic relief was reported in 82-100%. Acute toxicity with diarrhoea was reported in 9-20%, late toxicity was insufficiently reported. CONCLUSIONS Reirradiation of rectal cancer to limited volumes is feasible. When curative resection is possible, the goal is radical resection and long-term survival, and hyperfractionated chemoradiotherapy should be preferred to limit late toxicity. Reirradiation yielded good symptomatic relief in palliative treatment.

Dose painting by numbers in a standard treatment planning system using inverted dose prescription maps

ABSTRACT Background. Dose painting by numbers (DPBN) is a method to deliver an inhomogeneous tumor dose voxel-by-voxel with a prescription based on biological medical images. However, planning of DPBN is not supported by commercial treatment planning systems (TPS) today. Here, a straightforward method for DPBN with a standard TPS is presented. Material and methods. DPBN tumor dose prescription maps were generated from 18F-FDG-PET images applying a linear relationship between image voxel value and dose. An inverted DPBN prescription map was created and imported into a standard TPS where it was defined as a mock pre-treated dose. Using inverse optimization for the summed dose, a planned DPBN dose distribution was created. The procedure was tested in standard TPS for three different tumor cases; cervix, lung and head and neck. The treatment plans were compared to the prescribed DPBN dose distribution by three-dimensional (3D) gamma analysis and quality factors (QFs). Delivery of the DPBN plans was assessed with portal dosimetry (PD). Results. Maximum tumor doses of 149%, 140% and 151% relative to the minimum tumor dose were prescribed for the cervix, lung and head and neck case, respectively. DPBN distributions were well achieved within the tumor whilst normal tissue doses were within constraints. Generally, high gamma pass rates (> 89% at 2%/2 mm) and low QFs (< 2.6%) were found. PD showed that all DPBN plans could be successfully delivered. Conclusions. The presented methodology enables the use of currently available TPSs for DPBN planning and delivery and may therefore pave the way for clinical implementation.

Validation of dose painting of lung tumours using alanine/EPR dosimetry

Biologic image guided radiotherapy (RT) with escalated doses to tumour sub volumes challenges todays RT dose planning and delivery systems. In this phantom study, we verify the capability of a clinical dose planning and delivery system to deliver an 18F-FDG-PET based dose painted treatment plan to a lung tumour. Furthermore, we estimate the uncertainties of the dose painted treatment compared to conventional RT plans. An anthropomorphic thorax phantom of polystyrene and polyurethane was constructed based on CT images of a lung cancer patient. 101 EPR/alanine dosimeters were placed in separate cavities within the phantom. IMRT and VMAT plans were generated in Eclipse (version 10.0, Analytical Anisotropic Algorithm version 10.2.28, Varian Medical Systems, Inc.) for 6 and 15 MV photons, based on 18F-FDG-PET/CT images of the patient. A boost dose of 3.8 Gy/fraction was given to the 18F-FDG-avid region (biological planning volume; BTV), whereas 3.1 Gy/fraction was planned to the planning target volume (PTV, excluding the BTV). For the homogenous plans, 3.2 Gy/fraction was given to the PTV. Irradiation of the phantom was carried out at a Varian Trilogy linear accelerator (Varian Medical Systems, Inc.). Uncertainties involved in treatment planning and delivery were estimated from portal dosimetry gamma evaluation. Measured and calculated doses were compared by Bland-Altmann analysis. For all treatment plans, all dose-volume objectives could be achieved in the treatment planning system. The mean absolute differences between calculated and measured doses were small (<0.1 Gy) for BTV, PTV-BTV, lung and soft tissue. The estimated uncertainty of the planned doses was less than 3% for all plans, whereas the estimated uncertainty in the measured doses was less 2.3%. Our results show that planning and delivery of dose escalated lung cancer treatment on a clinical dose planning and delivery system has high dosimetric accuracy. The uncertainties associated with the dose escalated treatment plans are comparable to the conventional plans.

EP-1439: IMRT and IMPT of cervical cancer and effect of reduced margins

Purpose/Objective: The objective of the study was to compare intensity modulated radiotherapy (IMRT) and intensity modulated proton therapy (IMPT) for locally advanced cervical cancer in terms of dose-volume parameters, dose coverage and conformity. Furthermore, to study the effect of reduced margins. Materials and Methods: External beam radiotherapy planning of the pelvic region was carried out for 5 patients with locally advanced cervical cancer. Planning target volume (PTV) was defined by primary tumour, pelvic and regional lymph nodes. Dose prescription was 50.4 Gy in 28 fractions. PTV dose coverage criteria was set to D98% 95%. Two sets of treatment plans were prepared based on different CTV-PTV margins: clinical margin ( 7 mm L-R, 10 mm S-I, 15 mm A-P) and reduced margin (7 mm isotropic). The IMRT and IMPT plans were generated using the Eclipse treatment planning system. Dose-volume histograms (DVHs) were analyzed for the PTV and various organs at risk (OARs; rectum, bladder, bowel, sigmoideum and pelvic bone). Student’s t-test was used for all statistical comparison. Results: All IMRT and IMPT plans covered 98% of PTV with 95% isodose, so the dose prescription was well achieved. IMPT demonstrated the potential in sparing doses to OARs, where significant differences were seen compared to IMRT for many dose-volume parameters (table 1). Concerning the reduced margins, increased differences between IMPT and IMRT were seen for the bladder (data not shown). However, for the high dose regions in bowel and sigmoideum the potential sparing by IMPT was found to be less with reduced margins.

PO-0879: Short-course PET based SIB for cervical cancer

Purpose/Objective: State of the art treatment of locally advanced cervical cancer with image guided intensity modulated external radiotherapy followed by image guided brachytherapy provide good clinical outcome. However, there are still 10-15% loco-regional failures and 10-20% who experience moderate to severe side effects. In the current work we propose to use FDG PET as basis for a short-course simultaneous integrated boost (SIB) with external beam therapy. This concept may increase tumour control and improve tumour shrinkage before brachytherapy. The latter may reduce complexity and improve organ sparing at brachytherapy. Materials and Methods: This study included 10 patients with locally advanced cervical cancer all treated with curative image guided external beam and brachytherapy. FDG PET/CT was obtained prior to therapy for all patients. To explore the potential use of PET based dose escalation, a new approach was tested in silico. Here, the FDG avid tumour volume was dose escalated by intensity modulated radiotherapy from the conventional 1.8Gy to 2.8Gy per fraction for the 10 first fractions; a short-course SIB. For the remaining 18 external beam fractions, standard treatment to the pelvic area is followed to a total dose to the PTV and boost volume of 50.4Gy and 60.4Gy, respectively. For intensity modulation, both photons and protons were considered using dual arc VMAT and three-field IMPT, respectively. All treatment plans were generated using the Eclipse Treatment Planning System (v.11, Varian Medical Systems, Palo Alto, CA). Results: For the patients included, the PET based boost volume had a mean volume of 36 ± 6cm as compared to average volumes for the GTV and PTV of 69 ± 10cm and 1508 ± 55cm, respectively. The dose escalation was straightforward to implement for both VMAT and IMPT, with a D98 ≥ 95% for the boost volume being achieved in all cases. The sum of the short-course SIB (10 fractions) and the subsequent 18 conventional fractions was compared to the conventional, 28-fraction non-SIB approach by analysing dose volume histograms (Table 1). Only marginal increased doses to the relevant organs at risk (OARs) were found for all investigated parameters. IMPT had, compared to VMAT, reduced OAR doses in the intermediate dose range, but showed no relative advantage in dose escalation.

Systematic ReviewReirradiation of locally recurrent rectal cancer: A systematic review

BACKGROUND Many patients with rectal cancer receive radiotherapy as a component of primary multimodality treatment. Although local recurrence is infrequent, reirradiation may be needed to improve resectability and outcomes. This systematic review investigated the effects of reirradiation in terms of feasibility, toxicity, and long-term outcomes. METHODS A Medline, Embase and Cochrane search resulted in 353 titles/abstracts. Ten publications describing seven prospective or retrospective studies were included, presenting results of 375 patients reirradiated for rectal cancer. RESULTS Median initial radiation dose was 50.4Gy, median 8-30months before reirradiation. Reirradiation was mostly administered using hyperfractionated (1.2-1.5Gy twice-daily) or 1.8Gy once-daily chemoradiotherapy. Median total dose was 30-40Gy to the gross tumour volume with 2-4cm margins. Median survival was 39-60months in resected patients and 12-16months in palliative patients. Good symptomatic relief was reported in 82-100%. Acute toxicity with diarrhoea was reported in 9-20%, late toxicity was insufficiently reported. CONCLUSIONS Reirradiation of rectal cancer to limited volumes is feasible. When curative resection is possible, the goal is radical resection and long-term survival, and hyperfractionated chemoradiotherapy should be preferred to limit late toxicity. Reirradiation yielded good symptomatic relief in palliative treatment.

Reirradiation of locally recurrent rectal cancer

BACKGROUND Many patients with rectal cancer receive radiotherapy as a component of primary multimodality treatment. Although local recurrence is infrequent, reirradiation may be needed to improve resectability and outcomes. This systematic review investigated the effects of reirradiation in terms of feasibility, toxicity, and long-term outcomes. METHODS A Medline, Embase and Cochrane search resulted in 353 titles/abstracts. Ten publications describing seven prospective or retrospective studies were included, presenting results of 375 patients reirradiated for rectal cancer. RESULTS Median initial radiation dose was 50.4Gy, median 8-30months before reirradiation. Reirradiation was mostly administered using hyperfractionated (1.2-1.5Gy twice-daily) or 1.8Gy once-daily chemoradiotherapy. Median total dose was 30-40Gy to the gross tumour volume with 2-4cm margins. Median survival was 39-60months in resected patients and 12-16months in palliative patients. Good symptomatic relief was reported in 82-100%. Acute toxicity with diarrhoea was reported in 9-20%, late toxicity was insufficiently reported. CONCLUSIONS Reirradiation of rectal cancer to limited volumes is feasible. When curative resection is possible, the goal is radical resection and long-term survival, and hyperfractionated chemoradiotherapy should be preferred to limit late toxicity. Reirradiation yielded good symptomatic relief in palliative treatment.

PO-0774: PET-guided simultaneous integrated boost of lung tumors: Alanine/EPR dosimetry in an anthropomorphic phantom

Conclusions: TG119 structures and plans were found to be easily adaptable to Delta4 phantom CT enabling a rigorous evaluation procedure for IMRT plans verification. Preliminary results on VMAT plans showed that TG119 could be a practical commissioning procedure for modulated arc therapy too. Delta4 allows a fast on-line 3D dose distributions analysis substituting more traditional dosimeters suggested in TG119, but this solution is more expensive than the one proposed inside this report and it is not available in every department for intercomparison purposes.