Amr Taha

PURPOSE: To evaluate the potential for dose escalation with intensity-modulated radiotherapy (IMRT) in positron emission tomography-based radiotherapy planning for locally advanced non-small-cell lung cancer (LA-NSCLC).

METHODS AND MATERIALS: For 35 LA-NSCLC patients, three-dimensional conformal radiotherapy and IMRT plans were made to a prescription dose (PD) of 66 Gy in 2-Gy fractions. Dose escalation was performed toward the maximal PD using secondary endpoint constraints for the lung, spinal cord, and heart, with de-escalation according to defined esophageal tolerance. Dose calculation was performed using the Eclipse pencil beam algorithm, and all plans were recalculated using a collapsed cone algorithm. The normal tissue complication probabilities were calculated for the lung (Grade 2 pneumonitis) and esophagus (acute toxicity, grade 2 or greater, and late toxicity).

RESULTS: IMRT resulted in statistically significant decreases in the mean lung (p <.0001) and maximal spinal cord (p = .002 and 0005) doses, allowing an average increase in the PD of 8.6-14.2 Gy (p ≤.0001). This advantage was lost after de-escalation within the defined esophageal dose limits. The lung normal tissue complication probabilities were significantly lower for IMRT (p <.0001), even after dose escalation. For esophageal toxicity, IMRT significantly decreased the acute NTCP values at the low dose levels (p = .0009 and p <.0001). After maximal dose escalation, late esophageal tolerance became critical (p <.0001), especially when using IMRT, owing to the parallel increases in the esophageal dose and PD.

CONCLUSION: In LA-NSCLC, IMRT offers the potential to significantly escalate the PD, dependent on the lung and spinal cord tolerance. However, parallel increases in the esophageal dose abolished the advantage, even when using collapsed cone algorithms. This is important to consider in the context of concomitant chemoradiotherapy schedules using IMRT.

BACKGROUND AND PURPOSE: In this study on PDR treatment planning of utero-vaginal carcinoma, we analysed the dosimetry of traditional X-ray based plans as it presents on MR images. The potential gain of MRI-based dose optimisation was assessed.

PATIENTS AND METHODS: Sixteen patients boosted with PDR brachytherapy after external beam therapy were included. The clinical X-ray based plans were projected on MR images. The GTV, HR-CTV and IR-CTV were retrospectively contoured, as well as the bladder, rectum and sigmoid colon. The dose in the critical organs and target coverage was investigated. In a second phase, the plans were manually optimised using the MR information. The objectives were to lower the dose in the critical organs (or= 85 Gy(alphabeta10).

RESULTS: In the X-ray based plans, D(2cc) in bladder and sigmoid colon exceeded the tolerance doses in 10/16 and 7/16 patients, respectively. Coverage of the IR-CTV with the 60 Gy(alphabeta10) was acceptable. D90 of the HR-CTV was below 85 Gy(alphabeta10) in 13 out of 16 patients. After optimisation, the dose constraints in the OAR were not exceeded anymore in any patient. The average D(2cc) dose reduction was 7+/-6 Gy(alphabeta3) in the bladder and 7+/-4 Gy(alphabeta3) in the sigmoid colon for those patients in which the dose constraint was initially exceeded. In addition, an average dose increase of 3 Gy(alphabeta10) was accomplished in the HR-CTV.

CONCLUSIONS: MRI-based dose optimisation can play an important role to reduce the dose delivered to the critical organs and to improve target coverage.