Strategies for online organ motion correction for intensity-modulated radiotherapy of prostate cancer: prostate, rectum, and bladder dose effects.

PURPOSE: To quantify and evaluate the accumulated prostate, rectum, and bladder dose for several strategies including rotational organ motion correction for intensity-modulated radiotherapy (IMRT) of prostate cancer using realistic organ motion data. METHODS AND MATERIALS: Repeat computed tomography (CT) scans of 19 prostate patients were used. Per patient, two IMRT plans with different uniform margins were created. To quantify prostate and seminal vesicle motion, repeat CT clinical target volumes (CTVs) were matched onto the planning CTV using deformable registration. Four different strategies, from online setup to full motion correction, were simulated. Rotations were corrected for using gantry and collimator angle adjustments. Prostate, rectum, and bladder doses were accumulated for each patient, plan, and strategy. Minimum CTV dose (D(min)), rectum equivalent uniform dose (EUD, n = 0.13), and bladder surface receiving >/=78 Gy (S78), were calculated. RESULTS: With online CTV translation correction, a 7-mm margin was sufficient (i.e., D(min) >/= 95% of the prescribed dose for all patients). A 4-mm margin required additional rotational correction. Margin reduction lowered the rectum EUD(n = 0.13) by approximately 2.6 Gy, and the bladder S78 by approximately 1.9%. CONCLUSIONS: With online correction of both translations and rotations, a 4-mm margin was sufficient for 15 of 19 patients, whereas the remaining four patients had an underdosed CTV volume <1%. Margin reduction combined with online corrections resulted in a similar or lower dose to the rectum and bladder. The more advanced the correction strategy, the better the planned and accumulated dose agree

The PET-boost randomised phase II dose-escalation trial in non-small cell lung cancer

Purpose: The local site of relapse in non-small cell lung cancer (NSCLC) is primarily located in the high FDG uptake region of the primary tumour prior to treatment. A phase II PET-boost trial (NCT01024829) randomises patients between dose-escalation of the entire primary tumour (arm A) or to the high FDG uptake region inside the primary tumour (>50% SUVmax) (arm B), whilst giving 66 Gy in 24 fractions to involved lymph nodes. We analysed the planning results of the first 20 patients for which both arms A and B were planned. Methods: Boost dose levels were escalated up to predefined normal tissue constraints with an equal mean lung dose in both arms. This also forces an equal mean PTV dose in both arms, hence testing pure dose-redistribution. Actual delivered treatment plans from the ongoing clinical trial were analysed. Patients were randomised between arms A and B if dose-escalation to the primary tumour in arm A of at least 72 Gy in 24 fractions could be safely planned. Results: 15/20 patients could be escalated to at least 72 Gy. Average prescribed fraction dose was 3.27 +/- 0.31 Gy [3.01-4.28 Gy] and 3.63 +/- 0.54 Gy [3.20-5.40 Gy] for arms A and B, respectively. Average mean total dose inside the PTV of the primary tumour was comparable: 77.3 +/- 7.9 Gy vs. 77.5 +/- 10.1 Gy. For the boost region dose levels of on average 86.9 +/- 14.9 Gy were reached. No significant dose differences between both arms were observed for the organs at risk. Most frequent observed dose-limiting constraints were the mediastinal structures (13/15 and 14/15 for arms A and B, respectively), and the brachial plexus (3/15 for both arms). Conclusion: Dose-escalation using an integrated boost could be achieved to the primary tumour or high FDG uptake regions whilst keeping the pre-defined dose constraints