Part 2: Dynamic mixed beam radiotherapy (DYMBER): Photon dynamic trajectories combined with modulated electron beams.

PURPOSE: The purpose of this study was to develop a treatment technique for dynamic mixed beam radiotherapy (DYMBER) utilizing increased degrees of freedom (DoF) of a conventional treatment unit including different particle types (photons and electrons), intensity and energy modulation and dynamic gantry, table, and collimator rotations. METHODS: A treatment planning process has been developed to create DYMBER plans combining photon dynamic trajectories (DTs) and step and shoot electron apertures collimated with the photon multileaf collimator (pMLC). A gantry-table path is determined for the photon DTs with minimized overlap of the organs at risk (OARs) with the target. In addition, an associated dynamic collimator rotation is established with minimized area between the pMLC leaves and the target contour. pMLC sequences of photon DTs and electron pMLC apertures are then simultaneously optimized using direct aperture optimization (DAO). Subsequently, the final dose distribution of the electron pMLC apertures is calculated using the Swiss Monte Carlo Plan (SMCP). The pMLC sequences of the photon DTs are then re-optimized with a finer control point resolution and with the final electron dose distribution taken into account. Afterwards, the final photon dose distribution is calculated also using the SMCP and summed together with the one of the electrons. This process is applied for a brain and two head and neck cases. The resulting DYMBER dose distributions are compared to those of dynamic trajectory radiotherapy (DTRT) plans consisting only of photon DTs and clinically applied VMAT plans. Furthermore, the deliverability of the DYMBER plans is verified in terms of dosimetric accuracy, delivery time and collision avoidance. For this purpose, The DYMBER plans are delivered to Gafchromic EBT3 films placed in an anthropomorphic head phantom on a Varian TrueBeam linear accelerator. RESULTS: For each case, the dose homogeneity in the target is similar or better for DYMBER compared to DTRT and VMAT. Averaged over all three cases, the mean dose to the parallel OARs is 16% and 28% lower, D2% to the serial OARs is 17% and 37% lower and V10% to normal tissue is 12% and 4% lower for the DYMBER plans compared to the DTRT and VMAT plans, respectively. The DYMBER plans are delivered without collision and with a 4-5 min longer delivery time than the VMAT plans. The absolute dose measurements are compared to calculation by gamma analysis using 2% (global)/2 mm criteria with passing rates of at least 99%. CONCLUSIONS: A treatment technique for DYMBER has been successfully developed and verified for its deliverability. The dosimetric superiority of DYMBER over DTRT and VMAT indicates utilizing increased DoF to be the key to improve brain and head and neck radiation treatments in future.

Preoperative chemoradiotherapy improves local recurrence free survival in locally advanced rectal cancer.

PURPOSE: Preoperative chemoradiotherapy (pre-CRT) followed by total mesorectal excision (TME) is the recommended therapy for patients with locally advanced rectal cancer (LARC). The primary aim of this study was to compare the rates of local and distant recurrence and overall survival (OS) in LARC patients who received pre-CRT vs postoperative (post) CRT. METHODS: The medical records of 158 rectal cancer patients with clinical stage T3, T4 or N positive disease who received either pre-CRT or post-CRT between 2000-2009 were retrospectively analysed. Pre-CRT employed protracted 5-fluorouracil (5FU) infusion, whereas post-CRT included bolus 5FU and leucovorin concurrently with radiation therapy (RT). Radiation dose was 50.4 Gy in 82% and 45 Gy in 18% of the patients. RESULTS: 158 patients (65 females, 93 males) were analysed. Median age was 56.5 years (range 19-78). Fifty-three (34%) patients received pre-CRT and 105 (66%) post-CRT. Median follow-up was 43.3 months (range 8-182) and 47.6 months (range 9-194) in pre-CRT and post-CRT patients, respectively. After pre-CRT, significant downstaging was achieved. However, the type of surgical resection was not influenced by the administration of pre-CRT in tumors ≥5 cm distant from the anal verge (p=0.3). Pathologic complete response was achieved in 20% of the patients in the pre-CRT group. Local recurrence free survival (LRFS) at 5-years was 89.2% in the pre-CRT and 74.8% in the post-CRT group (p=0.04). Distant recurrence free survival (DRFS) at 5-years was 81.7% and 68.5 % in pre-CRT and post-CRT groups, respectively (p=0.1). OS was similar in the two groups (71.4 vs 64.4%, p=0.9). CONCLUSION: Treatment of LARC with pre-CRT followed by surgery improved LRFS as compared to surgery followed by post-CRT, but failed to improve DRFS or OS in our patient population.

Comparison of two different IMRT planning techniques in the treatment of nasopharyngeal carcinoma. Effect on parotid gland radiation doses.

PURPOSE: To compare the effect of two different intensity-modulated radiation therapy (IMRT) planning techniques on parotid gland doses in patients with nasopharyngeal carcinoma (NPC). PATIENTS AND METHODS: Radiotherapy for 10 NPC patients referred to the University of Istanbul Cerrahpasa Medical School was planned with arc- and static seven-field IMRT. The simultaneous integrated boost (SIB) technique was used to deliver 70 Gy (2.12 Gy per fraction) to the primary tumor and involved nodes; 60 Gy (1.81 Gy per fraction) to the entire nasopharynx and 54 Gy (1.63 Gy per fraction) to elective lymph nodes in 33 fractions. Plans also aimed to keep the mean parotid dose below 26 Gy and limit the maximum doses to the spinal cord and brain stem to 45 and 54 Gy, respectively. Mean parotid gland doses for the two planning techniques were compared using a paired t-test. Target coverage and dose inhomogeneity were evaluated by calculating conformity- (CI) and homogeneity index (HI) values. RESULTS: Target coverage and dose homogeneity were identical and good for both planning techniques: CI = 1.05 ± 0.08 and 1.05 ± 0.08; HI = 1.08 ± 0.02 and 1.07 ± 0.01 for arc- and static field IMRT, respectively. Mean doses to contralateral parotid glands were 25.73 ± 4.27 and 27.73 ± 3.5 Gy(p = 0.008) for arc- and static field IMRT plans, respectively, whereas mean ipsilateral parotid doses were 30.65 ± 6.25 and 32.55 ± 5.93 Gy (non-significant p-value), respectively. Mean monitor units (MU) per fraction for the 10 patients were considerably lower for arc- than for static field treatments-540.5 ± 130.39 versus 1288.4 ± 197.28 (p < 0.001). CONCLUSION: Normal tissues--particularly the parotid glands--are better spared with the arc technique in patients with NPC. MU and treatment times are considerably reduced in arc IMRT plans.