ABSTRACT
BACKGROUND: Intensity-modulated radiotherapy (IMRT) improves dose distribution in head and neck (HN) radiation therapy. Volumetric-modulated arc therapy (VMAT), a new form of IMRT, delivers radiation in single or multiple arcs, varying dose rates (VDR-VMAT) and gantry speeds, has gained considerable attention. Constant dose rate VMAT (CDR-VMAT) associated with a fixed gantry speed does not require a dedicated linear accelerator like VDR-VMAT. The present study explored the feasibility, efficiency and delivery accuracy of CDR-VMAT, by comparing it with IMRT and VDR-VMAT in treatment planning for HN cancer. METHODS AND MATERIALS: Step and shoot IMRT (SS-IMRT), CDR-VMAT and VDR-VMAT plans were created for 15 HN cancer patients and were generated by Pinnacle3 TPS (v 9.8) using 6 MV photon energy. Three PTVs were defined to receive respectively prescribed doses of 66 Gy, 60 Gy and 54 Gy, in 30 fractions. Organs at risk (OARs) included the mandible, spinal cord, brain stem, parotids, salivary glands, esophagus, larynx and thyroid. SS-IMRT plans were based on 7 co-planar beams at fixed gantry angles. CDR-VMAT and VDR-VMAT plans, generated by the SmartArc module, used a 2-arc technique: one clockwise from 182° to 178° and the other one anti-clockwise from 178° to 182°. Comparison parameters included dose distribution to PTVs (Dmean, D2%, D50%, D95%, D98% and Homogeneity Index), maximum or mean doses to OARs, specific dose-volume data, the monitor units and treatment delivery times. RESULTS: Compared with SS-IMRT, CDR-VMAT significantly reduced the maximum doses to PTV1 and PTV2 and significantly improved all PTV3 parameters, except D98% and D95%. It significantly spared parotid and submandibular glands and was associated with a lower Dmean to the larynx. Compared with VDR-VMAT, CDR-VMAT was linked to a significantly better Dmean, to the PTV3 but results were worse for the parotids, left submandibular gland, esophagus and mandible. Furthermore, the Dmean to the larynx was also worse. Compared with SS-IMRT and VDR-VMAT, CDR-VMAT was associated with higher average monitor unit values and significantly shorter average delivery times. CONCLUSIONS: CDR-VMAT appeared to be a valid option in Radiation Therapy Centers that lack a dedicated linear accelerator for volumetric arc therapy with variable dose-rates and gantry velocities, and are unwilling or unable to sanction major expenditure at present but want to adopt volumetric techniques.
ABSTRACT
BACKGROUND: Small cell lung cancer (SCLC) is a chemoresponsive tumor but overall survival remains poor even in limited disease (LD). With the aim of eradicating chemoresistant tumor cells and reducing toxicity, we investigated in this phase II trial the feasibility and outcome of a sequential approach of induction chemotherapy (CT) followed, in responding patients with LD-SCLC, by intensified platinum-based CT and concurrent thoracic irradiation (TI). MATERIALS AND METHODS: We treated 55 consecutive LD-SCLC patients with three 21-day cycles of cyclophosphamide, epiadriamycin and vincristine (CEV) as induction CT. In 44 (80%) patients there was an objective response and they received treatment intensification consisting of TI and concomitant CT with carboplatin and etoposide plus recombinant granulocite colony stimulating factor. Twenty-five (57%) patients were submitted to twice-daily thoracic irradiation (TDTI; 1.5 Gy per fraction, to a total dose of 45 Gy) and 19 (43%) to once-daily thoracic irradiation (ODTI; 2 Gy per fraction, to a total dose of 50 Gy). RESULTS: Median follow up was 75 months (range, 42-102). Of 44 patients submitted to intensification with TI plus CT, 32 (73%) had a complete and 12 (27%) a partial response. Median overall survival of all 55 patients was 17 months with actuarial survival probabilities of 2 and 5 years, 32 and 25%, respectively. Analysis of patient sub-groups showed a 5-month median survival in non-responders, 19 in TDTI and 17 in ODTI patients, respectively. Two and 5 year survival probabilities were 0% in non-responders, 40 and 35% in TDTI and 39 and 21% in ODTI patients, respectively. At present, 13 of 44 responders are still alive, of which nine (20%) have been progression-free from 45 to 93 months (median 60). Treatment failure was registered in 31 (70%) of 44 patients who received both induction and intensification treatment. One-half of patients had intrathoracic recurrence, eight of which only local and the remaining seven local and distant. Fourteen (32%) patients had brain metastases. Grade 3-4 neutropenia occurred in 24 (55%) patients with no differences between treatment groups. Grade 3 esophagitis was registered in four (9%) patients: in 3/25 (12%) and 1/19 (5%) of those who received TDTI and ODTI, respectively (P=not significant). Acute radiation pneumonitis occurred in three (12%) patients submitted to TDTI. No clinically debilitating pulmonary fibrosis, permanent esophageal stricture or toxic death was observed. CONCLUSIONS: In LD-SCLC patients late concurrent CT plus TI is feasible and effective. Our long-term results are similar to the best reported in the literature. Despite the high incidence of complete response obtained, however, one-half of the patients had intrathoracic relapse and one-third brain metastases.
