Primary Target Volume Research Articles

Smart (simultaneous modulated accelerated radiation therapy) boost: a new accelerated fractionation schedule for the treatment of head and neck cancer with intensity modulated radiotherapy

Purpose: To report the initial experience in the definitive treatment of head and neck carcinomas using SMART (Simultaneous Modulated Accelerated Radiation Therapy) boost technique. Radiation was delivered via IMRT (Intensity Modulated Radiotherapy). The following parameters were evaluated: acute toxicity, initial tumor response, clinical feasibility, dosimetry and cost. Methods and Materials: Between January 1996 and December 1997, 20 patients with primary head and neck carcinomas were treated with SMART boost technique. The treatment fields encompassed two simultaneous targets. The primary target included palpable and visible disease sites. The secondary target included regions at risk for microscopic disease. Daily fractions of 2.4 Gy and 2 Gy were prescribed and delivered to the primary and secondary targets to a total dose of 60 Gy and 50 Gy, respectively. Lower neck nodes were treated with a single conventional anterior portal. This fractionation schedule was completed in 5 weeks with 5 daily fractions weekly. Toxicity was evaluated by RTOG acute toxicity grading criteria, evidence of infection at immobilization screw sites, subjective salivary function, weight loss, and the need for treatment split. Mean follow-up was 15.2 months. Initial tumor response was assessed by clinical and radiographical examinations. Clinical feasibility was evaluated by the criteria: time to treat patient, immobilization, and treatment planning and QA time. In dosimetry, we evaluated the mean doses of both targets and normal tissues and percent targets’ volume below goal. To evaluate cost, Medicare allowable charge for SMART boost was compared to those of conventional fractionated and accelerated radiotherapy. Results: Acute toxicity: None of the patients had a screw site infection and all patients healed well after completion of radiotherapy. Sixteen of 20 patients (80%) completed the treatment within 40 days without any split. Sixteen patients (80%) had RTOG Grade 3 mucositis while 10 patients (50%) had Grade 3 pharyngitis. Three of 20 patients (15%) had weight loss greater than 10% of their pretreatment weight. Ten patients (50%) required intravenous fluids, tube feeding or both. Nine patients (45%) reported moderate xerostomia with significant relief reported within 6 months. Initial tumor response: 19 patients (95%) had complete response (CR) while one had partial response (PR). The patient with PR had stable disease on imaging at 12 months follow-up. Two patients were found to have lung metastases at 2 months and 5 months follow-up. To date, there have been two local recurrences in the complete responders. Both patients had nasopharyngeal primary; one was retreated with radioactive Cesium-137 implant and the other died from the disease. Clinical feasibility: The average treatment time for a three-arc treatment was 17.5 minutes and 2.5 minutes for each additional arc. Eleven patients (55%) had four-arc treatment while six patients (30%) had five-arc treatment and three patients (15%) had three-arc treatment. Immobilization was reproducible within less than 2 mm. The treatment planning, QA and documentation prior to treatment averaged 2 days. Dosimetry: The mean doses to the primary and secondary targets were 64.4 Gy and 54.4 Gy, respectively; 8.9% of the primary target volume and 11.6% of the secondary target volume were below prescribed dose goal. The mean dose delivered to the mandible was 30 Gy, spinal cord 17 Gy, ipsilateral parotid 23 Gy, and contralateral parotid 21 Gy. Cost: Total Medicare allowable charge for SMART boost was $7000 compared to $8600 (conventional ) and $9400 (accelerated fractionation). Conclusions: SMART boost technique is an accelerated radiotherapy scheme that can be delivered with acceptable toxicity. It allows parotid sparing as evidenced both clinically and by dosimetry. Initial tumor response has been encouraging. It is clinically feasible and cost saving. A larger population of patients and a long-term follow-up are warranted to evaluate ultimate tumor control and late toxicity.

Treatment of stage I nasopharyngeal carcinoma: Analysis of the patterns of relapse and the results of withholding elective neck irradiation

This is a retrospective analysis of 196 patients with nasopharyngeal carcinoma Stage I (Ho's classification) treated by megavoltage radiation during 1980–1984. The primary target volume included all potential sites of local invasion and the first station lymph nodes at retropharyngeal spaces. Two different dose schedules were used, both gave a total tumor dose biologically equivalent to 65 Gy by conventional fractionation, and both achieved a 5-year actuarial local-recurrence-free survival of 88%. Elective neck irradiation was withheld in all except seven patients. The overall 7-year actuarial survival was 85%, but the relapse-free survival was only 62%. The patterns of relapse, prognostic factors, and treatment complications were analyzed. Eighteen patients (9%) recurred locally. Radical retreatment with radiation achieved complete remission in seven out of fifteen cases. Distant failure occurred in 17 patients (9%). Although 57 (30%) of the 189 patients without elective neck irradiation subsequently showed lymph node involvement, none of the seven regionally-treated patients relapsed. The successful regional salvage rate was 81% overall (46 out of 57 patients), but 90% (44 of 49) for those properly treated with whole neck irradiation. However, the 7-year actuarial survival was lower in patients with nodal relapse than those without (70% versus 87%) because of the associated higher incidence of hematogenous dissemination. The various aspects of treatment, the value of elective neck irradiation in particular, are discussed.

A highly visible helium target for medium energy physics

Good refrigeration of an extended-area liquid 3He or 4He target has been accomplished by surrounding the primary target volume with a thin sheet of superfluid.