Decreasing the dosimetric effects of misalignment when using a mono-isocentric technique for irradiation of head and neck cancer.

PURPOSE: The purpose of this study was to quantify and develop methods to decrease inhomogeneities created with field edge mismatch when using a mono-isocentric beam-split technique. METHODS AND MATERIALS: We validated techniques to determine dose across a half-blocked field edge and quantified potential sources of systematic matchline error. Then, two methods were used to evaluate matchline doses. The first used film dosimetry data from a half-beam field and a spreadsheet. Duplication and reversal provided two columns, each representing a beam-split field edge. Summation simulated perfect abutment and shifting created various gaps and overlaps. The second method involved obtaining dose profiles at midfield along the ray perpendicular to abutted, overlapped, and gapped beam-split fields on six linear accelerators. To enlarge the penumbra, we designed several field edge modifiers, then re-evaluated matchline doses. The field edge modifiers applicability to a 3-field head and neck treatment technique was also examined. RESULTS: Film-determined dose profiles provide similar information across a beam-split field edge as an ionization chamber. With the mono-isocentric beam-split technique, a 4-mm overlap or gap produces inhomogeneities nearly 60% above or below the intended dose. A 2-mm overlap or gap produces inhomogeneities nearly 30% above or below the intended dose. A customized penumbra generator decreased the magnitude of these inhomogeneities to 20% and 10%, respectively. CONCLUSION: The two methods of evaluating matchline dose described above gave similar results. When using the mono-isocentric half-field technique, small misalignments produce worrisome regions of inhomogeneity. Our penumbra generator substantially decreases the magnitude of the dose inhomogeneities, although the volume receiving an inhomogeneous dose increases.

Extremity soft-tissue sarcomas selectively treated with surgery alone.

PURPOSE: This study determined local control (LC), freedom from distant recurrence (FFDR), overall survival (OS), and potential prognostic factors in 34 adult patients with primary extremity or limb girdle soft-tissue sarcoma selectively managed with limb-conservation surgery alone. METHODS AND MATERIALS: The medical records of 34 patients who underwent surgery alone for localized soft-tissue sarcoma of the extremity were reviewed. Median duration of follow-up in survivors was 55 months (range, 24-143). There were 13 (38%) females. Eighteen (53%) of the tumors were low-grade, 15 (44%) were superficial, 15 (44%) were small (5 cm or less), and 16 (47%) involved the distal extremity. RESULTS: Actuarial 5-year LC was 80%, FFDR was 86%, and OS was 82%. All recurrences (local and distant) were in patients with high-grade tumors; their 5-year LC was 60%, FFDR was 71%, and OS was 69%. In 2 patients, metastatic disease developed either concurrent with or after their local recurrence. Univariate analysis revealed better OS, FFDR, and LC for patients with low-grade tumors (p < 0.05). Female patients had significantly better FFDR and OS (p < 0.05). CONCLUSION: It is appropriate to consider withholding irradiation for selected patients with low-grade tumors resected with negative margins if, in the event of a local failure, a function-preserving surgical salvage is anticipated. For patients with high-grade sarcomas, the control of local and distant disease was not acceptable with limb-conservation surgery alone.

Humoral and cellular immunity to EBV and lymphoid cell line antigens in human lymphoma.

Although elevated antibody levels to the Epstein-Barr virus (EBV) have been reported in a number of lympho-proliferative neoplasms, it has not been possible to determine whether these antibodies were the result of a specific response to an oncogenic agent (EBV), whether they were a non-specific humoral compensation for depressed cell-mediated immunity (CMI), or whether a different mechanism was responsible. We have previously shown in a group of lymphoma patients that depressed cellular immunity to a number of standard antigens (Candida, SKSD, etc.) is not associated with an increase in antibody to EBV. In this study, we tried to compare CMI to possible EBV and lymphoid cell line antigens with humoral antibody to EBV. The two basis CMI assays utilized were lymphocyte cytotoxicity (LC) and skin testing (ST) for delayed hypersensitivity. In the LC assay, an EBV-containing cell line (F265) was used as the target. Reactivity against F265 was stronger in normal individuals than in cancer patients, suggesting a relationship to general cellular immune competence. ST studies showed that membrane extracts from lymphoid cell lines derived from patients with Burkitt's lymphoma and nasopharyngeal carcinoma (NPC) were more likely to elicit a delayed hypersensitivity in lymphoma and NPC patients than cell lines derived from normal individuals. Patients with ST reactivity against the membrane preparations from the tumour-derived cell lines were as likely to have elevated EBV antibodies as patients without such reactivity. The data strongly indicated that the elevated EBV titres in lymphoma patients are not related to a specific or non-specific depression of CMI.