Microscopic Disease Extension in Three Dimensions for Non–Small-Cell Lung Cancer: Development of a Prediction Model Using Pathology-Validated Positron Emission Tomography and Computed Tomography Features

Accelerated partial breast irradiation: the need for well-defined patient selection criteria, improved volume definitions, close follow-up and discussion of salvage treatment

Breast-conserving therapy, including whole breast irradiation, has become a well-established alternative to mastectomy in early-stage breast cancer patients, with similar survival rates and better cosmetic outcome. However, many women are still treated with mastectomy, due to logistical issues related to the long course of radiotherapy (RT). To reduce mastectomy rates and/or omission of RT after breast-conserving surgery, shorter, hypofractionated RT treatments have been introduced. More recently, the necessity of routinely treating the entire breast in all patients has been questioned, leading to the development of partial breast radiotherapy. With accelerated partial breast irradiation (APBI) these two approaches have been combined: the tumor bed with a 1-2 cm margin is irradiated either intra-operatively (single fraction) or postoperatively over 5-15 days. Different techniques have been developed, including interstitial brachytherapy, intra-cavity brachytherapy, intra-operative radiotherapy and external beam radiotherapy. These techniques are being evaluated in several ongoing phase III studies. Since its introduction, APBI has been the subject of continuous debate. ASTRO and GEC-ESTRO have published guidelines for patient selection for APBI, and strongly recommend that APBI be carried out within ongoing clinical trials. Recently, the patient selection criteria for APBI have also been up for debate, following the publication of results from different groups that do/do not confirm a difference in recurrence risk among the ASTRO defined risk groups. This paper reviews the different APBI techniques, current recommendations for patient selection, available clinical data and ongoing clinical trials. A case report is included to illustrate the need for careful follow-up of patients treated with APBI.

The impact of microscopic disease on the tumor control probability in non-small-cell lung cancer

PURPOSE

To indicate which clinical target volume (CTV) margin (if any) is needed for an adequate treatment of non-small-cell lung cancer (NSCLC) using either 3D conformal or stereotactic radiotherapy, taking the distribution of the microscopic disease extension (MDE) into account.

METHODS AND MATERIALS

On the basis of the linear-quadratic biological model, a Monte-Carlo simulation was used to study the impact of MDE and setup deviations on the tumor control probability (TCP) after typical 3D conformal and stereotactic irradiation techniques. Setup deviations were properly accounted for in the planning target volume (PTV) margin. Previously measured distributions of MDE outside the macroscopic tumor in NSCLC patients were used. The dependence of the TCP on the CTV margins was quantified.

RESULTS

The presence of MDE had a demonstratable influence on the TCP in both the 3D conformal and the stereotactic technique when no CTV margins were employed. The impact of MDE on the TCP values was greater in the 3D conformal scenario (67% TCP with MDE; 84% TCP without MDE) than for stereotactic radiotherapy (91% TCP with MDE; 100% TCP without MDE). Accordingly, an increase of the CTV margin had the greatest impact for the 3D conformal technique. Larger setup errors, with appropriate PTV margins, lead to an increase in TCP for both techniques, showing the interdependence of CTV and PTV margins.

CONCLUSIONS

MDE may not always be eradicated by the beam penumbra or existing PTV margins using either 3D conformal or stereotactic radiotherapy. Nonetheless, TCP modeling indicates an overall local control rate above 90% for the stereotactic technique, while a non-zero CTV margin is recommended for better local control of MDE when using the 3D conformal technique.