small cell...need help

I would insist on getting a
I would insist on getting a Cat Scan but even more important is to identify the mass/growth
that has grown larger and have pathologist view under microscope and provide a path report on the sample of the growth. The growth could be either in lymph node(s) or in chest wall or the diaphragm or the pleura between the lungs or membranes surrounding the heart.

When DR says "we should not worry that it could be inflammation or scarring" from radiation or and chemo, that may be correct but its very important to rule out a canerous tumor. If it is cancerous and growing then DR needs to adjust his strategy for treatment by either add, replace, or change strength and/or schedule of chemo meds rather than wait

Certain types of chemo's and radiation do cause scarring as does pneumonia but better to be safe then sorry

There are a different ways to perform a biopsy and are listed below.

Lymph node biopsy:
The removal of all or part of a lymph node. A pathologist views the tissue under a microscope to look for cancer cells.

Mediastinoscopy:
A surgical procedure to look at the organs, tissues, and lymph nodes between the lungs for abnormal areas. An incision (cut) is made at the top of the breastbone and a mediastinoscope is inserted into the chest. A mediastinoscope is a thin, tube-like instrument with a light and a lens for viewing. It may also have a tool to remove tissue or lymph node samples, which are checked under a microscope for signs of cancer.

Needle Biopsy of Lung (Chest) Nodules
A lung nodule is relatively round lesion, or area of abnormal tissue located within the lung. Lung nodules are most often detected on a chest x-ray and do not typically cause pain or other symptoms. Nodules or abnormalities in the body are often detected by imaging examinations. However, it is not always possible to tell from these imaging tests whether a nodule is benign (non-cancerous) or cancerous.

A needle biopsy, also called a needle aspiration, involves removing some cells—either surgically or in a less invasive procedure involving a hollow needle—from a suspicious area within the body and examining them under a microscope to determine a diagnosis.
In a needle biopsy of lung nodules, imaging techniques such as computed tomography (CT) and fluoroscopy are often used to help guide the interventional radiologist's instruments to the site of the abnormal growth.

Bronchoscope biopsy.
This type of biopsy uses a lighted instrument (bronchoscope) inserted through the mouth or nose and into the airway to remove a lung tissue sample. This method may be used if an infectious disease is suspected, if the abnormal lung tissue is located next to the breathing tubes (bronchi), or before trying more invasive methods, such as an open lung biopsy.