**6. Discussion and summary**

Leukemia is a disease classification for an imbalance within the hemopoietic system. Acute leukemias are characterized with unregulated cell growth while chronic leukemias exhibit incomplete maturation of cells and some increase proliferation. Bone marrow or stem cell transplantation is a viable treatment option for the leukemia patient. Stem cells collected

Photon Total Body Irradiation

available by contacting the authors.

**7. Appendix** 

framework

Fig. A-1 Front and side view of AP/PA stand .

for Leukemia Transplantation Therapy: Rationale and Technique Options 547

chemotherapy treatments as part of the preparatory program for transplant. Two treatment options, opposed laterals and AP/PA fields and associated apparatus have been presented. The limitation of dose delivered to the lung/liver is specified in several protocols and is accomplished with partial transmission blocks placed in conjunction with AP/PA fields. Both techniques were designed to insure accurate dose delivery, comfortable patient support, and easy patient setup. Calculation spreadsheets referenced in this manuscript are

Legend: 1. 5/8" stainless steel rod, 2. Angle iron for stabilization and support, 3. Adjustable cassette holder, 4. Double track system support for bicycle seat placement, 5. Platform with ¾"plywood on oak

from an HLA matching donor or cells collected from the patient while in remission are provided to the leukemia recipient. The clinical desire of the transplant is repopulation and re-growth of the stem cells triggering a balanced regulated hemopoietic system.

Preparative regimens for marrow transplantation are required to rid the leukemia patient of any microscopic disease. Rigorous protocols of chemotherapy or radiation therapy combined with chemotherapy are provided prior to transplantation to reduce relapse. Radiotherapy includes fractionated treatments delivered to the total body (TBI). TBI treatments pose several concern issues in methodology and fractionation. High-energy fields with opposing beam arrangements lead to improved dose uniformity. Acrylic plates can serve as beam spoilers to increase the dose to an adequate dose for shallow depths. The lung tissue is sensitive to radiation and limits the dose delivered to the rest of the body. Accurate lung dose calculations are necessary to determine if attenuators are necessary to reduce the total lung dose. Fractionation of the TBI dose requires an increase in the total dose delivered as repair and repopulation occurs between fractions. Repair processes are minimal for the leukemia cell and therefore the therapeutic ratio is enhanced. Analysis of the disease-free survival rates and evaluation of the percentage of patients relapsing or recurring measure the effect of these preparatory regimens. TBI shows a marked improvement in both factors for AML and ALL. Studies reviewing the effects of treatments for CML show excellent results for both chemotherapy only protocols and TBIchemotherapy combined protocols.

Over the last 35 years, TBI delivery protocols have evolved due to toxicity concerns. Radiationinduced toxicity is influenced by the dose rate and total dose. The total dose was predominantly restricted by pulmonary toxicity from interstitial pneumonitis. Single fraction TBI was replaced with fractionated and hyperfractionated techniques. Radiobiological principles of preferential normal tissue repair with fractionation forecast improved antileukemic effects without increasing toxicity. Dose rate was considered a strong factor in the causation of interstitial pneumonitis and most protocols restrict the delivery dose rate to less than 10 cGy/min. TBI protocols vary with the primary malignancy and complementary chemotherapy conditioning regimen. Current TBI protocols include: a single fraction of 200 Gy; two BID fractions of 2 Gy/fraction; eight BID fractions of 1.5 Gy/fraction with or without lung and liver dose reduction to 8-10 Gy; and eight BID fractions of 1.65 Gy/fraction with or without partial transmission blocking of the lung and liver.

Factors influencing large field treatment technique choice include dose homogeneity, accurate and reproducible delivery, ease of set up, treatment room limitations, and the treatment protocol used. For example, if a reduced organ dose is required with blocking, an AP/PA treatment technique is required. Different techniques have been described recently including those utilizing tomotherapy or translational couch options. Two methods of comfortable total body irradiation using conventional linear accelerators without machine modifications are presented here. A technique for lateral treatments and a process for AP/PA treatments with blocking are described. Techniques described here enhance other reported design specifications. The technique options represent an evolution in our process and should aid facilities looking to begin a TBI program or facilities desiring modifications to adjust to different treatment protocols.

Dose uniformity is the primary criterion when creating a treatment technique. The use of beam spoilers, strategically placed bolus, missing tissue compensators, and opposed fields with high energy x-rays will accomplish the uniformity goal. While dose uniformity is the major priority in developing a suitable treatment technique, patient comfort and support are equally important. Patients presenting for TBI are often weak and recovering from other chemotherapy treatments as part of the preparatory program for transplant. Two treatment options, opposed laterals and AP/PA fields and associated apparatus have been presented. The limitation of dose delivered to the lung/liver is specified in several protocols and is accomplished with partial transmission blocks placed in conjunction with AP/PA fields. Both techniques were designed to insure accurate dose delivery, comfortable patient support, and easy patient setup. Calculation spreadsheets referenced in this manuscript are available by contacting the authors.
