**3.1 Accelerator room**

TBI treatments should be performed with a high energy accelerator capable of providing photons of 15MV or greater. Lower x-ray energies can be utilized, but as the energy is decreased, dose homogeneity becomes more difficult to achieve with opposed fields. The distance to the closest wall with the gantry angled at 90 or 270 degrees will dictate the maximum field size to encompass the patient. Offset of the isocenter in the treatment vault design may allow for a greater treatment distance. Unfortunately, the desire to add TBI to the radiation therapy services may occur after a vault has been constructed. Most vaults are configured with a 20 foot width. Without an isocenter offset, this room width provides a source-wall distance of approximately 4m. Our institution's vault design provided a sourcewall distance of slightly less than 4m. A 40x40 cm2 field at 1m projects to 1.58m2 without collimator rotation and 2.2m2 with a 45° collimator rotation. Only a minor room

Photon Total Body Irradiation

rail arm support.

for Leukemia Transplantation Therapy: Rationale and Technique Options 539

Fig. 2. Acrylic head and neck compensator mounted on post connected to accelerator couch

modification may be necessary to provide audio and visual communication with a patient positioned at this location.

#### **3.2 Opposed lateral field TBI table**

A portable surgical couch was obtained from a medical equipment reclamation firm. This modified couch is utilized for providing TBI treatments with opposed lateral fields. It is the technique of choice where treatment goals include dose uniformity without specific organ blocking. Figure 1 is a front view schematic of the couch arrangement. The effective length of the patient was reduced as sections of the couch are angled 45°. Four inch urethane foam cushions are used to separate the patient from any metal located on the couch. An additional egg crate cushion is provided for patient comfort. The couch height is adjusted vertically to coincide with the isocenter height of 1.3m.

After patient positioning, four beam spoiler plates constructed of ¼" lexan polycarbonate are inserted into aluminum slots added to the couch. The width of the treatment table including the lexan polycarbonate plates is 52cm. Factoring in couch clearance to the wall, the sourcetray distance for these lateral treatments is 374 cm. Our wall choice required a gantry angle selection of 270° (IEC). A collimator position of 20° and 340° is used for right lateral and left lateral fields, respectively.

Prior to treatment, a head and neck missing tissue compensator is positioned. An acrylic compensator is secured to a tray and supported with the accelerator hand support which is affixed to the accelerator couch rail (Fig. 2). The compensator angle position can be pivoted on the tray to match each patient. The compensator tray is rotated for the opposing lateral treatment and the couch longitudinal position is adjusted accordingly. The compensator bottom is curved to match the alignment between the patient neck and shoulders.

Tissue-equivalent rice bolus is used for additional missing tissue compensation for the body below the patient neck level. Figure 3 demonstrates the bolus placement. Since the patient's torso represents the widest section of the patient, bolus is typically only provided below the waist level between and around the legs and feet. The rice bag placement essentially makes the patient separation constant below the neck level and matching the maximum torso separation. Since the dose prescription point is typically at mid-depth at the umbilicus level. Tubes of rice and smaller individual plastic bags of rice with disposable outer covering are used for this aspect of patient preparation.

This treatment assumes that the treatment goal is to provide the same dose to the lungs as provided at the mid-umbilicus level. Prior to treatment, a lateral separation is determined at the nipple level. Previous chest x-ray review for over 50 patients revealed a relationship between this separation and the lateral width of the lungs. Of the lateral tissue separation, 77-83% of the tissue was comprised by the lower density lungs. Rather than measuring the lung width with a chest x-ray on each patient, we calculate the lung thickness as 80% of the full tissue thickness and assume a lung physical density of 0.35g/cm3. An effective thickness at this level is determined.

The arms are positioned at the patient's side thus adding higher density thickness to the chest area (Fig. 3.). The arm separation is determined and added to the effective thickness. This total is compared to umbilicus separation. If additional thickness is needed at the arm level to meet the thickness uniformity criterion of +/-1cm, additional "bolus with skin" (CIVCO, Orange City, IA) is added around the arm in 0.5cm increments until this criterion is met. A simple spreadsheet is used to perform these calculations as well as print setup instructions.

modification may be necessary to provide audio and visual communication with a patient

A portable surgical couch was obtained from a medical equipment reclamation firm. This modified couch is utilized for providing TBI treatments with opposed lateral fields. It is the technique of choice where treatment goals include dose uniformity without specific organ blocking. Figure 1 is a front view schematic of the couch arrangement. The effective length of the patient was reduced as sections of the couch are angled 45°. Four inch urethane foam cushions are used to separate the patient from any metal located on the couch. An additional egg crate cushion is provided for patient comfort. The couch height is adjusted

After patient positioning, four beam spoiler plates constructed of ¼" lexan polycarbonate are inserted into aluminum slots added to the couch. The width of the treatment table including the lexan polycarbonate plates is 52cm. Factoring in couch clearance to the wall, the sourcetray distance for these lateral treatments is 374 cm. Our wall choice required a gantry angle selection of 270° (IEC). A collimator position of 20° and 340° is used for right lateral and left

Prior to treatment, a head and neck missing tissue compensator is positioned. An acrylic compensator is secured to a tray and supported with the accelerator hand support which is affixed to the accelerator couch rail (Fig. 2). The compensator angle position can be pivoted on the tray to match each patient. The compensator tray is rotated for the opposing lateral treatment and the couch longitudinal position is adjusted accordingly. The compensator

Tissue-equivalent rice bolus is used for additional missing tissue compensation for the body below the patient neck level. Figure 3 demonstrates the bolus placement. Since the patient's torso represents the widest section of the patient, bolus is typically only provided below the waist level between and around the legs and feet. The rice bag placement essentially makes the patient separation constant below the neck level and matching the maximum torso separation. Since the dose prescription point is typically at mid-depth at the umbilicus level. Tubes of rice and smaller individual plastic bags of rice with disposable outer covering are

This treatment assumes that the treatment goal is to provide the same dose to the lungs as provided at the mid-umbilicus level. Prior to treatment, a lateral separation is determined at the nipple level. Previous chest x-ray review for over 50 patients revealed a relationship between this separation and the lateral width of the lungs. Of the lateral tissue separation, 77-83% of the tissue was comprised by the lower density lungs. Rather than measuring the lung width with a chest x-ray on each patient, we calculate the lung thickness as 80% of the full tissue thickness and assume a lung physical density of 0.35g/cm3. An effective thickness

The arms are positioned at the patient's side thus adding higher density thickness to the chest area (Fig. 3.). The arm separation is determined and added to the effective thickness. This total is compared to umbilicus separation. If additional thickness is needed at the arm level to meet the thickness uniformity criterion of +/-1cm, additional "bolus with skin" (CIVCO, Orange City, IA) is added around the arm in 0.5cm increments until this criterion is met. A simple spreadsheet is used to perform these calculations as well as print setup

bottom is curved to match the alignment between the patient neck and shoulders.

positioned at this location.

lateral fields, respectively.

at this level is determined.

instructions.

used for this aspect of patient preparation.

**3.2 Opposed lateral field TBI table** 

vertically to coincide with the isocenter height of 1.3m.

Fig. 2. Acrylic head and neck compensator mounted on post connected to accelerator couch rail arm support.

Photon Total Body Irradiation

offered to the patient.

the authors upon request.

levels to accommodate different patient heights.

determined using a simple spreadsheet calculation.

beam during the posterior field delivery.

for Leukemia Transplantation Therapy: Rationale and Technique Options 541

The current version of the AP/PA TBI stand is pictured in Figure 4. Detailed drawings describing the construction of this stand are available from the authors to aid in duplicating this construction. The stand begins with a 29"(w)x29"(l)x27"(h) wooden platform. This height allows field coverage at the treatment distance with the accelerator gantry positioned at 272° and a collimator rotation of 45°. A patient rehabilitation walker was affixed to the platform after wheel removal. The cushioned arm supports can be positioned at varying

A fabric harness is attached around the patient's waist and thighs. This harness is then attached with plastic buckles to the frame of the walker support. The harness system provides the patient significant stability and tolerance for the required lengthy standing time for this procedure. Patients have experienced episodes of significant weakness or even fainting and the harness system allowed potential injury to be avoided before care could be

Additional patient support and comfort is provided by an adjustable bicycle seat attached to a slide affixed to the platform. The current seat arrangement represents the evolution from a seat supported from the platform rear to a single post from the platform middle. Other stools were investigated and rejected due to adjustment restrictions or beam attenuation. The blocking support is attached to a portable beam spoiler (Fig. 5). The plastic spoiler is fabricated with 3/8" lexan polycarbonate and supported on a mobile assembly that is positioned directly in front of the patient after configuring the patient on the harness and stool. Angle iron is placed on the sides of the beam spoiler away from the beam to provide additional rigidity when the blocks are added. Again, detailed drawings are available from

The cerrobend partial transmission blocks are affixed to a separate ¼" lexan tray. The blocking tray is supported on a tray slot placed on each side of the bam spoiler. The thickness of the transmission blocks is calculated utilizing attenuation properties measured previously. The block thickness also varies with the patient separation and the desired transmitted dose, 8 or 10Gy. Typical thickness varies between 2-4cm of cerrobend and is

The positioning of the block is verified with imaging. In our case, we utilize the Kodak ACR 2000 CR system. However, a film cassette requiring chemical processing could also be used. Fig. 4 also shows a cassette holder attached to the rear of the platform. This spring-loaded cassette holder allows easy height adjustment and was obtained from a medical equipment reclamation service for less than \$50. If lateral adjustment in block placement is necessary after imaging, the blocking tray can be adjusted horizontally using a top-loaded bearing system. This adjustment provides +/- 7cm adjustment. Refer to the appendix for details. Two worm screws are added to the sides of the block assembly and vertical adjustment is accomplished by cranking up or down along this mechanism. After an acceptable image is obtained, the block shadow is traced onto the patient's surface for subsequent fractions. As with the opposed lateral TBI treatment, the accelerator output rate is adjusted such that the midline dose rate is less than 10cGy/minute. Entrance and exit in-vivo dosimeters are placed to verify dose uniformity. Since the hands and forearms are not placed at the patient's side, but on the cushioned arm supports, there was a concern about dose uniformity in this region. Measurements confirm uniformity within +/- 5% as the hands and forearms are closer to the beam during the anterior field treatment and further from the

Monitor unit settings are calculated for the mid-depth at the umbilicus level. In-vivo entrance and exit dosimeters are placed at the head, neck, nipple, umbilicus, knee and ankle levels. After delivery of one half of the fractional dose, the patient remains positioned and the table is rotated 180°. The collimator is rotated to correspond to the new lateral orientation. The head and neck compensator is repositioned. The remainder of the treatment is provided. The dose rate from the accelerator is reduced between 100-200MU/min at isocenter. This machine dose rate reduction, the measured distance correction output factor, and attenuation will provide a dose delivery near 7cGy/minute. Dose rate has been determined to have a significant effect on lung toxicity. Most treatment protocols require dose delivery less than 10cGy/minute. Treatment times are approximately 15 minutes per field. This method of TBI delivery offers a uniform dose, easy and reproducible field arrangement, and a comfortable patient setup.

Fig. 3. Schematic of patient on TBI table with beam spoilers and rice bolus in place.

#### **3.3 AP/PA TBI treatment stand**

The opposed lateral field TBI table method does not allow for partial transmission blocking of the lung or liver as required by various protocols. Towards this goal, an alternative stand was developed to accommodate AP/PA field arrangement, cerrobend blocking, and verification of block placement in a reproducible and comfortable environment for the patient. The initial design of this stand utilized specifications described previously.6,7 Over the years, significant modifications to these designs have been made largely to accommodate weak patients who had difficulty standing for lengthy periods. The majority of patients presenting for TBI have received a chemotherapy regimen as a complementary preparation before the transplant.

Monitor unit settings are calculated for the mid-depth at the umbilicus level. In-vivo entrance and exit dosimeters are placed at the head, neck, nipple, umbilicus, knee and ankle levels. After delivery of one half of the fractional dose, the patient remains positioned and the table is rotated 180°. The collimator is rotated to correspond to the new lateral orientation. The head and neck compensator is repositioned. The remainder of the treatment is provided. The dose rate from the accelerator is reduced between 100-200MU/min at isocenter. This machine dose rate reduction, the measured distance correction output factor, and attenuation will provide a dose delivery near 7cGy/minute. Dose rate has been determined to have a significant effect on lung toxicity. Most treatment protocols require dose delivery less than 10cGy/minute. Treatment times are approximately 15 minutes per field. This method of TBI delivery offers a uniform dose, easy and reproducible field

Fig. 3. Schematic of patient on TBI table with beam spoilers and rice bolus in place.

The opposed lateral field TBI table method does not allow for partial transmission blocking of the lung or liver as required by various protocols. Towards this goal, an alternative stand was developed to accommodate AP/PA field arrangement, cerrobend blocking, and verification of block placement in a reproducible and comfortable environment for the patient. The initial design of this stand utilized specifications described previously.6,7 Over the years, significant modifications to these designs have been made largely to accommodate weak patients who had difficulty standing for lengthy periods. The majority of patients presenting for TBI have received a chemotherapy regimen as a complementary

arrangement, and a comfortable patient setup.

**3.3 AP/PA TBI treatment stand** 

preparation before the transplant.

The current version of the AP/PA TBI stand is pictured in Figure 4. Detailed drawings describing the construction of this stand are available from the authors to aid in duplicating this construction. The stand begins with a 29"(w)x29"(l)x27"(h) wooden platform. This height allows field coverage at the treatment distance with the accelerator gantry positioned at 272° and a collimator rotation of 45°. A patient rehabilitation walker was affixed to the platform after wheel removal. The cushioned arm supports can be positioned at varying levels to accommodate different patient heights.

A fabric harness is attached around the patient's waist and thighs. This harness is then attached with plastic buckles to the frame of the walker support. The harness system provides the patient significant stability and tolerance for the required lengthy standing time for this procedure. Patients have experienced episodes of significant weakness or even fainting and the harness system allowed potential injury to be avoided before care could be offered to the patient.

Additional patient support and comfort is provided by an adjustable bicycle seat attached to a slide affixed to the platform. The current seat arrangement represents the evolution from a seat supported from the platform rear to a single post from the platform middle. Other stools were investigated and rejected due to adjustment restrictions or beam attenuation.

The blocking support is attached to a portable beam spoiler (Fig. 5). The plastic spoiler is fabricated with 3/8" lexan polycarbonate and supported on a mobile assembly that is positioned directly in front of the patient after configuring the patient on the harness and stool. Angle iron is placed on the sides of the beam spoiler away from the beam to provide additional rigidity when the blocks are added. Again, detailed drawings are available from the authors upon request.

The cerrobend partial transmission blocks are affixed to a separate ¼" lexan tray. The blocking tray is supported on a tray slot placed on each side of the bam spoiler. The thickness of the transmission blocks is calculated utilizing attenuation properties measured previously. The block thickness also varies with the patient separation and the desired transmitted dose, 8 or 10Gy. Typical thickness varies between 2-4cm of cerrobend and is determined using a simple spreadsheet calculation.

The positioning of the block is verified with imaging. In our case, we utilize the Kodak ACR 2000 CR system. However, a film cassette requiring chemical processing could also be used. Fig. 4 also shows a cassette holder attached to the rear of the platform. This spring-loaded cassette holder allows easy height adjustment and was obtained from a medical equipment reclamation service for less than \$50. If lateral adjustment in block placement is necessary after imaging, the blocking tray can be adjusted horizontally using a top-loaded bearing system. This adjustment provides +/- 7cm adjustment. Refer to the appendix for details. Two worm screws are added to the sides of the block assembly and vertical adjustment is accomplished by cranking up or down along this mechanism. After an acceptable image is obtained, the block shadow is traced onto the patient's surface for subsequent fractions.

As with the opposed lateral TBI treatment, the accelerator output rate is adjusted such that the midline dose rate is less than 10cGy/minute. Entrance and exit in-vivo dosimeters are placed to verify dose uniformity. Since the hands and forearms are not placed at the patient's side, but on the cushioned arm supports, there was a concern about dose uniformity in this region. Measurements confirm uniformity within +/- 5% as the hands and forearms are closer to the beam during the anterior field treatment and further from the beam during the posterior field delivery.

Photon Total Body Irradiation

stand.

for Leukemia Transplantation Therapy: Rationale and Technique Options 543

Fig. 5. Front view of mobile spoiler and blocking mechanism used in conjunction with TBI

Fig. 4. Front view of TBI stand used for AP/PA fields.

Fig. 4. Front view of TBI stand used for AP/PA fields.

Fig. 5. Front view of mobile spoiler and blocking mechanism used in conjunction with TBI stand.

Photon Total Body Irradiation

for Leukemia Transplantation Therapy: Rationale and Technique Options 545

Fig. 6. A typical survival curve for mammalian cells exhibiting an initial shoulder followed by an exponential region. An initial shoulder characterizes the curve with some slope to it

Leukemia is a broad classification for several types of this disease. This variety of leukemias differs based on pathological examination of cell definition. Bredeson et al. (2002) provide a summary and results of clinical trials including TBI. Patients with acute myeloid leukemia (AML) have shown to be fairly responsive to stem cell transplants with TBI preparation. Results of randomized studies comparing TBI containing regimens with total chemotherapy preparatory regimens indicate a 75% actuarial survival with TBI compared to 51% without. Relapse rates are lower with the TBI regimens as well. 14% relapsed within 2 years with TBI

Bredeson et al. (2002) reports acute lymphoblastic leukemia (ALL) results show significant improvement with TBI regimens. 52% disease-free survival rates are reported when TBI is utilized as compared to 37% with chemotherapy alone. The percentage relapse is nearly identical from both types of regimens. Studies of treatments for chronic myeloid leukemia patients show fairly high yet identical disease-free survival rates. Nearly 80% survival rates

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

were reported for both protocols. Relapse rates were indistinguishably different.

(1Do), the exponential slope (Do), n (extrapolation number) and Dq.

**5. Effectiveness of TBI for various leukemias** 

while 34% relapsed under chemotherapy regimens.

**6. Discussion and summary** 

#### **3.4 Combination of treatment methods**

Despite efforts to provide a comfortable treatment in the TBI stand, the opposed lateral TBI table still is viewed as the most comfortable for patients and easy to set up. Patients receiving TBI that requires dose reduction to the lungs and/or liver are treated using a combination of these two techniques. All current protocols requiring dose reduction to these organs require treatments to be administered over four days or 8 fractions. We routinely treat 4 fractions with the AP/PA TBI stand technique and 4 fractions with the opposed lateral TBI table option.
