Calibration of hypoxic region focused radiotherapy treatment plans

The present invention features calibration methods for radiotherapy treatment plans. An image-guided radiotherapy system for tumor treatment featuring a hypoxic-region-focused (HRF) radiation dose is calibrated using a phantom. The treatment plans may also feature a boosted dose to the resistance region of the tumor. The HRF radiation dose may be greater than 120% of a predetermined prescribed radiation dose for the tumor.

FIELD OF INVENTION

The present invention relates to calibration of radiotherapy methods. More particularly, it relates to calibration of radiotherapy methods for hypoxic region focused tumor treatment.

BACKGROUND OF THE INVENTION

Tumor hypoxia refers to the condition in which cells within a tumor are deprived of oxygen. This condition can occur when a rapidly growing tumor lacks a functional vasculature system and thus has inadequate blood supply to regions in the interior of the tumor. Hypoxic regions within a tumor can be visualized using imaging techniques such as PET. Such non-invasive imaging techniques allow for identification of the boundaries of the hypoxic region or regions.

Phantom Calibration of Radiotherapy Treatment Plans:

Radiotherapy plans are designed to provide sufficient dose levels to target tissues and limit the dose levels to surrounding organs at risk. Given the importance of proper radiation dosing, the treatment plans are routinely calibrated using a phantom before use in a patient. Irradiation of a phantom using the proposed treatment plan allows for a measurement of the actual radiation levels which are delivered using the plan. These actual radiation levels can be compared to the calculated radiation levels and the difference can be used to determine if the treatment plan requires revision.

Radiotherapy is a proven modality for cancer cure like surgery for tumors of all sites. The probability to destroy a cancer locally is proportional to the radiation dose delivered to the cancer site. Most often, an effectiveness of radiotherapy is limited by the radiation does that can safely be delivered to a normal organ adjacent to the tumor. Serious complications may occur if the normal organs received a radiation does that exceeds their tolerance to radiation. Paralysis (spinal cord injury), blindness (optic nerve injury), stroke (brain injury), bleeding (blood vessels injury), inflammation of lung (lungs injury) and bowels (bowels injury) may lead to death or seriously affect patient quality of life. These are well known complications of radiation treatment. Current methods of radiation treatment set a maximum limit for the radiation dose.

For example, in section 6.4.2.4 Radiation Therapy Oncology Group (RTOG) study number 0225: A Phase II Study of Intensity Modulated Radiation Therapy (IMRT) +/ Chemotherapy for Nasopharyngeal Cancer, it is specified that “No more than 20% of any PTV70 (the gross tumor volume with a 5 mm margin) will receive 110% of the prescribed dose.” The rule limits the toxicity of treatment to avoid complications.

FIG. 1Bshows schematic representation of “volumes” in radiation therapy in terms of Gross Target Volume, Clinical Target Volume, Planning Target Volume from Page 5, Chapter 1: The Discipline of Radiation Oncology, Book: Perez and Brady's Principles and Practice of Radiation Oncology, 5th Edition, published by Lippincott Williams & Wilkins with ISBN-10: 078176369X. This figure clearly shows that the planning target volume (PTV) is beyond the tumor boundary.

Table 1 shows the Memorial Sloan-Kettering Cancer Center (MSKCC) Clinical Dose Limits and Inverse Planning Algorithm Constraints for Primary Nasopharynx Tumors, excerpted from book “A practical guide to intensity-modulated radiation therapy” (Medical Physics Pub., 2003, ISBN: 1930524137), Chapter 10: IMRT for head and neck Cancer, Table 10.3, page 201. The table clearly regulates that the maximum dose is 105%.

Table 2 shows the compliance criteria of radiation treatment in Radiation Therapy Oncology Group (RTOG) study number 0920: A Phase III Study of Postoperative Radiation Therapy (IMRT) +/− Cetuximab for Locally-Advanced Resected Head and Neck Cancer, section 6.7, page 27. The criteria list in Row 1 that any Radiation dose (RT)>66Gy as a major variation should be avoided at any rate. The 66Gy corresponds to a 10% increase over PTV 60Gy.

Table 3 shows the Critical Normal Structures in Radiation Therapy Oncology Group (RTOG) study number 0225: A Phase II Study of Intensity Modulated Radiation Therapy (IMRT) +/ Chemotherapy for Nasopharyngeal Cancer, section 6.4.3 Critical Normal Structures, page 7. The Critical Normal Structures discloses clearly that 60 Gy or 1% of the PTV cannot exceed 65 Gy (which is close to 10% increase over PTV 60Gy radiation.

TABLE 3Critical Normal Structures6.4.3DVH's must be generated for all critical normal structures and the unspecified tissues. Doseconstraints to normal tissues will be as follows:Brainstem, optic nerves, chiasm54 Gy or 1% of the PTV cannot exceed 60 GySpinal Cord45 Gy or 1 cm3(if 1% is used, depends on length ofthe cord outlined) of the PTV cannot exceed 50 GyMandible and T-M joint70 Gy or 1 cm3of the PTV cannot exceed 75 GyTemporal lobes60 Gy or 1% of the PTV cannot exceed 65 GyUnspecified tissue outside the targets: ≤100% of the dose prescribed to PTV70. No morethan 5% of the non-target tissue can receive greater than 70 Gy. Participants are stronglyencouraged to remain within these limits.

FIG. 2shows the hotspot radiation regulation in a presentation (slide 13) of a research taken at Dana-Farber/Brigham & Women's Cancer Center and Harvard Medical School (“Variability in planning criteria and plan evaluation”, Laurence Court, the American Association of Physicists in Medicine annual meeting 2010). The slide clearly shows the aiming for hotspots radiation is limited to <110% of the radiation dose.

However, a use of low radiation dose can be ineffective for curing cancer and a patient can die from uncontrolled tumor growth or from complications resulting from tumor destruction of normal organs. Thus, a clinician is often faced with a dilemma: either let the cancer kill the patient or expose the patient to serious injury from radiation complications. Therefore, there is a need for a balanced method for image-guided radiotherapy for providing higher dose for tumor tissue, such as hypoxia region of tumor, while avoiding excessive radiation to normal tissue.

SUMMARY OF THE INVENTION

The present invention features calibration of an image-guided radiotherapy treatment plan for a hypoxic tumor. The treatment plans feature a hypoxic region focused (HRF) dose which may be greater than 120% of a predetermined prescribed radiation dose for the tumor. Additionally, the treatment plans may feature a resistance region focused (RRF) dose which is greater than the predetermined prescribed dose and less than the HRF dose.

One of the unique and inventive technical features of the present invention is that three-dimensional imaging is used to identify a hypoxic region of a tumor, and a resistance region is designated between the hypoxic region and a sensitive region. Without wishing to limit the invention to any theory or mechanism, it is believed that the technical feature of the present invention advantageously provides for calibration of HRF and RRF doses using irradiation of a phantom. None of the presently known prior references or work has the unique inventive technical feature of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “hypoxic region” refers to a tumor region which has inadequate oxygen. As a non-limiting example, a hypoxic region may be a region in which is identified using a PET scan and a hypoxia sensitive biomarker. As used herein, “resistance region” refers to a tumor region which exhibits radiation resistant properties. As a non-limiting example, a resistance region may be a region in which surrounds the hypoxic area and in which the cancer cells are primarily dormant and non-dividing.

As used herein, the terms “prescribed radiation dose” or “prescribed dose” means the conventional dose established in the literature for cancer cure. The prescribed dose may be determined from external beam radiotherapy alone or radiotherapy combined with chemotherapy for locally advanced head and neck cancer. As non-limiting examples, the “prescribed dose” for Oropharyngeal cancer, Oral cavity cancer, Laryngeal cancer, Hypopharyngeal cancer is about 7000 cGy, at about 200 cGy per day.

As used herein “homogenous” refers to the quality of being substantially the same or similar throughout. For example, a homogenous dose may refer to a dose which is substantially the same throughout the homogenous volume. As another example a homogenous dose may refer to a dose which has no point throughout the homogenous volume where the dose differs from an average dose for the homogenous volume by more than about 1, 2, 3, 5, 10, or 15 percent. As used herein, the terms “boosted radiation dose” or “boosted dose” is defined as a dose that is at least 110% higher than the prescribed dose.

In one embodiment, the present invention features a method of calibrating a resistance region focused (RRF) dose in a radiotherapy treatment plan for a tumor using a phantom model. As a non-limiting example, the method may comprise: obtaining a three-dimensional image of a tumor in a patient; identifying a peripheral boundary of the tumor using the three-dimensional image; identifying a hypoxic region within the tumor using the three-dimensional image; designating a region immediately inside the peripheral boundary as a sensitive region, the sensitive region having an average width W; designating a region between the hypoxic region and the sensitive region as a resistance region; generating a radiation treatment plan; irradiating a phantom following the treatment plan; measuring the irradiation in said phantom; testing the measured irradiation to the phantom region corresponding to the peripheral boundary to determine if the boosted RRF dose had increased irradiation at the peripheral boundary above a threshold value; and calibrating the RRF dose based on the determination of the irradiation to the phantom region corresponding to the peripheral boundary.

In a preferred embodiment, the treatment plan may comprise: a hypoxic region focused (HRF) dose, the HRF dose directed to the hypoxic region; a resistance region focused (RRF) dose, lower than the HRF dose but boosted above a spillover dose from the HRF dose, the RRF dose directed to the resistance region; and a sensitive region focused (SRF) dose, lower than the RRF dose, the SRF dose directed to the sensitive region.

In some embodiments, the tumor may be a radiation resistant tumor. In other embodiments, the three-dimensional image may be obtained using positron-emission tomography (PET). In still other embodiments, the HRF radiation dose or the RRF radiation dose may be greater than a prescribed treatment dose for the tumor. In yet other embodiments, a combined volume of the resistance region and the hypoxic region may be more than 20% of a total volume of the tumor. As a non-limiting example, the combined volume of the resistance region and the hypoxic region may be more than 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 95, or 99 percent of a total volume of the tumor.

In a selected embodiment, the present invention may feature an image-guided radiotherapy method for treatment of a tumor. As a non-limiting example, the method may comprise: obtaining a three-dimensional image of a tumor in a patient; identifying a peripheral boundary of the tumor; identifying a hypoxic region within the tumor using the three-dimensional image; designating a region immediately inside the peripheral boundary as a sensitive region, the sensitive region having an average width W; designating a region between the hypoxic region and the sensitive region as a resistance region; designating and applying a hypoxic region focused (HRF) radiation dose to the hypoxic region; and designating and applying a resistance region focused (RRF) radiation dose to the resistance region. According to one embodiment, the HRF radiation dose may be greater than the RRF radiation dose.

In some embodiments, the method may further comprise designating and applying a sensitive region focused (SRF) radiation dose to the sensitive region. As a non-limiting example, the SRF radiation dose may be lower than the RRF radiation dose. In some additional embodiments, the radiation doses may be escalated in an iterative manner. As a non-limiting example, a patient may be treated with a first radiation dose, imaged to determine the effect of the radiation dose on the tumor, and treated with a second radiation dose which is either larger or smaller than the first radiation dose, depending on if the effect of the radiation dose on the tumor.

In one embodiment, the HRF radiation dose or the RRF radiation dose may be greater than a prescribed treatment dose for the tumor. In another embodiment, the RRF dose may be greater than a spillover dose from the HRF dose. As a non-limiting example, a spillover dose may decrease 10% in intensity with each additional mm of distance from the region to which the dose was directed. As another non-limiting example, a spillover dose may decrease 1, 2, 3, 4, 5, 7, 15, 20, 30, 40, 50, 60, 70, 80, or 90% in intensity with each additional mm of distance from the region to which the dose was directed. According to one preferred embodiment, the tumor may be larger than about 3 cm in diameter. According to another preferred embodiment, the tumor may be larger than about 0.5, 1, 1.5, 2, 2.5, 3.5, 4, 4.5, 5, 6, 7, 8, 9, or 10 cm in diameter.

In another embodiment, the present invention features an image-guided radiotherapy method for treatment of a tumor. As a non-limiting example, the method may comprise: obtaining a three-dimensional image of a tumor; identifying a hypoxic region of the tumor, using the three-dimensional image; and designating and applying a hypoxic region focused (HRF) radiation dose to the hypoxic region. In a preferred embodiment, the HRF radiation dose may be at least 120 percent of a prescribed treatment dose for the tumor. In other preferred embodiments, the HRF radiation dose may be at least 105, 110, 115, 125, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 400, 500 or 1000 percent of a prescribed treatment dose for the tumor. In some embodiments, the HRF radiation dose may be at least 30 Gy. In other embodiments, the HRF radiation dose may be at least 5, 10, 15, 20, 25, 35, 40, 45, 50, 60, 70, 80, 90, or 100 Gy.

In some embodiments, the dose may reflect the dose delivered in one treatment session. In other embodiments, the dose may reflect the total dose delivered over a number of treatment sessions. According to yet other embodiments, the method may further comprise designating a resistance region within the tumor and applying a resistance region focused (RRF) radiation dose to the resistance region. As a non-limiting example, the RRF radiation dose may be lower than the HRF radiation dose.

In some embodiments, the three-dimensional image may be obtained using positron-emission tomography (PET). In other embodiments, the three-dimensional image may be obtained by magnetic resonance spectroscopy (MRS) or MRI. In a selected embodiment, the HRF radiation dose or the RRF radiation dose may greater than a prescribed treatment dose for the tumor. As a non-limiting example, the HRF radiation dose may be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, or 100 Gy. As another non-limiting example, the RRF radiation dose may be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90, or 100 Gy. In some embodiments the HRF may be about 105, 110, 115, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, or 1000 percent of the RRF dose. According to another embodiment, the method may further comprise designating and applying a sensitive region focused (SRF) radiation dose to the sensitive region. In preferred embodiments, the SRF radiation dose may be lower than the RRF radiation dose. In some embodiments the RRF may be about 105, 110, 115, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, or 1000 percent of the HRF dose.

In one embodiment, a volume of the hypoxic region may be more than 20% of a total volume of the tumor. In other embodiments, the volume of the hypoxic region may be more than 1, 2, 5, 10, 15, 25, 30, 40, 50, 60, 70, 80, 90 or 95% of a total volume of the tumor. In another embodiment, a combined volume of the resistance region and the hypoxic region may be more than 20% of a total volume of the tumor. In still other embodiments, the combined volume of the resistance region and the hypoxic region may be more than 1, 2, 5, 10, 15, 25, 30, 40, 50, 60, 70, 80, 90 or 95% of a total volume of the tumor. In an embodiment, the average width of the sensitive region, W, may be about 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 mm. In some embodiments the width of the sensitive region may be constant. In other embodiments, the width of the sensitive region may vary. According to one non-limiting example, a tumor having an average diameter of about 3 cm may have a sensitive region width of about 3-4 mm. According to another non-limiting example, a tumor having an average diameter of about 5 cm may have a sensitive region width of about 3-5 mm. According to yet another non-limiting example, a tumor having an average diameter of about 10 cm may have a sensitive region width of about 10 mm.

In another embodiment, the radiation doses may be escalated in an iterative manner. As a non-limiting example, an iterative treatment plan may double or triple the dose from one treatment to the next or reduce the dose from one treatment to the next. In yet another embodiment, the HRF dose may be homogenous over 95 percent by volume of the hypoxic region. In alternative embodiments, the HRF dose may be homogenous over 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90 or 99 percent by volume of the hypoxic region. Similarly, in some embodiments, the RRF dose may be homogenous over 95 percent by volume of the resistance region. In other alternative embodiments, the RRF dose may be homogenous over 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90 or 99 percent by volume of the resistance region.

The HRF radiation dose may be over 120% of a predetermined prescribed radiation dose for the tumor (110). As a non-limiting example, for radiation sensitive tumors, the predetermined prescribed radiation dose may range from about 180-200 centiGray per day and the HRF radiation dose may range from about 360 to 400 centiGray per day. As another non-limiting example, for radiation resistant tumors, the predetermined prescribed radiation dose may be about 250 centiGray per day and the HRF radiation dose may be about 500 centiGray per day.

Due to tail effect of an HRF radiation beam, a safety distance may affect the maximum HRF radiation dose. The HRF radiation dose may decrease at a rapid rate with increasing distance from the center of the hypoxic region such that sensitive region of the tumor (110) receives less than 40% of the HRF radiation dose.

According to some embodiments, the tumor may be a radiation resistant tumor. Examples of tumors that can be treated using this method include radiation sensitive tumors and radiation resistant tumors. Non-limiting examples of radiation sensitive tumors include: Squamous Carcinoma, Adeno Carcinoma, Small Cell Carcinoma, Lymphoma Carcinoma and Transitional Cell Carcinoma. Non-limiting examples of radiation resistant tumors include Melanoma and Renal cancer.

EXAMPLES

The image-guided radiotherapy treatment plans in Table 4 may be calibrated using a phantom:

A patient may be treated according to any of the image-guided radiotherapy treatment plans in Table 4.