COVID-19 Pneumonitis Low Dose Lung Radiotherapy (COLOR-19)

BACKGROUND

Since the first case of Severe Acute Respiratory Syndrome - Coronavirus - 2 (SARS-CoV-2)
infection and its subsequent clinical manifestation (COronaVIrus Disease 19, COVID-19) in the
city of Wuhan (Hubei, China) in December 2019, contagion abruptly spread to different regions
of China and, subsequently, to all continents. To date, 1 521 252 cases have been confirmed
worldwide. With the first case ascertained in Lombardy at the end of February 2020, Italy
soon became the first European country to face the exponential growth in the number of
infected people (to date -May 3, 2020-210,717 total cases, currently positive 100,179).The
disease turned into an actual health emergency due to the rapid spread and the need of
hospitalization and respiratory function support in Intensive Care Unit (ICU) for a
significant fraction of the patients. However, the clinical presentation of COVID-19 is
non-specific and extremely heterogeneous. Many patients are asymptomatic or exhibit mild
symptoms, which include cough, fever, general malaise with myalgias, anosmia and ageusia. The
most common changes in blood tests include lymphopenia, thrombocytopenia and increased
C-reactive protein and ferritin.

As emerged by clinical data, the viral infection could be divided into three different
phases: stage I, asymptomatic incubation period with little or undetectable viral load; stage
II, mild symptomatic period with considerable and detectable viral load; stage III, severe
symptomatic period with high viral load.

The definitive diagnosis requires a positive molecular test with Real Time PCR (RT-PCR)
method for SARS-CoV-2 on nasopharyngeal swab. However, this technique suffers from
sub-optimal sensitivity, which may require repetition on bronchoalveolar lavage. The
execution of chest CT is therefore essential, as it is characterized by high sensitivity and
can detect highly suggestive findings even in patients with negative RT-PCR.

Although the majority of infections resolve spontaneously without the need for specific
therapy, up to 20% of patients can develop severe clinical pictures with pneumonia
characterized by dyspnea, tachypnea and hypoxemia that requires treatment in a hospital
setting. Pulmonary involvement is typically bilateral, peripheral and basal in most cases,
presenting on CT scan with multifocal ground glass opacities and interstitial infiltrations;
complete resolution usually takes several weeks. Despite active treatment, about 5-10% of
cases can precipitate, often suddenly, into critical conditions including respiratory
failure, ARDS and multi-organ dysfunction that require ICU admission and are burdened with
high mortality.

Even though the understanding of the pathogenesis of COVID-19 is still incomplete, the
central role of the immune response in determining the development of severe clinical
pictures is increasingly being defined. Organ damage could therefore not be induced by the
direct effect of the infection, but mediated by an uncontrolled immune response resulting in
the development of a "cytokine storm", as suggested by the high levels of inflammatory
cytokines (among which interleukin 6 (IL-6), tumor necrosis factor (TNF) and interferon γ
(IFNγ) play a major role) in patients who exhibit severe or fatal disease. To date, no drug
has been approved with a specific indication for the treatment of COVID-19. The current
treatment encompasses antiviral agents approved for other viral infections, including
protease inhibitors (lopinavir and ritonavir), anti-influenza drugs (oseltamivir and arbidol)
and compassionate use of nucleotide analogues. Several studies are evaluating the possible
effectiveness of the inhibition of pro-inflammatory cytokines activity in preventing or
treating severe COVID-19, through the use of immunomodulators (chloroquine and
hydroxychloroquine) or monoclonal antibodies such as tocilizumab, which targets the IL-6
receptor. Despite promising preliminary results, a multitude of patients need an immediate
treatment while the results of ongoing clinical trials are awaited.

RATIONALE

Although most COVID-19 infections resolve spontaneously without the need for specific
therapy, up to 20% of patients can develop severe clinical pictures with
interstitial-alveolar pneumonia characterized by dyspnoea, tachypnea and hypoxemia up to an
acute respiratory distress syndrome (ARDS), severe respiratory failure and multi-organ
dysfunction requiring ICU hospitalization and burdened with high mortality.

To date, the pathogenesis of SARS-CoV-2 pneumonia is poorly understood, but the
immune-inflammatory response to infection is progressively emerging as pivotal in the
development of severe clinical manifestations. An adequate viral load might stimulate the
immune cells to synthesize pro-inflammatory cytokines as interleukin 1 and 6 (IL-1, IL-6),
tumor necrosis factor α (TNF α) and attract macrophages, responsible for the secretion of
several chemokines that could trigger an unregulated "cytokine storm". A few reports of
histological analysis of lung tissue specimens from COVID-19 patients highlighted nonspecific
inflammatory changes with the appearance of edema, hyaline membranes and an inflammatory
infiltrate dominated mainly by lymphocytes. Peripheral blood tests often reveal
lymphocytopenia and a high neutrophil count are found, especially in case of severe disease,
with a high value of neutrophil to lymphocyte ratio (NLR), and a relevant increase in
circulating pro-inflammatory cytokines levels.

While vaccines and drugs directly targeting the virus are currently being developed and are
not yet available, preventing the excessive and uncontrolled cytokine release and
inflammatory response could be the key to avoid the occurrence of severe disease.

Different clinical trials are exploring this path, evaluating immunomodulators and monoclonal
antibodies targeting mediators such as interleukin 6(IL-6).

Although conventionally fractionated (1.8-2 Gy/fraction) and hypofractionated (> 3 Gy
fraction) radiotherapy, used in the field of neoplastic diseases, provides its therapeutic
effect also inducing pro-inflammatory molecules, it has widely been documented in the first
decades of the last century that low-dose radiotherapy (LD-RT) is potentially effective and
relatively safe in the control of acute and/or chronic inflammatory diseases (e.g. skin
diseases such as psoriasis, necrotizing abscesses, tendonitis, impingement syndrome).

Many studies reported the effectiveness of radiation treatment after a single application,
with a prompt improvement of symptoms, usually occurring within 24 ours and often definitive
or long-lasting. Low dose radiotherapy exerts its effect on several cells involved in the
immune response: endothelial cells, polymorphonuclear leukocytes, lymphocytes and
macrophages. This is true also for pneumonia.

Endothelial cells play a crucial role in the inflammation process, both for the "homing"
process of leukocytes, and for the expression of a wide variety of cytokines and growth
factors. Different studies have shown that a dose of 0.5 Gy induces an over-expression of
tumor growth factor β (TGF-β), which has immunosuppressive activity and leads to a reduction
in leukocyte adhesion on endothelial cells.

The leukocyte "rolling" on the endothelium in the sites where inflammation is present
represents the initial step of the inflammatory cascade. The effects of LD-RT were analyzed
in vitro; after radiation doses of 0.3 - 0.6 Gy, there was a 25-40% reduction in adhesion
compared to control after 24 hours from irradiation.

Ionizing radiation at doses below 1 Gy are also capable to polarize macrophages towards the
M2 anti-inflammatory phenotype. Conversely, doses greater than 1 Gy tend to induce
polarization towards the M1 pro-inflammatory subtype. The use of low doses of radiation seems
to act on macrophages also reducing their cytotoxic action, reducing the production of nitric
oxide (NO) through to the inhibitory action on the enzyme cytokine inducible nitric oxide
synthetase (iNOS) .

Neutrophils play a central role in lung damage induced by Middle East Respiratory Syndrome
(MERS) and SARS-CoV, and likewise in COVID-19, as they migrate into the alveoli where they
release proteinases and trigger the innate response, with consequent development of cell
damage and clinical presentations like ARDs (30,31). Low-dose radiation therapy is able to
initiate the apoptotic process of polymorphonuclear granulocytes (neutrophils), thus reducing
their cytotoxic activity (32). This treatment can therefore exert an anti-inflammatory
activity through several mechanisms of action, with an optimal and long lasting effect
demonstrated for a dose of 0.5 Gy (32).

In the absence of a specific treatment, while ongoing trial are evaluating pharmacological
approaches and vaccines, innovative approaches could be undertaken to face the emergency and
allow a satisfactory management of the disease.

A single fraction radiation treatment delivering low doses to the entire bilateral lung
parenchyma (whole lung treatment) is a reasonable and conceptually valid option to inhibit
inflammation and obtain a prompt improve of the symptoms in the short term.

Unlike most of the drugs analyzed so far in the framework of COVID-19 infection, low dose
radiotherapy is characterized by a minor risk of side effect (negligible, considering the
acute phase) and could therefore represent an optimal complementary therapeutic approach due
to its safety and absence of interaction with pharmacological treatments. Moreover, this
treatment requires less than one hour including treatment planning and administration.

TREATMENT DELIVERY

The patient will undergo radiation treatment on both lungs in a single session. From the
physical-dosimetric point of view, the treatment plan will be calculated in an isocentric
manner. The isocenter will be positioned at a depth of 10 cm with respect to an anterior skin
landmark specifically defined during CT-scan acquisition. The treatment plan will be
elaborated using a field in field irradiation technique, with 2 beams each one composed by 3
beamlets: one conformed to the volume resulting by the union of the lungs with a 2 cm margin,
the other two will be obtained by shielding the spine and alternately one lung each. This set
up allows to obtain a dose distribution in which the vertebral bodies receive a dose lower
than 55 cGy with an average lung dose of 70 cGy and maximum lungs dose lower than than 90
centigray (cGy). The Pinnacle ® treatment planning system (TPS) with Collapsed Convolution
calculation algorithm will be used. Prescription doses were determined according to data and
indications currently published and optimized to minimize the dose to the vertebrae.